High-Purity Forming Gas

Forming gas is a shielding gas, usually nitrogen with a small amount of hydrogen. It is applied to the hot root side so that no oxygen gets there. Otherwise scale forms and the root oxidizes, which is called root oxidation. This happens especially with stainless steel; the root must stay clean, otherwise the part will rust away on the inside later. You simply blow the gas onto the back of the weld during welding, then the surface stays bright and metallic.