Research On Magnetic Field Calculation Model Of Ellipsoid Defect In Pipeline Magnetic Flux Leakage Internal Inspection 0

As one of the five major transportation industries in China,pipeline transportation of oil and gas plays an important role.It has the advantages of large transportation volume,not affected by other factors such as climate and ground,high cost performance and sustainable operation.It plays an important role in promoting the development of China's national economy and is known as "energy blood".In the pipeline safety inspection project,the pipeline on-line detection technology is the basic means to ensure the safe transportation of the pipeline,and the magnetic flux leakage internal detection technology is the most widely used and relatively mature.In the actual production,the shape of the pipeline pit defect is close to the semi ellipsoid irregular shape,so it is important to study the magnetic parameters of the ellipsoid defect for the detection of the actual pipeline defects.In this paper,the mathematical relationship between the geometric size of ellipsoid defect and magnetic leakage field in MFL internal inspection is studied.Based on the technology of pipeline MFL internal inspection,the application of Laplace equation in electrostatic field and static magnetic field is established.Firstly,the charge distribution on the surface of ellipsoid defect with external electric field is solved,and the magnetic charge on the surface of ellipsoid defect is further solved according to the principle of electromagnetic coupling Density distribution.Then the magnetic charge distribution on the surface of ellipsoidal defects is analyzed,and the magnetic flux leakage characteristics of different ellipsoidal defects are studied.The magnetic charge density distribution of different size defects is simulated and observed,and the influence of defect size on the surface magnetic charge distribution is studied.In view of the same defect,the whole simulation observation research is carried out first,and the simulation is carried out according to the mathematical model,and the whole change trend is observed and compared with the calculation results.Then the distribution of magnetic charge on the surface of the same defect at different heights is studied.The control variable method is used to simulate the magnetic charge distribution at different heights.The results show that the simulation results of the magnetic charge density distribution on the surface of ellipsoidal defects with different sizes obtained by internal magnetic flux leakage inspection are consistent with the calculation results,which verifies the effectiveness of the proposed model to describe the magnetic charge density distribution on the surface of pipeline defects.For the same size defect model,the simulation results show that the magnetic charge density distribution is positively correlated with the curvature of the point,that is,the larger the curvature is,the greater the magnetic charge density is,which is consistent with the calculation results.There is a corresponding relationship between the calculation data and the simulation data,so that an accurate analytical model of magnetic charge density distribution on the surface of pipeline ellipsoidal defects can be established based on the internal detection of pipeline magnetic flux leakage.It lays a foundation for further engineering practice.