Effect of crack angle on the fracture parameter of pipeline surface crack

The defect of surface crack is inevitably produced on steel gas pipelines in the process of manufacture, installation and operation. Under the effect of external force and corrosion, the surface cracks propagate and even result in pipeline rupture and failure, impacting the safe operation of high-pressure gas pipelines badly. Therefore, it is necessary to study the effect laws of surface crack angle on fracture parameter. In this paper, a finite element model for pipelines with different surface cracks under the effect of internal pressure was established by the finite element simulation software ANSYS. And then J-integral change laws of surface cracks with different angles were analyzed. It is shown that the J-integral value of crack tip changes with crack angles approximately in the form of cosine function. If the boundary condition is the same, J-integral value is the maximum when the surface crack is parallel to the pipeline's axial direction. And in this case, the surface crack could propagate the most easily. When the surface crack is perpendicular to the pipeline's axial direction, the J-integral value is the minimum and the propagation of surface cracks is less possible.