Research On Signal Characteristics Of Pipeline Stress Internal Detection Based On Remanence Method

In the world,most of the oil and natural gas are transported by underground pipelines.The key to the safe operation of oil and gas pipelines is the detection and maintenance of pipelines.Due to the long-term load,the pipeline will produce stress concentration and even plastic deformation,which will cause serious harm to the safety of pipeline operation,and serious accidents such as pipeline leakage and burst will occur,which will threaten the safety of pipeline transportation.In order to prevent the occurrence of major accidents such as pipe burst,it is necessary to regularly detect the stress inside the pipeline in service in order to carry out safety maintenance.Conventional nondestructive testing methods such as magnetic particle,ultrasonic and X-ray have played a key role in the detection of pipeline defects.However,the application of these methods in the field of stress detection in pipelines has limitations,which can not meet the needs of in-service pipeline detection technology.Residual magnetic stress detection is a new stress detection technology.After the magnetic leakage detector detects the macroscopic defects of the pipeline,the residual magnetic field is used to detect the stress inside the pipeline,which can effectively judge the stress concentration area of ferromagnetic pipeline.However,the mechanism and influencing factors of remanence signal are complex.It is difficult to quantitatively analyze the characteristics of remanence signal with different stress concentration,which hinders the development of the detection technology.Therefore,it is of great significance to establish an analytical model of residual magnetic stress detection for theoretical research and engineering practice of remanence detection technology.Based on the theory of J-A,the analytical model of residual stress of pipeline under external force is established.The influence of stress in elastic stage on B-H curve of ferromagnetic material is calculated.The change law of residual magnetic signal in stress concentration area is analyzed.In order to clarify the characteristics of residual magnetic signal in actual detection,the three-dimensional finite element simulation analysis of the steel plate with cracks is carried out based on the residual stress analysis model.The influence of crack width and depth,and the tensile stress on the residual magnetic signal in the stress concentration zone at the crack tip is analyzed,and the signal characteristics of the tangential component and normal component of the residual magnetic signal in the stress concentration area are analyzed,It provides theoretical basis for the application of remanence detection technology in the field of stress detection in pipelines.In order to verify the accuracy of theoretical calculation and simulation analysis,the remanence tensile experiment and the magnetic remanence experiment of external magnetic field are designed,and the experimental results are analyzed.The results show that the residual magnetic signal in the stress concentration region is approximately linear correlated with the stress in the elastic range;The peak value of the tangential component of remanence signal and wave trough appear in normal component;With the increase of crack depth and width,the stress at the crack tip increases linearly,and the residual magnetic signal in the stress concentration region increases;When the stress is certain,the remanence signal is stable after the magnetic saturation is achieved by repeated excitation of the external magnetic field.