Threat category
External Corrosion
This threat family covers external metal-loss review, including isolated corrosion, grouped corrosion, orientation-sensitive loss, and corrosion interaction that can change screening results.
Quick scan
Category summary
6 topics currently available in this threat family.
Common concern drivers
- Depth, profile, and grouping behavior
- Growth evidence and corrosion-control history
- Weld, dent, or strain interaction
- Weak confidence in morphology or location
Common data gaps
- Missing wall thickness, grade, or prior comparison
- Weak grouping confidence or incomplete field validation
- Uncertain orientation or local context near bends and welds
Common decision pitfalls
- Treating segmented colonies as isolated features
- Ranking depth without checking profile or interaction
- Using corrosion-only logic where another threat may be active
Field verification themes
- Field work should confirm actual corrosion shape, grouping, coating condition, and whether another threat is present locally.
Quick Methods and Reference Cards
B31G / Modified B31G framework
Corrosion screening and remaining-strength thinking used as the starting point for external corrosion review.
Effective area / grouped corrosion review
Profile-sensitive review used when corrosion colonies, irregular shape, or grouping matter more than one summary box.
In-Line Inspection of Pipelines
AMPP / NACE
Why it fits: Useful for corrosion review context, inspection capability questions, and understanding tool limitations.
Limitation: Provides broad inspection context rather than a topic-by-topic workflow for every anomaly.
In-line Inspection Systems Qualification Standard
API
Why it fits: Useful for data quality checks, feature confidence review, matching questions, and any topic driven by ILI limitations.
Limitation: This is a qualification and use framework, not a defect-specific engineering decision tool by itself.
Manual for Determining the Remaining Strength of Corroded Pipelines
ASME
Why it fits: Most useful for general metal loss, axial corrosion, pitting, and corrosion screening discussions.
Limitation: Included here only as reference context. This app does not perform calculations and users should follow approved company procedures.
Modified B31G / RSTRENG Method References
Industry Practice
Why it fits: Most relevant to interacting metal loss, irregular corrosion morphology, and grouping decisions.
Limitation: Use only through approved company workflows and software implementations; the method still depends on reliable profile data.
References and Further Reading
Core applicable standards
Core Applicable Standards
Most directly relevant to this topic and commonly used to frame the main review path.
Manual for Determining the Remaining Strength of Corroded Pipelines
ASME
Why it applies: Most useful for general metal loss, axial corrosion, pitting, and corrosion screening discussions.
What it generally addresses: Common corrosion assessment reference used to support remaining-strength thinking and corrosion response framing.
Limitations: Included here only as reference context. This app does not perform calculations and users should follow approved company procedures.
Modified B31G / RSTRENG Method References
Industry Practice
Why it applies: Most relevant to interacting metal loss, irregular corrosion morphology, and grouping decisions.
What it generally addresses: Widely used corrosion-profile methodology references that support interaction and profile-based corrosion review.
Limitations: Use only through approved company workflows and software implementations; the method still depends on reliable profile data.
Supporting context
Supporting / Cross-Discipline References
Helpful when the review needs integrity-management, regulatory, or cross-discipline context beyond the primary method family.
In-Line Inspection of Pipelines
AMPP / NACE
Why it applies: Useful for corrosion review context, inspection capability questions, and understanding tool limitations.
What it generally addresses: Reference material related to selecting, planning, and interpreting in-line inspection programs.
Limitations: Provides broad inspection context rather than a topic-by-topic workflow for every anomaly.
In-line Inspection Systems Qualification Standard
API
Why it applies: Useful for data quality checks, feature confidence review, matching questions, and any topic driven by ILI limitations.
What it generally addresses: Foundational guidance for understanding ILI system qualification, performance, validation, and responsible use of inspection outputs.
Limitations: This is a qualification and use framework, not a defect-specific engineering decision tool by itself.
DNV-RP-F101
DNV
Why it applies: Useful as corrosion-assessment context for isolated, interacting, and complex-shaped metal-loss features and for thinking beyond simple box dimensions.
What it generally addresses: Profile-sensitive corrosion assessment concepts, interacting defects, and combined loading context for corroded pipelines.
Limitations: It is a corrosion-focused method family and does not by itself resolve dent interaction, crack-like behavior, or non-corrosion damage mechanisms.
API 579
API
Why it applies: Useful as broad FFS context when the corrosion condition becomes irregular, interacting, or difficult to close with ordinary screening assumptions alone.
What it generally addresses: General fitness-for-service framing for metal loss, pitting, laminations, dents/gouges, and documentation discipline.
Limitations: API 579 is not a direct replacement for pipeline-specific corrosion methods or operator-approved response criteria.
API RP 1160
API
Why it applies: Provides integrity-management process context for anomaly prioritization, remediation planning, and defensible documentation.
What it generally addresses: Workflow discipline, repair scheduling context, and record quality rather than defect mechanics alone.
Limitations: Guidance framework only; enforceable timing comes from applicable CFR requirements and operator procedures.
PRCI research and guidance
PRCI
Why it applies: Useful when operator workflows need research-backed context on defect interaction, assessment limits, or field validation practice.
What it generally addresses: Industry best-practice and research support for complex or uncertain conditions.
Limitations: Research context is not itself an operating procedure or repair criterion.
49 CFR Parts 192 and 195
PHMSA
Why it applies: Provide the U.S. regulatory framework that operators commonly review when anomaly evaluation, remediation, documentation, and timing decisions need to be tied back to pipeline safety rules.
What it generally addresses: High-level regulatory context for integrity management, repair timing, maintenance, evaluation, and documented response.
CSA Z662 Oil and Gas Pipeline Systems
CSA Group
Why it applies: Provides Canadian technical and program context where the operator or jurisdiction uses CSA Z662 to frame integrity, maintenance, repair, and evaluation practices.
What it generally addresses: Canadian pipeline systems context for integrity management, maintenance expectations, and defect-related technical framework.
Managing System Integrity for Hazardous Liquid Pipelines
API
Why it applies: Useful for prioritization, remediation planning, and defensible workflow when corrosion review needs broader integrity-management context rather than only a screening method.
What it generally addresses: Integrity-management process discipline and anomaly prioritization.
Additional learning
Additional Learning Resources
Good places to deepen understanding of practical behavior, research context, and broader industry guidance.
Pipeline Research Council International (PRCI)
PRCI
Why it applies: Publishes research that helps engineers understand real-world behavior, inspection limitations, interaction effects, and emerging practices across many threat types.
What it generally addresses: Research-backed context for defect behavior, validation limits, and applied integrity practice.
NACE / AMPP corrosion and cracking guidance
NACE / AMPP
Why it applies: Useful for deeper understanding of corrosion mechanisms, SCC context, and related integrity practices that sit alongside pipeline-specific methods.
What it generally addresses: Mechanism-focused corrosion and cracking knowledge and supporting guidance.
DNV recommended-practice context
DNV
Why it applies: Useful when engineers want deeper conceptual grounding for interacting defects, corrosion behavior, or other complex assessment cases.
What it generally addresses: Cross-discipline recommended-practice context for advanced assessment thinking.
Drill Down by Workflow
Topics
Browse this threat family
Each topic follows the same summary-plus-accordion guidance model, but the drill-down is organized by sub-workflow.
Metal Loss
Axial Corrosion
Axial corrosion describes metal loss elongated in the pipe axis direction. It is often reviewed as a remaining-strength concern, but practical screening still depends on how the feature relates to nearby anomalies, welds, bends, and prior growth history.
Metal Loss
Circumferential Corrosion
Circumferential corrosion is metal loss with notable circumferential orientation or span. It often warrants a more careful review than routine axial corrosion because feature orientation, local bending, and sizing confidence can change the practical concern.
Interaction Issues
Corrosion Colony / Cluster
Corrosion colony or cluster guidance is for areas where many nearby corrosion indications form a broader damaged zone and the engineering question is no longer about one box but about the local corrosion system.
Metal Loss
General Metal Loss
General metal loss is the starting point for corrosion review when wall loss is reported but the practical question is still whether the feature is isolated, interacting, growing, or part of a broader integrity mechanism.
Interaction Issues
Interacting Metal Loss
Interacting metal loss is the review path used when multiple nearby corrosion features could combine into a more severe effective condition than any single listed anomaly suggests.
Metal Loss
Pitting
Pitting is localized metal loss with concentrated depth over a relatively small footprint. In practice, engineers often need to determine whether the call is a single pit, a colony, or part of a more irregular corrosion area.