Research On Weld Crack Propagation Of Oil And Gas Pipeline Based On MFL And VCCT

The operation environment of oil and gas pipeline in petroleum industry is complex,and the cracking of pipeline weld is one of the most important failure modes.Generally,the fracture of pipeline steel is ductile fracture.Once ductile fracture occurs,the crack will gradually expand until catastrophic accident occurs.Therefore,it is of great significance to carry out research on the key scientific problems of in-service detection of weld crack propagation in pipeline.When there are cracks in pipeline welds,under fluid erosion,the crack propagation speed is rapidly accelerated,resulting in fluid-solid coupling between the contact surface of the defect space on the inner wall of pipeline welds and the conveying fluid during the magnetic flux leakage detection,and accompanied by the multi-field coupling problem of the magnetic field.In this context,the finite element simulation and analysis of weld crack propagation of oil and gas pipelines are carried out based on magnetic flux leakage method(MFL)and virtual crack closure technology(VCCT),and four kinds of models are established,including single crack on the outer wall of oil and gas pipeline welds,single crack on the inner wall of pipeline welds,multiple cracks on the same line of pipeline welds and multiple cracks on the circumferential symmetry of pipeline welds.With the dynamic application of fluid pressure,the virtual crack closure technology is used to calculate the propagation of pipeline weld cracks.The four models mentioned above are used as research objects to study the fluid-solid magnetic multi-field coupling algorithm for the magnetic flux leakage behavior caused by the dynamic propagation of pipeline weld cracks.The research steps are to extract the results of each fluid pressure load step in the crack propagation process,then update the node coordinates in real time according to the amount of propagation deformation in the extraction results,reconstruct the grid at the crack location,and conduct the crack propagation calculation and magnetic field analysis in a cycle.Based on the model and algorithm established in this paper,the propagation degree of weld cracks in in-service pipeline can be characterized,and the risk level of weld damage can be judged,which can provide theoretical basis for guiding the actual pipeline safety assessment.