| 摘要 |
PURPOSE:To improve piping quality by removing a surface oxide film, regulating surface roughness under a specified value and using reducing gas containing the specified quantity of H2 gas in inert gas as interior shielding gas on the steel pipe interiors in the vicinity of a weld predetermined zone. CONSTITUTION:On the steel pipe 1 interiors, the surface oxide film is removed and the surface roughness is regulated to <=Rmax5mum and the reducing gas containing >=5vol.% H2 gas in the inert gas is used as the interior shielding gas at the time of welding. When stainless steel pipes 1 are subjected to TIG welding with the interiors shielded by using a W electrode 2, there are three kinds of welding scales produced on a steel pipe interior side welded zone, namely, oxide scales produced on a weld heat-affected zone 3, oxide scales produced on weld metal 4 and spotlike floats 5 produced in the spotlike form on the weld metal 4. In order to prevent these oxides from being produced, the H2 gas is mixed in the shielding gas and further, it is effective to remove the oxide film on the steel pipe surfaces. By this method, even in the case of the small diameter pipes, excellent corrosion resistance can be given to the weld zone. |
