ATR Header overhaul

Dave, you do some nice work for sure. Either you or Don please explain what solar flux is and how do you use it. Do you use it with Gas or Tig or what?
Solar Flux is a fine silica powder you mix with methyl alcohol and apply to the backside of the weld with a small paint brush. It forms a glass like protective coating that keeps oxygen away from your weld pool. It basically does the same thing to the back of the weld as the shielding gas does for the front of the weld.

Backpurging or solar flux is only needed when welding thin stainless steel. I assume TIG and MIG, but I've got no experience MIG welding stainless.

If you don't protect the backside of the weld, oygen hits the weld pool and nasty carbides form. The carbides make a sugary looking , weak weld that will fail.
A couple of "what works for me" items:
1. The flanges are cut between each cylinder.
2. The center cyl bolt holes are on size. Each cylinder out from center, the holes are + 1/8".
Nice headers!