A Novel Non-destructive Testing Method by Measuring the Change Rate of Magnetic Flux Leakage

The application of magnetic sensors in the traditional magnetic flux leakage (MFL) technique has a significant influence on the detection results. The sensor is typically used to directly measure the amplitude of the magnetic leakage flux intensity as the detection signal. In view of noise effects on the detection result and the subsequent misinterpretation of defect signals, a new non-destructive testing method is proposed. The proposed method intends to measure the magnetic flux change rate using two sensors. A mathematical model is first established to present the principle of the change rate measurement. Based on the magnetic dipole theory, it is inferred that the new method is applicable and sensitive to the detection and location of defects. Moreover, this method is advantageous as it inhibits the interference of MFL noises such as the distension noise, background noise, and vibration noise. The model predictions are then verified by a series of simulations. Finally, an experimental platform is set up to practically detect the defect of a steel plate, and the results agree with the demonstrations and simulations.