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Old 03-22-2006, 05:46 PM
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TIG Welding Stainless Exhaust

I am in the process of building a S/S exhaust system for my '32 Ford roadster. In my practice welds (Miller, Syncrowave 180SD, TIG welder), I am getting quite a bit of "dross" or slag on the inside of my welds. The outside looks pretty good, but I am concerned that this slag on the inside (beyond reach to it grind out) will affect the performance of my engine.

I tried "purging, or using backing gas" on the inside of the pipe, and this seems to help a bit. I put together a simple shop-made purging system, but really do not know how much CFH to push into the pipe to create the optimal welding environment.

Any suggestions on purging, and/or general stainless pipe welding techniques for producing a solid and pretty exhaust system would be appreciated.

Thanks

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Old 03-22-2006, 06:03 PM
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I just finished a TIG welding class using a Miller Aerowave and I used everything to try to stop the "dross" on the backside of the weld of stainless. So I asked the instructor about the problem, and he said it has to be purged with gas and preferrably Helium. The Helium creates a more intense localized heat, evidently.
He said you have to experiment a little with the amount of gas pressure and gas exit, but when you get it right little or no "dross" will be present. Also, he said to use very little filler rod, mostly fusion weld. He used to be a welder for a semi conductor company and all their machines are SS with high purity welds.
And I assume the filler rod should be the same composite as the tubing. Or would a rod with more nickel do a better job? Hmmm, I'll have to research that one!

If you get a better weld, let us know - always trying to improve my welds!
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Old 03-22-2006, 07:04 PM
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Thanks for the info. I will try the "light on the filler rod" technique. Sounds reasonable to me. I am using Argon as my back gas, since this is what I use for my shielding gas. As for the filler rod, all I can find is ER308L, and I am welding 304 stainless. The guys at my welding supply store say that's OK, but I still have my doubts. I will post a reply when I have a chance to experiment a little more.

Buster
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Old 03-22-2006, 07:50 PM
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Buster

Your on the right track with the back purge. Make sure to seal the ends of the pipe with tape and purge at around 10 cfh for ten minutes( this forces out the air so only the argon remains inside ). Purge from one end and exhaust from the other. Use a 1/4" exhaust hole and reduce the purge to around 3 or 4 cfh prior to welding. The 308 wire is OK. Use minimum amount possible to reduce dropthru. A little practice and it will look fine.

Oljoedog

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Old 03-22-2006, 08:15 PM
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I was a welder at a stainless steel pipe and tube mamufacturer for 30 yrs,and i have never seen slag on a stainless pipe. You either have burned weld or sunken weld. If you have a good fit you can run a low amp bead to seal the crack then fill with gas and do a full penetration weld. You can just duct tape the ends and leave a small opening on the exit end. Have your joint lower than the exit hole since argon is heavieer than air. 308 wire is correct for type 304, the 308L is just a better grade made for 304L metal.
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Old 03-22-2006, 08:28 PM
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Thanks to the input by Oljoedog and clintb I've learned some more!!
I've seen the inside condition of the weld that Buster is referring and I know it's not dross or slag but it's the best description for this problem, I believe.
I suspect it's some sort of oxidation such as what happens to aluminum when it's not properly cleaned or gas shielded, but I'm only guess here.
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