Argon is a colorless, odorless and chemically inactive, or inert, gas. It is commonly used as a shield gas or for purging interior weld joints in the gas tungsten arc welding (GTAW) or tungsten inert gas (TIG) welding processes.
Welding Grade
Welding grade argon typically has a purity of between 99.996 and 99.997 percent, depending on the supplier. It contains between 5 parts per million (ppm) and 7 ppm of oxygen and a maximum of 40 ppm of other impurities, such as water and carbon dioxide.
High Purity
High purity argon has an even greater purity, up to 99.999 percent. It contains just 2 ppm of oxygen and 10 ppm of other impurities; the addition of gas purifiers during the purging process can reduce impurities to the parts per billion (ppb) level.
Importance
The purity of argon is crucial to the welding process --the higher the level of impurities -- oxygen and water, in particular -- the more oxidation takes place on the base material after welding. Stainless steel is resistant to oxidation at room temperature, but much less so heated to very high temperatures.
