In order to achieve safety and reliability of long-distance gas transmission pipeline installed in seismic and permafrost region, it is quite important to apply high strength linepipes with sufficient strain capacity against buckling and weld fracture by large ground movement. Grades X70-X80 linepipe steels with bainite-MA (Martensite-Austenite constituent) microstructure have been developed by applying advanced plate manufacturing technologies with the combination of accelerated cooling (AcC) and heat treatment on-line process (HOP™). This microstructure shows higher strain capacity which has low yield to tensile (Y/T) ratio and high elongation in the longitudinal direction even after pipe coating heat treatment. In...