High-Speed Ultrasonic Ran Inspection by Passive Noncontact Technique

Broken rails are a major concern in the safety and operation of railroads. Ultrasonic inspection operated by rolling search units (RSUs) is the most common rail inspection technique aimed at detecting internal rail discontinuities before they grow to critical sizes. However, RSUs using ultrasonic inspection techniques currently operate between 20 and 45 mph (30 to 70 km/h) and require carefully scheduled inspections that may interfere with revenue traffic. This paper proposes a radically new noncontact ultrasonic inspection approach that exploits the rolling train wheels as the acoustic excitation of the rail. The potential for high-speed inspection would enable a concept of "smart trains" that perform the inspection during normal operation, enabling redundant inspections from multiple passes, and increasing the ultimate reliability of discontinuity detection. An initial proof-of-concept field test, implemented in a noncontact manner by air-coupled ultrasonic sensors, was performed at the Transportation Technology Center (TTC) near Pueblo, Colorado, at speeds of up to 80 mph (128 km/h).