Ultrasonic testing is widely used to probe railroad rails for internal defects. Rails are continuously inspected by hi-rail vehicles operating ultrasonic Rolling Search Units (RSUs) at speeds up to ~30 mph. In addition, flaw detection is usually followed by flaw verification using a hand-held ultrasonic probe to determine the flaw size and orientation. Ongoing research in many laboratories worldwide is aimed at improving the performance of ultrasonic rail inspections in terms of practicality and reliability of defect detection. This paper will present recent advances on two topics: (1) achieving rail inspection at high speed by “smart trains”, and (2) improving ultrasonic flaw imaging at walking speed. These efforts are being pursued at University of California San Diego (UCSD) with the collaboration of the U.S. Federal Railroad Administration (FRA) and MxV Rail, Inc. On the first topic, the latest version of a non-contact ultrasonic testing prototype will be presented to allow flaw detection at revenue speeds. Once fully developed, this capability would allow trains to perform inspections during normal operations (“smart train”), hence minimizing traffic disruptions and exploiting the redundancy of multiple train passes over the same segment of rail. Results from field tests conducted in collaboration with MxV Rail, Inc. will be presented in terms of Receiver Operating Characteristic (ROC) curves assessing the trade-off between Probability of Detection (POD) and Probability of False Alarm (PFA). On the second topic, research is being conducted to implement ultrasonic Synthetic Aperture Focus (SAF) in rail flaw imaging using a transducer array hosted in an RSU wheel. Specifically, an RSU imaging prototype is being developed based on recent advances in SAF imaging, including sparse firing, multi-mode detection and eigen-filter analysis. The latest feature allows eliminating artifacts affecting RSU rail imaging (e.g., reflections from the wheel-rail interface and from the railhead bottom flange) so as to successfully isolate the target flaws. Results will be shown during scanning of a sample rail segment in the laboratory, motivating expanding the idea for defect imaging in walking speed.
Hosseinzadeh et al. (2025) studied this question.