Sunday, 17 February 2013

Corrosion in bolts, wires caused MRT disruptions in March 2012, August 2012 and January 2013

Parts broke, leading to power supply failure in three major NEL incidents
By Royston Sim And Jermyn Chow, The Straits Times, 16 Feb 2013

CORRODED stainless steel wires and bolts were to blame for three major disruptions on the North- East MRT line (NEL) during the last 12 months, Transport Minister Lui Tuck Yew said yesterday.

In each incident, the damaged parts broke, causing the line's overhead power supply to fail and disrupt the journeys of tens of thousands of commuters.

These were the findings of a joint team set up last October to look into the breakdowns and devise measures to improve the reliability of the NEL in the long run.

Trains on the NEL draw power from overhead cables, unlike other MRT lines where power is supplied by a third rail along the tracks.

An NEL breakdown last March occurred after chloride from water that seeped into the tunnel corroded two stainless steel cables of a counterweight which held the overhead power lines in place.

When the cables snapped, the concrete weights attached to them fell and the power lines sagged. No trains could pass through and about 90,000 commuters were affected.

Last August and in January this year, trains were disrupted when U-shaped bolts broke. The bolts secured a cantilever arm attached to the power lines.

All three incidents happened in a stretch of tunnel between HarbourFront and Outram Park stations.

Mr Lui said that in the two later incidents, the bolts were corroded by chloramine - a combination of ammonia and chlorine. He noted that these incidents took place in areas where there was no water seepage.

The joint team - made up of Land Transport Authority (LTA) and SBS Transit engineers - is still working to locate the source of the chloramine.

They noted that three factors had to be present for stress corrosion cracking to take place: a corrosive agent, material susceptible to corrosion and sufficient tensile stress to induce the cracking.

Asked why the wires and bolts were not built to better withstand corrosion, Mr Lui said: "When we went for this system... this was the best available then, used in many other countries."

He added that there could have been problems during their manufacture.

The breakdown in March was one of at least four incidents linked to water leakage in MRT tunnels, raising questions about the robustness of Singapore's rail infrastructure. Water had caused power cables to deteriorate, leading to breakdowns along the Circle Line last September and in September 2011.

It was also named as a possible cause of an electrical cable short- circuit, which led to Wednesday's fire at Newton station.

Asked if there were infrastructural flaws in the rail system, an LTA spokesman said the NEL's design was based on international standards while stainless steel wires and U-bolts are widely used in other tunnel environments.

But he added that the transport operators have to keep those environments dry.

SBS Transit has replaced all counterweight wires along the problematic stretch between HarbourFront and Outram Park stations. It will also change all 1,600 U-bolts in that stretch by mid-April and checks will be intensified.

In the long run, the joint team aims to replace all U-bolts with more corrosion-resistant materials. It plans to find a suitable material before the end of the year.

It will also replace the counterweight system cables with ones made of new materials by the middle of 2014 and examine ways to ensure that trains can still run if a cable snaps.

A consultant will be engaged to do a full review of the line - most likely by the middle of next year.

Root cause of Newton fire must be found: Lui
By Royston Sim, The Straits Times, 16 Feb 2013

INVESTIGATORS will need to get to the root cause of a fire that broke out along the train tracks near Newton station earlier this week, said Transport Minister Lui Tuck Yew yesterday.

Speaking to reporters after visiting SBS Transit's Sengkang Depot, Mr Lui noted that although the fire was small, any fire in the tunnels or stations is "very serious" and "potentially very catastrophic".

He said that while it was clear that a cable insulator fault was to blame, how it happened was still undetermined."Is it because of ageing, is it because it is time to be changed, these are all speculative at this point in time."

While such fires are rare, he said it should serve as a warning and an opportunity to take a careful look at rail maintenance and operations.

He noted that the last time a fire occurred was in 2004, when a small one broke out in a tunnel near Newton. Investigators found that rubber padding supporting the base plate at the railway track had caught fire.

In Wednesday's incident, SMRT said a fault could have occurred with a power cable's insulation.

Cable insulators ensure electricity does not flow away from the conductor and also keep people safe from electric current.

The cables' insulation is checked visually and with instruments at least once every six months, said an SMRT spokesman.

In his assessment of how SMRT handled Wednesday's disruption, Mr Lui said bus bridging services were "generally well done".

But the train operator can improve on information flow, particularly to those already riding the trains, he said.

"We need to keep commuters better informed, and we need to make sure that information is given out in a more timely manner."

Hours after Mr Lui spoke about measures to improve the MRT network's reliability, commuters on the East-West Line saw their journeys delayed by a train fault during the evening peak hour yesterday at 7pm.

The faulty train was withdrawn from service, adding 20 minutes of travelling time to east-bound commuters' journeys.

Joint News Release by the Land Transport Authority & SBST - LTA-SBST Joint Team to Enhance Train Service Reliability -15 Feb 2013

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