X100 Linepipe With Excellent HAZ Toughness and Deformability

Good low-temperature toughness of the base material (BM) and weld heat-affected zone (HAZ), and good deformability of the pipe body together with good field weldability are required for X100 linepipe to ensure the safety of pipelines and to facilitate field welding. It is, however, very difficult to attain these properties simultaneously because of the large addition of alloys. The technology of improving HAZ toughness by reducing carbon content through the reduction of M-A constituents harmful to low-temperature toughness was developed, and accelerated cooling after controlled rolling was applied to attain good low-temperature toughness of BM and high uniform elongation together with sufficient strength corresponding to X100. Two newly developed types of X100 linepipe, a “high HAZ toughness type” and a “high uniform elongation type”, exhibited excellent low-temperature toughness of the HAZ and high uniform elongation together with sufficient strength, respectively.