Do Those TV/YooTubers Backpurge Their Stainless Exhausts Like All The Textbooks Say You Should?

Metal Shop
#1

I’m sure you’re been there, watching the Yootoobs and/or TV shows where the Good Ol’ Boys whip up a [whatever, exhaust is a fav] out of stainless tubing and there’s no discussion whatsoever about encasing the entirety of the stainless in a nifty inert atmosphere. To all appearances, the tube is cut on an abrasive saw, jigged up in the chassis, and “zipped up with the TIG gun by my buddy Zeke!”…
But everything I read tells me “Ya gotta backpurge stainless tubing or it’ll sugar”. More reading tells me this means the stainless will react with oxygen once heated, creating a crystalline structure in the joint which resembles (you guessed it!) sugar. Apparently this is “bad” and reduces the integrity of the weld by magnitudes. These shows make it look like it does not really matter, and they get away without doing that all the time… So why don’t these shows touch on it? And how the heck would you do that, anyway?

Well, I don’t know why they don’t really talk about it. I assume because they assume it’s common knowledge. Also, not very romantic and hard to get “action shots” of. But I finally bumbled across such a YooToob where the host not only swears to have spoken on it before (I haven’t seen it, but then, I’m not a regular viewer of said show) but he’s willing to show you how he does it.
Interest piqued.
Here ya go.


(At the point where backpurging is discussed…feel free to rewind to the beginning to see the whole episode if you got that kind of time).
2 Likes
Occasional welders wanted
#2

You can use a flux as well. That will keep it from oxidizing.

#3

I suspect in the case of exhaust, not being more than a self supporting, trivially pressurized, gas tight system, the loss of integrity from sugaring the inside is generally not of concern to the function or life of the exhaust.

1 Like
#4

If you are TIG welding it then yes you want a purge. Stainless steel will react to oxygen and give you sugar if you are TIG welding it. At the same time if you are doing a full pen butt weld then your weld will concave on itself. The purge acts as a counter force for the weld. The steel is a liquid and thus has viscosity, if there is no counter force the steel will drop on you.

With this being said you do not need a fancy setup to do a purge. You just need a second argon line going into the tube, a relief on it so the argon tube doesn’t pop of and something to seal the tube. Plenty of people use aluminum foil to cover the tube, others will use blue painters tape as well. If you do use painters tape make sure it is far enough from the weld so it doesn’t catch on fire.

#5

I loved Roadkill and all the silliness involved. I think there’s a “brotherhood of the been here done that” you can feel with every breakdown and sketchy solution. Finnegan’s channel is more serious - build it, drive it stuff, which I like even better, frankly. Except the most recent episode where he bought a “ready to drive across the country” old race car hauler truck that had old tires and rusted tanks. It was awesome.

#6

Ok, that was great, as was the 90 minute detour in the labyrinth that is youtube. Thanks, I think.

2 Likes