An update on revenue service tests of bainitic steel rail crossing diamonds: continued maintenance reduction and predicted longer service life are the results in year two of diamond testing - Ttci R&D - Transportation Technology Center

Railway Track and Structures, Jan, 2003 by David D. Davis

Performance measurements

TTCI is measuring the performance of the crossing diamond through frequent inspections. Measurements made include running surface elevations, profiles and hardnesses. Observations of maintenance performance are being made and components are being replaced. Figure 6 shows TTCI personnel measuring the running surface elevation of the mainline rails. With this device, the running surface height loss from wear and metal flow can be determined.

Running surface wear and deformation are calculated from the change in elevations with tonnage. Non-running surface points are also measured to serve as reference marks. Comparison to the previous two pearlitic rail crossing diamonds can be made since similar measurements were taken when these diamonds were removed from track.

TTCI will continue to monitor the performance of these diamonds to determine long-term performance, average service life and typical failure modes.

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Table 1

Revenue service bainitic rail crossing diamond test sites.

Test         Crossing    Rail     Owning   Crossing     Annual     Speed
Location       Angle    Section  Railroad  Railroad    Tonnage     Limit
             (Degrees)                               Rate(mgt/yr)  (mph)

Gilman, IL      78       136RE    CN/IC      TP&W         37        40
Zeigler, IL     76       136RE      UP       BNSF         60        40
Hoxie, AR       84       136TW      UP       BNSF        110        40

Test         Installation
Location         Date


Gilman, IL    July 2000
Zeigler, IL    May 2001
Hoxie, AR     Nov. 2001

References

(1.) Singh, Satya and David Davis, "Reducing Impact Forces on High-Angle Crossing Diamonds," Technology Digest TD98-021, Association of American Railroads, Transportation Technology Center, Inc., August 1998.

(2.) Davis, D.; D. Guillen; J. Robeda and C. Sasaoka, "Field Performance of Bainitic Steel Rail Crossing Diamonds," Technology Digest TD01-025; Association of American Railroads, Transportation Technology Center, Inc., November 2001.

RELATED ARTICLE: Heavy axle load proven bainitic rail

The rail used in the diamond is a medium carbon (~0.25 percent) bainitic microstructure steel developed by AAR and given the code name: J6. J6 is the lower-alloy bainitic microstructure steel developed for curve-rail applications. Its chief advantages over pearlitic rail steels for crossing diamonds are its superior hardness and toughness. The rail has a surface hardness of 410 BHN and an internal hardness of 430 BHN. It also has a fracture toughness of three-to-five times conventional rail steel with room temperature Charpy V-notch test values of 10-20 ft-lbs. The additional strength and toughness allow the J6 rail to hold its shape better and withstand impacts better than other rails.

In heavy axle load testing at FAST, bainitic rail has proven itself to be durable for crossing diamonds. J6 has survived three times as long as the best available pearlitic rail under the same 39-kip wheel load test. Using the same crossing diamond, three sets of running rails were tested; a fully heat-treated pearlitic rail (340 BHN), a head-hardened premium pearlitic rail (370 BHN), and the J6 bainitic rail (410 BHN). The first two were tested with 62-degree flangeway gaps. The bainitic rail was given a more severe test with 90-degree gaps. Ninety degrees is the most severe case for impact loading as the wheel must jump a full flangeway gap. Sixty-two degrees is also a severe case. This is the angle where the wheel begins jumping a small, unsupported gap.