Shoutout to the guy who showed me how to properly pre-heat a 4-inch thick plate

I was fighting porosity on a pressure vessel weld for a solid hour. He walked over, told me to bring the plate up to 400 degrees for 30 minutes first. The next bead went down smooth as glass, zero inclusions. Anyone else have a simple trick that saved a huge headache?

4 comments

4 Comments

wadejenkins3mo ago

Pre-heat is a game changer for thick stuff. I learned the hard way on some 2-inch pipe, kept getting cold cracks until an old-timer told me to warm the whole joint area with a rosebud first. That extra heat soak makes the metal behave completely different.

adams.river3mo ago

Man, I've seen guys torch pre-heat on 3/4 inch carbon and it just warps the whole joint. On thinner wall pipe, that soak can pull the fit-up out of line before you even strike an arc. Sometimes you just need a quick pass with a hand torch to knock the chill off, not a full rosebud treatment.

caseywalker3mo ago

Last year on a refinery job, we had a guy cook a 10-inch schedule 40 joint so bad it looked like a banana. He used a full rosebud for a five minute soak like it was 2-inch wall. Adams is right, you just need to take the edge off the metal, not try to bake it. Too much heat on thin stuff just makes it move all over the place before you even get your hood down. A quick lick with a hand torch is the difference between a clean weld and a nightmare you have to cut out.

barbaradavis16d ago

Funny you mention that, @wadejenkins I remember a job where a guy tried to pre-heat some 6-inch stainless with a rosebud, and it warped the pipe so bad the flanges didn't line up anymore. We had to cut out a whole section and start over. A hand torch would have been plenty for that wall, but he wanted to go big. Sometimes less is more when it comes to heat, especially on smaller pipe. Ever seen someone try to fix a warp by hitting it with more heat and making it worse?