API 510 closed book: 110 questions, BOK scope and a recall method

The afternoon open-book part works differently, and we cover it in a separate guide to the API 510 open-book part. This page only touches it where the two parts meet.

The closed-book part in numbers

The API 510 exam information page sets out the current structure:

• ✓ 110 of the 170 questions are closed-book. The other 60 are open-book.
• ✓ 2.75 hours for the closed-book portion. It follows a short tutorial and comes before a 45-minute lunch break.
• ✓ 140 of the 170 questions are scored. The remaining 30 are pretest questions.
• ✓ In person only, at designated Prometric test centers, where papers, notes and books are not allowed.

Our arithmetic from those figures: 2.75 hours is 165 minutes, so the closed-book part allows an average of 1.5 minutes per question. That is less than half the open-book average, which works out to 3.75 minutes per question.

How the pretest questions affect you. API doesn't say how the 30 pretest questions are split between the two parts. Its pretest policy says candidates can't tell which questions are scored, that scoring counts only the scored items, and that the pass mark is set by equating rather than on a curve. The practical upshot is that you treat all 110 questions as if they count.

Two time figures, one exam. API's exam page describes a 7.5-hour exam day. The exam tutorial (page 1) gives 390 minutes for all 170 questions. They fit together: 2.75 hours plus 3.75 hours is 390 minutes of testing, and the tutorial and lunch break fill the rest of the day.

What the screen gives you

The tutorial describes the tools that apply in both parts:

• A non-scientific on-screen calculator that handles basic arithmetic, similar to the one in Microsoft Windows (page 7). At an in-person center you can ask the proctor for a handheld calculator instead (page 1).
• Flag, strike-out and highlight. You can flag a question to come back to, strike out options with a right-click, and highlight text in the question stem, though not in the answer options (pages 13 to 15).
• Section Review, a grid you can filter by unattempted, attempted and flagged questions (page 19).
• Timer alerts at 30, 15 and 5 minutes left in the section (page 4). The timer keeps running during unscheduled breaks, while you write question comments and if you reopen the tutorial (pages 2 and 18).

The closed-book section has no reference button. The tutorial says the code references for the open-book part are made available on screen after the break (page 1).

Question formats: what the tutorial shows and what it doesn't settle. The Body of Knowledge (page 1) says you choose the best answer from the options given. The tutorial's multiple-choice screen says the exam uses questions with one correct answer (page 9), but the next screens also demonstrate multiple-response, drag-and-drop and matching items, with no partial credit on drag-and-drop or matching (pages 10 to 12). The tutorial is shared by the API 510, 570 and 653 exams, and none of the API 510 documents we checked says which of those formats appear on API 510 itself. Practice reading every stem for "select all that apply" wording, and don't assume every question has a single key.

When the closed-book part ends

The tutorial is plain about the handover. You finish with the Finish Section button and confirm through pop-ups. Once the section is submitted you can't return to it, and any unanswered question is marked incorrect (page 1). That makes two habits important before you click:

• Open Section Review and filter for unattempted questions. A pop-up also warns you if flagged questions remain (page 13).
• Leave no blanks. A blank scores the same as a wrong answer, so a reasoned guess costs nothing.

Neither the exam page nor the tutorial says whether closed-book time you don't use carries over to the open-book part. The tutorial says each section has its own time allowance (page 4). Plan on using your 165 minutes for the 110 closed-book questions, and treat finishing early as review time.

Our open-book guide covers the afternoon: which PDFs load, what the viewer can't do and how to drill lookups without a search function.

What the closed-book part draws on

API's Body of Knowledge for this cycle is the document to work from. It makes three points that shape closed-book preparation.

The split is by depth, not by document. Page 1 says the closed-book part tests knowledge and tasks that call for everyday working familiarity with API 510 and the referenced documents. The open-book part asks for more detailed information an inspector would be expected to find in the documents but wouldn't normally hold in memory. The BOK doesn't assign its five sections to one part or the other, and it publishes no weights.

The source list is the same for both parts. API's exam page says questions come from the listed publications. The BOK (page 1) limits questions to information in its referenced documents, at the editions on the effectivity sheet, and says a question can come from anywhere in a listed document unless the BOK excludes that part. The listed documents are API 510, API RP 571, 572, 576, 577 and 578, ASME BPVC Sections V, VIII Division 1 and IX, and ASME PCC-2.

Some calculation methods are named as possibly closed-book. On page 2 the BOK says the formulas and rules for metal loss, corrosion rate, remaining corrosion allowance, remaining life and inspection interval (API 510 7.4, 7.1, 7.2 and Section 6) may be closed-book. It is the only place where the BOK names closed-book content directly.

Our reading of those points, labeled as inference: any BOK topic can show up in the morning, framed as something a working inspector knows without looking it up. That covers a lot of ground. The five sections are the calculations (Section I), welding procedure and qualification review (II), nondestructive examination (III), general practical knowledge across 16 listed topics (IV), and the specific documents in Section V, including 15 named RP 571 paragraphs and 14 PCC-2 articles. Our Body of Knowledge guide walks through each section.

Scope limits help in both parts. The BOK lists 22 engineering topics you won't be expected to know (page 4), such as wind and earthquake loading, flange calculations and relief valve sizing. It also says calculations are for in-service vessels under internal pressure only, and that you need both US customary and SI units (page 2).

One open point in API's own documents: page 1 of the BOK includes RP 572 Annex B and excludes the other annexes, while page 9 includes Annexes A and B and excludes Annex C. If Annex A matters to your plan, ask API which reading applies.

Building recall without exam items

We don't use real or recalled exam questions, and you don't need them. The BOK already tells you what to know, and recall practice works best on prompts you write yourself.

1. Turn BOK lines into prompts. Go through the BOK one line at a time and write a short question in your own words that you must answer from memory. Keep the topic and section number on the back of the card, never code text. Some example shapes:

• "Which document and section number set the rules for the internal inspection interval?"
• "What changes when a vessel is rerated, and which API 510 section covers it?"
• "For a yoke magnetic particle examination, which Section V article applies?"
• "Name the RP 571 paragraph for damage under insulation and two places it tends to show."

Answer each one out loud or on paper with no notes, then check it against your own copy of the reference.

2. Learn the possibly-closed-book methods cold. For the five calculations on BOK page 2, build a method sheet from your copy of API 510. Practice it with fresh numbers until you can do it with the sheet face down. Here is an invented example of the arithmetic, not taken from any exam:

Step	US example	SI example
Previous reading	0.540 in	13.70 mm
Current reading	0.495 in	12.50 mm
Years between readings	5	6
Metal loss	0.045 in	1.20 mm
Corrosion rate	0.009 in/yr	0.20 mm/yr
Required thickness (given)	0.420 in	10.90 mm
Remaining corrosion allowance	0.075 in	1.60 mm
Remaining life	about 8.3 years	8.0 years

The last step is to apply the interval rules in API 510 Section 6 to that remaining life from memory, then open your copy and check that you applied them correctly. Our remaining life calculator shows each step, so you can check your arithmetic after you've worked a problem by hand. The API 510 calculations guide lists every calculation area in BOK Section I.A with the paragraph to open.

3. Memorize the small facts the BOK states outright. A few are written into the BOK itself and are easy marks to bank. Static head is based on a specific gravity of 1.0, and the BOK names the pressure-per-foot conversion factor (page 2). It also names the factor for converting a fillet weld's throat to its leg (page 3). Write a card for each.

4. Practice under the morning's conditions. Shuffle prompts across all five BOK sections rather than working one section at a time. Use a basic four-function calculator, with no notes in reach, and aim for an average under 1.5 minutes per prompt. Keep a log. For example, an invented log from one set of 40 mixed prompts:

BOK section	Prompts	Correct from memory
I. Calculations	10	6
II. Welding review	6	5
III. NDE	8	4
IV. Practical, general	8	7
V. Practical, specific	8	5

In this invented log, the NDE section is weakest at 4 of 8, so the next set gets more prompts on the ASME Section V articles. The calculations result, 6 of 10, sends the candidate back to the method sheet.

5. Keep recall and lookup apart. A closed-book miss means you didn't know it. An open-book miss usually means you couldn't find it in time. Log them separately, because they need different practice.

Before your window

Download the Body of Knowledge and effectivity sheet for your window from the exam information page, and read the tutorial once so the screen is familiar on the day. Then take the free 10-question check to see which BOK sections to start your prompt cards with. Its questions are original and aren't drawn from either part of the exam.

Sources

Show the list

• API 510 Pressure Vessel Inspector: exam information, American Petroleum Institute. Retrieved 20 Oct 2026.
• ICP Tutorial: API 510, API 570, API 653 (ICP-PD-201a, revised 28 Dec 2023), American Petroleum Institute, pages 1-22. Retrieved 20 Oct 2026.
• ICP Examinations (in-person exam day), American Petroleum Institute. Says in-person candidates have a calculator, scratch paper and pencil, and that papers and reference books are not allowed. Retrieved 20 Oct 2026.
• Pretest Questions on API Examinations (ICP-POL-205, revised 18 Sep 2023), American Petroleum Institute. Retrieved 20 Oct 2026.
• API 510 Body of Knowledge, September 2026, January 2027 and May 2027, American Petroleum Institute, pages 1-9. Retrieved 20 Oct 2026.