High-Speed Inspection of Rails by Passive Ultrasonic Monitoring

Abstract

This paper presents a high-speed non-contact rail inspection technique that has the potential of detecting internal rail defects at regular (revenue) train speeds. The technique utilizes an array of capacitive air-coupled ultrasonic transducers in continuous recording mode to extract a reconstructed transfer function for a rail segment in a passive manner. The passive approach utilizes the ambient excitation of the rail induced by the wheels of the test car and eliminates the need of a controlled source. A normalized cross correlation operator with modified Welch's periodogram technique is used to extract the transfer function in a manner that is independent of the uncontrolled excitation source (rolling wheels). Discontinuities in the rail (e.g., joints, welds and defects) alter the reconstructed transfer function which is statistically tracked using an outlier analysis for detection robustness and sensitivity. Field tests were carried out with a prototype at the Transportation Technology Center Inc (TTCI) in Pueblo, Colorado at testing speeds of up to 80 mph. The performance of the system in detecting rail discontinuities was assessed via Receiver Operating Characteristic curves for a range of varying operational parameters such as excitation strength, baseline distribution length, testing speed, and multiple runs.