how does a argon tank get contaminated

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I have read a lot about how argon tanks can get contaminated wich can lead to bad aluminum welding. My question is how can this happened in the tank. Is there anyway of preventing ir things you should do to prevent your chances .
Reply:Happens before you get the bottle.  Probably no evac/vacuum before fill.Storage at home is no problem.
Reply:Make sure the pressure inside the bottle always remains above atmospheric pressure (14.7 psi).
Reply:Originally Posted by KelvinMake sure the pressure inside the bottle always remains above atmospheric pressure (14.7 psi).
Reply:If you run a cylinder completely empty and leave the valve open, there a chance that air can enter the cylinder. Lots of places tend to do this because it helps keep them from grabbing a cylinder and turning on the valve, hearing gas come out, only to find the cylinder is empty after they hook it up. If they leave the valve open, they always know it's empty. Not the best habit to get into though.What happens is that when hp gas expands as it moves from HP to low pressure, the temperature of the cylinder drops. The faster the gas goes out of the system, the greater the temp drop. Now when the cylinder is "empty" it's cold. As the cylinder warms up, the gas inside is actually less than the gas outside in volume and you get a slight negative pressure. This causes air to get sucked in thru the valve that was left open.In theory a good gas supplier will pull a vacuum on a cylinder prior to filling. That way it won't matter what gas was in there originally, or if any air entered the cylinder. They simply suck everything out and have a clean slate to work with.  Some guys simply will grab a cylinder and just hook it up and start filling. This is especially true of places that fill your own cylinder on site. If you allowed any air to enter the cylinder, it's now trapped inside when they add gas on top. That air now contaminates the gas. Contamination could also occur if for example the cylinder originally had mig mix in it. If they vac the cylinder, it won't matter, they simply relable the cyl. to match the new gas. This can happen if they need more argon cylinders to ship out and don't have enough on hand and have to use some mig cyl to make up the difference, or it could happen because a mig cylinder gets mixed up on the dock by accident. Since the CGA valves are the same for both, they might not notice when they go to fill..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by DSWAs the cylinder warms up, the gas inside is actually less than the gas outside in volume and you get a slight negative pressure. This causes air to get sucked in thru the valve that was left open.
Reply:Correct. I was a bit vague on that in an attempt to keep things simple. Thanks for clarifying that..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:No prob.  Not very often that I know enough to contribute anything...MillerMatic 252, HTP 221 w/cooler, Hypertherm PM45, Lincoln IdealArc 250 AC/DC"I'd like to believe as many true things and as few false things as possible"
Reply:The most likely culprit of "Bad" argon is some other issue when welding aluminum. Too much flow, not enough flow, poor cleaning practice, bad work lead connection, wrong electrode, wrong filler, poor welding technique. I have heard, and heard, and heard the 'bad gas' story so many times it is pathetic, as the gas seems to go bad halfway through the bottle. It is just untrue. Argon doesn't go bad, nor is it filled wrong that many times. nor do bad contaminants settle to the bottom of the tank, etc.It is just some other issue that gets blamed on the gas by people who don't know what they are doing, and lack of skill is getting blamed on the gas. Any time I am having trouble welding aluminum, I always go back to basics. I get a piece of known weldable alloy, known filler rod (stamp still visible), check label on the gas (make sure I have the right bottle hooked up), check the flow rate, pull my electrode and verify, clean with a new SS brush, wipe with acetone, check machine polarity (a/c, dc-, dc+), etc. Usually the problem goes away.
Reply:Originally Posted by walkerThe most likely culprit of "Bad" argon is some other issue when welding aluminum. Too much flow, not enough flow, poor cleaning practice, bad work lead connection, wrong electrode, wrong filler, poor welding technique. I have heard, and heard, and heard the 'bad gas' story so many times it is pathetic, as the gas seems to go bad halfway through the bottle. It is just untrue. Argon doesn't go bad, nor is it filled wrong that many times. nor do bad contaminants settle to the bottom of the tank, etc.It is just some other issue that gets blamed on the gas by people who don't know what they are doing, and lack of skill is getting blamed on the gas.Usually the problem goes away.
Reply:Great info guys. Thanks for explaining it to me.
Reply:I have a related question so I didn't want to start a new thread. I found two O2 bottles that I want to convert to pure argon, Will there be contamination issues because of the O2 being in there previously, Or does it all get sucked out in the vacuum/ fill process?
Reply:Originally Posted by Mango MattoI have a related question so I didn't want to start a new thread. I found two O2 bottles that I want to convert to pure argon, Will there be contamination issues because of the O2 being in there previously, Or does it all get sucked out in the vacuum/ fill process?
Reply:Thanks for the quick reply. I found a place to get the valve changed for 25 bucks. (20 for the valve 5 labor)
Reply:Originally Posted by Mango MattoThanks for the quick reply. I found a place to get the valve changed for 25 bucks. (20 for the valve 5 labor)
Reply:It's not common but I've personally had it before. Huge pain too as I had no idea what was going on for a good few days of trouble shooting. Tried 4 different pieces of cleaned 6061, different tungstens, all sorts of settings I knew had worked the day prior....pretty much everything you could try. Ended up just taking the bottle to a friends house and tried it on his machine. Same distinctive "lack of cleaning area" around the weld and black contaminate forming with increased amperage. Put a dessicator in line just to see if maybe moisture was it and sure enough it turned blue from trace water vapor Had two bad bottles in a row so I figure there must have been an issue on Airgas' fill line. The LWS was very nice about swapping the tanks and after I showed them in shop  a small bit of dessicant changing color in the gas flow they called up their Airgas rep to rage for trucking in dud bottles hehe.I'd have to agree with zap though that thinking "bad gas" should be one of the last things on your "stuff that went wrong" list. It might seem like it happens often due to the occasional post here, BUT, think of the sheer number cylinders that are used with no problem and that folks who had a problem will be looking for info and probably end up here. Ergo, it appears worse than it is (at least I would like to hope so lol).HTP Invertig 221-DV -- get's dragged everywhere.Syncro 200 -- "The Boat Anchor" at the lab.Lincoln 125 MIG
Reply:Originally Posted by rlitmanNope, no problem, except that you will need the valve changed.
Reply:I ran mine completely empty a number of times but I figured out a way to stop it from getting contaminated. I hooked it up to my HVAC pump & pumped it down for 30 minutes or longer then hit it with nitrogen and then bled it off and then did that same procedure again. I then kept the valve closed until I got it to my filling station.
Reply:zap i dont get this whole bad gas thing either in my 17 years of welding i have never gotten this "bad" Gas only bad gas i have gotten has came out of my rear endLast edited by WeldorWes; 11-13-2012 at 05:25 PM.Miller Xmt 350Lincoln Ln-25Ahp 200xSmith Gas Mixer AR/HTig is my Kung FuThrowing down dimes and weaving aboutInstagram http://instagram.com/[email protected]
Reply:Originally Posted by InkydoggyI ran mine completely empty a number of times but I figured out a way to stop it from getting contaminated. I hooked it up to my HVAC pump & pumped it down for 30 minutes or longer then hit it with nitrogen and then bled it off and then did that same procedure again. I then kept the valve closed until I got it to my filling station.
Reply:Originally Posted by Mango MattoI had to use the bottles that were converted from oxygen to argon on some stainless this weekend they were contaminated. The welds had what looked like tiny black crystals in it. We tried both bottles and they both gave the same result, then we switched to a bottle that we got from another vendor and it was back to pretty stainless welds.  Is it possible that they didn't pull a vaccuum before they were filled or are the bottles contaminated?
Reply:I took a couple of bottles I got off craigslist one nitrogen one oxygen and was hoping to get them filled with argon to my lws.My inside guy told me that my gas would be contaminated period.
Reply:Originally Posted by farmallSo much for being "inside". He's mistaken.No "other gas" is left after the cylinder is filled with water for hydro. It's then drained, sometimes painted, and often fitted with a new valveI look for nitrogen cylinders on Craigslist because they are cheap. I've had four of five hydro'ed and filled with MIG mix or argon. (Waiting to use up the nitrogen on the last cylinder.) No gas problems.
Reply:My guy wont fill a oxygen or nitrogen with argon, says he's had to much issue in the past.He's been doing it for 25+ years. Not saying your wrong Farmall but my guy seems like a straight shooter and it's just money he's not making if he doesn't fill. He usually just swaps bottles with me.
Reply:it comes from people leaving the valves open for after they run out, then LWS just fills the tank off a manifold and sends it back it out. Happens all the time from one LWS in particular in my area...Constant Current Weldor.