RESEARCH AND DEVELOPMENT ON LARGE-DIAMETER LINE PIPE FOR ARCTIC USAGE.

Increasing demands for thick and high grade line pipe for arctic usage has promoted research on strength, toughness and weldability. This paper deals with the metallurgical background for producing high quality line pipe steel. Microalloying technology (Ti, Nb, V, B etc. ) through precipitation hardening, grain refinement and transformation hardening has led to the achievement of high grade without impairment of toughness and weldability. The introduction of the accelerated cooling process after controlled rolling has made it possible to lower the carbon content, which provides numerous advantages regarding toughness and weldability. Lastly, the heat-affected-zone toughness was improved by both decreasing the proportion of M-A constituents and refinement of fracture facet size. The addition of Ti and Ca as well as the reduction of Si content were useful for this purpose.