Abstract:
Generally, the subject matter disclosed herein relates to torque calibrating systems. A torque calibrating system includes a torque arm having a first end and a second end, a stem positioned proximate the first end of the torque arm, the stem adapted to be removably and operatively coupled to a power tong, and a load cell adapted to be positioned proximate the second end of the torque arm.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/038,505, filed Mar. 2, 2011, which claims priority from U.S. Provisional Patent application Ser. No. 61/309,635 filed on Mar. 2, 2010, and is hereby incorporated by reference for all it contains. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Disclosure 
         [0003]    Generally, the present disclosure relates to tongs for making up and breaking out threaded joints. More specifically, the present disclosure relates to a method and apparatus for calibrating tong torque. 
         [0004]    2. Description of the Related Art 
         [0005]    Making up (tightening) and breaking out (loosening) threaded joints between tubular products (tubulars) are important operations in the various industrial applications involving the transfer of fluids. In oilfield applications, for example, it is quite common to make up (tighten) and/or break out (loosen) the threaded joints between various types of tubular products, such as tubing, casing, drill pipe, and the like. In some applications, threaded joints between tubulars may be made up to form lengths of tubular products (tubular strings) that are sufficient to perform operations such as the drilling of a borehole or the production of fluid from a borehole, and the like. In order to make up or break out a threaded joint between two tubulars, a “backup” tong engages a first of two tubulars, and a “power” tong engages a second of the two tubulars. The backup tong is adapted to hold the first tubular in relatively firm manner, while the power tong is adapted to apply torque to the second tubular so as to rotate it relative to the first tubular held by the backup tong. The direction of the torque applied to the second tubular by the power tong indicates whether a threaded joint is being made up (tightened) or broken out (loosened). 
         [0006]    Power tongs used to apply torque to tubular products during make up and/or break out are typically classified as “open-head” or “closed-head.” An “open-head” power tong has a central opening and a side opening providing a passage to the central opening. The side opening of an open-head power tong is sometimes referred to as the “throat.” Both the central opening and the throat are large enough to receive a tubular, and the throat permits the open-head power tong to engage tubular by allowing the tubular to pass sideways through the throat and into or out of the central opening—i.e., horizontally. On the other hand, a “close-head” power tong only has a central opening, and does not have a throat to permit the sideways movement of the tubular into the central opening. Therefore, a closed-head power tong can only engage a tubular by allowing the tubular to pass into and out of the central opening through the top or the bottom of the closed-head power tong—i.e., vertically. Some aspects of various prior art power tongs are illustrated in  FIGS. 1 and 2 , which will now be discussed. 
         [0007]      FIG. 1  shows an illustrative embodiment of a prior art open-head power tong from U.S. Pat. No. 4,170,907 (issued to Cathcart). It should be noted that the reference numbers used in Cathcart have not been preserved in  FIG. 1 , so as to avoid any duplication in numbering with the embodiments illustrated in the present disclosure. One embodiment of an open-head power tong  1  disclosed in Cathcart includes a bifurcated frame  2  defining a central opening  3  and a side opening  4 . As shown in  FIG. 1 , jaws  5  are disposed within the central opening  3  for engaging a drill pipe, that is, when the drill pipe is positioned within the central opening  3 . The jaws  5  are driven through a drive train (not shown) by a hydraulic motor  6 , which receives fluid pressure from a hydraulic pump (not shown) through a hydraulic control valve  7 . The hydraulic control valve  7  is movable between three spool positions: 1) a first position that drives the motor  6  in a clockwise direction; 2) a second position that drives the motor  6  in a counterclockwise direction; and 3) a third position that places the motor  6  in neutral. A door  8  is provided at the side opening  4  to control access to the central opening  3 . Typically, the door  8  is closed while operating the power tong so as to protect the operator of the power tong from the moving jaws  5 . 
         [0008]      FIG. 2  shows an illustrative embodiment of a prior art open-head power tong from U.S. Pat. No. 4,445,403 (issued to Janzen et al.) As shown in  FIG. 2 , the power tong has a frame  10  defining a throat  20  for receiving a pipe (not shown). A circular opening  21  is provided in the center of the frame  10 , and a pipe can pass through the throat  20  into the circular opening  21 . A pair of arcuate bearing and guide segments  22 ,  24  is mounted on opposite sides of the throat  20  and a drive ring  38  is mounted for rotation relative to the frame  10 . The drive ring  38  has an opening  40  that is of substantially the same size as the throat  20  and that is aligned with the throat  20 . The drive ring  38  is guided along its outer periphery and retained within the frame by the bearing and guide segments  22 ,  24 . Gear teeth (not shown) are secured to a projection that extends radially from the outer circumference of the drive ring  38 . The gear teeth mesh with rotary idler gears  88  and  90  of a drive train  52  that is powered by a motor (not shown). Although not shown in  FIG. 2 , the power tong also includes a die carrier with means for gripping a pipe placed in the circular opening  21 . When the drive ring  38  rotates, the die carrier also rotates, and cam action between the drive ring  38  and the die carrier rotates the means for gripping a pipe in contact with a pipe received in the circular opening  21 . 
         [0009]    In general, when making up a threaded joint, the torque applied to the tubular by the power tong should not be too high, as the threads may become overstressed and possibly even damaged. On the other hand, the applied torque should not be too low, as the threaded joint may leak and/or become loose during operation. Additionally, excessive torque that may be applied to tubular products, either when making up or breaking out threaded joints, may also damage the surfaces of the tubulars. Thus, monitoring or measuring the amount of torque applied by the power tong during a make-up or break-out operation may be an important component of operating the power tong. However, the equipment that is commonly available for measuring the make-up or break-out torque of a power tong can be expensive to buy, or to rent, and cumbersome to use. For example, in some prior art systems, a hydraulic load cell is positioned in a line extending from the power tong to a fixed point. As the tubular goods are being made up (or loosened), the hydraulic load cell measures the torque being applied on the tubular goods that are currently in the tong. The measurement of the torque is read from the hydraulic load cell, and it can be read either manually or automatically. This hydraulic load cell technique is typically applied when making or breaking every connection. 
         [0010]    Consequently, in some operations, operators may choose to forego direct measurement of tong torque, and instead rely on secondary indications of applied torque, such the pressure reading of a pressure gage used to monitor hydraulic pressure in a hydraulic line connected to the tong. In other cases, operators may not even use secondary indications of torque, such monitoring hydraulic pressure, and may instead rely on experience alone to determine whether or not tong torque is within an appropriately safe range. The latter “experience-based” approach may often lead to many, if not most, of the threaded joints being over-torqued. 
         [0011]    Accordingly, there is a need to provide a functional, accurate, and low cost torque-calibrating device for the type of power-tong operations often performed to make up or break out threaded joints between tubular products, so as address or reduce at least some of the problems outlined above. 
       SUMMARY OF THE DISCLOSURE 
       [0012]    The following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects disclosed herein. This summary is not an exhaustive overview of the disclosure, nor is it intended to identify key or critical elements of the subject matter disclosed here. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
         [0013]    Generally, the subject matter disclosed herein relates to illustrative embodiments of a torque calibrating system. Disclosed herein is one illustrated example of a torque calibrating system that comprises a torque arm having a first end and a second end, a stem positioned proximate the first end of the torque arm, the stem adapted to be removably and operatively coupled to a power tong, and a load cell adapted to be positioned proximate the second end of the torque arm. 
         [0014]    In another illustrative embodiment of the present disclosure, a torque calibrating system includes an open-head power tong having a drive ring, the drive ring having an axis of rotation. The system further includes, among other things, a load cell assembly adapted to be positioned in a throat of the open-head power tong, wherein the drive ring is adapted to impose a load on the load cell assembly when the power tong is actuated, the imposed load corresponding to a torque generated by the open-head power tong about the axis of rotation. Additionally, the exemplary system includes a hydraulic system adapted to actuate the open-head power tong, the hydraulic system including a hydraulic motor that is adapted to drive the drive ring and a pressure gage that is adapted to measure a hydraulic pressure in the hydraulic system when the power tong is actuated, the measured hydraulic pressure corresponding to the imposed load and the generated torque. 
         [0015]    In yet a further exemplary embodiment, a torque calibrating system is disclosed that includes, among other things, a power tong, a load cell assembly, and a torque arm having first and second ends, the first end being adapted to impose a load on the load cell assembly when the power tong is actuated to impose a torque on the second end. The disclosed torque calibrating system further includes a hydraulic system adapted to actuate the power tong, the hydraulic system including a pressure gage that is adapted to measure a hydraulic pressure in the hydraulic system when the power tong is actuated, the measured hydraulic pressure corresponding to the load imposed on the load cell assembly and to the torque imposed on the second end of the torque arm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
           [0017]      FIG. 1  is a plan view of an illustrative prior-art open-head power tong; 
           [0018]      FIG. 2  is a plan view of another illustrative prior-art open-head power tong; 
           [0019]      FIG. 3  is a schematic view of an illustrative open-head power tong torque measuring system of the present disclosure; 
           [0020]      FIGS. 4  is a cross-sectional view of an illustrative load cell assembly of the illustrative open-head power tong torque measuring system of  FIG. 3 ; 
           [0021]      FIG. 5  is a cross-sectional view of an illustrative handling apparatus of the illustrative open-head power tong torque measuring system of  FIG. 3 ; 
           [0022]      FIG. 6  is another cross-sectional view of the illustrative handling apparatus of  FIG. 5 ; 
           [0023]      FIG. 7  is a schematic view of an illustrative closed-head power tong torque measuring system of the present disclosure; and 
           [0024]      FIGS. 8-12  are various views of yet another closed-head power tong torque measuring system of the present disclosure. 
       
    
    
       [0025]    While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0026]    Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0027]    The present subject matter will now be described with reference to the attached figures. Various structures and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
         [0028]    It should be understood that, unless otherwise specifically indicated, any relative positional or directional terms that may be used in the descriptions below—such as “upper,” “lower,” “above,” “below,” “over,” “under,” “top,” “bottom,” “vertical,” “horizontal,” “toward,” “away,” and the like—are used for convenience, and should be construed in light of that term&#39;s normal and everyday meaning relative to the depiction of the components or elements in the referenced figures. Moreover, it should also be understood that in any actual application or installation, the illustrative valve assemblies disclosed herein may be positioned and/or rotated to any angle relative to the orientations depicted in the attached figures and described herein. 
         [0029]      FIG. 3  schematically depicts one illustrative embodiment of a torque calibrating system  100  for an illustrative open-head power tong  109  disclosed herein. As shown in  FIG. 3 , the torque calibrating system may comprise a load cell assembly  103  and a sensor indicator  105 . In some embodiments, the sensor indicator  105  may communicate with a load cell within the load cell assembly  103  via a communication line  104 , details of which are shown in  FIG. 4  and discussed below. The sensor indicator  105  may be any one of several suitably designed sensor indicators capable of receiving and interpreting data from a load cell, as are well known in the art. For example, in one illustrative embodiment of the present disclosure, the sensor indicator  105  may be an SSI Smart Sensor Indicator Plug &amp; Play, TEDS IEEE 1451.4, available from Transducer Techniques, Inc., of Temecula, Calif. For calibration purposes, in certain illustrative embodiments the load cell assembly  103  may be arranged in a throat (or side opening)  107  of an open-head power tong  109 , which, in an open-head power tong configuration as described previously, may facilitate passage of a tubular product (not shown) to a circular center opening  108  of the open-head power tong  109 . 
         [0030]    In order to facilitate the measurement of the torque that may be applied by the power tong  109  to a tubular product during make up and/or break out, the load cell assembly  103  may, in some illustrative embodiments, be brought into contact with the drive ring  111  at the throat  107  of the power tong  109 . In the illustrative embodiment depicted in  FIG. 3 , the axis  112  of the load cell assembly  103  may be aligned substantially perpendicular to the face  111   f  of the drive ring  111  at the throat  107 . In some illustrative embodiments, the load cell assembly  103  may be positioned at the throat  107  such that the load cell within the load cell assembly  103  may be permitted to sense the load applied to the load cell assembly  103  by the drive ring  111  when the drive ring  111  is rotated during make up and/or break out operations, which may thereafter communicate the sensed data to the sensor indicator  105 . In one illustrative embodiment, the drive ring  111  of the power tong  109  may be driven by a hydraulic motor  113  through a drive train (not shown), and in certain embodiments, the hydraulic motor  113  may be powered by fluid pressure from a hydraulic pump (not shown) through a hydraulic control valve  115 . 
         [0031]    In some illustrative embodiments, the sensor indicator  105  may process the load data obtained from the load cell and display the processed data to an operator. In one illustrative embodiment of the present disclosure, the processed data displayed to the operator may be in the form of, for example, a torque reading, which may be determined based on the specific load data obtained from the load cell, and the geometry of the power tong  109 . In certain illustrative embodiments of the present disclosure, the torque calibrating system  100 , including the load cell assembly  103  and sensor indicator  105 , may be used to calibrate a power tong such as the illustrative open-head power tong  109  shown in  FIG. 3 , i.e., to establish a safe operating torque range for the power tong during make up and/or break out operations. After the power tong  109  is properly calibrated, the power tong  109  may be used in actual operation without the necessity of measuring the torque applied during every breaking or making of a tubular connection, as was common with some prior art techniques. By calibrating the power tong  109 , the power tong  109  may be used in a more efficient and safer manner in that additional measuring tools and equipment need not be present every time the power tong  109  is actuated. One illustrative embodiment of a calibration method utilizing the torque measuring system  100  of the presently disclosed subject will be now described in detail below. 
         [0032]    As shown in the illustrative embodiment of the torque measuring system  100  in  FIG. 3 , one illustrative method of calibrating the power tong  109 , efforts may be undertaken to determine the minimum and maximum desired torque values that may be imparted by the power tong  109  to a threaded joint during a make-up and/or a break-out. The minimum and maximum torque values may, in some instances, depend on the tubular good to be handled by the power tong  109 . The American Petroleum Institute (API) sets forth the minimum and maximum loading for various tubular goods. The API load ratings together with the handle length H of the power tong  109  can be used to determine the minimum and maximum torque values for the power tong  109 . The handle length H of the tong  109  is measured from approximately the center of the contact between the load cell assembly  103  and the drive ring  111  to approximately the center of rotation of the drive ring  111  (which coincides with the center of the opening  108 ). Before or after the steps described above, a pressure gage  116  may be installed on a hydraulic line of the power tong  109 . A hydraulic quick connect assembly  117 , or other suitable device, may be used for connection of the pressure gage  116  to the hydraulic line. The hydraulic line is a conduit or network of conduits carrying the fluid necessary to power the hydraulic motor  113 . The pressure gage  116  measures the hydraulic pressure on the hydraulic line. 
         [0033]    An illustrative calibration method may include a step of arranging the load cell assembly  103  in the throat  107  of the power tong  109  as shown in  FIG. 3 . Before or after arranging the load cell assembly  103  in the throat of the power tong  109 , and while in low gear, the power tong  109  is slowly closed against the load cell assembly  103 . In addition, the hydraulic pressure is gradually increased with the engine (of the hydraulic motor) at full throttle. This action causes the drive ring  111  to apply a torque to the load cell assembly  103 . The load cell within the load cell assembly  103  senses the applied torque and sends the sensed data to the sensor indicator  105 . The sensor indicator  105  is monitored until a reading corresponding to the desired minimum torque value is shown. At this point, the position of the pressure gage  116  is recorded or noted, e.g., by noting down the position of the pressure gage  116 , by physically marking the position on the pressure gage  116 , etc. This recorded position corresponds to the desired minimum torque value. While still in low gear, the hydraulic pressure is gradually increased until the sensor indicator  105  displays a reading corresponding to the desired maximum torque value. At this point, the position of the pressure gage  116  is again recorded or noted. This second recorded position corresponds to the desired maximum torque value. The power tong  109  is now calibrated. The load cell assembly  103  can be removed from the power tong  109  and set aside to allow use of the tong for make-up or break-out operations. The operation of the power tong  109  will be guided by the noted or marked positions of the pressure gage  116 . 
         [0034]      FIG. 4  depicts one illustrative embodiment of the load cell assembly  103 . As shown therein, the illustrative load cell assembly  103  includes a housing  121  having an internal chamber  123 . The internal chamber  123  has a top chamber  125  and a bottom chamber  127 . The housing  121  has an internal shoulder  129  between the top chamber  125  and the bottom chamber  127 . In one illustrative embodiment, a load cell  131  is disposed within the top chamber  125  and arranged on the seat provided by the internal shoulder  129 . A load cell is a device that converts force acting on it into an electrical signal. The load cell  131  includes a force transducer enclosed in a housing—the housing is what is visible in  FIG. 4 . The force transducer converts force acting on the load cell  131  into an electrical signal. Load cells suitable for use in the load cell assembly  103  are available on the market. The capacity of the load cell  131  will be dictated by the application. In some embodiments, a load cell having a capacity of at least 5,000 lbf may be used. In other embodiments, a load cell having a capacity of at least 20,000 lbf may be used. The load cell  131  may be any type of load cell capable of sensing torque or load, e.g., hydraulic load cell, electric load cell, and strain gage load cell. In one illustrative embodiment, the load cell  131  will be a strain-gage load cell. Suitable strain-gage load cells are available from, for example, Transducer Techniques, Inc., Temecula, Calif. A cable  104 A extends out of the load cell  131  and passes through a port  133  in the housing  121  to the exterior of the housing  121 . The cable  104 A will be connected to the sensor indicator ( 105  in  FIG. 3 ) for communication between the load cell  131  and the sensor indicator. It is also possible that such signals may be sent wirelessly. 
         [0035]    In one embodiment, as illustrated in  FIG. 4 , the load cell  131  is an annular load cell with a central (through-hole) opening  135 . A schematically depicted load contact  137  is partially arranged in the central opening  135 . The load contact  137  has a stem  139  and a head  141 . The stem  139  is received in the central opening  135 . The diameter of the stem  139  is substantially the same as the diameter of the central opening  135 . A lock  143  is inserted into the bottom of the stem  139  to lock the stem  139  in place within the central opening  135  and prevent the stem  139  from moving longitudinally relative to the central opening  135 . In one example, the lock  143  includes a screw  145  received in a threaded opening  147  in the stem  139 . A washer or retention plate  149  may be provided between the head of the screw  145  and the bottom face  150  of the load cell  131 . The lock  143  is accessible through the bottom chamber  127 . The head  141  of the load contact, which is attached to the stem  139  of the load contact, protrudes from the central opening  135  and the top face  151  of the load cell  131 . The bottom face  153  of the head  141  makes contact with the top face  151  of the load cell  131 , and the stem  139  extends from the bottom face  153  of the head  141  into the central opening  135 . The load contact  137  receives an external force and transmits the external force (via contact with the load cell  131 ) to the load cell  131 . The load contact  137  contacts the load cell  131  via the head  141  and the stem  139 . In the example where the load cell assembly  103  is arranged at a throat of a power tong to measure torque, the head  141  of the load contact  137  would be the part of the load cell assembly  103  that makes contact with the drive ring  111  in order to receive a turning force or torque from the drive ring and transmit the force to the load cell  131 . The load contact  137  may be made of a rigid material to enable it to transmit the force. Typically, the rigid material is a metal or alloy such as stainless steel, but other types of materials such as hard plastic may be also be used. 
         [0036]    The load cell  131  may be retained within the top chamber  125  by a top plate  155  mounted on the top face  157  of the housing  121 . The top plate  155  may be secured to the top face  157  of the housing  121  using any suitable means. For example, the top plate  157  may be secured to the top face  157  of the housing  121  using screws  159  inserted into aligned holes in the top plate  155  and top face  157 . Other removable fasteners may be used in lieu of screws. The top plate  155  may also be permanently affixed to the top face  157  (such as by welding), but this would make it difficult to retrieve the load cell  131  from the top chamber  125  at a later time. The top plate  155  is provided with a central opening  160 , which is coaxial with the internal chamber  123  of the housing  121 . The central opening  160  in the top plate  155  is large enough to receive the head  141  of the load contact  137 , but not large enough to receive the load cell  131  (thus, the load cell  131  cannot fall out of the top chamber  125  through this opening). 
         [0037]    In  FIG. 5 , an illustrative handling apparatus  161  is coupled to the load assembly  103 . The handling apparatus  161  includes a bottom plate  163 , which is attached to the bottom face  165  of the housing  121  using a suitable means. The suitable means could be, for example, screws  167  inserted into aligned holes in the bottom plate  163  and bottom face  165 . Other removable fasteners may be used in lieu of screws. Alternately, the bottom plate  163  may be permanently affixed to the bottom face  165 , but this would make it difficult to access the bottom chamber  127  of the housing  121 . In one illustrative embodiment, the bottom plate  163  is inserted into a slot  169  formed in a bracket  171 . 
         [0038]    As shown in  FIG. 6 , the bracket  171  has a longitudinal hole  173  inside of which is received a bar  175  with an attached handle  177 . The handle  177  is located on the exterior of the bracket  171 . The bar  175  is secured to the bracket  171  using suitable means. For example, screws  179  may be inserted in aligned holes in the bar  175  and bracket  171  to secure the bar  175  to the bracket  171 . Other fasteners besides screws may also be used to secure the bar  175  to the bracket  171 . The bar  175  may also be secured in the longitudinal hole  173  by an adhesive. 
         [0039]    The load cell assembly  103  can be handled by means of the handling apparatus  161 . The handling apparatus  161  may be useful when using the load cell assembly  103  to measure torque in an open-head power tong  109 . Without any modifications to the throat  107  of the power tong  109 , an operator or other device can position the load cell assembly  103  in the throat  107  of the power tong  109  and hold onto the handle  177  while measurements are being taken. The handle  177  can be shaped such that a human operator or a tool or robot can hold it. 
         [0040]    The load cell assembly  103  may also be used for torque measurements in a closed-head power tong as well.  FIG. 7  shows an embodiment where the load cell assembly  103  is used for torque calibration in an illustrative closed-head power tong  181 . In  FIG. 7 , a backup tong  182  is coupled to the power tong  181 , as is typical of Foster-style tongs. In the embodiment of  FIG. 7 , a torque arm  183  includes an elongated arm  185  and a head  187 . In the illustrative embodiment depicted in  FIG. 7 , the torque arm  183  is adapted to be inserted from the top into the closed-head power tong  181 . The head  187  is attached crosswise to one end of the arm  185  and is inserted into the central opening  189  of the closed-head tong  181  for making torque measurements for calibration purposes. The torque arm  183  is provided with a lifting handle  188 , which facilitates insertion and removal of the head  187  from the central opening  189  of the closed-head tong  181 . During torque measurements, a die carrier  190  with gripping means engages the head  187  and applies torque to the head  187 . At the other end of the elongated arm  185  is a holder  191  for the load cell assembly  103 . In one embodiment, the holder  191  includes a flat plate  193  attached to the elongated arm  185 , for example, by welding. A semicircular wall  195  is attached to the flat plate  193 , for example, by welding. The semicircular wall  195  forms a receptacle for holding or retaining the load cell assembly  103 . In some embodiments, the load cell assembly  103  is removably positioned within the receptacle without being physically attached to the torque arm  183 . Torque applied to the head  187  is transmitted to the load cell within the load cell assembly  103  through the elongated arm  185 . As torque is applied to the load arm  183 , the load cell assembly is urged against the tong hanger bracket plate (not shown in  FIG. 7 ), and the torque reading is obtained via the sensor indicator  105 , as previous described. The torque arm  183  is a rigid member capable of transmitting force. The torque arm  183  may be made of a metal or alloy such as stainless steel. Other types of rigid materials such as hard plastic may be also be used to make the torque arm  183 . 
         [0041]      FIGS. 8-12  depict yet another illustrative embodiment of a closed-head power tong torque calibrating system.  FIG. 8  depicts an illustrative closed-head power tong  109  that includes a backup tong  200 . The backup tong  200  is coupled to the power tong  109  via a front support  202  and a rear support  204 . The front of the backup tong  200  is releasably coupled to the power tong  109  by a removable support pin  206  that extends between two support brackets  208 , as shown in  FIG. 8 . The rear support  204  permits the backup tong  200  to swing down and away from the position shown in  FIG. 8  to the position shown in  FIG. 9 . In some illustrative embodiments, the rear support  204  may also permit the backup tong  200  to swivel about a vertical axis extending upward through the rear support  204 . As will be described more fully below,  FIG. 9  also depicts an illustrative embodiment of the load cell assembly  103  positioned between the support brackets  208 . 
         [0042]      FIGS. 10-12  depict various illustrative views of a load cell assembly  103  and torque arm  210  that may be employed as described herein. In the illustrative embodiment depicted herein, the torque arm  210  is adapted to be inserted into the bottom of a closed-head power tong. In the depicted example, the illustrative torque arm  210  comprises a stem  212  on one end of the arm  210  and a load cell bracket  214  positioned on the opposite end of the torque arm  210 . In one illustrative embodiment, the stem  212  has a five-sided configuration and it is adapted to be inserted into the central opening  108  of the power tong  109  to facilitate engagement with the dies within the power tong  109 . The load cell assembly  103  may be positioned so as to freely float within the bracket  214  or is may be removably coupled or permanently affixed within the bracket  214 . 
         [0043]    One illustrative technique for calibrating the torque of the power tong  109  depicted in  FIGS. 8-12  will now be described. Initially, the support pin  206  is removed, thereby permitting the backup tong  200  to be lowered out of the way, e.g., to the position shown in  FIG. 9 . As noted earlier, the rear support  204  may also be a double swivel type connection so as to permit the backup tong  200  to be rotated both horizontally and vertically. With the dies (not shown) of the power tong  109  in the open position, the stem  212  of the torque arm  210  is inserted from the bottom into the central opening  108  of the power tong  109  until the top flange  216  of the stem  212  comes to rest on top of the dies. At this point, the load cell assembly  103  is positioned in the support bracket  214  with the data cord  104  passing between the two. At this point, the hydraulic pressure is slowly increased so as to slowly rotate the power tong  109 . The dies are then gently closed on the stem  212 . With the torque arm  210  and load cell assembly  103  so positioned, the desired minimum and desired maximum torque values can be determined and, if desired, marked on the pressure gage  116  as described earlier with respect to other illustrative embodiments of the present invention. 
         [0044]    As noted earlier, calibration of power tongs using the devices and techniques disclosed herein enables cost-effective, efficient and safe use of power tongs as compared to prior art techniques that monitored or measured the applied torque to tubular goods every time a connection was made or broken. By calibrating power tongs as described herein, in one illustrative embodiment, operators may readily make reference to calibrated hydraulic fluid pressure to control the desired minimum and/or maximum torque to be applied to the tubular goods without having to use cumbersome measurement devices every time a connection is made or broken. 
         [0045]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.