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What happened

On 28 August 2015, a Pacific National fully loaded coal train MB520 departed from Maules Creek, NSW destined for Port Waratah, NSW. Shortly after passing Ardglen and descending the grade towards Pages River, a wheel failure occurred on the leading right hand wheel on the 19th wagon. This led to the wheel moving off the wheel seat towards the centre of the axle. The bogie rotated causing the other wheels on the bogie to derail. The train continued travelling until a damaged inter car brake cable activated the train’s brakes. There were no injuries, but the derailment caused damage to over 590 metres of track including 963 sleepers.

What the ATSB found

The ATSB investigation found that the derailment was caused by a wheel failure. A metallurgical analysis conducted after the derailment found that the wheel had multiple cracks in the wheel rim; one crack extended from the rim to the boss of the wheel. This likely originated from a transverse thermal crack on the wheel tread surface. Thermal cracks of this type are generally associated with high thermal input under service brake conditions.

An increasing level of wayside alerts starting a month before the derailment indicated the likelihood of the fault being present then. Despite the increasing impact level readings, no immediate action was taken to inspect the wheel before it eventually failed.

It was found that the wheel inspection processes were not effective in detecting surface damage or cracks. The failed wheel was approaching the end of its service life with a rim thickness of 25 mm. This low rim thickness increases propensity to thermal distortion and is likely a significant factor into the thermal crack formation and propagation that occurred.

At the time of writing this report there have been seven reports of fractures detected in wheels, within a 3-year period, on Pacific National coal wagons in NSW. Three occurred before the derailment with the first incident on 31 May 2013. Three more fractured wheels were identified within a two-month period after the derailment. Following the first three wheel failures internal reports recommended changes to reduce the risk of wheel defects. Only limited action was taken by the operator prior to the derailment on 28 August 2015.

What's been done as a result

Since the derailment, the rollingstock operator has advised that they have established a process to remove wheels considered to be at greater risk of fracture. To this end, they have implemented a program to remove wheels with a rim thickness under 25 mm. Pacific National also intends to improve their internal standards to include revised criteria and actions for thin rims and wheel impacts.

Safety message

Rollingstock operators with heavy haul wagons using wheels near the end of their service life should be aware of the increased risk of wheel failure due to cracking. They should ensure that wheel inspection and maintenance programs include systems and techniques for detecting and assessing wheel defects with the potential to lead to cracking. These systems and techniques should be validated to ensure they are effective to detect such defects.

 

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The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

Appendices

 

Safety issues

RO-2015-015 SI-01 - RO-2015-015 SI-02 -  

Wheel inspection processes

The wheel inspection processes and systems were not effective in detecting surface damage or cracks on the R4 wheel on wagon NHIH97081 prior to the wheel failure.

Safety issue details
Issue number:RO-2015-015 SI-01
Who it affects:All owners and operators of heavy haul freight wagons


 

Low rim thickness

Despite a number of incidents, Pacific National did not take adequate action, before the derailment, to reduce the risk of wheel defects, especially in light of previously identified contributors such as low rim thickness. 

Safety issue details
Issue number:RO-2015-015 SI-02
Who it affects:All owners and operators of heavy haul freight wagons.

 
General details
Date: 28 Aug 2015 Investigation status: Completed 
Time: 0618 EST Investigation type: Occurrence Investigation 
Location   (show map):Pangela  
State: New South Wales  
Release date: 30 Jun 2016 Occurrence category: Incident 
Report status: Final Highest injury level: None 
 
Train details
Line operator: Australian Rail Track Corporation (ARTC) 
Train operator: Pacific National 
Train registration: MB520 
Type of operation: Freight 
Sector: Freight 
Damage to train: Minor 
Departure point:Narrabri, NSW
Destination:Port Waratah, NSW
 
 
 
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Last update 30 June 2016