Defect detection in rails using ultrasonic surface waves

Defects in rails caused by rolling contact fatigue (RCF) are of growing concern to the railway industry. Conventional ultrasonic inspection methods are often not reliable in detecting critical RCF defects. The aim of this work was to develop a reliable screening tool that discriminates between critical and tolerable defects and therefore complements the existing inspection methods. The method presented here employs ultrasonic surface waves which propagate several metres along the railhead. They are excited by a local immersion probe which is operated in pulse-echo mode and scanned along the rail; in practice this would be done using a wheel probe. The excitation frequency was chosen to be around 200 kHz at which there exists a suitable surface wave mode with a sufficient penetration depth. A spatial averaging technique is applied to suppress unwanted guided wave modes and reduce signal complexity. The method has been tested successfully on a number of specimens containing artificial and real defects.