Investigation of rail defects using an ultrasonic inspection method: A case study of aksaray-airport light rail transit line in Istanbul

Both ballasted and non-ballasted railway superstructures have been highly affected by the increased traffic on railway lines, heavier axle loads and higher train speeds. These forces acting on rails can lead to rail damage that may cause derailments. Therefore, non-destructive inspection of rails has become more important. The primary purpose of this study is to detect rail defects using an ultrasonic inspection method on Aksaray-Airport Light Rail Transit Line which has a daily ridership of 320,000 passengers. Besides, this study aims to determine the characteristics of rail defects and to investigate the behaviour of defects on different rail welding types used on the track. Detection of rail defects is performed by an ultrasonic inspection car including ultrasonic probes which are capable of producing, transmitting and receiving ultrasonic waves that inspect the entire rail section. Ultrasonic probes enable the determination of basic characteristics of defects. Results of the ultrasonic inspection are evaluated on the basis of successive track sections between the stations in the track. In every track section, the “number of rail defects per km” is calculated and the distribution of defects in rail and rail welds is analysed comparatively. According to the results of ultrasonic inspection, the majority of rail defects are found to occur at rail welds. The “number of rail defects per km” in aluminothermic welded track sections is higher than the “number of rail defects per km” in flash-butt welded track sections. Besides, the defect rate in aluminothermic welds is higher than the defect rate in flash-butt welds. Although the majority of aluminothermic weld defects occur in the head region of the weld, the majority of flash-butt weld defects arise in the web region of the weld.