Poor description on my part. Where it broke at the union between the collector and the pipe flange. The weld had obviously been ground and polished; and there wasn't a lot of filler material there to begin with. What was left when the flange came off the collector was just a thin ridge where it had been welded. It looked like it had corroded away, maybe. Or possibly the flange material corroded out from under where it had been welded.

what I've seen in the past in different applications is the tubing right next to the weld would break, but the weld would be intact. In this case, nothing broke, per se. The pipe pulled out of the flange. Like the weld didn't "stick" to the flange. Yet, it had been joined there just fine to begin with.

 

I'd guess there wasn't enough penetration when it was welded. Mild steel to SS shouldn't have any issues as long as the right filler was used.

 

Basically what he said.

They use very little filler. Its almost a fusion weld where the 2 base metals are heated just enough to get them to melt together. They use little to no filler rod to keep it molten and the 2 base metals flowing. It creates a very flat weld but is very weak

 

Thanks for the explanation, fellas.