Improved rail inspection boosts safety
Non-destructive testing (NDT) is used widely in civil engineering for inspection of parts and detection of defects before potentially catastrophic damage occurs. The railway sector conducts periodic in-track rail inspections primarily using ultrasonic technology. Conventional ultrasonic technology relies on continuous contact with the rail track making inspection speeds quite slow. In addition, defect detection is highly dependent on continuous probe-surface contact such that it is sensitive to rail surface condition and rail or defect geometry in addition, of course, to noise and vibration in the system itself. Although such methodology has been relatively successful in detecting many types of cracks and defects, its limitations have resulted in rails that passed inspection subsequently breaking and causing derailments. In order to improve ultrasonic NDT technology and thus the safety of the European rail system, researchers initiated the ‘Non-contact ultrasonic system for rail track inspection’ (U-RAIL) project. The goal was to develop a NDT ultrasound system that does not require contact between the probe and the rail surface and so is better and faster at finding defects. The U-RAIL system consisted of a pulsed laser and an air-coupled (rather than water-coupled) transducer. Scientists developed software to control the laser system and characterise defects from the signals obtained as well as a user friendly interface. After mounting the U-RAIL system on a modified rail vehicle, researchers tested the system extensively on selected flaws. U-RAIL was able to inspect more than 80 % of a rail section with excellent detection of cracks not identified with conventional methods. Commercial implementation of the U-RAIL system should provide major savings in time, effort and cost while significantly increasing safety.
