An inadequate rail joint likely led to a South Australian derailment last July, the Australian Transport Safety Bureau has found.
Genesee & Wyoming Australia (GWA) train 24KW was travelling towards the port of Whyalla on July 7, 2014, when a break in the line occurred, causing seven fully-loaded bottom-dumper wagons to derail.
The incident took place on a railway belonging to ASX-listed miner Arrium, between Iron Branch and 21km Junction.
Arrium’s track is continuous welded rail, meaning rail segments are joined together through flash welding.
But in the months prior to the incident, the section of rail in question had undergone tamping and re-railing. As a result, rail segments in that section were joined with bolted fishplates (welding was planned for a later date).
A fishplate joint features a pair of metal bars (fishplates) which are placed either side of a rail, and fastened together with a number of bolts.
Some rail lines are joined together permanently via the fishplate method. In these cases, Australian standard joints usually feature six total bolts – three on either side of the rail joint – according to the ATSB’s report, released on April 28.
The temporary use of fishplate joints is common practice on a continuous welded line, after maintenance work has taken place. In these cases, just four bolts are typically used – two on either side of the joint – the ATSB said.
But according to the safety bureau, evidence shows that one of the fishplate joints which failed in the South Australian derailment had been secured with just two bolts – one on either side of the joint.
“Examination of the southern rail joint showed that the Iron Baron end of the joint had been fastened with only one bolt,” the ATSB said.
“While the Whyalla end of the southern rail joint had completely separated during the derailment sequence, the components were recovered and examined,” the bureau continued.
“The holes through both fractured fishplates and the rail web showed no definitive indication that bolting had been installed through two of the three bolt holes, suggesting that the assembly had also been secured through a single bolt through this end of the joint.”
On top of this, the ATSB found that bolt holes on the southern rail joint had been widened through a flame cutting method, making it hard for the bolts to be sufficiently tightened.
“It was … evident that both the field and gauge-side fishplates had been modified by slotting (elongating) the bolt hole using an oxy/acetylene thermal cutting tool,” the ATSB explained.
According to the safety bureau, flame cutting of joint components “is usually only acceptable for emergency repairs,” and when such repairs are made, a speed restriction of 10km/h is usually applied.
In this instance, however, no such restriction was applied. Train 24KW was travelling at 50km/h when the incident occurred.
Adding to the alleged use of just two bolts and widened holes on the southern joint, several fishplates in both the north and south rail joints showed signs of pre-existing fatigue, the ATSB said.
“The southern fishplated rail joint was assembled using inappropriately-modified fishplates with an inadequate number of through-bolts,” the bureau summarised, “reducing its structural integrity and allowing relative movement within the joint under the load of a train.”
Arrium’s rail line was shut for two days following the incident, while recovery personnel and track and train maintenance crew conducted recovery and restoration works.
The train sustained “serious” damage, according to the bureau’s report.
As a result of the derailment, Genesee & Wyoming Australia replaced all the fishplate joints with mechanical welding.
GWA and the contracted maintenance company, Transfield Services Australia, also completed an audit of maintenance standards and processes, and in November 2014 Transfield disseminated a document Mechanical Joint Rectification to all track maintenance staff.