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At about 1856 on 24 January 2010 a loaded freight train designated 2224, travelling from Medway Junction to Berrima Junction, derailed one bogie on the second-last wagon at Exeter, NSW.

It was determined that wagon NPZH 35700U derailed due to a 'screwed journal' as a result of a wheel bearing failure. As the bearing failed, it generated and transmitted sufficient heat to the axle journal, to make it 'plastic' and allow the end carrying the failed roller bearing assembly to 'screw off'.

There was insufficient evidence to determine the cause of the bearing failure.

The investigation identified two safety issues in relation to:

  • the in-service condition monitoring of the wheel bearing which was ineffective in detecting the failing bearing before it led to the derailment, and,
  • bulk hopper wagons loaded with limestone which have been regularly operated at speeds up to 15 km/h higher than the mandated limit for some classes of track.

In both cases the train operator has taken safety action to address the issue.

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