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London Underground train life extension

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As is often seen on heritage railways, it is possible to keep old rail vehicles in service virtually indefinitely, although to do so often involves extensive repair and restoration work. Sometimes, circumstances are such that it is necessary for trains in front line operation to undergo similar extensive work.

It was with this thought in mind that Rail Engineer recently visited London Underground’s project team to view some of the work taking place on the forty-year-old Bakerloo line trains to keep them in service for at least another 10 years.


The Bakerloo line (Baker Street to Waterloo Railway) opened just over 110 years ago in 1906. Since then, it has been extended, had a branch opened, been truncated and eventually settled on its current route from Elephant and Castle in south east London to Harrow and Wealdstone in north east London. From Queen’s Park to Harrow and Wealdstone, it runs over Network Rail’s tracks, shared with London Overground’s Class 378 trains.

Stabling sidings are provided at London Road, Lambeth, and at Queen’s Park. The main depot at Stonebridge Park is unique in that it is connected to Network Rail’s track and not to London Underground’s.

The Bakerloo line is operated by a fleet of 36, seven-car, 1972 tube stock trains originally delivered in 1973/74. These trains are made up of a four-car unit and a three-car unit coupled together. They were designed for a nominal life of 36 years.

At 42 years, the Bakerloo trains are the oldest on the Underground, and amongst the oldest operating anywhere in the UK (other than heritage railways). Their design was based on the original Victoria line fleet, and has an aluminium-framed body with aluminium cladding mounted on a steel underframe.

They have four motor cars, each with four DC motors controlled by a camshaft-operated resistance controller and fitted with rheostatic braking. In addition, the entire train has electro-pneumatic brakes with a Westinghouse emergency brake, and there are electro-pneumatic sliding doors, and train protection is provided by tripcocks.

Waterloo NB

The fleet of 36 trains is made up of 33 Mk II and three Mk I units. The differences are superficial, and have mostly been eradicated over the years, but there are still some left to catch out anyone thinking they are all the same. They last had major work in the mid-1990s when they were refurbished – an extensive visual modernisation whilst eliminating materials that were a fire hazard. For this work they were hauled over the National Rail network to the dockyard at Rosyth, which included travelling over the historic Forth Bridge.

The trains were originally planned for replacement by 2019 as part of the former PPP contracts, and then as the first use of the New Tube for London project. However, in 2013, London Underground decided to extend the life of the Bakerloo line trains to at least 2026.

Current projects

It was to understand more about what it takes to extend the life of a Tube train that Rail Engineer visited London Underground to talk to the project team and see the works over two days in May 2016.

The life extension project is just one of many projects that LU is carrying out on its older trains. LU has set up a Rolling Stock Renewals programme team to manage them all. The team’s head, David Caulfield, outlined the various projects being carried out by his team. These include significant modifications to the Central line trains, upgrading 1960s and 1970s battery locomotives, and creating a Rail Adhesion Train (RAT) from some old District line cars to apply Sandite during the autumn leaf fall season.

The aim with all these projects is to keep older trains going to help Keep London Moving (from the Mayor’s Transport Strategy). David explained how LU is approaching these works.

LU has always carried out modifications to trains and has generally determined the sourcing strategy for each project on a one-off basis. For the future, LU has carried out a strategic review and has decided that it will invest in facilities to manage and execute work in house, bringing in specialist design and implementation resources or using in-house labour as appropriate.

This approach delivers a number of benefits including not having to send trains off site, which can add a week to each train’s time out of service. LU train fleets achieve high utilisation and few trains are available to be taken out of service for modifications. An extra week in transit could add a year or more to a programme for fleets the size of LU’s.

Bakerloo line

Back to the 42-year old Bakerloo line trains. One of the reasons that life extension was considered was, perversely, because extensive work was already under way to repair cracks and corrosion on the underframe and body. One might imagine these problems would hasten their demise, but the work was essential simply to keep the trains in service until the earliest date that new trains could be delivered.

In designing repairs, it is usually easiest to restore the original strength of the structure. It would be harder, and almost certainly no cheaper, to try and design repairs that would last just, say, five years. Thus the repair works deliver bodies that are structurally as good as new. As such, the work will easily last for the additional time required. Anything else necessary in sub-systems and components can and will be dealt with during routine maintenance, following proper engineering assessment of those components not normally replaced but being required to last beyond their normal lifespan.

The main consequence of extending the life beyond 2020 is the need to carry out modifications to comply with the Rail Vehicle Accessibility Regulations (2010). This contains similar requirements to those in the Technical Specification for Interoperability for People of Reduced Mobility – TSIs do not apply to LU.

The RVAR work was explained by Paul Summers, project sponsor from the Asset Strategy and Investment team, and Zoe Dobell, RVAR project engineer (yes, my daughter!). The RVAR requires a number of features that make it easier to use such as handholds, passenger information displays, priority seats and provision for wheelchairs. Compliance is mandatory by 2020.

However, the Regulations recognise that strict compliance may not be possible for older trains. LU has therefore carried out extensive feasibility studies on the RVAR elements. These studies were then discussed with the Department for Transport with the aim of maximising the degree of compliance whilst not incurring excessive cost for minimal benefit; DfT has been really supportive.

The main elements that will be installed are the wheelchair spaces (which will be in the trailer car of the three car unit), and an audio/visual passenger information system. The biggest challenge of all is the gap between the train and the platform. LU’s practice on other lines is to use a mixture of platform humps and manual boarding ramps depending on the curvature and other factors. For the Bakerloo, LU has agreed with the DfT that no boarding aids will be provided where there is no interchange and no foreseeable prospect of providing street to platform step free access.

Carbody shop

With agreement on all these features, the scope of the works is now frozen and work will start in mid-2018 for completion early in 2020, based on having two trains out of service at a time. To provide the wheelchair positions involves removing the seats on one side of the middle seat bay of the designated trailer cars. In common with all LU tube gauge cars, there is equipment under the seats – this will have to be relocated and new flooring fitted to match the new floors being fitted as part of the body repairs (see below). Installing the passenger information system will involve work on all cars, and, although mandated by RVAR, will be of benefit to all passengers.

Acton Works

It was with considerable nostalgia that I set off from Acton Town station towards the large Acton Works complex, having first made that journey nearly 47 years ago.

The purpose was to see some of the repair works under way, a programme that will cost LU some £60 million or just over £200,000 per car. I was met by the underframe and body repairs project engineer Rob Bonarski, who is charged, inter alia, with making sure there is an approved repair system for every structural fault found.

Rob took me to shop AC15, which old timers like me will recall as the Heavy Repair shop. On the way, we visited some of the other workshops in which we saw Central line bogies being overhauled, Bakerloo line bogies being repaired, some battery locomotives being refurbished, D stock cars being converted for the new RAT and some 1938 tube stock cars being overhauled for the London Transport Museum.

Since I was last at Acton, AC15 shop has had extensive work carried out to prepare it for the Bakerloo line repairs. In former times, cars would have been lifted in Acton’s lifting shop and moved by traverser to the relevant workshop. This is no longer possible because the lifting shop was demolished many years ago to make way for LU’s Railway Equipment overhaul Workshop (REW). The old wood block floor has been replaced with reinforced concrete to support the Mechan jacks that LU bought to lift the cars (four sets of 4 x 10 tonne jacks for passenger vehicles and one set of 4 x 20 tonne jacks that can also lift battery locomotives). There are nine roads, most of which can accommodate two cars. There has also been extensive work to improve lighting, and provide services for electric and pneumatic power tools.

Incompatible Train Movements

Bakerloo line trains start their journey for repairs at Stonebridge Park Depot in northwest London. From here, they make an overnight journey to Acton via Baker Street, Elephant and Castle, back to Baker Street, onto the Jubilee line to Wembley Park, onto the Metropolitan line to Rayners Lane, where they reverse and then travel via the Piccadilly line to Acton Town (see map right).

They travel overnight because there is no signalling nor train protection on the Jubilee line for Bakerloo line trains (Jubilee line trains use in-cab signalling with ATO and ATP). They travel over the Jubilee line section under special rules called an Incompatible Train Movement Plan.

On arrival at Acton Works, the cars are uncoupled on the reception road next to AC15 and moved via a traverser into AC15 where they are lifted. Here the real work starts.

Swan necks, floor traps and fasteners

Rob explained the “voyage of discovery” on the first few trains as they discovered the true extent of repairs required and the differences between apparently identical cars. Even he had been surprised by the extent of the work required, despite being involved since the beginning of the job. It soon became clear that what had to be done could only be confirmed, individually on each car, once they were stripped. During my visit, they were working on train five, and Rob was confident that most of the problems had been discovered. Underframe swan neck repairs: Sole bars are straight, but the underframe also has two steel girders, approximately 300mm deep and 12mm thick, running the length of the car. In the main, as one would expect, the girders are under the floor but, over the bogies, this structure is above floor level and forms the seat risers for the longitudinal seats. The joint that connects the underfloor frame to the above floor frame is known as the swan neck. They are all cracked along the welds. The metal forming the joint is being cut out and replaced by a steel bracket of exactly the right shape machined from solid by WECS Precision of Epsom.

This allows welding to be carried out in locations where stresses are somewhat lower than they were in the original weld locations. The photo of the cut out section shows the cracks; anyone used to welding will not be surprised that they cracked.

Body pillars: Despite coatings applied during manufacture to protect against electrolytic corrosion between aluminium panels and the steel frame and underframes, the accumulation of moisture and cleaning fluids over 40 years has led to corrosion and cracks. These are being cut out and repaired. One of the challenges has been finding fittings that can be used in place of the hot rivets used on the original construction, especially where access is only available on one side. Fortunately, Alcoa Huck BOM fittings (rather like giant pop rivets) came to the rescue.

Body ends: Some of the body end brackets connecting the body end to the underframe have cracked. Investigations showed that many of the underframes were slightly distorted as a result of welding during manufacture and the brackets were ’adjusted’ to fit. They have cracked at the point of the adjustment. Rob explained that the replacements are being refitted with a metal putty being used to level the headstock plate.

Floors: The floor fitted during the 1990s refurbishment is a composite of polymer cladding and fire retardant ply on top of stainless steel in doorways and mild steel in seating bays. When the vehicles were stripped, it was found that the cladding was hiding a ’multitude of sins’. The covering and ply is all stripped and the mild steel floor plates in the end seat bays are being replaced. From here, the entire floor is rebuilt with new fire retardant ply and a covering of Tiflex Treadmaster TM7 (see below). A feature of this era of tube train is trapdoors in the floor to access equipment on the underframe. One of the improvements made has been to rationalise the different designs of trapdoors used from 21 to seven.

Roofs: Over 40 years, some of the roof fasteners have become loose and these are being replaced by heavy duty blind fixings and fire retardant Terostat sealant (formerly Sikaflex).

Asbestos: Most of the materials containing asbestos are being replaced. Heat-barrier material is being replaced by Promat DURASTEEL, and the saloon heaters are being replaced by AmTecs low voltage heaters connected in series across the 600V traction supply.

Compressors: The three Mk I trains use a different, less reliable compressor than the remainder of the fleet, and the opportunity is being taken to replace them with compressors recovered from D stock trains (which are being replaced by S stock). This involves welding new mounts onto the underframe.

Drawings: As-built drawings lacked most of the detail necessary to source new parts and, as a result, over 600 new drawings have been produced.

The next challenge is to replace all the removed equipment, including the doors. The doors are a particular issue. Despite putting each door back in the same position from which it was removed, the scale of works on the vehicle has introduced small distortions that necessitate adjustments to each door so that it runs freely without binding.

From here it’s a case of testing each car, reassembling the vehicles into trains (in the right order!), testing as a train, and returning the train to Stonebridge Park, from which it can enter service more or less immediately.

Rob told me that the plan is to increase the number of trains in work from one to two. This will have a great benefit in terms of both getting the work done more quickly and in terms of utilisation of the specialist teams who work on the trains. The repair work is due to be completed in 2018.

Bakerloo new seat and floor

It was evident that the very high quality work being carried out will, in all probability, provide a structure that is stronger than new. The Bakerloo line structural repairs team are to be congratulated on what they have achieved.

Interior refresh

In parallel with the repair works, the interiors of the Bakerloo trains are being refreshed at Stonebridge Park Depot. Even things as apparently simple as new seat and floor coverings needed significant engineering input from the engineering team based in the LU operations department.

The seats, supplied by Pro Style, Coventry, had both to comply with modern fire standards and be comfortable. The floor had to be cleanable and slip resistant, and there is also a requirement to have a colour contrast between doorways and seating areas, to comply with the RVAR. Conventional wisdom was that the doorways had a higher footfall, would be more prone to dirt and so should be darker than seating areas.

In practice, cleaning around nooks and crannies in seating areas meant that the seated areas were not as clean as they ought to be, so following a trial, the lighter floor was specified for the doorway areas. In addition, to improve slip resistance, a new groove pattern was specified which also contributes to draining water from the floor to the outside.

On a final point, the observant reader might be wondering why the RVAR works were not merged with the weld repairs. It is simply a matter of urgency and timing. The structural repairs were urgent, couldn’t be delayed and were under way before the decision was made to extend the life. In contrast, the RVAR works only became necessary as a result of the life-extension decision and a lot of feasibility work had to be completed before the scope could be decided and the works authorised. The teams are making every effort to make these two works streams as integrated as possible.

Thanks to LU’s David Caulfield and his team, especially Guy Harris and Rob Bonarski, to Paul Summers from the Asset Strategy and Investment team, and to Sean Long from Operations LU – Engineering for their assistance in preparing this article.

Written by Malcolm Dobell

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  1. The Piccadilly line and Bakerloo line has got history and yes the Bakerloo Line would of been extended to Watford Junction and could also be extended to Lewisham and Hayes (taking over the Hayes line which is 3rd Rail and Southeastern trains operate to/from Hayes which could be taken over by the extension of the Bakerloo Line from Elephant & Castle. Plus the rolling stocks on the Bakerloo and Piccadilly lines are ageing but still running and coping very well with more passengers using these lines but these rolling stocks are soon to be replaced by the next generation London Underground rolling stocks that will replace the 1972 and 1973 stocks on the Piccadilly and Bakerloo lines and also the new tube stocks will also replace the 1992 stocks on the Central and Waterloo & City lines.






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