Welding is absolutely one of the hardest trades there is when it comes to proving yourself. There are codes, specifications, and procedures that have to be mastered, then proven time after time. Certification papers make you a "certified" welder. They show you've passed a welding test. (The Importance of Weld Tests )
Being a certified welder means you can pass a test, but it does not necessarily mean you are a good hand. Someone who goes to welding school may spend hours doing nothing but welding test plates. If they have any talent at all, and with all that practice, they will probably pass the code to become certified. But it's a whole different story out on the job site. Welding in a booth at school ain't the same as standing on a 2" wide beam, 20 floors up in the air, with the wind blowing like crazy.
I'm a journeyman Iron Worker, have 2 degrees, and have been in the welding field for over 25 years, 13 of them teaching. Yet I could go to the union hall, get sent to a job with a greenhorn whose been welding just a couple of years, and still both of us have to take a weld test!
I've done exactly that, walked into the test shack at a coal-fired powerhouse with my certification papers like I owned the place. My certification paper was from the American Welding Society code allowing me to weld in all positions, all thicknesses, and were good for both mild steel and stainless. When I showed them to the guy in charge of testing he said…"Hey, that's really impressive, you're certified. Now grab some plates and go test!"
There are several different codes which are usually nationally established. Three of the top organizations establishing welding codes for welder certification are the American Welding Society (AWS), the American Petroleum Institute (API), and the American Society of Mechanical Engineers (ASME).
AWS The American Welding Society is primarily concerned with structural applications such as high-rise office buildings, power houses, dams, etc.
API The American Petroleum Institute is just what the title 'sez. It regulates the welding on all petroleum vessels such as oil storage tanks, carbon dioxide spheres and the like.
ASME - The American Society of Mechanical Engineers regulates welding on pressure vessels such as steam drums and boilers.
For a welder to become certified with one of these agencies, he or she will follow the specific code set forth in the organization's Welding Procedure Specifications or WPS. Even though these organizations have different standards, they are very similar in the tests they give for welding certifications as well as their set codes.
Having welding certification papers from the AWS does not necessarily mean you can use them for a job using the ASME code. The more certifications a welder has, the better because in life every feather you put in your cap will help. However, even with all the certifications in the world, depending on the job, you'll be proving yourself all over again!