API 579: Fitness-For-Service
Comprehensive standard for systematic fitness-for-service assessment of components with detected defects. API 579 provides methods for determining whether components with flaws can continue safe operation. It combines NDT results, material properties, and fracture mechanics analysis. API 579 allows safe continued service of components with minor defects that would otherwise require replacement.
The American Petroleum Institute (API) publishes the in-service inspection standards that govern downstream and midstream petroleum equipment.
OSHA Process Safety Management (29 CFR 1910.119) and EPA Risk Management Program rules cite API inspection standards as recognised and generally accepted good engineering practice (RAGAGEP), so non-compliance is enforced indirectly through PSM audits.
API 579 is invoked when the scope of work matches its title — fitness-for-service — and when the contract or regulatory regime cites it as the controlling document. In power and nuclear work, the inspection plan is built directly off the standard's tables; an auditor will cite the paragraph that was followed (or the one that was missed) when writing a finding. On petroleum and petrochemical equipment, API 579 usually feeds into a written mechanical-integrity program: inspection intervals, examination methods, and acceptance criteria are all traced back to a clause number in the document. In fabrication shops the standard is reproduced inside the written procedure book and referenced from every inspection report so that the auditor's paper trail leads back to the same paragraph the inspector worked from.
Methods covered
Industries
- Oil & Gas
- Petrochemical
- Power Generation
- Manufacturing
- Personnel qualification: examinations under API 579 must be performed by inspectors qualified and certified to a recognised scheme (typically ASNT SNT-TC-1A, CP-189, or ISO 9712 depending on jurisdiction), with documented training hours, vision tests, and a controlling written practice.
- Written procedure: every examination requires a written, controlled procedure that names the method, equipment, calibration steps, scanning pattern, and acceptance criteria — and is qualified before first use.
- Equipment verification: ultrasonic instruments must be verified against a calibration block (V1, V2, IIW, or job-specific reference) at intervals defined by the procedure — typically before use, every four hours of scanning, on operator change, and at end of shift.
- Image-quality verification: every radiograph or digital exposure carries a penetrameter / IQI of the type and thickness specified by the standard; the IQI must be visible and at the required sensitivity for the radiograph to be acceptable.
- Radiation safety: source handling, exclusion zones, dosimetry, and source recordkeeping must follow the licensing authority's rules in addition to the inspection standard itself.
- Acceptance criteria: indications are evaluated against the standard's tabulated limits (length, depth, alignment, frequency); any indication exceeding the criteria is recorded, dispositioned, and either repaired or evaluated for fitness-for-service.
- Documentation: examination reports must include enough information for a third party to reproduce the inspection — equipment serial numbers, calibration records, inspector ID, sketches of indications, and the controlling procedure revision.
- Inspection intervals: API 579 sets maximum intervals between inspections based on remaining-life calculations or fixed default intervals; an authorised inspector must approve any extension based on documented risk-based-inspection analysis.
- Latest Edition
- API 579-1/ASME FFS-1 (2021)
- First Published
- 2000
- Scope
- Fitness-for-service assessment for in-service equipment with damage or deviations from new-construction code.
- Acceptance Criteria
- Three-level assessments: Level 1 (screening), Level 2 (closed-form), Level 3 (advanced FEA + fracture mechanics); RSF ≥ 0.9 typical pass.
- Calibration / Qualification
- Performed by qualified engineer (typically PE or chartered with FFS experience); inputs from API 510/570/653 inspection.
Key Clauses Inspectors Cite
- Part 4 — Brittle Fracture
- Part 5 — General Metal Loss
- Part 6 — Local Metal Loss
- Part 7 — Pitting
- Part 9 — Crack-like Flaws
- Part 10 — High-Temperature Operation
Companion / Parent Standards
BS 7910 · R6 · WES 2805 · API 510 · API 570 · API 653
Sample Contract Language
“Indications exceeding code acceptance shall be evaluated per API 579-1/ASME FFS-1 prior to repair/disposition.”
API revises its inspection codes on roughly a five-to-seven-year cycle, with addenda issued in between. Recent updates to API 579 have continued the move toward risk-based-inspection (RBI) as an accepted basis for setting inspection intervals, expanded coverage of damage mechanisms, and updated cross-references to the latest editions of API 579 (fitness-for-service) and API 580/581 (RBI). The version cited in a written mechanical-integrity program should be tracked in the document control system so that any update flows through to the inspection plan.
A typical refinery turnaround applies API 579 to the inspection scope for high-temperature piping and pressure vessels: corrosion-monitoring locations are read with UT thickness gauges, girth welds on repaired sections are radiographed or PAUT-scanned, and any indication outside the standard's acceptance table is dispositioned through API 579 fitness-for-service before the unit restarts.
What does API 579 cover?
API 579 (Fitness-For-Service) is published by API. Comprehensive standard for systematic fitness-for-service assessment of components with detected defects.
What is the history of API 579 and the most common misuse to avoid?
API 579-1/ASME FFS-1 (joint API/ASME publication) is the fitness-for-service standard. First issued in 2000, it consolidated decades of utility-industry and refinery FFS practice. Parts 1-13 cover specific damage mechanisms (general/local thinning, pitting, blisters, weld misalignment, crack-like flaws, fire damage, fatigue, dents, laminations). FFS Level 1 assessments are NOT required to use a Level 3 assessment to disposition. Many inspectors leap to Level 3 finite-element modeling when a Level 1 screening would have closed the disposition. Level 3 is intended only for cases that fail Level 2.
Which sister standards is API 579 typically used with?
Pairs with API 510, 570, 653 (which invoke 579 for any indication exceeding the in-service code acceptance criteria) and ASME PCC-2 for the actual repair design.
Is API 579 mandatory or voluntary?
API 579 is a consensus standard. It becomes mandatory when invoked by a contract, by another code that cites it (for example ASME Section V calling out an ASTM practice), or by a regulator that has adopted it into law in a specific jurisdiction.
Who is qualified to perform inspections under API 579?
Inspections under API 579 must be performed by personnel qualified and certified to a recognised NDT certification scheme — most commonly ASNT SNT-TC-1A or CP-189 in the United States, ISO 9712 in much of the rest of the world, and NAS 410 for aerospace work. The written practice that controls qualification must be in place before any examination is started.
How does API 579 interact with ASME Section V?
API 579 typically references ASME Section V for the underlying examination methods and acceptance criteria, then layers on the API-specific inspection intervals, damage-mechanism coverage, and Authorised Inspector requirements that apply to in-service equipment.
Standard Code
API 579
Organization
API
Methods Covered
4 method(s)
Industries
4 sector(s)
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