Research On The Characteristics Of Pipeline Magnetic Memory Internal Detection Signal Under Load

Pipeline transportation has become one of the main methods for transporting energy such as oil and natural gas due to its low transportation cost,low susceptibility to surrounding environmental influences,and high reliability.According to recent statistics on pipeline accidents in the past few years,weld crack is one of the main reasons for the failure of long-distance oil and gas pipelines.Pipeline internal inspection technology is currently recognized as one of the most effective pipeline safety inspection methods internationally.This technology refers to using the transmitting medium such as oil and natural gas to push the internal inspection equipment forward(at a speed of 1m/s～5m/s)while the pipeline is in normal operation,in order to detect pipeline defects.The metal magnetic memory detection method uses the magnetomechanical relationship of ferromagnetic materials to detect and analyze the magnetic field distribution on the surface of components,in order to determine the location and extent of stress damage.It has a good application prospect in the field of pipeline stress internal inspection.Based on the J-A theory,this thesis establishes a pipeline force-magnetic coupling model to calculate the relationship between stress and magnetization intensity.The magnetic memory signal characteristics of pipeline welds,pipeline weld cracks,and pipeline base metal cracks are analyzed.The feature parameter gradient K,maximum gradient Kmax,and energy factor S(K)of the magnetic memory signals at pipeline welds,pipeline weld cracks,and pipeline base metal cracks under different load conditions are compared.Finally,the simulation results are validated through a systematic experiment.The research provides theoretical and experimental evidence for identifying the stress state of long-distance oil and gas pipelines.The axial component of the magnetic memory signal has the maximum value at the crack location of the pipeline weld and the pipeline base material,while the radial component has the magnetic signal characteristics of sinusoidal fluctuations;At the crack of the pipeline weld seam,the characteristic of the magnetic memory signal is that the axial component exhibits a maximum value,while the radial component exhibits two sinusoidal fluctuations.The characteristic parameter gradient K and maximum gradient Kmax of magnetic memory signals at in-service pipeline welds,pipeline weld cracks,and pipeline base material cracks gradually increase with the increase of load.The characteristic parameter S(K)of magnetic memory signals at in-service pipeline welds,pipeline weld cracks,and pipeline base material cracks increases with increasing load.At the pipeline weld,the axial average change of energy factor S(K)is 96.25% higher than the axial average change of the maximum gradient value Kmax,and the radial average change of energy factor S(K)is 94.69% higher than the radial average change of the maximum gradient value Kmax;At the crack of the pipeline weld seam,the axial average change of energy factor S(K)is89.36% higher than the axial average change of the maximum gradient value Kmax,and the radial average change of energy factor S(K)is 92.52% higher than the radial average change of the maximum gradient value Kmax;At the crack of the pipeline base material,the axial average change of energy factor S(K)is 57.73% higher than the axial average change of the maximum gradient value Kmax,and the radial average change of energy factor S(K)is85.36% higher than the radial average change of the maximum gradient value Kmax.The energy factor S(K)of the characteristic parameter of magnetic memory signals can be used as an indicator to determine the changes in magnetic memory signals in the stress concentration area of pipelines.