I'm on the design end of things and have never heard of PWHT acronym. I guess it might stand for Post Weld Heat Treat based on your title. We use a non-standard welded up L12x12x1.5 made from 2 plates welded together and I will inquire from our supplier how they do it when I get back to work next week. For general fabrication of lattice towers, we do not use much welding and I don't think they use any heat treatment for small plates welded to angles. All our stuff is galvanized so when it goes into the 800°F molten zinc tank, I guess it will get a little stress relief, but metallurgy is not my area of expertise.

I'll check and post back when I find something.

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