Fitness-for-Service per API 579

Defensible Level 1/2/3 FFS assessments, remaining-life calculations and audit-ready reports for pressure equipment, piping and tanks — signed by ASNT Level III + API 510/570/653 Authorized Inspectors.

API 579-1 covers nine damage types — brittle fracture, general metal loss, local metal loss (LTA), pitting, blisters and hydrogen damage, crack-like flaws, creep, fire damage, and dents/gouges. Each has Level 1 (screening), Level 2 (engineering assessment) and Level 3 (advanced analysis) options, with progressively less conservatism and progressively more required data. The goal: a defensible engineering recommendation that holds up in front of the regulator, the AI body, the corporate process-safety committee and (if necessary) a court.

Atlantis NDT delivers FFS reports across all nine API 579 parts. Our reports are signed by ASNT Level III consultants with API 510/570/653 AI credentials, and have been accepted by jurisdictional inspectors (ABSA, TSSA, PESO, OISD, Texas/Louisiana/California BPV authorities), operator inspection departments (Aramco, ADNOC, KOC, KIPIC, Pertamina, PEMEX) and AI bodies (ABS Group, BV, Lloyd's, DNV) on four continents.

UT thickness maps, crack-sizing PAUT/TOFD data, material certificates, design data sheet are validated against API 579 Part 1 input requirements.

Conservative screening per the relevant API 579 part. If the equipment passes Level 1, the assessment can stop here with a documented decision.

Refined assessment using actual material properties, operating conditions, RSF, Folias factor, stress-intensity factor or other Part-specific methods.

FEA, EPFM, probabilistic methods. Invoked only when Level 2 does not pass and replacement is uneconomic.

Quantitative remaining-life per API 579-1 Annex F. Documented assumptions, corrosion-rate projection, sensitivity analysis.

Audit-defensible FFS report. Where required, MAWP de-rating, T/P restrictions and re-inspection schedules.

Anonymised examples from recent FFS engagements.

Most engagements start with a 60-minute scoping call — free, no obligation, NDA available on request. Bring your inspection data and we will tell you whether Level 1 will suffice or whether you need to escalate.

What this page covers

Run, repair, replace — defensibly
API 579 damage types we assess
What you get
Methodology
ASNT Level III + API AI credentials
Industries served
Sample client outcomes
Engagement model
Frequently asked questions
Found a flaw? Need a defensible FFS?
Inspection Data Validation
Level 1 Screening
Level 2 Engineering Assessment
Level 3 Advanced Analysis (if required)

Key points covered

Rapid screening per API 579-1 Part 4-12, with conservative criteria designed for quick run/repair/replace decisions when the inspection finding is fresh.
Refined assessment using actual material properties, operating conditions and detailed flaw characterisation — the typical 'commercial' FFS deliverable.
Finite-element analysis (FEA), elastic-plastic fracture mechanics, and probabilistic methods when Level 2 criteria are not met and the equipment cannot be replaced.
Quantitative remaining-life per API 579-1 Annex F for corrosion, creep, fatigue and HTHA damage — with documented assumptions, inputs and sensitivity analysis.
Defensible engineering recommendation with cost-benefit analysis, regulatory implications and operating-envelope restrictions if continued service is approved.
Full FFS report with executive summary, assessment methodology, inputs, calculations, conclusions, and reviewer/signatory credentials. Suitable for jurisdictional inspector and AI body sign-off.
Where continued service requires limits — MAWP de-rating, T/P envelope tightening, inspection re-frequencing — these are documented and integrated into your operating procedures.
Screening against MAT (minimum allowable temperature) curves, exemption charts and impact-test requirements.
Wall-thickness assessment of broad uniform thinning, with corrosion-rate projection.
Localised thin-area (LTA) assessment using RSF and Folias factor methods.
Pitting density, depth and pattern assessment with structural-integrity criteria.
Fracture-mechanics-based crack assessment using stress-intensity factor (K) vs. material toughness.
Creep-life assessment via Larson-Miller parameter, Omega method or Robinson rule for high-T equipment.
Post-fire equipment assessment, hardness surveys, replication and re-rating per API 579 Part 11.
Pipeline-style dent + gouge assessment using B31.4/B31.8/B31G adapted to ASME equipment.
ASNT Level III in UT (including PAUT/TOFD for crack-sizing inputs to Part 9)
API 510, 570, 653 — the three Authorized Inspector credentials whose codes invoke API 579
ASME Section VIII Div 1/2 — design-code fluency required for Level 2/3 assessments
Engineering degrees + PE / CEng / EurIng licensure for senior assessors
40+ FFS reports per year across refining, petrochemicals, upstream and LNG sectors
Avoided replacement cost — Level 3 FFS justified continued service on a 30-year-old hydrocracker shell (Gulf Coast)
Acceptance rate of FFS reports by jurisdictional inspectors and AI bodies (last 3 years)
API 579-1 / ASME FFS-1 (2021 edition) is the joint API-ASME standard for fitness-for-service assessment of pressurised process equipment. It provides quantitative methods for evaluating whether equipment with damage (corrosion, cracks, dents, fire, creep) is fit to continue in service, requires repair, requires de-rating, or must be retired. It is invoked by API 510, 570 and 653, and recognised by jurisdictional inspectors worldwide.
Any time an inspection finding exceeds the acceptance criteria of the relevant code — wall thickness below tmin, a crack found by UT, a dent on a pipeline, post-fire equipment, HTHA evidence, creep cavitation, etc. Rather than defaulting to repair or replacement, an FFS lets you make a defensible run/repair/replace decision based on actual remaining strength and risk.
Level 1 is a conservative screening, fast and easy, suitable for clear-cut decisions. Level 2 uses actual material properties and refined assessment — the typical commercial deliverable. Level 3 invokes FEA, EPFM (elastic-plastic fracture mechanics) and probabilistic methods, reserved for high-stakes equipment where Level 2 does not pass but replacement is uneconomic. We typically start at Level 2 and escalate only if needed.
API 579-1 Part 1 requires the assessor to be qualified by training and experience, with the depth of qualification matched to the assessment level. In practice, Level 2 reports are signed by a senior ASNT Level III with API 510/570/653 credentials and 5+ years of FFS experience. Level 3 reports typically require a PE / CEng license plus fracture-mechanics specialisation.
Level 1 screening: 2-5 days. Level 2 assessment: 3-8 weeks depending on flaw complexity and material data availability. Level 3 (FEA): 8-20 weeks. The pacing constraint is usually access to actual material certificates and complete inspection data — bring those to kick-off and we move fast.
Yes — API 579 is recognised by ABSA, TSSA, PESO, OISD, Aramco Inspection, ADNOC Inspection, KOC, KIPIC, Pertamina, PEMEX, jurisdictional inspectors across the US (Texas, Louisiana, California, Alaska BPV laws), and the AI bodies (ABS Group, Bureau Veritas, Lloyd's, DNV). We have signed reports accepted in every jurisdiction we have worked in.
API 579 applies. For piping we additionally invoke API 570, ASME B31G (for pipelines), B31.8S, and the relevant piping code's repair provisions. We have completed many B31.3 process-piping FFS, B31.4 liquid pipeline FFS, B31.8 gas pipeline FFS, and B31.1 power-piping FFS.
Yes — API 653 explicitly invokes API 579 for fitness-for-service of in-service storage tanks. Bottom thinning, shell distortion, settlement, and floor-soil interface corrosion are all routinely assessed via FFS. We deliver tank FFS reports accepted by API 653 AI bodies and jurisdictional inspectors.

An API 579-1/ASME FFS-1 assessment determines whether equipment with an identified flaw — metal loss, pitting, a crack-like indication — can keep running, needs a rerate, or must be repaired. The standard defines three assessment levels of increasing rigor, and which one applies depends on how conservative the initial screening result is and how much inspection data is available to support a more detailed analysis.

API 579-1/ASME FFS-1 organizes assessments by damage type across a series of parts: Part 4 covers general metal loss, Part 5 local metal loss, Part 6 pitting corrosion, Part 9 crack-like flaws, with additional parts for HIC/blistering, weld misalignment, and other mechanisms. Every assessment starts at Level 1 — a simple, deliberately conservative screening using tables and charts that can often be applied directly from measured minimum thickness or flaw dimensions. If the component fails Level 1 (meaning it doesn't pass the conservative screen, not that it's unsafe), the assessment moves to Level 2, which uses the same part-specific methodology but with more refined calculations and partial safety factors. Level 3 is the most rigorous tier, typically involving finite element analysis, and is reserved for complex geometries, multiple interacting flaws, or cases where Level 2 still can't demonstrate fitness with acceptable margin.

Source: API 579-1/ASME FFS-1

The Level 1/2/3 structure, and what triggers moving up a tier

Level 1 assessments are built to be usable with minimal data and minimal engineering judgment — a set of applicability tables, screening curves, and closed-form equations keyed to damage type. For general metal loss under Part 4, that typically means comparing a measured minimum thickness against a calculated minimum required thickness using a simplified formula and a conservative remaining strength factor. The tradeoff for that simplicity is conservatism: a component that fails a Level 1 screen isn't necessarily unfit for service — it's that the simplified method can't prove fitness with the margin it's built to require.

Level 2 uses the same governing equations as Level 1 but relaxes some of the built-in conservatism — more refined remaining strength factor calculations, component-specific stress analysis instead of generic screening curves, and in some parts, statistical treatment of flaw data rather than worst-case bounding. It needs more from the inspection: not just a single minimum thickness reading, but a thickness profile or grid, or for pitting, actual pit depth and pit density data rather than an assumed distribution.

Level 3 is reserved for cases Level 2 can't resolve — complex flaw geometry, multiple interacting flaws, non-standard component shapes, or situations near the edge of applicability for the closed-form methods. It typically means finite element analysis calibrated against the actual measured geometry, which means the NDT scope has to produce a detailed enough map of the flaw to build an accurate model in the first place — this is where full-coverage UT thickness mapping or detailed surface scanning of a corroded region actually earns its cost.

Which FFS part applies, and what NDT data it needs

General and local metal loss (Parts 4 and 5 of API 579-1/ASME FFS-1) are the most common assessments in a refinery or petrochemical setting — a corroded shell course, a thinned nozzle, an eroded elbow. The NDT input is a thickness map: enough grid density or scan coverage to characterize both the minimum reading and the metal loss profile around it, since Part 5's local metal loss methodology specifically depends on the shape and extent of the thinned region, not just its deepest point.

Pitting (Part 6) needs a different kind of data entirely — pit depth and pit density over a defined area, because the assessment methodology treats pitting statistically rather than as a single worst-case dimension. Undersampling a pitted area, or measuring depth without characterizing density, produces an assessment built on incomplete information regardless of which level is applied.

Crack-like flaws (Part 9) are the least forgiving of poor NDT input, because the assessment is a fracture-mechanics calculation driven directly by flaw length, depth, and orientation relative to the applied stress. This is where technique selection matters most: phased array UT with a proper sizing technique, or in some cases TOFD, because an undersized crack indication produces an FFS result that looks more favorable than the actual condition warrants.

What happens after the assessment — remaining life, disposition, and feeding the RBI interval

An FFS assessment doesn't end with a pass/fail determination. A component that passes at whatever level was applied also gets a remaining life calculation — how long until the measured or projected degradation would bring it back below the fitness threshold, based on the corrosion or degradation rate established from inspection history. That remaining life number is what actually drives the next decision: run as-is with a defined re-inspection date, rerate the component to a lower allowable pressure or temperature, or schedule a repair.

The disposition decision is a business and engineering call informed by the FFS result, not dictated by it alone — a component with a short remaining life on a critical line might still get repaired at the next planned turnaround rather than immediately, if the remaining life comfortably exceeds the time until that turnaround. What FFS provides is the defensible technical basis for making that call rather than guessing.

The remaining life figure, and the degradation rate behind it, is also the direct input into the next RBI interval calculation for that circuit — an FFS assessment done in isolation from the site's RBI program is a missed opportunity, because the same data that justified the current disposition should also be updating the probability-of-failure score for that circuit going forward.

What's the difference between a Level 1 and Level 2 FFS assessment?

Level 1 uses conservative, closed-form screening tables and equations with minimal data; Level 2 applies the same governing methodology with more refined calculations and typically needs more detailed inspection data, such as a thickness profile instead of a single reading.

When does an FFS assessment require finite element analysis?

Level 3 assessments, which use FEA, are reserved for cases Level 1 and 2 can't resolve — complex flaw geometry, multiple interacting flaws, or non-standard component shapes near the edge of the closed-form methods' applicability.

What NDT technique is required for a crack-like flaw FFS assessment?

Part 9 crack-like flaw assessments are fracture-mechanics calculations driven by flaw length, depth, and orientation, so accurate sizing — typically phased array UT or TOFD — is critical; undersizing the flaw produces a result more favorable than the actual condition.

Does a passed FFS assessment mean no further action is needed?

No. A passing result still comes with a remaining life calculation based on the measured degradation rate, which sets the next re-inspection date or interval rather than closing the item out permanently.

How does an FFS assessment connect to a site's RBI program?

The degradation rate and remaining life established during the assessment should feed directly into the probability-of-failure score for that circuit in the site's risk-based inspection program, rather than existing as a one-off calculation.