How bad is mig welding stainless with C25?
 

PO of my NB1 put an OBX header and 01+ EGR pipe on. The EGR pipe fitting has broken off the #4 runner. I have a small mig welder and a bottle of C25. I can pick up some 308 wire.

I know the C25 will mix with the stainless and make it suseptable to rust, but, is this a "it will last a few days" thing or "it will last a few years" thing? I would rather not have to get another bottle that I won't use.

And before anyone says EGR delete, I need to get through inspection in December. After that I am good for 2 years though.

I would avoid welding stainless with mig, but that's me.
Tig would give significantly better results.

I don't have access to a tig setup.

It will hold up fine, it will just corrode over time, less so than a comparable mild steel piece.

There is no reason to avoid MIG welding Stainless in a Miata application.

C25 is the gas of choice.

It will eventually corode unless you use stainless steel wire (which can be purchased at just about any welding supply store)

Perfect. I will pull the header out and give it a go. I have about 1-2h of arc time experiance with flux, and will practice a bit with mig before I actually go for it and see how it goes.

I bought some 1mm wall thickness 304 tube to put inside of it and add reenforcement as well since I tried using the exhaust putty at first (didn't work, too brittle and just cracked off)

It will be more susceptible to brittle failure and oxidation. But it should hold up for a while.

So what you are saying is, lay it on extra thick.

When it fails, it's not going to be in the weld. It will be at the toe of the weld or just outside of it. No monster bead required.

Ahh, that makes sense. I will try and keep it small then so there is space to re-weld when it goes.

Finally got the parts out that I need to weld. Any suggestions on how to go about this? Got the machine set up for gas, gonna try and find a piece or two of scrap 304 around to practice.

Best I can figure is I have some 8mm OD 1mm wall stainless tube, shove that inside, weld it, then weld the piece on? Gonna have a good sized gap since the EGR nipple pipe thing is oval (11mmx8.8mm). Need to attack everything with wire brushes first.

https://www.miataturbo.net/attachmen...1&d=1569372289

https://www.miataturbo.net/attachmen...1&d=1569372289

Huge thanks guys! It went great. Once I figured out my garage circuit had too much voltage drop to run the welder correctly with mig wire. It works fine with flux core though? I am a bit baffled. With the mig wire it would just pop, not a nice stead arc. Flux was fine. Once I ran an extension cord from the kitchen circuit, it was perfectly happy with the mig wire though.

Anyway, my first stainless weld, tested it in a vice.

https://www.miataturbo.net/attachmen...1&d=1569706979

Second one came out even better. Penetration looked good.

https://www.miataturbo.net/attachmen...1&d=1569706979

https://www.miataturbo.net/attachmen...1&d=1569706979


And the finished fix. I reinforced the inside with some 8mmOD 1mm wall thickness 304 tubing. So hopefully it will be sturdy.

https://www.miataturbo.net/attachmen...1&d=1569706979

https://www.miataturbo.net/attachmen...1&d=1569706979