Experts warn of third-rail cracks on NS, EW lines
Call for immediate checks is one of 33 recommendations
By Christopher Tan, The Straits Times, 16 May 2012
A SIX-MEMBER team of technical experts told the Committee of Inquiry yesterday that the power-supplying third rail of the North-South and East-West train lines could have hairline cracks.
It is therefore asking for immediate checks to be carried out.
This is among 33 recommendations that the team has made to the Committee on what should be done to prevent breakdowns such as the ones in December.
Presenting its view of what caused the worst breakdown in the MRT's 25 years of operations on Dec 15 last year, team leader David Ewins, professor of vibration engineering at Imperial College London's Department of Mechanical Engineering, said one crack was discovered along the incident site between City Hall and Dhoby Ghaut stations northbound.
Prof Ewins said the cracks on the third rail - which supplies power to the trains - were not discovered 'until some weeks later', and called for ultrasonic tests to be done on the network, starting with the two incident sites.
Following up on this, the Land Transport Authority (LTA) has asked SMRT to check for cracks and replace third rails where cracks are visible.
'While the cracks do not cause immediate concern, as a precautionary measure, LTA has asked SMRT to implement measures for added safety,' a spokesman said.
'SMRT will therefore be replacing the third rails at those locations where the cracks are more visible with immediate effect.'
She said LTA has also told SMRT of the need to monitor closely the condition of third rail joints across the entire network.
Prof Ewins also said the December breakdowns were caused by 'a combination of events that were linked to each other', but it may not be possible to establish 'the exact sequence of events'.
The team, made up of vibration, noise and rail dynamics experts, agreed that the Dec 15 incident was likely to have been triggered by a damaged fastener in the third rail support assembly.
The faulty fastener caused a claw holding the third rail to be dislodged and the third rail to sag marginally, it explained.
This sagged section was then prone to a higher level of vibration as trains passed, causing more supports - some of which also had faulty components - to give way. In all, six supports gave way, leading to a major sagging of the third rail, disrupting power supply to trains.
The sagged third rail also damaged the current collector devices - which make contact with the third rail - of five trains, it noted.
The team gave two scenarios as explanations for the second disruption on Dec 17.
The first was attributed to a train with damaged current collector devices that might not have been spotted and rectified after the Dec 15 accident.
The second scenario has to do with a crack in the third rail, which made the structure more prone to vibration. One member of the team of experts said thick carbon deposits in the crack suggest that it could have pre-dated the third rail sagging by several days.
The experts rounded off their testimony by presenting 33 recommendations on what could be done to prevent future incidents.
The suggestions covered six categories, including how to maintain wheel condition of trains and third rails to better monitoring of procedures and maintenance of assets.
It also asked both SMRT and the LTA to ensure their respective roles are clearly stated and understood by all parties.
With the six expert witnesses, the inquiry has heard evidence from a total of 100 witnesses so far since it started on April 16.
The experts and their recommendations: Maintenance, checks and investment necessary
EXPERTS FOR STATE
David Ewins, professor of vibration engineering at the Department of Mechanical Engineering at London's Imperial College
Huang Xianya, vice-president and chief consultant for inspection and failure analysis at Singapore-based testing laboratory TUV SUD PSB
EXPERTS FOR LAND TRANSPORT AUTHORITY
Richard Greer, a director of engineering group Arup, specialising in railway vibration and noise
Jerry Evans, principal engineer of Interfleet Technology and a specialist in rail vehicle dynamics
EXPERTS FOR SMRT CORP
Graham Brown, head of advanced analysis and test group at Sinclair Knight Merz
Ben Harding, a director of UK engineering firm Atkins
KEY RECOMMENDATIONS
THE six experts made a total of 33 recommendations that are divided into six strategic categories.
1 Maintain wheel condition of trains, as flat spots on the metal wheels cause excessive vibration.
2 Do regular checks on train current collector devices (which draw electricity from the third rail). They can have tell-tale signs of faults on the third rail.
3 Invest in more robust fastening assemblies for third rail support. This will prevent the third rail from sagging - the primary cause of December's breakdowns.
4 Do regular third rail alignment checks, so faults can be detected and fixed early.
5 Have a proper asset management framework in place, which includes proper specifications during the design stage, installation at the construction stage, and a robust maintenance and replacement system during operation.
6 Monitoring of procedures, which cover maintenance, inspections and risk assessment.
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