The structural integrity of wheel sets used in rolling stock is of great importance to the rail industry and its customers. In the last 15 years, 33 deaths and 48 injuries have occurred in Europe alone because of failure of train axles. This is not to mention the financial aspect of some reported derailments, which fortunately did not result in deaths or injuries but burdened the train operators with huge expense and disruption to their services. This has led to increased demands for the inspection and maintenance of axles.
Visual inspection and magnetic particle inspection (MPI) are the current standard inspection practices used for manual Non-Destructive Testing (NDT) of axles. However, these inspection processes require removal of the wheelset from the wagon/locomotive bogie and the full disassembly of the wheelset in order to facilitate access.
Some wagon providers also carry out inspection using conventional ultrasonic testing (UT), but its application is limited to disassembled wheelsets in order to facilitate probe access. An axle on a wheelset can be connected to a number of ancillary components including brakes, bearings and other supporting structures and the disassembly (and subsequent reassembly) of axles from the wheelsets and from the wagon bogey is therefore very time consuming and expensive. Indeed, there is evidence that even partial disassembly and reassembly of the wheelset could introduce future axle reliability problems.
To minimise disruption to their train services whilst ensuring continued safety, train operator companies require frequent and regular inspection methods that can allow quick inspection at the depot with the minimum of wheelset and bogey disassembly.