davew wrote:You can weld stainless with a MIG using normal mild steel wire/gas, you don't need anything special for it for something like an exhaust. The weld pool fuses with the stainless anyway and seems to become "stainless" itself, resisting rust.
I did mine with gas-less mig and it's still in one piece three years later, although at the time I was not confident in welding SS like this so I layered a bit on just in case
I even managed to get it gas tight by using leak detector and a rag up the outlet and puddling the little blow holes.
I probably wouldn't be happy welding anything that is stressed in this manner, but the last few inches if pipe is fine - especially if it is out of sight