| With the development of modern industrial technology,ferromagnetic materials are widely used in the field of energy transportation,and the transportation of oil and natural gas mainly relies on ferromagnetic pipelines.After a long-term use of the pipeline,the mechanical strength and service life of the pipeline can be easily affected by changes in the external environment and the corrosion of the transport medium.Once an accident occurs,it will cause serious consequences.Therefore,regular non-destructive testing of the pipeline is of great significance to its safe operation.As a non-destructive testing method for ferromagnetic pipelines,pipeline MFL internal detection technology has the advantages of strong applicability,multiple detectable types,high degree of automation and widely used.The geometric size of pipeline defects is related to the service capacity of pipelines.Establishing an accurate description between the geometric size of pipeline defects and the defect leakage magnetic field is of great significance for pipeline defect detection.In this paper,aiming at the mathematical relationship between the geometric size of the rectangular defect and the defect leakage magnetic field in the magnetic flux leakage internal detection,the defect leakage magnetic field is analyzed based on the pipeline magnetic flux leakage internal detection technology,and the magnetic charge distribution law at the defect after the pipeline rectangular defect is magnetized,and the magnetic charge density at the defect is deduced,and the magnetic charge distribution characteristics at the ridgeline and sidewall of the rectangular defect of the pipeline are obtained.The distribution characteristics of the leakage magnetic field of rectangular defects in pipelines are studied,the mathematical relationship between the leakage magnetic field and the size of the rectangular defects in the pipeline is explored,and the three-dimensional magnetic dipole model at the ridgeline and sidewall of the rectangular defects in the pipeline is established,and the vector synthesis is carried out to obtain Three-dimensional analytical model of leakage magnetic field of pipeline rectangular defect.The simulation software is used to solve the three-dimensional model of the leakage magnetic field of the rectangular defect,and the spatial distribution of the leakage magnetic field of the defects with different geometric sizes is modeled.An experimental platform was built under laboratory conditions to conduct experiments on rectangular defects with different widths and depths.The simulation data and experimental data were compared and analyzed to obtain the distribution law of the leakage magnetic field of rectangular defects.The distribution characteristics of the leakage magnetic field of rectangular defects were studied.The accuracy of the three-dimensional magnetic dipole model of the defect leakage field is verified.The results show that the magnetic flux leakage signals of rectangular defects with different depths obtained by pipeline magnetic flux leakage internal detection technology show positive correlation in a certain range,and the peak to peak spacing of defect magnetic flux leakage signals increases with the increase of defect width.A series of laws obtained by the three-dimensional magnetic dipole model at the edge line and side wall of rectangular defects are consistent with the laws obtained from the experimental results,The effectiveness of the analytical model to describe the spatial distribution of leakage magnetic field of rectangular defects in pipeline is verified,which provides a reference for the analytical quantification of defects. |
