API 510 vs API 653: which API exam is right for you?
API 510 is the pressure vessel exam, built on ASME Section VIII Division 1 and API 510 interval and repair rules. API 653 is the storage tank exam, built on API 653 and API 650, with shell and bottom evaluation, settlement and tank-specific damage such as soil corrosion, MIC and ethanol SCC. Both are 170-question, 7.5-hour exams with closed- and open-book parts, and both test Section IX welding and Section V NDE. Plant inspectors often hold both.
API 510 vs API 653 at a glance
| API 510 | API 653 | |
|---|---|---|
| Full name | API 510 Pressure Vessel Inspector Exam | API 653 Aboveground Storage Tank Inspector Exam |
| Questions | 170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book | 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 | 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 | 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 | Closed-book part, then an open-book part with the effectivity-sheet documents as on-screen PDFs. No paper books or notes; on-screen calculator |
| 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 | 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 |
| Languages | English; Spanish and Chinese translations available on request | English; Spanish and Chinese translations available on request |
| Where | Prometric test centers, in person only (no remote option for API 510) | Prometric test centers, in person only (no remote option for API 653) |
| Level | API Inspector Certification | API Inspector Certification |
What each exam covers
API 510
- 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
API 653
- Shell Evaluation and Minimum Thickness
- Bottoms, Settlement and Foundations
- Inspection Intervals and Practices
- Repairs, Alterations and Hot Taps
- API 650 Design, Materials and Testing
- Damage Mechanisms, Cathodic Protection and Linings
- Welding and NDE
Which should you take?
API 510 is the pressure vessel exam, built on ASME Section VIII Division 1 and API 510 interval and repair rules. API 653 is the storage tank exam, built on API 653 and API 650, with shell and bottom evaluation, settlement and tank-specific damage such as soil corrosion, MIC and ethanol SCC. Both are 170-question, 7.5-hour exams with closed- and open-book parts, and both test Section IX welding and Section V NDE. Plant inspectors often hold both.
Try both, free
Each free practice test takes about 10 minutes and shows your score by topic. No signup.
FAQ
What is the difference between API 510 and API 653?
API 510 is the pressure vessel exam, built on ASME Section VIII Division 1 and API 510 interval and repair rules. API 653 is the storage tank exam, built on API 653 and API 650, with shell and bottom evaluation, settlement and tank-specific damage such as soil corrosion, MIC and ethanol SCC. Both are 170-question, 7.5-hour exams with closed- and open-book parts, and both test Section IX welding and Section V NDE. Plant inspectors often hold both.
Which is harder, API 510 or API 653?
API 510: 170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book in 7.5-hour exam day: short tutorial, 2.75 hours closed book, 45-minute lunch, 3.75 hours open book. API 653: 170 multiple-choice questions (140 scored, 30 unscored pretest items): 110 closed-book and 60 open-book in 7.5-hour exam day: short tutorial, 2.75 hours closed book, 45-minute lunch, 3.75 hours open book. The longer exam covers more ground, but the harder one is the one further from your daily work. Take both free practice tests to see where you stand.
Can I hold both API 510 and API 653?
Yes. API 510, 570 and 653 are separate certifications, and many inspectors hold two or all three. Each needs its own application, experience and exam, and each is renewed on its own three-year cycle.
How do I prepare for API 510 and API 653?
Start with the free practice test for each, then study by topic. Premium is per exam ($147 a month each), so most people start with the exam they'll sit first and add the second when they're ready.
More comparisons
Exam details are summarized from API's published information as of November 2026. Confirm with API before you book. APIInspectorExam is not affiliated with the American Petroleum Institute (API), ASME or Prometric.