The API 510 exam structure, explained properly

Candidates lose marks on API 510 for reasons that have nothing to do with pressure vessels. They mismanage a two-session structure they had not rehearsed, or they prepared against last year’s code editions. Both are avoidable.

How is the API 510 exam structured?

The exam runs as two sessions in a single day:

Session	Questions	Time	Books
First	110	2 h 45 min	Closed
Break	—	45 min	—
Second	60	3 h 45 min	Open

That is 170 questions across roughly seven and a half hours including the break.

The asymmetry is deliberate and worth reading carefully. The closed-book session gives you about 90 seconds per question. The open-book session gives you nearly four minutes. That is not generosity — it reflects that open-book questions require you to locate a requirement in a reference set and apply it, which takes time.

Which questions actually count?

140 of the 170 are scored. The remaining 30 are unscored pretest items that API uses to trial future questions.

They are not identified. You cannot tell which is which, so the only rational approach is to answer everything as though it counts. There is no penalty for a wrong answer, so leaving anything blank is strictly worse than guessing.

How is API 510 scored?

Passing is a scaled score of 400 on a 200-500 scale.

Scaled scoring maps raw scores onto a fixed range so that candidates sitting a marginally harder form are not disadvantaged. The consequence is that the raw number of correct answers required varies between forms, and API does not publish it.

This means any statement of the form “you need 70% to pass API 510” is not a rough guide — it is unsupported. Nobody outside API knows the raw cut score for a given form.

For practice purposes, treat 70-75% on well-built material as a readiness signal, while understanding it is your benchmark and not API’s standard.

What is in scope?

The Body of Knowledge covers five areas:

1. Thickness Measurements, Inspection Intervals and Vessel Integrity
2. Welding Procedure and Qualification Evaluation
3. Nondestructive Examination
4. Practical Knowledge — General
5. Practical Knowledge — Specific

API publishes these section names but does not publish percentage weights for them. Any vendor quoting an exact split has estimated it. A reasonable estimate can be inferred from the 110/60 structure — general practical knowledge dominates the closed-book session, while the technical sections divide the open-book questions — but it remains an estimate and should be described as one.

The reference set changes, and it matters

This is where preparation most often goes stale.

API publishes an effectivity sheet for each exam window, listing exactly which documents and which editions are in scope. Those editions move.

For the September 4-25 2026, January 2-22 2027 and May 7-28 2027 windows, the sheet lists API 510 11th Edition with Errata 1 and 2, together with the 2025 editions of ASME BPVC Sections V, VIII Division 1 and IX, plus the relevant API recommended practices and specified ASME PCC-2 articles.

Two practical consequences:

• Check the sheet for your own window before you buy anything. Material written to a superseded edition will teach you requirements that no longer apply.
• The in-scope portions matter as much as the document names. The sheet often scopes particular articles or sections rather than an entire code.

Preparing for the closed-book session

The closed-book session rewards two things: fluent recall of the calculation methods, and familiarity with the damage mechanisms.

Formulas you should be able to reproduce cold, in both US customary and SI units:

• Corrosion rate, long-term and short-term
• Remaining life
• Next inspection interval, including the half-life rule
• Minimum required thickness for shells and heads
• MAWP from measured thickness

Two habits pay for themselves. First, practise in both unit systems — both are examinable, and a question bank written only in US customary leaves you exposed. Second, when a question gives you long-term and short-term corrosion rate data, remember that API 510 has you compare them and apply the greater one. A rising short-term rate signals that something in the service has changed, and averaging the two hides exactly the signal you were meant to catch.

Preparing for the open-book session

Open book is a navigation skill, not a memory skill, and it needs separate rehearsal.

The references are supplied as on-screen PDFs. If your entire preparation involved thumbing through tabbed paper copies, exam day will be slower than you expect. Practise with a digital copy and a search box.

Build a mental index rather than a memorised one: know which document answers which kind of question. Repair and alteration authorisation, examination method selection, welder qualification, and acceptance criteria all live in predictable places, and knowing which book to open is most of the battle.

A realistic preparation plan

• Weeks 1-2 — Read API 510 itself end to end once. Do not attempt mastery; you are building a map.
• Weeks 3-5 — Domain by domain, with closed-book retrieval after each. Write formulas from memory daily.
• Weeks 6-7 — Full practice sets. Classify every error by cause: calculation, code requirement, field judgement, or misread.
• Week 8 — One full timed rehearsal with the real 2:45 / break / 3:45 structure, using on-screen references only.

The timed rehearsal is the step most candidates skip and the one that most reliably changes the outcome. Seven and a half hours of sustained technical attention is itself a skill, and the first time you attempt it should not be the day it counts.