Just about any shop, or field job that does structural, pressure vessels, or pipe will have you take cert tests for their procedures. Even if you go to a job with your own certs, you will most likely be required to take new tests for the company hiring you. Haveing your own certs will give you a better shot at getting a job over someone who has never held certs. Like I said though, you may have a 6g 5p root, lh fill/cap. cert on lets say 6" sch160, and that is what the employer requires, the employer will still probably have you retake the test for them.