Application of the ACFM inspection method to rail and rail vehicles

The ACFM inspection technique is an electromagnetic inspection method, which is widely used in the oil and gas industry for the detection and sizing of surface-breaking cracks. It provides a number of advantages over conventional inspection methods, particularly in the ability to inspect without removing coatings or grease, and has recently been adapted for a number of specific rail applications. The technique has now been accredited in the UK for use on vehicle wheelsets and for the inspection of plain rail. This paper describes the background to the ACFM technique and its application to in-service inspection. The development of a new 'Walking Stick' for inspection of the rail head is described, together with some of the challenges of inspecting the complex crack geometries associated with cracks generated by rolling contact fatigue (RCF). ACFM has also been applied to both plain and driven axles: examples of these applications together with its use on bogies are also given. This paper also considers some of the challenges faced when transferring technology from one industry to another. Operator training has to be considered as well as the validation requirements for acceptance of a new technique. Validation often requires comparison with existing technologies in blind trials but these are not necessarily quantitative in terms of performance. Destructive sectioning provides an absolute measure of system capability and was also used during these developments. Results from both destructive and non-destructive trials are discussed.