Backing gas
Backing gas is a shielding gas that protects the root side from oxidation and scale. It is used when welding titanium, nickel-based alloys, and stainless steel.
Physical-Chemical Working Principle
Backing gas forms a protective layer on the root side of the weld that keeps oxygen and scaling agents away. It can be inert (like argon) or slightly reducing (like carbon dioxide).
Metallurgical Relevance & Welding Risks
Without backing gas, oxides form on the root, leading to scaling and cracking. For titanium and stainless steel, this can cause severe hardness at the weld line, which impairs mechanical strength.
Workshop Practice & Instructions
Use backing gas at a flow rate of at least 10 liters per kilogram of welding material. Make sure the gas is directed directly to the root side and applied for at least 3 minutes. For titanium and stainless steel, a carbon dioxide mixture (approx. 90% argon, 10% CO2) is recommended.