METHOD FOR MANUFACTURING SPIRAL-SEAM-WELDED STEEL PIPE BY GAS SHIELDED ARC WELDING

摘要

A method for manufacturing a spiral-seam-welded steel pipe comprises forming a cylindrical pipe-blank by bringing into butt contact side edges of a moving steel strip while spirally winding the moving steel strip and continuously effecting an inside welding and an outside welding of the pipe-blank thus formed along a spiral seam line thereof by a gas shielded arc welding method while continuing to move the steel strip : the inside welding and said outside welding are effected each by means of a plurality of solid wire consumable electrodes having a diameter of from 3 to 8 mm, each of which is fed at a prescribed position, in a mixed gas comprising an inert gas and CO2 gas and/or O2 gas and fed at a rate of from 7 to 400 ? per minute per consumable electrode under the following conditions: a DC welding current of from 600 to 2,000 amperes, a welding voltage of from 20 to 36 volts and a welding speed of from 500 to 1,500 mm per minute; the inside welding being effected at a position within a range between a point deviated by a center angle of 12.degree. of the pipe-blank from the lowest point of said pipe-blank toward the downstream of the moving direction of said steel strip, and a point deviated by a center angle of 20.degree. of the pipe-blank from said lowest point toward the upstream of the moving direction of the steel strip; and the outside welding being effected at a position within a range between a point deviated by a center angle of 30.degree. of the pipe-blank from the highest point of the pipe-blank toward the upstream of the moving direction of the steel strip, and the highest point.