Executive summary
At approximately 0650 on 19 April 2008, freight train 5PS6, travelling from Perth to Sydney, derailed near Bates, SA. The derailment occurred about 13 track kilometres east of Bates. Thirteen wagons were derailed and about 800 m of track was damaged. There were no injuries.
The investigation concluded that an undetected crack at an unused bolt-hole increased in size until the rail completely fractured. The rail probably failed under the previous train (5MP5). As the wheels of train 5PS6 passed over the fracture, the impact forces caused the progressive failure of sleepers, a secondary rail fracture and the ejection of a small section of rail. Once a section of rail was missing, the impact forces on the rail increased significantly, causing the progressive failure of rail and sleepers until the freight wagons inevitably derailed.
The investigation acknowledged that new maintenance procedures were issued to reduce the risks related to bolt-hole cracks. However, the Australian Transport Safety Bureau has issued two safety advisory notices, concluding that there were further opportunities for improvement relating to:
- additional development of the ultrasonic testing process aimed at reducing operator dependence
- the relationship between heat-affected metal and stress concentration when specifying how far a bolt-hole should be from the rail ends before welding.
Safety issue
The process for identifying potential rail defects is limited by
the ultrasonic test vehicle operator's ability to detect and assess
the echo patterns correctly.
Action taken by the ARTC
Rail Technology International (RTI) is actively conducting further
development of their ultrasonic testing process. For example, RTI
are developing software based on 'Artificial Neural Networks' for
recognising ultrasonic reflection patterns that represent potential
rail defects such as bolt-hole cracks. RTI have conducted post test
re-analysis of ultrasonic test data using the neural network
software to identify any defects that may have been missed during
the test run. RTI's plan is to run the neural network software in
the background and conduct this analysis while ultrasonic testing
is being undertaken. RTI have indicated that implementation is
planned for early 2010.
ATSB assessment of action
The ATSB acknowledges that the ARTC and RTI are developing
processes to reduce the risks associated with operator dependence.
While some of those
initiatives have been introduced, especially in relation to
bolt-hole cracks, other rail defects are also exposed to the issue
of operator dependence. The opportunity exists for continued
development and implementation of strategies aimed at reducing
operator dependence.
ATSB safety advisory notice
RO-2008-005-SAN-035
The Australian Transport Safety Bureau advises that the ARTC
should consider the implications of this safety issue and take
action where considered appropriate.