Marty
It's actually ironic you should mention trailer repair or fabrication. I've just recently figured out that there IS a certification for such a thing. I've been repairing and modifying trucks and trailers for about 15 years now and I'm licensed with SAE and NHTSA/DOT as a trailer manufacturer. And you're right... it was a difficult and time consuming process to obtain the authorization from those agencies, not to mention that I had to find out first, WHO to contact! It took me about a year to get it all together and get approved. But through all the red tape and typical governmental foot dragging, not to mention MONEY, nothing was ever mentioned and there is nothing in any of the paper work about welder qualifcation. Everything else that relates to manufacturing quality and consistency was addressed and I had to prove just about everything I stated in all my documentation. My shop was even inspected and I had to prove myself worthy of possessing certificates of origin. I also had to provide examples of my trailers so that the design could be deemed sound, but again, no mention of welder competency!
Just thought you might find this interesting.