Cracks found in the bodyshells of several types of Hitachi trains almost a year ago were caused partly by salt in the air, according to a new report from the Office of Rail and Road. The problems were first discovered at GWR’s Intercity Express depot in Bristol, and similar trains running on LNER were involved as well. Class 385 units on ScotRail and 395s on Southeastern were also examined, along with units being operated by TransPennine Express and Hull Trains. The affected trains were immediately withdrawn, disrupting services. Hitachi said it had taken immediate action after cracks had appeared in yaw damper brackets and anti-roll bar fixing points on some of the trains.

The ORR’s review has concluded that in the area above the wheels fatigue cracking had been caused by greater loads from train movement than allowed for in the original design. It is not yet known for certain why this happened, although potential factors include wheel wear and track design.

The ORR said ‘additional cracks found in the area where the lifting plates attach to the body were the result of stress corrosion cracking', which it has attributed to a particular type of 7000 series aluminium in various parts of the Hitachi Class 800 series. The cracks were a result of the characteristics of the aluminium alloy in combination with built-in stresses from being welded to the body and exposure to air containing salt.

The ORR is recommending that the industry should conduct further work to identify the reasons for the higher levels of fatigue loading. Since the Hitachi design complied with the applicable industry standards, the industry as a whole should evaluate whether the standards take into account the loads which can arise. It added that ‘This industry collaboration will require the involvement of those parties responsible for design, manufacture and maintenance of rolling stock including, but not limited to, Hitachi Rail.’

The ORR also wants Hitachi to carry out its own formal review of welding practices, and for rolling stock designers to take into account the risks posed by stress corrosion cracking when 7000 series aluminium is being used.