SINGAPORE - The hairline cracks found on the 26 China-made trains did not pose a safety concern, hence the issue was not made public when the defects were first discovered in 2013, said Transport Minister Khaw Boon Wan on Tuesday (July 12).
The defects, which required the trains to be sent back progressively to the manufacturer in Qingdao to have their car-bodies replaced, also did not impact reliability or capacity, Mr Khaw said during a press briefing.
This issue - which was first brought to light by Hong Kong media FactWire last week - is a "seemingly routine matter" that had been "mis-spun" by "mischievous hands", said Mr Khaw.
The trains are manufactured by Chinese-Japanese consortium, Kawasaki-Sifang, and are used on the North South-East West Line (NSEWL).
While the trains - which each required around four months to be rectified - were sent back to China one at a time, this did not affect service operations.
This is because there is a "buffer" of trains, said Mr Khaw, meaning that currently only 124 of the 140 trains available on the NSEWL are needed to meet commuter demand.
To date, five of the 26 trains manufactured by Kawasaki-Sifang have been rectified, with one train now in China for the rectification works.
The Land Transport Authority expects all 26 trains to be rectified by 2019, as two trains, instead of one, will be sent back each time from next year (2017).
The hairline cracks, which were discovered in July 2013, were found on the surface of the car-body bolster - the aluminium alloy structure under the train carriage.
About 85 per cent of the hairline cracks are shorter than 20cm and did not pose a safety risk. This was ascertained through tests conducted by LTA, Kawasaki-Sifang as well as an independent consultant from Germany, TUV.
The cracks developed because of a defect in the manufacturing process resulting in impurities being introduced in the aluminium material.
Tests found that despite the hairline cracks, the bolsters could still withstand loads of three times greater than its normal use, and this is an acceptable safety margin, said the LTA.
Under the rectification works, the bolsters used will be cast in Japan rather than from China.