Metal Damage & Failure Mechanisms | Knowledge

DM-001Uniform aqueous corrosionAqueous & localized corrosion · General metal loss

Umbrella damage mechanism

Mechanism pathway

Service conditions

Conductive water; oxidant or reducible species; no single acid required

Physical processes

Anodic metal dissolution
Coupled cathodic reaction over the wetted surface

Observable damage

Broad thinning; rust or scale; weight loss

Possible failure mode

Perforation or pressure rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: General corrosion; general wastage
Industries / exposed sectors: Water; chemical processing; marine; utilities
Typically affected parts: Tank walls; piping; exposed wetted surfaces
Susceptible materials: Iron and steel; other susceptible metals require environment-specific assessment
Required chemicals / environment: Conductive water; oxidant or reducible species; no single acid required
Influencing parameters: pH; temperature; oxygen; salinity; wetting time
Physical explanation (1–3 processes): Anodic metal dissolution
Coupled cathodic reaction over the wetted surface
Signs and symptoms: Broad thinning; rust or scale; weight loss
Prevention / slowing the damage: Keep surfaces dry where practical; use suitable barriers and engineered cathodic protection
Typical failure outcome: Perforation or pressure rupture
Possible consequences: Release; contamination; reduced load capacity
Can be mistaken for: Erosion-corrosion; oxidation; localized corrosion
How to distinguish it: Map thickness over a grid; identify electrolyte and products; separate general loss from isolated pits
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is Corrosion? Definition and Prevention — Technical reference (accessed 2026-09-08)
80 PHMSA — Fact Sheet: Corrosion — Regulatory technical/statistical reference (accessed 2026-09-08)
70 AMPP — Forms of Corrosion — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-002Atmospheric corrosionAqueous & localized corrosion · Thin-film corrosion

Damage mechanism

Mechanism pathway

Service conditions

Atmospheric moisture and deposited marine salts

Physical processes

Thin electrolyte films enable electrochemical attack
Wet/dry cycling concentrates contaminants

Observable damage

Rust; coating undercutting; section loss

Possible failure mode

Structural fracture or collapse after sufficient section loss

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Weathering corrosion; atmospheric rusting
Industries / exposed sectors: Infrastructure; transport; marine; storage
Typically affected parts: Exposed bridge steel and comparable outdoor steelwork
Susceptible materials: Mild steel; painted or thermally sprayed aluminium-coated steel
Required chemicals / environment: Atmospheric moisture and deposited marine salts
Influencing parameters: Sheltering; orientation; coastal distance; salt deposition and weather
Physical explanation (1–3 processes): Thin electrolyte films enable electrochemical attack
Wet/dry cycling concentrates contaminants
Signs and symptoms: Rust; coating undercutting; section loss
Prevention / slowing the damage: Drainage; durable coatings; wash salt deposits; select exposure-appropriate alloys
Typical failure outcome: Structural fracture or collapse after sufficient section loss
Possible consequences: Reduced structural capacity; falling components
Can be mistaken for: CUI; filiform corrosion; soil corrosion
How to distinguish it: Establish exposure and wetting pattern; inspect coating and sheltered surfaces
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Bullard, S.J., Holcomb, G.R. & Matthes, S.A. (2002). Atmospheric Corrosion of Steel and Coated Steel in Coastal Environments. CORROSION 2002, paper 02216. — Primary field-study abstract (accessed 2026-09-08)
80 TWI — What is Corrosion? Definition and Prevention — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-003Soil corrosionAqueous & localized corrosion · Buried-electrolyte corrosion

Damage mechanism

Mechanism pathway

Service conditions

Moist soil electrolyte; oxygen gradients; microbes may contribute

Physical processes

Unequal soil exposure creates coupled anodic and cathodic regions

Observable damage

External pits; coating disbondment; thinning at soil transitions

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Buried external corrosion
Industries / exposed sectors: Pipelines; water; foundations; power
Typically affected parts: Buried steel pipes, piles and reinforced infrastructure
Susceptible materials: Carbon steel; cast iron; metallic coatings
Required chemicals / environment: Moist soil electrolyte; oxygen gradients; microbes may contribute
Influencing parameters: Soil resistivity; moisture; pH; drainage; coating condition
Physical explanation (1–3 processes): Unequal soil exposure creates coupled anodic and cathodic regions
Signs and symptoms: External pits; coating disbondment; thinning at soil transitions
Prevention / slowing the damage: Coating plus monitored cathodic protection; drainage; compatible backfill
Typical failure outcome: Leak or rupture
Possible consequences: Soil/water contamination; supply interruption
Can be mistaken for: MIC; stray-current corrosion; graphitic corrosion
How to distinguish it: Excavation evidence; soil/CP surveys; morphology and metallography; do not diagnose from resistivity alone
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 National Academies — Corrosion of Buried Steel at New and In-Service Infrastructure, chapter 6 — Scientific consensus report (accessed 2026-09-08)
80 PHMSA — Fact Sheet: External Corrosion — Regulatory technical reference (accessed 2026-09-08)
70 AMPP — Cathodic Protection for Corrosion Control — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-004Galvanic corrosionAqueous & localized corrosion · Electrically coupled corrosion

Damage mechanism

Mechanism pathway

Service conditions

Shared electrolyte and electrical continuity are necessary

Physical processes

Electrical coupling drives anodic dissolution of the less noble member

Observable damage

Preferential attack beside dissimilar-metal contact

Possible failure mode

Local perforation; joint failure

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Bimetallic corrosion; dissimilar-metal corrosion
Industries / exposed sectors: Marine; aerospace; utilities; process plants
Typically affected parts: Mixed-metal joints; fasteners; exchanger tubesheets
Susceptible materials: A less noble metal coupled to a more noble conductive surface
Required chemicals / environment: Shared electrolyte and electrical continuity are necessary
Influencing parameters: Relative electrochemical potential; exposed anode-to-cathode area; continuity of protection
Physical explanation (1–3 processes): Electrical coupling drives anodic dissolution of the less noble member
Signs and symptoms: Preferential attack beside dissimilar-metal contact
Prevention / slowing the damage: Electrically isolate joints; compatible alloys; coat both members appropriately; avoid small-anode/large-cathode geometry
Typical failure outcome: Local perforation; joint failure
Possible consequences: Leak; loss of attachment
Can be mistaken for: Crevice corrosion; selective leaching
How to distinguish it: Confirm electrical continuity, electrolyte and polarity; compare attack on both coupled metals
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is Galvanic Corrosion and How Can it be Prevented? — Technical reference (accessed 2026-09-08)
80 Al-Mazeedi, H.A., Al-Farhan, A., Tanoli, N. & Abraham, L. (2019). A Study of Galvanic Corrosion in Stagnant Ammonium Bisulfide Solution. International Journal of Corrosion, 1325169, 9 pages. — Primary experimental paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-005Pitting corrosionAqueous & localized corrosion · Localized passive-film breakdown

Damage mechanism

Mechanism pathway

Service conditions

Electrolyte plus film-destabilizing chemistry; chloride common, not mandatory

Physical processes

Local failure of passivity permits concentrated attack into the metal

Observable damage

Deep isolated cavities; small openings may hide large subsurface pits

Possible failure mode

Pinhole leak; rupture of a severely weakened section

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Localized penetration; pit attack
Industries / exposed sectors: Chemical; marine; food; water
Typically affected parts: Chemical tanks and other wetted alloy equipment
Susceptible materials: Passivating alloys; the verified case concerns 316Ti stainless steel
Required chemicals / environment: Electrolyte plus film-destabilizing chemistry; chloride common, not mandatory
Influencing parameters: Temperature; potential; halides; surface finish; stagnation
Physical explanation (1–3 processes): Local failure of passivity permits concentrated attack into the metal
Signs and symptoms: Deep isolated cavities; small openings may hide large subsurface pits
Prevention / slowing the damage: Control halides/deposits; select resistant alloys; passivate appropriately; inspect locally
Typical failure outcome: Pinhole leak; rupture of a severely weakened section
Possible consequences: Containment loss; hidden strength reduction; pits may initiate subsequent fatigue or SCC
Can be mistaken for: MIC; crevice corrosion; erosion craters
How to distinguish it: Measure pit depth and distribution; cross-section; analyse deposits and chemistry; morphology alone is insufficient
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G46-21 — Examination and Evaluation of Pitting Corrosion — Official public standard scope (accessed 2026-09-08)
80 ASTM G48-25 — Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution — Official public standard scope (accessed 2026-09-08)
80 TWI — Tank corrosion investigation — Primary case investigation (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-006Crevice corrosionAqueous & localized corrosion · Shielded localized attack

Damage mechanism

Mechanism pathway

Service conditions

Conductive liquid trapped in a restrictive gap; chlorides often aggravate

Physical processes

Oxygen depletion inside a crevice
Acidification and ion concentration destabilize passivity

Observable damage

Attack under gaskets or overlaps; intact adjacent open surface

Possible failure mode

Perforation; joint leakage

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Occluded-cell corrosion
Industries / exposed sectors: Marine; chemical; water; desalination
Typically affected parts: Gaskets, washers, threads, lap joints and clamps
Susceptible materials: Stainless steels; aluminium; other passivating alloys
Required chemicals / environment: Conductive liquid trapped in a restrictive gap; chlorides often aggravate
Influencing parameters: Gap geometry; temperature; stagnation; oxygen access
Physical explanation (1–3 processes): Oxygen depletion inside a crevice
Acidification and ion concentration destabilize passivity
Signs and symptoms: Attack under gaskets or overlaps; intact adjacent open surface
Prevention / slowing the damage: Eliminate crevices; seal-weld where suitable; resistant alloys; clean deposits
Typical failure outcome: Perforation; joint leakage
Possible consequences: Release; loss of sealing/support
Can be mistaken for: Pitting; under-deposit corrosion
How to distinguish it: Demonstrate correspondence with the physical gap; section the joint and map the attack
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Crevice Corrosion — Technical reference (accessed 2026-09-08)
80 TWI — Lab Scale Corrosion Testing for Heat Exchangers (2019) — Primary testing summary (accessed 2026-09-08)
80 ASTM G48-25 — Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-007Under-deposit corrosionAqueous & localized corrosion · Deposit-created microenvironment

Location-defined damage family

Mechanism pathway

Service conditions

Wetted deposits; corrosive species may concentrate beneath them

Physical processes

Boiling beneath porous deposits can concentrate aggressive dissolved species

Observable damage

Local wall loss beneath deposits

Possible failure mode

Leak or local rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Deposit-associated localized corrosion
Industries / exposed sectors: Boilers; cooling water; oil/gas; chemical
Typically affected parts: Tube surfaces; low-flow pipe sections; tank bottoms
Susceptible materials: Carbon steel; low-alloy and stainless steels
Required chemicals / environment: Wetted deposits; corrosive species may concentrate beneath them
Influencing parameters: Deposit porosity; heat flux; flow; bulk and local chemistry
Physical explanation (1–3 processes): Boiling beneath porous deposits can concentrate aggressive dissolved species
Signs and symptoms: Local wall loss beneath deposits
Prevention / slowing the damage: Control fouling and water chemistry; maintain flow; qualified cleaning
Typical failure outcome: Leak or local rupture
Possible consequences: Tube failure; process cross-contamination
Can be mistaken for: MIC; caustic gouging; oxygen pitting
How to distinguish it: Preserve deposits; analyse layers and local conditions; distinguish the specific chemical driver
How often is it seen?: Alberta, 2025: 19% of internal-corrosion pipeline failures were assigned to this mechanism. Denominator: internal-corrosion failures, NOT all 229 pipeline failures or all industries. No representative worldwide rate identified.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 11: Preboiler and Boiler Corrosion Control — Manufacturer technical handbook (accessed 2026-09-08)
80 PHMSA — Fact Sheet: Internal Corrosion — Regulatory technical reference (accessed 2026-09-08)
80 Alberta Energy Regulator — Pipeline Performance: Industry Performance Metrics, 2025 — Regulatory failure statistics (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-008Corrosion under insulationAqueous & localized corrosion · Hidden external attack

Location-defined damage family

Mechanism pathway

Service conditions

Water ingress; salts can intensify damage

Physical processes

Wet insulation retains an electrolyte against metal
Concentration during drying intensifies localized attack

Observable damage

Rust staining; damaged jackets; concealed thinning

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: CUI; external corrosion under insulation
Industries / exposed sectors: Refining; chemical; power; offshore
Typically affected parts: Insulated piping; vessels; supports; penetrations
Susceptible materials: Carbon/low-alloy steel; stainless steel can develop chloride SCC
Required chemicals / environment: Water ingress; salts can intensify damage
Influencing parameters: Wetting/drying; temperature cycles; jacket integrity; drainage
Physical explanation (1–3 processes): Wet insulation retains an electrolyte against metal
Concentration during drying intensifies localized attack
Signs and symptoms: Rust staining; damaged jackets; concealed thinning
Prevention / slowing the damage: Maintain an engineered moisture barrier and inspect concealed surfaces; TSA coatings have been studied for CUI mitigation
Typical failure outcome: Leak or rupture
Possible consequences: Unexpected loss of containment; difficult inspection
Can be mistaken for: Atmospheric corrosion; external chloride SCC; soil attack
How to distinguish it: Inspect beneath insulation; thickness mapping; distinguish metal loss from cracking in stainless steel
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Begg, H. — Evaluation of a New Corrosion Under Insulation Test Method. TWI Report Summary 1097/2018. — Primary research summary (accessed 2026-09-08)
80 TWI — Corrosion Under Insulation at Seminar (13 March 2020) — Technical reference (accessed 2026-09-08)
80 TWI — Research into corrosion under insulation (20 February 2019) — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-009Microbiologically influenced corrosionAqueous & localized corrosion · Biologically influenced electrochemistry

Damage mechanism

Mechanism pathway

Service conditions

Microbial activity in a compatible wet environment; nutrient and redox conditions vary

Physical processes

Microbial activity changes local corrosion reactions and chemistry

Observable damage

Localized attack under biofilms; deposits; sometimes tubercles

Possible failure mode

Pinhole leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: MIC; biocorrosion
Industries / exposed sectors: Water, wastewater, marine and hydrocarbon/process systems
Typically affected parts: Deadlegs; tanks; pipelines; heat exchangers
Susceptible materials: Steels; stainless steels; copper and aluminium alloys
Required chemicals / environment: Microbial activity in a compatible wet environment; nutrient and redox conditions vary
Influencing parameters: Biofilm; stagnation; temperature; redox conditions; treatment history
Physical explanation (1–3 processes): Microbial activity changes local corrosion reactions and chemistry
Signs and symptoms: Localized attack under biofilms; deposits; sometimes tubercles
Prevention / slowing the damage: Control biofilms and deposits; suitable treatment; flow management; compatible materials
Typical failure outcome: Pinhole leak or rupture
Possible consequences: Contamination; release; downtime
Can be mistaken for: Abiotic pitting; under-deposit attack; sulfide corrosion
How to distinguish it: Combine microbiology, chemistry, metallography and operations evidence; finding microbes alone does not prove MIC
How often is it seen?: Alberta, 2025: 7% of internal-corrosion pipeline failures were assigned to this mechanism. Denominator: internal-corrosion failures, NOT all 229 pipeline failures or all industries. No representative worldwide rate identified.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Microbiologically Influenced Corrosion (MIC) — Technical reference (accessed 2026-09-08)
80 Little, B.J. & Lee, J.S. (2006). Diagnosing Microbiologically Influenced Corrosion: A State-of-the-Art Review. CORROSION 62(11), 1006–1017. — Research abstract (accessed 2026-09-08)
80 Alberta Energy Regulator — Pipeline Performance: Industry Performance Metrics, 2025 — Regulatory failure statistics (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-010DC stray-current corrosionAqueous & localized corrosion · Electrical interference

Damage mechanism

Mechanism pathway

Service conditions

Electrolyte and unintended DC current path

Physical processes

Metal dissolves where conventional current leaves the structure into the electrolyte

Observable damage

Concentrated external pits; time-varying structure-to-soil potentials

Possible failure mode

Perforation or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Electrolytic corrosion; stray direct-current attack
Industries / exposed sectors: Pipelines and infrastructure near DC transit or other current sources
Typically affected parts: Buried steel pipes, tanks and electrically continuous piles
Susceptible materials: Conductive metals exposed to an electrolyte
Required chemicals / environment: Electrolyte and unintended DC current path
Influencing parameters: Current magnitude/direction; coating holidays; rail-return design
Physical explanation (1–3 processes): Metal dissolves where conventional current leaves the structure into the electrolyte
Signs and symptoms: Concentrated external pits; time-varying structure-to-soil potentials
Prevention / slowing the damage: Identify current source; engineered drainage/bonding; insulation; coordinated CP
Typical failure outcome: Perforation or rupture
Possible consequences: Leak; shortened asset life
Can be mistaken for: Soil corrosion; AC corrosion; galvanic corrosion
How to distinguish it: Time-synchronized potential/current surveys linked to source operation; locate current-discharge areas
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 The Electrochemical Origin of Internal Stray Currents (2020). Materials Performance 59(9), 26. — Primary technical article (accessed 2026-09-08)
70 AMPP — Cathodic Protection for Corrosion Control — Technical reference (accessed 2026-09-08)
80 PHMSA — Fact Sheet: External Corrosion — Regulatory technical reference (accessed 2026-09-08)
80 National Academies — Corrosion of Buried Steel at New and In-Service Infrastructure, chapter 6 — Scientific consensus report (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-011AC-induced corrosionAqueous & localized corrosion · Electrical interference

Damage mechanism

Mechanism pathway

Service conditions

Soil electrolyte plus induced/conducted AC

Physical processes

Proposed explanations include nonlinear electrochemical rectification and cyclic changes to surface films; no single model explains all AC corrosion.

Observable damage

Severe localized loss at small coating defects

Possible failure mode

Pinhole leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Alternating-current corrosion
Industries / exposed sectors: Pipelines beside AC power lines or rail systems
Typically affected parts: Coating holidays on buried steel pipelines
Susceptible materials: Cathodically protected carbon steel
Required chemicals / environment: Soil electrolyte plus induced/conducted AC
Influencing parameters: AC/DC current density; holiday size; soil chemistry; CP level
Physical explanation (1–3 processes): Proposed explanations include nonlinear electrochemical rectification and cyclic changes to surface films; no single model explains all AC corrosion.
Signs and symptoms: Severe localized loss at small coating defects
Prevention / slowing the damage: AC-interference assessment; engineered grounding/decoupling; monitor coupons and CP
Typical failure outcome: Pinhole leak or rupture
Possible consequences: Pipeline release; electrical safety hazard may coexist
Can be mistaken for: DC corrosion; ordinary external corrosion
How to distinguish it: Measure AC and DC current/potential, coupon loss and coating defects; adequate CP potential alone does not exclude AC damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 The AC Corrosion Mechanisms and Models: A Review. CORROSION 76(2), 188 (2020). — Research abstract (accessed 2026-09-08)
80 Hosokawa, Y. et al. (2004). Alternating-Current Corrosion Risk Arising from Alternating-Current-Powered Rail Transit Systems. CORROSION 60(4), 408–413. — Primary field-study abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-012Intergranular corrosionAqueous & localized corrosion · Grain-boundary selective attack

Damage mechanism

Mechanism pathway

Service conditions

Corrosive electrolyte compatible with the depleted/segregated boundary region

Physical processes

Boundary segregation or precipitation creates locally susceptible regions
Selective boundary dissolution can detach otherwise intact grains

Observable damage

Boundary attack, grain loss and reduced mechanical integrity

Possible failure mode

Leak or brittle-appearing separation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: IGC; intercrystalline corrosion
Industries / exposed sectors: Chemical; aerospace; heat treatment; food
Typically affected parts: Sensitized weld HAZ; heat-exchanger tubes; alloy sheet
Susceptible materials: Susceptible stainless steels and aluminium alloys
Required chemicals / environment: Corrosive electrolyte compatible with the depleted/segregated boundary region
Influencing parameters: Thermal history; sensitization; chemistry; temperature
Physical explanation (1–3 processes): Boundary segregation or precipitation creates locally susceptible regions
Selective boundary dissolution can detach otherwise intact grains
Signs and symptoms: Boundary attack, grain loss and reduced mechanical integrity
Prevention / slowing the damage: Control alloy composition and thermal exposure; appropriate solution treatment; validated corrosion testing
Typical failure outcome: Leak or brittle-appearing separation
Possible consequences: Unexpected loss of ductility and containment
Can be mistaken for: SCC; liquation cracking; exfoliation
How to distinguish it: Metallographic boundary attack plus sensitization/chemistry evidence; assess whether tensile stress was essential
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Intergranular Corrosion — Technical reference (accessed 2026-09-08)
80 TWI — Embrittlement of austenitic steel welds at high temperature — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-013Exfoliation corrosionAqueous & localized corrosion · Advanced intergranular corrosion

Damage mechanism

Mechanism pathway

Service conditions

Corrosive moisture, often chloride-bearing

Physical processes

Intergranular attack follows elongated grain paths
Expanding corrosion products lift surface layers

Observable damage

Leaf-like lifting; bulging; delamination

Possible failure mode

Component separation or fracture after section degradation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: EXCO; layer lifting
Industries / exposed sectors: Aerospace; transport; marine
Typically affected parts: Heavily worked aluminium sections, especially exposed end grains at edges or holes
Susceptible materials: Susceptible high-strength aluminium with flattened, elongated grains
Required chemicals / environment: Corrosive moisture, often chloride-bearing
Influencing parameters: Grain orientation; temper; residual stress; salt wetting
Physical explanation (1–3 processes): Intergranular attack follows elongated grain paths
Expanding corrosion products lift surface layers
Signs and symptoms: Leaf-like lifting; bulging; delamination
Prevention / slowing the damage: Resistant temper/alloy; coatings and sealants; drainage; inspect lap joints
Typical failure outcome: Component separation or fracture after section degradation
Possible consequences: Reduced structural capacity
Can be mistaken for: Lamination defects; blistering; general IGC
How to distinguish it: Cross-section shows corrosion along elongated grain boundaries and wedging products, not a clean manufacturing interface
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Exfoliation — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: aluminium alloys, Job Knowledge 21 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-014DezincificationAqueous & localized corrosion · Dealloying

Damage mechanism

Mechanism pathway

Service conditions

Aqueous electrolyte; chemistry determines susceptibility

Physical processes

Net zinc loss produces a copper-rich porous layer; dissolution and copper redeposition can contribute.

Observable damage

Porous copper-rich layers or localized plugs; strength loss

Possible failure mode

Leak; brittle-appearing fitting break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Selective zinc leaching from brass
Industries / exposed sectors: Water; plumbing; marine; process
Typically affected parts: Brass valves; fittings; tubes; fasteners
Susceptible materials: Susceptible copper-zinc alloys
Required chemicals / environment: Aqueous electrolyte; chemistry determines susceptibility
Influencing parameters: Temperature; stagnation; chloride; pH; alloy phase balance
Physical explanation (1–3 processes): Net zinc loss produces a copper-rich porous layer; dissolution and copper redeposition can contribute.
Signs and symptoms: Porous copper-rich layers or localized plugs; strength loss
Prevention / slowing the damage: Dezincification-resistant brass; water chemistry control; suitable alternative alloy
Typical failure outcome: Leak; brittle-appearing fitting break
Possible consequences: Flooding; loss of isolation
Can be mistaken for: General brass corrosion; ammonia SCC
How to distinguish it: Cross-section and elemental analysis show zinc depletion/porosity rather than a stress-driven crack
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Dealloying (selective leaching) — Technical reference (accessed 2026-09-08)
CUterms

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-015Graphitic corrosion of cast ironAqueous & localized corrosion · Dealloying

Damage mechanism

Mechanism pathway

Service conditions

Corrosive water or moist soil

Physical processes

Iron dissolves around the pre-existing graphite network
Graphite and corrosion products preserve shape while strength falls

Observable damage

Soft dark surface; original shape despite severe weakening

Possible failure mode

Crushing; brittle break; leakage

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Graphitic selective leaching; graphitic corrosion
Industries / exposed sectors: Water; wastewater; buried services
Typically affected parts: Cast-iron mains; valves; pump bodies
Susceptible materials: Graphite-containing cast iron, especially grey iron
Required chemicals / environment: Corrosive water or moist soil
Influencing parameters: Time; soil/water chemistry; graphite morphology
Physical explanation (1–3 processes): Iron dissolves around the pre-existing graphite network
Graphite and corrosion products preserve shape while strength falls
Signs and symptoms: Soft dark surface; original shape despite severe weakening
Prevention / slowing the damage: Protective linings/coatings; appropriate CP; condition assessment and replacement
Typical failure outcome: Crushing; brittle break; leakage
Possible consequences: Sudden main break; flooding
Can be mistaken for: Thermal graphitization: a different metallurgical process
How to distinguish it: Metallography reveals removed iron around pre-existing graphite; thermal graphitization instead precipitates new graphite in steel
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Dealloying (selective leaching) — Technical reference (accessed 2026-09-08)
80 TWI — What is graphitisation? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-016DenickelificationAqueous & localized corrosion · Dealloying

Damage mechanism

Mechanism pathway

Service conditions

Corrosive process condensate; particular deposited/hot-spot environments

Physical processes

Preferential nickel loss creates a copper-rich weakened layer

Observable damage

Porosity; local wall loss; copper-rich residue

Possible failure mode

Tube leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Selective nickel leaching
Industries / exposed sectors: Refining; heat exchange; marine systems
Typically affected parts: Copper-nickel condenser tubes at deposit-associated hot spots
Susceptible materials: Susceptible copper-nickel alloys, including 70/30 Cu-Ni
Required chemicals / environment: Corrosive process condensate; particular deposited/hot-spot environments
Influencing parameters: Temperature differences; deposits; local chemistry; thermal coupling
Physical explanation (1–3 processes): Preferential nickel loss creates a copper-rich weakened layer
Signs and symptoms: Porosity; local wall loss; copper-rich residue
Prevention / slowing the damage: Address deposits, hot spots and stagnant regions within an approved operating programme
Typical failure outcome: Tube leak or rupture
Possible consequences: Cross-contamination; process outage
Can be mistaken for: Dezincification; general Cu-Ni corrosion
How to distinguish it: Elemental mapping confirms nickel depletion, not zinc loss; correlate with temperature/deposit pattern
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 Copper Development Association — Copper-nickel: corrosion resistance and antifouling — Technical reference (accessed 2026-09-08)
CUterms

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-017Filiform corrosionAqueous & localized corrosion · Coating-underfilm attack

Damage mechanism

Mechanism pathway

Service conditions

Moisture penetrates a breached or permeable surface coating

Physical processes

An active filament head advances under the coating
Differential aeration separates head and trailing products

Observable damage

Thread-like tracks below paint; cosmetic blistering

Possible failure mode

Coating disbondment or cosmetic rejection; structural failure is not inevitable

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Underfilm filamentary corrosion
Industries / exposed sectors: Automotive; aerospace; coated products
Typically affected parts: Painted aluminium, steel or magnesium sheet
Susceptible materials: Coated reactive metals
Required chemicals / environment: Moisture penetrates a breached or permeable surface coating
Influencing parameters: Coating defects, moisture permeability and adhesion
Physical explanation (1–3 processes): An active filament head advances under the coating
Differential aeration separates head and trailing products
Signs and symptoms: Thread-like tracks below paint; cosmetic blistering
Prevention / slowing the damage: Use a well-adhered coating with appropriate resistance to water-vapour transmission
Typical failure outcome: Coating disbondment or cosmetic rejection; structural failure is not inevitable
Possible consequences: Appearance degradation; reduced coating protection
Can be mistaken for: General underfilm corrosion; scratch marks; fungal growth
How to distinguish it: Lift coating locally and examine corrosion filaments and metal attack; do not identify from paint pattern alone
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

70 AMPP — Filiform Corrosion (page title: Fillform Corrosion) — Technical reference (accessed 2026-09-08)
80 Van Loo, M. et al. (1953). Filiform Corrosion. CORROSION 9(8), 277–283. — Primary research abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-018Carbon dioxide corrosionProcess-specific aqueous corrosion · Acid-gas aqueous corrosion

Damage mechanism

Mechanism pathway

Service conditions

Free water and dissolved CO2; impurities can change behaviour

Physical processes

Dissolved CO2 establishes an acidic aqueous environment
Iron dissolution competes with protective carbonate-scale formation

Observable damage

General thinning; local pits or mesa-like attack

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: CO2 corrosion; sweet corrosion
Industries / exposed sectors: Oil and gas production and wet CO2-containing process streams
Typically affected parts: Wet pipelines; production tubing; vessels
Susceptible materials: Carbon and low-alloy steels
Required chemicals / environment: Free water and dissolved CO2; impurities can change behaviour
Influencing parameters: CO2 and other gas composition; water chemistry; operating conditions; material
Physical explanation (1–3 processes): Dissolved CO2 establishes an acidic aqueous environment
Iron dissolution competes with protective carbonate-scale formation
Signs and symptoms: General thinning; local pits or mesa-like attack
Prevention / slowing the damage: Manage water and impurities; validated inhibitors; resistant materials; monitor scale/flow
Typical failure outcome: Leak or rupture
Possible consequences: Hydrocarbon/CO2 release; shutdown
Can be mistaken for: Wet H2S corrosion; oxygen corrosion; erosion-corrosion
How to distinguish it: Analyse gas/liquid and carbonate scale; morphology alone does not identify CO2
How often is it seen?: Alberta, 2025: 6% of internal-corrosion pipeline failures were assigned to this mechanism. Denominator: internal-corrosion failures, NOT all 229 pipeline failures or all industries. No representative worldwide rate identified.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — CO2 Corrosion — Technical reference (accessed 2026-09-08)
80 TWI — Selection of Materials for High Pressure CO2 Transport — Technical research paper (accessed 2026-09-08)
80 PHMSA — Fact Sheet: Internal Corrosion — Regulatory technical reference (accessed 2026-09-08)
80 Alberta Energy Regulator — Pipeline Performance: Industry Performance Metrics, 2025 — Regulatory failure statistics (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-019Wet hydrogen sulfide corrosionProcess-specific aqueous corrosion · Acid-gas aqueous corrosion

Damage mechanism

Mechanism pathway

Service conditions

Water and H2S

Physical processes

Iron dissolution forms iron-sulfide products
Film damage or unstable scales permit continued attack

Observable damage

Black sulfide deposits; thinning or pitting

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Sour corrosion; aqueous H2S metal loss
Industries / exposed sectors: Sour oil/gas and associated process equipment
Typically affected parts: Pipelines; separators; sour-water piping
Susceptible materials: Carbon/low-alloy steel; other alloys depending on environment
Required chemicals / environment: Water and H2S
Influencing parameters: pH; H2S activity; temperature; flow; sulfide-film stability
Physical explanation (1–3 processes): Iron dissolution forms iron-sulfide products
Film damage or unstable scales permit continued attack
Signs and symptoms: Black sulfide deposits; thinning or pitting
Prevention / slowing the damage: Sour-service materials; chemistry and flow control; suitable inhibition; monitoring
Typical failure outcome: Leak or rupture
Possible consequences: Toxic H2S release; outage
Can be mistaken for: Sulfidation; SSC; HIC; CO2 corrosion
How to distinguish it: Prove wet service and metal loss; test separately for hydrogen-assisted cracking; black scale alone is not diagnostic
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Sour Testing — Technical reference (accessed 2026-09-08)
80 Al-Mazeedi, H.A., Al-Farhan, A., Tanoli, N. & Abraham, L. (2019). A Study of Galvanic Corrosion in Stagnant Ammonium Bisulfide Solution. International Journal of Corrosion, 1325169, 9 pages. — Primary experimental paper (accessed 2026-09-08)
80 PHMSA — Fact Sheet: Internal Corrosion — Regulatory technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-020Hydrochloric acid corrosionProcess-specific aqueous corrosion · Mineral-acid corrosion

Damage mechanism

Mechanism pathway

Service conditions

Aqueous hydrochloric acid

Physical processes

Acid-driven electrochemical dissolution consumes susceptible metal

Observable damage

Rapid thinning; rough etched surfaces; localized attack

Possible failure mode

Leak; local rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HCl attack; hydrochloric-acid dewpoint corrosion
Industries / exposed sectors: Chemical processing
Typically affected parts: Overhead condensers; piping; acid tanks
Susceptible materials: Carbon steel; many stainless grades; alloy resistance depends on concentration
Required chemicals / environment: Aqueous hydrochloric acid
Influencing parameters: Acid concentration; temperature; oxidizing impurities
Physical explanation (1–3 processes): Acid-driven electrochemical dissolution consumes susceptible metal
Signs and symptoms: Rapid thinning; rough etched surfaces; localized attack
Prevention / slowing the damage: Control chloride sources and condensate chemistry; engineered wash/neutralization; qualified alloy selection
Typical failure outcome: Leak; local rupture
Possible consequences: Acid exposure; process contamination
Can be mistaken for: NH4Cl corrosion; other acid attack
How to distinguish it: Sample initial condensate and deposits; determine chloride, acidity and temperature history
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Haynes International — Corrosive Environments — Manufacturer technical guide (accessed 2026-09-08)
50 Haynes International — HASTELLOY HYBRID-BC1 alloy — Primary manufacturer test data (accessed 2026-09-08)
80 TWI — Corrosion in Petrochemical and Refinery Industries (27 June 2022) — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-021Sulfuric acid corrosionProcess-specific aqueous corrosion · Mineral-acid corrosion

Damage mechanism

Mechanism pathway

Service conditions

Sulfuric acid with water; oxidants/impurities modify attack

Physical processes

Acidic electrochemical attack depends on alloy and the stability of protective surface films

Observable damage

Thinning; etched surfaces; local erosion-corrosion

Possible failure mode

Leak; rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: H2SO4 attack
Industries / exposed sectors: Fertilizer; chemical; mineral processing; batteries
Typically affected parts: Acid tanks; pumps; piping; exchangers
Susceptible materials: Steel and corrosion-resistant alloys, depending strongly on acid concentration
Required chemicals / environment: Sulfuric acid with water; oxidants/impurities modify attack
Influencing parameters: Acid concentration, temperature, impurities and flow
Physical explanation (1–3 processes): Acidic electrochemical attack depends on alloy and the stability of protective surface films
Signs and symptoms: Thinning; etched surfaces; local erosion-corrosion
Prevention / slowing the damage: Select alloy/lining for the actual concentration-temperature envelope; prevent unintended dilution
Typical failure outcome: Leak; rupture
Possible consequences: Acid burns; environmental release
Can be mistaken for: Acid-dewpoint corrosion; HCl attack
How to distinguish it: Analyse acid concentration and impurities; reconstruct dilution/temperature excursions
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Haynes International — Corrosive Environments — Manufacturer technical guide (accessed 2026-09-08)
50 Haynes International — HASTELLOY HYBRID-BC1 alloy — Primary manufacturer test data (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-022Hydrofluoric acid corrosionProcess-specific aqueous corrosion · Mineral-acid corrosion

Damage mechanism

Mechanism pathway

Service conditions

HF-containing service; water and contaminants change severity

Physical processes

Metal dissolution and fluoride-film formation compete
Local film instability accelerates metal loss

Observable damage

Thinning; scale; isolated highly corroded components

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HF corrosion
Industries / exposed sectors: Refinery alkylation; fluorochemical processing
Typically affected parts: HF-alkylation piping, including elbows
Susceptible materials: Carbon-steel components; residual copper/nickel chemistry matters
Required chemicals / environment: HF-containing service; water and contaminants change severity
Influencing parameters: Component composition and actual HF-service conditions
Physical explanation (1–3 processes): Metal dissolution and fluoride-film formation compete
Local film instability accelerates metal loss
Signs and symptoms: Thinning; scale; isolated highly corroded components
Prevention / slowing the damage: Strict chemistry/material control; component-level inspection; engineered containment and isolation
Typical failure outcome: Leak or rupture
Possible consequences: Highly toxic release; fire if hydrocarbons are present
Can be mistaken for: HCl corrosion; localized erosion; weld-related attack
How to distinguish it: Verify HF duty, water history and component chemistry; thickness-map individual fittings
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: Philadelphia Energy Solutions, 21 June 2019: a severely corroded HF-service elbow ruptured, causing explosions/fire and an HF release. CSB linked accelerated corrosion to component chemistry.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 US Chemical Safety Board (2022) — Final report into 2019 PES fire and explosion in Philadelphia — Primary accident investigation (accessed 2026-09-08)
50 Haynes International — Corrosive Environments — Manufacturer technical guide (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-023Phosphoric acid corrosionProcess-specific aqueous corrosion · Mineral-acid corrosion

Damage mechanism

Mechanism pathway

Service conditions

Aqueous phosphoric acid with process-dependent sulfate, metal-ion, fluoride and chloride impurities

Physical processes

Acid dissolution attacks insufficiently resistant alloys
Impurities can destabilize passive films

Observable damage

General loss; pits or preferential weld attack

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: H3PO4 attack
Industries / exposed sectors: Fertilizer; phosphates; chemical processing
Typically affected parts: Fertilizer-grade phosphoric-acid evaporator tubing and related process equipment
Susceptible materials: Steels; stainless and nickel alloys depending on purity
Required chemicals / environment: Aqueous phosphoric acid with process-dependent sulfate, metal-ion, fluoride and chloride impurities
Influencing parameters: Acid concentration, temperature, impurity content and deposits
Physical explanation (1–3 processes): Acid dissolution attacks insufficiently resistant alloys
Impurities can destabilize passive films
Signs and symptoms: General loss; pits or preferential weld attack
Prevention / slowing the damage: Select against actual wet-process acid, not reagent-acid data alone; control impurities and flow
Typical failure outcome: Leak or rupture
Possible consequences: Acid/slurry release; production loss
Can be mistaken for: Slurry erosion; HCl/HF corrosion
How to distinguish it: Analyse acid impurities and solids; compare shielded and impinged areas; inspect weld/base metal
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Lizlovs, E.A. (1969). Corrosion Behavior of Types 304 and 316 Stainless Steels in Hot 85% Phosphoric Acid. CORROSION 25(9), 389–393. — Primary research abstract (accessed 2026-09-08)
50 Haynes International — HASTELLOY G-35 alloy — Primary manufacturer test data (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-024Caustic corrosionProcess-specific aqueous corrosion · Concentrated-alkali corrosion

Damage mechanism

Mechanism pathway

Service conditions

Locally concentrated sodium hydroxide in boiler water

Physical processes

Concentrated caustic dissolves protective magnetite, exposing steel to continued metal loss

Observable damage

Irregular gouges or thinning

Possible failure mode

Tube leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Caustic gouging; alkaline metal loss
Industries / exposed sectors: Boilers; refining; chemical; pulp
Typically affected parts: Boiler tubes under deposits; caustic piping; evaporators
Susceptible materials: Carbon/low-alloy steels; susceptible stainless alloys
Required chemicals / environment: Locally concentrated sodium hydroxide in boiler water
Influencing parameters: Local concentration; temperature; deposits; heat flux; dryout
Physical explanation (1–3 processes): Concentrated caustic dissolves protective magnetite, exposing steel to continued metal loss
Signs and symptoms: Irregular gouges or thinning
Prevention / slowing the damage: Prevent caustic concentration/dryout; control deposits and chemistry; suitable materials
Typical failure outcome: Tube leak or rupture
Possible consequences: Hot fluid release; outage
Can be mistaken for: Caustic SCC; acid phosphate corrosion; FAC
How to distinguish it: Metallography distinguishes wall loss from stress-driven cracks; analyse deposit chemistry and heat-flux pattern
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 11: Preboiler and Boiler Corrosion Control — Manufacturer technical handbook (accessed 2026-09-08)
50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-025Amine-unit corrosionProcess-specific aqueous corrosion · Solvent-system corrosion

Damage mechanism

Mechanism pathway

Service conditions

Aqueous amine with acid gases/degradation products; heat-stable salts can aggravate

Physical processes

Heat-stable salts can increase solution corrosiveness; the effect depends on salt identity and concentration

Observable damage

Metal loss; morphology must be confirmed for the actual solvent

Possible failure mode

Leak or equipment rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Amine corrosion; acid-gas treating corrosion
Industries / exposed sectors: Gas sweetening; refining; carbon capture
Typically affected parts: Regenerators; reboilers; rich-amine lines; exchangers
Susceptible materials: Carbon steel and304 stainless steel in the verified MEA study; alloy response is chemistry-dependent
Required chemicals / environment: Aqueous amine with acid gases/degradation products; heat-stable salts can aggravate
Influencing parameters: Temperature and acid-gas composition; solvent and heat-stable-salt composition
Physical explanation (1–3 processes): Heat-stable salts can increase solution corrosiveness; the effect depends on salt identity and concentration
Signs and symptoms: Metal loss; morphology must be confirmed for the actual solvent
Prevention / slowing the damage: Control solvent quality and heat-stable salts; oxygen exclusion where appropriate; flow and material review
Typical failure outcome: Leak or equipment rupture
Possible consequences: Toxic/flammable release; solvent contamination
Can be mistaken for: Amine SCC; wet H2S corrosion; CO2 corrosion
How to distinguish it: Analyse solvent, gas loading and salts; distinguish cracks from metal loss
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Tanthapanichakoon, W., Veawab, A. & McGarvey, B. (2006). Electrochemical Investigation on the Effect of Heat-stable Salts on Corrosion in CO2 Capture Plants Using Aqueous Solution of MEA. Industrial & Engineering Chemistry Research 45(8), 2586–2593. — Primary experimental paper (accessed 2026-09-08)
80 Javidi, Ghassemi & Lalehparvar (2017). Amine corrosion and cracking of API 5L X52 in diethanolamine service. Corrosion Engineering, Science and Technology 52(7). — Primary investigation (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-026Ammonium bisulfide corrosionProcess-specific aqueous corrosion · Sour-water salt corrosion

Damage mechanism

Mechanism pathway

Service conditions

Water containing ammonia and hydrogen sulfide/bisulfide species

Physical processes

Electrochemical iron loss accompanies formation of sulfide-containing corrosion products

Observable damage

Rapid thinning; localized grooves; sulfide products

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: NH4HS corrosion; ammonium hydrosulfide corrosion
Industries / exposed sectors: Hydroprocessing; refining; sour-water stripping
Typically affected parts: Sour-water ammonia-rectifier heat-exchanger nozzle in the verified case
Susceptible materials: Carbon steel in the verified nozzle investigation
Required chemicals / environment: Water containing ammonia and hydrogen sulfide/bisulfide species
Influencing parameters: Salt concentration; temperature; turbulence; velocity; wash-water distribution
Physical explanation (1–3 processes): Electrochemical iron loss accompanies formation of sulfide-containing corrosion products
Signs and symptoms: Rapid thinning; localized grooves; sulfide products
Prevention / slowing the damage: Engineered water-wash distribution; concentration/flow control; appropriate materials and thickness mapping
Typical failure outcome: Leak or rupture
Possible consequences: Toxic/flammable release; exchanger outage
Can be mistaken for: Wet H2S corrosion; erosion-corrosion; NH4Cl attack
How to distinguish it: Analyse NH4HS-related chemistry, products and flow locations; check for concurrent HIC
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: Published 2026 refinery case: metallurgical/electrochemical investigation attributed sour-water exchanger damage to NH4HS-related corrosion. A fatal/offsite catastrophe was not established in that paper.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Al-Mazeedi, H.A., Al-Farhan, A., Tanoli, N. & Abraham, L. (2019). A Study of Galvanic Corrosion in Stagnant Ammonium Bisulfide Solution. International Journal of Corrosion, 1325169, 9 pages. — Primary experimental paper (accessed 2026-09-08)
80 Nicacio, J.A.P., de Freitas Cunha Lins, V. & de Arruda Santos, L. (2026). Failure Analysis of a Heat Exchanger in the Sour Water Unit of an Oil Refinery due to Ammonium Bisulfide Corrosion. Journal of Failure Analysis and Prevention 26, 559–570. — Primary failure investigation (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-027Ammonium chloride corrosionProcess-specific aqueous corrosion · Hygroscopic-salt corrosion

Damage mechanism

Mechanism pathway

Service conditions

Solid ammonium chloride deposits that absorb environmental moisture

Physical processes

Hygroscopic salt wetting establishes a concentrated corrosive environment

Observable damage

Localized thinning beneath salt; pits; plugging

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: NH4Cl salt corrosion
Industries / exposed sectors: Refining; hydroprocessing
Typically affected parts: Hydroprocessing reactor-effluent equipment exposed to NH4Cl deposits
Susceptible materials: Carbon steel and susceptible stainless/alloy materials; response differs by material
Required chemicals / environment: Solid ammonium chloride deposits that absorb environmental moisture
Influencing parameters: Relative humidity, temperature and alloy
Physical explanation (1–3 processes): Hygroscopic salt wetting establishes a concentrated corrosive environment
Signs and symptoms: Localized thinning beneath salt; pits; plugging
Prevention / slowing the damage: Limit salt precursors; engineered water washing; avoid dry salt accumulation; inspect deposition zones
Typical failure outcome: Leak or rupture
Possible consequences: Toxic/flammable release; blockage
Can be mistaken for: HCl dewpoint corrosion; NH4HS corrosion
How to distinguish it: Identify chloride-rich salt and wetting conditions; distinguish first-condensate attack from hygroscopic salt wetting
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Toba, K., Suzuki, T., Kawano, K. & Sakai, J. (2011). Effect of Relative Humidity on Ammonium Chloride Corrosion in Refineries. CORROSION. — Primary experimental paper (accessed 2026-09-08)
80 TWI — Corrosion in Petrochemical and Refinery Industries (27 June 2022) — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-028Flue-gas acid-dewpoint corrosionProcess-specific aqueous corrosion · Condensate corrosion

Damage mechanism

Mechanism pathway

Service conditions

Sulfur oxides and water in sulfur-bearing-fuel combustion gas

Physical processes

Acid condenses on sufficiently cold surfaces
Liquid acid consumes exposed metal

Observable damage

Cold-end thinning; rust/acid deposits; perforation

Possible failure mode

Perforation; duct leakage or collapse

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Cold-end corrosion; sulfuric-acid dewpoint corrosion
Industries / exposed sectors: Power; boilers; furnaces; incineration
Typically affected parts: Air heaters; economizers; ducts; stacks
Susceptible materials: Carbon/low-alloy steels; unsuitable linings/alloys
Required chemicals / environment: Sulfur oxides and water in sulfur-bearing-fuel combustion gas
Influencing parameters: Metal temperature relative to actual acid dewpoint; fuel chemistry; deposits
Physical explanation (1–3 processes): Acid condenses on sufficiently cold surfaces
Liquid acid consumes exposed metal
Signs and symptoms: Cold-end thinning; rust/acid deposits; perforation
Prevention / slowing the damage: Control cold spots and combustion chemistry; suitable coatings/materials; drainage
Typical failure outcome: Perforation; duct leakage or collapse
Possible consequences: Flue-gas escape; efficiency loss; outage
Can be mistaken for: Atmospheric corrosion; high-temperature hot corrosion
How to distinguish it: Compare surface temperature with measured/composition-based acid dew point and examine acidic condensate
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 22: Cold-End Deposition and Corrosion Control — Manufacturer technical handbook (accessed 2026-09-08)
50 Haynes International — Corrosive Environments — Manufacturer technical guide (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-029Oxygen pitting in boiler/feedwater systemsProcess-specific aqueous corrosion · Oxidant-driven localized corrosion

Damage mechanism

Mechanism pathway

Service conditions

Dissolved oxygen in water

Physical processes

Cathodic oxygen reduction supports anodic iron dissolution

Observable damage

Localized pits, sometimes beneath oxide caps

Possible failure mode

Tube or pipe leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Dissolved-oxygen attack; oxygen corrosion
Industries / exposed sectors: Power; industrial steam; district heating
Typically affected parts: Feedwater lines, economizers and boiler tubes
Susceptible materials: Carbon/low-alloy steels
Required chemicals / environment: Dissolved oxygen in water
Influencing parameters: Oxygen ingress; stagnation; temperature; pH; deposits
Physical explanation (1–3 processes): Cathodic oxygen reduction supports anodic iron dissolution
Signs and symptoms: Localized pits, sometimes beneath oxide caps
Prevention / slowing the damage: Control unintended oxygen ingress and use a plant-specific operating and layup programme
Typical failure outcome: Tube or pipe leak
Possible consequences: Steam/water release; shutdown
Can be mistaken for: MIC; chloride pitting; under-deposit corrosion
How to distinguish it: Correlate oxygen/layup records, pit/deposit chemistry and biological evidence; tubercles alone do not establish MIC
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 11: Preboiler and Boiler Corrosion Control — Manufacturer technical handbook (accessed 2026-09-08)
50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-030Acid phosphate corrosionProcess-specific aqueous corrosion · Deposit-related boiler corrosion

Damage mechanism

Mechanism pathway

Service conditions

Locally concentrated acidic phosphate beneath deposits

Physical processes

Deposits and local phosphate chemistry dissolve the protective magnetite layer

Observable damage

Gouging under adherent deposits; maricite may identify the reaction products

Possible failure mode

Tube leakage or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: APC; acid-phosphate boiler-tube attack
Industries / exposed sectors: Power; industrial boilers
Typically affected parts: Deposited boiler waterwalls and HRSG evaporator tubes
Susceptible materials: Carbon and low-alloy boiler steels
Required chemicals / environment: Locally concentrated acidic phosphate beneath deposits
Influencing parameters: Phosphate treatment history; local Na:P balance; hideout; heat flux
Physical explanation (1–3 processes): Deposits and local phosphate chemistry dissolve the protective magnetite layer
Signs and symptoms: Gouging under adherent deposits; maricite may identify the reaction products
Prevention / slowing the damage: Qualified boiler chemistry programme; avoid inappropriate phosphate dosing; manage deposits
Typical failure outcome: Tube leakage or rupture
Possible consequences: Forced outage; hot-fluid release
Can be mistaken for: Caustic gouging; oxygen pitting; boiler hydrogen damage
How to distinguish it: Preserve deposits for phase analysis and compare treatment/hideout history; phosphate hideout alone is insufficient
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Dooley, B. & McNaughton, W. (EPRI, 1997). Don’t let those boiler tubes fail again. Power Engineering. — Primary institutional authors’ technical article (accessed 2026-09-08)
50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)
80 Dooley, R.B. and Bursik, A. (2010). Acid Phosphate Corrosion. PowerPlant Chemistry 12(6), 368–372. — public_full_text (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-031Chloride stress corrosion crackingEnvironment-assisted cracking & hydrogen · Anodic environment-assisted cracking

Damage mechanism

Mechanism pathway

Service conditions

Chloride-bearing moisture plus tensile stress and a susceptible microstructure

Physical processes

Film rupture and localized dissolution assist crack initiation/growth
Crack-tip chemistry and deformation sustain environmentally assisted propagation

Observable damage

Often branched transgranular cracks; small leaks; little general corrosion

Possible failure mode

Leak or brittle-appearing rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Chloride SCC; Cl-SCC
Industries / exposed sectors: Chemical; refining; marine; power
Typically affected parts: Hot stainless piping; exchangers; insulated surfaces
Susceptible materials: Susceptible austenitic stainless steels; susceptibility varies by alloy
Required chemicals / environment: Chloride-bearing moisture plus tensile stress and a susceptible microstructure
Influencing parameters: Temperature; chloride concentration; potential; evaporation; residual stress
Physical explanation (1–3 processes): Film rupture and localized dissolution assist crack initiation/growth
Crack-tip chemistry and deformation sustain environmentally assisted propagation
Signs and symptoms: Often branched transgranular cracks; small leaks; little general corrosion
Prevention / slowing the damage: Prevent chloride concentration; resistant materials; stress reduction where qualified; inspect cracking-prone locations
Typical failure outcome: Leak or brittle-appearing rupture
Possible consequences: Unexpected containment loss
Can be mistaken for: Thermal fatigue; other SCC; intergranular corrosion
How to distinguish it: Combine crack-path metallography, chloride evidence and tensile-stress history; branching alone is not proof
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Stress Corrosion Cracking Testing — Technical reference (accessed 2026-09-08)
80 ASTM G48-25 — Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution — Official public standard scope (accessed 2026-09-08)
80 Begg, H. — Evaluation of a New Corrosion Under Insulation Test Method. TWI Report Summary 1097/2018. — Primary research summary (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-032Caustic stress corrosion crackingEnvironment-assisted cracking & hydrogen · Alkaline environment-assisted cracking

Damage mechanism

Mechanism pathway

Service conditions

Concentrated hydroxide plus tensile stress

Physical processes

Stress-assisted passive-film breakdown promotes localized cracking
Preferential grain-boundary attack can support propagation

Observable damage

Frequently intergranular, branched cracks near stressed regions

Possible failure mode

Leak or sudden rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Caustic SCC; caustic embrittlement
Industries / exposed sectors: Refining; boilers; chemical; pulp
Typically affected parts: Welds; concentrated-caustic piping; vessels
Susceptible materials: Carbon/low-alloy steel; susceptible stainless and nickel alloys
Required chemicals / environment: Concentrated hydroxide plus tensile stress
Influencing parameters: Temperature; caustic concentration; stress; deposits; alloy condition
Physical explanation (1–3 processes): Stress-assisted passive-film breakdown promotes localized cracking
Preferential grain-boundary attack can support propagation
Signs and symptoms: Frequently intergranular, branched cracks near stressed regions
Prevention / slowing the damage: Control concentration and temperature; suitable alloy; qualified stress relief; avoid deposits/dryout
Typical failure outcome: Leak or sudden rupture
Possible consequences: Hot caustic exposure; outage
Can be mistaken for: Caustic gouging; weld H cracking; carbonate SCC
How to distinguish it: Cracks rather than gouges; confirm caustic chemistry and stress/thermal history; section weld and HAZ
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Stress Corrosion Cracking Testing — Technical reference (accessed 2026-09-08)
50 Veolia Water Technologies — Water Handbook, chapter 11: Preboiler and Boiler Corrosion Control — Manufacturer technical handbook (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-033Ammonia stress corrosion cracking of copper alloysEnvironment-assisted cracking & hydrogen · Ammoniacal environment-assisted cracking

Damage mechanism

Mechanism pathway

Service conditions

Ammoniacal moisture; oxygen/oxidizing conditions commonly participate

Physical processes

Ammonia-containing chemistry destabilizes stressed surface regions
Localized dissolution and film rupture support crack growth

Observable damage

Intergranular or transgranular cracks; tarnish may occur

Possible failure mode

Fitting fracture or tube leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Season cracking; ammonia SCC of brass
Industries / exposed sectors: Refrigeration surroundings; marine; chemical; storage
Typically affected parts: Brass fittings; tubes; stressed fasteners
Susceptible materials: Susceptible brasses and other copper alloys; not all Cu-Ni equally susceptible
Required chemicals / environment: Ammoniacal moisture; oxygen/oxidizing conditions commonly participate
Influencing parameters: Residual stress; alloy composition; ammonia activity; pH; temperature
Physical explanation (1–3 processes): Ammonia-containing chemistry destabilizes stressed surface regions
Localized dissolution and film rupture support crack growth
Signs and symptoms: Intergranular or transgranular cracks; tarnish may occur
Prevention / slowing the damage: Exclude ammoniacal contamination; reduce residual stress; qualified resistant materials
Typical failure outcome: Fitting fracture or tube leak
Possible consequences: Loss of containment; component separation
Can be mistaken for: Dezincification; fatigue; general ammoniacal corrosion
How to distinguish it: Use metallography and zinc mapping; prove ammonia exposure and stress; accelerated tests rank susceptibility, not life
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G37-98(2021) — Use of Mattsson’s Solution of pH 7.2 to Evaluate the Stress-Corrosion Cracking Susceptibility of Copper-Zinc Alloys — Official public standard scope (accessed 2026-09-08)
70 Copper Development Association — Copper-nickel: corrosion resistance and antifouling — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-034Carbonate stress corrosion crackingEnvironment-assisted cracking & hydrogen · Alkaline environment-assisted cracking

Environment-specific SCC subtype

Mechanism pathway

Service conditions

Aqueous carbonate/bicarbonate chemistry plus tensile stress

Physical processes

Active/passive electrochemistry enables stress-assisted localized dissolution

Observable damage

Often intergranular branched cracks near stressed weld regions

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Carbonate SCC; carbonate/bicarbonate cracking
Industries / exposed sectors: Refining; CO2-removal/chemical plants
Typically affected parts: Carbonate-solvent equipment; wet process piping; welds
Susceptible materials: Carbon steel
Required chemicals / environment: Aqueous carbonate/bicarbonate chemistry plus tensile stress
Influencing parameters: pH; potential; temperature; carbonate concentration; weld stress
Physical explanation (1–3 processes): Active/passive electrochemistry enables stress-assisted localized dissolution
Signs and symptoms: Often intergranular branched cracks near stressed weld regions
Prevention / slowing the damage: Control the actual solvent/process chemistry; qualified stress relief and inspection
Typical failure outcome: Leak or rupture
Possible consequences: Process release; outage
Can be mistaken for: Caustic SCC; amine SCC; high-pH pipeline SCC
How to distinguish it: Establish service chemistry and potential; compare crack path with weld condition; do not infer carbonate solely from deposits
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Schutt, H.U. (1992). Corrosion Inhibition Alternatives in Carbonate Solvent Based Carbon Dioxide Removal Systems. NACE paper 92455, 1–9. — Primary technical paper (accessed 2026-09-08)
80 TWI — Stress Corrosion Cracking Testing — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-035Polythionic acid stress corrosion crackingEnvironment-assisted cracking & hydrogen · Shutdown-related intergranular SCC

Damage mechanism

Mechanism pathway

Service conditions

Sulfide scales exposed to moisture and oxygen; tensile stress

Physical processes

Sulfide scales react during wet air exposure
Acidic sulfur species attack chromium-depleted boundaries under tensile stress

Observable damage

Intergranular cracking, commonly discovered during/after shutdown

Possible failure mode

Leak or rupture on restart

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: PASCC; polythionic SCC
Industries / exposed sectors: Refining; petrochemical; sulfur-bearing high-temperature service
Typically affected parts: Sensitized stainless furnace tubes; piping; weld HAZ
Susceptible materials: Sensitized austenitic stainless and susceptible nickel alloys
Required chemicals / environment: Sulfide scales exposed to moisture and oxygen; tensile stress
Influencing parameters: Shutdown wetting; sensitization; air entry; sulfur scale
Physical explanation (1–3 processes): Sulfide scales react during wet air exposure
Acidic sulfur species attack chromium-depleted boundaries under tensile stress
Signs and symptoms: Intergranular cracking, commonly discovered during/after shutdown
Prevention / slowing the damage: Qualified shutdown protection; exclude moist oxygen; avoid sensitization; approved neutralization procedures
Typical failure outcome: Leak or rupture on restart
Possible consequences: Hydrocarbon release; fire; outage
Can be mistaken for: IGC; chloride SCC; high-temperature cracking
How to distinguish it: Demonstrate sensitization, sulfur scale and wet shutdown exposure; section grain-boundary cracks
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Shargay, C.A. (2017). Assessing Stress Corrosion Cracking Risks on Stainless Steel Piping and Equipment. CORROSION 2017, paper C2017-08899, pp. 1–22. — Primary technical paper (accessed 2026-09-08)
70 AMPP — Intergranular Corrosion — Technical reference (accessed 2026-09-08)
80 TWI — Embrittlement of austenitic steel welds at high temperature — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-036Near-neutral-pH pipeline stress corrosion crackingEnvironment-assisted cracking & hydrogen · External pipeline SCC

Damage mechanism

Mechanism pathway

Service conditions

Groundwater with dissolved CO2 beneath shielding coatings; tensile stress

Physical processes

Environmental dissolution and hydrogen effects assist cracking
Cyclic loading can accelerate transgranular crack growth

Observable damage

Axial crack colonies; often transgranular cracks with some corrosion

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Low-pH pipeline SCC; near-neutral SCC
Industries / exposed sectors: Gas and liquid transmission
Typically affected parts: Pipe exterior beneath disbonded coatings
Susceptible materials: Carbon-steel linepipe
Required chemicals / environment: Groundwater with dissolved CO2 beneath shielding coatings; tensile stress
Influencing parameters: Pressure cycles; local pH; coating disbondment; hydrogen entry
Physical explanation (1–3 processes): Environmental dissolution and hydrogen effects assist cracking
Cyclic loading can accelerate transgranular crack growth
Signs and symptoms: Axial crack colonies; often transgranular cracks with some corrosion
Prevention / slowing the damage: Coating rehabilitation; pressure-cycle review; suitable SCC inspection and mitigation
Typical failure outcome: Leak or rupture
Possible consequences: Product release; possible fire/explosion
Can be mistaken for: High-pH SCC; corrosion fatigue; HIC
How to distinguish it: Combine external coating/soil evidence with crack path and chemistry; operating stress is essential context
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 PHMSA — Fact Sheet: Stress Corrosion Cracking — Regulatory technical reference (accessed 2026-09-08)
80 PHMSA — Pipeline Failure Causes (updated 20 April 2026) — Regulatory taxonomy (accessed 2026-09-08)
80 TWI — Hydrogen Embrittlement Testing — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-037High-pH pipeline stress corrosion crackingEnvironment-assisted cracking & hydrogen · External alkaline pipeline SCC

Damage mechanism

Mechanism pathway

Service conditions

Concentrated carbonate/bicarbonate electrolyte plus tensile stress

Physical processes

Active/passive film rupture and dissolution support predominantly intergranular cracking

Observable damage

Axial crack colonies; intergranular paths in characteristic chemistry

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Classical pipeline SCC
Industries / exposed sectors: Gas and liquid transmission
Typically affected parts: Pipe surfaces beneath disbonded coatings
Susceptible materials: Carbon-steel linepipe
Required chemicals / environment: Concentrated carbonate/bicarbonate electrolyte plus tensile stress
Influencing parameters: Temperature; potential; concentration; stress cycles; coating shielding
Physical explanation (1–3 processes): Active/passive film rupture and dissolution support predominantly intergranular cracking
Signs and symptoms: Axial crack colonies; intergranular paths in characteristic chemistry
Prevention / slowing the damage: Coating/CP coordination; temperature and cycling review; validated crack detection
Typical failure outcome: Leak or rupture
Possible consequences: Loss of containment; potential fire
Can be mistaken for: Near-neutral SCC; carbonate SCC in process equipment; fatigue
How to distinguish it: Intergranular path plus external alkaline environment; do not use crack orientation alone
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 PHMSA — Fact Sheet: Stress Corrosion Cracking — Regulatory technical reference (accessed 2026-09-08)
80 Schutt, H.U. (1992). Corrosion Inhibition Alternatives in Carbonate Solvent Based Carbon Dioxide Removal Systems. NACE paper 92455, 1–9. — Primary technical paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-038Primary-water stress corrosion crackingEnvironment-assisted cracking & hydrogen · Nuclear primary-water SCC

Damage mechanism

Mechanism pathway

Service conditions

High-temperature primary water plus tensile stress

Physical processes

Grain-boundary oxidation and crack-tip deformation interact under tensile loading

Observable damage

Often intergranular cracking; leakage products; limited external warning

Possible failure mode

Leak; possible pressure-boundary rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: PWSCC
Industries / exposed sectors: Pressurized-water nuclear plants
Typically affected parts: Penetrations; nozzle welds; pressurizer heaters; steam-generator tubes
Susceptible materials: Susceptible nickel alloys, notably Alloy 600 and weld metals 82/182
Required chemicals / environment: High-temperature primary water plus tensile stress
Influencing parameters: Temperature; dissolved hydrogen/oxygen potential; cold work; microstructure
Physical explanation (1–3 processes): Grain-boundary oxidation and crack-tip deformation interact under tensile loading
Signs and symptoms: Often intergranular cracking; leakage products; limited external warning
Prevention / slowing the damage: Resistant qualified alloys; stress mitigation; primary-water control; targeted volumetric inspection
Typical failure outcome: Leak; possible pressure-boundary rupture
Possible consequences: Unplanned outage; nuclear safety challenge
Can be mistaken for: Thermal fatigue; fabrication cracks; boric-acid metal loss
How to distinguish it: Identify alloy and primary-water exposure; metallography and crack-location evidence; inspect beyond surface staining
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 NRC — Pressurizer issues — Regulatory operating-experience reference (accessed 2026-09-08)
80 NRC — NUREG/CR-7276: Stress corrosion cracking of Alloy 690 and weld metals 52/152 (2023) — Primary institutional research abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-039Hydrogen embrittlementEnvironment-assisted cracking & hydrogen · Hydrogen-assisted loss of ductility

Umbrella damage mechanism

Mechanism pathway

Service conditions

Absorbed hydrogen from corrosion, processing, CP or gaseous hydrogen

Physical processes

Hydrogen-enhanced localized plasticity (HELP)
Hydrogen-enhanced decohesion (HEDE)
Other coupled mechanisms may contribute; no single model explains every alloy

Observable damage

Delayed brittle-appearing cracks; reduced ductility/toughness

Possible failure mode

Sudden fracture or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HE; hydrogen-assisted cracking; hydrogen stress cracking
Industries / exposed sectors: Fasteners; energy; plating; marine; hydrogen systems
Typically affected parts: High-strength bolts; springs; welds; pressure boundaries
Susceptible materials: High-strength steels; susceptible titanium, nickel and other alloys
Required chemicals / environment: Absorbed hydrogen from corrosion, processing, CP or gaseous hydrogen
Influencing parameters: Hydrogen availability; strength; tensile stress; trapping; temperature
Physical explanation (1–3 processes): Hydrogen-enhanced localized plasticity (HELP)
Hydrogen-enhanced decohesion (HEDE)
Other coupled mechanisms may contribute; no single model explains every alloy
Signs and symptoms: Delayed brittle-appearing cracks; reduced ductility/toughness
Prevention / slowing the damage: Control hydrogen entry and strength; qualified processing/baking; avoid excessive CP; hydrogen-service testing
Typical failure outcome: Sudden fracture or leak
Possible consequences: Loss of load/containment; injury potential
Can be mistaken for: SSC; brittle cleavage; fatigue; HTHA
How to distinguish it: Exposure/processing history plus fractography and material testing; low measured hydrogen after delay does not exclude prior hydrogen
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is Hydrogen Embrittlement? Causes, Effects and Prevention — Technical reference (accessed 2026-09-08)
80 TWI — Hydrogen Embrittlement Testing — Technical reference (accessed 2026-09-08)
80 Woollin, P. & Murphy, W. (2001). Hydrogen Embrittlement Stress Corrosion Cracking of Superduplex Stainless Steel. CORROSION 2001, paper 01018. — Primary failure investigation (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-040Sulfide stress crackingEnvironment-assisted cracking & hydrogen · Wet-H2S hydrogen-assisted cracking

Damage mechanism

Mechanism pathway

Service conditions

Wet H2S plus tensile stress

Physical processes

Sour corrosion promotes hydrogen entry
Hydrogen-assisted fracture occurs in a stressed susceptible material

Observable damage

Brittle-appearing cracks; little warning; possible weld/HAZ concentration

Possible failure mode

Sudden break or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: SSC; sulphide stress cracking
Industries / exposed sectors: Oil/gas; refining; sour service
Typically affected parts: Bolts; weld HAZ; tubing; valves; pressure equipment
Susceptible materials: Susceptible high-strength/hard steels; some other alloys
Required chemicals / environment: Wet H2S plus tensile stress
Influencing parameters: Hardness; microstructure; pH; H2S partial pressure; stress
Physical explanation (1–3 processes): Sour corrosion promotes hydrogen entry
Hydrogen-assisted fracture occurs in a stressed susceptible material
Signs and symptoms: Brittle-appearing cracks; little warning; possible weld/HAZ concentration
Prevention / slowing the damage: Qualified sour-service material and hardness; weld control; environment management
Typical failure outcome: Sudden break or leak
Possible consequences: Toxic/flammable release; loss of restraint
Can be mistaken for: HIC; SOHIC; weld hydrogen cracking
How to distinguish it: Assess hardness/stress and sour exposure; distinguish stress-driven cracks from rolling-plane HIC arrays
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — A review of the effect of cold-work on resistance to sulphide stress cracking (March 2007) — Technical research paper (accessed 2026-09-08)
80 TWI — Sour Testing — Technical reference (accessed 2026-09-08)
80 TWI — What is Hydrogen Embrittlement? Causes, Effects and Prevention — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-041Hydrogen-induced crackingEnvironment-assisted cracking & hydrogen · Internal hydrogen damage

Damage mechanism

Mechanism pathway

Service conditions

Hydrogen charging, commonly wet H2S

Physical processes

Hydrogen accumulates at internal traps and recombines
Internal pressure creates planar cracks which can link stepwise

Observable damage

Internal laminarlike cracks parallel to rolling; possible blistering

Possible failure mode

Leak or rupture after linked cracking

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HIC; stepwise cracking
Industries / exposed sectors: Sour oil/gas; refining
Typically affected parts: Linepipe walls; vessel plates; wet sour-service equipment
Susceptible materials: Susceptible rolled carbon/low-alloy steel with traps/inclusions
Required chemicals / environment: Hydrogen charging, commonly wet H2S
Influencing parameters: Steel cleanliness; trapping sites; pH; charging severity
Physical explanation (1–3 processes): Hydrogen accumulates at internal traps and recombines
Internal pressure creates planar cracks which can link stepwise
Signs and symptoms: Internal laminarlike cracks parallel to rolling; possible blistering
Prevention / slowing the damage: HIC-resistant clean steel; appropriate sour-service control; qualified testing and UT
Typical failure outcome: Leak or rupture after linked cracking
Possible consequences: Loss of containment; reduced pressure capacity
Can be mistaken for: Laminations; SOHIC; lamellar tearing
How to distinguish it: Section cracks and inclusions; establish charging history; applied tensile stress is not required for HIC initiation
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Pargeter, R.J. (2007). Susceptibility to SOHIC for Linepipe and Pressure Vessel Steels: Review of Current Knowledge. NACE 2007. — Technical research paper (accessed 2026-09-08)
80 TWI — Sour Testing — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-042Stress-oriented hydrogen-induced crackingEnvironment-assisted cracking & hydrogen · Stress-directed hydrogen damage

Damage mechanism

Mechanism pathway

Service conditions

Hydrogen charging, typically wet H2S, plus tensile stress

Physical processes

Hydrogen forms small internal cracks
Tensile stress promotes stacked crack arrays linking through thickness

Observable damage

Ladder-like stacked HIC arrays; through-wall linkage near welds

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: SOHIC
Industries / exposed sectors: Refining; sour oil/gas; chemical
Typically affected parts: Pressure-vessel plates near welds; stressed sour piping
Susceptible materials: Susceptible carbon/low-alloy steels
Required chemicals / environment: Hydrogen charging, typically wet H2S, plus tensile stress
Influencing parameters: Triaxial/residual stress; weld geometry; hydrogen flux; cleanliness
Physical explanation (1–3 processes): Hydrogen forms small internal cracks
Tensile stress promotes stacked crack arrays linking through thickness
Signs and symptoms: Ladder-like stacked HIC arrays; through-wall linkage near welds
Prevention / slowing the damage: Reduce local stress; select tested resistant steel; control sour conditions; qualified volumetric inspection
Typical failure outcome: Leak or rupture
Possible consequences: Toxic/flammable release
Can be mistaken for: HIC; SSC; lamellar tearing
How to distinguish it: Cross-sections show stress-oriented stacks linking through wall; distinguish from single rolling-plane laminations
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Pargeter, R.J. (2007). Susceptibility to SOHIC for Linepipe and Pressure Vessel Steels: Review of Current Knowledge. NACE 2007. — Technical research paper (accessed 2026-09-08)
80 TWI — Sour Testing — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-043Hydrogen blisteringEnvironment-assisted cracking & hydrogen · Internal hydrogen damage

Damage mechanism

Mechanism pathway

Service conditions

Hydrogen entry, often from wet acidic/sour corrosion

Physical processes

Hydrogen recombines to gas at internal discontinuities
Gas pressure deforms or separates the overlying metal

Observable damage

Bulges; domed blisters; planar subsurface separations

Possible failure mode

Blister rupture; leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Blister damage; hydrogen pressure blistering
Industries / exposed sectors: Refining; wet sour service; chemical
Typically affected parts: Vessel plates; piping walls; tank shells
Susceptible materials: Susceptible carbon steels with internal traps/laminations
Required chemicals / environment: Hydrogen entry, often from wet acidic/sour corrosion
Influencing parameters: Hydrogen flux; inclusion/lamination population; wall restraint
Physical explanation (1–3 processes): Hydrogen recombines to gas at internal discontinuities
Gas pressure deforms or separates the overlying metal
Signs and symptoms: Bulges; domed blisters; planar subsurface separations
Prevention / slowing the damage: Limit hydrogen charging; clean HIC-resistant materials; evaluate remaining ligament and connected cracks
Typical failure outcome: Blister rupture; leak
Possible consequences: Containment loss; reduced ligament capacity
Can be mistaken for: Coating blisters; HIC; fabrication laminations
How to distinguish it: Verify metal-wall bulging and subsurface gas cavity; distinguish from paint-only blisters
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Sour Testing — Technical reference (accessed 2026-09-08)
80 Pargeter, R.J. (2007). Susceptibility to SOHIC for Linepipe and Pressure Vessel Steels: Review of Current Knowledge. NACE 2007. — Technical research paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-044Liquid metal embrittlementEnvironment-assisted cracking & hydrogen · Liquid-metal environment-assisted fracture

Damage mechanism

Mechanism pathway

Service conditions

A compatible embrittling liquid metal wetting a stressed susceptible solid

Physical processes

Liquid metal reaches highly stressed surface/crack regions
Adsorption/penetration assists loss of cohesion and crack advance

Observable damage

Rapid low-ductility cracks, often intergranular

Possible failure mode

Sudden fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: LME; liquid-metal-assisted cracking
Industries / exposed sectors: Galvanizing; welding; chemical; metal processing
Typically affected parts: Loaded steel during galvanizing; contaminated welds; susceptible liquid-metal equipment
Susceptible materials: Specific couples, e.g. steel/liquid zinc or copper; aluminium/liquid mercury
Required chemicals / environment: A compatible embrittling liquid metal wetting a stressed susceptible solid
Influencing parameters: Wetting; temperature above liquidus; stress; contact chemistry
Physical explanation (1–3 processes): Liquid metal reaches highly stressed surface/crack regions
Adsorption/penetration assists loss of cohesion and crack advance
Signs and symptoms: Rapid low-ductility cracks, often intergranular
Prevention / slowing the damage: Exclude incompatible metal contamination; qualified galvanizing/welding practices; reduce restraint
Typical failure outcome: Sudden fracture
Possible consequences: Loss of structural support or containment
Can be mistaken for: Solidification cracking; reheat cracking; ordinary brittle fracture
How to distinguish it: Identify embrittling metal on/in crack path and liquid-state exposure; preserve evidence before cleaning
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No verified LME catastrophe assigned here. Flixborough (1 June 1974) is not used as a proven LME case: the regulator’s account describes failure of a temporary bypass, not an established LME root cause.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Liquid metal embrittlement and common embrittling metal couples — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: aluminium alloys, Job Knowledge 21 — Technical reference (accessed 2026-09-08)
80 HSE — Flixborough, 1 June 1974 — Primary regulator accident summary (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-045Irradiation-assisted stress corrosion crackingEnvironment-assisted cracking & hydrogen · Radiation/environment interaction

Damage mechanism

Mechanism pathway

Service conditions

Reactor water, neutron exposure and tensile stress

Physical processes

Radiation changes grain-boundary chemistry and hardening
Localized deformation/oxidation under water promotes intergranular cracking

Observable damage

Intergranular cracks; bolt/internal-component failures

Possible failure mode

Bolt fracture; component separation; loss of structural function

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: IASCC
Industries / exposed sectors: Nuclear power
Typically affected parts: Core internals; baffle-former bolts; irradiated structural parts
Susceptible materials: Irradiated austenitic stainless steels and susceptible alloys
Required chemicals / environment: Reactor water, neutron exposure and tensile stress
Influencing parameters: Dose; temperature; water chemistry; stress; microstructure
Physical explanation (1–3 processes): Radiation changes grain-boundary chemistry and hardening
Localized deformation/oxidation under water promotes intergranular cracking
Signs and symptoms: Intergranular cracks; bolt/internal-component failures
Prevention / slowing the damage: Qualified irradiation-resistant materials; chemistry/stress management; targeted in-service inspection
Typical failure outcome: Bolt fracture; component separation; loss of structural function
Possible consequences: Loose parts; internal support degradation; outage
Can be mistaken for: Irradiation embrittlement; fatigue; unirradiated SCC
How to distinguish it: Confirm dose and aqueous exposure; correlate boundary cracking and material changes; irradiation alone is not proof of IASCC
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Chen, Y., Chopra, O.K., Gruber, E.E. & Shack, W.J. (2010). NUREG/CR-7018, irradiation-assisted stress corrosion cracking. NRC / Argonne. — Primary institutional research abstract (accessed 2026-09-08)
80 NRC — Reactor Vessel Integrity — Regulatory technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-046High-temperature oxidationHigh-temperature chemical damage · Gas/metal reaction

Damage mechanism

Mechanism pathway

Service conditions

Oxygen-bearing hot gas; liquid water is unnecessary

Physical processes

Oxide grows by interfacial reaction and diffusion
Cracking/spallation exposes fresh metal and renews consumption

Observable damage

Scale; section loss; spalled flakes; dimensional change

Possible failure mode

Thinning-related rupture; scale blockage

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Dry oxidation; scaling
Industries / exposed sectors: Power; furnaces; steel processing; aerospace
Typically affected parts: Furnace tubes; exhausts; turbine parts; hot structures
Susceptible materials: Steels; nickel alloys; other metals with inadequate oxide protection
Required chemicals / environment: Oxygen-bearing hot gas; liquid water is unnecessary
Influencing parameters: Temperature; time; oxygen potential; thermal cycling; alloy chemistry
Physical explanation (1–3 processes): Oxide grows by interfacial reaction and diffusion
Cracking/spallation exposes fresh metal and renews consumption
Signs and symptoms: Scale; section loss; spalled flakes; dimensional change
Prevention / slowing the damage: Oxidation-resistant alloy/coating; temperature control; reduce severe cycling; monitor scale and remaining wall
Typical failure outcome: Thinning-related rupture; scale blockage
Possible consequences: Overheating; debris damage; outage
Can be mistaken for: Hot corrosion; sulfidation; atmospheric rust
How to distinguish it: Identify scale phases and hot-service exposure; verify whether molten salts or sulfur caused the attack
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Corrosion behavior of an HVOF sprayed Fe3Al coating in a high-temperature oxidizing/sulfidizing environment (2004) — Primary experimental paper (accessed 2026-09-08)
80 TWI — High temperature material selection for a powder processing environment — Primary material-selection case (accessed 2026-09-08)
80 TWI — What is an MCrAlY coating? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-047Steam-side oxidation and exfoliationHigh-temperature chemical damage · Steam/metal reaction

Damage mechanism

Mechanism pathway

Service conditions

High-temperature steam

Physical processes

Steam-side oxide thickens and consumes metal
Growth/thermal mismatch causes oxide spallation

Observable damage

Internal scale; exfoliated particles; restricted tube flow

Possible failure mode

Tube rupture or flow blockage by exfoliated scale

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Steam oxidation; oxide-scale exfoliation
Industries / exposed sectors: Fossil power; heat recovery; high-temperature steam
Typically affected parts: Superheater/reheater tubes; steam piping
Susceptible materials: Ferritic and austenitic heat-resistant steels
Required chemicals / environment: High-temperature steam
Influencing parameters: Temperature; time; alloy chromium; surface condition; thermal transients
Physical explanation (1–3 processes): Steam-side oxide thickens and consumes metal
Growth/thermal mismatch causes oxide spallation
Signs and symptoms: Internal scale; exfoliated particles; restricted tube flow
Prevention / slowing the damage: Appropriate steam-resistant alloy/surface treatment; manage temperature and cycling; inspect scale/blockage
Typical failure outcome: Tube rupture or flow blockage by exfoliated scale
Possible consequences: Overheating; outage; downstream erosion or turbine damage from detached scale
Can be mistaken for: Creep; fireside oxidation; deposit fouling
How to distinguish it: Locate oxide on steam side; analyse scale layers and deposits; separate oxidation loss from creep cavities
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Kurley, J.M. & Pint, B.A. (2020). The effect of shot peening on steam oxidation of 304H stainless steel. Oxidation of Metals 93, 159–174. — Primary ORNL study (accessed 2026-09-08)
80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-048High-temperature sulfidationHigh-temperature chemical damage · Sulfur/metal reaction

Damage mechanism

Mechanism pathway

Service conditions

Reactive sulfur species at elevated temperature; no water required

Physical processes

Metal reacts to form sulfide scale
Insufficiently protective scale permits continuing wall loss

Observable damage

Sulfide scale; broad thinning; individual components may corrode faster

Possible failure mode

Leak or catastrophic rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Sulfidic corrosion; sulfur corrosion
Industries / exposed sectors: Refining; petrochemical; high-temperature processing
Typically affected parts: Crude-unit piping; furnace tubes; sulfur-bearing process equipment
Susceptible materials: Carbon/low-alloy steels; susceptibility depends on alloy chemistry
Required chemicals / environment: Reactive sulfur species at elevated temperature; no water required
Influencing parameters: Temperature; sulfur species; silicon/chromium content; flow
Physical explanation (1–3 processes): Metal reacts to form sulfide scale
Insufficiently protective scale permits continuing wall loss
Signs and symptoms: Sulfide scale; broad thinning; individual components may corrode faster
Prevention / slowing the damage: Verify materials component-by-component; resistant alloys; targeted thickness monitoring
Typical failure outcome: Leak or catastrophic rupture
Possible consequences: Hydrocarbon release; fire
Can be mistaken for: Wet H2S corrosion; naphthenic acid corrosion; oxidation
How to distinguish it: Confirm hot service, sulfide scale and alloy chemistry; inspect fittings individually, not only adjacent pipe
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: Chevron Richmond, 6 August 2012: severe sulfidation thinning in low-silicon carbon-steel piping led to rupture and a major refinery fire. CSB completed its investigation in 2015.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 CSB — Chevron Richmond Refinery Fire — Primary accident investigation (accessed 2026-09-08)
80 CSB / Cal OSHA (13 February 2013) — Technical report on Chevron 2012 pipe rupture and fire: sulfidation corrosion — Primary metallurgical-investigation summary (accessed 2026-09-08)
80 TWI — Corrosion behavior of an HVOF sprayed Fe3Al coating in a high-temperature oxidizing/sulfidizing environment (2004) — Primary experimental paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-049Hot corrosion by molten saltsHigh-temperature chemical damage · Salt-assisted high-temperature corrosion

Damage mechanism

Mechanism pathway

Service conditions

Aggressive deposits, often sulfates or vanadium-bearing salts

Physical processes

Molten deposits dissolve or destabilize protective oxides
Accelerated oxidation/sulfidation consumes exposed alloy

Observable damage

Pitted scale; undercut coatings; sulfide/oxide penetration

Possible failure mode

Blade/tube fracture or perforation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Type I/Type II hot corrosion; deposit-induced hot corrosion
Industries / exposed sectors: Gas turbines; aviation; boilers; incineration
Typically affected parts: Turbine blades/vanes; combustors; hot tubes
Susceptible materials: Nickel/cobalt superalloys; heat-resistant steels
Required chemicals / environment: Aggressive deposits, often sulfates or vanadium-bearing salts
Influencing parameters: Salt chemistry; temperature/melting behaviour; oxygen/sulfur potential; deposit flux
Physical explanation (1–3 processes): Molten deposits dissolve or destabilize protective oxides
Accelerated oxidation/sulfidation consumes exposed alloy
Signs and symptoms: Pitted scale; undercut coatings; sulfide/oxide penetration
Prevention / slowing the damage: Fuel/air contaminant control; resistant coatings/alloys; approved deposit removal
Typical failure outcome: Blade/tube fracture or perforation
Possible consequences: Rotor damage; forced outage
Can be mistaken for: Ordinary oxidation; sulfidation; erosion
How to distinguish it: Analyse deposit and scale chemistry; confirm relevant molten-salt regime; temperature alone cannot assign Type I/II
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is an MCrAlY coating? — Technical reference (accessed 2026-09-08)
50 Haynes International — HAYNES HR-160 alloy — Primary manufacturer test data (accessed 2026-09-08)
80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-050Naphthenic acid corrosionHigh-temperature chemical damage · Hot-oil acid attack

Damage mechanism

Mechanism pathway

Service conditions

Reactive organic acids in hot oil; aqueous phase unnecessary

Physical processes

Organic acids react with iron to form oil-soluble iron carboxylates
Film stability and sulfur interactions govern local attack

Observable damage

Sharp grooves; localized or broad wall loss in hot-oil circuits

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: NAC; hot organic-acid corrosion
Industries / exposed sectors: Crude refining; heavy-oil processing
Typically affected parts: Hot crude/vacuum distillation piping; transfer lines; pumps
Susceptible materials: Carbon/low-alloy steel; alloy resistance depends on molybdenum and environment
Required chemicals / environment: Reactive organic acids in hot oil; aqueous phase unnecessary
Influencing parameters: Acid structure; temperature; flow; sulfur chemistry; scale stability
Physical explanation (1–3 processes): Organic acids react with iron to form oil-soluble iron carboxylates
Film stability and sulfur interactions govern local attack
Signs and symptoms: Sharp grooves; localized or broad wall loss in hot-oil circuits
Prevention / slowing the damage: Evaluate real feed corrosivity, not TAN alone; appropriate resistant alloys; control flow/hot spots
Typical failure outcome: Leak or rupture
Possible consequences: Hot hydrocarbon release; fire
Can be mistaken for: Sulfidation; erosion-corrosion
How to distinguish it: Correlate acid/sulfur chemistry, temperature and morphology; total acid number alone is not diagnostic
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Mechanism of magnetite formation in high temperature corrosion by model naphthenic acids (2016). Corrosion Science 111, 822–834. — Primary experimental paper (accessed 2026-09-08)
80 Huang, B.S., Yin, W.F., Sang, D.H. & Jiang, Z.Y. (2012). Synergy of naphthenic acid and sulfur corrosion. Applied Surface Science 259, 664–670. — Primary experimental paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-051High-temperature hydrogen/hydrogen-sulfide corrosionHigh-temperature chemical damage · High-temperature gas-phase corrosion

Environment-specific sulfidation subtype

Mechanism pathway

Service conditions

Hot H2/H2S gas; liquid water not required

Physical processes

Sulfur-bearing hot gas reacts with alloy constituents
Sulfide formation consumes or penetrates the load-bearing metal

Observable damage

Wall loss and internal sulfide penetration

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: H2/H2S corrosion; reducing-gas sulfidation
Industries / exposed sectors: Hydrotreating; hydrocracking; gas processing
Typically affected parts: Reactor-effluent piping; heater tubes; hot exchangers
Susceptible materials: Steels and heat-resistant alloys; resistance depends on alloy and gas conditions
Required chemicals / environment: Hot H2/H2S gas; liquid water not required
Influencing parameters: Temperature; exposure; gas composition; sulfur/oxygen potentials; alloy chemistry
Physical explanation (1–3 processes): Sulfur-bearing hot gas reacts with alloy constituents
Sulfide formation consumes or penetrates the load-bearing metal
Signs and symptoms: Wall loss and internal sulfide penetration
Prevention / slowing the damage: Duty-qualified alloys; chemistry/temperature management; thickness monitoring
Typical failure outcome: Leak or rupture
Possible consequences: Hydrogen/hydrocarbon/H2S release; fire
Can be mistaken for: HTHA; wet H2S corrosion; ordinary sulfidation
How to distinguish it: Prove gas-phase hot reducing exposure; metallography separates surface loss from internal methane damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Haynes International — HAYNES HR-160 alloy — Primary manufacturer test data (accessed 2026-09-08)
80 TWI — Corrosion behavior of an HVOF sprayed Fe3Al coating in a high-temperature oxidizing/sulfidizing environment (2004) — Primary experimental paper (accessed 2026-09-08)
80 API — Recommended Practice 571: Damage Mechanisms Affecting Fixed Equipment in the Refining Industry — Official standard overview (accessed 2026-09-08)
50 Haynes International — Sulfidation & Chlorine Environment Resistance of High-temperature Alloys — public manufacturer test data (accessed 2026-09-08)
80 TWI — What is high temperature hydrogen attack? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-052High-temperature hydrogen attackHigh-temperature chemical damage · Methane-forming internal damage

Damage mechanism

Mechanism pathway

Service conditions

Hydrogen at elevated temperature and sufficient activity/partial pressure

Physical processes

Hydrogen reacts with carbon to form trapped methane
Methane cavities grow and link while steel decarburizes

Observable damage

Internal fissures/cavities; decarburization; late-stage cracking

Possible failure mode

Brittle-appearing rupture or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HTHA; hot hydrogen attack
Industries / exposed sectors: Refining; hydrogen processing; ammonia
Typically affected parts: Hot hydrogen vessels; exchanger shells; piping; weld regions
Susceptible materials: Carbon/low-alloy steels with insufficient carbide stability for the duty
Required chemicals / environment: Hydrogen at elevated temperature and sufficient activity/partial pressure
Influencing parameters: Temperature; hydrogen pressure; time; carbides; weld condition
Physical explanation (1–3 processes): Hydrogen reacts with carbon to form trapped methane
Methane cavities grow and link while steel decarburizes
Signs and symptoms: Internal fissures/cavities; decarburization; late-stage cracking
Prevention / slowing the damage: Use duty-qualified resistant materials; verify operating envelope; specialized validated inspection
Typical failure outcome: Brittle-appearing rupture or leak
Possible consequences: Major fire/explosion; fatalities possible
Can be mistaken for: Ambient HE; creep; thermal decarburization
How to distinguish it: Metallography identifies methane-type cavities and carbon depletion; no single negative NDT test proves absence
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: Tesoro Anacortes, 2 April 2010: HTHA in a heat-exchanger shell caused a catastrophic rupture/fire; seven workers died.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is high temperature hydrogen attack? — Technical reference (accessed 2026-09-08)
80 US Chemical Safety Board (2016) — Safety alert stemming from fatal Tesoro Anacortes investigation — Regulatory safety alert (accessed 2026-09-08)
80 US Chemical Safety Board — Tesoro Anacortes Refinery Fatal Explosion and Fire — Primary accident investigation (accessed 2026-09-08)
80 CSB — Tesoro investigation finds HTHA damage to heat exchanger — public primary investigation summary (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-053CarburizationHigh-temperature chemical damage · Interstitial uptake

Damage mechanism

Mechanism pathway

Service conditions

Carbon-rich gas with sufficiently high carbon activity

Physical processes

Carbon enters the exposed alloy
Carburized microstructure changes local properties; defects in a protective coating can concentrate attack

Observable damage

Subsurface carburization; locally deep attack at protective-coating defects

Possible failure mode

Cracking or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Carbon uptake; internal carburization
Industries / exposed sectors: Petrochemical cracking; reforming; heat-treatment furnaces
Typically affected parts: Furnace tubes; retorts; high-temperature internals
Susceptible materials: Heat-resistant nickel alloys; steels in related carbon-uptake service
Required chemicals / environment: Carbon-rich gas with sufficiently high carbon activity
Influencing parameters: Temperature; carbon activity; time; oxide protection
Physical explanation (1–3 processes): Carbon enters the exposed alloy
Carburized microstructure changes local properties; defects in a protective coating can concentrate attack
Signs and symptoms: Subsurface carburization; locally deep attack at protective-coating defects
Prevention / slowing the damage: Control carbon potential; resistant alloy/coating; preserve protective scale; monitor microstructure
Typical failure outcome: Cracking or rupture
Possible consequences: Tube failure; fire/outage
Can be mistaken for: Metal dusting; intentional case hardening; sigma embrittlement
How to distinguish it: Carbon profiles and carbide identification; distinguish intact carburized metal from disintegrating metal dusting
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is plasma carburising / plasma nitriding? — Technical process reference (accessed 2026-09-08)
80 TWI — High temperature material selection for a powder processing environment — Primary material-selection case (accessed 2026-09-08)
80 TWI — High temperature corrosion testing — Primary research programme (accessed 2026-09-08)
80 TWI — Optimising Manufacturing for Aggressive Environments — public technical article (accessed 2026-09-08)
80 On the mechanism of catastrophic carburization: metal dusting (1993) — publisher abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-054DecarburizationHigh-temperature chemical damage · Interstitial loss

Damage mechanism

Mechanism pathway

Service conditions

Atmosphere able to remove carbon, e.g. oxidizing/wet gases; environment-specific

Physical processes

Carbon diffuses toward a low-carbon-potential surface
Surface reactions remove carbon, reducing hardenability/strength

Observable damage

Soft ferritic surface layer; reduced hardness; fatigue initiation

Possible failure mode

Wear-out, distortion or later fatigue fracture; immediate failure is not inevitable

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Carbon depletion; surface decarburization
Industries / exposed sectors: Heat treatment; forging; high-temperature service
Typically affected parts: Spring surfaces; forgings; tubes; steel components
Susceptible materials: Carbon and low-alloy steels
Required chemicals / environment: Atmosphere able to remove carbon, e.g. oxidizing/wet gases; environment-specific
Influencing parameters: Temperature; time; carbon potential; scale integrity
Physical explanation (1–3 processes): Carbon diffuses toward a low-carbon-potential surface
Surface reactions remove carbon, reducing hardenability/strength
Signs and symptoms: Soft ferritic surface layer; reduced hardness; fatigue initiation
Prevention / slowing the damage: Control furnace atmosphere and thermal exposure; verify the affected depth before acceptance
Typical failure outcome: Wear-out, distortion or later fatigue fracture; immediate failure is not inevitable
Possible consequences: Reduced life; potential component break
Can be mistaken for: HTHA decarburization; overtempering; carburization gradients
How to distinguish it: Compare carbon-sensitive microstructure and hardness depth profiles; distinguish surface carbon loss from internal methane-cavity damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASM Handbook 4B (2014). Steel Heat Treating Technologies. — Authoritative handbook overview (accessed 2026-09-08)
80 ASM Handbook 4F (2024). Steel Heat Treatment Failures due to Quenching, pp. 575–592. — Authoritative handbook abstract (accessed 2026-09-08)
80 TWI — What is high temperature hydrogen attack? — Technical reference (accessed 2026-09-08)
80 Eddy currents and hardness testing for evaluation of steel decarburizing (2006) — publisher abstract and public section snippets (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-055Metal dustingHigh-temperature chemical damage · Carbon-driven disintegration

Damage mechanism

Mechanism pathway

Service conditions

Strongly carburizing gas; carbon activity above graphite equilibrium

Physical processes

Carbon supersaturation/carburization destabilizes near-surface metal
Metal breaks down into particles associated with coke/carbon

Observable damage

Pits; metal powder in coke; rapid local wastage

Possible failure mode

Perforation or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Catastrophic carburization; carbon-induced disintegration
Industries / exposed sectors: Syngas; reforming; petrochemical; heat treatment
Typically affected parts: Process tubes; heat exchangers; furnace internals
Susceptible materials: Iron, nickel and cobalt alloys under susceptible conditions
Required chemicals / environment: Strongly carburizing gas; carbon activity above graphite equilibrium
Influencing parameters: Temperature; CO/H2 chemistry; water content; surface scale
Physical explanation (1–3 processes): Carbon supersaturation/carburization destabilizes near-surface metal
Metal breaks down into particles associated with coke/carbon
Signs and symptoms: Pits; metal powder in coke; rapid local wastage
Prevention / slowing the damage: Control gas chemistry and temperatures; resistant materials/coatings; maintain protective scales
Typical failure outcome: Perforation or rupture
Possible consequences: Syngas release; fire; outage
Can be mistaken for: Carburization without dusting; erosion; sulfidation
How to distinguish it: Identify metal particles/carbon and disintegrated microstructure; correlate with carbon activity and process conditions
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — High temperature corrosion testing — Primary research programme (accessed 2026-09-08)
80 TWI — High temperature material selection for a powder processing environment — Primary material-selection case (accessed 2026-09-08)
80 On the mechanism of catastrophic carburization: metal dusting (1993) — publisher abstract (accessed 2026-09-08)
80 Metal dusting and coking of alloy 803 (2004) — publisher abstract and public introduction (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-056Uncontrolled nitriding damageHigh-temperature chemical damage · Interstitial uptake

Uncontrolled uptake / property degradation

Mechanism pathway

Service conditions

Nitrogen-bearing gas with sufficient nitriding potential, often NH3-containing

Physical processes

Ammonia dissociation supplies nitrogen that enters the alloy
Brittle nitride formation and protective-oxide defects promote cracking

Observable damage

Brittle nitride formation; cracks; quasi-cleavage in the reported coil case

Possible failure mode

Cracking or brittle break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: In-service nitridation; nitrogen uptake
Industries / exposed sectors: Ammonia; chemical; high-temperature processing
Typically affected parts: Heating coils; ammonia-service hot components
Susceptible materials: FeCrAl heating alloys; other nitride-forming alloys require service-specific assessment
Required chemicals / environment: Nitrogen-bearing gas with sufficient nitriding potential, often NH3-containing
Influencing parameters: Temperature; exposure; ammonia pressure; protective-oxide integrity
Physical explanation (1–3 processes): Ammonia dissociation supplies nitrogen that enters the alloy
Brittle nitride formation and protective-oxide defects promote cracking
Signs and symptoms: Brittle nitride formation; cracks; quasi-cleavage in the reported coil case
Prevention / slowing the damage: Qualify alloy and protective surfaces for actual ammonia conditions; monitor cracking
Typical failure outcome: Cracking or brittle break
Possible consequences: Loss of containment or internal-component failure
Can be mistaken for: Carburization; sigma phase; intentional nitriding
How to distinguish it: Nitrogen profile and nitride identification; deliberate controlled nitriding is not automatically damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: A 2024 laboratory failure investigation attributed premature failure of FeCrAl heating coils in hot, pressurized ammonia to destructive nitridation. It is not a population incidence estimate or a public-accident report.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is plasma carburising / plasma nitriding? — Technical process reference (accessed 2026-09-08)
50 Haynes International — HAYNES HR-160 alloy — Primary manufacturer test data (accessed 2026-09-08)
80 Laws et al. (2024) — Failure analysis of FeCrAl heating coils exposed to a high-temperature, high-pressure ammonia environment — publisher abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-057Creep deformation and cavitationCreep & metallurgical ageing · Time-dependent elevated-temperature damage

Umbrella damage mechanism

Mechanism pathway

Service conditions

None essential; oxidation/corrosion may accelerate damage

Physical processes

Dislocation/diffusion-controlled deformation accumulates
Grain-boundary cavities can nucleate and link under stress

Observable damage

Bulging; elongation; cavitation; creep cracks; warning may be limited

Possible failure mode

Stress rupture; leak; excessive deformation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Creep damage; time-dependent deformation; legacy title: creep and stress rupture
Industries / exposed sectors: Power; refining; turbines; high-temperature processing
Typically affected parts: Steam pipes; headers; tubes; turbine blades; hot bolts
Susceptible materials: Steels; nickel/cobalt alloys; other metals at material-dependent high homologous temperature
Required chemicals / environment: None essential; oxidation/corrosion may accelerate damage
Influencing parameters: Metal temperature; sustained stress; time; microstructure
Physical explanation (1–3 processes): Dislocation/diffusion-controlled deformation accumulates
Grain-boundary cavities can nucleate and link under stress
Signs and symptoms: Bulging; elongation; cavitation; creep cracks; warning may be limited
Prevention / slowing the damage: Control metal temperature/stress; suitable alloy/heat treatment; life assessment and targeted inspection
Typical failure outcome: Stress rupture; leak; excessive deformation
Possible consequences: Steam/hydrocarbon release; blade failure; outage
Can be mistaken for: Short-term overheating; HTHA; creep-fatigue
How to distinguish it: Assess service history, dimensions, cavities and microstructure; surface replication alone may miss internal damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Detection of Early-Stage Creep Damage in Welded Steels, Report 1113/2019 — Primary research summary (accessed 2026-09-08)
80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)
80 TWI — What is type IV cracking, and how is it detected? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-058Creep-fatigue interactionCreep & metallurgical ageing · Time/cycle interaction

Damage mechanism

Mechanism pathway

Service conditions

None essential; oxidation often contributes

Physical processes

Cyclic plasticity initiates/grows cracks
Creep during hot holds damages boundaries
Interaction can shorten life beyond separate mechanisms

Observable damage

Mixed intergranular/transgranular cracking; cavities near cyclic cracks

Possible failure mode

Crack/leak; rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Creep–fatigue damage
Industries / exposed sectors: Flexible power generation; turbines; process heaters
Typically affected parts: Headers; thick-section joints; blades; thermal-transition regions
Susceptible materials: High-temperature steels and superalloys
Required chemicals / environment: None essential; oxidation often contributes
Influencing parameters: Hold times; strain range; temperature; cycling sequence; stress relaxation
Physical explanation (1–3 processes): Cyclic plasticity initiates/grows cracks
Creep during hot holds damages boundaries
Interaction can shorten life beyond separate mechanisms
Signs and symptoms: Mixed intergranular/transgranular cracking; cavities near cyclic cracks
Prevention / slowing the damage: Manage start/stop transients and dwell stress; joint design; validated interaction-life assessment
Typical failure outcome: Crack/leak; rupture
Possible consequences: Forced outage; hot-fluid release
Can be mistaken for: Thermal fatigue alone; creep alone; reheat cracking
How to distinguish it: Combine cycle/dwell records with fracture path and cavitation; do not assume linear damage addition is always valid
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)
80 TWI — Review of type IV cracking of weldments in 9–12%Cr creep-strength-enhanced ferritic steels — Research paper (accessed 2026-09-08)
50 Tetra Engineering — HRSG Tube Failure Statistics — Primary consulting-cohort summary (accessed 2026-09-08)
80 Creep–fatigue endurance of 304 stainless steels (2014) — publisher public article text (accessed 2026-09-08)
80 Creep-fatigue interaction behaviour of type 308 stainless steel weld metal and type 304 stainless steel base metal (1993) — publisher abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-059Type IV creep crackingCreep & metallurgical ageing · Weld-HAZ creep subtype

Creep subtype

Mechanism pathway

Service conditions

None essential

Physical processes

Creep strain localizes in the weaker outer HAZ
Boundary cavities coalesce into a through-wall crack

Observable damage

HAZ cavity bands; cracks away from fusion boundary; limited overall strain

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Type IV weld failure
Industries / exposed sectors: Power; petrochemical steam systems
Typically affected parts: Fine-grained/intercritical HAZ in ferritic weldments
Susceptible materials: Cr-Mo and creep-strength-enhanced ferritic steels, including 9–12% Cr grades
Required chemicals / environment: None essential
Influencing parameters: Temperature; sustained stress; weld/PWHT microstructure; time
Physical explanation (1–3 processes): Creep strain localizes in the weaker outer HAZ
Boundary cavities coalesce into a through-wall crack
Signs and symptoms: HAZ cavity bands; cracks away from fusion boundary; limited overall strain
Prevention / slowing the damage: Qualified material/weld/heat treatment; stress and temperature control; HAZ-targeted volumetric inspection
Typical failure outcome: Leak or rupture
Possible consequences: High-energy steam release; outage
Can be mistaken for: Reheat cracking; Type I/II/III weld creep; HTHA
How to distinguish it: Locate damage in fine/intercritical HAZ and demonstrate creep cavities; examine subsurface material
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is type IV cracking, and how is it detected? — Technical reference (accessed 2026-09-08)
80 TWI — Review of type IV cracking of weldments in 9–12%Cr creep-strength-enhanced ferritic steels — Research paper (accessed 2026-09-08)
80 TWI — Detection of Early-Stage Creep Damage in Welded Steels, Report 1113/2019 — Primary research summary (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-060Dissimilar-metal weld creep/interface failureCreep & metallurgical ageing · Dissimilar-joint creep subtype

Joint-specific creep family

Mechanism pathway

Service conditions

None essential; oxidation may assist exposed interfaces

Physical processes

Carbon migration creates a carbon-depleted zone with lower creep strength
Creep damage can localize beside the fusion boundary

Observable damage

Cracks near fusion boundary; carbide-depleted region; creep damage

Possible failure mode

Leak or weld separation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: DMW creep; fusion-boundary creep damage
Industries / exposed sectors: Power; refining; high-temperature piping
Typically affected parts: Ferritic-to-austenitic/nickel welds; dissimilar ferritic joints
Susceptible materials: Dissimilar heat-resistant steels and nickel filler combinations
Required chemicals / environment: None essential; oxidation may assist exposed interfaces
Influencing parameters: Alloy/carbon-activity difference; heat treatment; operating stress; temperature; time
Physical explanation (1–3 processes): Carbon migration creates a carbon-depleted zone with lower creep strength
Creep damage can localize beside the fusion boundary
Signs and symptoms: Cracks near fusion boundary; carbide-depleted region; creep damage
Prevention / slowing the damage: Qualify filler and heat treatment for the dissimilar joint; assess cross-weld creep strength
Typical failure outcome: Leak or weld separation
Possible consequences: Steam/hydrocarbon release; outage
Can be mistaken for: Type IV creep; lack of fusion; reheat cracking
How to distinguish it: Locate crack relative to fusion boundary and HAZ; carbon/hardness mapping plus cavities and service history
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Review of type IV cracking of weldments in 9–12%Cr creep-strength-enhanced ferritic steels — Research paper (accessed 2026-09-08)
80 TWI — Detection of Early-Stage Creep Damage in Welded Steels, Report 1113/2019 — Primary research summary (accessed 2026-09-08)
80 TWI — What is type IV cracking, and how is it detected? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-061Overheating-induced softening and rapid deformationCreep & metallurgical ageing · Acute thermal overload

Damage mechanism

Mechanism pathway

Service conditions

No corrosive species essential; deposits or blocked cooling can raise metal temperature

Physical processes

Acute overheating reduces the wall’s load-bearing capacity
Plastic flow under internal pressure can rapidly open a rupture

Observable damage

Bulging; thin-lipped burst in acute overheating; thermally altered microstructure

Possible failure mode

Tube burst

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Short-term overheating damage; legacy title: short-term overheating rupture
Industries / exposed sectors: Boilers; fired heaters; furnaces
Typically affected parts: Waterwall/superheater tubes; flame-impinged coils
Susceptible materials: Carbon/low-alloy steel; heat-resistant alloys
Required chemicals / environment: No corrosive species essential; deposits or blocked cooling can raise metal temperature
Influencing parameters: Peak metal temperature; duration; pressure; heat flux; cooling flow
Physical explanation (1–3 processes): Acute overheating reduces the wall’s load-bearing capacity
Plastic flow under internal pressure can rapidly open a rupture
Signs and symptoms: Bulging; thin-lipped burst in acute overheating; thermally altered microstructure
Prevention / slowing the damage: Maintain cooling flow; prevent dryout/flame impingement; protective trips and temperature monitoring
Typical failure outcome: Tube burst
Possible consequences: Hot-fluid release; fire; forced outage
Can be mistaken for: Long-term creep; thinning-induced burst; thermal shock
How to distinguish it: Reconstruct excursion and remaining wall; metallography distinguishes acute heating from long-term cavitation
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)
80 Dooley, B. & McNaughton, W. (EPRI, 1997). Don’t let those boiler tubes fail again. Power Engineering. — Primary institutional authors’ technical article (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-062Thermal graphitization of steelCreep & metallurgical ageing · Thermal microstructural degradation

Microstructural degradation

Mechanism pathway

Service conditions

None essential

Physical processes

Metastable carbides decompose
Graphite precipitates; linked particles/bands weaken the steel

Observable damage

Graphite particles or linked HAZ bands; associated loss of strength/toughness

Possible failure mode

Low-ductility rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Graphitisation; carbide decomposition
Industries / exposed sectors: Older power/process high-temperature systems
Typically affected parts: Carbon/carbon-molybdenum steel pipe; weld HAZ
Susceptible materials: Susceptible carbon and carbon-molybdenum steels
Required chemicals / environment: None essential
Influencing parameters: Long thermal exposure; composition; weld thermal history
Physical explanation (1–3 processes): Metastable carbides decompose
Graphite precipitates; linked particles/bands weaken the steel
Signs and symptoms: Graphite particles or linked HAZ bands; associated loss of strength/toughness
Prevention / slowing the damage: Appropriate alloy selection; metallographic surveillance; replace critically affected material
Typical failure outcome: Low-ductility rupture
Possible consequences: High-energy release; structural failure
Can be mistaken for: Graphitic corrosion of cast iron; creep cavities; inclusions
How to distinguish it: Identify newly precipitated graphite in steel without selective external iron dissolution
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is graphitisation? — Technical reference (accessed 2026-09-08)
80 TWI — What is type IV cracking, and how is it detected? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-063Spheroidization-related thermal softeningCreep & metallurgical ageing · Loss of strengthening microstructure

Property degradation family

Mechanism pathway

Service conditions

None essential

Physical processes

Lamellar cementite changes toward a spheroidal morphology during thermal exposure
Associated softening can reduce fatigue life at a given stress amplitude

Observable damage

Spheroidized carbides; reduced hardness; changed fatigue response

Possible failure mode

Excessive deformation; later creep rupture or fatigue fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Pearlite spheroidization; thermal softening; related carbide-coarsening softening
Industries / exposed sectors: Rail transport; hot-service steel equipment
Typically affected parts: Railway wheels; other thermally exposed pearlitic-steel parts
Susceptible materials: Pearlitic steels; direct study concerns railway wheelset steels
Required chemicals / environment: None essential
Influencing parameters: Temperature; time; initial microstructure; prior heat treatment
Physical explanation (1–3 processes): Lamellar cementite changes toward a spheroidal morphology during thermal exposure
Associated softening can reduce fatigue life at a given stress amplitude
Signs and symptoms: Spheroidized carbides; reduced hardness; changed fatigue response
Prevention / slowing the damage: Limit thermal exposure; correct initial treatment; assess mechanical properties before continued service
Typical failure outcome: Excessive deformation; later creep rupture or fatigue fracture
Possible consequences: Reduced load/life margin
Can be mistaken for: Decarburization; normal annealed structure; graphitization
How to distinguish it: Compare carbide morphology and hardness with the original material; distinguish carbon depletion and intentionally spheroidized supply condition
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)
80 TWI — Are quenched and tempered steels readily weldable? — Technical reference (accessed 2026-09-08)
80 ASM Handbook 4B (2014). Steel Heat Treating Technologies. — Authoritative handbook overview (accessed 2026-09-08)
80 Eddy currents and hardness testing for evaluation of steel decarburizing (2006) — publisher abstract and public section snippets (accessed 2026-09-08)
80 Thermal softening of fine pearlitic steel and its effect on the fatigue behaviour (2010) — publisher abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-064Temper embrittlementCreep & metallurgical ageing · Grain-boundary segregation embrittlement

Damage mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Impurities segregate to grain boundaries
Boundary cohesion decreases and brittle-transition behaviour worsens

Observable damage

Reduced notch toughness; intergranular brittle fracture; little hardness change may occur

Possible failure mode

Brittle fracture, especially during cool/pressurized conditions

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Reversible temper embrittlement
Industries / exposed sectors: Refining; power; heavy forgings
Typically affected parts: Cr-Mo vessels; turbine rotors; thick low-alloy steel
Susceptible materials: Susceptible alloy steels with impurity/chemistry combinations
Required chemicals / environment: None essential
Influencing parameters: Thermal exposure/cooling history; impurity content; alloy composition
Physical explanation (1–3 processes): Impurities segregate to grain boundaries
Boundary cohesion decreases and brittle-transition behaviour worsens
Signs and symptoms: Reduced notch toughness; intergranular brittle fracture; little hardness change may occur
Prevention / slowing the damage: Low-impurity suitable steel; qualified heat treatment; toughness assessment and controlled startup
Typical failure outcome: Brittle fracture, especially during cool/pressurized conditions
Possible consequences: Major pressure-boundary failure
Can be mistaken for: Hydrogen embrittlement; irradiation embrittlement; cleavage
How to distinguish it: Toughness/transition testing, thermal history and boundary fracture; routine hardness alone is inadequate
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is temper embrittlement, and how can it be controlled? — Technical reference (accessed 2026-09-08)
80 TWI — What is a fracture toughness test? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-065475°C embrittlementCreep & metallurgical ageing · Ferrite decomposition embrittlement

Microstructural embrittlement

Mechanism pathway

Service conditions

None essential

Physical processes

Ferrite separates into iron-rich and chromium-rich regions
Nanoscale decomposition hardens and embrittles ferrite

Observable damage

Toughness/ductility loss; hardening; often no obvious optical change

Possible failure mode

Brittle-appearing cracking/fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Alpha-prime embrittlement; 885°F embrittlement
Industries / exposed sectors: Chemical; power; duplex/high-chromium equipment
Typically affected parts: Ferritic/duplex stainless parts; ferrite in weld metal
Susceptible materials: Chromium-rich ferrite in ferritic/duplex stainless steels
Required chemicals / environment: None essential
Influencing parameters: Temperature-time exposure; ferrite composition; initial phase balance
Physical explanation (1–3 processes): Ferrite separates into iron-rich and chromium-rich regions
Nanoscale decomposition hardens and embrittles ferrite
Signs and symptoms: Toughness/ductility loss; hardening; often no obvious optical change
Prevention / slowing the damage: Avoid unsuitable thermal exposure; validated material/heat-treatment selection; mechanical-property assessment
Typical failure outcome: Brittle-appearing cracking/fracture
Possible consequences: Reduced tolerance to defects and transients
Can be mistaken for: Sigma embrittlement; strain ageing; HE
How to distinguish it: Use exposure history and suitable microstructural/mechanical testing; ordinary optical microscopy may miss nanoscale decomposition
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Embrittlement of austenitic steel welds at high temperature — Technical reference (accessed 2026-09-08)
80 TWI — What is temper embrittlement, and how can it be controlled? — Technical reference (accessed 2026-09-08)
80 Microstructure evolution and mechanical behavior of a lean duplex stainless steel aged at 475°C (2021) — publisher abstract and public introduction (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-066Sigma/chi-phase embrittlementCreep & metallurgical ageing · Intermetallic precipitation

Microstructural embrittlement

Mechanism pathway

Service conditions

None essential; corrosion resistance can deteriorate afterward

Physical processes

Brittle sigma/chi phases precipitate during unsuitable thermal exposure
Phase formation changes hardness, toughness and corrosion response

Observable damage

Intermetallic particles; toughness loss; selective corrosion of depleted zones

Possible failure mode

Brittle fracture or subsequent localized-corrosion leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Intermetallic-phase embrittlement
Industries / exposed sectors: Chemical; refining; power; welded stainless equipment
Typically affected parts: Duplex components; stainless welds; heat-exchanger parts
Susceptible materials: Duplex/austenitic stainless and some high-alloy systems
Required chemicals / environment: None essential; corrosion resistance can deteriorate afterward
Influencing parameters: Thermal history; Cr/Mo content; phase balance; cooling rate
Physical explanation (1–3 processes): Brittle sigma/chi phases precipitate during unsuitable thermal exposure
Phase formation changes hardness, toughness and corrosion response
Signs and symptoms: Intermetallic particles; toughness loss; selective corrosion of depleted zones
Prevention / slowing the damage: Correct welding/heat-treatment windows; qualified phase testing; avoid prolonged unsuitable temperature
Typical failure outcome: Brittle fracture or subsequent localized-corrosion leak
Possible consequences: Unexpected cracking; reduced corrosion margin
Can be mistaken for: 475°C embrittlement; sensitization; carbides
How to distinguish it: Identify secondary phases using metallography and suitable compositional analysis; correlate with heat history and mechanical testing
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Embrittlement of austenitic steel welds at high temperature — Technical reference (accessed 2026-09-08)
70 AMPP — Intergranular Corrosion — Technical reference (accessed 2026-09-08)
80 Ghosh and Mondal (2008) — High temperature ageing behaviour of a duplex stainless steel — publisher abstract and public introduction (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-067Strain-ageing embrittlementCreep & metallurgical ageing · Interstitial/dislocation interaction

Property degradation

Mechanism pathway

Service conditions

None essential

Physical processes

Carbon/nitrogen segregate to dislocations
Dislocation pinning raises yield response and can reduce ductility/toughness

Observable damage

Yield-point return; hardness/strength increase; toughness loss

Possible failure mode

Low-ductility cracking or fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Static strain ageing; strain aging
Industries / exposed sectors: Structural steel; fabrication; pipelines
Typically affected parts: Cold-worked/bent plates; formed parts; strain-hardened regions
Susceptible materials: Susceptible ferritic steels containing mobile carbon/nitrogen
Required chemicals / environment: None essential
Influencing parameters: Prior plastic strain; ageing time/temperature; free interstitial content
Physical explanation (1–3 processes): Carbon/nitrogen segregate to dislocations
Dislocation pinning raises yield response and can reduce ductility/toughness
Signs and symptoms: Yield-point return; hardness/strength increase; toughness loss
Prevention / slowing the damage: Suitable killed/low-free-interstitial steel; control cold work; qualified processing and toughness checks
Typical failure outcome: Low-ductility cracking or fracture
Possible consequences: Reduced forming/service margin
Can be mistaken for: Temper embrittlement; cold-work hardening alone; HE
How to distinguish it: Compare prestrain/ageing history and mechanical response; do not infer from hardness alone
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Why must aluminium content exceed twice the nitrogen content? — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: carbon manganese and low alloy steels, Job Knowledge 19 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-068Neutron irradiation embrittlementCreep & metallurgical ageing · Radiation-induced microstructural damage

Property degradation

Mechanism pathway

Service conditions

None chemically essential; energetic-neutron exposure

Physical processes

Neutron exposure changes the steel microstructure
Fracture toughness decreases, increasing sensitivity to existing flaws

Observable damage

Toughness/impact-property deterioration in surveillance specimens

Possible failure mode

Brittle fracture if loading exceeds degraded resistance

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Radiation embrittlement; vessel embrittlement
Industries / exposed sectors: Nuclear power
Typically affected parts: Reactor-vessel beltline and welds; irradiated structural parts
Susceptible materials: Reactor pressure-vessel steels and welds
Required chemicals / environment: None chemically essential; energetic-neutron exposure
Influencing parameters: Neutron fluence/flux; exposure temperature; steel chemistry and heat treatment
Physical explanation (1–3 processes): Neutron exposure changes the steel microstructure
Fracture toughness decreases, increasing sensitivity to existing flaws
Signs and symptoms: Toughness/impact-property deterioration in surveillance specimens
Prevention / slowing the damage: Material surveillance, fluence and operating-envelope assessment; approved vessel-integrity programs
Typical failure outcome: Brittle fracture if loading exceeds degraded resistance
Possible consequences: Pressure-boundary safety challenge
Can be mistaken for: Temper embrittlement; IASCC; ordinary thermal ageing
How to distinguish it: Use dosimetry/surveillance and toughness data; IASCC additionally needs an environment-assisted crack process
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 NRC — Reactor Vessel Integrity — Regulatory technical reference (accessed 2026-09-08)
80 Chen, Y., Chopra, O.K., Gruber, E.E. & Shack, W.J. (2010). NUREG/CR-7018, irradiation-assisted stress corrosion cracking. NRC / Argonne. — Primary institutional research abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-069High-cycle fatigueFatigue · Cyclic crack initiation and growth

Damage mechanism

Mechanism pathway

Service conditions

None essential; corrosion can accelerate growth

Physical processes

Localized cyclic slip initiates a crack
Repeated loading grows it until remaining section fails

Observable damage

Progressive crack growth; striations in some materials; visual inspection can miss tight cracks

Possible failure mode

Final break; occasionally leak before break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HCF; nominally elastic fatigue
Industries / exposed sectors: Rotating machinery; transport; aerospace; structures
Typically affected parts: Shafts; weld toes; blades; bolts; structural joints
Susceptible materials: Most engineering metals
Required chemicals / environment: None essential; corrosion can accelerate growth
Influencing parameters: Stress range/mean; cycles; notch geometry; residual stress; surface defects
Physical explanation (1–3 processes): Localized cyclic slip initiates a crack
Repeated loading grows it until remaining section fails
Signs and symptoms: Progressive crack growth; striations in some materials; visual inspection can miss tight cracks
Prevention / slowing the damage: Reduce stress concentration and cyclic loads; improve surface/joint quality; damage-tolerant inspection
Typical failure outcome: Final break; occasionally leak before break
Possible consequences: Rotor/structure failure; shutdown; injury potential
Can be mistaken for: LCF; vibration fatigue; SCC; overload
How to distinguish it: Fractography plus stress/cycle reconstruction; no beach marks does not exclude fatigue
How often is it seen?: DNV reports fatigue as 30% of >1,000 oil/gas-maritime investigations; it does not disclose an HCF-only percentage. Do not assign 30% to this subtype.
Historical case / verification status: Aloha Flight 243 (1988): undetected fatigue/disbonding caused fuselage separation and one fatality. This is a verified fatigue example; the cited accident summary does not classify local HCF versus LCF strain.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is fatigue failure and how can it be avoided? — Technical reference (accessed 2026-09-08)
80 ASTM E466-21 — Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials — Official public standard scope (accessed 2026-09-08)
80 TWI — What is peening? — Technical reference (accessed 2026-09-08)
80 NTSB — Aloha Airlines Flight 243, Boeing 737-200, N73711; DCA88MA054 — Primary accident investigation (accessed 2026-09-08)
70 DNV (2020) — Tubes and piping are most failure-prone components in oil and gas and maritime industries — Primary investigation-cohort summary (accessed 2026-09-08)
80 Fatigue crack nucleation in iron and a high strength low alloy steel (2001) — publisher abstract and public section snippets (accessed 2026-09-08)
80 Fractography survey on high cycle fatigue failure in Fe–C–Cr–Mo–X alloys (2007) — publisher abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-070Low-cycle fatigueFatigue · Cyclic plastic deformation

Damage mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Repeated plastic strain localizes damage
Cracks propagate under successive large strain excursions

Observable damage

Fatigue cracks associated with cyclic plastic strain; cyclic hardening/softening can occur

Possible failure mode

Fracture or through-wall leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: LCF; plastic-strain fatigue
Industries / exposed sectors: Power cycling; aerospace; pressure equipment
Typically affected parts: Notches; vessel/nozzle transitions; turbine discs; highly strained joints
Susceptible materials: Structural metals; direct cited experiments used 42CrMo4 steel
Required chemicals / environment: None essential
Influencing parameters: Plastic strain range; mean strain; cycles; temperature; hold time
Physical explanation (1–3 processes): Repeated plastic strain localizes damage
Cracks propagate under successive large strain excursions
Signs and symptoms: Fatigue cracks associated with cyclic plastic strain; cyclic hardening/softening can occur
Prevention / slowing the damage: Limit strain concentration and severe transients; strain-based design; suitable material and inspection
Typical failure outcome: Fracture or through-wall leak
Possible consequences: Loss of containment or load capacity
Can be mistaken for: HCF; ratcheting; creep-fatigue
How to distinguish it: Reconstruct local strain history and crack growth; cycle count alone does not distinguish the fatigue regime
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM E606/E606M-21 — Strain-Controlled Fatigue Testing — Official public standard scope (accessed 2026-09-08)
80 TWI — Fatigue Analysis — Technical reference (accessed 2026-09-08)
80 Saravanan, M., Raghava, G., Vishnuvardhan, S. & Samuel Knight, G.M. Fatigue ratcheting studies on pressurised stainless steel straight pipes. Journal of Structural Engineering. — Primary experimental paper abstract (accessed 2026-09-08)
80 Creep-fatigue interaction behaviour of type 308 stainless steel weld metal and type 304 stainless steel base metal (1993) — publisher abstract (accessed 2026-09-08)
80 Plastic strain-controlled short crack growth and fatigue life — publisher abstract and public section snippets (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-071Very-high-cycle fatigueFatigue · Long-life fatigue regime

Fatigue life-regime subtype

Mechanism pathway

Service conditions

None essential

Physical processes

Small defects or microstructural regions initiate cracks after long cycling
Internal cracks may grow into fish-eye/FGA features before final fracture

Observable damage

Internal origins; fish-eye regions in some alloys; absence does not exclude VHCF

Possible failure mode

Unexpected fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: VHCF; gigacycle fatigue
Industries / exposed sectors: Aerospace; bearings; rail; high-speed machinery
Typically affected parts: Shafts; bearings; high-cycle loaded internal defects
Susceptible materials: High-strength steels; titanium/aluminium and other alloys
Required chemicals / environment: None essential
Influencing parameters: Very large cycle counts; inclusion size/location; stress gradient; surface condition
Physical explanation (1–3 processes): Small defects or microstructural regions initiate cracks after long cycling
Internal cracks may grow into fish-eye/FGA features before final fracture
Signs and symptoms: Internal origins; fish-eye regions in some alloys; absence does not exclude VHCF
Prevention / slowing the damage: Control inclusions/defects; use applicable long-life data; do not assume universal infinite endurance
Typical failure outcome: Unexpected fracture
Possible consequences: High-speed component failure
Can be mistaken for: HCF; inclusion-origin overload; hydrogen-assisted fatigue
How to distinguish it: Fractography of origin plus demonstrated loading duration/cycles; fish-eye is not universal
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Subsurface crack initiation and propagation mechanisms in gigacycle fatigue (2010). Acta Materialia 58(18), 6046–6054. — Primary research paper (accessed 2026-09-08)
80 Influence of Non-Metallic Inclusions on Very High-Cycle Fatigue Performance of High-Strength Steels and Interpretation via Crystal Plasticity Finite Element Method (2024). Metals 14(8), 948. — Primary experimental paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-072Thermal fatigueFatigue · Temperature-gradient-driven fatigue

Damage mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Nonuniform thermal expansion creates cyclic stress/strain
Repeated local strain initiates and advances cracks

Observable damage

Surface crack networks; cracks at thermal mixing or gradients

Possible failure mode

Leak or fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Thermal cycling damage; heat checking
Industries / exposed sectors: Power; nuclear; refining; tooling
Typically affected parts: Mixing tees; boiler ligaments; dies; hot/cold interfaces
Susceptible materials: Steels; cast irons; stainless and heat-resistant alloys
Required chemicals / environment: None essential
Influencing parameters: Temperature swing; gradient; ramp rate; restraint; cycle count
Physical explanation (1–3 processes): Nonuniform thermal expansion creates cyclic stress/strain
Repeated local strain initiates and advances cracks
Signs and symptoms: Surface crack networks; cracks at thermal mixing or gradients
Prevention / slowing the damage: Reduce gradients/ramp severity; improve mixing/design; compatible expansion; inspect hot spots
Typical failure outcome: Leak or fracture
Possible consequences: Hot-fluid release; tool or plant outage
Can be mistaken for: Thermal shock; mechanical fatigue; chloride SCC
How to distinguish it: Correlate crack map with thermal transients and restraint; test for corrosive species when plausible
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Examination of cracking in boiler tubes — Primary failure investigation (accessed 2026-09-08)
80 TWI (2025) — Numerical Modelling of Thermal Fatigue at Pipe Mixing Points in Nuclear Power Plants — Primary research summary (accessed 2026-09-08)
80 TWI — A review of ball grid arrays for electronic assembly (1998) — Technical research paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-073Corrosion fatigueFatigue · Corrosion/cycle interaction

Damage mechanism

Mechanism pathway

Service conditions

Corrosive environment plus cyclic loading

Physical processes

Corrosion pits/film breakdown accelerate initiation
Environment-assisted crack growth combines with cyclic loading

Observable damage

Pit-origin or multiple cracks; corroded fracture features

Possible failure mode

Break or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Environment-assisted fatigue
Industries / exposed sectors: Offshore; marine; pipelines; pumps; power
Typically affected parts: Welded risers; shafts; wet cyclically loaded joints
Susceptible materials: Steels; aluminium and other engineering alloys
Required chemicals / environment: Corrosive environment plus cyclic loading
Influencing parameters: Frequency; stress range; electrochemical potential; pH; hydrogen; temperature
Physical explanation (1–3 processes): Corrosion pits/film breakdown accelerate initiation
Environment-assisted crack growth combines with cyclic loading
Signs and symptoms: Pit-origin or multiple cracks; corroded fracture features
Prevention / slowing the damage: Control both corrosion and cyclic stress; compatible protection; environment-specific fatigue assessment
Typical failure outcome: Break or leak
Possible consequences: Loss of structure/containment
Can be mistaken for: SCC; dry fatigue; hydrogen-assisted cracking
How to distinguish it: Demonstrate cyclic loading and exposure; growth behaviour/frequency effects help separate from sustained-load SCC
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Corrosion fatigue behaviour of welded risers and pipelines (June 2007) — Technical research paper (accessed 2026-09-08)
80 TWI — Corrosion of welded components in marine environments (April 2003) — Technical research paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-074Fretting fatigueFatigue · Oscillatory-contact fatigue

Damage mechanism

Mechanism pathway

Service conditions

None essential; oxidation often accompanies fretting

Physical processes

Oscillatory contact creates high local tractions and surface damage
Cracks initiate near contact edges and grow under cyclic bulk loading

Observable damage

Contact-edge cracks; polished/dark wear patches; oxide debris

Possible failure mode

Fatigue break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Contact-assisted fatigue
Industries / exposed sectors: Aerospace; turbines; rail; rotating machinery
Typically affected parts: Blade roots; press fits; bolted joints; splines
Susceptible materials: Steels; titanium; aluminium and other metallic contacts
Required chemicals / environment: None essential; oxidation often accompanies fretting
Influencing parameters: Microslip; contact pressure; bulk cyclic stress; contact geometry
Physical explanation (1–3 processes): Oscillatory contact creates high local tractions and surface damage
Cracks initiate near contact edges and grow under cyclic bulk loading
Signs and symptoms: Contact-edge cracks; polished/dark wear patches; oxide debris
Prevention / slowing the damage: Manage contact geometry/preload and microslip; qualified coatings/lubrication; appropriate material pairing
Typical failure outcome: Fatigue break
Possible consequences: Blade/shaft/joint failure
Can be mistaken for: Fretting wear alone; ordinary fatigue; corrosion fatigue
How to distinguish it: Locate fatigue origin at the contact edge and establish small-amplitude slip plus cyclic stress
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM E2789-10(2021) — Fretting Fatigue Testing — Official public standard scope (accessed 2026-09-08)
50 SKF (2011) — Golden opportunities — Primary manufacturer technical analysis (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-075Rolling-contact fatigueFatigue · Repeated Hertzian-contact fatigue

Damage mechanism

Mechanism pathway

Service conditions

None essential; lubricant contamination and water modify severity

Physical processes

Repeated contact shear initiates surface or subsurface cracks
Cracks link to release flakes/spalls

Observable damage

Pitting/spalling on contact tracks; vibration; debris

Possible failure mode

Bearing wear-out or seizure; possible secondary fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: RCF; contact spalling; surface/subsurface fatigue
Industries / exposed sectors: Bearings; gears; rail; wind turbines
Typically affected parts: Raceways; rolling elements; gear flanks; wheel/rail contacts
Susceptible materials: Bearing/gear steels; surface-hardened contact materials
Required chemicals / environment: None essential; lubricant contamination and water modify severity
Influencing parameters: Contact stress; lubrication; roughness; inclusions; alignment; cycles
Physical explanation (1–3 processes): Repeated contact shear initiates surface or subsurface cracks
Cracks link to release flakes/spalls
Signs and symptoms: Pitting/spalling on contact tracks; vibration; debris
Prevention / slowing the damage: Correct load/alignment; clean adequate lubricant; suitable hardness/cleanliness; condition monitoring
Typical failure outcome: Bearing wear-out or seizure; possible secondary fracture
Possible consequences: Machine failure; secondary damage
Can be mistaken for: Electrical erosion; indentation; abrasive wear
How to distinguish it: Cross-section and microscopy locate crack origins; compare with fluting/melt craters and contamination
How often is it seen?: SKF (2022) assigns 16% of identified bearing failure modes to surface-initiated fatigue. This is not the fraction for all RCF or the probability a bearing will fail.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 SKF (2019) — Wear and surface fatigue in rolling bearings — Primary manufacturer research (accessed 2026-09-08)
50 SKF (2022) — Bearing damage analysis: ISO 15243 is here to help you — Primary manufacturer investigation dataset (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-076Vibration-induced fatigueFatigue · Dynamically excited fatigue

Loading-specific HCF subtype

Mechanism pathway

Service conditions

None essential

Physical processes

Dynamic excitation creates repeated stress
Local fatigue cracks grow, often at branch or weld notches

Observable damage

Cracks near supports/branches; vibration; intermittent leakage

Possible failure mode

Through-wall leak or fatigue break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: VIF; acoustic/pulsation-induced fatigue
Industries / exposed sectors: Process piping; rotating machinery; aerospace
Typically affected parts: Small-bore branches; instrument connections; supports; compressor lines
Susceptible materials: Metals, especially welded/stress-concentrated details
Required chemicals / environment: None essential
Influencing parameters: Excitation frequency/amplitude; resonance; damping; support stiffness; weld geometry
Physical explanation (1–3 processes): Dynamic excitation creates repeated stress
Local fatigue cracks grow, often at branch or weld notches
Signs and symptoms: Cracks near supports/branches; vibration; intermittent leakage
Prevention / slowing the damage: Measure excitation; address resonance/source; engineer supports; avoid merely adding unassessed restraints
Typical failure outcome: Through-wall leak or fatigue break
Possible consequences: Process release; detached parts
Can be mistaken for: Other HCF; thermal fatigue; overload
How to distinguish it: Operating vibration/modal measurements plus fracture origin; a vibrating component is not proof of causal fatigue
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Fatigue Analysis — Technical reference (accessed 2026-09-08)
80 TWI — Comparison of fatigue of girth welds in full-scale pipes and small-scale strip specimens — Primary research paper (accessed 2026-09-08)
80 ASTM E466-21 — Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-077Thermomechanical fatigueFatigue · Coupled thermal/mechanical cycling

Damage mechanism

Mechanism pathway

Service conditions

None essential; oxidation can interact

Physical processes

Mechanical and thermal strains cycle with a defined phase relationship
Temperature-dependent plasticity, oxidation and sometimes creep interact

Observable damage

Surface cracks; oxide-assisted cracking; evolving cyclic response

Possible failure mode

Cracking or fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: TMF; in-phase/out-of-phase TMF
Industries / exposed sectors: Turbines; engines; aerospace; high-temperature power
Typically affected parts: Hot-section blades; exhaust manifolds; constrained heated parts
Susceptible materials: Superalloys; heat-resistant steels; other thermally cycled metals
Required chemicals / environment: None essential; oxidation can interact
Influencing parameters: Temperature/strain phasing; mechanical strain range; dwell; gradient
Physical explanation (1–3 processes): Mechanical and thermal strains cycle with a defined phase relationship
Temperature-dependent plasticity, oxidation and sometimes creep interact
Signs and symptoms: Surface cracks; oxide-assisted cracking; evolving cyclic response
Prevention / slowing the damage: Reduce thermal/mechanical strain mismatch; design for actual phase history; qualified coatings and life models
Typical failure outcome: Cracking or fracture
Possible consequences: Engine/turbine loss of function; outage
Can be mistaken for: Thermal fatigue; isothermal LCF; creep-fatigue
How to distinguish it: Reconstruct mechanical strain separately from free thermal strain and establish phasing; damage morphology alone is insufficient
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM E2368-25 — Strain Controlled Thermomechanical Fatigue Testing — Official public standard scope (accessed 2026-09-08)
80 TWI — What is a thermal barrier coating? — Technical reference (accessed 2026-09-08)
80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-078Adhesive wear and gallingWear, flow & surface damage · Sliding-contact damage

Wear family; galling is a severe form

Mechanism pathway

Service conditions

None essential; lubricant failure increases risk

Physical processes

Asperities form adhesive junctions
Junction tearing transfers metal; severe interaction can seize contact

Observable damage

Smeared/transferred metal; torn surfaces; rising friction

Possible failure mode

Seizure; leakage; secondary break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Scuffing; seizure; adhesive transfer
Industries / exposed sectors: Fasteners; valves; pumps; machinery
Typically affected parts: Threads; valve trim; sliding guides; wear rings
Susceptible materials: Metal couples, including stainless and titanium pairs
Required chemicals / environment: None essential; lubricant failure increases risk
Influencing parameters: Contact load; sliding; material pairing; roughness; lubrication; alignment
Physical explanation (1–3 processes): Asperities form adhesive junctions
Junction tearing transfers metal; severe interaction can seize contact
Signs and symptoms: Smeared/transferred metal; torn surfaces; rising friction
Prevention / slowing the damage: Compatible material pair/coating; correct lubrication; alignment; controlled assembly
Typical failure outcome: Seizure; leakage; secondary break
Possible consequences: Loss of motion/isolation; machine outage
Can be mistaken for: Abrasive wear; overheating; fretting wear
How to distinguish it: Look for metal transfer and torn junctions, not solely parallel scratches; inspect mating surface
How often is it seen?: SKF (2022): adhesive wear is 7% of identified bearing failure modes. This bearing-cohort result is not a galling incidence across all industries.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G98-23 — Galling Resistance of Materials — Official public standard scope (accessed 2026-09-08)
50 SKF (2022) — Bearing damage analysis: ISO 15243 is here to help you — Primary manufacturer investigation dataset (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-079Abrasive wearWear, flow & surface damage · Hard-particle/asperity wear

Damage mechanism

Mechanism pathway

Service conditions

No reactive chemical required; hard particles/asperities are necessary

Physical processes

Hard particles cut or plough a surface
Repeated contact removes or displaces material

Observable damage

Grooves; polishing; dimensional loss; embedded particles

Possible failure mode

Wear-out; excessive clearance; eventual leak or break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Two-body/three-body abrasion; scratching wear
Industries / exposed sectors: Mining; earthmoving; cement; bearings; machinery
Typically affected parts: Liners; chutes; tools; seals; contaminated bearings
Susceptible materials: Most metals; resistance depends on hardness, toughness and microstructure
Required chemicals / environment: No reactive chemical required; hard particles/asperities are necessary
Influencing parameters: Particle hardness/shape/size; load; sliding distance; impact
Physical explanation (1–3 processes): Hard particles cut or plough a surface
Repeated contact removes or displaces material
Signs and symptoms: Grooves; polishing; dimensional loss; embedded particles
Prevention / slowing the damage: Exclude/filter abrasives; wear-resistant surfaces; suitable hardness-toughness balance; replaceable liners
Typical failure outcome: Wear-out; excessive clearance; eventual leak or break
Possible consequences: Reduced efficiency; contamination; downtime
Can be mistaken for: Adhesive wear; solid-particle erosion; machining marks
How to distinguish it: Match groove/particle geometry and relative motion; analyse debris and contact conditions
How often is it seen?: SKF (2022): abrasive wear is 26% of identified bearing failure modes, highest in its displayed dataset. Sample size and observation period are not disclosed.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G65-16(2021) — Abrasion Using the Dry Sand/Rubber Wheel Apparatus — Official public standard scope (accessed 2026-09-08)
50 SKF (2019) — Wear and surface fatigue in rolling bearings — Primary manufacturer research (accessed 2026-09-08)
50 SKF (2022) — Bearing damage analysis: ISO 15243 is here to help you — Primary manufacturer investigation dataset (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-080Fretting wearWear, flow & surface damage · Small-amplitude contact wear

Damage mechanism

Mechanism pathway

Service conditions

No reactive species essential; air/moisture commonly oxidize debris

Physical processes

Oscillatory slip removes surface films and material
Wear debris oxidizes and can act as abrasive

Observable damage

Red/brown or dark debris; localized wear scars; roller-spaced marks

Possible failure mode

Loss of fit or wear-out; possible later fatigue break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Fretting corrosion; false brinelling in some bearing contexts
Industries / exposed sectors: Bearings; turbines; transport; electrical/mechanical joints
Typically affected parts: Press fits; shaft seats; parked bearings; connectors
Susceptible materials: Metallic contacting surfaces
Required chemicals / environment: No reactive species essential; air/moisture commonly oxidize debris
Influencing parameters: Microslip amplitude; contact pressure; vibration; lubrication
Physical explanation (1–3 processes): Oscillatory slip removes surface films and material
Wear debris oxidizes and can act as abrasive
Signs and symptoms: Red/brown or dark debris; localized wear scars; roller-spaced marks
Prevention / slowing the damage: Control unwanted microslip/vibration; appropriate fit/preload; lubrication and storage/transport measures
Typical failure outcome: Loss of fit or wear-out; possible later fatigue break
Possible consequences: Misalignment; vibration; reduced joint reliability
Can be mistaken for: Fretting fatigue; true brinelling; electrical fluting
How to distinguish it: Confirm oscillatory contact wear; section for fatigue cracks; plastic indentations without wear suggest brinelling
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 SKF (2011) — Golden opportunities — Primary manufacturer technical analysis (accessed 2026-09-08)
50 SKF (2019) — Wear and surface fatigue in rolling bearings — Primary manufacturer research (accessed 2026-09-08)
80 ASTM E2789-10(2021) — Fretting Fatigue Testing — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-081Solid-particle erosionWear, flow & surface damage · Impact-driven material removal

Damage mechanism

Mechanism pathway

Service conditions

No corrosive chemical required; impinging particles in gas/flow

Physical processes

Particle impacts cut/plough ductile surfaces or fracture brittle regions

Observable damage

Directional wastage; impact craters; leading-edge thinning

Possible failure mode

Perforation; blade loss; wear-out

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Particle impingement erosion; gas-borne erosion
Industries / exposed sectors: Power; mining; pneumatic conveying; turbines
Typically affected parts: Duct bends; boiler tubes; turbine blades; chutes
Susceptible materials: Engineering metals and coatings
Required chemicals / environment: No corrosive chemical required; impinging particles in gas/flow
Influencing parameters: Velocity; impact angle; particle size/shape/hardness; temperature
Physical explanation (1–3 processes): Particle impacts cut/plough ductile surfaces or fracture brittle regions
Signs and symptoms: Directional wastage; impact craters; leading-edge thinning
Prevention / slowing the damage: Reduce particle loading/velocity; improve flow path; resistant liners/coatings; targeted inspections
Typical failure outcome: Perforation; blade loss; wear-out
Possible consequences: Release; turbine/boiler damage; downtime
Can be mistaken for: Slurry erosion; corrosion thinning; abrasion
How to distinguish it: Identify particles and impact trajectories; compare sheltered and impinged locations
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G76-26 — Erosion Tests by Solid Particle Impingement Using Gas Jets — Official public standard scope (accessed 2026-09-08)
80 TWI — What are the limiting factors in gas turbine hot section components? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-082Slurry erosionWear, flow & surface damage · Liquid-borne particle damage

Damage mechanism

Mechanism pathway

Service conditions

Liquid carrying hard solids; corrosive liquid may add synergy

Physical processes

Liquid carries particles into sliding/impact contact
Cutting, ploughing or repeated impact removes metal

Observable damage

Localized grooves; impeller/outer-bend loss; dimensional wear

Possible failure mode

Leak; loss of pump performance; rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Slurry abrasion; solids-in-liquid wear
Industries / exposed sectors: Mining; dredging; mineral processing; slurry transport
Typically affected parts: Pump impellers; elbows; valves; liners
Susceptible materials: Steels; cast irons; alloys; metallic coatings
Required chemicals / environment: Liquid carrying hard solids; corrosive liquid may add synergy
Influencing parameters: Solids concentration; velocity; angle; particle distribution; material properties
Physical explanation (1–3 processes): Liquid carries particles into sliding/impact contact
Cutting, ploughing or repeated impact removes metal
Signs and symptoms: Localized grooves; impeller/outer-bend loss; dimensional wear
Prevention / slowing the damage: Duty-specific pump/flow design; resistant liners; solids control; thickness monitoring
Typical failure outcome: Leak; loss of pump performance; rupture
Possible consequences: Slurry release; downtime
Can be mistaken for: Cavitation; erosion-corrosion; dry abrasion
How to distinguish it: Analyse slurry and flow paths; identify impact/wear features and any chemical contribution
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G75-24 — Slurry Abrasivity (Miller Number) and Slurry Abrasion Response of Materials (SAR Number) — Official public standard scope (accessed 2026-09-08)
80 ASTM G76-26 — Erosion Tests by Solid Particle Impingement Using Gas Jets — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-083Cavitation erosionWear, flow & surface damage · Vapour-bubble-collapse damage

Damage mechanism

Mechanism pathway

Service conditions

A liquid capable of local vaporization; no corrosive chemistry essential

Physical processes

Low local pressure creates vapour cavities
Collapse near metal produces microjets/shock loads
Repeated impacts fatigue and remove surface material

Observable damage

Honeycomb-like craters; noise; vibration; performance loss

Possible failure mode

Through-wall leak; loss of component performance; possible secondary fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Cavitation pitting
Industries / exposed sectors: Pumps; hydropower; marine; valves
Typically affected parts: Impellers; propellers; turbine runners; throttling zones
Susceptible materials: Engineering metals exposed to cavitating liquid
Required chemicals / environment: A liquid capable of local vaporization; no corrosive chemistry essential
Influencing parameters: Pressure relative to vapour pressure; temperature; velocity; inlet conditions
Physical explanation (1–3 processes): Low local pressure creates vapour cavities
Collapse near metal produces microjets/shock loads
Repeated impacts fatigue and remove surface material
Signs and symptoms: Honeycomb-like craters; noise; vibration; performance loss
Prevention / slowing the damage: Correct suction/pressure conditions; suitable geometry/operation; resistant surfaces
Typical failure outcome: Through-wall leak; loss of component performance; possible secondary fracture
Possible consequences: Loss of flow/efficiency; equipment outage
Can be mistaken for: Corrosion pitting; droplet erosion; particle erosion
How to distinguish it: Establish cavitating hydraulics and crater distribution; no diagnosis from pits alone
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G32-16(2021)e1 — Cavitation Erosion Using Vibratory Apparatus — Official public standard scope (accessed 2026-09-08)
80 ASTM G73-10(2021) — Liquid Impingement Erosion Using Rotating Apparatus — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-084Liquid-droplet impingement erosionWear, flow & surface damage · Repeated liquid-impact damage

Damage mechanism

Mechanism pathway

Service conditions

High-relative-speed droplets or intermittent liquid impact

Physical processes

Droplet impact generates high transient surface stress
Repeated impacts deform/fatigue the surface and detach material

Observable damage

Leading-edge pits; roughened impact zone; progressing material loss

Possible failure mode

Loss of blade performance; possible blade fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Liquid impact erosion; droplet erosion
Industries / exposed sectors: Steam turbines; aviation; high-speed flow systems
Typically affected parts: Wet-steam blade leading edges; high-speed metallic surfaces
Susceptible materials: Steels; titanium; nickel and other blade alloys
Required chemicals / environment: High-relative-speed droplets or intermittent liquid impact
Influencing parameters: Impact velocity; droplet size; angle; exposure; material fatigue response
Physical explanation (1–3 processes): Droplet impact generates high transient surface stress
Repeated impacts deform/fatigue the surface and detach material
Signs and symptoms: Leading-edge pits; roughened impact zone; progressing material loss
Prevention / slowing the damage: Reduce wetness/impact severity; erosion-resistant shields/coatings; inspect leading edges
Typical failure outcome: Loss of blade performance; possible blade fracture
Possible consequences: Turbine/engine damage; outage
Can be mistaken for: Cavitation; solid-particle erosion; corrosion
How to distinguish it: Relate attack to droplet trajectories and wetness; no vapour-collapse zone or abrasive particles is necessary
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASTM G73-10(2021) — Liquid Impingement Erosion Using Rotating Apparatus — Official public standard scope (accessed 2026-09-08)
80 ASTM G32-16(2021)e1 — Cavitation Erosion Using Vibratory Apparatus — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-085Erosion-corrosionWear, flow & surface damage · Mechanical/chemical synergy

Damage mechanism

Mechanism pathway

Service conditions

Corrosive fluid plus mechanical surface/film damage

Physical processes

Mechanical action removes/damages protective films
Fresh metal corrodes; corrosion can facilitate further erosion

Observable damage

Flow-oriented grooves; local thinning; combined oxide/wear evidence

Possible failure mode

Leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Flow-assisted erosion–corrosion; tribocorrosion in flow
Industries / exposed sectors: Marine; chemical; refining; water/slurry systems
Typically affected parts: Elbows; pump impellers; valves; exchanger inlets
Susceptible materials: Steels; copper alloys; stainless and other metals
Required chemicals / environment: Corrosive fluid plus mechanical surface/film damage
Influencing parameters: Velocity; turbulence; particles/bubbles; chemistry; film recovery
Physical explanation (1–3 processes): Mechanical action removes/damages protective films
Fresh metal corrodes; corrosion can facilitate further erosion
Signs and symptoms: Flow-oriented grooves; local thinning; combined oxide/wear evidence
Prevention / slowing the damage: Control chemistry and impingement; suitable flow design; resistant material/coating
Typical failure outcome: Leak or rupture
Possible consequences: Process release; loss of performance
Can be mistaken for: FAC; pure erosion; general corrosion
How to distinguish it: Demonstrate both mechanical damage and corrosion; distinguish magnetite-dissolution FAC from particle/bubble action
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Corrosion of welded components in marine environments (April 2003) — Technical research paper (accessed 2026-09-08)
70 Copper Development Association — Seawater Corrosion Resistance and Antifouling — Technical reference (accessed 2026-09-08)
80 ASTM G76-26 — Erosion Tests by Solid Particle Impingement Using Gas Jets — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-086Flow-accelerated corrosionWear, flow & surface damage · Oxide dissolution controlled by mass transfer

Damage mechanism

Mechanism pathway

Service conditions

Water or wet steam and chemistry allowing oxide dissolution

Physical processes

Protective magnetite dissolves into moving water
Re-forming oxide and continuing dissolution consume metal

Observable damage

Scalloped/orange-peel thinning; local severe wall loss

Possible failure mode

Pipe rupture or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: FAC; flow-assisted corrosion
Industries / exposed sectors: Fossil/nuclear power; industrial steam
Typically affected parts: Carbon-steel feedwater; condensate; wet-steam piping; elbows
Susceptible materials: Carbon/low-alloy steels, strongly influenced by chromium content
Required chemicals / environment: Water or wet steam and chemistry allowing oxide dissolution
Influencing parameters: Temperature; pH; redox/oxygen; mass transfer; alloy chromium
Physical explanation (1–3 processes): Protective magnetite dissolves into moving water
Re-forming oxide and continuing dissolution consume metal
Signs and symptoms: Scalloped/orange-peel thinning; local severe wall loss
Prevention / slowing the damage: Plant-specific water chemistry; resistant replacement alloy; predictive screening plus thickness inspection
Typical failure outcome: Pipe rupture or leak
Possible consequences: High-energy hot-water/steam release
Can be mistaken for: Erosion-corrosion; droplet erosion; caustic gouging
How to distinguish it: Confirm aqueous chemistry/flow context and oxide-dissolution loss; hard particles/cavitation are not required
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: Surry Unit 2, 9 December 1986: feedwater-system pipe rupture from wall thinning killed four workers; NRC documents the event in its erosion/corrosion operating-experience guidance.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Poulson, B. (2014). Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant. International Journal of Nuclear Energy, 423295. — Research paper abstract (accessed 2026-09-08)
80 NRC — Generic Letter 89-08: Erosion/corrosion-induced pipe wall thinning — Primary regulator operating-experience record (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-087Electrical erosion of bearingsWear, flow & surface damage · Discharge-driven surface damage

Damage mechanism

Mechanism pathway

Service conditions

No chemical necessary; current through the bearing is required

Physical processes

Electrical discharge locally melts/vaporizes contact spots
Repeated discharge and rolling develop pitting/fluting

Observable damage

Microscopic melt craters; washboard fluting; darkened lubricant; noise

Possible failure mode

Bearing wear-out or seizure

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Current leakage damage; electrical pitting; fluting
Industries / exposed sectors: Electric motors; generators; variable-speed drives; rail
Typically affected parts: Bearing raceways and rolling elements
Susceptible materials: Conductive bearing steels
Required chemicals / environment: No chemical necessary; current through the bearing is required
Influencing parameters: Shaft voltage; current density; lubricant film; grounding; drive switching
Physical explanation (1–3 processes): Electrical discharge locally melts/vaporizes contact spots
Repeated discharge and rolling develop pitting/fluting
Signs and symptoms: Microscopic melt craters; washboard fluting; darkened lubricant; noise
Prevention / slowing the damage: Engineered shaft grounding; insulated/hybrid bearings where suitable; correct drive/cable installation
Typical failure outcome: Bearing wear-out or seizure
Possible consequences: Motor downtime; secondary shaft damage
Can be mistaken for: RCF; false brinelling; corrosion pitting
How to distinguish it: Microscopy for re-solidified craters plus shaft-current measurements; fluting alone is not uniquely diagnostic
How often is it seen?: SKF (2022): current leakage is 7% of identified bearing failure modes. Not an incidence for every motor or bearing installation.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

50 SKF (2011) — Golden opportunities — Primary manufacturer technical analysis (accessed 2026-09-08)
50 SKF (2022) — Bearing damage analysis: ISO 15243 is here to help you — Primary manufacturer investigation dataset (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-088Ductile overload fractureFracture & instability · Plastic fracture

Terminal fracture mechanism, not a root cause

Mechanism pathway

Service conditions

None essential

Physical processes

Plastic deformation nucleates voids at particles/interfaces
Void growth and coalescence form a tearing fracture

Observable damage

Dimples; shear lips; necking may occur but constraint can suppress it

Possible failure mode

Break or burst

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Microvoid-coalescence fracture; ductile tearing
Industries / exposed sectors: All industries using loaded metal components
Typically affected parts: Bolts; shafts; pressure boundaries; structural members
Susceptible materials: Ductile engineering metals
Required chemicals / environment: None essential
Influencing parameters: Load; stress triaxiality; temperature; defects; strain rate
Physical explanation (1–3 processes): Plastic deformation nucleates voids at particles/interfaces
Void growth and coalescence form a tearing fracture
Signs and symptoms: Dimples; shear lips; necking may occur but constraint can suppress it
Prevention / slowing the damage: Avoid overload; adequate section/toughness; control defects and loading; protect against excursions
Typical failure outcome: Break or burst
Possible consequences: Loss of load/containment; possible injury
Can be mistaken for: Brittle fracture; fatigue final-overload zone; creep rupture
How to distinguish it: SEM dimples plus deformation/loading evidence; distinguish the final overload region from the initiating mechanism
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is a fracture toughness test? — Technical reference (accessed 2026-09-08)
80 TWI — Engineering Critical Assessment (ECA) — Technical reference (accessed 2026-09-08)
80 Crosti, C. & Duthinh, D. (2010). Buckling of steel gusset plates. IABMAS 2010; NIST. — Primary numerical/experimental research (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-089Brittle cleavage fractureFracture & instability · Rapid low-plasticity fracture

Terminal fracture mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

A sharp defect initiates crystallographic cleavage
Crack propagates rapidly when driving force exceeds resistance

Observable damage

Cleavage facets/river patterns; little macroscopic deformation

Possible failure mode

Sudden break or vessel rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Cleavage; low-toughness fracture
Industries / exposed sectors: Structures; pressure equipment; transport; power
Typically affected parts: Notched/welded steel; thick sections; vessels; low-temperature parts
Susceptible materials: Susceptible ferritic steels and other cleavage-prone metals
Required chemicals / environment: None essential
Influencing parameters: Temperature; toughness; constraint; crack size; loading rate; stress
Physical explanation (1–3 processes): A sharp defect initiates crystallographic cleavage
Crack propagates rapidly when driving force exceeds resistance
Signs and symptoms: Cleavage facets/river patterns; little macroscopic deformation
Prevention / slowing the damage: Toughness-qualified material; defect control; suitable temperature/load envelope; integrity assessment
Typical failure outcome: Sudden break or vessel rupture
Possible consequences: Fragment release; structural collapse; high-energy release
Can be mistaken for: Intergranular HE/embrittlement; fatigue; ductile overload
How to distinguish it: Fractography separates cleavage facets from dimples or boundary fracture; establish toughness and loading temperature
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is a fracture toughness test? — Technical reference (accessed 2026-09-08)
80 TWI — Engineering Critical Assessment (ECA) — Technical reference (accessed 2026-09-08)
80 TWI — What is temper embrittlement, and how can it be controlled? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-090Plastic collapse and pressure burstFracture & instability · Load-bearing instability

Terminal structural failure mode

Mechanism pathway

Service conditions

None essential; corrosion may create the weakness

Physical processes

Load exceeds the section’s plastic load-carrying capacity
Large deformation destabilizes the component or opens a rupture

Observable damage

Bulging; permanent deformation; ductile tearing; reduced wall

Possible failure mode

Burst; collapse; gross deformation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Limit-load collapse; gross plastic instability
Industries / exposed sectors: Pressure equipment; pipelines; structures
Typically affected parts: Thinned pipes; vessels; overloaded members; weakened joints
Susceptible materials: Engineering metals with insufficient remaining section
Required chemicals / environment: None essential; corrosion may create the weakness
Influencing parameters: Pressure/load; wall thickness; geometry; yield/flow strength; temperature
Physical explanation (1–3 processes): Load exceeds the section’s plastic load-carrying capacity
Large deformation destabilizes the component or opens a rupture
Signs and symptoms: Bulging; permanent deformation; ductile tearing; reduced wall
Prevention / slowing the damage: Design/protection against overload; adequate corrosion allowance; thickness/integrity assessment
Typical failure outcome: Burst; collapse; gross deformation
Possible consequences: Major release; loss of structure
Can be mistaken for: Brittle fracture; creep rupture; buckling
How to distinguish it: Measure section loss and reconstruct load/temperature; distinguish plastic capacity failure from crack-controlled instability
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Engineering Critical Assessment (ECA) — Technical reference (accessed 2026-09-08)
50 Veolia Water Technologies — Water Handbook, chapter 14: Boiler System Failures — Manufacturer technical handbook (accessed 2026-09-08)
80 PHMSA — Pipeline Failure Causes (updated 20 April 2026) — Regulatory taxonomy (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-091Buckling instabilityFracture & instability · Compressive/geometric instability

Structural instability, not a chemical damage mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Compressive loading destabilizes the original geometry
Post-buckling deformation may lead to yielding, tearing or collapse

Observable damage

Lateral bowing; wrinkles; ovalization; sudden loss of stiffness

Possible failure mode

Collapse or crippling

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Elastic/inelastic buckling; shell collapse
Industries / exposed sectors: Structures; pipelines; tanks; offshore; aerospace
Typically affected parts: Columns; thin shells; vacuum vessels; tubes; gusset plates
Susceptible materials: All structural metals; geometry dominates susceptibility
Required chemicals / environment: None essential
Influencing parameters: Compression/external pressure; slenderness; imperfections; restraints; eccentricity
Physical explanation (1–3 processes): Compressive loading destabilizes the original geometry
Post-buckling deformation may lead to yielding, tearing or collapse
Signs and symptoms: Lateral bowing; wrinkles; ovalization; sudden loss of stiffness
Prevention / slowing the damage: Adequate stiffness/stiffening; realistic imperfection design; prevent unintended vacuum/overload
Typical failure outcome: Collapse or crippling
Possible consequences: Loss of support; containment; structural safety
Can be mistaken for: Plastic collapse without instability; creep deformation; impact damage
How to distinguish it: Compare deformation mode and compression history with stability analysis including imperfections
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: NIST’s gusset-plate studies address the 2007 I-35W bridge collapse context and demonstrate how geometry, eccentricity and restraint influence plate buckling. No single-mechanism casualty claim is inferred here.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Crosti, C. & Duthinh, D. (2010). Buckling of steel gusset plates. IABMAS 2010; NIST. — Primary numerical/experimental research (accessed 2026-09-08)
80 TWI — Engineering Critical Assessment (ECA) — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-092Ratcheting deformationFracture & instability · Progressive cyclic plastic strain

Progressive deformation mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Combined mean and cyclic loading causes asymmetric plastic increments
Permanent strain accumulates cycle by cycle

Observable damage

Progressive bulging/ovalization; permanent strain; subsequent fatigue cracks

Possible failure mode

Excessive deformation; fatigue leak or rupture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Incremental plastic collapse; cyclic strain accumulation
Industries / exposed sectors: Pressure piping; nuclear; cyclic process equipment
Typically affected parts: Pressurized elbows; pipes; thermal discontinuities
Susceptible materials: Ductile engineering metals
Required chemicals / environment: None essential
Influencing parameters: Steady plus cyclic load; mean stress; plastic hardening; geometry; temperature
Physical explanation (1–3 processes): Combined mean and cyclic loading causes asymmetric plastic increments
Permanent strain accumulates cycle by cycle
Signs and symptoms: Progressive bulging/ovalization; permanent strain; subsequent fatigue cracks
Prevention / slowing the damage: Design for shakedown; reduce mean/cyclic load combination; validated cyclic-plasticity assessment
Typical failure outcome: Excessive deformation; fatigue leak or rupture
Possible consequences: Reduced life; loss of clearance/containment
Can be mistaken for: LCF without net strain; creep; single overload
How to distinguish it: Measure accumulated residual strain per cycle and reconstruct combined loads; distinguish time-driven creep
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Saravanan, M., Raghava, G., Vishnuvardhan, S. & Samuel Knight, G.M. Fatigue ratcheting studies on pressurised stainless steel straight pipes. Journal of Structural Engineering. — Primary experimental paper abstract (accessed 2026-09-08)
80 ASTM E606/E606M-21 — Strain-Controlled Fatigue Testing — Official public standard scope (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-093Weld solidification crackingFabrication cracking · Last-stage solidification failure

Fabrication cracking mechanism

Mechanism pathway

Service conditions

None externally essential; low-melting segregants promote susceptibility

Physical processes

Final interdendritic liquid films cannot carry shrinkage strain
Inadequate feeding/cohesion leaves a crack during solidification

Observable damage

Centreline/crater cracks; interdendritic fracture morphology

Possible failure mode

Fabrication rejection; later leak/fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Solidification hot cracking; weld-centreline cracking
Industries / exposed sectors: Welded fabrication; repair; additive fusion processing
Typically affected parts: Weld centreline; craters; interdendritic regions
Susceptible materials: Susceptible steels; aluminium; nickel and other weld metals
Required chemicals / environment: None externally essential; low-melting segregants promote susceptibility
Influencing parameters: Composition; restraint; bead shape; solidification pattern; travel conditions
Physical explanation (1–3 processes): Final interdendritic liquid films cannot carry shrinkage strain
Inadequate feeding/cohesion leaves a crack during solidification
Signs and symptoms: Centreline/crater cracks; interdendritic fracture morphology
Prevention / slowing the damage: Qualified filler/composition and welding parameters; suitable bead shape; reduce restraint; crater control
Typical failure outcome: Fabrication rejection; later leak/fracture
Possible consequences: Rework or latent service failure
Can be mistaken for: Liquation cracking; cold hydrogen cracking; lack of fusion
How to distinguish it: Locate within solidifying weld metal; identify dendritic path and weld timing; lack of fusion follows an unfused interface
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — What is hot cracking (solidification cracking)? — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: aluminium alloys, Job Knowledge 21 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-094Weld liquation crackingFabrication cracking · Localized grain-boundary melting

Fabrication cracking mechanism

Mechanism pathway

Service conditions

None externally essential

Physical processes

Local grain-boundary liquid forms during heating
Tensile weld strain separates the weakened boundary before healing

Observable damage

Intergranular cracks beside fusion boundary or reheated passes

Possible failure mode

Weld rejection; later service fracture or leak

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: HAZ hot cracking; partially melted-zone cracking
Industries / exposed sectors: Aerospace; high-alloy welding; repair; fusion processing
Typically affected parts: Partially melted HAZ; reheated prior weld metal
Susceptible materials: Susceptible nickel, aluminium and other alloys
Required chemicals / environment: None externally essential
Influencing parameters: Peak thermal cycle; segregants; precipitates; restraint; heat input
Physical explanation (1–3 processes): Local grain-boundary liquid forms during heating
Tensile weld strain separates the weakened boundary before healing
Signs and symptoms: Intergranular cracks beside fusion boundary or reheated passes
Prevention / slowing the damage: Qualified thermal input/filler and material condition; control restraint and heat cycling
Typical failure outcome: Weld rejection; later service fracture or leak
Possible consequences: Rework; reduced structural integrity
Can be mistaken for: Solidification cracks; reheat cracks; LME
How to distinguish it: Locate in previously solid material affected by partial melting; examine resolidified boundary products
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Laser Welding of Crack-Susceptible Materials, literature review 31002/2018 — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: aluminium alloys, Job Knowledge 21 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-095Delayed hydrogen cracking in weldsFabrication cracking · Fabrication hydrogen-assisted cracking

Fabrication hydrogen-assisted cracking

Mechanism pathway

Service conditions

Diffusible hydrogen from moisture, consumables or contamination

Physical processes

Hydrogen diffuses into stressed susceptible regions during/after cooling
Hydrogen-assisted cracking develops, sometimes after inspection

Observable damage

Delayed weld/HAZ cracks; brittle paths; hard microstructure may be present

Possible failure mode

Fabrication rejection or later service fracture

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Cold cracking; weld hydrogen cracking; underbead cracking
Industries / exposed sectors: Steel fabrication; construction; repair
Typically affected parts: Hard HAZ; weld root/toe; weld metal
Susceptible materials: Hardenable/high-strength steels; susceptible weld deposits
Required chemicals / environment: Diffusible hydrogen from moisture, consumables or contamination
Influencing parameters: Hydrogen; susceptible microstructure; tensile restraint; cooling/preheat history
Physical explanation (1–3 processes): Hydrogen diffuses into stressed susceptible regions during/after cooling
Hydrogen-assisted cracking develops, sometimes after inspection
Signs and symptoms: Delayed weld/HAZ cracks; brittle paths; hard microstructure may be present
Prevention / slowing the damage: Dry low-hydrogen process; qualified preheat/heat input; control restraint; code-appropriate delayed inspection
Typical failure outcome: Fabrication rejection or later service fracture
Possible consequences: Rework; loss of integrity
Can be mistaken for: SSC; solidification cracking; lack of fusion
How to distinguish it: Check crack timing, hardness, hydrogen-control records and location; increasing heat input is not universally beneficial
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Hydrogen cracks in steels: prevention and best practice, Job Knowledge 46 — Technical reference (accessed 2026-09-08)
80 TWI — Do increased preheat and heat input always reduce hydrogen cracking risk? — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: carbon manganese and low alloy steels, Job Knowledge 19 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-096Reheat and stress-relief crackingFabrication cracking · Elevated-temperature strain-relaxation failure

Fabrication or early-service cracking

Mechanism pathway

Service conditions

None essential

Physical processes

Grain interiors strengthen during reheating
Stress relaxation concentrates strain on weak grain boundaries

Observable damage

Intergranular coarse-HAZ cracks, often at stress raisers

Possible failure mode

Fabrication rejection; leak/fracture in service

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Reheat cracking; stress-relaxation cracking
Industries / exposed sectors: Power; pressure-vessel fabrication; high-alloy welding
Typically affected parts: Coarse-grained HAZ; weld metal during PWHT or hot service
Susceptible materials: Susceptible Cr-Mo/low-alloy steels; some precipitation-strengthened alloys
Required chemicals / environment: None essential
Influencing parameters: Residual stress; grain size; precipitates; impurity segregation; thermal cycle
Physical explanation (1–3 processes): Grain interiors strengthen during reheating
Stress relaxation concentrates strain on weak grain boundaries
Signs and symptoms: Intergranular coarse-HAZ cracks, often at stress raisers
Prevention / slowing the damage: Qualified alloy/welding/PWHT procedure; avoid severe coarse grains and notches; inspect after heat treatment
Typical failure outcome: Fabrication rejection; leak/fracture in service
Possible consequences: Rework; high-temperature integrity loss
Can be mistaken for: Type IV creep; liquation cracking; temper embrittlement
How to distinguish it: Locate coarse-grain damage and relate timing to reheating/relaxation; Type IV targets fine/intercritical HAZ
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Defects/imperfections in welds: reheat cracking, Job Knowledge 48 — Technical reference (accessed 2026-09-08)
80 TWI — What is type IV cracking, and how is it detected? — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-097Lamellar tearingFabrication cracking · Inclusion-assisted weld-shrinkage tearing

Fabrication tearing mechanism

Mechanism pathway

Service conditions

None essential

Physical processes

Weld shrinkage strains the plate through thickness
Inclusion decohesion and plastic tearing link step-like cracks

Observable damage

Stepped cracks roughly parallel to plate surface; woody fracture

Possible failure mode

Weld rejection; later joint separation

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Through-thickness tearing; lamellar cracks
Industries / exposed sectors: Heavy plate fabrication; offshore; structural welding
Typically affected parts: Restrained T/corner/cruciform joints in rolled plate
Susceptible materials: Rolled steels with poor through-thickness ductility/inclusion stringers
Required chemicals / environment: None essential
Influencing parameters: Through-thickness shrinkage strain; restraint; inclusion morphology; joint orientation
Physical explanation (1–3 processes): Weld shrinkage strains the plate through thickness
Inclusion decohesion and plastic tearing link step-like cracks
Signs and symptoms: Stepped cracks roughly parallel to plate surface; woody fracture
Prevention / slowing the damage: Through-thickness-quality plate; improved joint/load direction; reduce restraint; qualified buttering where suitable
Typical failure outcome: Weld rejection; later joint separation
Possible consequences: Rework; structural integrity loss
Can be mistaken for: HIC; laminations; weld H cracking
How to distinguish it: Show stepped inclusion-linked tearing in parent plate and Z-direction shrinkage loading; HIC requires hydrogen charging evidence
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 TWI — Defects: lamellar tearing, Job Knowledge 47 — Technical reference (accessed 2026-09-08)
80 TWI — Weldability of materials: carbon manganese and low alloy steels, Job Knowledge 19 — Technical reference (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-098Quench crackingHeat treatment & thermal shock · Thermal/transformation-stress cracking

Heat-treatment cracking mechanism

Mechanism pathway

Service conditions

No corrosive chemical essential; quench medium controls heat transfer

Physical processes

Uneven cooling and phase transformation create incompatible strains
Local tensile stress exceeds the low-temperature fracture resistance

Observable damage

Cracks after hardening; sharp-corner initiation; brittle fracture features

Possible failure mode

Manufacturing rejection or later break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Hardening cracks; quench-induced fracture
Industries / exposed sectors: Heat treatment; automotive; tools; manufacturing
Typically affected parts: Hardened gears; shafts; dies; tube/cylinder parts
Susceptible materials: Hardenable steels and susceptible heat-treated metals
Required chemicals / environment: No corrosive chemical essential; quench medium controls heat transfer
Influencing parameters: Cooling rate/distribution; section changes; hardenability; residual stress; inclusions
Physical explanation (1–3 processes): Uneven cooling and phase transformation create incompatible strains
Local tensile stress exceeds the low-temperature fracture resistance
Signs and symptoms: Cracks after hardening; sharp-corner initiation; brittle fracture features
Prevention / slowing the damage: Qualified heat-treatment/quench process; sound geometry; clean steel; timely specified tempering; NDT
Typical failure outcome: Manufacturing rejection or later break
Possible consequences: Scrap; latent component fracture
Can be mistaken for: Grinding cracks; hydrogen cracks; pre-existing forging laps
How to distinguish it: Trace heat-treatment timing; metallography and oxide/temper evidence; assess transformation and thermal stresses
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: ASM documents 4140 seamless hydraulic-cylinder tubing rejected for quench cracks associated with inclusions and excessive severity for the geometry; not reported as a catastrophic public accident.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASM (2019). Failure of Seamless Tubing Due to a Quench Crack. ASM Failure Analysis Case Histories: Design Flaws. — Primary failure case abstract (accessed 2026-09-08)
80 ASM Handbook 4F (2024). Steel Heat Treatment Failures due to Quenching, pp. 575–592. — Authoritative handbook abstract (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-099Grinding burn and grinding crackingHeat treatment & thermal shock · Machining-induced thermal damage

Manufacturing property degradation/cracking

Mechanism pathway

Service conditions

None essential; inadequate cooling/process control may contribute

Physical processes

Grinding heat locally tempers or rehardens the surface
Thermal strain produces harmful residual stress and sometimes cracks

Observable damage

Hardness gradients; tensile subsurface stress; burns/cracks; discoloration may be absent

Possible failure mode

Premature fatigue fracture or contact-surface failure

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Grinding thermal damage; retempering/rehardening burn
Industries / exposed sectors: Gear/bearing manufacture; aerospace; precision engineering
Typically affected parts: Ground gear teeth; bearing races; shafts; ball screws
Susceptible materials: Hardened ferromagnetic steels; other metals can suffer grinding damage
Required chemicals / environment: None essential; inadequate cooling/process control may contribute
Influencing parameters: Grinding heat input; wheel condition; removal rate; coolant; initial hardness
Physical explanation (1–3 processes): Grinding heat locally tempers or rehardens the surface
Thermal strain produces harmful residual stress and sometimes cracks
Signs and symptoms: Hardness gradients; tensile subsurface stress; burns/cracks; discoloration may be absent
Prevention / slowing the damage: Control grinding energy/cooling and wheel condition; qualified inspection; reject/remediate damage
Typical failure outcome: Premature fatigue fracture or contact-surface failure
Possible consequences: Reduced life; precision-system failure
Can be mistaken for: Quench cracking; adhesive scuffing; normal grinding marks
How to distinguish it: Calibrated Barkhausen/etch/hardness or metallographic checks; surface appearance alone misses subsurface damage
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 Sub-Surface Analysis of Grinding Burns with Barkhausen Noise Measurements (2023). Materials 16(1), 159. — Primary experimental paper (accessed 2026-09-08)
80 Grinding Burn Detection via Magnetic Barkhausen Noise Analysis Independently of Induction Hardened Depth (2023). Materials 16(5), 2127. — Primary experimental paper (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

DM-100Thermal-shock fractureHeat treatment & thermal shock · Single/severe-transient thermal fracture

Transient thermomechanical fracture

Mechanism pathway

Service conditions

None chemically essential; coolant can impose the thermal step

Physical processes

Rapid unequal thermal expansion/contraction creates transient stress
A severe excursion drives a crack beyond material resistance

Observable damage

Cracks after a sudden transient; surface-origin fracture; limited prior cycling

Possible failure mode

Fracture; possible through-wall leak or complete break

Original conceptual map. Processes may act together or be alternative explanations; not a ranked sequence, no scale, no remaining-life prediction.

Other names: Thermal shock cracking; acute thermal-gradient fracture
Industries / exposed sectors: Foundries; heat treatment; boilers; high-temperature equipment
Typically affected parts: Castings; hot components hit by cold fluid; thick-section interfaces
Susceptible materials: Metals with insufficient toughness/ductility for the gradient and restraint
Required chemicals / environment: None chemically essential; coolant can impose the thermal step
Influencing parameters: Temperature step; heat-transfer rate; thickness; restraint; toughness
Physical explanation (1–3 processes): Rapid unequal thermal expansion/contraction creates transient stress
A severe excursion drives a crack beyond material resistance
Signs and symptoms: Cracks after a sudden transient; surface-origin fracture; limited prior cycling
Prevention / slowing the damage: Avoid abrupt incompatible transients; controlled heating/cooling; appropriate geometry/toughness
Typical failure outcome: Fracture; possible through-wall leak or complete break
Possible consequences: Hot-fluid release; loss of component function
Can be mistaken for: Thermal fatigue; quench cracking; cold brittle fracture
How to distinguish it: Establish acute thermal transient; distinguish repeated-cycle growth and transformation-related quench stresses
How often is it seen?: No representative subtype-specific incidence was identified in the reviewed sources. This is a data gap, not evidence of rarity.
Historical case / verification status: No mechanism-attributed catastrophe was verified in the sources reviewed; this does not mean none has occurred.

Photographs — 5 needed (real-life, not diagrams)

SLOT 1
Macro / field view

Macro / field view. the damage as an inspector first meets it on the component, in context; identify part and material.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 2
Close-up or micrograph

Close-up or micrograph. morphology at magnification: attack front, pit shape, product, phase; scale bar if a micrograph.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 3
Cross-section

Cross-section. metallographic section through the damage: depth, sub-surface extent, affected microstructure.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 4
In-service failure

In-service failure. the consequence: perforation, leak or weep trail, fracture face, or the replaced component.Not yet sourced — being collected with source, licence, date and a credibility tier.

SLOT 5
Distinguishing feature

Distinguishing feature. the single visual that separates this mechanism from its look-alikes.Not yet sourced — being collected with source, licence, date and a credibility tier.

Sources

80 ASM Handbook 4F (2024). Steel Heat Treatment Failures due to Quenching, pp. 575–592. — Authoritative handbook abstract (accessed 2026-09-08)
80 TWI — What is a fracture toughness test? — Technical reference (accessed 2026-09-08)
80 TWI — Examination of cracking in boiler tubes — Primary failure investigation (accessed 2026-09-08)

Educational synthesis, not a diagnosis or repair instruction. Confirm the actual alloy, environment, loading and damage before selecting mitigation. Generic signs are not unique proof of a mechanism.

How metals degrade,and how to tell them apart.

What the failure statistics actually say

Oil, gas & maritime

Alberta pipelines

Rolling bearings

Helicopter components

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

Possible failure mode

Photographs — 5 needed (real-life, not diagrams)

Sources

Mechanism pathway

Service conditions

Physical processes

Observable damage

How metals degrade,
and how to tell them apart.