I keep seeing guys skip the preheat on thick plate and it's costing them.

Last month, I was helping a buddy on a job for a feed mill in Cedar Rapids, and he jumped right into welding a 1.5 inch thick pressure vessel patch without preheating. The weld looked fine, but after hydro testing, we found a hairline crack right in the HAZ. We had to cut it out and start over, which wasted a full day. The spec clearly called for a 250 degree preheat, and skipping it causes too much stress as the metal cools. I've seen this happen at least three times in the past year. What's the thickest plate you've worked on where preheat was absolutely non-negotiable?

3 comments

3 Comments

victor_davis1725d ago

Wait, he didn't preheat an inch and a half patch? That's asking for trouble. @flores.emma is right, the stress just locks up in something that thick. I saw a guy skip preheat on a one inch wear plate and it shattered like glass after the first cold night. What's the point of having a spec if you just ignore it?

the_beth8d ago

Holy COW, a pressure vessel too? That's not just skipping a step, that's playing with fire in a literal way. The spec exists for a reason, it's not just some suggestion! That thickness on something that holds pressure is begging to fail. I can't even imagine the sound it made when it finally let go.

flores.emma25d ago

Wait, a 1.5 INCH patch on a pressure vessel and he just started welding? That's insane! I get skipping it on some half inch stuff maybe, but that's a whole different ball game. The stress has nowhere to go on something that massive. No wonder it cracked like an egg.