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— by Walter Weart
Just as people can suffer sunburn or heat stroke from too much exposure to sunlight and hot temperatures, rail can bend or warp because of a blistering sun and sweltering temps.
If the rail malformations known as a "sun kink" or "track buckle" aren't repaired in a timely manner, trains can derail. Rail will undergo tensile stress in extreme cold and can fracture from excessive stress, or experience compressive stress from extreme heat that can cause a buckle if the force grows too strong.
A primary cause of buckles is excessive compression resulting from either high temperatures or "rail creep," a longitudinal movement of rail produced by the constant passage of trains, says John Zuspan, president of Track Guy Consultants, which provides track inspection, project management and various consulting services.
The "neutral rail temperature" — or the point at which the net longitudinal force in the rail is zero — should not be set too low per an area's actual air temperature range, he says. There is no expansion or contraction, or compression or tension at neutral temperature.
Since the neutral temperature can't be set when rail is laid, "we must set the desired neutral temperature, which is determined by each railroad based on their criteria," says Zuspan, adding that the American Railway Engineering and Maintenance-of-Way Association (AREMA) provides a formula to compute a desired neutral temperature.
For example, well-built and maintained ballasted track might not buckle until it registers an increase above the neutral temperature of 50 F to 70 F, and the same track might not pull apart until it experiences a decrease below neutral temperature of 105 F to 130 F, emphasizing the need to correctly set the desired neutral temperature, says Zuspan.
De-stressing rail minimizes the risk of a buckle, he says. There are several ways to de-stress rail, including the use of a rail puller and special rail heaters, which direct a flame into the web of an unrestrained piece of rail to heat it and elongate it by a specific amount, depending on the current rail and neutral temperatures, he says.
To help railroads prevent track buckles and bends, a number of companies offer various products and/or services, in addition to pullers and heaters.
Amsted RPS provides rail anchors that can affix a rail to the support, resisting movement of the rail and inhibiting buckles, wide gauge and rail rollover, says Director of Engineering Jose
Mediavilla. Track forces are transferred through the rail to the support structure and, ultimately, to the subgrade.
"We also manufacture unit spring anchors, which are elastic fasteners generally used on concrete ties, slab tracks and steel structures, but also some timber ties," he says, adding that the anchors have heavy-haul, mass-transit, high-speed and other applications.
In addition, Amsted's elastic fastener can resist rail forces that would displace the rail vertically and raise the rail out of the rail seat area laterally, causing wide gauge or rail rollover, says Mediavilla. The fastener also helps prevent longitudinal displacement.
The elastic fastener line is a fairly new addition Amsted inherited from the acquisition of AirBoss Railway Products Inc. in 2008, says Mediavilla.
With its joint venture partner
edilon)(sedra, Amsted also offers the
Edilon Corkelast® Embedded Rail System that's used by commuter-rail and mass transit systems to hold rail in place, avoiding sun kinks and protecting against rust. The technology has been employed by edilon)(sedra in Asia, Europe and the Middle East for more than 20 years.
"The [system] uses a polyurethane elastomer material to fully and continuously support and fix the rail," says Mediavilla.
The Edilon Corkelast system is designed to resist track buckling at the rail-seat level by continuous expansion and contraction of the elastomeric material to dissipate the rail energy created by thermal and tractive loads. The first Edilon Corkelast system installation in North America began last month at the Port of Vancouver for a 50-ton crane embedded rail project, says Mediavilla.
At L.B. Foster Co.'s Salient Systems Inc. unit, a next-generation detection device can help prevent kinks and buckles by determining the actual rail temperature and identifying rail stress, says Salient Systems President James Aten.
The RailStress Monitor™ (RSM), which attaches directly to a rail, is designed to compute longitudinal stress using proprietary hardware and software. In development for about 10 years, the RSM will report rail temperature, as well, says Aten.
The device sends real-time stress and temperature measurements at a rate of once per minute to either a wayside or handheld reader. Using L.B. Foster's
IntelliTrack® Navigator software, a RSM user can do exception-based management of large areas of track, says Aten, adding that the software issues alarms and warnings on potential buckling hazards to permit corrective action.
Railroads issue slow orders when the temperature warrants it, but they generally don't know the longitudinal stress, he says. Railroads now can take preventive action based on the readings from the RSM, says Aten.
Another device designed to manage rail stress: VERSE®, a system offered by VORTOK International that can mechanically measure neutral rail temperature. VERSE was first used in the United Kingdom in 1998, introduced in the United States and Canada in 1999, and employed by CN beginning in 2002.
"The VERSE requires that the rail be in tension and fasteners be removed from about 100 feet of rail on both sides, and the VERSE equipment is attached to rail," says James O'Kelly, president of AET Rail Group, which represents VORTOK in the United States and Canada.
Using a load cell and displacement transducer, the force and displacement used to lift the rail translates to a calculation, which provides the neutral temperature, he says. The data is immediately displayed on a handheld computer.
"This allows the user to make maintenance decisions that reduce the risk of rail buckling," says O'Kelly, adding that the actual rail temperature should be measured at the beginning and end of a test.
Depending on the weather and air temperatures, a test might best be performed in early morning or evening, he adds.
One of VORTOK's newest products is the MultiSensor™, a device installed on rail that features a sensor that can continuously measure stress-free temperature/neutral temperature, rail core temperature and strain.
The device provides "highly accurate data [that] can be transmitted a number of ways, including cellular or radio," says O'Kelly, adding that a MultiSensor can come equipped with an alarm.
The device is being used in a remote location in Australia, where solar panels are used to power the monitoring equipment.
The MultiSensor also is being used in the United States. In 2009, a first generation of the device was installed in a MTA Metro-North Railroad tunnel. VORTOK now is preparing a proposal to upgrade the sensors since trackwork in the tunnel needs changes and the new version of MultiSensor has greatly enhanced communications capabilities, says O'Kelly.
A MultiSensor, along with a data acquisition and transmission system, also has been installed on a Class I and currently is under evaluation, he adds.
Another way to prevent kinks and buckles is to maintain ballast condition, including the shoulders, says Track Guy Consultants' Zuspan. Without sufficient shoulder ballast or if the ballast is contaminated or muddy, the track structure will be relatively weak, he says.
Balfour Beatty Rail Inc. offers a way to determine ballast condition. Introduced about 18 months ago, the Rail Asset Scanning Car (RASC) is a multi-sensor, hi-rail vehicle-based system featuring laser scanning, ground penetrating radar (GPR) and video inspection systems, says Steve Atherton, Balfour Beatty Rail's technical services manager.
The GPR examines ballast quality and profiles to identify maintenance issues, such as ballast depth and condition, fouling and sub-grade profile.
"The RASC can look at the shoulders and track center, determining thickness, if the ballast is clean and in good condition, or if there are muddy or wet spots, or pockets," says Atherton.
Rail can be de-stressed as part of welding operations, as well. When rail is welded, it can be stretched to reduce stress. Rail welding services provider Holland Co. L.P. offers 125 mobile welding vehicles equipped with rail pullers that can be used to adjust the desired neutral rail temperature.
"We use a Holland Puller-Lite, a 160-ton 'super puller' that our crews use as part of their rail welding tasks," says Holland Manager of Engineering Richard Kral.
The Puller-Lite features four independently controlled hydraulic jacks designed to enable precise rail alignment.
While product developments and technological advances are vital to preventing kinks and buckles, so is educating crews about well-prepared track and ways to find and fix problems before they occur. Harsco Rail's ZETA-TECH unit provides those types of training services for the maintenance and inspection of continuous-welded rail (CWR), says Don Holfeld, the company's director of training and field engineering. ZETA-TECH has offered training services since 1996 and provides customized training for each client, he says.
The Federal Railroad Administration (FRA) has several regulations
regarding CWR and added a safety standard requirement mandating that all railroads have a FRA-approved training program in place.
The Federal Transit Administration (FTA) also has published a "Compilation of Rail Transit Industry Best Practices for Track Inspection and Maintenance" guideline that recommends transit agencies have written procedures for the
installation, inspection and maintenance of CWR, as well as provide a training course to all personnel responsible for maintaining the rail.
ZETA-TECH's two-day CWR training course was prepared in part to meet FRA and FTA requirements, as well as to be in compliance with AREMA requirements, says Holfeld.
"The aim of this course is to provide a training program that will be taught to all track maintenance forces that have responsibility for the inspection, maintenance and de-stressing of CWR," he says.
The main points covered by the program include the theory of thermal expansion, understanding the cause of track buckles and pull aparts, inspection techniques, and the repair and reinstatement of thermally defective track.
ZETA-TECH has provided training services to most Class Is, but the company's major clients these days are transit agencies, including the Washington Metropolitan Area Transit Authority, Maryland Transit Administration, Southeastern Pennsylvania Transportation Authority, Chicago Transit Authority, Dallas Area Rapid Transit, Metrolink and Tren Urbano in Puerto Rico, says Holfeld.
Jointed track isn't exempt from kinks or buckles, either. So, lubricating rail joints to ensure they don't become "frozen" with rust and can offer some slight movement is one of the best
options, he says.
The problem of heat-induced kinks and buckles has worsened since railroads moved from jointed rail to CWR, which became more popular in the 1980s and 1990s, and is broadly used today, says Track Guy Consultants' Zuspan.
If a jointed track is built properly, small gaps were left in each joint to allow the 39-foot rail to expand and contract, he says.
The joint bars would need to be oiled so the rail will expand and contract only at the joints, but when a joint seizes up, it now becomes CWR, says Zuspan.
As CWR became more popular, kinks began forming more often and caused a lot of damage due to derailments. Now, the industry understands how to control the forces in CWR, and that type of rail is "here to stay," says Zuspan.
"[But] we still have track buckle-
related accidents," he says. "Last spring, there were five major ones."
So, railroads will continue to count on suppliers to provide even more ways to prevent buckles and bends on all types of track.
Walter Weart is a Denver-based free-lance writer.