Learning the lessons: ORR review into Hitachi Class 800 series and Class 385 cracking issue


ORR immediately launched a review of both the passenger and safety impact following Hitachi Rail Class 800 series trains withdrawn from service for safety checks on Great Western Railway, London North Eastern Railway, TransPennine Express and Hull Trains, along with cracks being separately discovered after examination on ScotRail’s Class 385 and Southeastern’s Class 395 trains in May 2021.

When cracks were found on the bodyshell (yaw damper bracket and anti-roll bar fixing points) of some trains, rigorous safety checks by Hitachi Rail and the train operators impacted were carried out, with oversight from ORR. 

Stringent mitigation measures were put in place to allow the trains to re-enter service without passenger safety being compromised, which have assured no safety failures and trains have performed as specified while in service.

ORR has worked closely with Hitachi Rail and the train operators, providing oversight, to ensure robust process are being followed. 

We reported on the passenger impact on 25 June 2021 and produced an interim report covering the history, withdrawal and reintroduction of the rolling stock on 9 September 2021.  

Our final safety review sets out the root cause of the cracking, provides detail on Hitachi Rail’s plan for long term fleet recovery and management, and identifies several areas of improvement for the industry.

Safety lessons

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  1. Our review was structured to addressing the aims around two themes:
    1. the capability of the operators’ safety management systems (SMS) to manage the withdrawal and reinstatement of vehicles; and
    2. a technical review, from root cause analysis to rectification and modification progress.
  2. Our review is based on the documentation arising from the industry’s work such as safety certificate applications, risk assessments, and detailed technical analyses and reports. We did not undertake an independent technical analysis. We have not undertaken an investigation that uses our powers arising from the Health and Safety at Work etc. Act 1974 because at no point did we identify a potential breach of health and safety law.

Our review sets out: 

  • Aim 1: Determine the root cause of the cracking at the lifting end of the bolster and around the yaw damper / anti-roll bar connections to the body.
  • Aim 2: Examine how the industry went about identifying the problem, assessing the safety risk, withdrawing the trains from service and returning trains to service.
  • Aim 3: Identify areas for improvement.

Our conclusions of Hitachi’s technical review are that:

  • fatigue cracking was caused by the area of the bolster subject to yaw damper and Anti-Roll Bar (ARB) loads being greater than allowed for in the original design.
  • the degree of fusion in the weld between the bolster and the car body was likely to be a factor in relation to the emergence of the cracking.
  • Hitachi has identified that the geometry of the components prior to welding contributed to the poor weld fusion identified above.
  • The conclusion of the technical review is that stress corrosion cracking (SCC) was caused by the use of 7000 series aluminium, and in particular plates exceeding 10mm in thickness. Thicker material is particularly susceptible to SCC in a typical rail environment in the UK, in circumstances where the residual stresses introduced as a result of the welding operation have not been mitigated.
  • All operators were able to demonstrate that they had appropriate safety management systems in place to manage the fleet stand down, to liaise appropriately with Hitachi and to make suitable and sufficient risk assessments for returning trains with cracks meeting defined criteria back into passenger service. 

To ensure further safety improvements, ORR is recommending that:

  1. The industry should conduct further work to identify the reasons for the higher levels of fatigue loading experienced by rolling stock. Since the Hitachi Rail design complied with the applicable industry standards, the industry as a whole should evaluate whether the applicable standards take into account the loads arising from operation on the rail network in Great Britain. 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. 
  2. Hitachi Rail should carry out a formal review of the effectiveness of their processes for welding when the component geometry is more challenging, which should include consideration of whether the existing approach adequately mitigates the risks of a weld with insufficient fusion being accepted. 
  3. Designers of rolling stock should understand the risk posed by stress corrosion cracking and give it specific consideration when proposing the use of 7000 series aluminium components. This does not mean that the specific type of aluminium should not be used in future, or that the aluminium used in the current trains compromises safety; but when used, steps should be taken to ensure protection of structures.
  4. The industry should consider whether a standard for mitigating SCC risk should be developed, as no dedicated standard currently exists.
  5. The industry should develop a process for responding to similar future cross-industry crisis events and appoint a strong, independent chair who can maintain pace, focus and ensure all voices are heard.

Passenger impact

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We have worked closely with TOCs and passenger groups to review the impact on passengers from the withdrawal of trains, with a specific focus on the operators of Hitachi class 800 trains – Great Western Railway, London North Eastern Railway, TransPennine Express and Hull Trains (although the impact on the latter was more limited). The passenger review does not include ScotRail given there was minimal impact to passengers using its services.

The review covers:

  • consistency and clarity of travel information, both over the weekend of 8 May as the safety issues became apparent but also in the following week(s) including information provided by National Rail Enquiries; 
  • ticket refunds - information provided by train companies, National Rail Enquiries, and independent rail retailers to passengers about their refund rights and the application of administration fees;
  • advice to passengers on alternative travel arrangements including ticket acceptance on other operators;
  • the steps taken to contact passengers who had booked assistance to travel and the accessible alternative arrangements offered.