Development of high-speed inspection technique based on motion-induced eddy current testing for surface railway defects

Thailand’s rail infrastructure is undergoing expansion through investment in double-track and high-speed rail projects, such as the Thailand–China railway. With increasing traffic loads, surface defects including cracking, rolling contact fatigue (RCF) and spalling are becoming more extensive issues. Conventional non-destructive testing (NDT) methods often struggle to maintain efficiency during high-speed inspections. To address the challenges, this study proposes a modified Motion-Induced Eddy Current Testing (MIECT) technique utilising a self-induced magnetic field principle. A custom-built high-speed rotational simulator with controllable speed was designed and fabricated to simulate the high-speed inspection of rail tracks. Particularly, a set of specialised probes, integrating a unique configuration of permanent magnet with a Tunnelling Magneto-Resistance (TMR) sensor, was developed and optimised through simulation and experimental validation. To demonstrate the performance of the MIECT, the system was evaluated against various types of artificial defects on the speed simulator. The results showed that the presented MIECT technique successfully detects cracks as small as 0.5 mm in width and 1 mm in depth, as well as 2 mm diameter round defects, at speeds up to 30 km/h. Consequently, this approach offers a promising alternative for robust, high-speed railway inspection and overcoming the velocity limitations of traditional inspection methods.