Asset Integrity Management

Corrosion Risk & Fitness-for-Service (FFS) Assessment

API 579-1 / ASME FFS-1 Level 1/2/3 — engineering judgement that defers $-millions of capex safely

Start your projectBack to Asset Integrity
Technical overview

Corrosion Risk &
Fitness-for-Service (FFS) Assessment

Fitness-for-Service per API 579-1 / ASME FFS-1 (joint publication, currently 3rd Ed. 2021) is the dominant engineering framework for evaluating pressure equipment with degradation (corrosion, cracking, dents, fire damage, creep, hydrogen-induced damage, fatigue, microbiological attack). The framework provides three assessment tiers — Level 1 (conservative screening per simple equations), Level 2 (more rigorous engineering analysis), Level 3 (finite-element analysis or fracture mechanics) — and 14 chapters covering specific damage mechanisms from general thinning to weld misalignment to brittle fracture. Industry practice now also routinely integrates API 571 damage-mechanism interpretation, NACE SP0472 / SP0170 corrosion-control programmes, API 580/581 RBI feedback, and ASME B31.G / Modified B31.G for pipelines. The 2021 revision tightened High-Temperature Hydrogen Attack (HTHA) procedures following the 2010 Tesoro Anacortes event (CSB 2014 final report) and added expanded fracture mechanics for sour-service equipment. Modern FFS practice is most consequential where it defers turnaround scope, justifies operating-condition adjustments, and replaces the binary 'fix-or-replace' decision with engineered run-with-monitoring.

Corrosion Risk & Fitness-for-Service (FFS) Assessment — Overview
Engineering process

Corrosion Risk & Fitness-for-Service (FFS) Assessment workflow

Corrosion Mechanism & Damage Survey

Catalogue corrosion mechanisms per API RP 571 — general thinning, localised pitting, CUI, HIC/SSC, HTHA, MIC, erosion-corrosion; conduct inspection survey (UT, RT, AUT, eddy current, MFL) to quantify wall thickness, defect size, and distribution.

Damage Mode Selection (API 579 Part)

Select applicable FFS procedure per API 579-1 / ASME FFS-1 — Part 4 (general thinning), Part 5 (local thinning), Part 6 (pitting), Part 7 (HIC/SOHIC blistering), Part 8 (weld misalignment), Part 9 (crack-like flaws), Part 10 (HTHA), Part 11 (creep).

Level 1 / 2 / 3 Assessment

Conduct tiered assessment — Level 1 (screening, conservative), Level 2 (engineering, balanced), Level 3 (advanced FEA, refined); select level based on screening result and remediation cost; align with operator competency and FFS specialist team.

RSF & MAWP / MAOP Re-Rating

Calculate Remaining Strength Factor (RSF) per API 579; if RSF < target (typically 0.9), re-rate MAWP / MAOP per code formula; document operating-pressure-reduction option; align with API 510 / 570 inspection programme.

Remaining Life & Inspection Interval

Calculate remaining life from observed corrosion rate (long-term and short-term per API 510 / 570); set inspection interval at half remaining life (per API 510 / 570 default) or per RBI assessment; integrate with PHA / LOPA risk evaluation.

Run-Repair-Replace Decision & MOC

Author run / repair / replace recommendation with cost-benefit; specify temporary repair (clamp, sleeve, fillet weld, composite wrap) vs permanent repair vs replacement; integrate with MOC and PHA revalidation; align with insurer / underwriter notification requirement.

Corrosion Risk & Fitness-for-Service (FFS) Assessment — Scope
Scope of work

Every deliverable — from basis to handover

Complete Corrosion Risk & Fitness-for-Service (FFS) Assessment scope — every calculation, drawing, specification, and construction support activity.

Active damage mechanism identification per API RP 571 — typically 3–6 per equipment item
Level 1 FFS — conservative thinning, blister, lamination, dent screening per simple equations
Level 2 FFS — engineering analysis with thickness measurement averaging, FFS pressure calculation
Level 3 FFS — finite-element analysis (ANSYS, ABAQUS), elastic-plastic fracture mechanics
Remaining Strength Factor (RSF) calculation with 0.9 acceptance threshold
Brittle fracture assessment per API 579 Part 3 — critical exposure temperature, MAT/MDMT logic
Hydrogen-induced damage — HIC, SOHIC, SSC per Part 6; HTHA per Part 11 with Nelson Curves
Creep damage per Part 10 — Larson-Miller, Omega method, accumulated damage fraction
Fatigue and dent assessment for fluctuating-pressure service
Remaining-life prediction with corrosion rate, monitoring frequency, and re-assessment trigger
Engineering outcomes

Outcomes of Corrosion Risk & Fitness-for-Service (FFS) Assessment

Corrosion & Defect Integrity Assurance
  • Confirms continued safe operation of degraded equipment with quantitative basis
  • Surfaces imminent-failure conditions where leak-before-burst no longer holds
  • Drives inspection-method selection that catches the active damage mechanism
  • Closes the Tesoro Anacortes / Husky Superior-class HTHA detection gap
API 579-1 / ASME FFS Defence
  • Audit-defensible under API 579-1 / ASME FFS-1 (3rd Ed., 2021)
  • Provides AI / AHJ-acceptable evidence for run-until-next-turnaround decisions
  • Withstands NACE / AMPP compliance audit on sour-service equipment
  • Supports insurance underwriter scrutiny on ageing-asset portfolios
Inspection Interval & Scope Optimisation
  • Defers full equipment replacement through engineered run-with-monitoring
  • Anchors RBI re-baseline with quantitative remaining-life basis
  • Drives turnaround scope optimisation — focusing on FFS-failed items
  • Supports operating-pressure or temperature de-rating where capex is deferred
FFS-Based Run-Repair Cost Efficiency
  • Defers $-million capex on pressure-vessel and piping replacement
  • Optimises turnaround scope — only what FFS demands
  • Avoids unplanned outage cost from late damage detection
  • Trims underwriter loadings on ageing-asset portfolios
Get Started

Ready to start your project?

Speak with our team to scope an engagement tailored to your facility, regulatory context, and lifecycle stage.

Start your projectView all services