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Rail Weld Quality in the Spotlight5th Technical Meeting
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| A full house at the 5th Technical Meeting |  |
Rail weld quality was the subject of the latest IoRW Technical Meeting held in Derby. There was an extremely high level of interest in the event such that the conference room was completely full. The meeting was organised jointly by the IoRW and the East Midlands Branch of the Welding & Joining Society. The Branch Chairman, John Simmons, acted as Chairman of the event.
The day began with updates from the two main aluminothermic welding process suppliers in the UK. Richard Johnson of Thermit Welding (GB) Ltd outlined the recent process developments that had contributed to improved quality. Particular mention was made of the 'Quality Assurance Package' consisting of: process/product approval; product quality assurance; welder training/competence; contractor audit; and weld inspection. The message was that attention to all these elements was required in order to have the best chance of consistently delivering the required weld quality. Particular mention was made of inspection with examples being shown of the types of imperfections that can, and can not, be found by visual inspection. It was suggested that acceptance criteria could be made clearer and divided into those which are solely workmanship based and those which relate to service performance.
Ian Davidson indicated that the Railtech (UK) Ltd aluminothermic welding process was designed to make the welder's task simpler and reduce imperfections. The process was continuously undergoing improvements. Currently, the most prevalent imperfections seemed to be 'oxidised' welds and gas pores. Whilst it was rare for a defect type to have a single cause, current process control improvements were likely to be directed towards preheating methods and moisture elimination.
Improvements in arc welding quality and productivity was the subject of a presentation by Paul Hardy of ESAB Group (UK) Ltd. It was proposed that such improvements could be achieved by applying mechanisation to arc welding repair of rails. Details were given of the 'Railtrac BV' equipment which, by maintaining a constant arc length and welding speed, can achieve the required quality and a smooth weld profile, and with higher productivity than with manual welding. Post weld grinding may also be reduced. The equipment was currently undergoing in-track trials.
Bob Sawdon of Balfour Beatty Rail Infrastructure Services returned to a theme which had been raised earlier by the aluminothermic welding process suppliers, namely the emergence of new European standards applicable to rail welding. The main advantages of such standards were: harmonisation of welding practices, universal approval systems, easier management of compliance and underpinning of European interoperability. The standards are all under the umbrella of EN 13674-1:1999, Railway Applications. Track Rail. They cover: flash butt welding, aluminothermic welding and arc welding. Some were already in use eg flash butt welding in a fixed plant and approval of the aluminothermic welding process, and benefits were being derived from them. Work was continuing to complete the set.
In an event like this, which was attempting to address all the issues affecting quality, it was important to get an impression of what happens in practice. This task fell to Stuart Plumstead of Balfour Beatty Rail.
On the theme of optimising inspection, the presentation firstly indicated the reasons for inspection: complying with Network Rail specifications, safety and improving welding/weld quality. Three 'levels' of inspection were also identified: the welder, the welding inspector and non-destructive testing (NDT); and the activities and duties within each level were explained. As a result, delegates were given a very clear indication of the difficulties experienced at the 'sharp end' and how they were overcome.
The NDT theme was expanded upon by two presentations on ultrasonic testing of rail. The purpose of such testing is to detect rail defects before they can give rise to problems or failures. Bob Crocker of Sperry Rail International outlined the Sperry approach which is widely used throughout North America, Europe and Asia. The key component of the system is a Roller Search Unit (RSU): a liquid filled tyre containing multiple ultrasonic transducers. The transducers are arranged to give comprehensive inspection of the rail as it rolls along the surface. Testing needs to be fast and frequent: welds and plain line are treated the same. With regard to the UK network, pedestrian equipment, the Sperry Walking Stick, and the first Sperry vehicle were introduced during 2003 and they will be supplemented by four further vehicles in September 2004. Examples of test data presentation were shown. The objective was pro-active defect management rather than reactive crisis recovery. More detail of this technique is given in an article by Dr Bob Crocker in this issue.
Mark Evans of Guided Ultrasonics (Rail) Ltd explained the recently developed long range ultrasonic testing (LRUT) system as applied to aluminothermic rail welds. This uses lower frequencies compared to conventional ultrasonic testing allowing a single, static test unit to examine an entire weld. Preliminary results from a trail of the LRUT equipment (called G-Scan) showed good correlation between the test results and the three-point-bend breaking load of rail welds for a large variety of weld defect types. Further development is planned.
Whilst the main thrust of the event was towards future improvements it is important to learn from the past and this was the subject of the presentation from Gareth Evans of Corus Rail Technologies. It was firstly pointed out that instances of rail breaks had reduced substantially in recent years and that 25% of all rail breaks arise from welds. Flash butt welds, made using either fixed or whole mobile plant, represent less than 2% of rail failures. Fractures originate more frequently from aluminothermic welds than from flash butt welds and they generally arise from porosity, lack of fusion or hot tears within the weld metal. However, it has proved difficult to correlate defect size and type with the likelihood of failure. Weld geometry, track support conditions and traffic must also be considered. It was concluded that efforts aimed at improving welder competence and adherence to standard procedures were key to achieving further reductions in weld failures. Improvements in inspection, such as those highlighted in earlier presentations, would also contribute significantly.
Tim Jessop of TWI and the Institute of Rail Welding gave an update on progress in IoRW with regard to competence demonstration in welding and NDT. The importance of competence and the important role being played by IoRW had been mentioned in most of the preceding presentations. The work covers the development of: harmonised welder training packages and welder assessment; National Occupational Standards for rail welding; training and qualification of rail welding inspectors, NDT personnel and rail welding engineers; and the certification of rail welder training organisations. Flexibility in competence certification was maintained because employer-based routes and third party certification body routes (eg CSWIP) were available. Much of the work had now been completed and the first certificates under the rail sector of the Certification Scheme for Welder Training Organisations were presented during the meeting.
The 130 or so participants at this event were treated to some excellent presentations interspersed with searching question and answer sessions. It was a worthwhile day for all those involved.
Eur Ing Tim Jessop
Executive Officer
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