Study on high-speed rail defect detection methods based on ECT, MFL testing and ACFM

Electromagnetic testing (ET) has been widely used in high-speed rail defect detection due to its non-contact, simplicity and efficiency, and mainly includes Eddy Current Testing (ECT), Magnetic Flux Leakage Testing (MFL) and Alternative Current Field Measurement (ACFM). In this paper, a comparative study is carried out on characteristics and speed effects of these three methods. Firstly, through theoretical and finite element simulation analysis, the influences of diffusion and convection effect of magnetic field in ECT, MFL and ACFM are explored, finding that the eddy current move backward and form a trail at high speed in ECT, the magnetic lines of flux inside the specimen shift backward and tend to the surface of specimen at high speed in MFL, and the uniform current shift slightly backward at high speed in ACFM. Then in the rail defect detection experiment at the speed of 20 km/h, the signal of different defect parameters such as depth, internal angle, and surface angle are compared and analyzed, and finding the characteristics and applicable conditions of each method. Finally, the rail defect detection experiment is carried out in the speed range of 20 ∼ 220 km/h. The results show that the ECT signal decreases with the increase of speed, the MFL signal increases with the increase of speed, and the ACFM signal is basically unchanged with the increase of speed.