High deformability UOE linepipes produced by advanced TMCP technology

Extensive studies to develop high deformability linepipe have been conducted. In case of linepipes laid in a seismic region, higher resistance to buckling against large strains induced by earthquake related ground movement is required. In order to improve the deformability of pipes, two different types of microstructural control technologies were proposed, based on theoretical and analytical studies on the effect of microstructural characteristics on stress-strain behavior. Grade X65 to X100 linepipes with ferrite-bainite microstructure were manufactured by optimizing the microstructural characteristics. Grade X80 linepipe with bainitic microstructure containing dispersed fine M-A constituents was also developed by applying new conceptual TMCP process. Deformability of developed linepipes with two different types of microstructure was evaluated by axial compression and bending tests, and all the developed linepipes showed superior resistance to buckling comparing with conventional pipes. Tensile properties after thermal coating of developed high deformability pipe were also investigated. It was shown that an increase in yield strength by thermal strain aging was minimized and a roundhouse type stress-strain curve was maintained for the linepipe manufactured by the new conceptual TMCP process. (AU)