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Heat may have masked defects prior to 2015 accident

Hot temperatures during ultrasonic testing may have masked defects in a rail which later broke, leading to the derailment of a BHP iron ore train three years ago.

The Australian Transport Safety Bureau (ATSB) on October 12 released its final report into the derailment of BHP train M03544 on the morning of December 3, 2015.

At around 0530 on the day in question BHP’s train controller, based in Perth, was alerted to a dragging equipment detector alarm on the Newman main line, 67 kilometres from Port Hedland.

Seven seconds later, the train recorded a loss of brake pipe air pressure before coming to a stop. The driver walked towards the rear of the train and found it had separated and derailed.

26 ore cars, which were part of the train’s second group, or ‘rake’ of cars, were significantly damaged in the derailment, the ATSB’s report says. No injuries occurred.

200 metres of west track – upon which the train was travelling – was rebuilt, along with 50 metres of the adjacent east track, following the incident.

The ATSB investigation found the train’s separation and derailment was caused by a broken rail.

“A fracture of the rail was probably initiated by the rapid growth of a detectable, yet unidentified, fatigue-related transverse defect(s) in the west rail near the 67 kilometre mark during the passage of the train,” the Bureau said.

The Bureau’s report also suggests a defect, or multiple defects in the rail may have gone undetected due to high temperatures during ultrasonic testing.

Hot temperatures often seen during the day in the Pilbara region can increase the compressive forces within a rail, potentially pushing the surfaces of a defect together such that the sound waves used in ultrasonic testing may pass through the defect, rather than reflecting of the defect’s surface, the Bureau explains.

“A review of one of [BHP’s] internal investigation reports for this occurrence noted that ‘small transverse defects are easier to detect when the track is cooler’,” the Bureau pointed out.

BHP’s internal report also noted: “previous ultrasonic inspections of track were only carried out at night, where the advantage of ultrasonic testing, when the rail is cool with reduced thermal stress, allowed for greater detection of transverse defects.

“The night inspections were carried out on the Mt Newman railway, however this practice ceased many years ago for non-technical reasons.”

Following the derailment at the end of 2015, BHP accelerated the re-railing of 833 kilometres of track, including the track in the vicinity of the incident.

According to the ATSB, BHP has also introduced processes to reduce the initiation of rolling contact fatigue cracks in rail track, and to improve rail defect detection.

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