Interim factual report published 30 November 2018

On the evening of 28 September 2017, train 9T90 carrying about 1.67 million litres of sulphuric acid in GATX freight tanker wagons, was travelling within Queensland, west from Townsville to Phosphate Hill, Mount Isa. At 2307 Eastern Standard Time,^[1] the leading wheel set of the trailing bogie of the fourteenth wagon in the consist (OSZY44795) failed and derailed at a recorded speed of 72 km/h. Evidence of wheel strikes to the track infrastructure were found west from the 216.460 km mark, measured from Townsville. The train crew were initially unaware of the axle failure and derailment as it had no noticeable effect on the performance of the train.

Consequently, the train travelled about 1,300 m further at up to 75 km/h. At 2308, just after passing the Campaspe River Bridge, the driver looked in the rear vision mirror and saw sparks emanating from the derailed wagon. The driver applied the brake to stop the train gradually. The train stopped at about 2309, about 685 m after the brake application (and 2,028 m after the derailment).

At 2310, the driver contacted the network control centre (NCC) in Townsville to report the train had stopped. He also advised that the other driver had exited the locomotive to inspect the train and determine the source of the sparks. A short time later, the driver confirmed to the NCC that an axle on the train had fractured, allowing one wheel set on the fourteenth wagon to derail (Figure 1).

Figure 1: Failed axle in-situ from train 9T90

Source: Incitec Pivot

There were no injuries or sulphuric acid spill. The track and rolling stock sustained minor damage. The train was repaired and the Mount Isa line was reopened at about 1630 the following day.

Similar subsequent derailment

On 15 August 2018, some 10 months after this derailment, a second derailment involving the same type of axle occurred. Train 9T92, transporting GATX freight tanker wagons containing sulphuric acid, was en‑route from Townsville to Phosphate Hill. At about 0257, two of its wagons derailed at low speed near Hughenden, about 375 km from Townsville. There were no injuries or sulphuric acid spill, however there was minor to moderate track damage over several kilometres. The operator’s examination confirmed that an axle from GATX freight tanker wagon OSZY44729 had fractured, allowing the trailing wheel set of the trailing bogie to derail (Figure 2).^[2] This caused all wheel sets on the following wagon to derail.

Figure 2: GATX freight tanker wagon OSZY44729 from train 9T92

Source: Incitec Pivot

The ATSB obtained evidence from the second derailment to analyse it as part of the investigation. The failed axles in both instances were the same type (840P1), same operation, and similar failure location.

Preliminary observations

The following preliminary observations are based on evidence analysed to date by the ATSB:

• Examinations of the failed axle from train 9T90 indicate that it fractured as a result of a fatigue crack that propagated until it reached a critical size resulting in an overstress fracture. The fracture resulted in the separation of the axle halves (and subsequent derailment).
• The ATSB determined that a fatigue crack in the axle from train 9T90 was likely of a detectable size at the time of its previous magnetic particle inspection (MPI) but it was not detected (hence the axle continued service).
• Following the derailment of train 9T90, from April 2018, the operator increased MPI intervals to additional in-situ yearly intervals.
• The axle from train 9T92 was due to be inspected by October 2018 in line with the increased inspection frequency (it failed about 2 months earlier, in August 2018).
• The available evidence indicates that the failure mechanism of the axle from train 9T92 was probably the same as that of the axle from train 9T90 (and with similar consequences).

Safety actions

Proactive safety action

Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.

Incitec Pivot

Incitec Pivot (IPL) owns and maintains (through a maintenance provider) its GATX freight tanker wagon fleet. Following the derailment of train 9T92, IPL performed in-situ MPIs on the entire GATX wagon fleet. By the end of September 2018, it had detected 17 cracked axles and removed them from service. The company is considering further increasing non-destructive testing intervals, as well as an improved axle design for its GATX fleet.

Aurizon

Aurizon provided wheel set maintenance services to Incitec Pivot’s maintenance provider. These services included MPI of GATX freight tanker wagon axles during routine wheel set maintenance. Aurizon has advised that it has reviewed MPI practices in all of its maintenance facilities, and raised awareness across its staff.

Investigation progress

As part of the investigation activities conducted to date, the ATSB has:

• examined the fractured axle from train 9T90 and reviewed materials failure analysis reports
• conducted a review of the previous GATX freight tanker wagon axle failures, including failure analysis reports, from 2012, 2014, and 2016
• analysed on-board and trackside recorded information for the train 9T90 and 9T92 derailments
• attended the Rockhampton maintenance facility to observe, assess and review the GATX freight tanker wagon axle non-destructive inspection processes
• communicated preliminary observations and potential safety issues directly with directly involved parties, including Incitec Pivot and Aurizon.

The ATSB continues to work closely with directly involved parties to gather further information and encourage proactive safety action.

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The information contained in this update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the accident as outlined in this update. As such, no analysis or findings are included in this update.

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1. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
2. The involved axle had travelled about 86,000 km prior to failure and was last inspected in October 2017.

At approximately 2310 on 28 September 2017, the driver of train 9T90 noticed sparks coming from the rear of the train. After stopping the train near Kimburra to investigate, the driver identified a broken axle on the sixteenth wagon. This was reported to the network control officer in Townsville who then arranged the appropriate recovery response.

There were no injuries or reported sulphuric acid product spill. The track and rolling stock sustained minor damage.

The ATSB has commenced an investigation and is collecting relevant evidence, including metallurgical examination of the failed axle and interviews with directly involved parties. The evidence will be analysed and a draft investigation report compiled. This draft report will be forwarded to relevant parties for comment prior to the completion and release of the final report.