API 510 Practice Test

API 510 is the American Petroleum Institute certification for pressure vessel inspectors. Candidates are usually inspectors, engineers and technicians with pressure vessel experience who want to prepare before sitting a computer-based exam at a Prometric test center. This page offers free practice sets by topic, a map of the official content areas, worked questions, a study plan and answers to common questions.

API 510 Exam at a Glance

What the API 510 is and how it works

According to American Petroleum Institute, “There are 170 questions on the exam, of which only 140 are scored.”^[1]

API 510 certifies that a person can inspect, repair, alter and rate pressure vessels in service. The American Petroleum Institute runs the program, and the certification is accredited by the American National Standards Institute. Once earned, it is valid for 3 years.

The exam is computer-based and given in person at Prometric test centers only. API stopped offering remote testing for its core certification programs as of September 2024. The exam has 170 questions, and 140 of them are scored. The passing mark is a scaled score. API uses a statistical process called equating to set the pass point for each exam period, so the raw number of correct answers needed can differ between exam forms. Score reports come by email from Prometric within 24 hours of testing.

To apply, you need a mix of education and pressure vessel experience: education plus 1-5 years of experience, with the experience falling within the last 10 years. The exact combination is set out in Appendix B of the API 510 standard, so check it against your own background before you apply.

Fees for 2026 are $875 for API members and $1,125 for non-members. A late application costs $200 extra, and a reschedule or retest costs $350. You have 12 consecutive months from your first scheduled exam date to pass. Fees, windows and deadlines can change, so confirm them on the API website before you pay.

API 510 content outline and where to practise each area

The content areas below are copied from the official API 510 content outline published by American Petroleum Institute. The right-hand column shows which of our practice sets covers it.

Worked examples: how to reason through API 510 questions

These are practice questions written for this site, not questions from the real exam. Each explanation shows why the right answer is right and why the others are wrong.

Example 1

Question: Which weld discontinuity is described as non-metallic material, such as flux or oxide, trapped within the weld metal?

1. Porosity
2. Slag inclusion
3. Cold lap
4. Crater crack

Answer: B. Slag inclusion

Explanation:

The correct answer is slag inclusion. Slag is non-metallic material, such as flux residue or oxide, that ends up trapped inside the weld metal or between passes, usually because the weld was not cleaned properly between passes.

Porosity is wrong because it describes gas pockets, which are voids, not trapped solid material. Cold lap is wrong because it is a lack of fusion where weld metal rolls over the base metal without bonding. Crater crack is wrong because it is a crack at the end of a weld bead where the arc stopped, not an inclusion.

Rule to remember: sort discontinuities by what they physically are. Gas gives porosity, trapped solids give inclusions, poor bonding gives lack of fusion or lap, and stress or shrinkage gives cracks.

Example 2

Question: Which document details safety design requirements for vessels?

1. Operation manual
2. Material test report
3. ASME Section VIII
4. P&ID diagram

Answer: C. ASME Section VIII

Explanation:

The correct answer is ASME Section VIII. It is the part of the ASME Boiler and Pressure Vessel Code that sets the rules for designing and constructing pressure vessels, covering materials, fabrication, inspection, testing and certification.

An operation manual is wrong because it tells operators how to run the equipment, not how it must be designed. A material test report is wrong because it records the properties of a specific heat or lot of material, and sets no design requirements. A P&ID diagram is wrong because it shows piping, instruments and process flow, not code design rules.

Rule to remember: when a question asks which document sets design or construction requirements, look for the code. Records and drawings describe a particular vessel, while the code sets the rules it was built to.

Example 3

Question: What defines the minimum design metal temperature (MDMT)?

1. The temperature at which painting begins.
2. The maximum temperature of steel melting.
3. The minimum allowable operating temperature
4. The curing temperature of rubber seals.

Answer: C. The minimum allowable operating temperature

Explanation:

The correct answer is the minimum allowable operating temperature. The minimum design metal temperature is the lowest metal temperature at which the vessel is permitted to carry pressure. Below it, steel can lose toughness and fail by brittle fracture, especially where there are flaws or high stress. Cold weather, startup and shutdown are the situations to watch.

Painting temperature is wrong because coating conditions have nothing to do with the vessel's design limit. The temperature at which steel melts is wrong because it describes a maximum, and the term is about the cold end. The curing temperature of rubber seals is wrong because it is a manufacturing detail of one component.

Rule to remember: MDMT is a low-temperature limit tied to brittle fracture, not a general operating range.

How to use these practice tests

Start with the official material. Read the API 510 content areas listed on this page and note which ones you can already explain without notes. Use that list to decide where to spend your time.

Work through one practice set at a time instead of mixing topics. Take a set untimed, and for every question you miss, write down the rule behind the answer in a sentence. Then open the relevant section of the code or standard and find that rule in the original text. The goal is to be able to locate an answer in the documents, not to remember a question.

Give extra time to the areas that involve calculation, such as thickness readings, corrosion rate, remaining life and inspection intervals. Redo the same calculation from scratch on a different day until the steps are routine. For welding, keep a short list of which changes require requalification and test yourself on it.

As test day approaches, switch from topic sets to mixed review and sit longer sessions without pausing. Check the API website for your test window and registration deadline, and confirm what you may bring into the Prometric test center. Our questions are written by us with AI tools and are not real exam questions, so treat them as practice for understanding, not as a preview.

Sources & last verified

1. American Petroleum Institute — number of questions, validity, eligibility (official source). “There are 170 questions on the exam, of which only 140 are scored.” Verified Oct 28, 2026 · source checked Oct 23, 2026.
2. American Petroleum Institute — passing score, score release (official source). “API uses an industry-standard statistical process called equating to adjust the passing scaled score according to the relative difficulty of the exam form.” Verified Oct 28, 2026.
3. American Petroleum Institute — exam fee, retake fee, registration deadline, testing window (official source). “510, 570, 653 $875 $1125” Verified Oct 28, 2026 · source checked Oct 23, 2026.
4. American Petroleum Institute — retake policy (official source). “API gives each candidate 12 consecutive months to pass an exam. This 12-month period begins with the first scheduled exam date.” Verified Oct 28, 2026 · source checked Oct 23, 2026.
5. prometric.com — delivery (official source). “As of September 2024, API will no longer provide remote testing for our core certification programs: API 510, 570, 653, 1169 and 1184.” Verified Oct 28, 2026.
6. American Petroleum Institute — other (official source). “nondestructive examination” Verified Oct 28, 2026.

How we verify: editorial & fact-checking policy. Report an error: contact us.