Most API 570 candidates treat the calculations section as one big formula sheet. API’s list is shorter and odder than that: a few formulas to hold in your head, and a larger group of lookups where the marks go to whoever finds the right clause first.
What calculations does API actually list for API 570?
The calculations section opens with a scope statement. Code calculation questions are oriented toward existing in-service piping, not new piping. You are not designing a line. You are checking one that has been running, and asking what corrosion, a repair, a rerate or an alteration has done to it.
Then comes a list of eight categories. Here they are with the clause API names for each.
| Topic | What the inspector works out | Where API points |
|---|---|---|
| Corrosion rates and intervals | Rate, remaining life, next interval | API 570, 7.1.2, 6.3.3 and Table 1, plus the remaining life paragraph |
| Quality factors | Casting factor and weld joint factor | ASME B31.3, 302.3.3(b) and 302.3.4 |
| Internal pressure | Required thickness, blank thickness, corroded MAWP | B31.3, 304.1.1, 304.1.2, 304.5.3; API 570, 7.5 |
| Pressure testing | Hydrostatic or pneumatic test pressure | B31.3, 345.4 and 345.5 |
| Impact testing | Exempt temperature, required Charpy values | B31.3, 323.2.2 and 323.3 |
| Preheat and heat treatment | Which welds need it, what temperature | B31.3, 330 and Table 330.1.1 |
| Thermal expansion | Total expansion between two temperatures | B31.3, Appendix C, Table C-1 |
| Flanges | Working pressure, minimum dimensions | ASME B16.5, Section 2 and the dimension tables |
Eight rows, and only the first holds formulas you build from memory. The others are tables and short equations sitting in a code book.
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Which calculations may be closed book?
Category one. The Body of Knowledge says the formulas for corrosion rate, remaining life and the rules for setting inspection intervals may be closed book during the exam. The exam has 110 closed-book questions followed by 60 open-book ones, so the first part is where a shaky formula costs you with no book to catch you.
It also says candidates must understand US customary units (inches, feet, psi) and the SI system, and use both sets of formulas. That sounds like a small detail until a question hands you millimeters and kilopascals on a day you only practiced inches.
How do the lookup calculations work?
They are chains. Take required thickness. The Body of Knowledge says the weld joint quality factor may be part of an internal pressure problem, because that factor sits inside the formulas for required thickness or design pressure. So one question can ask you to find a joint factor in a B31.3 table, carry it into a thickness formula, and then add or subtract the corrosion allowance, depending on what the problem says.
Each step is easy alone. The marks go to the candidate who keeps the chain straight under a clock.
Two habits help. Write the clause number next to every number you pull from a table, so you can retrace a step in ten seconds. And do the units check before the arithmetic, not after.
The API 570 Complete Exam Kit works these chains under timed conditions in both unit systems, with every answer explained.
How do inspectors use these calculations on a plant?
Nobody on a plant computes a corrosion rate for fun. The number decides whether a line stays in service, gets a shorter interval, or goes on a repair list. A required thickness tells you how much of the wall is spoken for before corrosion is counted at all.
Reratings and repairs work the same way. If the service conditions change, the pressure the line can carry changes with them, and the check goes back to the same B31.3 clauses the exam points at. A pressure test after a repair or alteration is a calculation too: someone has to work out the test pressure, then confirm the line can take it.
There is one trap that site work and the exam share. Many plants and jurisdictions run on other editions than the exam does. API’s own note says some organizations use documents or editions other than those on the effectivity sheet, and that the exam is based on the sheet. Answer from the sheet, not from what your site binder says.
Where do candidates lose marks on the calculations?
The first place is the closed-book formulas. Candidates who rely on a book they cannot open in that part of the exam find out the hard way.
The second is wrong editions. The effectivity sheet for the February and June 2027 windows lists ASME B31.3 in the 2024 Edition, B16.5 in the 2020 Edition, and ASME Section V and IX in the 2023 Edition. A table from an older B31.3 can give a different answer from the one the exam wants.
The third is chasing excluded material. The Body of Knowledge lists B31.3 requirements the inspector will not be expected to know: most of clause 302 except the two quality factors, curved and mitered pipe, branch connections, closures, reducers, flexibility analysis and more. Time spent on those is time not spent on the eight topics above.
The fourth is the pairing of inputs. A joint factor read from the wrong row, a corrosion allowance added when the problem said to subtract it, or a temperature in the wrong scale all give a clean, wrong answer that sits right among the options.
How should you practice these calculations?
Split your sessions the way the exam splits its content. Spend one block on the three closed-book calculations until you can write them out in both unit systems without a source. Spend another on the lookups, using the on-screen PDFs rather than paper, because paper is not allowed in the test center.
Then mix them. A real question rarely announces which kind it is. The two sample questions below are free, and both are calculation questions framed the way the exam frames them.
Check your own window too. The next API 570 window on the schedule is January 29 to February 19, 2027, with an application deadline of November 26, 2026, and it falls under the February 2027 and June 2027 Body of Knowledge.
What should you do next?
Open API’s Body of Knowledge from the API 570 exam page, go to the calculations section, and mark each of the eight topics as memorize or look up. Then read how worked formulas and the general practical knowledge section connect to them.
Try the free sample quiz, read the certification guide, see the other API 570 posts, and look at the practice tests when you want timed drilling.
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