Pro tip: Choosing between a full weld repair or a patch plate on a 3/8 inch boiler shell

Had a job last month on a 30 year old boiler in a plant outside Toledo. The shell had a 4 inch long crack near a nozzle. The choice was grinding it out and doing a full weld repair, which meant a lot of prep and heat control, or cutting out a section and putting in a patch plate. I went with the patch plate. It took a full day to cut, bevel, and fit the new piece, but the weld passes were cleaner and the X-ray came back perfect on the first shot. The inspector said it was a solid call because the metal around the crack was pretty thin. Has anyone else had to make that call on an older vessel? What made you pick one way over the other?

2 comments

2 Comments

the_fiona13d ago

Patch plates are a solid fix, but they do add stress risers at the corners. On a 30 year old shell, the metal thinning is the real issue. A full weld repair might have been better long term if the surrounding area was still thick enough to handle the heat input. The patch basically puts a permanent band-aid over a weak spot. Your inspector was right for that specific crack, but it's not always the best call for every old vessel.

oscar_hunt6112d ago

Man, that's a tough call to make. I get why you went with the patch. When the metal's thin, grinding it all out can just make a bigger problem. @the_fiona has a point about stress risers, but sometimes the band-aid is the only thing that works on old metal. I saw a similar thing on a feedwater heater where a full repair would have meant replacing half the shell. The patch got it running again for years. You gotta work with what's in front of you.