The Simulation Analysis And Test Research Of Magnetic Flux Leakage Detection Based On Compound Excitation Method

With the development of non-destructive detection technology, magnetic flux leakage detection has been used in more broad fields. This paper applies the method of complex excitation, originally used in electrical technology, to magnetic flux leakage detection field, according to the principle of magnetic flux leakage testing. Combine electromagnetic magnet excitation with permanent magnet excitation, through regulating current and controlling the strength of the exciting field, which makes the compound excitation flux leakage detector to control the strength of the exciting field according to the thickness of tank bottom, which alleviates the labor intensity in comparison with permanent magnet MFL instrument.This paper analyzed the principle of magnetic flux leakage testing with compound excitation, and proposed the testing method; Established series compound excitation structure model, single-channel parallel compound excitation structure model, multichannel parallel compound excitation structure model and the compound excitation structure model with a replacement of permeability materials; Simulated five kinds of models respectively, and concluded the leakage magnetic field space distribution characteristics of five compound excitation models; Using the control variable method, analyzed the five models respectively in conditions of different defect shape, depth, width, different test plate thickness, and different number of ampere-turns applying the finite element software ANSYS.According to the results of simulation calculation, get the leakage magnetic field characteristics of defects. In terms of leakage magnetic flux density in the horizontal component-Bx in five kinds of models, the magnetic flux density of horizontal component-Bx of single-channel parallel structure model is strongest, followed by series of composite magnetic excitation structure model, multichannel parallel structure model made up of silicon steel armature, while the magnetic flux density of horizontal component-Bx of parallel excitation structure model of single channel and multi-channel parallel excitation structure model are the smallest and the peaks of them are nearly same.Compound excitation magnetic flux leakage detection system was developed. The system consists of four kinds of excitation structure, which are series compound excitation structure, multichannel parallel compound excitation structure, silicon steel armature of single-channel parallel compound excitation structure and silicon steel armature of multichannel parallel compound excitation structure. The compound excitation magnetic flux leakage detector developed under laboratory conditions was used for a large number of experiments, and the experimental results showed that the compound excitation method can control the field strength by decreasing and increasing current. Under the same conditions, the effect of compound excitation is more stronger than the single excitation modes. A compound excitation magnetic structure of the silicon steel sheet road parallel structure is put forward according to the results of simulation and experimental. This structure can achieve 20% defect detection of 15 mm thickness wall.Based on the experimental data of compound excitation flux leakage detector and Pearson product-moment correlation coefficient, Established the complex field magnetic flux leakage testing defect prediction model, with the capabilities of predicting and analyzing cylindrical defect depth. The analysis results and the actual defect prediction error is less than 3%. What is more, the relevancy of heoretical value and experimental values is greater than 0.92.