Numerical and experimental study on critical crack tip opening displacement of X80 pipeline steel

High strength pipelines is widely used for the long distance transportation of oil and gas resources. Fracture toughness is a significant material property for these high strength pipeline steels. In this study, the critical crack tip opening displacement (CTOD) of X80 pipeline steel was studied both experimentally and numerically. 3 point bending tests were conducted for 6 specimens with 2 thicknesses. Numerical model using the extended finite element method was also established, with maximum principle strain criterion used for damage initiation. Results show that, the critical CTOD decreases with the increase of specimen thickness. And to give reasonable simulation results in the numerical model, larger maximum principle strain criterion should be used for thin specimens. This study can be referenced for the performance evaluation and quality assurance for X80 steel gas pipelines.