Transnet Freight Rail faces the constant threat of derailments of its heavy-haul freight trains, especially on the Orex iron-ore and Richards Bay coal-line tracks.
Many of these derailments can be caused by broken rails.
Considering the fact that the trains on these routes may be up to 3,7 km long, derailments are costly as they damage equipment and infrastructure, while also causing significant delays, says Council for Scientific and Industrial Research (CSIR) Materials Science and Manufacturing division sensor science and technology manager Jeremy Wallis.
In order to prevent derailments caused by broken rails, Transnet contracted the Institute for Maritime Technology (IMT), in Simon’s Town, to develop a broken-rail detector system for the continuously-welded tracks of their heavy-freight lines.
The parastatal, posting its request thirteen years ago, wanted something that could operate in real time, and remotely – in other words, something that could be left there, unattended, to do its work.
Local railway lines are normally checked using a specialised ultrasonic inspection car which travels on the line, as well as by personnel pushing portable ultrasonic scanners along the rails, with both processes being labour and time intensive.
The solution the IMT came up with, in partnership with the CSIR, makes use of ultrasonic waves that are transmitted along the rail between transmitting and receiving stations that are placed on the track.
If the required ultrasonic signals are not received, an alarm is activated, indicating a broken rail.
To be a bit more technical: A transducer is bolted in place on the rail. When it vibrates, the railway line vibrates at an ultrasonic frequency nobody can hear. The displacement of these vibrations is in the nanometre range. The sound propagates down the rail for a distance of up to 1,5 km, where the electronics check for the arrival of a valid signal. Here the rail ultrasonic signal is processed, with an alarm sent to the centralised train control room, should a valid signal not be detected within a set time period, notes Wallis.
This means that hundreds of kilometres of rail can be monitored continuously and remotely, with Transnet able to pinpoint the section where the rail break has occurred.
Interestingly enough, the system adapts underwater sonar technology and neatly translates it for use in places like the Northern Cape, where temperatures can range from -10 ˚C to 50 ˚C, notes Wallis.
The ultrasonic broken rail detection system has been evaluated in service on Transnet freight lines for a number of years, and successfully detected a number of rail breaks. During the last year alone, the system detected and warned the operator of two rail breakages, stopping two potentially costly derailments.
Many others have tried, but the Transnet/IMT/CSIR partnership is the first to get it working, says Wallis.
The detector project has already attracted considerable attention from the international rail community.
It has been tested in Canada, on the New York subway, Hong Kong and is currently undergoing trials in Japan.
Some of these tests were more successful than others, admits Wallis, as rail tracks have different shapes and lengths, and operate under different ambient temperatures.
“We have worked on it to now make it functional on almost any line.”
IMT has registered patents on the overall system, and CSIR is busy patenting key aspects of the ultrasound technology.
“We are currently trying to secure funding to present a final, industrialised design. The idea is to transfer the technology to a commercial partner in the next two to three years,” says Wallis.