Executive summary
Train 6WP2 operated by Pacific National Ltd (PN) derailed at 2222 (central summer time) on Sunday 9 November 2003 as it was passing through Bates, South Australia. The train had departed Port Augusta that morning and was proceeding to Perth, Western Australia.
The derailment was limited to wagon number RKCX24 positioned 21st in a train of 73 wagons. The condition of a Roller Bearing Unit (RBU) on the right hand third axle of the wagon had progressively deteriorated to a point where friction induced heat caused the portion of axle between the RBU and the wheel to become 'plastic ' causing the RBU to seize where upon the axle separated or 'screwed' off as the axle turned.
After approximately 200 metres in this state, the leading end bogie side frame dropped to the outside of the right hand rail. The wheels did not leave the rails until reaching the western end of Bates where the crossing loop points caused a destabilising effect. The train was brought to a stop in just over 1000 metres by the train crew from a speed at the time of derailment of 77 km/h.
Approximately 1,275 metres of track sleepers and 150 metres of rail were damaged as a result of the derailment. No injuries were reported and no dangerous goods were involved.
It was concluded that train 6WP2 derailed due to the failure of a RBU on wagon RKCX24. A number of causal factors relating to bearing roller assembly cage failure were identified in the investigation associated with: bearing refurbishment and assembly; storage; and handling of the wheel set.