In recent years, the construction of high-pressure gas pipelines with API X80 grade submerged arc welding (SAW) pipes is progressing for the improvement of transportation efficiency. However, it is generally known that the deformability of the SAW pipes is decreased by increasing strength of the pipes. Therefore, application of strain-based design (SBD) has been discussed primarily by the demand of construct pipelines in permafrost regions and seismic regions. It is important to understand the deformability of the SAW pipes, and the full scale pipe bending tests are performed as one of the evaluation method. Though a lot of test methods exist in the full scale pipe bending test, standardization of the test method is not done. In this study, two kinds of different full scale pipe bending tests by using the same X80 SAW pipes and finite element analysis (FEA) were performed to investigate the effect of the test methods on the evaluation results of the pipes.
High strength line pipe for gas transmission pipeline has been developed for cost reduction of gas transportation by high pressure operation. The applicability of high strength line pipe has been studied by full scale trial of construction and burst test (Demofonti, 2004; Macia, 2004). As the ductility of steel decreases in high strength line pipe, the deformability of line pipe related to strain capacity of pipeline has been focused on the application of high strength line pipes for high-pressure gas pipelines. In recent years, studies on buckling strain limit of the line pipe were performed by full scale bending test (Shitamoto, 2009; Tsuru, 2010; Mannucci, 2011; Tajika, 2011). However it is thought that the buckling strain limit value obtained by the bending test depends on the pipe bending test method.