Research On Magnetic Eddy Current Testing Technology For Corrosion Defects On The Back Of Tank Bottom Plate

Large oil storage tank is one of the most common methods of oil storage in the world at present,with less investment,fast construction,convenient management and maintenance,along with the safety of the storage tank.Since almost all oil storage tanks are ferromagnetic materials,there are mainly corrosion,cracks and other defects.Due to the characteristics of tank floor contact with the ground,corrosion defects on the back of the tank are the top priority in the detection.Failure to find them in time will result in huge safety accidents.In the current research on tank bottom plate detection,the magnetic leakage detection and the saturation magnetized eddy current detection cannot distinguish the upper and lower surface defects clearly,and the magnetizer is too heavy and has high working intensity.Based on the principle of unsaturated magnetization eddy current detection,this thesis studies the magnetization of tank bottom plate with different plate thicknesses,the optimization of excitation frequency and the identification of rear corrosion defects.The main research contents are summarized as follows:1.Finite element modeling and simulation of magnetic eddy current detection.The finite element model of magneto-eddy current detection was established based on the static magnetic field and eddy current frequency field.By changing the magnetization distance and excitation frequency,the change rule of eddy current coil impedance signal under different magnetization and different frequency of 8mm steel plate was obtained,and the magnetization intensity and excitation frequency were optimized.The simulation results show that the optimal magnetization is 2438A/m,15% of the critical value of saturation magnetization,and the optimal excitation frequency is 400 k Hz.2.Research on parameter optimization of magnetic eddy current detection.The hardware system,software system,detection car and magnetizer of the magnetic eddy current detection system were designed.The magnetization and excitation frequency required by the detection of specimens with different plate thicknesses and coils with different size parameters were optimized by the magnetic eddy current detection system.The impedance variation law of differential coils under different magnetization spacing was explored,and the optimal magnetization intensity and excitation frequency of different plate thicknesses were determined.The experimental results show that the optimal magnetization of 8mm,16 mm and 18 mm are 3940A/m,4017A/m and5075A/m,which are 25%,25% and 32% of the critical value of saturation magnetization,respectively,and the optimal excitation frequency is 400 k Hz.The optimal magnetization of the two contrast coils are 4872A/m and 6092A/m,respectively,which are 31% and 38% of the critical value of saturation magnetization.The optimal magnetization is related to the coil sensitivity,and the optimal excitation frequency is400 k Hz.3.Corrosion defect identification method of upper and lower surface of tank bottom plate based on support vector machine.Kernel function and HOG feature extraction were used to extract features from the upper and lower surface corrosion defect database.The program interface was written by LABVIEW and the intelligent recognition software was developed by calling MATLAB.The experimental results show that the accuracy of model training is 100% and the intelligent recognition of corrosion defects on upper and lower surfaces is realized.In this thesis,the optimization method of magnetization and the identification method of corrosion defects on upper and lower surfaces are proposed,and the optimal magnetization and excitation frequency of different plate thickeners are determined.This has important guiding significance for further corrosion detection and defect identification on upper and lower surfaces of tank bottom plate under unsaturated magnetization.This thesis has 86 figures,14 tables and 83 references.