Research On Magnetic Field Calculation Method Of Pipeline Magnetic Flux Leakage Internal Detection Defect

With the rapid development of the national economy,the increasing demand for energy has led to more and more fierce competition for energy in various countries.There are many kinds of energy sources,the most important of which are oil and natural gas.These important energy resources play an extremely important role and significance in human life,industrial and agricultural production and national defense construction.There are many modes of oil and gas transportation,among which pipeline transportation occupies an important position.Once the pipeline is laid,it needs to run for a long time.In this process,it is easy to cause the pipeline to be damaged to varying degrees due to changes in the external environment.Once the pipeline leaks due to defects,the consequences to human society and natural environment are unwilling to be seen by people.Therefore,it is particularly important to inspect the defects of oil and gas pipelines regularly.Defects with different shapes and sizes in pipelines will affect the distribution of magnetic leakage field,it is great significance to establish the relationship between them and defect magnetic flux leakage signals to describe the distribution and change of magnetic flux leakage.Based on the theory of magnetic dipole,this paper demonstrates through the interaction force between the magnetic charges in the equivalent magnetic charge viewpoint that there will be two kinds of magnetic charges on the cross section of ferromagnetic materials after magnetization,namely the ridgeline magnetic charge and the surface magnetic charge.Derives the linear magnetic charge density of the uniform distribution of the magnetic charge on the defect ridgeline,discussed the magnetic field strength of the leakage magnetic field at the defect surface and the ridgeline of the pipeline to any field point in space,and establishes three types of models for the pipeline,Three-dimensional magnetic dipole models of v-shaped defects and trapezoidal defects,and three-dimensional magnetic dipole models of rectangular defects on the inner and outer walls of the pipeline.The magnetic leakage signal generated by rectangular defects is calculated and studied,and the characteristics of the magnetic leakage field generated by different rectangular defect sizes are analyzed,and the leakage magnetic field of the rectangular defects with different length,width,and depth is solved and simulated by software,and the defects of different sizes are simulated.The leakage magnetic field distribution is compared and analyzed.Set up an experimental platform,use equipment to conduct experimental inspections,detect rectangular defects with different lengths,widths,and depths,and compare the simulation calculation model with the actual engineering experiment results to verify the accuracy of the establishment of the three-dimensional model.The results show that the change of the depth and width of the rectangular defect is positively correlated with the change of MFL signal to a certain extent.Due to the magnetic shielding effect,the magnetic flux leakage signal of the tube outer wall defect is smaller than that of the tube inner wall defect,but the different defect size has the same rule on the magnetic flux leakage.The experiment verifies the effectiveness of establishing the three-dimensional model of the magnetic flux leakage field of the tube inner and outer wall defect.