Rail Welding Developments - an International Perspective
6th Technical Seminar
IoRW's 6th Technical Seminar attracted a large audience
Another extremely successful and well attended IoRW event was held at TWI, Cambridge in October. This time the theme was rail welding developments outside the UK and a team of experts from Japan, Germany, Sweden and France had been assembled. An associated exhibition contained stands from Amey Rail, Rail Plant Ltd and Vital Rail. Thermit Welding (GB) Ltd also supported the event.
The first speaker was Ryu-ichi Yamamoto from the Railway Technical Research Institute, Japan. In order to extend the service life of continuously welded rail, it is important to perform reliable welding by utilising appropriate welding processes, inspection methods and well-trained welding personnel. It is well known that flash butt welding (FBW) and aluminothermic welding (ATW) are commonly used in the world. However, gas pressure welding (GPW) and enclosed arc welding (EAW) have progressively been expanded in Japan. Gas pressure welding processes have been especially applied to the high-speed tracks of SHINKANSEN (bullet trains in Japan) since 1964.
However, rail weld failures which are initiated from weld discontinuities, occasionally occur. It is thought that welds performed by fusion welding such as ATW and EAW have less reliability than those of FBW and GPW and therefore these former types of welds require ultrasonic testing in Japan. As a result, attempts have been made to improve the ultrasonic inspection method for preventing rail weld failures. Consequently, it was established that the double-probe technique of the ultrasonic inspection method is suitable to detect discontinuities in rail welds.
D.-Ing.Matthias Pöge from SLV, Hannover summarised the characteristics of rail welding (materials, track, switches and welding methods) and different railway systems operators (Deutsche Bahn AG, regional railways, industrial railways, streetcars, etc) Quality assurance for the welding of rail was described using the regulations of Deutsche Bahn AG as an example. Deutsche Bahn AG is one of the largest network operators in Europe. In the last fifty years or so, in conjunction with the introduction of fully welded track, a quality guarantee system for rail welding has been developed taking into consideration the most varied criteria, eg train speed, level and frequency of demand, etc. This is described in a set of rules which is recognised as binding by other network operators in Germany.
Companies (including the railway's own) who want to weld rails with the Deutsche Bahn AG area, must demonstrate their suitability before starting to weld. The proof is provided by an 'Authorised body' assigned by the Railway Federal Office EBA (National Supervisory Establishment) according to the criteria specified in the regulations. The criteria include operational requirements and equipment, and the necessary personnel. Quality control companies must likewise be certified.
The system existing in Germany for the training of specialist personnel for rail welding (welder and welding supervisor) was also shown. It was noted that there were approximately 100 trained and qualified rail welding engineers in Germany.
Developments in arc welding in Sweden was the subject of a presentation by Jeff Ramsay of ESAB AB, focusing on the repair of switchblades. Minor repairs are conducted on site whereas major repairs, of switchblades up to 26m in length, are conducted in the workshop. Repairs require welders to be trained and qualified, and documented procedures are used. All repairs are also subjected to rigorous and continuous control. The object is to monitor all components for wear and to record the damage so that a repair can be effected before wear becomes excessive. New developments include the use of light weight mechanised arc welding systems.
Many countries, including the UK, were interested in the wider exploitation of flash butt welding. Martin Benkler of Sersa Group management Ltd gave a European view.
In the quest for high productivity in rail welding there are advantages in integrating individual processes. This can increase the effective use of possession times, especially if the processes produce high quality and repeatable results. One such example is combining flash butt welding and destressing into one process.
A highly mobile road/rail flash butt welding machine with a Schlatter welding head was described which can be ready to weld within minutes. It has a high output (eight welds per hour), high precision and weld parameter recording facilities. Destressing is performed by preheating units or hydraulic tensors.
Using this approach, productivity increases were achieved. Repeatability was enhanced by the use of operator-independent processes as much as possible. However, very precise and thorough site planning and organisation was required.
Continuing the theme of European trends, Tim Jessop of TWI Ltd gave a brief overview of the RAILSAFE project which had just started. RAILSAFE is an EU funded collaboration project under the Leonardo da Vinci Programme. Its aim is to develop a harmonised system for education, qualification and certification of track welders throughout Europe. It is hoped that, at the end of this three year project, there will be the opportunity for exchange of rail welders within Europe as a result of the harmonised training procedures.
Like in Sweden, there have also been significant developments in the mechanisation of arc welding for rail repair in France. Marc Rominger of SNCF showed that a high level of success had been achieved using an automated self-shielded flux cored wire welding system. This had involved resolving metallurgical problems (through consumables and procedure optimisation) and ergonomic problems. Improvement objectives have been met and this has led to further development in organisational and working practices.
Anders Frick of Banverket HK, reported on a project to upgrade a heavy haul line in northern Sweden. With greater axle loads and thus greater forces in the rails there is a risk for faster degradation of track components. For this reason, maintenance of the track will become even more important. Track welding, joint as well as repair welding, is an essential part of the maintenance work. Aluminothermic welds and repair welding of crossings are of special interest.
It was found that a method using a 'soft' portion and hardening the running surface by selective alloying (HPW method) results in aluminothermic welds with better fracture toughness and ductility properties. This fact makes this selective alloying process the appropriate choice for use on the Ore Line. Test welds with the method have been performed in 2003 and 2004. The results look very promising so far.
The repair welding of rail crossings has to some extent been shown to be imperfect. A modified welding procedure, sandwich welding, has shown great advantages compared to conventional procedures. This involves using alternate layers of 'soft' and 'hard' arc welded deposits. Especially on heavy haul lines such as the Ore Line, but also on lines with axle loads of 25 tons, this method has increased the service life of the crossings and resulted in considerable improvements.
Throughout the day there were many questions from delegates indicating a high level of interest in the material being presented. The overall consensus was that there are many opportunities to develop improvements by sharing best practice on an international basis. The 120 or so delegates who attended seemed to go home well satisfied with their day.
Eur Ing Tim Jessop
Three more organisations to achieve certification under the rail section of the Certification Scheme for Welder Training Organisations were presented with their certificates at the 6th Technical Meeting.
Brian Powell, Anthony Kilcran & Timothy Kniveton of Network Rail (previously Jarvis) received certificates from Eur Ing Bob Sawdon of Balfour Beatty
Mark Waters, Jolian McErlean, Rod Taylor & Malcolm Edwards of AMEC Spie received certificates from Brian Whitney of Network Rail
Gary Felton, Steve Hodgetts & Mick Wainwright of Thermit Welding (GB) Ltd received certificates from Brian Whitney of Network Rail