No. Marking on a "curve" means that you are comparing the scores of one candidate to all other candidates who took the examination and then assigning grades or passing status according to a fixed percentage. The implication is that whether an individual passes the examination or not might depend on the ability level (or preparation) of all the other candidates who took the examination. This would not be fair for a credentialing examination.
For API 510, 570, 653, TES and 936 programs API uses a statistical method called "equating" to score the examinations. The original passing point of the examination is set by a committee of experts and it represents an absolute standard of knowledge (the minimum amount that a competent inspector should know in order to be certified). Each examination has different questions in it. The equating process then adjusts the passing point of each examination to compensate for differences in the difficulty level of those questions. Thus, the passing point always represents the minimum knowledge required and the absolute knowledge standard is held constant. The test results of candidates only reflect whether they have this minimum amount of knowledge or not. Passing the examination is not affected by any other candidate's performance.
For API 571, 577, 580 and SI programs the passing point is set at 70%.