Research On Magnetic Flux Leakage Technique For Rail Cracks

The rail crack is a kind of common damage for railway, which may cause severe traffic accidents. Itis important for railway sector to implement online detection to rail crack in fast, safe and accurateway. Magnetic Flux Leakage (MFL) nondestructive testing is a non-contact inspection technique andis suitable for the rail crack. However, for the high speed MFL testing, it should be studied to ensurethat the rail magnetization intensity is the strongest. For direct-current MFL testing at hand push typespeed, the problem that the signal is susceptible to interference should be solved.At first, this paper studies influencing factors to magnetization of rail during direct-current MFLinspection, and explains mechanism that the leakage magnetic field detected will increase as theinspection speed increases by the equivalent permeability model. The experiment found thatexcitation increase and lifting off reduction should enhance magnetization of rail. Then, the model ofalternating MFL testing is designed, the design effort includes hardware design and choosing digitalsignal processing method. The effect of excitation current frequency and inspection speed onalternating MFL testing is analysed by experiment. It has been found that detection result ofalternating MFL testing is optimal when inspection speed is hand push type inspection speed,excitation current frequency is100Hz and digital signal processing method is quadraturedemodulation. It may compensate bad detection result and susceptible to noise interference fordirect-current MFL at hand push type inspection speed. Finally, the design of the direct-current MFLinspection system based on sensor array is introduced, including hardware design, software designand experimental verification, and the algorithm of rail crack judgment is presented.