Every inspection program eventually finds something the original construction code cannot bless: a shell thinner than minimum required thickness, a dent, a laminar flaw, a crack. The construction code governs new equipment. Once metal is in service and damaged, the question changes from "was this built right" to "can this keep operating as it is," and API 579 is the discipline for answering it. Knowing when to invoke it, and at what level, is a program decision worth getting right.
The trigger
The clean trigger is simple: a fitness-for-service assessment is warranted when equipment contains a flaw or damage that puts it outside its original acceptance basis, and the owner wants to continue operating rather than immediately repair, rerate, or retire. Common cases:
- General or local thinning below minimum required thickness, where the corrosion allowance is spent but the metal may still carry the load.
- Pitting dense or deep enough that CML averages no longer describe the condition.
- Crack-like flaws found by surface or volumetric examination.
- Dents, gouges, and distortions from mechanical damage.
- Fire or overheating exposure, where material properties themselves are in question.
The wrong trigger is habit. Running an assessment to postpone a repair that is clearly needed, or repeating assessments on the same degrading flaw to buy successive short extensions, is a pattern auditors and regulators recognize.
The three levels, honestly priced
API 579 is organized in three assessment levels, and the trade is always conservatism against effort.
- Level 1 uses simplified screening criteria with the most conservative assumptions. It needs modest data and can be executed by qualified inspection or plant engineers. Much equipment passes here, and when it passes, the documentation burden is light.
- Level 2 applies more detailed calculation with the same data plus better characterization of the flaw and loads. It sharpens the answer when Level 1 fails but the equipment looks recoverable.
- Level 3 is full engineering analysis, often numerical, reserved for high-value equipment, complex loading, or flaws the lower levels cannot handle. It requires an experienced engineer and produces a package that is itself a substantial record.
Failing a level is not a verdict, it is a fork: escalate the analysis, or repair, rerate, or retire. The decision at that fork, and who made it, belongs in the file.
The assessment changes the future record
A fitness-for-service result is not just permission to keep running. It typically comes with conditions: a remaining life, a revised corrosion allowance, a monitoring requirement, sometimes an operating restriction. Those conditions have to flow into the inspection plan, or the assessment is a document with no consequence. If the assessment assumed a thinning rate, subsequent readings must be checked against it. If it required periodic monitoring of a flaw, the monitoring has to be scheduled, done, and attached to the same equipment record.
This is where programs actually fail their FFS work. The engineering is done well, the report is filed, and two thickness surveys later nobody remembers that this vessel is operating under an assessment with an expiry logic attached.
What the file must show
Years later, the record should reconstruct: the finding that triggered the assessment, the level applied and its inputs, the result and its conditions, the acceptance sign-off, and the evidence that every condition has been carried out since. An FFS without its follow-through record is closer to a liability than an asset.
intelliSPEC keeps the finding, the assessment conditions, and the follow-up inspections in one equipment history, so the conditions cannot silently expire. Bring a live FFS case to a demo and see it tracked.
