Interface - The Journal of Wheel/Rail Interaction

WHEEL RAIL INTERACTION

Tuning in to the Systems Approach (continued)

Hooper shared some of the risk-management strategies that helped reduce service failures and broken rail derailments by 60% on a Class II railway. Frequent ultrasonic rail testing is a must. But, depending on the size of the defect and the surface condition of the rail, testing equipment doesn't always find a defect in the rail. Industry guidelines indicate that testing equipment should be 65% to 95% accurate, depending on the size of the defect. Accuracy of 65% leaves at a lot to be desired, Hooper said. “In cold weather, you don't need a very big defect.”

If anything, the risk of a broken rail derailment is greater in dark territory, he said. “And if you are applying the methods you're using in signaled territory directly onto dark territory without some consideration, you're missing some opportunity.”

The chance of finding some of the smaller defects can be improved by cleaning up the rail through grinding or by turning down the lubricators prior to testing. Track inspection is also important. “It is much more important to review the quality of the track inspection than the pieces of paper (it’s reported on),” he said. “What is missed or omitted from those inspections is as important as what's entered.”

Good data allows railway managers to identify trends, such as defect growth compared to tonnage, in order to determine the appropriate testing frequencies. “Test the hot spots more frequently,” Hooper said. A branch line with 85-pound rail may require more frequent testing than a main line with 136-pound rail. Late fall or winter testing is also beneficial. While no one wants to change out rail in December, that’s when defect-related problems are likely to appear.

Freight Car Performance
The increasing load and stress environment of primary railcar structures, as evidenced by top-chord and axle failures during extended 286,000-pound gross rail load (GRL) service, has become a growing concern on North American railroads. Design, inspection and maintenance practices may have to be revised to ensure that the vehicles can withstand 286,000-pound GRL operating conditions on a sustained basis.

The Transportation Technology Center, Inc., (TTCI) conducted a series of four over-the-road tests to measure the wheel forces, axle strain/stress, bolster loads, and top chord strain/stress under typical revenue service conditions. Instrumented wheelsets were used to measure vertical and lateral forces and torque. Dynamic wheel forces and axle strain were recorded during the first test. Transducers were added to measure top chord strain during the second test, which was conducted at higher average speeds than the first. Additional transducers were added to measure the vertical bolster loads during the third test and fourth tests, which were conducted over different routes emanating from the Powder River Basin in Wyoming.

Results from the four tests indicate that the primary variables affecting dynamic vertical wheel forces, bolster center bowl loads, and top chord compressive strains in hopper cars appear to be train speed and track surface deviation, said Kevin Koch, the TTCI’s Manager of Track Inspection and Development.

The most significant car response occurs with the following combination of parameters:

—Train speed in the range of 48 to 51 mph.

—Track surface vertical deviation greater than about 1.25 inches peak-to-peak.

—The period or distance of the deviation at about 40 to 60 feet.

The most obvious track geometry features associated with these events were vertical track perturbations, he said. High load events were correlated against track geometry data collected by the railways.

While ambient temperatures, which ranged from 15 degrees F to 80 degrees F during the tests, did not appear to affect car response, the use of a premium (or M976-compliant) truck did. The use of premium trucks provided a general reduction of 15% in top cord stresses and as much as an 18% to 20% reduction in vertical center bowl stress, Koch said.

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