Stainless Exhaust TIG welding

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Hi everyone. I'm new to the forum and have a few questions on an exhaust system I'm about to build for my 86 Fiero SS. First of all, I'm 20 years old and graduated from WyoTech last september. This is where I got my limited welding experience. Heres my project right now. My dad and I just managed to stick a Chevy ZZ3, 350 cu. in. crate motor into my Fiero and exhaust is a pretty big challenge. I got an assortment of bends in 2.5" pipe, 16 ga., 409 grade stainless. Not very good stainless, but it was the same price as the mild steel pipe. I'm borrowing a friends TIG welder for the exhaust. Not sure on the exact model and everything, but I know it is a higher end Miller. I have never welded stainless before but I'm decent at mild steel and aluminum in various thicknesses. I figure with some practicing I should be able to pick it up pretty good. It gets a little complicated when I come to the mufflers and tips. The pipe is 409, the mufflers are mild steel, and the tips are mirror polished and chromed 304 stainless. My questions are as follows:What size and type of electrode should I use for the two weld types? (409 to mild and 409 to 304)What size and type of fill rod to use for said welds?Can I get away with standard 75/25 gas?Is there anything special I should do to prepare any of the materials for welding (ie, wire wheel the chrome from the tips where I will weld)?Any other tips or advice is greatly appreciated. Thanks in advance for any help.   -Tim
Reply:TD37, 1/16 filler rod, 1/16 zirconium [brown tip] for ac    2%thoriated for dc   pure argon   tungsten pointed   60to80 amps    unless the manufacture stated the part is chrome plated I'd guess it's just polished, no need for chrome.
Reply:TD37,      309L filler should work
Reply:Td37, 1/16Last edited by alan waters; 05-02-2006 at 12:43 AM.
Reply:Backpurge or use some of the commercially available pastes as well.
Reply:Hey Alan, thanks a lot for the great info. I agree the tips don't need to be chromed. I got them off Ebay and they were listed on a pretty generic ad. But they specifically say, "The tips are chromed over stainless to give you that super deep, high polished look" And, the inside welds appear to have been left unpolished and chromed. I must assume they are indeed chromed as well. In this case what do I do? Wire wheel it off?Orphan68, forgive my ignorance. I have no idea what you are talking about haha. Please enlighten me.   -Tim
Reply:Tim, to purge means to remove the air inside your tubes and replace it with an inert gas. This is done by sealing the ends with tape or some type of cap and filling the inside with argon. You could do this if you wanted to, I would not if it were mine on this type of part. Technicaly stainless should be purged. Has to do with weld contamination inside the part.     I don't know the answer to the chrome thing. It might weld, I've never welded anything with the chrome on.
Reply:You can weld over the chrome, but it will contaminate the weld. Chroming on stainless is really unnecessary as it can be polished to a chrome looking shine without having to be plated. All it takes to get the shine is polishing and if it blues, it can be polished easily. Try using some scotch brite type pads to remove the chrome, if not, use a med-fien sadpaper. You can always polish them up after welding.
Reply:How badly could it contaminate?  Afterall, we are talking the low temperature portion of an exhaust system here.  Mechanical properties aren't overly important.  Stainless steel has chrome in it, anyways.
Reply:if you purge it, you should poke a pin hole in the opposite end from where you're welding , to actually let out the air, & let it fill w/argon. sure, you will lose a little argon. I've heard (don't know if actually true) that some welders in the Napa valley purge wine tanks (stainless steel) with the much cheaper nitrogen, but most of us won't normally use that , because we won't have it in our shop . oh, well , just thought i'd mention it .
Reply:To each his own.......
Reply:Purging is very important on stainless exhaust systems; often cracks will develop in the tubing adjacent to the weld if it's not purged.  Good luck - sounds like a cool project.  Scott
Reply:purging or solar flux is a must. the backside of the weld will form an ugly black crystalline mess that is very prone to corrosion and cracking. I reccomend purging with argon as the solar flux is tough to use in a butt joint. your exhaust will thank you!