PURPOSE: To eliminate the difference in the corrosion rate between a steel base metal part and a weld part and to prevent selective corrosion in a welded steel pipe by incorporating Cr into a weld metal while it is not incorporated into a steel for a line pipe or the like.
CONSTITUTION: The chemical compsn. of a steel base metal part in a welded steel pipe is formed of, by weight, 0.01 to 0.1% C, 0.1 to 1.0% Si, 0.1 to 2.0% Mn, 0.1 to 0.3% Ni, 0.01 to 0.05% Cu, 0.01 to 0.05% Nb, ≤0.01% S and the balance Fe with inevitable impurities. The chemical compsn. of a weld metal in a weld zone is formed of, by weight, 0.01 to 0.1% C, 0.1 to 1.0% Si, 0.1 to 1.0% Cr, 0.1 to 2.0% Mn, 0.1 to 0.3% Ni, 0.01 to 0.05% Cu, 0.01 to 0.05% Nb, ≤0.01% S and the balance Fe with inevitable impurities. The content of Ni in the weld metal is preferably increased compared to the content of Ni and Cu in the base metal part by about ≥0.5%.
OGAWA HIROYUKI
SHINADA KOICHI
TAMEHIRO HIROSHI
