Long Range Inspection of Rail Using Guided Waves - Field Experience

Ultrasonic techniques have been used for many years for the inspection of rail. These measurements can detect the presence of a wide variety of defects but there are practical difficulties with the technology. While large transverse cracks of the type likely to cause catastrophic failure can be detected, the large, critical defects can be masked by large numbers of small, surface defects along the length of the rail. It would be very useful to be able to determine reliably the largest defect size in a length of rail. Also alumino-thermic welds are difficult to inspect due to the typical defect orientation and the attenuation of the weld material. Guided waves provide a very attractive solution to these problems; they travel along the rail, for tens or hundreds of metres, and are partially reflected by any defects which are present. They are particularly sensitive to vertical defects and they are used at relatively low frequency so they are not significantly attenuated by weld material. With financial support from Network Rail, the authors have developed a practical inspection tool based on guided wave measurements. This paper describes the design of a pre-production prototype guided wave instrument suitable for site trials. Results obtained at a level crossing are presented that demonstrate the use of the system as a practical screening tool. Introduction: The current authors have previously described the development of a rail inspection system financially supported by Network Rail that uses low frequency guided acoustic waves to inspect long lengths of rail and alumino-thermic welds. A comprehensive description of this work may be found in Wilcox et al. [1]. The G-Scan guided wave rail testing system, as it is now called, is at its pre-production prototype stage and has been used in a number of site trials around the UK. In this paper results are presented from one such site trial that demonstrate how the system can be used to screen rail passing through a level crossing without disruption to either road or rail traffic. However, first the key features of the G-Scan system and guided wave inspection are summarised. Guided Wave Inspection vs. Conventional Ultrasonic Inspection: Conventional ultrasonic inspection systems that operate in the megahertz range have been used for many years for the in-service testing of rail. Two specific areas that can present significant challenges for ultrasonic testing as currently deployed are the detection of smooth transverse/vertical defects and the …