This post is at a perfect time for me, I have to weld inside the water jacket on a stainless (magnetic) out door wood boiler, non pressurized system. Great info here guys, thank's. I have a question though, with duel shield do I need to reverse the polarity like I would for flux core or do I keep it neg ground like straight mig welding? I am not afraid to contaminate the weld with mild steel becouse it looks like that is what they did (poorly) at the factory, all the welds are coated in rust what are a couple more going to hurt.