The Research Of Pulsed Magnetic Flux Leakage Techniques For Plate

The pulsed magnetic flux leakage (PMFL) technology is a kind of NDT technolog which is the first development in overseas. It has the merits of pulsed eddy current (PEC) testing and magnetic flux leakage (MFL) testing. Comparing with pulsed eddy current (PEC) testing, it has the deeper examination depth to the ferromagnetic material; Comparing with traditional magnetic flux leakage (MFL) testing, it use pulsed excitation magnet which has rich frequency components. Pulsed excitation provides the opportunity to apply an excitation signal that the rich frequency components can provide information from different depths of ferromagnetic material. So it provide the broad prospects for enhancement examination flaw size precision and detection surface and sub-surface defects in ferromagnetic materials.In this paper, pulsed magnetic flux leakage (PMFL) technology has been studied. The finite element model about magnetizer of detector was established for rectangular slot of plate defection and simulation result about leakage magnetic field is given. The influence examination's factor is studied through the finite element model. According to simulation result, pulsed magnetic flux leakage (PMFL) testing system's parameters were determined.The pulsed magnetic flux leakage (PMFL) testing system is designed to detect steel surface and sub-surface defects. It consists of examination probe, Pulse excitation source, signal conditioning circuits, data acquisition card and computer so on. The probe is composed of the enamel-insulated wire winding U high magnetic permeability magnetic core and the high sensitivity Hall sensor. Based on the design examination system, the detecting steel plate with machined rectangular slots is achieved. According to different depth rectangular slots voltage signal characteristic in the experiment,the program is finished based on the Labview software. In order to discriminate surface defects and sub-surface defects, the method of peak and valley value synchronization sampling curve about rectangular slot defect is adopted.Through the experimental analysis of the data shows that the method of Pulsed magnetic flux leakage techniques can detect the Q235 test plate defect depth 2mm,4mm, 6mm surface rectangular slot and defect depth of 2mm,4mm,6mm sub-surface rectangular slot. The analysis of experimental data shows the depth change rule of rectangular slot defect. And also the discrimination of the signal between surface defects and sub-surface defects is finished.