Very difficult process'
Roger Ford, industry and technology editor at the magazine Modern Railways, said the problem is "with the weld cracking underneath [the train's] body shell" which he explained led to about 180 trains being taken out of service on Saturday morning for inspection.
He told BBC business correspondent Katy Austin that while body shell cracking would not "cause the trains to crash or disintegrate or anything like that", he said it is a "serious point" that requires action because if metal fatiguing is allowed to continue, the "cracks will spread, and the body shell strength will be weakened".
Mr Ford added that repairing aluminium trains is a "very difficult process" because of the electronic equipment inside them.
He said: "If you get a welding torch up against the [electronics]... it can fry [them] so the first thing you have to do is take all the electronics out, disconnect all the electrical equipment, that takes a day or two, then you do the repair, then you have to put it all back again."
He added there were about 1,000 carriages to deal with, so it would be "quite a considerable job".