Monitoring of Rail Track Using Guided Wave Ultrasound

Continuously welded rail track is an example of an effectively onedimensional waveguide where guided waves can propagate large distances making it possible to monitor a length of rail from a single location. In heavy duty rail lines the high axle loads and varying levels of tension in the rail cause cracks and eventually complete breakage of the rail. While inspections, using conventional ultrasonic and magnetic induction techniques, are performed periodically and repairs are made when cracks are detected a disturbingly large number of rail breaks occur around the world. Fortunately, only a small number of breaks result in train derailments. Nevertheless, the consequences of derailments led to the development of a guided wave ultrasound break detection system in South Africa. This system operates by transmitting guided waves between permanently installed transmit and receive transducers spaced approximately 1km apart. The system is currently installed on 840 km of a heavy duty rail line and is described along with performance achieved and challenges. Research being conducted to add a pulse-echo mode of operation to the system for crack detection, location and monitoring is presented. This includes hybrid FESAFE modelling of the interaction of guided wave modes with different cracks and field measurements of reflections from welds using transducer arrays and model – based signal processing. Results indicate that it should be possible to detect cracks in the rail head at long range. Detection of cracks in the foot of the rail remains a difficult but important challenge.