Abstract: Oil and gas pipelines may be subject to high plastic strains before they enter service and during operation. To investigate the mechanical properties and fracture toughness of line pipe steel subjected to plastic deformation with tensile or compressive prestrain, tensile tests and crack-tip-opening (CTOD) tests are conducted on X80 steel. Meanwhile, specimen fracture morphologies of different fracture modes are also analyzed. The results indicate that the temperature has a significant influence on fracture toughness of line pipe steel and the fracture toughness reduces significantly with the decreasing of temperature resulting to brittle fracture. The yield strength and tensile strength of the workpieces with tensile prestrain generally increase due to work hardening and decreased with compressed prestrain due to the Bauschinger effect. But they all significantly reduce metals plasticity and fracture toughness, and further increase the possibility of brittle fracture. Thus the effects of the temperature and the prestrain should be considered in the line pipe design, material selection and safety analysis and evaluation.

Key words: Fracture toughness, Mechanical property, Prestrian, X80 pipeline steel