Choosing between a 3/8-inch and 1/2-inch backing bar for a 1-inch plate weld

I was working on a pressure vessel repair last week and had to pick a backing bar size for a full penetration butt weld on 1-inch thick plate. The spec called for a 3/8-inch bar, but the old guy running the shop insisted a 1/2-inch bar gives you a better heat sink and less chance of burn-through. I went with the 1/2-inch because he's been doing this for 30 years. The weld went in smooth with zero issues, and the X-ray passed first try. Has anyone else had to make a call like that against the written spec? Did it work out or bite you later?

3 comments

3 Comments

miam7516d ago

Did you check if the spec had a tolerance that allowed for the thicker bar?

seanlee16d ago

Honestly, I read a welding forum thread about this exact thing. A few guys said the spec is a minimum, and going thicker on the backing bar is a common field fix for heat control. Sounds like your old-timer knew his stuff, and the X-ray proves it.

adam73111d ago

Yeah, reading a welding forum for answers is about my speed too. I once tried to fix a lawnmower based on a forum post and ended up with three extra bolts. So that old-timer trusting his gut over the paper spec? Makes total sense to me. The proof is always in the pudding, or in this case, the X-ray.