Safely on track with OIS

Public confidence in the safety of Britain's rail system has been shaken by a series of train crashes in recent years. Now this confidence is being restored, thanks in part to pioneering technology from OIS and GE Inspection Technologies. OIS, a member of the Aberdeen-based Abbot Group, has developed a specialised technique capable of inspecting the millions of track welds that hold most of the UK's rail network together, and thus helping ensure the safety of travellers who use the system.

The national rail operator, Railtrack, is attempting to rebuild public confidence in the network after a series of accidents such as the Hatfield disaster in October 2000.

OIS is already well known as a market leader in NDT and advanced technology inspection services to the UK oil and gas industry. It has secured a major pilot contract for the rail industry with Railtrack through First Engineering, Scotland's largest infrastructure maintenance company. The number of broken rails attributed to weld defects is about 25 % of all broken rails. It is the intention of Railtrack to halve the number of broken rails over the next decade. As part of this improvement process NDT techniques will be used to critically examine the rail and the alumino-thermic welds. Radiography was carried out using the OIS ultra-safe SCAR (Small Controlled Area Radiography) system mounted on the in-house developed rail trolleys and the filmless Digital System developed by GE Inspection Technologies.

"We spent eight months developing the technology for use on rail joints before mounting it on a 'road railer' - a Landrover converted to operate on track," says OIS managing director Graham Cowperthwaite. "There have been road railers for a number of years, and because we had been using real time radiography on onshore pipelines, we thought we could adapt the technology for rail use." The SCAR system operates in a much smaller area than traditional radiography, and in a safer, more controlled manner. Now using specialised Se75 isotopes, OIS is able to produce a digital radiograph of the rail weld and scan the image into a computer, all in less than three minutes!

The SCAR system with RADView provides a rapid inspection system for the weld examination for the detection of both volumetric and planar defects. Neither flash butts nor alumino-thermic welds had been tested for the occurrence of through wall defects until the current programme of radiography using filmless systems.

The state-of-the-art RADView Computed Radiography system is capable of delivering instant results on-track from the fully independent road-rail Landrover. "One of the main aspects that made us choose the GE Inspection Technologies' RADView digital system instead of other systems was the lower risks posed by failures on line," explains Jim McNab, manager of the Technical Support Group. "In addition to the quick and comprehensive back-up from Agfa NDT, we were also convinced by the quality of GE Inspection Technologies' products and systems. In fact, we have been working with Agfa NDT for many years now."

After being exposed, the flexible phosphor screen is processed through a laser scanner, delivering the image onto a 2 megapixel monochrome monitor. This digital image can be enhanced and analysed, while the phosphor screen is automatically erased for immediate re-use. After the screen has been scanned, the digital image is interpreted, reported and digitally stored for future retrieval or analysis.

It is an environmentally friendly system, since neither film nor processing chemistry is used. The flexible phosphor plates can be re-used up to 10,000 times.

The images are stored on removable media immediately after being taken, minimising the risk of loss or degraded records. The system provides computerised analysis of the image, yielding consistent, repeatable interpretations and measurement of details.

The exposure time typically ranges from 2 to 20 times less than film, depending on the image quality requirements. The exposure latitude is over 1,000 times greater than film.

The digital radiographic image can be enhanced so that defects such as tearing can be easily seen before sending the report and radiograph electronically to the client.

All this is even more remarkable considering that less than a year ago the process would have taken hours rather than minutes!

This ensures that if a defective rail is located overnight by the OIS railrad crews, the rail infrastructure maintenance company can do any essential repairs within the same shift, without disruption to the train timetables, says Graham Cowperthwaite.

"That's a major advantage in the race to give us a safer rail system!"