I've done a decent bit of mild steel mig, but I'm about to tack up a 304 stainless exhaust and have some questions. It's easier for me to do the tacks with a mig, since that's what I have, and I can do it at the house then give the piping to my buddy to finish with the tig.

Basically I'm wondering if I use a mig with 308L wire just to tack it together using 75/25 gas will I get any real rust? I understand that the co2 will introduce carbon to the welds, but if it's just a few tack welds is it anything to worry about?

I'm a little OCD and I figure if I'm going to the trouble of doing everything in 304 (hangers in 409) then I don't want to eff it up and have rusty welds from the gas...

 

use a sharpie, n mark it down where the pipe meets n give it to ur buddy like that

 

use pure argon when tacking. The sharpie idea might work, but that seems like a lot of room for error by the time it is all welded together while not being on the car. I don't think it will fit good without having it tacked on the vehicle.

 

You're right, it would be close, but even with pre-bent piping, I'm adding a muffler, resonator, a two bolt flange and a v-band. I'll need to have everything up on stands and in place to tack it to make sure it's right.

Additional bottles of gas are what I'm trying to avoid, I don't want to pay out for another tank and gas that I won't likely ever use again, or at least not for a long time.

I was just asking to see if I could make due with what I've got, but I'm going to see if I can just take it over there and do it there. No biggie I was just trying to go at my own pace instead of having to do all the cutting, trimming, welding, etc at once. Thanks guys

 

You can't borrow the tig? When I do exhausts I still tack with the tig. If not You'll want to get a small bottle of argon, or borrow a bottle from the guy that is gonna tig it. I wouldn't wanna tig over someones non argon mig'd tack welds. But some people don't care about that stuff. whatever you're willing to let slide.

 

should be no issue at all. most will grind down the tack to give a clean pass for the tig. lay a bead between tacks, grind the tacks, then proceed with another bead. this will also ensure a clean surface for the final tig welds

 

The c25 gas won't rust the weld I've welded a entire stainless tank out that was 5'x5' inside and out with 308L wire and its still holding up today just make sure you don't use a flappy wheel that's been used on carbon steel or it will rust. The only thing is the weld will have a blackish color if not buffed and the c25 is better than using pure argon with the mig

 

I wouldn't worry about it, tac it with your mig and then have your buddy tig the rest, that's what I would do

 

yeah. for exhausts because they are so thin tig welding works best. you can use mig but you have a better chance of burning through. Best bet, go with tig welding. looks more attractive and lesser chance of burning through. good for tacks tho.

- im a welder