SS Shielding gas for GTAQ

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I am curious as I just finished a tubing project ( I posted it in another thread) and I used mild steel as I could not get SS. But while I was doing it I wondered to myself what I would have done if I was using SS? Would I tape up one end and backpurge from the open end? I have done SS without backpurging and it came out fine. It was a SS food vending surface that was wiped constantly. I never saw any rusting after the fact. It would be nice if my sandblasting cabinet was a purge chamber. But I wonder at what rate you should exhaust a chamber? Maybe at less volume than you are feeding in your gas? Is a positive pressure better for it?HmmmmLincoln Power Mig 210MP MIGLincoln Power Mig 350MP - MIG and Push-PullLincoln TIG 300-300Lincoln Hobby-Weld 110v  Thanks JLAMESCK TIG TORCH, gas diffuser, pyrex cupThermal Dynamics Cutmaster 101My brain
Reply:I belive you are correct, damper the exhaust to create a small back pressure.   I've seen an oil filled bubbler arrangement on the exhaust of an inert welding chamber.  It is like a fermentation lock used for home brewing.  The gas can escape through the liquid, but air cannot back flow into the chamber.  A simple way to rig this, also from the brewing industry, is to simply run a hose from the top of the chamber, down to the floor, with the end submerged a few inches in a container of oil.  Oil instead of water since you don't want water vapor to back flow into the chamber.  Adjust the deep of the oil and the tube to change the amount of back pressure.Also with Argon being heavier than air, it may make sense to pipe the inlet low on the chamber, and the outlet at the top, to allow the argon to push the air out.  This may work better if the argon is dispensed very gently, maybe though a diffuser like a large gas lens (tungsten hole plugged), so turbulence doesn't mix up the argon and air so much.Once the inital purge of the chamber is complete, you may be able to greatly reduce argon flow to maintain the inert atmosphere.You can tell if the atmosphere is good (inert) by checking the discoloration on a stainless steel fusion weld.  See this link for an example of SS color and Oxygen content.  http://www.intercononline.com/welding/ypurge.htmKeep the chamber small as possible, unless someone else is buying your Argon for you.