Purging?

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I keep hearing about purging when welding tubing and such, and after reading the stainless steel thread  I was wondering if you all could explain!1- when do you do it2-how 3-whyI've been making my own presumptions(which always gets me into trouble) on this but would like to hear from all the experienced welders here."Lack of planning on your part does not constitute an emergency on mine"However "lack of planning on my part may constitute an emergency on yours"
Reply:Purging displaces the oxygen inside the tubing to keep it from sugaring(surface crystals) when you use the T.I.G. procedure. You purge the inside pryor to tacking and welding. You tape the ends, or use dam paper, tape the bevels and peel back to tack. Peel the tape as you weld around as you go.Hope that helps you. It would be a lot easier to comprehend if you could see it done first hand. Personaly, I use a tool an oldtimer pipefitter showed me how to make an use with Dam Paper. (thats another thread)If it's HOT, Don't touch it
Reply:You also purge your gas hoses to elimainate air prior to welding.DennisThermal Arc 185-TSWMillermatic Challenger 172VictorO/AAtlas Craftsman 12 by 24 LatheEsab PCM-875Wholesalem Tool Mill-Drill
Reply:so you keep the air in the tube while you weld it to eliminate contamination from air, right?   Is this just for Tig and stainless, or just stainless or just Tig?"Lack of planning on your part does not constitute an emergency on mine"However "lack of planning on my part may constitute an emergency on yours"
Reply:Originally Posted by stumpsterso you keep the air in the tube while you weld it to eliminate contamination from air, right?   Is this just for Tig and stainless, or just stainless or just Tig?
Reply:Originally Posted by Root Dog...an oldtimer pipefitter showed me how to make an use with Dam Paper. (thats another thread)
Reply:you get some nasty blowout on the tube
Reply:Originally Posted by stumpsterThis must be what I noticed when welding my cart up! I had some drill holes in the tube I was using so I decided to fill them and grind it off so you couldn't tell they were there. I noticed on a couple of them that as it would cool it would pressure out like a little blowhole and leave a tit in that area, only some did it so I guess now it would have been the ones that I did last sealing the tube completely.  Does that sound right?
Reply:When you are getting ready to mig weld and you turn on the gas, how do you know the gas has worked up through the hose to the nozzle when you first start?   Thanks!!!
Reply:Originally Posted by irocWhen you are getting ready to mig weld and you turn on the gas, how do you know the gas has worked up through the hose to the nozzle when you first start?   Thanks!!!
Reply:Generally, you need to set or verify your flow at the gauge anyway, and this has to be done while gas is flowing.  That is more then sufficient to also purge your lines.
Reply:Thanks guys!!!   Won't be long and I might get brave enough to try the mig out.