Welding technique for forming passive chromium oxide film in weld and gas feed system for welding

摘要

Welding of material such as a piping using ferrite system stainless steel, in which a back sealed gas used for conventional welding is switched from argon gas (or a hydrogen gas/argon gas mix) to an argon gas to which an oxidizing gas is doped at the time of forming a chromium oxide passivation film. Welding conditions are set at the temperature in which the inner surface of the piping does not melt at the time of forming the chromium oxide passivation film. The temperature of the welding piping is set uniformly between welding conditions in conventional welding and welding conditions at the time of forming the chromium oxide passivation film, and in order to replace gases used with conventional welding with gases used at the time of forming the chromium oxide passivation film. A cycle of one round or more is performed under the welding conditions for forming a chromium oxide passivation film, thereby, to form the chromium oxide passivation film on a weld in concurrence with welding.