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Undetected problems

Rail undetected problems

Following an investigation into the partial separation of an express passenger train, the ATSB is reminding rail operators of the need for effective inspection regimes and to ensure that rail components meet service requirements.

The investigation was initiated in August 2011, after a scheduled Melbourne to Sydney express passenger train (XPT) partially separated as it passed over a dip in the track near Broadmeadows, Victoria. The train suffered a total loss of power and was unable to continue its journey, coasting for a short distance. Initial inspection of the train suggested that the electrical disconnection was a result of the leading power car decoupling from the carriages; but it was clear that the power car and carriages stayed close together because the brake lines remained connected.

The ATSB found that the problem lay in an element of the draft gear (the connecting assembly between cars). The element in question was the tail pin, a steel component 590 mm in length. The tail pin failed as a result of an overstress fracture that was initiated by fatigue cracking – cracking that, worryingly, recent routine ultrasonic testing had not detected. Post-incident material testing established that the mechanical properties of the tail pin were below the required standard.

As a result of the investigation, a new batch of tail pins has been manufactured to an upgraded standard which includes improved quality control and acceptance testing...

Following this incident, the ultrasonic testing procedure was revised to improve the detection of smaller cracks in the tail pin. However, the separation of another XPT near Seymour, Victoria, on 1 August 2012 in similar circumstances showed that the ultrasonic testing regime was still not detecting all fatigue cracks in critical areas of the tail pin.

On 3 August 2012, the ATSB issued a safety issue notice to RailCorp, the operator of the XPT fleet, warning of the preliminary findings. Although this sort of coupler failure was extremely unlikely to lead to a derailment, the consequences of such an event involving a passenger train, should it occur at speed, were potentially very significant. In response, RailCorp set about developing a new testing process and fitting newly designed tail pins.

As a result of the investigation, a new batch of tail pins has been manufactured to an upgraded standard which includes improved quality control and acceptance testing and RailCorp is currently in the process of fitting these new tail pins. RailCorp has also further revised the tail pin inspection regime with the aim of improving its effectiveness.

This investigation did not examine how the idiosyncrasies and condition of the track may have contributed to the partial separation of the train. Those issues will be considered as part of the ATSB’s broader safety issue investigation into the interstate rail line between Melbourne and Sydney.

Read the full investigation report, RO-2011-012

 
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Last update 26 April 2013