UK: Rail industry processes ensured that passenger safety was not compromised following the discovery of bodyshell cracks on the Hitachi-built Class 800 series trainsets in May 2021, according to a report published by the Office of Rail & Road on April 7.
The economic and safety regulator has made a number of recommendations in its final report arising from its ‘lessons learned’ review. These address how the rail industry responded to the problems which led to the withdrawal of the trains, the root cause of the cracking problems, and the rectification programme being put in place.
The final report follows an earlier review of the passenger impact of the disruption issued on June 25 2021 and an interim safety report published on September 9.
In particular, ORR recommends that the UK rail sector ‘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’.
HM Chief Inspector of Railways Ian Prosser confirmed to Rail Business UK that ORR would work with the Great British Railways Transition Team to ensure that the recommendations on cross-industry collaboration are fed into the emerging future structure for the UK rail sector.
Cracks were initially found on the yaw damper bracket and anti-roll bar fixing points on Class 800, 801 and 802 inter-city trainsets operated by Great Western Railway, London North Eastern Railway, TransPennine Express and Hull Trains. Further examination discovered cracking around the nearby lifting plates that are used to support the vehicles during maintenance.
These trains are all variants of Hitachi Rail’s AT300 series, embracing a mix of electric and electro-diesel trainsets procured by the Department for Transport and leasing company Eversholt Rail for use by different operators and maintained by the manufacturer under a series of train service provision contracts.
Following extensive checks, stringent mitigation measures were put in place to allow the trains to re-enter service with frequent inspections to ensure that safety was not being compromised.
Cracks were subsequently found on Class 385 operated by ScotRail and Class 395 operated by Southeastern, but these were not withdrawn as their designs were different to the AT300 and the actual and potential cracking were assessed as low risk.
Two types of cracking
Hitachi Rail brought in independent experts to undertake a rigorous technical analysis, in order to understand the causes of the cracking and help develop a rectification programme.
This analysis concluded that fatigue cracking in the area around the yaw damper bracket and anti-roll bar fixing points was being caused by the vehicles ‘experiencing greater loads from train movement than had been allowed for in the original design’.
ORR says it is ‘not yet known for certain why this happened’, although potential factors include wheel wear and track design. The regulator has recommended that further work is undertaken to identify the reasons for the higher levels of fatigue loading, given that the trains were designed to comply with current European standards.
Asked whether the stresses could be attributed to the use of 26 m long vehicles on sharply curved routes, ORR Senior Engineer Giles Turner said that this had been addressed in the train technical specification, primarily in relation to ride quality. ORR would expect the industry to conduct a detailed assessment if the trains were to be redeployed on other routes in the future.
The cracks where the lifting plates attach to the vehicle body were attributed to stress corrosion cracking, resulting from the use of 7000 series aluminium. This alloy appears susceptible to exposure to air containing chloride, in combination with residual welding stresses.
ORR recommends that Hitachi Rail should review its welding processes, particularly where the component geometry is ‘more challenging’. This should include consideration of whether the existing quality control is adequate to mitigate the risks of a weld with insufficient fusion.
Another recommendation is that rolling stock designers should understand the risk posed by stress corrosion cracking, particularly when proposing the use of 7000 series aluminium components. As there is currently no dedicated standard for mitigating SCC risk, the industry should consider whether such a standard should be developed.
Working with industry partners, Hitachi Rail is about to start a major programme to repair 1 247 AT300 vehicles and a further 487 of classes 385 and 395. This follows test running with instrumented trainsets and prototype modifications. As well as the Class 800, 801 and 802 trainsets, the programme will also cover the Lumo Class 803 electric units which entered service at the end of 2021 and the Class 805 and 807 sets for Avanti West Coast, which are currently at an advanced stage of manufacturing.
The rectification work is expected to be spread out over six years, in order to minimise the number of units out of traffic at any one time and the resulting disruption to passenger services. According to ORR, Hitachi Rail will prioritise the trains for repair on the basis of need, drawing on monitoring data compiled from fleet engineering and safety checks.
Hitachi Rail’s proposed solution to the fatigue cracking in the bolster area is to remove the affected part of the body structure, including the mounting brackets and the longitudinal welds where the cracks have occurred. The structure will be rebuilt using a modified design that provides an unchanged interface for the yaw damper bracket and anti-roll bar, but addresses the load capability of the design.
In the case of the SCC affecting the lifting plates, Hitachi Rail suggests that there is no significant risk of the component detaching. However, it proposes to add bolts to retain the plate in the unlikely event that the welds fail completely as a result of the cracking.
ORR says it will continue its oversight and promote the inclusion of the lessons learned in the train operators’ Safety Management Systems. Noting that the ‘industry has established processes for improving standards’, ORR said it expected that these would be followed ‘promptly’.
‘Hitachi Rail and operators have put in place robust plans to make sure the right safety issues are being managed’, said HM Chief Inspector of Railways Ian Prosser. ‘Our review provides a clearer picture of the issue, and we will continue our oversight to ensure work moves forward to agree the permanent solution. It is important that the whole industry works together to learn lessons from what has happened and our recommendations will help with that.’
Responding to the publication of the ORR report, a Hitachi Rail spokesperson said it ‘identifies that all Hitachi trains meet relevant standards and that we took the appropriate action to prioritise safety and maintain train availability’. It also ‘provides a detailed account of the tireless work to simultaneously keep trains running safely, while working towards the long-term solutions.
‘The proposed engineering solutions outlined in the report are currently being reviewed by all partners. We are working together to finalise the plan for their implementation, while always prioritising safety and train availability to support consistent passenger services.’