The Office of Rail and Road (ORR) has said in an interim review that Hitachi Class 800 and 365 trains had been affected by stress corrosion and fatigue cracks. The result of this was a “significant” number of trains being withdrawn from service in May, it said in a statement.
ORR commended the industry’s quick response and the work undertaken to safely reintroduce the trains into service.
Cracks found in the area of the bolster close to the yaw damper bracket and anti-roll bar fixing points were a result of fatigue, and cracks found in the area where the lifting plates attach to the vehicle body were the result of stress corrosion cracking.
Stress corrosion cracking occurs when susceptible materials are exposed to a specific corrosive substance while subject to stress.
The interim report says the industry worked together as soon as the cracks were identified to quickly withdraw the trains and put in place a process to assess which trains could go back into service.
Since being returned into service, trains have performed as specified, with no unsafe conditions or harm arising from the cracking.
A final report, after further work with Hitachi and the industry, is expected in December.
HM chief inspector of railways at ORR, Ian Prosser CBE, said: “Our interim findings confirm the cracking in the yaw damper and lifting plate are a result of fatigue and stress corrosion cracking – and that Hitachi made the sensible decision to withdraw all trains.
“Since then, the majority of trains have been put back into service with no unsafe conditions and no harm arising from the cracking.
“I welcome the good collaboration that has taken place since this issue arose. We are continuing to work with all parties to determine the root cause and will publish our final report in December.”
The final report will look into the root cause of the cracking, and consider Hitachi’s plans regarding the long term fleet recovery and management. It will identify any areas for improvement for the industry.
In June, ORR published its review of the impact on passengers which found train operators affected by the cracks provided clear and consistent information to passengers during the disruption.
ORR’s passenger review also identified areas aimed at further reducing the impact on passengers should similar disruption occur in future.