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3X00-Modified wrote:I've never had to and it's stated that you don't need back flow gas for mild steel. I actually did some mild steel tubing tig welding and the inside weld looked just as good as the outside, the stainless on the other hand yeah was all oxidized up.

I was referring more to MIG welding recommending the back-flow, but that is more for a 'perfect' structural weld with 100% penetration too. TIG welds have their own 'cleaning' action on the material that removes impurities (like gas welding).

I've done enough pipe welding with MIG and with flux-core to know you are right, back-flow shield-gas isn't strictly necessary on mild steel tube, but stainless steel just amplifies the issue that mild steel has to the point where you can see it. Imagine running a weld and pulling the wand away while the metal is still molten, rather than leaving it in place while the remaining flow of shield-gas still protects the material -the oxidation isn't always severe, but it is there. Anyway, what matters is the results, and I don't care what opinions are or what has been written in books,if it is working consistently for you, no one can say it is being done wrong.

I will agree that the requirements differ greatly depending on what your actually welding, or what it's going to be used for. But for me doing exhaust tubing back flow on mild just isn't necessary, or at least I've found that to be true. I've also read that MIG welding SS you don't always need a back flow and I noticed that with pipes that I welded MIG on my Legacy vs the up pipe I did recently on my TIG... This was the first time I ever saw the really bad inside bead, which in reality the whole bead is compromised from what I've read online, so I do need to replace what I did with a better setup soon.

the back flow is only for asthetics or food industry when it comes to Stainless generally. I have thousands of SS exhaust components out in the field and back flow very few yet have never had a failure from the weld itself. What I mean by that is generally the failure was someone grinding the material or running into something else.

Don't be afraid of stainless.

Jon if you want something to practice on I'd like to fab a stainless midpipe for my truck to replace the aluminized stuff that is getting nasty already. I can fab & tack it and then bring it by! haha

That's fine with me... You let me know. I'm getting quite good at it and I hope to be doing my legacy pipes soon... Waiting on a new stainless down pipe then I need to position and install a resonator on the cat back I have.

Sweet! I had to replace my aluminized tailpipe with stainless after 4 years and next year will be the 4th with the headers & midpipe already... My headers look terrible, and whenever I tow a long distance with the truck now the collectors start to leak. The rusty ball flanges actually collapse and I have to crank them down tighter. I've lost about an inch and just had to put shorter bolts in it this last time.

yikes... I hate cheap exhaust parts... The system I'm putting on the legacy (cat back is essentially the same thing on there now) the down pipe is 304 stainless and the cat back is a 400 grade but after welding in the resonator and flex coupler I'm sending it to have the whole thing ceramic coated so it wont rust again.