Old timer told me to try preheating my base metal on a cold morning. I thought he was crazy.

Last January we had a stretch of mornings under 20 degrees and I was getting cracks on every single weld cap. One old guy I work with kept telling me to bring a torch and warm up the steel for a good 5 minutes before striking an arc. I finally tried it on a big boiler patch job and not a single crack showed up. Has anyone else found that preheating saves more time than it costs, or do you think it's just for certain alloys?

2 comments

2 Comments

leo60311d ago

Well, you're close on the shrinkage thing, but it's not exactly that the cold metal shrinks faster. It's more that when it's cold, the weld pool cools way too quick and the metal doesn't have time to expand and contract evenly, which is what causes the stress cracks. Preheating slows down that cooling rate so the material can move and settle without snapping. I had a job once where we were welding thick plate and skipped preheating, ended up with a crack that ran the whole length of the joint. That was a long day. So yeah, Mitchell is right about it fixing problems, but the science is about controlling the cooling, not just fighting stiffness.

mitchell.dakota11d ago

Preheating is one of those things that sounds like wasted time but actually fixes everything downstream. Same principle as warming up a car engine before driving hard. Skip it and you're just fighting against the material's natural stiffness. Cold metal shrinks faster. That's where the cracks come from. Once you learn that lesson you start seeing it everywhere.

-1