The paper is 170 questions. 140 are scored and 30 are unmarked trial questions you cannot identify.
It splits in two: 110 closed book, then 60 open book with a longer clock.
The open book half is where the calculations live, and where most of the time pressure is.
Wrong options are built from real mistakes, not nonsense, so guessing badly is easy.
Ten questions below, each with the full reasoning and why every wrong answer is wrong.
What the questions actually look like
Every question is multiple choice with four options and exactly one defensible answer. There is no negative marking, so an unanswered question and a wrong one score the same. Answer everything.
The questions are not trivia. They tend to put you in a situation and ask what you would do or what a number works out to. That is a different skill from remembering a definition, and it is the reason people who have read everything still come out short.
The two halves, and why they feel different
The paper runs in two sections with separate clocks, and once you leave a section you cannot go back.
The closed book half is 110 questions in 2 hours 45 minutes. That is about 90 seconds each. It rewards recognition: you either know the interval rule or you do not, and hesitating costs you a question elsewhere.
The open book half is 60 questions in 3 hours 45 minutes. Nearly four minutes each sounds generous until you realise this is where the calculations sit, and where looking something up eats the difference.
110 closed book in 165 minutes, roughly 90 seconds a question
60 open book in 225 minutes, roughly 225 seconds a question
30 of the 170 are unmarked trial questions, spread across both halves
No negative marking, so never leave one blank
You cannot return to a section after you finish it
Try ten questions
These are written to the current exam scope and pitched at the same level as the real paper. Four options, one right answer, and a full explanation either way.
Answer honestly rather than looking things up. A score you did not earn tells you nothing useful.
Free practice
Try 10 API 510 questions
Same shape as the real paper. Pick an answer and you get the full reasoning, including why each wrong option is wrong.
Question 1 of 10
API 510 Prep
613 more like these, every one explained the same way. Timed mocks and a predicted score that tells you when you are ready.
In review. Live on both stores shortly.
The calculations that come up again and again
A predictable set of calculations carries most of the numerical marks. They are not hard individually. What catches people is doing them under time pressure, in the right order, with the corroded thickness rather than the nominal one.
Corrosion rate, both long term and short term, and knowing which one to use
Remaining life, and the interval that falls out of it
Maximum allowable working pressure for a corroded shell or head
Static head, and remembering to add it to the operating pressure
Joint efficiency, read off the joint type and the amount of radiography
Required thickness, and the difference between required and actual
Fillet weld throat and leg conversions
Hydrostatic test pressure and the metal temperature that goes with it
How the wrong answers are built against you
This is the part that surprises people. The three wrong options are not filler. Each one is a mistake somebody actually makes.
In a corrosion rate question, one wrong option is the total metal lost rather than the annual rate. Another divides by the wrong thickness. A third uses the short term rate where the long term one applies. Every one of them is arrived at by doing real arithmetic slightly wrong.
The practical consequence is that a confident wrong answer feels exactly like a right one. You cannot sanity check by asking whether a number looks plausible, because they all do.
How to practise so it actually transfers
Reading questions is not practising. The thing that moves your score is answering under a clock, getting it wrong, and understanding why before you see it again. It is also cheaper than paying the resit fee.
Two habits do most of the work. Practise in short daily sets rather than long weekend sessions, because spacing is what makes things stick. And send everything you get wrong back at yourself at widening intervals until you get it right several times running.
Short daily sets beat occasional long ones, by a wide margin
Sit at least two full timed mocks before the real thing
Track your score by domain, not overall, so you know where the gap is
Treat every wrong answer as a question to be re-asked, not a fact to be reread
Knowing when you are ready to book
There is no published pass mark and no published pass rate, so nobody can tell you the number you need with certainty. The working assumption most people use is somewhere around 70 to 75 percent on the scored questions.
What matters more than a single overall figure is consistency across domains. A candidate averaging 78 percent with one domain at 40 is in worse shape than one averaging 72 percent with nothing below 65. The exam samples every one of the eleven areas, so a single weak area drags the whole result.
Frequently asked questions
How many questions are on the API 510 exam?
170 in total. 140 are scored and 30 are unmarked trial questions that do not count towards your result. You cannot tell which is which, so treat every question as if it counts.
Is the API 510 exam open book?
Half of it. The paper runs as 110 closed book questions in 2 hours 45 minutes, then 60 open book questions in 3 hours 45 minutes. The open book references are supplied as PDFs on the exam computer. You cannot bring your own books or notes into the test centre.
What is the pass mark for API 510?
API does not publish one, and it does not publish a pass rate either. Most preparation targets around 70 to 75 percent on the scored questions, which is a working assumption rather than a stated requirement.
Are there free API 510 practice questions?
Yes. Ten of them are on this page, with a full explanation for the right answer and a reason for each wrong one. They are written to the current exam scope rather than recycled from old papers.
How many practice questions should I do before the exam?
Volume matters less than coverage and repetition. Getting through several hundred questions spread across every domain, with the ones you miss coming back at you, does more than grinding thousands in the areas you already know.
Is there negative marking on the API 510 exam?
No. A wrong answer and a blank score the same, so there is never a reason to leave a question unanswered. If you are running out of time, answer everything remaining rather than leaving gaps.
