Oh so you are not done ... ok here it goes ...
Look up the videos on youtube of where the leaks come from ... they are all at the welds ... when you heat up metal and you don't move fast enough you burn right through the metals fact ... that is what can cause these pinsize holes in the welds or the surrounding area of the welds ...
Not enough heat and your welds wont stick ... too much and you can burn right through it and cause the metal to become weak ..
I was done talking about the headers, but figured I could get onboard with this separate conversation about weld quality, since that is a subject I am quite qualified to discuss. I’ve written and qualified weld procedures, and inspected welds for integrity visually and through various methods of NDE, and I’ve tested materials that have been welded, including base metal, weld meta and heat affected zone, for the effects of the welding process, for the better part of the last 15 years from a quality standpoint and from an engineering standpoint (no, I’m not an engineer).
when you burn through a weld, you dont get a pinhole, you get a burn through that is visible to the naked eye. If they’re burning through their welds, then selling the parts, that’s a while different conversation. The puddle literally falls out of the joint. I doubt they’re doing that. Burn through will not cause pin holes in the base metal (header tubes, flanges, etc) or in the heat affected zone (area of flange, pipe, etc that is structurally affected by the heat of the wed). Pinholes are usually an environmental issue (contaminants, gas issues, etc) and are in the weld typically. The weld puddle would fall out long before you had the input enough heat to cause problems in the base metal, especially at the thicknesses we’re talking about.