Research On MFL Field Analysis And Visualization Technology Of The Corrosion Defect In Tank Floor

As the developing of our country and the foundation of the nation strategic crude oil reserve system, the number and the volume of tanks increase quickly. At the same time, companies and technicians pay more attention to their safety. The corrosion in tank floor is the main cause that leads to failure of tanks. So it's important to detect corrosion in tank floors. To finish more and more test tasks and actualize the visualization of defect while testing, it's insistent on carrying out research on wholly digital test system, high precision location system, highly intelligent evaluation system. Now, many techniques, including analysis of MFL signal, extraction of signal eigenvalue and defects reconstruction, have not formed systemic method in MFL testing field. Especially, there is no mature system on MFL test visualization technology. According to the situation and requirement, the quantitative analysis of the corrosion defect and the 3D reconstruction are selected as the study emphasis. It's hoped that technical breakthrough is obtained in MFL field analysis and visualization technology of the corrosion defect in tank floor.The paper mainly studies the principal of MFL testing and that how is the MFL field of corrosion defects engendered. Also, two theoretical calculation methods of MFL field are identified, namely, analytics method and numerical method. Three basic magnetic-dipole models are analyzed with analytics method, i.e., equivalent double point model, double line model and double zone model. Because these three basic models can't correctly describe the corrosion defect in tank floor, the cylindrical and ellipsoidal corrosion defect models are founded. On the basis of the Maxwell equations, the finite element theory analysis is carried out. And the MFL field is studied with finite element method of electromagnetic numerical computation.The ellipsoidal corrosion defect is simulated and analyzed with ANSYS software, and the spatial distribution of the defect MFL field and lots of emulation data are gained. According to the emulation data of the corrosion defect MFL field, MFL field eigenvalues are extracted, and they are gained that the qualitative and quantity relationship between the feature parameters of the defect shape and the MFL field eigenvalues. The 3D reconstruction method of the corrosion defect MFL test is founded on the basis of the quantity relationship between the feature parameters of the defect shapes and the MFL field eigenvalues. And the equivalent position, depth, length and width of defect are found. The MFL visualization technology of the corrosion defect in tank floor is achieved.The visual MFL testing experiment system of the corrosion defect in tank floor is founded. The quantity relationship and the 3D reconstruction method of the corrosion defect are validated by experiment analysis.