Two standards do the work. API 571 names the mechanisms that attack metal and tells you how to recognise them. API 579-1/ASME FFS-1 takes it from there: once a component no longer meets the rules it was built to, is it still safe, at what pressure, and for how long?
Most study material for both is a wall of text. Corrosion mechanisms are described in paragraphs when what you need is a picture of what the wall looks like afterwards. Fitness-for-service equations are given as symbols when what you need is to move one number and watch the answer move. This resource is the other way round.
Every mechanism below is tagged with the certificates that examine it. Choose one and the library filters itself; choose it again to clear.
A teaching resource written by an engineer, given away free. It explains mechanisms and methods, and the demonstrations use real equations so the behaviour you see is the real behaviour.
It is not an assessment tool and must never be used as one. There is no way to enter your plant's data here and get a verdict, and that is deliberate. Every demonstration runs on a fixed teaching case that you can vary within limits, so you can learn how the numbers behave without ever producing something that looks like a result for real equipment.
If you need to assess real equipment, that is a different job needing a different tool, a competent engineer and a signature. There is a link at the bottom of this page.
Longer pieces on choosing an inspection method and on what the standard actually asks for — each one answering a question that comes up in real inspection planning.
Two things damage a wall in completely different ways and both are called corrosion. What determines how the codes treat them is not what caused them — it is the shape the damage has: spread out, concentrated in a patch, drilled into pits, or sharp and planar.
General thinning goes to API 579 Part 4. A local thin patch goes to Part 5. Pits go to Part 6. Anything crack-like goes to Part 9 — whether a chloride made it, fatigue made it, or a welder did. Learn that mapping and half of fitness-for-service falls into place.
Sixty-four mechanisms. For each one: a cross-section of what it does to the wall, the giveaway that identifies it, what causes it, which materials it attacks, which inspection method finds it, and which part of API 579 assesses it if you find it.
Every mechanism in the library has a shape, and every inspection method has a set of shapes it can see and a set it cannot. This is the map between the two: what each method actually finds, what it misses, and what it costs you in access.
Any brochure will tell you what a method finds. What decides an inspection plan is the other line — the damage a method will walk straight past. Guided wave screens a hundred metres of buried line and cannot see a pit. Radiography images a weld and can miss a tight crack pointing the wrong way. Every entry here says so plainly.
Put an inspection photograph in and it gets measured: how the damaged area breaks up, how round or how linear the features are, how much of the frame they cover, and what colour the surface has gone. Those measurements are matched to the twelve morphologies API 579 recognises, and then against the sixty-four mechanisms in the library.
A rule-based expert system over machine vision — the oldest and the most transparent branch of the field. It is not a neural network and it was not trained on a corpus of photographs, which means it cannot recognise a mechanism it has never been told about, and it also means it can show you every measurement and every rule behind its answer. Press what it read on any photograph to see exactly which pixels it decided were damage. Nothing is uploaded; all of it runs in this browser.
Your inspection code tells you when a component no longer meets the rules it was built to. It does not tell you whether the equipment is still safe, and it is not supposed to. That is the job of a separate standard, jointly published by API and ASME, and this is how it is put together.
Each of these does one thing. Move a slider, watch the answer move, and read the takeaway underneath. The equations are the real ones — what has been removed is the ability to type in your own plant's numbers and get a verdict.
Twelve component geometries, sixty-four damage mechanisms, every assessment part from 3 to 14, at Level 1 or Level 2, worked either as a single answer or as a probability of failure over time. For when you have a reading in front of you and want to know roughly where you stand — or to sanity-check an assessment somebody handed you.
This runs the real API 579 procedures — all twelve assessment parts, Level 1 and Level 2, deterministic and probabilistic — on whatever numbers you type in. It is a screening estimate for learning and orientation. It is not a fitness-for-service assessment and must not be used as one.
It deliberately produces no report, no printable output and no record, because a screening estimate that looks like a deliverable is a hazard. It takes one flaw at a time, uses an allowable stress you supply, and considers no nozzles, supplemental loads, weld proximity or operating history. A result here that says “nothing fails” means the checks it can do did not fail — not that the equipment is fit.
The quantities that turn up in every fitness-for-service conversation. Each one says what it is, what it is for, and the mistake people usually make with it.
These are not past examination papers — reproducing those would be both illegal and useless. They are written to test the specific things this material is easy to get wrong. Answer first, then read the working whether you were right or not.
A study resource written by one engineer has one engineer's blind spots. The things below fix that, and every one of them is something you can send in ten minutes.
Who writes this. A mechanical engineer with twelve years in oil and gas — in-line inspection, fired heater and furnace inspection, and pipeline integrity. What is here comes from the published standards and from what those years in the field actually looked like. It is not written by an API-certified inspector: nothing on this site is a certified inspector’s opinion, and where the standards and this page disagree, the standards are right.
The Integrity Field Guide is a free resource covering the damage mechanisms of API 571, the assessment framework of API 579-1/ASME FFS-1, and the inspection methods that detect them. It is written for people studying for inspector certification and for engineers who want to understand the reports they receive. It is not an assessment tool, it produces no deliverable, and nothing on it may be used to justify a decision about real equipment. Assessing plant requires the current editions of the applicable codes, data from a licensed source, and a competent engineer who signs for the answer.