Steel pipe welding method

Abstract

An improved welding method for welding an inner seam of a longitudinally welded steel pipe along an inner groove by welding electrodes held by a boom which is supported by a tracing roller moving along the inner groove of the steel pipe. According to the invention, at least one metal plate is urged against at least one end of the steel pipe after tack welding the seam on an opposite side of the inner groove of the steel pipe to be welded. Lateral angular deformations of the end of the steel pipe are prevented on both sides of the seam. Such deformations are due to the load of the boom when the tracing roller leaves the end of the steel pipe for the metal plate. Thus, the invention provides for prevention of hot cracking at the end of the pipe. Moreover, according to the invention, portions of the steel pipe on both sides of the distal end of the weld bead, at the end of the pipe, are heated to cause expansion displacements of the heated portions directing toward the center of the weld bead, or high temperature portions of the steel pipe, after a heat source for the seam welding has passed therethrough, are cooled, thereby reducing tearing forces acting upon the weld bead so as to prevent more effectively the hot cracking at the end of the pipe.