Abstract: In order to improve accuracy of pipeline safety risk assessment, taking pipeline with internal surface defects as research object, influence of different size defects on crack initiation law was analyzed by using ABAQUS software linear elastic and elastic-plastic,3-point bending model of pipeline and full-scale static load physical test were established by using extended finite element method, and nonlinear fitting of crack growth size was used to study crack propagation at the inner surface defects. The results show that crack initiation is very easy at the center of inner surface defect.As the size of the defect increases, the external force required for crack initiation changes greatly when the relative length of the defect is 0.08 and the relative depth is 0.4,and influence of defect depth on crack initiation is greater. Comparison between numerical simulation and full-scale physical test shows that crack size rapidly expands under displacement load of less than 70 mm or external force of 147.25 kN, and then nonlinear fitting of crack size can obtain more accurate prediction results of crack growth size.

Key words: external force, inner surface defects, crack propagation, numerical simulation, physical test of full scale pipe, oil and gas pipeline