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Summary

Summary

At approximately 0710 on 23 October 2010, 15 wagons on freight train 3PW4 derailed near Wodonga, Victoria. There were no injuries but serious damage to rolling-stock and rail track (including a bridge structure) was sustained during the derailment.

The investigation concluded that an axle bearing on wagon RKWY-4125C failed and completely seized, causing the inner rings to spin on the axle journal, generating and transmitting sufficient heat to the journal to make it 'plastic' and causing it to separate from the axle (commonly referred to as a screwed journal). The most likely cause of bearing seizure was a loss of interference fit between the inner rings and journal which allowed the inner rings to turn or spin on the axle journal leading to increased wear and ultimately generating significant heat and damage until the bearing completely seized. It was possible that fretting and rotational creep contributed to the loss of interference fit.

Examination of data recorded by the ARTC Bearing Acoustic Monitoring system (RailBAM) found that, over the previous 12 months, the system detected potential looseness or fretting defects on wagon RKWY-4125C, but did not record any apparent fault trend. Nor did the system record any bearing defect on wagon RKWY-4125C when train 3PW4 passed through the system on 21 October 2010.

While there was no documented evidence of such, Pacific National advised that they actively in-service monitor the risk of looseness and fretting damage to bearing components, but since mid-2007 have not relied solely on fault indications identified by RailBAM. It is recognised that, with current maintenance processes in place, bearing failure due to looseness and fretting is relatively rare. However, without documented records, bearing failure due to looseness and fretting damage cannot be effectively monitored.

 
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