The structural integrity of wheelsets 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 train axles failures. 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 are the current standard inspection practices used for manual non-destructive testing 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, 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 produce future axle reliability problems.
To minimize 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. In this paper, new inspection technologies based on Phased Array Ultrasonic Testing
(PAUT) and Electromagnetic (EM) techniques suitable for the inspection of both solid and hollow axles have been developed with the overall idea of improving the efficiency in the use of axles by extending their life and monitoring their safe deployment. The key difference between the developments of this technology compared to other existing manual inspection techniques is that the inspection can be conducted in-situ without removing the axles and associated bogies from the train and with minimal disassembly of the wheelset. For solid axles, an inspection technique from the end face of the axles has been developed using new and novel 2D matrix PAUT technology. The technique is able to detect transverse cracking of the order of 1–3 mm on all parts of the solid axle, and in particular the wheel seat and neighboring areas, whilst the axle is assembled in its wheelset and bogey. For hollow axles, probes based on conventional ultrasonic testing (UT) and EM inspection techniques have been developed to detect cracks of 0.5 mm deep anywhere within the axle. The electromagnetic technique is used to detect surface breaking cracks that cannot be detected by ultrasonic technique. Data fusion combines UT and EM results to give 100% coverage of hollow axles.
