A full-scale bending test apparatus which can bend 48" high-strain linepipes was constructed to conduct the bending tests with internal pressure. Three bending tests of X80-grade, 48" line pipes pressurized to 60% SMYS were conducted to investigate local buckling and postbuckling behavior. The sizes of three pipes were all same; thickness and D/t ratio were 22.0 mm and 55.4, respectively. The characteristics of mechanical property of the pipe body varied. The mean Y/T ratio of the high-strain pipes was 0.83, 0.82 and 0.91 respectively. Former two pipes were high-strain pipes (hereinafter No. 1 and 2), and latter one was conventional pipe (No. 3). No. 3 test pipe was chosen with comparatively higher Y/T ratio than other two pipes to investigate the effect of Y/T ratio to the bending capacity. The bending test results clarified that the pipes have the 2D average critical compressive strain of 1.51%, 1.67% and 0.92%. Test pipe No. 1 and 2 endure 18.8 and 18.1 degree of end rotation. Test pipe No. 3 was finally ruptured on its tension side near the buckling wrinkle, at 19.7 degree of end rotation.
High-strength, high-strain and large diameter line pipes have been highlighted in recent years to construct high pressure and long distance natural gas pipelines in seismic regions and discontinuous permafrost regions (Glover, 2002; Glover, et al., 2003; Zhou, et al., 2006; Li, et al., 2007, Ji, et al., 2007, Gao, et al., 2007, Suzuki, et al., 2003, Suzuki, et al., 2004). In order to ensure integrity of the pipelines in the hostile environments, compressive strain limits of the pipes must be verified (Zimmerman, et al., 1995, 2004). Moreover the compressive strain limits must be improved (Suzuki, et al., 2001, 2002) in accordance with requests from pipeline projects.