Advantage of a combined ultrasonic and eddy current examination for railway inspection trains
Some years ago, two railway inspection trains (RIT) already equipped with ultrasound, had additional advanced eddy current techniques installed. Recently, a new RIT was equipped with a system that was designed, from the beginning, to employ a combination of these two techniques for non destructive rail inspection. The eddy current technique has been developed to enable identification and evaluation of rolling contact fatigue (RCF) defects. The ultrasound technique is aimed at measurements in the rail bulk volume, which are not feasible using the eddy current technique. Experience gained from application has shown that clear improvement on rail inspection can be achieved. For example, following Deutsche Bahn DB (German Rail) AG guideline, defects which are classified as group 2 using ultrasound testing can be further labelled as 'distinguished positions' if, for example, head checking can be identified in the same position using the eddy current technique. In other words, the new technique is capable of identifying two fundamentally different types of defects occurring at the same location. Such defects can then be classified as Group 1, equivalent according to the DB AG guideline. Furthermore, problem cases in the past, such as the decision whether a weld or rail joint is present for a fishing table, can be reliably determined using additional information from the eddy current technique. In this paper, examples will be provided to demonstrate application.