Institute of Rail Welding 17th Technical Seminar

Current Developments in Rail Welding and Repair

At this latest IoRW event the opportunity was taken to update delegates on a range of recent and on-going developments including rail head repair by aluminothermic welding, repair of tri-metal zones, closure welding, gas cylinders and training. For a second time BOC generously hosted the event at their Wolverhampton facility which again proved ideal. In particular, the practical demonstrations on view in their workshops during the lunch break were a key feature with delegates having the opportunity to see and ask questions about, for example: a closure rail process, monitoring of aluminothermic welding and hydrogen fuel cells.

Ian Banton of Thermit Welding GB describes current work being carried out in partnership with BOC on monitoring of aluminothermic welding. In the background Geismar's closure rail equipment can be seen

Bob Sawdon of Balfour Beatty Rail Technologies chaired the event with his usual blend of humour and precision. However the event began on a sad note with a minute's silence being observed in memory of the late Carol Colegate (see Obituary on page 3).

Although rail head repair is normally by arc welding, there are advantages to be gained by using aluminothermic welding (ATW) particularly with regard to speed: an arc weld repair can take around four hours but an ATW repair can be completed in less than half that time. This is a significant saving as possession times become more and more squeezed. Another advantage is that ATW rail head repair can eliminate the need to cut the rail. This saves casts by keeping the rail longitudinal stresses intact. Furthermore, ATW repair is likely to introduce defects than arc welding.

Ian Banton of Thermit Welding GB plotted the development of the Thermit head repair process covering the progress that had been made. Currently the process is designed for repairing:

• Single repairs for visible rail defects
• Isolated squat defects
• Internal Tache Ovale defects
• Overlaid repair for wheel burns

The development work covered: gas cutting excavation techniques, mould development, preheater design and post weld trimming although normal Thermit welding practice and equipment were preserved wherever possible. Particular attention was paid to preheater design and it was found that overheating could be overcome by setting the torch at an angle. Trimming tears due to trimming commencing early and poor shear blade quality, led to development of powered weld shear resulting in relaxation of trimming time.

The process is currently approved by Network Rail for R220 and R260 rails and the technique won the National Rail Innovation Award in 2009. Further developments, for example on the repair of grooved rails, are currently underway.

Railtech International has developed its own rail head repair welding process which is called the Head Wash Repair (HWR) process. This process has been tested in United States by the Transport Technology Center Inc in Pueblo approved by the American Railway Engineering and Maintenance-of-Way Association (AREMA) and is starting to be used because of its advantages.

Based on this successful experience, Railtech International has decided to promote the product all over the world and especially in the United Kingdom where Network Rail has a strong interest in the technology. Railtech UK Ltd has started the product approval procedure.

A presentation by Nicholas Penverne of Railtech (UK) covered details about the welding process itself and underlined its main characteristics and advantages. In addition to gas cutting excavation techniques, mechanical cutting has also been developed, using the Matweld frog grinder and found to be successful.

The main advantages are that there is no risk of having a gap under the rail head due to the use of hybrid moulds which are located on the foot of the rail. Tests showed that this gap could cause flashing or cold lapping and could therefore reduce the fatigue endurance of the weld. There is also a reduced risk of confusion because the process uses the same welding parameters, hardware and methodology as for conventional Railtech PLA welding. There is also no need for specific training and no new investment in equipment required.

Tri-metallic zones (TMZs) are a feature of the joining of austenitic manganese steel (AMS) crossings to normal carbon-manganese steel rail grades. These two materials cannot be successfully welded directly to one another and therefore a narrow stainless steel transition piece is flash welded into place between them. Defects occur in the rail head in these regions and weld repair options are limited because of the conflicting requirements, in terms of welding, of the materials. On the one hand, AMS need to be kept relatively cool during welding, whereas carbon-manganese steel need high preheat temperatures. Replacement is an extremely expensive and time-consuming procedure and therefore extending the repair options is attractive.

By exploiting the safety margins present in current welding procedures, Ian Davison of Network Rail showed how it was possible to carry out a successful repair across an entire TMZ. However, the procedures used have very little tolerance and therefore appropriate site supervision of the repair operation is paramount.

For large repairs, the procedure is:

• Weld on AMS first (maximum 204°C) whilst the TMZ is cold
• Use a transverse weld bead on the stainless steel to protect the R260 rail
• Complete the repair on the AMS
• If necessary, use artificial cooling (for example, wet towels) when AMS gets hot
• Preheat R260 rail to 275°C and complete the repair.

For small repairs the procedure is:

• Preheat the R260 rail to 275°C, but keep the AMS below 204°C
• Weld from R260 towards AMS
• If necessary, use artificial cooling when AMS gets too hot.

Successful stressing using the VolkerRail method with Puller Lite technology and mobile flash butt welding (MFBW) was the subject of a presentation given jointly by David Philpott and Scott Wilson, with the former giving an overview and the latter focusing on the equipment, QA and planning aspects.

The application of MFBW to rail joining on site was limited in the past due to the fact that there was no approval for the final closure weld. Gaining such approval would open the door to wider exploitation of the process and this was achieved in 2009 and the technology has been successfully applied since. A modular form of MFBW was chosen in order to have flexibility of modules for complex renewals and projects and to enable work to be carried out on the same line, the adjacent line or out of track.

MFBW unit inside the puller. (The puller is a set of tensors wide enough to accommodate the MFBW inbetween the rams.) The puller action is integrated with the MFBW

Stressing requirements for the closure weld are calculated in a similar fashion to that used for ATW closure welds. The main difference is that in ATW allowance has to be made for the weld gap (25 or 27mm) whereas with MFBW the displacement (loss of rail) during forging of 30mm is part of the equation.

Thermit Welding GB rail head repair

The rail needs to be measured, cut with overlap of ends and bellied out to leave the ends in line to be held by the MFBW and puller. Low friction slides are used to support the bellied rail and about 70m of rail needs to be unclipped. During welding and pulling the rail slides into place laterally.

Quality control is achieved by batch destructive testing. A test weld is produced at the start of each welding shift, prior to the MFBW being operated on site. The welds are bend tested to confirm the equipment is performing correctly. It is extremely rare that these tests fail.

The theme of closure welding was also the topic of a presentation by John Booth of Geismar UK in association with Weld-a-Rail. A lightweight piece of kit has been developed that enables two ATW closure welds to be made simultaneously saving a precious 30 minutes of possession time. The kit includes a new type of alignment device which was claimed to be safer and more accurate.

The procedure is as follows:

• Cut out the defective rail
• Note rail movement using telltales
• Accurately cut the new rail length and place it in position - this may be anything from 4.5 to 30m in length
• Position first stressing kit and hold the welding gap mechanically
• Position second stressing kit, reinstate stress, set the welding gap and hold mechanically
• Align both sets of rail ends using the new alignment device
• Carry out ATW welds simultaneously
• Shear, grind and stamp.

The technique has recently been successfully applied on the London Underground. During this work the two ATW welds were made by one welding team with the two members of the team working separately at certain times.

Mike Atkins of BOC gave an insight into BOC's current thinking on future designs of gas cylinders aimed at addressing customers' needs, particularly with regard to weight reduction and increased gas content. Two new designs (composite wrap and welded seam) were outlined and prototypes were on display. As well as addressing customers' requirements, BOC also hope to reduce considerably the size of their cylinder portfolio which will bring cost savings and make it easier for customers to find the right product. The final two presentations were on the subject of rail welder training and qualifications. Lee Janczyszyn, Network Rail, summarised the current quest to produce the best quality training and assessment material. This work is being tackled by a Content Review Group (CRG) comprising Network Rail representation from: engineering and maintenance plus training material specialists and a training delivery specialist. Furthermore, in June Network Rail will be holding a training material brief for all internal and external trainers using Network Rail training material.

A particular feature of the development work is the deployment of the latest animation and emulation techniques and Network Rail now have experts in place in these techniques. An animation is a photographed sequence of slightly varying drawings or models, so that they appear to move and change when the sequence is shown. An emulation is a form of visual aid, usually a form of animation in which the representation performs in exactly the same way as in reality, though perhaps not at the same speed.

Finally, Allan Macdonald of EMTA Awards Ltd (EAL) gave an overview of the current National and Scottish Vocational Qualifications (NVQs and SVQs) available for rail welding. These have existed for several years but have yet to be taken up and there is a danger that if they remain unused they will be removed from the national system. The N/SVQs cover all types of rail welding situations (rail manufacture and track renewal and maintenance) and all processes, ATW, arc welding, FBW and MFBW. The qualifications are derived from National Occupational Standards developed in 2003 with input from IoRW members, and published by Sector Skills Council for science, engineering and manufacturing technologies - SEMTA.

Organisations involved in rail welder training and assessments would find it straightforward to become involved in the issuing of these qualifications and two significant benefits in doing so were foreseen: rail welding competencies would be linked to the UK National Framework providing evidence of best practice and the training would be eligible for public funding.

Organisations with an interest in this were invited to contact EAL which is the recognised Awarding Body for these qualifications.

Simultaneous ATW closure welding using two sets of Geismar equipment

Feedback from the delegates attending the event was excellent with particularly high scores being given to the use of video material in the presentations and to the practical demonstrations. Some delegates expressed a wish for more time to be allocated to discussion and demonstrations and this will be taken into account for future events.

Tim Jessop,
Executive Officer, IoRW