Mystery source of deadly fractures that weaken tracks

Railtrack engineers said yesterday that "gauge corner cracking", a series of fractures in the rail, was the most likely cause of the derailment.

Railtrack engineers said yesterday that "gauge corner cracking", a series of fractures in the rail, was the most likely cause of the derailment.

Cracking happens on high-speed lines, particularly at tight corners, where the sheer force exerted by the wheels of 90-tonne engines causes fissures in the steel. The cracks, however, can also occur on straight stretches.

Dennis Rapley, a senior engineer at Railtrack, said this form of metal fatigue had started to appear over the past decade and that it might be caused by the increased use of the track. However, the fundamental cause of the phenomenon, which clearly relates to the way in which wheels come into contact with rails, was something of a mystery

The problem initially manifests itself as shallow diagonal cracks, which are visible on the head of the rail. Eventually, the cracks turn down vertically and can lead to the rail fracturing. It can appear in different types of steel and sometimes in relatively new rails, Mr Rapley confirmed. Ultra-sound testing was used to detect the presence of the potentially dangerous vertical cracks.

Railtrack deals with the problem in its early stages by grinding or filing down the railhead before it becomes unsafe. Some rail experts argued yesterday that such a process in itself weakened the rail and that the only real answer was to replace the track.

A Railtrack spokesman said the company did not have figures for the extent of the cracking problem across the network, but added that testing was being stepped up on stretches of track posing a higher risk of fatigue.

The company's engineers pointed out that continental railways had encountered similar problems.

Railtrack engineers would meet representatives of the Health and Safety Executive and Railway Inspectorate to develop a more rigorous engineering process to deal with the problem, he added.