Old timer told me my preheat on a 2-inch plate was way too low

He said I was gonna crack the weld running at 150 degrees on a cold morning in Chicago. Switched to 250 and sure enough, the bead laid way smoother and no cracking after hydro test. Has anyone else had an old-timer save them from a rookie mistake like that?

3 comments

3 Comments

kimblack20h ago

What gets me about this whole preheat thing is nobody talks about how the base metal thickness plays into it with the ambient temp. I had a job on a 3 inch wall pipe in January and the old foreman told me to figure the preheat based on the interpass temp not just the initial pass. So I was cranking 250 on the root but then letting it drop too much before the next bead. He showed me to keep a temp stick on the plate between passes and hold it steady. That cold Chicago air was sucking the heat out faster than I realized. Fixed my cracking issue on the second try.

emma_jones21h ago

Oh man that is a good one. It's wild how something as simple as heat input can totally make or break a weld. I had a similar thing happen to me but not with welding, with brazing copper pipe on an old house. This crusty plumber told me I was using too small a tip for the size of the joint and that I needed to let the metal soak up the heat slower. I thought he was full of it but he was right, my joints stopped leaking after that. There's just some stuff that doesn't show up in a book or a YouTube video, you gotta burn your fingers a few times to really get it. It's humbling when you realize the old guy has been there and done that a thousand times.

rosepark17h ago

Honestly, that whole thread is like a perfect little lesson on how most things in life work. It's not just welding or plumbing, it's like anything you try to learn. You can watch all the tutorials and read the instructions, but there's always some tiny detail that only comes from getting your hands dirty and messing it up a few times. It's like how you can read about making good bread but you don't really get how the dough should feel until you've had a few bricks come out of the oven.