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API Inspector Certification · Last updated November 2026

API 510 Pressure Vessel Inspector Exam: free practice test

The API certification exam for in-service pressure vessel inspectors, based on API 510 and the documents on the effectivity sheet. Exam windows run in January, May and September, with application deadlines about two months before each window. The September 2026 to May 2027 exams use API 510 11th Edition and the 2025 ASME Boiler and Pressure Vessel Code.

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About the API 510 exam

The API certification exam for in-service pressure vessel inspectors, based on API 510 and the documents on the effectivity sheet. Exam windows run in January, May and September, with application deadlines about two months before each window. The September 2026 to May 2027 exams use API 510 11th Edition and the 2025 ASME Boiler and Pressure Vessel Code.

What's on the exam

API 510
Corrosion Rates, Remaining Life and Intervals
7 key facts
Vessel Calculations (ASME Section VIII, Division 1)
7 key facts
Damage Mechanisms and Inspection Practices
7 key facts
Repairs, Alterations and Rerating
6 key facts
Welding (ASME Section IX and API 577)
7 key facts
Nondestructive Examination (ASME Section V)
6 key facts
Relief Devices and Material Verification
6 key facts

Each branch is a topic in the official outline. Members see every key fact on the full mind map. Read the free study guide →

How to pass the API 510 exam

  • The closed-book part is 110 questions in 2.75 hours, about 1.5 minutes each. Corrosion rate, remaining life and interval rules must come from memory, because they can be asked closed book.
  • The open-book part gives you 60 questions in 3.75 hours with the codes as on-screen PDFs. Learn where things live (UG-27, UW-12, UG-99, QW-451) so you search, not scroll.
  • Calculations use internal pressure only, existing vessels only, and both US customary and SI units. Know when to add or subtract corrosion allowance.
  • Only the RP 571 mechanisms listed on the effectivity sheet are tested. Learn those 15 well instead of the whole document.

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Create a free account after the test: your score by topic, a mistakes bank, the complete study notes for the first topic, flashcards and the API Inspector Formula Sheet.

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What's in the premium API 510 prep

Premium API 510 prep is studied one topic at a time. Each step starts with that topic's key notes and flashcard deck, then its own question sets of 25, so you master one topic before you move to the next. When every topic is strong, the 6 full mock exams show you're ready.

3,000practice questions, every answer explained
6full-length mock exams, 170 questions each, timed
800flashcards with spaced repetition, sorted by topic
60comprehensive key notes across 7 topics

Your step-by-step study path

  1. 1
    Corrosion Rates, Remaining Life and Intervals9 key notes, 115 flashcards, then 450 practice questions in 18 sets of 25
    Notes free with an account
  2. 2
    Vessel Calculations (ASME Section VIII, Division 1)9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25
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  3. 3
    Damage Mechanisms and Inspection Practices9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25
    Premium
  4. 4
    Repairs, Alterations and Rerating9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25
    Premium
  5. 5
    Welding (ASME Section IX and API 577)8 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25
    Premium
  6. 6
    Nondestructive Examination (ASME Section V)8 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25
    Premium
  7. 7
    Relief Devices and Material Verification8 key notes, 110 flashcards, then 425 practice questions in 17 sets of 25
    Premium
  8. Final step: 6 full mock exams170 questions each, timed like test day. Pass them, then book your exam.
    Premium
Free with an account

Read the complete API 510 study notes for “Corrosion Rates, Remaining Life and Intervals”

Our first full set of comprehensive notes, about 15 minutes of reading: The four numbers you need · Long-term and short-term rates · Remaining life and remaining corrosion allowance · Inspection interval rules · MAWP for continued service, a worked exam example, the traps examiners use and a one-minute recap. Create a free account to read it and see how premium notes work before you decide.

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Study tools included

3,000 practice questions

3,000 exam-style questions per exam, organized topic by topic in sets of 25. Every answer explained, with the rule it comes from.

6 full mock exams

6 full-length timed mock exams per exam, with real question counts and time limits, so test day feels like practice day.

Exam Readiness Score

One 0 to 100 number that tells you when you're ready to book. Reach 80 and you're covered by our Pass Guarantee.

800 flashcards + spaced repetition

800 flashcards per exam, in a deck for each topic, that come back right before you'd forget them. Five minutes a day keeps every number fresh.

60 comprehensive key notes

60 key notes per exam, split across its topics and each explained in full: the concepts, worked exam examples, the traps examiners use and a quick recap. Your first set is free with an account.

Mind maps

See the whole exam on one screen: every topic and the facts under it.

Sample questions with answers

These are the questions in the free test above, with answers. Try the test first. You'll learn more by getting some wrong.

1. A vessel shell read 0.625 in. in 2016 and 0.565 in. in 2026 at the same CML. The required thickness is 0.445 in. Using this corrosion rate, what is the remaining life?
Answer: 20 years. Corrosion rate = (0.625 − 0.565) ÷ 10 years = 0.006 in./yr. Remaining life = (t actual − t required) ÷ corrosion rate = (0.565 − 0.445) ÷ 0.006 = 0.120 ÷ 0.006 = 20 years (API 510, Section 7).
2. A vessel's calculated remaining life is 14 years. Without an RBI assessment, what is the maximum interval to the next internal or on-stream inspection under API 510?
Answer: 7 years. API 510 limits the interval to one-half the remaining life or 10 years, whichever is less: 14 ÷ 2 = 7 years. If the remaining life were under 4 years, the interval could be the full remaining life, up to a maximum of 2 years.
3. A cylindrical shell has a corroded inside radius of 30 in., a thickness of 0.500 in. (no further corrosion allowance), S = 20,000 psi and E = 0.85. Using UG-27(c)(1), what is the MAWP based on circumferential stress?
Answer: 281 psi. P = SEt ÷ (R + 0.6t) = (20,000 × 0.85 × 0.500) ÷ (30 + 0.30) = 8,500 ÷ 30.3 = 280.5 psi, about 281 psi. Leaving out the 0.6t term gives 283 psi; using E = 1.0 gives 330 psi.
4. The MAWP at the top of a vertical vessel is 150 psi. The bottom head is 40 ft below the top and the vessel is full of water (specific gravity 1.0). What pressure must the bottom head be able to withstand?
Answer: 167.3 psi. Static head = 40 ft × 0.433 psi/ft = 17.3 psi. Pressure at the bottom head = 150 + 17.3 = 167.3 psi. This is why a vessel part's MAWP (UG-98) must include the static head above it.
5. A vessel has an MAWP of 200 psi. The allowable stress is 20,000 psi at test temperature and 17,100 psi at design temperature. What is the minimum hydrostatic test pressure under UG-99(b)?
Answer: 304 psi. UG-99(b): test pressure = 1.3 × MAWP × (stress at test temperature ÷ stress at design temperature) = 1.3 × 200 × (20,000 ÷ 17,100) = 260 × 1.170 = 304 psi. 260 psi ignores the stress ratio; 257 psi uses the pneumatic factor of 1.1 (UG-100).
6. A Type 1 butt joint (double-welded, or equivalent) in a Category A seam was spot radiographed. What joint efficiency E does Table UW-12 give?
Answer: 0.85. Table UW-12, Type 1: full radiography 1.00, spot 0.85, none 0.70. The 0.80 and 0.65 values are for Type 2 joints (single-welded with a backing strip left in place), spot and none.
7. A shell measures 0.600 in. The corrosion rate is 0.010 in./yr and the next inspection is in 5 years. Under API 510, what thickness should be used to calculate the MAWP for continued service?
Answer: 0.500 in.. API 510 uses the actual thickness minus twice the estimated corrosion loss before the next inspection: 0.600 − 2 × (0.010 × 5) = 0.600 − 0.100 = 0.500 in. Subtracting the loss only once (0.550 in.) is the common mistake.
8. According to API RP 571, in what metal temperature range is corrosion under insulation (CUI) a concern for carbon and low-alloy steels?
Answer: 10°F to 350°F (−12°C to 175°C). RP 571 gives 10°F to 350°F (−12°C to 175°C) for carbon and low-alloy steels. Equipment that cycles in and out of this range, or sits idle, is also at risk because wet insulation stays wet.
9. Which material is most susceptible to chloride stress corrosion cracking?
Answer: 300-series austenitic stainless steel. RP 571: all 300-series stainless steels are highly susceptible. Duplex stainless steels are more resistant, high-nickel alloys are highly resistant, and carbon and low-alloy steels are not susceptible. Cracking usually needs chlorides, water, tensile stress and a metal temperature above about 140°F (60°C).
10. Under API 510, who must authorize repair work on a pressure vessel before the repair organization starts?
Answer: The inspector. API 510 requires the inspector to authorize repair and alteration work before it starts (the inspector may give prior general authorization for limited or routine repairs). For an alteration, the inspector authorizes only after a pressure vessel engineer has approved the work.
11. Which change to an SMAW WPS is an essential variable under ASME Section IX when notch toughness is not required?
Answer: A change in the F-number of the filler metal. A change in F-number (QW-404.4) is essential and needs a new PQR. Electrode diameter (QW-404.6), groove design (QW-402.1) and position (QW-405.1) are nonessential for SMAW procedures: you revise the WPS without requalifying.
12. Under ASME Section IX QW-163, a guided-bend specimen fails if the convex surface shows an open discontinuity exceeding what size in any direction?
Answer: 1/8 in. (3 mm). QW-163: no open discontinuity over 1/8 in. (3 mm) in any direction in the weld or heat-affected zone on the convex surface. Open discontinuities at the corners don't count unless they come from lack of fusion, slag inclusions or other internal discontinuities.
13. Under ASME Section V Article 7, what minimum lifting power must an AC yoke have at the maximum pole spacing used?
Answer: 10 lb (4.5 kg). T-762: an alternating-current yoke needs at least 10 lb (4.5 kg) of lifting power at the maximum pole spacing that will be used. Direct-current and permanent-magnet yokes need at least 40 lb (18 kg).
14. Unless justified by RBI or service history, what is the maximum interval for testing and inspecting pressure-relieving devices in typical process service under API 510?
Answer: 5 years. API 510 sets 5 years for typical process services and 10 years for clean (nonfouling) and noncorrosive services. Devices with a history of fouling or sticking need shorter intervals.
15. During positive material identification under API RP 578, which element can a portable X-ray fluorescence (XRF) analyzer NOT measure?
Answer: Carbon. Portable XRF can't detect light elements such as carbon. When carbon matters (for example L-grade stainless or carbon content of steels), use optical emission spectroscopy (OES) or a laboratory analysis.

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Certification guide

API 510 exam guide (2026-2027): The API 510 Pressure Vessel Inspector exam is a 7.5-hour, 170-question computer-based test at Prometric test centers. It has a closed-book part and an open-book part where the codes on the effectivity sheet appear as on-screen PDFs. Here's how it works, what's on it and how to prepare.

API 510 exam FAQ

How many questions are on the API 510 exam?

170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book, with a time limit of 7.5-hour exam day: short tutorial, 2.75 hours closed book, 45-minute lunch, 3.75 hours open book. Format: closed-book part, then an open-book part with the effectivity-sheet code sections as on-screen pdfs. no paper books or notes; on-screen calculator.

What is the passing score for API 510?

Passing scaled score is 400 on API's 200 to 500 scale. The number of correct answers needed isn't published and varies by form; practice to 75% or higher.

How much does the API 510 exam cost?

US$875 API member / US$1,125 non-member (2026 fee table); US$890 / US$1,140 (2027 fee table). Reschedule US$350, late application US$200. API publishes a fee table for each year, so confirm the current fee on API's Schedules & Fees page before you apply.

Which languages is the API 510 exam offered in?

English; Spanish and Chinese translations available on request.

Where do I take the API 510 exam?

Prometric test centers, in person only (no remote option for API 510).

Is this API 510 practice test free?

Yes. The 15-question practice test on this page is free, with an explanation for every answer and no signup. A free account also unlocks the complete study notes for the first topic. The full API 510 prep is Premium at $147 a month for this exam.

What's in the premium API 510 prep?

3,000 practice questions organized topic by topic (Corrosion Rates, Remaining Life and Intervals: 450; Vessel Calculations (ASME Section VIII, Division 1): 425; Damage Mechanisms and Inspection Practices: 425; Repairs, Alterations and Rerating: 425; Welding (ASME Section IX and API 577): 425; Nondestructive Examination (ASME Section V): 425; Relief Devices and Material Verification: 425), 6 full-length timed mock exams of 170 questions, 800 flashcards and 60 comprehensive key notes split across all 7 topics, plus a mistakes bank and the Readiness Score.

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Exam details are summarized from the official candidate information available in November 2026. API changes formats and fees, so confirm with American Petroleum Institute (API) Individual Certification Programs (ICP) before you book. APIInspectorExam is not affiliated with the American Petroleum Institute (API), ASME or Prometric.

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