The future of railway wheelset and axle testing – Part 1

The modern world is rapidly evolving, with constant advancement and integration of technology. An abundance of information is instantly available at our fingertips. Industry is becoming more automated, improving time efficiency and maximising output, feeding an increasing demand for instant results from consumers. To be able to compete with this runaway train of technology and information overload, industry needs to embrace change and adapt processes to keep up with demand. In the railway industry, the maintenance of in-service locomotives and rolling stock vehicles can be time consuming and, with the huge cost of vehicles being out of service, train operators now need smarter solutions at overhaul to keep the rail industry moving.

In this article, I will be looking at the existing non-destructive testing (NDT) methods and the modern advancements leading the way for the future of railway maintenance.

Historically, industry has seen catastrophic failures in service, whether it be pipeline explosions, bridges collapsing or train derailment. These kinds of failure in service have seen financial devastation, irreparable loss of reputation and sadly fatalities. NDT has been at the forefront of keeping industry safe, using a variety of analysis techniques to inertly evaluate materials at manufacture or while in service. This allows components under test to enter or return to service with the assurance of being defect free. However, NDT is not always employed or applied often enough due to time constraints or a lack of NDT understanding, which can lead to incidents resembling the following example.

On the night of 28 September 2017, train 9T90 carrying about 1.67million litres of sulphuric acid in GATX freight tanker wagons derailed near Kimburra, Queensland, Australia. The train crew were initially unaware of the derailment as it had no noticeable effect on the performance of the train. Upon seeing sparks emanating from the derailed wagon, the driver applied the brake to stop the train gradually. The train stopped about 2028 m from the derailment point. There were no injuries or sulphuric acid spill and the track and rolling stock sustained minor damage. The train was repaired and the rail line was reopened at about 4.30 pm the following day. On 15 August 2018, a second derailment involving the same type of train, train 9T92, occurred. The ATSB analysed evidence from the second derailment as part of the investigation. Both derailments were found to be the result of axle failure. The failed axles in both instances were of the same type (840P1), being used for the same operation and had similar failure locations on the axle shaft.

What the ATSB found 

The organisation responsible for routine axle inspection advised that it had reviewed the inspection practices in all of its maintenance facilities and had raised awareness across its staff. The Australian Transport Safety Bureau acknowledges the safety action taken to improve the effectiveness of the axle inspection; however, it was assessed that more could be done to ensure best practice. Consequently, a related safety recommendation was issued to the inspecting organisation. Safety action was also taken to conduct more regular axle inspections while the axles are gradually replaced with an improved version. The ATSB will continue to monitor occurrences involving the GATX 840P1 axle but believes that, once fully implemented, this safety action will address the safety issue.

Safety message
Axles with undetected fatigue cracks that propagate to failure will usually result in a derailment. Recognising that axles should be resilient to fatigue cracking from in-service damage, effective axle inspection techniques that detect cracking prior to failure are fundamental to railsafety.^[1]

Today, we can see industry becoming faster, smarter, more efficient, more integrated and more automated. So how does non-destructive testing in the rail industry keep up with this and how do we keep everything running safely with exponential growth like this?

A common conventional NDT method is magnetic testing (MT), which is used to detect surface breaking and slightly subsurface defects using an induced magnetic field and magnetic particles applied to the surface in a fluorescent carrier fluid or black ink in conjunction with a white contrast paint. Non-destructive testing technicians perform these tests with portable equipment or fixed installations. Many businesses now operate ageing fixed installations as old as 40 years and over.

These ageing assets do not provide permanent records of results or data and rely on manual operation by skilled technicians. However, the NDT industry has developed these products and has made significant enhancements that better represent the technological capabilities of the modern era. Advancements in technology mean that new fixed installations can now provide permanent records and automated features. This provides full traceability of test and speeds up the process. A more advanced and specialised NDT method is manual ultrasonic axle testing (UAT), which uses pulses of ultrasound to detect subsurface obstructions in the path of the sound beam, where obstructions such as fatigue cracks should not exist. This interruption in the sound beam’s path reflects a signal back for evaluation. Manual UAT relies heavily on the skill of the technician and requires precise time-consuming calibration and pre-test performance checks for accurate examination. No permanent records are available with this method.