Welding Technology Development

Innovative weld deposition process for cost effective restoration of grooved rails.

Synopsis

The Sheffield Supertram network, like many other tramways, is characterised by many tight curves that are subjected to hard flange contact and hence suffer from accelerated side wear at such locations. The replacement of worn embedded rail is not only expensive but it also brings about disruption to road traffic and inconvenience to tram users and local residents. Weld repair of high carbon steel rails has been practiced employing both manual metal arc and submerged arc techniques but they require a high temperature preheating of the rails. However, the polymer surrounding the grooved rail starts to break down at around 160°C, well below the operational temperature of a high temperature process. Although a no preheat solution has been available for the medium carbon Grades 700/800, a solution avoiding the need for high temperature preheat was required for the more wear resistant Grade 260 rail steel.

Key Client Issues

The presence of tight curves and the desire to reduce vertical wear lead to the choice of Grade 260 rail steel for virtually all the curves in embedded track. Consequently the development of a weld repair process that did not damage the surrounding polymer was an essential requirement to maximise rail life and avoid rail replacement.

• To address this requirement, Sheffield Supertram Maintenance Ltd invested in a novel “cold rail” re-surfacing process for weld repairing worn rails. However, early experience revealed that this technique did not provide a robust weld and needed to be further developed, a challenge that was taken up by Corus

The Developed Solution

An essential prerequisite for the development of a robust solution was an understanding of the metallurgical transformation in the HAZ following the deposition of the root bead and the factors that needed to be controlled to prevent the formation of cracks and incipient defects at the weld metal-HAZ interface.

• Corus, employing their metallurgical expertise, have developed a procedure (patent applied) for steel Grades 220 and 260 that uses a “chill removal” pre-treatment to control closely the ensuing metallurgical transformation. This novel approach when combined with selection of the welding parameters and consumables has delivered a robust weld deposit that work hardens rapidly to give a hard wear resistant layer

Client Benefits

• Substantial cost savings
• Existing rail retained and surrounding polymer integrity maintained
• Repair undertaken in-situ without disruption to traffic
• A weld deposited layer that is more resistant than the parent steel and produces a polished finish to reduce friction and squeal noise  
• The ability to develop a preventative maintenance programme through timely weld restoration of worn rail to maximise rail life and facilitate long-term budget planning

Following successful application of the CRT grooved rail gauge face weld restoration process from 2006 in Sheffield, GrantRail now offer this service to tramway operators across the UK and Ireland, delivering high integrity welds to enhance rail life in Manchester, Nottingham and the West Midlands in 2008.