Optimizing the system on CPR's BC South Line: Despite the use of premium components and a high level of maintenance, wear and degradation on the line persisted - Canadian Pacific Railway - Statistical Data Included

Railway Track and Structures, July, 2001 by Mike Roney, Dave Meyler, Eric Magel, Peter Sroba

The BC South Line, an 80-mgt line through the Rocky Mountains of western Canada, is one of the most-demanding sections of track on the Canadian Pacific Railway, or any system, for that matter. A 1.1-percent ruling grade and high curvature characterize the line. Nearly half of this 750-mile, predominantly single-track territory is curved; 80 miles are six degrees or more.

Weather compounds the engineering challenge, with temperatures ranging from 110 F in Summer to -30 F with as much as 40 feet of snowfall in the Winter. CPR built 132 avalanche sheds to protect the line.

Despite the number of premium components used on the line, wear and degradation--and the high level of maintenance associated with them--persist. On the track side, accelerated vertical and gauge-face rail wear and crushed heads in some track sections dictate frequent rail replacement.

On the vehicle side, wheel shelling is responsible for premature wheel removal, along with associated train delay and availability and reliability problems.

CPR recognized early-on that it would need better materials and practices in order to extend component lives and reduce maintenance requirements on the line. CPR further recognized that it would take a multi-faceted "system" approach to significantly improve wheel/rail interaction. Over time, CPR incorporated the use of premium rail steels, specially-designed rail and wheel profiles, advanced preventive-maintenance rail-grinding practices, the use of steerable trucks on unit coal cars and an effective lubrication program into its efforts to optimize the system.

One of the first things CPR did to reduce wear and optimize the system was to introduce high-hardness (350- to 390-Bhn), chromium-alloyed, head-hardened rail into curves on the line. It also changed from a 132- to 136-pound rail section to take advantage of an additional 5-mm (3/16-inch) vertical wear allowance. Use of these cleaner, harder rail steels reduced wear and plastic flow as well as the "infant mortality" rate characterized by the early appearance of transverse defects.

Overall, rail life was extended by 25 percent to 100 percent. This year all sharp curves in the new rail program are being replaced with low-alloy, hypereutectoid steel that has been shown to increase rail life by a further 10 to 25 percent.

Since premium rails do not readily conform to the throat of the typical wheel flange, they are prone to development of deep gauge-corner shells under the "point" wheel loads. On CPR, rail grinding is an essential maintenance practice.

Rail grinding

CPR initiated a corrective grinding program to eliminate shelling and corrugations and to reshape the rail.

Ultimately, the railroad adopted a preventive-grinding approach to reduce rail wear and to control surface fatigue and plastic flow. While the program met the immediate need, it didn't necessarily optimize wheel/rail interaction.

To get a better understanding of what was happening with wheel and rail profiles, the National Research Council of Canada measured wheel profiles from trains that frequent the line.

This comprehensive study showed that CPR, by virtue of its existing grinding practices and the use of steerable trucks on its captive coal car fleet, had a substantially lower percentage of hollow wheels when compared to industry-wide population as reported by the AAR.

This further showed that the off-the-shelf low-rail profile (1) was consistently over-ground, and not the most suitable for operating conditions on the BC line. As a result, CPR commissioned the NRC to design an entirely-new series of rail templates that would better mate with the existing wheel profile distribution and take better advantage of the enhanced handling characteristics of the coal cars' steerable trucks.

The new NRC-designed profiles increased the low-rail head radius from 200 mm to 250 mm (eight to 10 inches). The new 10-inch head radius minimizes stress and reduces the amount of fieldside metal that must be removed by about two mm (0.080 inches). Since the low rail requires more effort than the high rail under preventive grinding, these new templates eventually will permit an increase in grinding speed on curves.

The high rail profiles also were optimized to reduce contact stresses and wear, and to promote wheelset steering. Together, the new profiles broaden the contact band and reduce the contact stress levels.

The NRC also developed two tangent profiles to broaden the wear band on the wheels and promote more uniform wheel wear. The CPR-TG (tangent-gauge) template moves the contact point about four mm (0.16 inches) towards the gauge side of center, compared to the previous template; the CPR-TF (tangent-field) moves the contact band about eight mm (0.32 inches) to the field side of center.

The TF profile was further refined for application to sections of track that are vulnerable to head crushes. The CPR-TF template spreads the stress widely across the rail head with a concentration to the field side (to spread wear on the wheel) but with gentle loading on the gauge side so as not to overload the field side of existing crushes (Figure 1).