Interface - The Journal of Wheel/Rail Interaction

REDUCING DERAILMENTS

Reducing Broken Rail Derailments in Dark Territory (continued)

Wheel defects (see Figure 6) occur disproportionately on the “B” ends of cars. Railways have to get the message to the operating crews and shippers to release hand brakes when moving cars. The wheel changeout rate and the ratio between A/B end wheel defects are Key Performance Indicators (KPIs). Railways should also ensure that locomotive engineers understand the relationship between gradient and brake release procedures, and that they go deep enough into the air in cold weather to ensure a brake release at the train end. (Hot wheels from sticking brakes is another KPI.) Railways should also consider the use of tread-guard or other premium brake shoes. BC Rail significantly reduced the number wheel defects on center-beam bulkhead cars by using premium brake shoes.

Wheel profile designs can also affect overall performance. The AAR1B wheel profile design, for example, is a compromise. It doesn’t always break in well and can generate stresses at the rail gauge corner and in the wheel root area. The Quebec Cartier Mining Railway, for example, found that modified wheel profiles can reduce wheel changeouts and rail wear.

Wheel Impact Load Detector (WILD) systems have shown to effectively monitor wheel conditions. BC Rail installed two WILD systems, after Canadian National’s pioneering work, to manage risk on the system. While switching out cars with defective wheelsets hinders operational schedules and delays loads, running cars with wheels that generate high-impact loads can crack concrete ties, wear out ballast and accelerate defect crack growth rates in rails.

The appropriate alarm thresholds are determined through the use of a formula that relates the probability of TD failure to the rail section, the size of the defect, temperature differential and wheel impacts (3). Alarm thresholds may be selected to identify defective wheels, but keep them in service and minimize impact to operations. In dark territory with older rail or areas in which TDs are a problem, lower impact thresholds that vary with temperature are advisable. Railways may also require track inspection after a high-impact load is detected.

Miscellaneous Advice

Railways in dark territory should make it a point to test all new thermite welds before winter and at least 1 MGT of tonnage. Testing immediately after a weld is made doesn’t identify defects that grow from small stress risers (see Figure 7).

Railways should consider using premium steel at highway/rail grade crossings, where salt and grit accelerate wear. The tires from passing vehicles remove the debris boundary layer on the rail, and cause the steel to wear at two to three times the rate of wear outside the crossing. Wet areas in tunnels, which are least likely to be closely inspected, are among the most likely areas to have stress corrosion problems under the head or on the base of the rail. They represent another good place to use premium rail steel.

Railway managers should assess and monitor maintenance practices to ensure that crews don’t dent the rail base with a spike maul when installing spikes, and that they are using a sledge for rail anchors. (Your testing won’t find cracks that develop at the base toe of the rail.

Poor tie support will increase vertical split heads, bolt hole failures and weld failures. Sometimes poor tie conditions are the root cause of rail failures. Under increasing axle loads, railroads can’t expect good rail fatigue performance if tie support and track gauge are approaching or exceeding safety standards or limits.

Finally, railway managers must ensure that plugs are not taken from high rail sections that have been removed because of too many TDs. This should be obvious, but if the web isn’t painted white down the entire rail sections; it will end up back in track somewhere else as a plug to match rail wear. (KPI is TD defect plug)

Generally, then, in order to reduce broken rail derailments in dark territory, railways should:
• Establish a formal Risk Management process with Key Performance Indicators.
• Gather and integrate data.
• Fully investigate all derailments and service failures.
• Work with Engineering, Operating and Mechanical Departments to reduce wheel impacts.
• Analyze and match rail specifications and purchases to the service conditions.
• Study and improve rail testing reliability and frequency.
• Treat the wheel rail interface as a system.
• Establish an effective rail grinding program.

This paper is based on a presentation made at Interface Journal and Advanced Rail Management’s 13th Annual Wheel/Rail Interaction Seminar, May 2007.

References
(1) Igwemezie, J., et.al., “Residual Stresses and Catastrophic Rail Failure,” International Heavy Haul Conference, June 1993
(2) Jeong, D., “Analytical Modeling of Rail Defects and its Applications to Rail Defect Management,” Volpe National Transportation Systems Center, January 2003.
(3) Igwemezie, J., et.al., “Defective Rail Fracture Under Dynamic, Thermal and Residual Stresses,” International Heavy Haul Conference, June 1993

Norman Hooper P.Eng, is Project Engineer, Hatch Mott MacDonald.

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