We had a carbon steel pipe weld that was full of porosity. We then brought the Ar bottle into the shop to test. When welding on CS, it would always result in porosity. Tested same gas on Stainless and no problem, no porosity. Switched out to several other argon bottles and both the CS and SS were fine, with no porosity. Read that nitrogen can be used for SS, but may cause porosity in CS. Not able to test the gas in the "bad" bottle at this point to check if the gas is contaminated. But if anyone knows what else in the gas could cause porosity in CS and be fine with SS, would welcome any suggestions. During the tests, the only thing changed was the gas bottles, other changing between CS and SS, so we know that one bottle is causing the problems. Any thoughts??? Thanks in advance