API 510 Exam Study Guide (2026)
Everything the API 510 Pressure Vessel Inspector Exam tests, topic by topic: what each section covers, the facts that come up most, and how to study it. Pair it with the free 15-question practice test.
The exam at a glance
| Questions | 170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book |
|---|---|
| Time | 7.5-hour exam day: short tutorial, 2.75 hours closed book, 45-minute lunch, 3.75 hours open book |
| Passing score | 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 |
| 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 |
| Certifying body | American Petroleum Institute (API) Individual Certification Programs (ICP) |
| Test provider | Prometric test centers, in person only (no remote option for API 510) |
Mind map: the whole exam on one screen
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.
1. Corrosion Rates, Remaining Life and Intervals
The calculations every API 510 inspector does: metal loss, long- and short-term corrosion rates, remaining life and the internal, external and on-stream inspection intervals. The formulas and interval rules can be asked closed book.
Key facts
- Long-term corrosion rate = (t initial − t actual) ÷ years between them. Short-term rate = (t previous − t actual) ÷ years between them. The inspector and corrosion specialist choose the rate that best reflects current conditions.
- Remaining life = (t actual − t required) ÷ corrosion rate. Remaining corrosion allowance = t actual − t required.
- Internal or on-stream inspection interval: one-half the remaining life or 10 years, whichever is less, unless an RBI assessment justifies otherwise.
- If the remaining life is under 4 years, the internal interval may be the full remaining life, up to a maximum of 2 years.
- External visual inspection: at least every 5 years or at the internal/on-stream interval, whichever is less, unless RBI justifies otherwise.
- For non-continuous service, the interval counts years of actual service if the idle vessel is isolated from process fluids and not exposed to a corrosive environment.
- An on-stream inspection may replace an internal inspection only when API 510's conditions are met (for example a low, known corrosion rate and no questionable condition).
Flashcards
Exam tip: Write the formulas at the top of your scratch screen as soon as the closed-book part starts. Most interval questions are two steps: remaining life, then halve it and cap at 10 years.
2. Vessel Calculations (ASME Section VIII, Division 1)
Internal-pressure calculations for existing vessels: joint efficiency from UW-11 and UW-12, shell and head thickness and MAWP from UG-27 and UG-32, static head, test pressures from UG-99 and UG-100, impact test exemptions and attachment weld sizes.
Key facts
- Cylindrical shell, circumferential stress (UG-27(c)(1)): t = PR ÷ (SE − 0.6P) and P = SEt ÷ (R + 0.6t), with R the inside radius in the corroded condition.
- Spherical shell or hemispherical head: t = PR ÷ (2SE − 0.2P). 2:1 ellipsoidal head: t = PD ÷ (2SE − 0.2P).
- Table UW-12 joint efficiency, Type 1 butt joint: 1.00 full RT, 0.85 spot, 0.70 none. Type 2 (backing strip left in place): 0.90, 0.80, 0.65.
- Static head: 0.433 psi per foot of water (specific gravity 1.0). A vessel part's MAWP includes the static head above it (UG-98).
- Hydrostatic test (UG-99(b)): 1.3 × MAWP × the lowest stress ratio (allowable stress at test temperature ÷ at design temperature). Inspection pressure is not less than test pressure ÷ 1.3.
- Pneumatic test (UG-100): 1.1 × MAWP × the stress ratio, raised gradually to half the test pressure, then in steps of about one-tenth, and inspected at test pressure ÷ 1.1.
- Fillet weld throat = 0.7 × leg. UCS-66 curves and UG-20(f) decide whether impact testing is needed for carbon and low-alloy steels.
Flashcards
Exam tip: Before you calculate, decide whether the question gives a new or corroded dimension. Adding the corrosion allowance to R (inside radius) and to t is where most marks are lost.
3. Damage Mechanisms and Inspection Practices
The 15 RP 571 mechanisms on the API 510 effectivity sheet (amine and caustic cracking, CUI, chloride SCC, brittle fracture, HTHA, wet H2S damage and others) and the inspection practices in RP 572.
Key facts
- CUI: carbon and low-alloy steels between 10°F and 350°F (−12°C and 175°C), worst where insulation stays wet; cyclic and idle equipment is at risk too.
- Chloride SCC: 300-series stainless steels are highly susceptible, usually above about 140°F (60°C); duplex is more resistant, carbon steel is not susceptible.
- Brittle fracture: most likely in carbon and low-alloy steels at low temperature, often during start-up, shutdown or a hydrotest.
- High-temperature hydrogen attack (HTHA): assessed against the Nelson curves in API RP 941; damage can be invisible until fissuring is advanced.
- Wet H2S damage covers blistering, HIC, SOHIC and sulfide stress cracking in carbon steel; hard welds and high-strength steels raise SSC risk.
- Caustic and amine cracking are controlled mainly by PWHT of carbon steel welds.
- RP 572 covers why, where and how to inspect vessels, from external and internal visual inspection to thickness surveys and records.
Flashcards
Exam tip: For every listed mechanism, learn four things: affected material, critical factors (temperature, environment), appearance and the best inspection method.
Test yourself on these topics
Take the free 15-question API 510 test, then save your results to unlock your Readiness Score and the mistakes bank.
4. Repairs, Alterations and Rerating
API 510 Section 8 and the listed ASME PCC-2 articles: who authorizes and approves repairs and alterations, welding and heat treatment for repairs, rerating and the pressure test after repair.
Key facts
- All repair and alteration work must be authorized by the inspector before it starts; alterations also need prior approval by a pressure vessel engineer.
- The inspector may give prior general authorization for limited or routine repairs.
Flashcards
Exam tip: Questions often swap 'inspector' and 'engineer'. Inspectors authorize work; engineers approve alterations and do the design calculations.
5. Welding (ASME Section IX and API 577)
Reviewing a WPS, PQR and WPQ against ASME Section IX (SMAW, GTAW, GMAW and SAW only, one process each), plus welding processes, inspection and metallurgy from API RP 577.
Key facts
- The WPS gives the ranges a welder must follow; the PQR records the actual values and test results of the qualification weld.
- Essential variables change the mechanical properties and need a new PQR; nonessential variables only need a revised WPS.
Flashcards
Exam tip: Review a WPS/PQR pair line by line with the QW-250 variable tables open: check each essential variable on the WPS against the PQR's actual value.
6. Nondestructive Examination (ASME Section V)
Articles 1, 2, 6, 7 and 23 (SE-797) of ASME Section V: general requirements, radiography, liquid penetrant, magnetic particle (yoke and prod) and ultrasonic thickness measurement, plus the NDE rules in Section VIII and API 510.
Key facts
- Article 1: the referencing code says which NDE is required and the acceptance standard; Section V says how to do it.
- Article 2 radiography: IQIs on the source side unless inaccessible (then film side with a lead 'F'); location markers; density limits; backscatter check with a lead 'B'.
Flashcards
Exam tip: Section V tells you how to examine; Section VIII or API 510 tells you whether to examine and what's acceptable. Exam questions test whether you know which document answers which question.
7. Relief Devices and Material Verification
Pressure-relieving device inspection and test intervals from API 510 and RP 576, and positive material identification (PMI) programs from RP 578.
Key facts
- API 510 relief device interval: up to 5 years for typical process services and 10 years for clean (nonfouling) and noncorrosive services.
- RP 576 recommends testing a valve in the as-received condition to learn how it would have performed in service.
Flashcards
Exam tip: Relief device and PMI questions are mostly closed book and short. They are quick marks once you know the 5 and 10 year limits and the XRF limitation.
How to pass
- 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.
Frequently asked questions
How long should I study for the API 510 exam?
Most working candidates need 4 to 8 weeks at 45 to 60 minutes a day. Book your exam once your Readiness Score has stayed at 80 or higher for about a week.
Can I take the API 510 exam online?
No. The API 510, 570 and 653 exams are taken in person at Prometric test centers only; API does not offer them by remote proctoring. 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. Check API's exam pages for the current rules.
What score do I need to pass the API 510 exam?
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. The exam has 170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book and a time limit of 7.5-hour exam day: short tutorial, 2.75 hours closed book, 45-minute lunch, 3.75 hours open book.
What are the most tested topics?
The outline covers corrosion rates, remaining life and intervals, vessel calculations (asme section viii, division 1), damage mechanisms and inspection practices, repairs, alterations and rerating, welding (asme section ix and api 577), nondestructive examination (asme section v), relief devices and material verification. Use the free practice test to see which ones you need most.
The premium API 510 study path
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.
Your step-by-step study path
- 1Corrosion Rates, Remaining Life and Intervals9 key notes, 115 flashcards, then 450 practice questions in 18 sets of 25Notes free with an account
- 2Vessel Calculations (ASME Section VIII, Division 1)9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25Premium
- 3Damage Mechanisms and Inspection Practices9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25Premium
- 4Repairs, Alterations and Rerating9 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25Premium
- 5Welding (ASME Section IX and API 577)8 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25Premium
- 6Nondestructive Examination (ASME Section V)8 key notes, 115 flashcards, then 425 practice questions in 17 sets of 25Premium
- 7Relief Devices and Material Verification8 key notes, 110 flashcards, then 425 practice questions in 17 sets of 25Premium
- Final step: 6 full mock exams170 questions each, timed like test day. Pass them, then book your exam.Premium
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Summarized from API's official candidate information and the rules cited, checked November 2026. Confirm current requirements with American Petroleum Institute (API) Individual Certification Programs (ICP).