A FREIGHT train wagon with two containers carrying zinc concentrate broke while the 977-metre-long train travelled through central New South Wales in January.

The structural failure of the wagon during the operation of a rail freight service was due to an existing fatigue crack at a weld in the wagon’s underframe, which was likely detectable during routine inspections, an Australian Transport Safety Bureau investigation found.

The ATSB said the incident shows the importance of properly managing ageing assets to ensure continued safe operation.

On the morning of 6 January 2021, a contractor working near the rail line near Kiacatoo, in central New South Wales, noticed one of the wagons of passing Pacific National freight train 3YN2 was broken and dragging along the track.

This was promptly referred to the train controller at Junee, who in turn notified the train’s crew. Upon stopping, the crew inspected the train and found the broken wagon with its air tank resting on the rail.

The two containers with zinc concentrate on the wagon remained secure.

The investigation into the incident, undertaken by the Office of Transport Safety Investigations, which conducts rail safety investigations in NSW on behalf of the ATSB, found the wagon had dragged along the track for at least 11 kilometres, with superficial scrape marks identified on the rail and at three level crossings.

Outside of the damage to the track and wagon, no further damage and no injuries were reported.

The investigation concluded it likely an existing crack in the wagon’s underframe had worsened between the train’s departure earlier that morning from Broken Hill, causing the centre of the wagon to sag and make contact with the track.

Oxidation on the bottom portion of the fracture suggested the existing crack had been there for some time, while the remaining fracture face was fresh, and likely progressed quickly during operation.

Given the oxidation, the investigation concluded the crack was likely detectable during numerous general examinations and roll-by inspections, including those undertaken in the hours prior to the incident.

The wagon was an ICX class wagon with a butt weld at the midpoint of its load-bearing centre sill, a location of known risk. ICX class wagons were manufactured from around 1968 onwards.

“This incident highlights the importance of managing ageing assets to ensure continued safe operation through the lifecycle of the asset,” OTSI chief investigator and CEO Dr Natalie Pelham said.

“Rolling stock operators should ensure that their maintenance and inspection regimes effectively monitor and detect conditions that might escalate and contribute to accidents.”

Following the incident, Pacific National released a rolling stock safety notice detailing the failure and requiring an inspection of all affected wagons within the class.

The operator has also said it plans to develop a lifecycle asset management strategy for the affected class of wagons with a butt weld and complete a risk assessment to assess the limitations of those wagons for ongoing use.

Pacific National has committed to review its wagon maintenance manual to include all necessary details for ICX wagons, and to review and adjust its current non-destructive inspection strategy across its full fleet of wagons.