I want to do my own SS exhaust on a 51 Chevy truck I am building as a Hot Rod. I do have a Mig & TIG welder and did take the Lincoln welding class a few years ago so learned the importance of purging backside of SS. Over the past few years I have seen a number of magazine articles showing guys welding SS but none have ever purged the tube based on pictures shown and no mention of the importance of purging mentioned in text. I know these "experts" were doing it wrong and I will be sending the editors some info on this but needed more than just my "opinion" to back up my Letter to the Editor.
At Lincoln I had access to some nice dual feed flow regulators but I wasn't ready to buy another regulator if I could manage it so I set up a test. I cobbled together some vinyl tube and did three tests on some 2" SS tube. For all three welds I used a Gas lens and #8 cup with 100% Ar shielding from the TIG torch.
I did one weld with no purge. One test with a 100% Ar purge using a borrowed tank of gas. The final test was using my Mig 75/25 Ar/CO2 gas. I then cut the tube open to see the results.
The results speak for themselves. I feel the 75/25 purge gave a very acceptable result and if my general welding skill improves to what it was in the past I am confident my Ss exhaust will outlast the stuff done by the "experts" in the magazines.
Outside of tube (yes too hot or cold and inconsistent but no corrosion of SS) I think all three welds look similar to untrained eye
![Image](http://i44.tinypic.com/359wpsg.jpg)
Inside of tube with No purge
![Image](http://i40.tinypic.com/fxuy3r.jpg)
Inside tube 100% Ar purge
![Image](http://i42.tinypic.com/acv287.jpg)
Inside tube 75/25 Ar/CO2 purge
![Image](http://i41.tinypic.com/do467l.jpg)
To me the 75/25 looks as good as the 100% Ar and other with less than $10 in various brass fittings and some vinyl tubing, I think I got something that will certainly be "good enough" to quote Jody, for a non-critical application.
Your thoughts and comments welcome.