Does anyone here have any experience mig welding stainless steel tubing.What kind of gas do you use,argon or co2 mix?I need to make some tubes with an inch and a 1/2 offset so my exhaust manifolds and mufflers line up.I bought the tubing and took it to a welder/fabricator friend of mine a month ago.Took us about 30 minutes to cut and tack up a prototype piece.went home and checked it and its perfect.Now over three weeks later he doesn't even have the first piece tig welded let alone the other pieces cut,so tommorow I'm going to get my chit and do it myself. I have access to several mig welders,one set up with argon gas and silicone bronze wire,would this work or do I need to buy some special wire for stainless.Any input would be appreciated.

You want stainless wire first off. I have never Mig welded stainless I always used a tig. However Mig should work fine. If you can get make some plugs for the ends then you may be able to get gas to stay inside and get a better weld but again not sure if you can do that with MIG. MAKE SURE you have NO burrs or dirt on it. Good luck

Jon

If you don't want the weld joint to leak, you are better off with TIG. It's also easier to TIG weld ss, unless someone gets everything adjusted properly on a mig welder. Spend some time getting good fits, no gaps, and it makes things much easier.

TIG welding ss usually uses argon shield gas. MIG welding ss usually uses a mixed gas. Where I use to work we used a mixture of argon-helium. The type of shield gas used really changes the way it welds drastically.

I personally think you should leave it to someone who has done it before. If you can handle the cutting and fitting, do it for him, that takes most of the time anyhow. Do a good job and the welder will appreciate it. If you were talking about capping the tubes, you must be planning on purging the inside of the tubes to improve the weld joint. All I usually do is tape up the ends with a purge line in one end and holes to let the gas out on the other (if the part isn't so short that it will burn the tape). You don't want to really pressurize the part, just replace the air inside with the shield gas.

Good luck!

Thanks for the input,I'm going to get my tubing cut and set
up then try to find another welder first,welding it myself will be my last resort.

Tig. Argon. 2% thoriated tungsten ground to a sharp point. Same metal filler wire (use of 304 is okay on any 300 series stainless, but it is best to use identical alloy).

If your joints are tight, then you don't NEED to use shield gas inside but if you have an extra tap for the purge line, then use it. If not, don't worry about it (it will just make white flakey chalk stuff inside that blows right out).

I agree that Mig would be questionable unless you are a good Mig hand (I'm not. I can Tig just about anything so well I never really learned how to Mig).

Wear long sleeves, and make sure you have good cross ventilation or else the argon will stay in your pores and stink for 4 days (gives me a raw throat).

mcollinstn is right on the money.
I spent four and a half years welding stainless. The vast majority of the welds had to be water tight too. It's not hard. Just be sure the parts mate squarely and take your time, pay attention to the details.
Best thing to do is practice on some scrap pieces of the same material you'll be welding together. Practice on getting the heat right. Practice your technique. If you use a wire brush, be sure to use nothing but a STAINLESS STEEL wire brush.
When you actually do get down to welding, the finished welds will be a light grey color. Don't worry, it'll polish out.

Good luck.

15 years welding process piping {High Pressure steam}.....Get a good Tig guy to weld it. No need to purge. I always Tig pipe. You can use Mig for production welding.

Bird Dog No need to purge S.S.?You must know better then that!

The only time I had to purge prior to welding was on a 22 gage S.S. float tank. It was too small to polish the inside and purging controlled the inner burn pattern. Also helped control burn-through.

Beyond coloration and burn-through why else would you purge S.S.?