Patent Publication Number: US-9429545-B2

Title: System and method for non-destructive testing of railroad rails using ultrasonic apparatuses mounted within fluid-filled tires maintained at constant temperatures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/406,926, filed Feb. 28, 2012, the contents of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improved systems and methods for performing non-destructive testing and analyses of railroad rails. More particularly, the present invention is directed to systems and methods for identifying flaws and defects in underlying railroad rails using ultrasonic detection means mounted within fluid-filled tires, wherein the fluid within the tires is maintained at a constant, desired temperature through the use of one or more heat exchangers. 
     2. Description of the Related Art 
     From time to time, and for various reasons, the rails of a railroad track may develop one or more detrimental flaws or defects. Such adverse conditions may include transverse defects, vertical shear or split-head defects, horizontal shear or split-head defects or the like that may originate from manufacturing and construction processes, environmental factors or wear-and-tear from normal use. These flaws or defects are typically observed in the head of a rail, but may also be found within the web and feet of the rail, around the peripheries of the bolt holes, or any other portion of the cross-section of the rail. Due to the nature of railway travel, in which locomotives weighing tens of thousands of pounds regularly carry hundreds of tons of freight over rails while traveling at varying speeds, cracks within the rails may expand or propagate throughout the rail heads over time. Such flaws or defects that are left unattended or unaddressed can lead to a variety of problems, the most serious of which may include catastrophic rail failures or train derailments, and may pose serious financial, health and safety risks to goods and personnel, as well as the railway industry as a whole. 
     Rail failures may be predicted and avoided through routine non-destructive inspection, which may enable railway operators to identify and cure hidden or infinitesimal flaws or defects within rails before they manifest into problems of much greater magnitudes. To detect such flaws or defects, vehicles or rail car-mounted apparatuses including ultrasonic inspection equipment have been built to travel along a railroad track, and to continuously perform ultrasonic testing of the underlying rails in situ by transmitting ultrasonic beams into the rails and analyzing any portions of the beams that may be reflected off flaws or defects. 
     One example of an ultrasonic railroad rail inspection system for in situ rail inspection including a wheel assembly having a fluid-filled tire for maintaining rolling contact with the head of an underlying rail is disclosed in U.S. Pat. No. 7,849,748 B2 to Havira. According to the teachings of Havira, the tire forms a contact patch with a head of an underlying rail and includes an ultrasonic transducer supported within the tire for projecting an ultrasonic beam along a beam axis through the fluid and the tire, and into the head of the underlying rail. The ultrasonic beam propagates through the underlying rail and is reflected by any defects or flaws that may be present therein, which may cause some or all of the beam signal to be returned to the transducer or received by another ultrasonic detector. The reflected portions of the signal are then analyzed by one or more computer processors to determine the type, magnitude or location of the flaw or defect from which the signal was reflected. 
     When an ultrasonic transducer is suspended within a fluid-filled tire, such as is disclosed in Havira, the tire and fluid provide the transmission medium between the ultrasonic transducer and the underlying rail. Due to the nature of sound travel, the strength and quality of the ultrasonic signals that are both delivered and received by the transducer depend upon the speed of sound in the fluid. 
     The speed of sound of longitudinal sound waves in a medium is generally dependent upon the medium&#39;s compressibility and density. In a liquid medium, the speed of sound is typically calculated according to the Newton-LaPlace formula shown in Equation (1), below: 
                   c   =       K   ρ               (   1   )               
where c is the speed of sound in the medium; K is the bulk modulus of the medium, i.e., a measure of the medium&#39;s resistance to uniform compression; and ρ is the density of the medium.
 
     Both the density and the bulk modulus (or compressibility) of a liquid are typically dependent upon the temperature of the liquid. In liquid water, the density varies widely within the range between the freezing and boiling temperatures of 0° C. and 100° C. (32° F. and 212° F.), respectively. For example, the density of water has been observed to follow a roughly parabolic plot between 0° and 100° C. (32° F. and 212° F.), with a peak density of approximately 1.0000 gram per milliliter (g/ml) at approximately 4° C. (39.2° F.), and with minimum densities of 0.9999 grams per milliliter (g/ml) at approximately 0° C. (32° F.), and 0.9581 grams per milliliter (g/ml) at approximately 100° C. (212° F.). Likewise, the bulk modulus of water also varies as a function of the temperature of the water, rising from a value of 293×10 3  pounds per square inch (psi), or 2.02 gigapascals (GPa), at 0° C. (32° F.), to a peak of 334×10 3  pounds per square inch (psi), or 2.30 gigapascals (GPa), at approximately 54.4° C. (130° F.), before descending to a value of 300×10 3  pounds per square inch (psi), or 2.07 gigapascals (GPa), at 100° C. (212° F.). 
     Variations in the density and the bulk modulus of a liquid at various temperatures result in concomitant variations in the speed of sound throughout the liquid. For example, in  Speed of Sound in Pure Water,  52 J. Acoust. Soc. of America 1442 (1972), Del Grosso and Mader developed a fifth-order polynomial equation for estimating the speed of sound within pure water as a function of temperature. Del Grosso and Mader identified a peak sound velocity in pure water of 1,555.147 meters per second (m/s) at 74.172° C. (165.51° F.), as well as speeds of 1,402.388 meters per second (m/s) at 0° C. (32° F.) and 1,543.109 meters per second (m/s) at 100° C. (212° F.). Therefore, according to Del Grosso and Mader, the speed of sound in liquid water may vary across the range of temperatures in the liquid phase by over ten percent. 
     Variations in the speed of sound in a liquid as a function of temperature are particular critical to the inspection and analysis of railroad rails using ultrasonic detection means mounted within fluid-filled tires. Because the liquid acts as the primary transmission medium between the transducer and the rail head, changes in the sound propagation and attenuation properties of the liquid may create widely varying ultrasonic inspection results, either within an individual analysis, such as when the temperature of the fluid within the tire heats up due to friction after many miles of travel, or between analyses, such as when tests are performed at different times of the year or at different ambient temperatures. Unless the variation in fluid temperature is accounted for, the results of ultrasonic inspections may not be standardized, and may prove unhelpful in identifying flaws or defects within the rail. In such instances, the diagnosis and correction of potentially catastrophic failures may be unnecessarily delayed or completely overlooked. 
     It is an object of the present invention to overcome one or more of the drawbacks and/or disadvantages of the prior art described above. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system for detecting and inspecting certain types of defects in a rail, including a fluid-filled tire for maintaining rolling contact with a head of an underlying rail on which the carriage travels. The fluid-filled tire may include both an ultrasonic transducer and a heat exchanger mounted within the tire. The ultrasonic transducer may transmit ultrasonic beams through the fluid and the tire into the head of the underlying rail, while the heat exchanger may maintain the fluid within the tire at a predetermined or desired temperature. 
     In accordance with one aspect, the present invention is directed to an improved system for performing non-destructive testing of rails of a railroad track. The system may include at least one wheel assembly mounted to a probe carrier, suspended from a carriage, or provided by any other vehicle, wherein the at least one wheel assembly has at least one fluid-filled tire for maintaining rolling contact with an underlying rail. The system may further include a heat exchanger mounted within the tire, which may be a part of an independent, closed-loop fluid system that draws heat from, or introduces heat to, the fluid within the rolling tire by circulating a heat transfer medium therethrough. The system may further include sensors and/or control systems for monitoring either the temperature of the fluid within the rolling tire or the temperature of the heat transfer medium, and for providing heating or cooling to the heat exchanger, as necessary, in order to maintain the temperature of the fluid within the tire at or near a predetermined set point. 
     The systems and methods of the present invention may provide numerous advantages over the prior art. First, the systems and methods may ensure that inspection results are standardized across a single inspection by providing a single, constant fluid temperature despite any variations in temperatures throughout the inspection process or any heat that may be generated due to friction. Second, for the same reasons, the systems and methods may also standardize the results of periodic inspections performed throughout the year, i.e., in every season and at any temperature. Third, because the temperature of the fluid medium may be controlled or maintained at a desired level, the systems and methods enable testing to be performed at the most advantageous temperature for a particular fluid medium, i.e., at the temperature at which the acoustic properties of the fluid are maximized. Finally, the systems and methods enable the same rolling search unit to be utilized to conduct inspections and analyses in any location, regardless of the temperatures in the respective locations. 
     Other aspects and advantages of the systems and methods for performing non-destructive testing disclosed herein may be determined upon review of the Summary of the Invention, Figures, Detailed Description and Claims. 
    
    
     
       DESCRIPTION OF THE SEVERAL VIEWS OF THE INVENTION 
         FIG. 1  is a schematic view of an ultrasonic railroad rail inspection system according to the prior art. 
         FIG. 2  is a perspective view of a carriage used in the rail inspection system of  FIG. 1 , according to the prior art. 
         FIG. 3  is a side view of a rolling search unit according to one embodiment of the present invention. 
         FIG. 4  is an isometric view of the rolling search unit of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the rolling search unit of  FIG. 3 , taken along the section lines  5 - 5 . 
         FIG. 6  is a cross-sectional view of the rolling search unit of  FIG. 4 , taken along the section lines  6 - 6 . 
         FIG. 7A  is an isometric view of one embodiment of a heat exchanger for use in a rolling search unit according to one embodiment of the present invention. 
         FIG. 7B  is an exploded isometric view of the heat exchanger of  FIG. 7A . 
         FIG. 7C  is an orthogonal view of one embodiment of a heat exchanger for use in a rolling search unit according to one embodiment of the present invention, showing an internal flow path for coolant flow in broken lines. 
         FIG. 8  is a piping diagram for a heat transfer system including a plurality of rolling search units according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a rolling search unit including a fluid-filled tire for rolling along an underlying rail, wherein an ultrasonic transducer and a heat exchanger are mounted within the tire. 
     Various systems and methods for performing non-destructive testing of railroad rails using ultrasonic transducers are known to those of ordinary skill in the art, such as the systems and methods disclosed in U.S. Pat. No. 7,849,748 B2 to Havira. Referring to  FIG. 1 , an ultrasonic railroad rail inspection system  10  for inspecting a railroad rail  12  according to the prior art is shown. The rail  12  has a typical, known cross-sectional design with a base  14 , a central web  16 , and a head  18 . The head  18  is shaped with a gauge side  20 , a field side  22 , and an upper running surface  24 . 
     The system  10  further includes a flaw detector or sensor  26  containing one or more ultrasonic transducers  28 , which are generally controlled by a central processing unit  30  of the computer  35 , which is connected to the transducer by a cable  32 . The ultrasonic transducers  28  are adapted to transmit and receive ultrasonic beams. When the central processing unit  30  sends a control signal to the transducer  28 , the transducer  28  generates and transmits an ultrasonic beam  34  along a beam axis  36  toward the upper surface  24  of the rail  12 . After a slight refraction, the beam  34  propagates through the head  18  until the beam  34  is reflected off of a flaw F embedded in the head  18 . As is shown in the illustrated case in  FIG. 1 , some of the ultrasonic beam  34  is reflected back from the flaw F along the beam axis  36 , and propagates through the head  18  of the rail  12 , through the upper surface  24  of the rail  12  to the transducer  26  where the reflected beam is detected. The transducer  28  converts the reflected beam into a reflection signal that is sent to the central processing unit  30  through the cable  32 . The central processing unit  30  analyzes the reflection signal in comparison to the transmitted signal, and identifies the existence, type, and location of the flaw F within the rail  12 . 
     Referring to  FIG. 2 , a carriage  40  or other probe carrier for performing an inspection operation is shown as suspended by links  43  under a rail car or inspection vehicle (not shown) that travels along rails  12  to perform in situ rail flaw detection and identification. The carriage  40  may include a set of four flanged carriage wheels  42  connected to the four corners respectively of a rectangular chassis  44  to guide the carriage  40  along the rails  12  in a substantially centered position when the carriage  40  is lowered onto the rails  12  to perform an inspection operation. 
     The carriage  40  may be equipped with any number of known railroad rail inspection devices and inspection accessories, such as an induction sensor assembly  46  and associated current induction brushes  48 . The carriage  40  may also be equipped with one or more known ultrasonic rail inspection wheels  50 ,  52 ,  60  which utilize transducers set at various angles to detect flaws ahead of and behind the wheels relative to the direction of travel, as well as defects below the carriage  40  in the web of the rails  12 . In addition, the carriage  40  may also be equipped with a plurality of rail cleaners  54  to remove debris from the rails  12  in advance of the sensors and flaw detectors. Any other form of probe carrier may be used to mount the rolling search units, and to perform an inspection operation, in accordance with the present invention. 
     Referring to  FIGS. 3 and 4 , a rolling search unit  100  according to the present invention is shown. The rolling search unit  100  includes a bracket assembly  110 , a shaft  112 , a connector  114 , a bleeder valve  116  and a tire  120  held between a clamping ring  122  and a wheel flange  136 . The rolling search unit  100  may be linked with a heat transfer system (not shown) through connectors  130  and hoses  132 , which provide a heat transfer medium to the rolling search unit  110  through supply and return headers. 
     The bracket assembly  110  is adapted to be mounted to the underside of a carriage or other vehicle capable of traveling on a railroad rail, and provides support for the shaft  112  and the tire  120 . The connector  114  is mounted to an extension of the shaft  112  and is adapted to connect with a computer or other processing unit, such as the central processing unit  30  shown in  FIG. 1 . Preferably, the connector  114  is a multi-pin connector adapted to provide a versatile array of connections between the rolling search unit  110  and a computer or other processing unit. 
     Referring to  FIGS. 5 and 6 , cross-sectional views of the rolling search unit  100  of  FIGS. 3 and 4  are shown. The rolling search unit  100  is shown as having an ultrasonic transducer  160  and a heat exchanger  170  supported within the tire  120 , which is filled with fluid G. 
     The shaft  112  is shown as mounted to the bracket assembly  110  and providing support to the wheel flange  136 . The shaft  112  may be formed from any material of sufficient strength, such as stainless steel. The tire  120  is clamped within clamping rings  122  through the use of fasteners  124 , which fix and seal the internal perimeter of the tire  120 . The clamping rings  122 , tire  120 , and wheel flanges  136  form a cavity that may be filled with a fluid. Preferably, the fasteners  124  are machine screws, although any form of fasteners may be used to fix the tire  120  within the clamping rings  122 . 
     The tire  120  rotates freely in connection with the clamping rings  122  and wheel flange  136 , and in contact with an underlying rail. In a currently preferred embodiment, the wheel flange  136  includes a bearing assembly positioned within retaining rings and held in place with a spring, to provide radial support for the shaft  112  and to reduce rotational friction. 
     The tire  120  is formed of a flexible material, such as polyurethane, and is filled with fluid G to a slight pressure, i.e., approximately 10 pounds per square inch (psi), or 68.950 kilopascals (kPa), gage. The tire  120  may be filled with fluid G prior to an inspection operation through filler valve  152 , shown covered by stem bumper  154 , or drained for servicing through bleeder valve  116 , which is shown as covered by a cap. The rolling search unit  100  also includes seals  150  which prevent the pressurized fluid G from escaping the tire  120 . 
     In a preferred embodiment, the fluid G within the tire is a mixture of water and ethylene glycol, although any suitable fluid may be used. Ethylene glycol is a preferred component of the fluid G because of its low freezing point, especially in mixtures with water. While pure ethylene glycol freezes at approximately −12° C. (+10° F.), a mixture of approximately fifty percent water and fifty percent ethylene glycol by volume freezes at approximately −35° C. (−31° F.). 
     Yoke assembly  156  is positioned within the tire  120 . The yoke assembly  156  provides structural support within the tire  120  for ultrasonic transducer  160  and heat exchanger  170 . The ultrasonic transducer  160  may be equipped to transmit ultrasonic beams through the fluid G and the tire  120 , and into an underlying rail, and may further be equipped to receive beams reflected off flaws, defects or other features within the underlying rail. 
     The heat exchanger  170  is designed to transfer heat between the fluid G outside of the heat exchanger  170  within the tire  120 , and a heat transfer medium passing internally through the heat exchanger  170 , to an external heat transfer system. The heat exchanger  170  is connected to external supply and return headers through connectors  130 , hoses  132  and elbows  134 , which provide the heat transfer medium to the heat exchanger  170  through channels within the shaft  112 . While heat exchangers according to the present invention may take any shape, the heat exchanger  170  shown in  FIGS. 5 and 6  has an arcuate shape of a circular sector, and is sized to maximize the external surface area for heat transfer within the tire  120 , and also to fit within the loaded free height of the tire  120 . Additionally, while the heat exchanger  170  is shown in  FIGS. 4-6  as having smooth, exterior surfaces, heat exchangers according to the present invention may have grooved or corrugated external surfaces in order to further enhance the transfer of heat, or have any other surface features as desired. 
     The heat exchanger  170  is designed to be a part of a closed-loop heat transfer system, which may include one or more heaters or chillers in fluid communication with the heat exchanger  170 . Preferably, the heat exchanger  170  is designed to withstand internal operating pressures of approximately 60 pounds per square inch (psi), or 413.685 kilopascals (kPa), gage, and to maintain the heat transfer medium within the heat transfer system separate from the fluid G within the tire  120 . Although the rolling search unit  100  is designed to maintain the fluid G and the heat transfer medium separate from one another, and to prevent the fluid G and the heat transfer medium from coming into direct contact with one another, the fluid G and the heat transfer medium are preferably the same fluid, i.e., a mixture of approximately fifty percent water and fifty percent ethylene glycol by weight. However, any suitable heat transfer medium may be utilized within a heat exchanger mounted inside a tire according to the present invention. 
     The connections  130  enable the rolling search unit  100  to be linked to a heat transfer system that may be maintained onboard a rail car, carriage or other inspection vehicle, and may include one or more heaters or chillers as well as temperature control equipment. Preferably, the connectors  130  are quick-connect male brass fittings that enable a rolling search unit  100  to be mated with a heat transfer system in a modular format, although any form of connector may be utilized to connect the heat exchanger  170  with the supply and return headers of a heat transfer system. Additionally, the hoses  132  may be formed of any material, such as insulated or sheathed rubber, in order to minimize the transfer of heat to or from the heat transfer medium from the ambient environment, and to maintain the heat exchanger  170  in fluid communication with the heat transfer system despite the various vibrations and shocks associated with the travel of the rolling search unit  100  along railroad rails. 
     Referring to  FIG. 7A , one embodiment of a heat exchanger  170  according to the present invention is shown. In  FIG. 7A , the heat exchanger  170  is shown as including a base  171 , a cover  172 , an inlet  174 , an outlet  175  and mounting holes  176 . Referring to  FIG. 7B , an exploded view of the heat exchanger  170  of  FIG. 7A  is shown, with the cover  172  removed from the base  171 , exposing locating pins  177  and a flow path  180 . Referring to  FIG. 7C , the heat exchanger  170  of  FIG. 7A  is shown as an assembled unit, with the flow path  180  shown in broken lines. 
     The base  171  and the cover  172  form the exterior and interior surfaces of the heat exchanger  170 , including the internal flow path  180 . The inlet  174  and the outlet  175  are adapted to receive and discharge the heat transfer medium, respectively, from and to a heat transfer system. The mounting holes  176  may be used to mount the heat exchanger  170  within the tire  120 , such as by bolts or other connection to the yoke assembly  156 , as is shown in  FIGS. 5 and 6 . 
     Preferably, the heat exchanger  170  is a brazed plate device containing a lengthy, tortuous internal flow path  180  intended to maximize the length of flow of the heat transfer medium within the heat exchanger  170 , and therefore to maximize the heat transfer between the fluid G and the heat transfer medium. The heat exchanger  170  may be formed from any desired materials, such as copper or brass. Additionally, although the heat exchanger  170  shown in  FIGS. 7A, 7B and 7C  includes a separate base and cover, heat exchangers according to the present invention may be formed as a single, integral unit, and need not include locating pins  177 . 
     During operation, a rolling search unit  100  may be lowered into contact with a railroad rail to conduct an inspection, and a computer or other processing unit, such as the central processing unit  30  and computer  35  shown in  FIG. 1 , may deliver a signal to the ultrasonic transducer  160  to transmit one or more ultrasonic beams through the fluid G and the tire  120 , and into the head of the underlying rail, as the unit  100  travels down the railroad track. Simultaneously, the temperature of the fluid G and/or the heat transfer medium leaving the heat exchanger may be monitored. If the temperature of the fluid G is too high or too low, the flow of heat transfer medium may be initiated, secured or controlled through the heat exchanger  170 , until the desired temperature is reached. Heat may be generated within the tire  120  due to friction, such as bearing friction, friction generated by the rolling contact of the tire  120  with the underlying rail, and also friction caused by the sloshing of the fluid G within the tire  120 . 
     The flow of heat transfer medium through the heat exchanger  170  may be controlled externally, based on the sensed temperatures of the fluid G or the heat transfer medium. The flow may be controlled by a computer or other processing unit, such as the central processing unit  30  and computer  35  shown in  FIG. 1 . Additionally, the flow may be controlled by the same computer or other processing unit that also controls the delivery of signals to the ultrasonic transducer  160 , or by a separate system. Moreover, the flow of heat transfer medium through the heat exchanger may be initiated or secured, or increased or decreased, based on sensed or predicted factors. For example, the flow of heat transfer medium may be increased or decreased in anticipation of an increase or decrease in the speed of the rail car, to account for increased or decreased friction. Similarly, the flow of heat transfer medium may be increased or decreased due to changes in the ambient temperature in the environment, or based on a forecast of a temperature change in the ambient environment. 
     Referring to  FIG. 8 , a piping diagram of one embodiment of a heat transfer system is shown. The system includes a carriage  200  mounted to an inspection vehicle  300 , such as a rail car. Beneath the carriage  200 , three rolling search units  100 , such as the rolling search units shown in  FIGS. 3-6  including tires  120 , are installed and aligned for rolling contact with an underlying rail. The carriage  200  also includes a supply manifold  220  from which supply lines  222  extend to the rolling search units  100 , and a return manifold  230  from which return lines  232  may extend from the rolling search units  100 . Additionally, the return manifold  230  also has a sensing connection for a thermocouple  240 , which monitors the temperature of the heat transfer medium within the return manifold  230 . Alternatively, there may be one or more thermocouples for sensing temperatures of the fluid within the tire  120 , temperatures of the heat transfer medium throughout the heat transfer system, or ambient temperatures. 
     The vehicle  300  includes a heat transfer apparatus  310 , which may be a chiller, a heater, or another heat transfer device adapted to act as a chiller and a heater, as well as a filter  312 . The heat transfer apparatus  310  provides a flow of a heat transfer medium at a desired temperature to supply line  320 , which provides heat transfer medium to supply feed  322 , and to the supply manifold  220  within the carriage  200 . The heat transfer apparatus  310  receives a flow of heat transfer medium through discharge line  330 , which receives heat transfer medium from the discharge manifold  230  through discharge feed  332 . Although only one carriage  200  is shown in  FIG. 8  as coupled with supply feed  322  and discharge feed  332 , those of ordinary skill in the art will recognize that additional carriages may be provided with the heat transfer system. For example, a second carriage  200  may be coupled with supply feed  324  and discharge feed  334 . Furthermore, although the carriage  200  shown in  FIG. 8  includes three rolling search units  100 , additional rolling search units may be added to the carriage  200  or other probe carrier according to the present invention. 
     The heat transfer apparatus  310  is functionally connected to a junction box  342  linked to the thermocouple  240 , and receives signals regarding the temperature of the heat transfer medium within the return manifold  230 . In the embodiment of the system shown in  FIG. 8 , the heat transfer apparatus may receive signals regarding the temperature of the fluid or the heat transfer medium, or other signals, and may increase or decrease the flow of the heat transfer medium, or may increase or decrease the temperature of the heat transfer medium, accordingly. 
     A heat transfer system, such as the system shown in  FIG. 8 , may be utilized to maintain the temperature of the fluid within a tire of a rolling search unit, such as the tire  120  of the rolling search units  100  shown in  FIGS. 3-6 , by controlling the flow rate and the temperature of the heat transfer medium passing through the heat exchangers mounted within the tires. For example, if the sensed temperature of the heat transfer medium within the return manifold  240  rises above or falls below a set point or beyond an acceptable range, the heat transfer system  310  may add heat to or remove heat from the heat transfer medium, or may increase or decrease the rate of flow of the heat transfer medium through the heat exchanger  170 . 
     Systems and methods for performing rail inspections utilizing the rolling search units of the present invention provide a number of advantages over the prior art. First, by enabling operators to maintain the temperature of the fluid within the tires at constant levels, standardized test results may be obtained regardless of the temperature in the environment at the time of inspection. Second, the rolling search units of the present invention are versatile enough to be utilized in any location, from a hot, dry desert to a snowy, mountainous region, because the rolling search units will accommodate for differences in temperature and provide standardized test results accordingly. Third, the rolling search units of the present invention are also able to accommodate for heat generated through friction or from any other external source during operation. Fourth, because increases in temperature lead to increased pressures of the fluid within a tire, controlling the temperature of the fluid within the tire enables operators to minimize the maintenance and wear-and-tear of the tire or other components within the heat transfer system. 
     Moreover, as is set forth above, the systems and methods disclosed herein may be used in a variety of applications and are not limited to use in inspecting railroad rails. For instance, the systems and methods may be used to conduct ultrasonic inspections of any surface, such as roadways, foundations or other structures, or for any desired reason. 
     It should be understood that, unless otherwise explicitly or implicitly indicated herein, any of the features, characteristics, alternatives or modifications described regarding a particular embodiment herein may also be applied, used, or incorporated with any other embodiment described herein. Also, it should also be understood that the accompanying drawings are not drawn to scale. 
     Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, but do not require, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. 
     As may be recognized by those of ordinary skill in the pertinent art based on the teachings herein, numerous changes and modifications may be made to the above-described and other embodiments of the present invention without departing from the spirit of the invention as defined in the claims. Accordingly, this detailed description of currently preferred embodiments is to be taken in an illustrative, as opposed to a limiting sense. 
     Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departing from the spirit and scope of the present disclosure.