The Australian Transport Safety Bureau says a fatigue crack on a failed axle has likely caused two derailments on the Mount Isa – Townsville railway line.
The ATSB are drafting a final report into the Derailment of Aurizon train 9T90 at Kimburra, near Pentland, on the night of September 28, 2017.
The train was travelling from Townsville to Phosphate Hill with 1.67 million litres of sulphuric acid.
The ATSB said the leading wheel set of the trailing bogie of a wagon failed and derailed at 72 km/h. The train crew were initially unaware of the axle failure and derailment as it had no noticeable effect on the performance of the train and the train travelled a further 1.3km.
After passing the Campaspe River Bridge, the driver looked in the rear vision mirror and saw sparks from the derailed wagon.
The driver applied the brake and stopped the train about 2km after the derailment. The driver contacted the network control centre in Townsville to report the train had stopped and advised the other driver had exited the locomotive to inspect the train and determine the source of the sparks.
Later, the driver confirmed to the NCC an axle on the train had fractured, allowing one wheel set on the fourteenth wagon to derail.
There were no injuries or sulphuric acid spill. The train was repaired and the line was reopened the following day.
An examination of the failed axle found it fractured due to “a fatigue crack that propagated until it reached a critical size resulting in an overstress fracture” which separated of the axle halves and caused the derailment.
The ATSB said the crack was big enough to be detected at the previous inspection but wasn’t and as a result Aurizon increased the number of inspections from April 2018.
However on August 15, 2018 another derailment involving the same type of axle occurred. Train 9T92 was taking sulphuric acid from Townsville to Phosphate Hill when two wagons derailed at low speed near Hughenden.
There were no injuries or sulphuric acid spill but an examination confirmed that an axle from the freight tanker wagon had fractured, allowing the trailing wheel set of the trailing bogie to derail causing all wheel sets on the following wagon to derail.
The axle from train 9T92 was due to be inspected by October 2018 in line with the increased inspection frequency.
The ATSB said evidence indicated the failure mechanism of the axle from train 9T92 was probably the same as train 9T90. The ATSB said wagon fleet owner Incitec Pivot inspecting the entire fleet and by end September 2018, it had removed 17 cracked axles from service.
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