Honestly, my foreman in Omaha told me to always pre-heat the 2-inch plate to 350 before the root pass, and it saved a huge weld on a pressure vessel last month.

I thought it was overkill for the job, but it prevented a major crack that would've scrapped the whole piece. Anyone else have a specific pre-heat rule they swear by?

3 comments

3 Comments

spencer_kelly1mo ago

Read a study showing pre-heat prevents hydrogen cracking in thick sections.

parkerm561mo ago

Man, your foreman knows his stuff. I had a job on some 1.5 inch T-1 steel, specs said 250 was fine. We bumped it to 300 and went slow, let it soak. The difference in how the puddle flowed was night and day, no underbead cracking at all. That extra 50 degrees is cheap insurance compared to a failed x-ray.

kelly.emma7d ago

The part about letting it soak is something people skip. I've seen guys slap a torch on it, hit temp, and start welding right away without thinking about the heat bleeding into the surrounding metal. Pre-heat isn't just about the surface temp right where you're welding, it's about warming up the whole zone so the heat doesn't run away from you. On thick plate like that 2-inch stuff, if you don't give it time to soak through, the weld cools too fast and you get that hydrogen cracking clear down to the root. That 350 with a good soak makes the puddle ride smoother and keeps the heat in the joint, which is the whole point.