It depends on who your asking....
If it wasn't for welders,a few of my trucks wouldn't HAVE a frame!!--I have had several trucks that had cracks at the steering box(even a 2wd!)and shock mounts pulled right thru the frame,and more than a few that had rot or other large cracks that had to be welded up--one truck I bought was very rotted on the frame rails from the cab back,and I bought another 1/2 frame from the boneyard and made it whole again by welding it back together and fishplating the seams...
I never had any issues with the welds,nor did the frames ever crack again,despite my many episodes of overloading and plowing--and I'm not a certified welder by any means(I used an arc welder that looks at least as old as I am!)..I've seen those "DO NOT WELD OR CUT" stickers on big rigs too--as tRusty said,they are different steel,and they carry thousands of pounds of freight on public highways--I feel the stickers are there to cover the manufacturers butt if anything the owner does affects structural integrity more than it will "ruin" the frame--nearly every roll back ramp truck and dumpster hauling 10 wheeler I have looked at had frame "surgury".and you dont see too many folded in half or anything...and many factory welds are holding brackets on and such--if they can weld it,why cant we??
If done properly,welds should be as strong or stronger than the peice your welding--even my crude bird poop welds never gave any greif,but my truck isnt an 18 wheeler either-if your worried just get an experienced welder with a MIG welder to do it for you..
Some states are now not allowing frames to be repaired or welded--I think NH is one--but if you are good with a grinder,you can make the welds difficult or impossible to see,and most places dont even look when inspecting,at least not very close..I havent seen many frames break,except for when salt eats thru them and they are paper thin..I'd rather have a welded frame than a rusted one......
