API 653 Practice Questions (Free, With Explanations)

By Sandeep Bandyopadhyay, Senior aerospace engineer · PMP, MBA, Six Sigma 6 October 2026

TL;DR

Six free API 653 practice questions sit further down this page, each with the full answer and explanation. They follow the exam's own shape: 110 closed-book questions in 2 hours 45 minutes, then 60 open-book questions in 3 hours 45 minutes, 170 in total and 140 scored. Passing is a scaled 400 on a 200-500 scale. Windows from March 2027 use the API 650 14th Edition sheet.

Original questions, not exam dumps. Every CertCrafter question is written from the published body of knowledge and the referenced codes. None is copied from a live exam, and CertCrafter is independent: not affiliated with or endorsed by any awarding body.

Free API 653 questions are easy to find and mostly worth very little. Much of what circulates was recycled from a pressure vessel bank, written to a code edition that no longer applies, or stripped of the one part that actually teaches something: the reason the right answer is right.

The six questions further down this page are original, written from the published body of knowledge and the referenced codes, and each carries a full explanation you can open as soon as you have committed to an answer. They come from the same free sample that backs the scored API 653 quiz, and they are labeled closed book or open book exactly as the exam splits them.

Work through them, but read this first. The structure of the exam day is the single biggest reason that well-prepared candidates still lose marks.

What do these free API 653 practice questions test?

The body of knowledge has five sections, and the six questions here touch all of them:

Calculations and tabular evaluations for thickness measurements, weld sizes and tank integrity
Welding on atmospheric aboveground storage tanks
Nondestructive examination
Practical knowledge, general
Practical knowledge, specific

Three are closed-book items and three are open-book. That matters more than the topic labels, because the two halves reward different skills. A closed-book item has to be answerable from what you carry in your head: which corrosion rate governs, which interval rule applies, what a particular table requires. An open-book item assumes you will go and look, so it is built around locating the right requirement in the right document and applying it to an awkward set of field facts.

You will also notice that the questions do not ask you to recite anything. Each one puts you in front of a decision an inspector has to make: a procedure that was never demonstrated, electrodes left out overnight, a tank file with no construction drawings, a thickness table published in units the field readings were not taken in. That is deliberate. Across the full bank the questions rotate through seven cognitive facets — calculation, code requirement, field decision, diagnosis, acceptance, authorization and records, and selection under constraint — because the exam tests judgment around the codes, not recall of them.

How is the API 653 exam structured?

API puts the exam day at 7.5 hours at the test center: a short tutorial session, 2 hours 45 minutes for the closed-book portion, a 45-minute lunch break, then 3 hours 45 minutes for the open-book portion. That is 390 minutes of actual testing.

There are 170 questions. Only 140 are scored; the remaining 30 are unscored pretest items, and they are not flagged, so you cannot spend less effort on them. Answer every question — an unanswered item scores the same as a wrong one.

The split is 110 closed-book questions and 60 open-book. Do the arithmetic and the pressure becomes obvious: roughly 1.5 minutes per closed-book question, and about 3.75 minutes per open-book question. The longer allowance is not generosity. It is the time an open-book item genuinely needs for you to decide which document applies, find the requirement and apply it. Candidates who have only ever practiced untimed tend to overspend early in the closed-book section and then rush the part of the exam that carries the most reading.

One more structural detail that catches people: once you submit the closed-book section you cannot go back into it.

The exam is administered in person at a Prometric test center. Papers and books are not allowed in the room — the reference documents appear as PDFs on your screen during the open-book portion only. If you have been studying with a tabbed paper copy of API 650, you have been training a skill the exam will not let you use. Rehearse on screen.

What score do you need to pass API 653?

A scaled 400 on a 200-500 scale. API publishes no raw percentage and no per-form cut score, so any site telling you that you need 70 or 80 percent is guessing or confusing the exam with the recertification webquiz, which is a separate 25-question assessment taken every six years.

For context on difficulty, the most recent published result at the time of writing is the November 2025 administration: 503 candidates at 60.8 percent.

Which code editions apply to the API 653 exam in 2027?

This is where stale practice material does real damage. Windows from March 2027 onward run on the March 2027 effectivity sheet, which lists:

API 650 in its 14th Edition, August 2025
ASME BPVC Sections V and IX in their 2025 Editions
API 653 with Addenda 1 through 4
API RP 652 in its 6th Edition
API RP 575 with Addenda 1 and 2

The November 2026 window is the last one on the older March 2026 sheet, which still used API 650 13th Edition and ASME BPVC 2023. Its application deadline was September 4, 2026, which has passed — so anyone applying now is sitting a 2027 window and should be studying the 2027 sheet. A practice set written against API 650 13th Edition will quietly point you at superseded table values and requirements.

Only the specific sections of publications listed on that sheet are available to you during the open-book portion, which is also worth knowing before you plan your reading.

When are the API 653 exam dates and application deadlines?

API 653 runs in March, July and November — not API 510’s January, May and September cycle, and not API 570’s February, June and October one. For 2027:

Exam window	Application deadline
March 12 - April 2, 2027	January 07, 2027
July 09 - 30, 2027	May 06, 2027
November 05 - 26, 2027	September 02, 2027

The deadlines sit roughly two months ahead of each window, which is the part candidates underestimate. Initial certification for 2027 is $890 for API members and $1,140 for non-members, and a late application costs a further $200. Certification runs for a three-year term, with 24 CPD hours and a 20 percent working-time requirement in each cycle.

Full detail, including the qualification table, is on API’s certification page and the schedules and fees page.

Which formulas does the exam give you, and which tables must you know?

Fewer formulas than candidates fear. The body of knowledge states that the corrosion rate, remaining life, remaining corrosion allowance, maximum fill height and bottom plate formulas will be provided in the exam.

What is not provided is the judgment around them. You still have to decide which corrosion rate governs, which interval rule applies and which thickness belongs in which variable. And the API 653 tables marked with an asterisk in the body of knowledge may be tested without document access, so those have to be carried in your head. Spending your study time rehearsing algebra you will be handed, while skipping the tables you will not, is a common and expensive misallocation.

Why do API 510 and API 570 notes mislead you here?

Because the referenced publications are genuinely different, and the overlap is smaller than the shared “API inspector” label suggests.

The construction standard for API 653 is API 650. ASME Section VIII is not a referenced publication for this exam at all, and neither are ASME PCC-2, ASME B16.5, ASME B31.3, API RP 572, API RP 574, API RP 578 or API 579. API RP 2350 is not on the sheet either, despite being an intuitive guess for a storage tank exam — several vendors list it anyway. The inspection practices reference is API RP 575.

There is also no rerating in API 653. A tank’s maximum fill height and maximum allowable liquid level get re-evaluated; an MAWP does not get rerated. If your notes talk about rerating a tank, they came from a pressure vessel syllabus.

How should you use six free questions?

Not as a readiness test. Six questions cannot tell you whether you will pass. What they can do is expose a habit, and that is worth more at this stage than a score.

So read every explanation, including on the questions you answered correctly — the explanation is where the reasoning lives, and a right answer reached by the wrong route will fail you on a differently worded item. When you miss one, log it twice: once by section, and once by what went wrong, whether that was the calculation, the code requirement, the field decision, the diagnosis, the acceptance criterion, the records and authorization question, or a choice under constraint. A pattern in the second column tells you what to study next.

After that, the only thing that measures readiness is full-length practice to the real rhythm: 170 questions, 110 closed book in 2 hours 45 minutes, the break, then 60 open book in 3 hours 45 minutes, on screen. The API 653 practice test bundle is built for exactly that — six complete tests, 1,020 questions in real exam order with the open-book items marked, written to the March 2027 effectivity sheet. The API 653 guide has the full fact sheet and a phased study plan.

What these questions will not do

None of them is copied from a live exam, and none cites a clause, paragraph, table or figure number — every requirement is described in words instead, so you learn the requirement rather than a citation. The per-section distribution across the bank is an estimate anchored to the 110 and 60 split, because API publishes no section weights; it should never be attributed to API.

And no practice set replaces the codes. API 653, API 650 and the rest of the sheet are what the exam is drawn from. Practice questions are how you find out whether your reading of them survives contact with a decision.

Try these free questions

A thickness table in the governing standard is published only in US customary units, while the field readings on TK-1204 were logged in millimetres. How should the evaluation be carried out?
1. Round the millimetre readings to the nearest sixteenth of an inch first, since the table is built on fractional inch steps and interpolation is not permitted.
2. Convert the readings to the units of the published table and keep the whole evaluation in that one system, since the two unit sets are independent and must not be mixed.
3. Apply the table as printed to the millimetre values, because the numerical steps in each system are close enough for an acceptance decision.
4. Treat the absence of an SI table as a gap and use the corresponding SI table from the construction standard in its place rather than converting any of the field data.
Show the answer and explanation
Answer: B.API 653 and API 650 publish US customary and SI values as parallel but independent sets, and the SI figures are rounded rather than exact conversions of their customary counterparts. Mixing a millimetre measurement with an inch table therefore produces an evaluation that belongs to neither system, and the correct handling is to convert the measurements into the units of the table being used and complete the whole calculation in that system. Both unit systems are examinable, and some tables exist in only one of them, so this situation is routine rather than exceptional. Option one adds rounding to fractions, which throws away real precision in the readings and has no basis in the standard. Option three reads inch values against millimetre numbers, an error of more than a factor of twenty five that would accept a badly thinned plate. Option four substitutes a table from a different context instead of doing the conversion the situation actually calls for.
Work planned on TK-3301 involves cutting in a new NPS 12 shell nozzle in course 1 and replacing a corroded 4 ft by 4 ft area of sketch plate with new plate of the same thickness. How should the two jobs be classified?
1. Both are repairs, because neither one changes the height or the diameter of the tank.
2. The new nozzle is an alteration and the sketch plate replacement is a repair.
3. Both are alterations, because both involve cutting and welding on material that retains product.
4. Both are reconstruction, because shell and bottom material are being removed and replaced.
Show the answer and explanation
Answer: B.API 653 separates the two terms by what the work does to the tank. A repair restores or maintains the tank in a condition suitable for safe operation, and replacing a corroded area of sketch plate with new plate of the same thickness does exactly that. An alteration is work that changes the physical dimensions or the configuration of the tank, and cutting a new NPS 12 penetration into course 1 changes the configuration of the shell, so it is an alteration and carries the design, reinforcement and examination requirements that go with it. Option 1 reads alteration as limited to changes in height or diameter, which is narrower than the definition. Option 3 assumes any cutting and welding makes work an alteration, which would sweep in every weld repair ever made. Option 4 misuses reconstruction, a term API 653 reserves for work involving dismantling and reassembly of a tank, usually after relocation, not for in place repair of a tank that stays where it is.
A canister of E7018 electrodes sat open on the scaffold overnight beside T-305 during rain, and the welder wants to run them out in the morning on a shell insert repair. What should the inspector direct?
1. Let the welder use them after a visual check for cracked or flaking coating, since moisture affects only the appearance of the flux and not the deposited weld metal.
2. Let the welder use them on fillet and attachment welds only, keeping them off the full penetration seams where weld soundness matters most.
3. Have the electrodes dried with a torch at the joint immediately before striking the arc, which drives off surface moisture and restores the coating.
4. Take them out of service for rebaking or disposal within the manufacturer's exposure limits, because a low hydrogen coating that has absorbed moisture invites porosity and hydrogen cracking.
Show the answer and explanation
Answer: D.The whole point of a low hydrogen electrode is a coating that carries very little moisture, and that property is lost once the coating has been exposed to a wet atmosphere beyond the permitted exposure time. Moisture dissociates in the arc and delivers hydrogen into the weld pool and the heat affected zone, where it produces porosity and, in a restrained shell insert, delayed cracking that may not appear until after the examination is finished. Exposed electrodes must therefore go back for rebaking within the limits the manufacturer and the site procedure allow, or be scrapped. The first option treats moisture pickup as cosmetic. The second confines suspect consumables to fillet welds, as though an attachment weld cracking into the shell were acceptable. The third substitutes a torch for controlled rebaking, which heats the surface without driving moisture from the depth of the coating and can damage the flux while giving false confidence.
[Open book] A contractor's written liquid penetrant procedure for repair welds on AST-18 is signed by his Level III but has never been demonstrated on a comparable joint. What does ASME Section V require here?
1. The Level III signature on the procedure is sufficient and no demonstration is called for at all.
2. Demonstration is required only for radiography, the other methods being largely operator independent.
3. The owner's engineer approves the procedure and the Inspector reviews only the examination results.
4. The written procedure must be demonstrated to the Inspector's satisfaction before it is used in the field.
Show the answer and explanation
Answer: D.ASME Section V requires examinations to be carried out to a written procedure, and where the referencing code or the Inspector calls for it, that procedure has to be demonstrated to the satisfaction of the Inspector on representative work before it is used. A Level III signature says the procedure has been technically reviewed; it does not stand in for the demonstration. The procedure also lists its variables, and a change to an essential variable means the procedure is revised and, where demonstration was required, shown again. The first option makes the signature sufficient and cuts the Inspector out. The second option limits demonstration to radiography, but the requirement is not method specific and penetrant results are very sensitive to dwell, temperature and cleaning. The third option hands approval to the owner's engineer and reduces the Inspector to a reviewer of results, reversing the roles Section V sets out. The inspector should witness the demonstration and record it.
[Open book] The approved repair procedure for the TK-1204 bottom specifies a 3/16 in. A36 lap patch, lapped at least 1 in. onto sound plate, with a continuous fillet on the exposed side. The lap measures 3/4 in. along one edge and the fillet is stitched on 4 in. centres. What is rejectable?
1. Only the stitched fillet, because the lap dimension is a fabrication preference rather than a requirement.
2. Only the short lap, because a stitched fillet weld is normally accepted on bottom plate repairs.
3. Both findings, since the lap must meet the stated minimum and the fillet must be continuous.
4. Neither finding, provided a vacuum box test over the fillet weld shows no leakage at all.
Show the answer and explanation
Answer: C.Both findings are rejectable against the procedure the owner approved. A lap-welded patch plate has to overlap sound plate by at least the dimension the procedure states, here 1 in., because the overlap carries load into the parent plate and gives the fillet something to sit on, so 3/4 in. along one edge is short. The fillet also has to be continuous, since the joint has to be liquid tight and a stitched weld leaves open crevices on the product side of the bottom that will corrode and then leak. The first option treats the lap dimension as a preference when it is a stated requirement. The second option accepts stitch welding and gives up tightness. The fourth option offers a vacuum box test as a substitute for the weld detail, but a passing leak test shows only that the weld is tight today, not that the joint has the strength and the corrosion resistance the detail was designed to give.
[Open book] Shell course 1 of TK-0940 now measures below the thickness required for the current maximum liquid level, the owner needs 18 more months of service, and no shell repair can be done with product in the tank. What is the correct path?
1. Re-evaluate and reduce the maximum allowable liquid level from the measured thickness, and record it.
2. Rerate the tank to a lower maximum allowable working pressure and stamp that value on the nameplate.
3. Fit a lap welded patch plate to shell course 1 while the tank stays in service with product in it.
4. Run a hydrostatic test to the original design liquid level to prove the course is still fit for duty.
Show the answer and explanation
Answer: A.API 653 does not rerate a tank. When a shell course no longer holds the thickness required for the liquid level in use, the route is to re-evaluate the maximum allowable liquid level from the minimum thickness relationship rearranged for height, using the measured thickness of the governing course, then set and document a reduced maximum fill height operations can hold for the eighteen months. The second option speaks of a maximum allowable working pressure and a nameplate stamp, which belongs to pressure vessel practice and has no meaning for an atmospheric tank. The third option puts a lap welded patch on a shell course, a detail permitted on bottoms and not on the shell, and it also calls for welding on a tank in service that the stated constraint rules out. The fourth option loads the weakened course to the very level the measurements say it can no longer carry.

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Frequently asked questions

How many free API 653 practice questions are on this page?

Six, each with its options and a full explanation behind a toggle. Three are closed-book items and three are open-book items, and between them they touch all five sections of the body of knowledge. A scored ten-question sample sits on the free quiz page, and the paid bundle holds 1,020 questions across six full-length tests.

Are these questions written to the 2027 code editions?

Yes. They follow the March 2027 effectivity sheet, which lists API 650 in its 14th Edition of August 2025 and ASME BPVC Sections V and IX in their 2025 Editions. Material written for the November 2026 window used API 650 13th Edition and ASME BPVC 2023, so older practice sets can point you at superseded requirements.

Can free practice questions tell you whether you are ready?

Six questions cannot. They tell you whether a particular habit is sound, such as reading an interval rule correctly or spotting which thickness belongs in which variable. Readiness shows up only in full 170-question runs timed to the real 2 hours 45 minutes closed-book and 3 hours 45 minutes open-book rhythm, scored by section.

Official sources

API 653 Aboveground Storage Tank Inspector certification page — accessed 6 October 2026
API ICP Schedules & Fees — accessed 6 October 2026

Exam rules change. Check the awarding body's official page before you apply. CertCrafter is independent and is not affiliated with or endorsed by any awarding body.