Finding flaws quickly, reliably: railroads must search for rail flaws without disrupting traffic—but they can't afford to sacrifice quality and reliability for speed

Railway Age, Nov, 2004 by Tom Judge

Rail flaws are treacherous. Finding them and removing them is a vital part of the m/w task, one that researchers and suppliers are always striving to do better.

At TTCI, researchers are looking into improved rail flaw detection under AAR Strategic Research Initiative 7A. SRI 7A's objective is to improve reliability and safety of railway operations by developing improved flaw detection methods and fostering development of improved flaw detection systems.

"Conventional dynamic rail detection systems are reliable in finding defects in the head and the web of the rail," says Greg Garcia, TTCI principal investigator. "Rail base inspection is currently not performed during conventional dynamic rail flaw inspections." Technologies being evaluated and/or developed are targeting higher reliability to detect defects 20% in size or smaller, inspection of the entire rail section, and inspection of rail with poor surface conditions.

FRA and AAR are sponsoring non-destructive technology research into Phased Array Ultrasonics and Laser Based Ultrasonics. "Phased arrays provide increased accuracy in flaw sizing," Garcia says. Research under FRA sponsorship using this method includes flaw monitoring this winter. Monitoring will provide characterization of the flaw during heavy-axle load operations. Laser based ultrasonics remote, non-contact inspection of the entire rail section head, web and base).

Technogamma SPA is developing a laser-based ultrasonic inspection system. The system is based on the Laser Air Hybrid Ultrasonic Technique (LAHUT) patented by Johns Hopkins University. Technogamma is sponsored by European consortia. "By using a laser transmitter and an air coupled transducer as a receiver, this inspection method gives you the capability of checking the entire rail section," Garcia says. "Currently, there are limitations on conventional technology because of the limited number of inspection angles that can be used. By using the laser air-coupled approach, you can enter the railhead at different angles. You're actually flooding the entire head with sound or mechanical energy, and are able to evaluate greater areas of the railhead with more detail. You're not really limited by railhead surface conditions because you don't have to have sound enter from the top."

TTCI will test and evaluate the system on the Rail Defect Test Facility in 2005. If successful, TTCI will help facilitate implementation of the laser-based system into North America. It's currently conducting research with Technogamma to try to minimize the number of lasers that will be needed to perform this inspection in service.

"The feasibility has been demonstrated, so now we're trying to do the engineering to design a product that is economical to put in service," says Garcia. The laser based system has demonstrated reliable detection for transverse defects, vertical and horizontal split heads, and base defects. Development continues for thermite welds and web defects.

DAPCO Technologies has developed a small vehicle for what the industry calls a trunk test car. "Normal detector cars have a hard time inspecting through crossings, switches, and frogs," says Dominic Pagano, president. "Individual railroads, such as Union Pacific or BNSF, use a one man small vehicle. An inspector would go out and manually unload a test carriage from the trunk, then push the test carriage with a sensor unit through the frogs and turnouts. We've automated a test unit, giving it the same power as in the big detector cars, with pattern recognition and classification. Railroads can also to use this vehicle for yards and other non-critical-type applications without tying up the resources of the big vehicles. We continue to enhance the artificial intelligence in this system, and we're waiting for the hardware to improve to the speeds where we can apply it."

Pagano points out that customers are asking for more intelligence from the flaw-detection vehicle. "For example, as an FRA- and railroad-driven issue, we've implemented mandatory stops," he says. "Once the vehicle detects an anomaly or potential defect, the operator has to acknowledge what might have caused that or the system automatically shuts down."

Herzog Services, Inc., is implementing an ultrasonic simulation software package that allows users to "see" the effect of different rail conditions on the sound path. By injecting defects into the simulation package, along with differing rail surface conditions, it is possible to determine what measures might be taken to aid in detection under less than optimal situations. Rail conditions can create the biggest challenges in rail-flaw detection, says Herzog. The surface profile is one of the main factors in getting the sound path into the steel correctly. If the head is worn on the gauge side due to curve wear, insufficient grinding (or for transposed rail, deviation from a flat surface) can alter the resulting sound path and reduce the efficiency of the testing array. Vital routine rail maintenance like lubricating and grinding also can play havoc on the testing system. Herzog says it takes all these situations into consideration.