Abstract

Rolling contact fatigue (RCF) is one of the main reasons why rails fail prematurely. Much of the understanding of RCF arose from work at CUED from the late 1970s through to the 1990s. Although the significance, potential dangers and methods to deal with RCF were recognised at that time, measures to treat the problem were not implemented on the UK passenger railway until a fatal derailment at Hatfield occurred in October 2000. The Hatfield derailment changed maintenance practice on passenger railways worldwide.

Similar problems exist on metros but there are also significant differences. There are seldom sufficient resources to deal with and to understand these problems. These shortcomings were highlighted in the consultancy project described here, which also took place during the Covid-19 shutdown. All work was undertaken remotely using photographs, email and video-conferencing. A further complication was a language difference.

Staff operating the metro in a European capital city noticed that there were apparently severe defects on their heavily used railway. Novel but apparently well-tested equipment had recently been introduced from a well-known supplier. This equipment had also been “certified” by a major European mainline railway and was used worldwide. Measurements suggested that defects were more than 7mm in depth over significant lengths of track. The common understanding was that if conventional RCF defects of this severity had existed, continued operation of trains was dangerous as rails could have shattered, causing trains to derail. Speed restrictions had been imposed and consideration had been given to halting operations completely. Colleagues who were responsible for the track consulted the author for advice on how to proceed and whether, and if so how, they could continue to operate trains.

The seminar presents the problem, some of the measurements that had been undertaken and advice that was given to ensure safe running of the railway in the very short and longer terms. Within a couple of months, rudimentary analysis was undertaken to estimate residual rail life, supplemented by laboratory testing of defective rails removed from track. It was demonstrated not only that defects were not the type of RCF that had been assumed by others, they were accordingly not an imminent danger. Moreover, the equipment that had been introduced to assess the severity of defects left much to be desired.

Similar defects exist and continue to be misdiagnosed on many railways of different types. London Underground are one of the few metro systems to recognise that these defects differ from what others accept. This understanding has saved them a few million GBP annually in the cost of maintenance and premature rail replacement since the late 2000s.