Started using a new pre-heat method on thick plate welds

We had a 2-inch thick pressure vessel plate that kept showing porosity after the first pass, so I tried heating it to 350 degrees for an hour before welding instead of the usual 250. The next x-ray came back clean, and we saved a full day on rework. What's your go-to pre-heat temp for heavy carbon steel?

4 comments

4 Comments

the_diana2mo agoProlific Poster

Two inches thick is a monster plate.

victor7792mo agoMost Upvoted

My grandma had plates like that from the 70s, they were basically ceramic shields. You could drop one and it would just laugh at you while chipping the floor tile. I swear they designed dinnerware back then to survive a minor earthquake. Makes modern plates feel like fancy crackers.

janah832mo agoTop Commenter

Wasn't that stuff basically bulletproof? My mom still has her old set from that time, and I swear you could use a plate as a stepping stool. I tried to break a chipped one once, just to get rid of it, and it took a full swing against the concrete patio edge. The concrete lost. Everything now feels so thin and sad in comparison.

victor_robinson1mo ago

Go with 350 to 400 on anything over an inch and a half, especially if it's a chrome-moly alloy... that's where the hydrogen really hides. You gotta hold it there long enough for the heat to soak all the way through, not just the surface. I usually shoot for an hour per inch of thickness, then keep the interpass temp above 300 so you don't lose the heat between passes. That porosity you were seeing was likely trapped hydrogen or moisture, and that extra heat gives it a path to escape before you seal the root...