HIGH STRENGTH LINEPIPE SUPERIOR IN COLLAPSE RESISTANCE AND SOUR RESISTANCE, AND METHOD FOR PRODUCING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a high strength linepipe which is inexpensively produced with high productivity without degrading collapse resistance and sour resistance, and to provide a method for producing the high strength linepipe.;SOLUTION: The high strength linepipe having excellent collapse resistance and sour resistance is a welded steel pipe, obtained by forming a base material composed of a thick steel sheet into a tubular shape and joining the butted parts by welding the butted parts in two or more layers, and contains, by mass, 0.02-0.08% of C, 0.01-0.50% of Si, 0.5-1.5% of Mn, a certain content of each of P, S, Al, Nb, Ca and O, and further contains a certain amount of at least one selected from Cu, Ni, Cr and Mo, wherein Ceq is 0.30 or more, PHIC is 1.00 or less, ACR is 1.0-6.0, and the remainder comprises Fe and inevitable impurities. In the high strength linepipe, the volume fraction of island martensite (M-A) is 1% or less in the whole area of pipe thickness, and the metal structure and hardness of the surface layer part of the base material and the center part of pipe thickness of the base material are specified. The method for producing the linepipe is also provided.;COPYRIGHT: (C)2013,JPO&INPIT