Effects of pre-strain on the mechanical properties of API 5L X65 pipe

This paper investigated the influence of pre-strain on the mechanical properties and fitness-for-service of the API 5L X65 pipeline subjected to large plastic deformation. Axial tensile pre-strains of 1.5, 5 and 10% were applied to plate-type tensile specimens extracted from the longitudinal direction of the pipe body prior to mechanical testing. Tensile test results revealed that yield strength and tensile strength increased with increasing tensile pre-strain. The rate of increase of the yield strength was greater than that of the tensile strength. Pre-strain up to 5% had little effect on decreasing the CTOD and Charpy impact along the LS notch direction. Charpy impact energy along the TL notch direction considerably decreased with increasing tensile pre-strain. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for-service code, API RP 579.