Need backpurge for stainless exhaust TIG

I need to weld an O2 sensor bung into my new stainless exhaust. I could get it done at an exhaust shop, or I could do it myself at DMS now that I’m signed off on TIG. Do we have backpurge bungs?

Is this a job that you would recommend someone at my skill level to perform? What does something like this normally cost at an exhaust shop, and do you have recommendations?

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You don’t need bungs. We have a backpurge setup, You can block the ends with tape or anything else just to keep a trickle of gas going through it.

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Perfect! Sounds like a plan to me.

Is a bung weld something you would recommend for someone at my skill level? I can’t afford to screw up my exhaust :sweat_smile:

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How else do you expect to learn? You have to mess stuff up to learn sometimes. Maybe buy some scrap to practice on first. I say go for it.

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Get some stock to practice on that’s the same stainless type (if you don’t know, get some 302) in the exact same thickness. The main issue for new players in Stainless and mufflers is that that thin wall tube goes up in smoke really fast. You’ll blow through if you’re not careful, but you need 100% pen to get strength out of the joint so it’s a balancing act. The other hard part is welding on a round. If you’ve only welded flat, try welding out of position on thin stuff and you’ll see why people charge good modey for it lol.

Look up “sugaring” and see make sure you work on getting your regulator setup so that you have complete argon coverage both sides of the joint. Also, just a heads up, if you set the second regulator pressure (flow rate) too high they you’ll blow out your welds. You want a really low flow rate like ~5CFH max.

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What everyone else said… get you some scrap to practice on. Also, Miller makes a good app to use as a starting place for weld parameters. You can enter in material, thickness, electrode, etc. and it’ll tell you how to set the machine up. On your scrap I’d start a little lower than recommended (say 80% rec. amps) and work your way up and past 110%. See what each test bead does to the penetration. Basically just what everyone else said… play with it.

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Definitely practice on SS scrap. The weld isn’t structural, just needs to be gas tight, if its ugly don’t take any photos and none of your buddies will be the wiser.

It will rust if you don’t passivate it. I made some SS tomato cages a few years and had heard of passivation but it didn’t seem necessary, by the next year all the welds had surface rust. Also only use SS wire wheels to clean the weld or you will introduce more iron that will rust. My understanding of passivation is you basically use an acid to quickly corrode and remove any iron oxide on the surface of the weld.

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Do we have a passivating kit at dms? What is the process required? I’m reading in finding that citric acid can be used after degreasing, but I’m not finding specific details.

I picked up some citrisurf 77 after digging around. Hopefully that will suffice, followed by a rinse to neutralize the acid.

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If you need citric acid look in the canning section of Walmart. It is there