Tig welding stainless steel exhaust

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I can't help but ask, why did I go through the trouble of using solar flux b welding my 409 stainless exhaust pipe when every car show that I watch on TV welds their stainless steel headers and exhaust both 304 and 409 without back purging or using solar flux b.  It makes me wonder if it is really necessary to back purge or use the flux.  Is the exhaust pipe strong enough that they don't really worry about cracking or a little bit of sugaring?  I can't help but ask this question.  And yes I understand that the users of the Welding Web hold themselves to a higher standard to those Yahoos on TV, but as said to Clint Eastwood, ids gotta know.
Reply:I purge mine because anything worth doing is worth doing right and why go through the expense of stainless if your going to start it's life as a exhaust compromised. Jmo
Reply:Back purging is not always necessary. The only time it's necessary is when you're getting sugaring. Before it sugars it will have a light gray scale build up but it will brush off and be silver underneath and will not rust. It all depends on the joint type, and how its being welded. It's always a good idea though, and definitely for a beginner.I weld very high quality stainless exhaust components every single day, all day, and I'm willing to bet most everybody else who chimes in has only dinked around with this kind of stuff on occasion, not put down thousands of feet of weld.Also it's worth nothing that everybody says you have to purge and they don't even know how to properly do so.Last edited by MikeGyver; 02-06-2014 at 07:59 PM.Welding/Fab Pics: www.UtahWeld.com
Reply:Originally Posted by MikeGyverBack purging is not always necessary. The only time it's necessary is when you're getting sugaring. Before it sugars it will have a light gray scale build up but it will brush off and be silver underneath and will not rust. It all depends on the joint type, and how its being welded. It's always a good idea though, and definitely for a beginner.I weld very high quality stainless exhaust components every single day, all day, and I'm willing to bet most everybody else who chimes in has only dinked around with this kind of stuff on occasion, not put down thousands of feet of weld.Also it's worth nothing that everybody says you have to purge and they don't even know how to properly do so.
Reply:BTW, that wasn't directed at you, showdog, I was typing my post before yours was up.A lot of people do a great job, but there's also an insane amount of hearsay misinformation that gets passed around on this specific topic.Welding/Fab Pics: www.UtahWeld.com
Reply:Mike if welded automotive exhaust as much as you do I might figure when I could get away without any purge but for what I do I figure it's cheap insurance.  I agree a lot of people don't have a clue how to properly purge and typically overthink it Imo. I looked at your slide show and can say I'm impressed, keep up the nice work.
Reply:OK, I'll ask since I'm still just learning; What's purging in welding?
Reply:Mike Gyver, just wanted to say you make very nice welds
Reply:Originally Posted by jlamesOK, I'll ask since I'm still just learning; What's purging in welding?
Reply:I've never back purge a stainless exhaust I probally should lol I've done a few one is 4yrs old now on a diesel 4x4 that they guys takes in the bush almost daily and haven't had a weld crack or fail .
Reply:Thank you 92. Does the gas remain sealed in the vessel during welding or is it flowed into it during welding?
Reply:I just built a full 3" stainless dual exhaust for my son's 69 Camaro from some salvaged hospital piping so I had to make about 20 cuts to get the angles and curves.  Used V bands on both sides of both mufflers for easy removal.  Didn't want to spend the rest of my life tigging it, so I stainless mig'd all the joints (308) without purging.  Came out just fine and I doubt the 427 big block will notice the difference in welds.  I flap-wheeled all the joints that would be visible until they were flush and hard to see. I guess my son will let me know if it cracks and falls off someday.  As usual, lots of different ways to do things.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:I only purge headers/manifolds.If you are using 409 stainless you may as well use er70 filler as well.
Reply:Originally Posted by jlamesThank you 92. Does the gas remain sealed in the vessel during welding or is it flowed into it during welding?
Reply:jlameswhen you purge you will have a flow of gas going thru it....usually everything is sealed up with tape or fixtures and you keep a light flow after you have given time for all the oxygen to get gone. If you try to seal up entirely you always run the risk of oxygen getting sucked into the weldment during work so it is just cheap insurance to keep a flow going in....plus you always have the joint itself open to some degree so.....
Reply:Thanks T. Did a bit of reading on it this afternoon also to help me understand. Starting to understand.