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  • TIG welding question?

    Here is the deal, I had bought a new gas cylinder (125 CF) from Praxair. It was filled up with Stargon VS, for those that aren't familiar with it, It's a Tri-Mix gas that is 82% Argon, 10% Helium and 8% Co2. This gas is for MIG.

    I used up that tank, and decided that I wanted to get that same exact tank filled up with 100% Argon. Prior to getting it filled up, I make sure to let all the pressure out of this tank, So it would be empty before filling with the Straight Argon.

    Now what is happening, is I am getting porosity in my TIG welds.

    Using Stainless Filler, I'm getting porosity always at the start of a bead and a very little amount later on. Then after it seems fine.

    Using ER70S-6, I'm getting porosity continuously and can not make a sound weld.

    Before this tank of gas, I was renting a 100% Argon tank and it was working fine. I am sure somehow the Carbon Dioxide (Co2) that was in my tank before is messing with my welds. Could this be possible.? I just want someone to verify that this is the case. I'm sure it is.

    I've also tried turning up the CFH, turning it down. No difference. My metal is clean and taken down to bare metal with no mill scale. Usually I have my CFH around 13. I have even taken it down to 8 CFH with no visual problems. But I usually set it from 13-16 CFH.

    Thanks.







    And my Sync 200.

    Last edited by myistar; 05-08-2009, 06:08 PM.

  • #2
    I've also heard that Co2 will start consuming the tungsten, but my tungsten is still sharp as a tack. I'm gonna go snap a picture of the weld piece.

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    • #3
      It didn't consume the Tungsten for me just frustrated the crap outta me.

      New bottle and all was good.
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      • #4
        Originally posted by Broccoli1 View Post
        It didn't consume the Tungsten for me just frustrated the crap outta me.

        New bottle and all was good.
        So it is the gas tank, and what was in it before, cause i'm sure the helium won't bother it, and neither will the argon that was in it before, has to have been the Co2?

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        • #5
          I guess it is possible that the welding store filled the tank with contaminated gas? or filled it with something other than straight argon? I guess, come Monday, I'll call them and say something is wrong with this gas, and get them to refill it again, hopefully for free.

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          • #6
            Dirty argon is the problem due to the co2 residual in that tank.
            The tank needs to be vacuumed out before filling with argon. A dedicated argon tank would be better.

            Try not to completely empty the tank before refilling, keep the valve tightly closed.
            An empty tank with the valve open can suck in atmospheric air due to temperature changes, and will contaminate the tank........

            mike sr
            mike sr

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            • #7
              It's a Tri-Mix gas that is 82% Argon, 10% Helium and 8% Co2. This gas is for MIG.

              I used up that tank, and decided that I wanted to get that same exact tank filled up with 100% Argon. Prior to getting it filled up, I make sure to let all the pressure out of this tank, So it would be empty before filling with the Straight Argon.
              Atmospheric pressure is 14.7 psia and 0 psig. And when you vent a tank, you almost equalize it to atmospheric pressure, but not quite because the gas cools on rapid venting and will regain some pressure upon standing. So lets say after it warmed back up, there was 25psia (10.3 psig) in it.

              This means there is 20.5 psia Argon, 2.5 psia Helium, and 2 psia CO2. Now add enough Argon to bring it to 2000psia and you have:
              1995.5 psia Argon (99.775%)
              2.5 psia Helium (0.125%)
              2 psia CO2 (0.100%)

              Is a tenth of a percent of CO2 enough to screw things up?

              Well, a general standard for industrial grade Argon is:
              99.997% purity
              less than 0.00050%O2
              less than 0.00105% H2O
              less than 0.00200% N2
              less than 0.00010% CO2

              Note that the limit on CO2 is less than one tenth of the limit on water and one fifth the limit on oxygen. It's that reactive.

              What you've got in your tank exceeds the allowable amount of CO2 by a factor of 1,000. Mathematically, it's only slightly better than using Ivory soap (99.440% pure).
              Last edited by Bodybagger; 05-09-2009, 03:26 AM.

              80% of failures are from 20% of causes
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              • #8
                Originally posted by myistar View Post
                So it is the gas tank, and what was in it before, cause i'm sure the helium won't bother it, and neither will the argon that was in it before, has to have been the Co2?
                Its just a contaminated tank, most likely due to the gas in it before with the co2.

                A new tank of argon will fix you up...........

                mike sr
                mike sr

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                • #9
                  Thanks all for replying to my question and giving me technical reasons why it happened, I appreciate the great help. So, come Monday i'll call around and see if anyone can vacuum out a tank and clean it out for me. But most likely I'll just try to purchase another 125 CF tank that is brand new and get it filled with 100% argon. THANKS!

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                  • #10
                    I would talk to them on it, maybe they will trade for another bottle with argon as the one you have will be OK for a tri mix gas......... worth asking them about it..

                    mike sr
                    mike sr

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                    • #11
                      not sure if it was mentioned because i'm in a huge hurry and didn't read the entire post, but one thing i learned the hard way is that C02 leaves and oily residue abd contaminates any tank it's been put into, this could be causing some contamination of your argon. Just a shot in the dark, but it's talked about quite frequently at my LWS.
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                      • #12
                        Originally posted by turboglenn View Post
                        not sure if it was mentioned because i'm in a huge hurry and didn't read the entire post, but one thing i learned the hard way is that C02 leaves and oily residue abd contaminates any tank it's been put into, this could be causing some contamination of your argon. Just a shot in the dark, but it's talked about quite frequently at my LWS.
                        yeah, i told the people there that it had MIG gas in it, and they didn't say anything about it, the guy filling it up knew that he was putting 100% argon in it, but the other guy standing around seemed more knowledgeable about things, but i didn't think he was aware that straight argon was going in it. but now i know of this situation and won't let it happen again.

                        what i'm most likely gonna do is try to just switch this out with another tank of straight argon, and let them have this one. i wanted to keep it cause it was pretty much brand new, and this is the tank that I bought from a local Praxair Store, and since I bought it, I wanted it to be in the best shape it could of been. I didn't want to buy a bad looking bottle like most stores have with scrapes all over it. Thanks.

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                        • #13
                          Originally posted by myistar View Post
                          I didn't want to buy a bad looking bottle like most stores have with scrapes all over it.

                          I would have never thought of that!
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