Gas choice for SS welding

[swamper8]

Welder: Hobart Handler 140
Current fill: 75% Argon/25% CO2

I have some stock exhaust downpipes to weld on. Car is an Audi, some have guessed 409 SS but I haven't been able to confirm. At any rate, I've read in my manual that the tri-mix is recommended but my AR/CO2 tank is new and would prefer to not trade it in. Is the tri-mix needed to maintain weld strength or only to maintain the non corrosive/rusting characteristics of SS? I don't want weak welds, so I'll get tri-mix if that's the case. However the exhaust is not polished and not seen, so if it should tarnish/rust a little from using the AR/CO2 it won't bother me.

[old blue]

Are you trying to perform a repair, or just rig it for short term? Is this your vehicle?

It's going to rust like crazy and ultimately fail. Depending on the degree of thermal expansion of the components at the joint that failure could be a long time in coming or not too far off.

I'd explore mechanical clamping if I couldn't do a proper weld.

[swamper8]

Yes my vehicle. It's on a downpipe which gets very hot. so no moisture but it will see high temperatures. I can get the right gas without a problem, but only want to do so if the correct shielding gas will contribute to the weld strength, not just asthetics. (i.e. surface rust etc) I'll be cutting the pipe and re-positioning it.

[calweld]

Why would you have to trade in a full bottle of 75/25? Just rent another bottle with tri-mix for as long as you need (or till you run the bottle out). Shouldn't cost more than $5 a month or so .....

[swamper8]

My local supply place requires $100 deposit. Plus they generally "encourage" people to just buy the bottle. Probably the whole process of printing/mailing a bill each month, then receiving and cashing the check just isn't worth it to them. I think each month my bill is like 4 and change.

[Hotfoot]

My local supply place requires $100 deposit. Plus they generally "encourage" people to just buy the bottle. Probably the whole process of printing/mailing a bill each month, then receiving and cashing the check just isn't worth it to them. I think each month my bill is like 4 and change.

(It helps if you put your location in your profile...others might offer suggestions on an alternate supplier). My LWS has no deposit, no contract, just $4.00 a month, and their gas is very reasonable....Have you checked any others..try a Mom & Pop, if there is one around. I've had no failure on a number of SS parts I have done with my regular wire and C25....the weld rusts...but so would it if this was regular steel pipe.

I have a feeling you want something to show off when finished, so, with all the other costs associated with that new turbo install, I say ...get the gas! :)

[swamper8]

no no, just the opposite; no one will see this, it's not for show. Up near the motor so some rust doesn't even matter. And no new turbos (yet!) . Just strictly wondering about weld strength. I do not want to weld these up (no matter what combo of wire/gas) only to have them fail and leak after 100 heat cycles. Taking the DP's out is like a 3-4 hour job on my car, everything's packed in like sardines.
I'm in West Springfield, MA and will take your suggestion on trying some other suppliers. I have only ever gone to the one, I'm not sure why exactly. Never had the need for multiple different gasses until now. This is my first MIG, before that I had a 1979 cybertig and just did steel projects with it. (never changed gasses)

[Jeff9329]

Are you switching to some 024 SS wire? I guess you are since you are asking about the gas, but you didnt say.

The tri-mix will reduce peripheral material heating and distortions, but depending on the weld type, I doubt this matters too much. Im not sure about the shielding, but I dont think that's an issue.

If you dont want to spend the money, I wouldnt use the tri-gas or SS wire. You will have a rusty weld bead in the future, but no one will see it. When fabbing exhaust systems, there are inevitably pieces of carbon steel or aluminized steel mating to SS pipe and the carbon steel welds always hold under extreme running.

[epjohnso]

I'm definitely no expert in gases for Stainless Steel, but someone else pointed me to this site awhile ago, and it gives a good account of what to use for welding SS, and what he recommends. Basically, all he said was Tri-Mix is marketing hype, but so see what this guy says.
http://www.weldreality.com/MIG_welding_gases.htm

I already had 100% Ar for Aluminum, so it made it an easy choice for me.

[Jeff9329]

I just did a SS exhaust project a few weeks ago using AR. The welds looked shiny & beautiful although their shape was terrible. I was welding 1/2" 304 rod bent to 3" radius (a separate nightmare) to 409 SS tubing as part of a factory Dodge exhaust hanger setup. Awfully frustrating, but it worked after burning holes like crazy in my test pieces.