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04.12.14

Delays to roll-out of safety-critical new tubular stretcher bars

The installation roll-out of Network Rail’s new tubular stretcher bars has been delayed. 

Chief executive Mark Carne raised the issue at a recent board meeting, with Network Rail’s minutes stating that there had been “design faults on the shallow depth stretcher bars, and the coordination and timing of the installation was complex”. 

The function of a stretcher bar is to keep the two rails in a railway switch a defined distance apart at all times and to ensure that both rails move simultaneously as a coupled pair when commanded. 

The failure of stretcher bars can, in extreme circumstances, lead to the derailment of a train, as has occurred at Potters Bar and Grayrigg in the past. 

Following these incidents Network Rail, in collaboration with Balfour Beatty, designed the new bars, which for the first time use tubular components. 

Created as a high-integrity replacement for existing designs of stretcher bar on the UK rail network, the tubular stretcher bar comprises of a cold drawn steel tube, connected to a motion unit at either end. Each motion unit contains pre-compressed elastomeric components designed to damp the transmission of loads imparted from railway vehicles into the tube. 

The new bars are said to be simpler to install, require less maintenance and are designed to withstand the rigours of the 21st-century railway. The project has, according to Network Rail, followed a groundbreaking, rigorous process to ensure that “completely redesigned safety-critical equipment” can be successfully introduced onto the passenger carrying railway. 

Going into CP5, Network Rail said: “The lessons learnt from the fatal accidents at Potters Bar and Lambrigg have led us to introduce measures to improve the overall condition of S&C, particularly in the maintenance of geometry and gauge; this includes the programme of installation of the improved stretcher bar design started in CP4. 

“The derailment risk from track buckling in hot weather will be mitigated by the improved management of ballast profiles and continued vigilance in the timely stressing of continuously welded rail (CWR). We will improve worker safety by using train based inspection to reduce the time on track and by increasing the level of proactive maintenance that can be planned more safely than fault corrective maintenance.” 

Three suppliers have been selected by Network Rail to supply the stretcher bars: Tinsley Bridge Rail; Progress Rail Services UK Limited; and Howells Railway Products. 

RTM spoke to Russell Crow, engineering development manager at Tinsley Bridge Rail, who said the delay had had no effect on its delivery of the stretcher bars. 

Asked about the design problem, he said: “It has just affected the mix we have been putting out until there is a design review of that particular part, so they have just been focusing on different installations. That has all been resolved now. It is all hands to the pumps to get as many out as possible.”

Recently, Tinsley Bridge made its first delivery of state-of-the-art stretcher bars, which is expected to be rolled out across the UK rail network this summer, from its newly formed rail division. 

However, at Network Rail’s recent board meeting it was stated that whilst the rigorous inspection regime to identify cracked stretcher bars continued, the delay was a material concern. And all the members agreed that “this required urgent executive attention to accelerate the programme”. 

To find out more about Network Rail’s tubular stretcher bars, click here

Tell us what you think – have your say below or email opinion@railtechnologymagazine.com

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Marius   06/03/2015 at 13:23

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