A back-up tong for assembling or disassembling threaded joints of tubing for use in oil and gas wells is provided. The back-up tong has both a first and second gripping mechanism. The first gripping mechanism has a plurality of jaws for engaging the tubing to prevent rotation of the tubing in a clockwise direction and the second gripping mechanism has a plurality of jaws for engaging the tubing to prevent rotation of the tubing in a counter-clockwise direction.

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a back-up tong of the type used in conjunction with a power tong to assemble or disassemble threaded joint connections between successive tubing sections that form the continuous tubing string extending through a well bore into underground deposits. More particularly this invention relates to a back-up tong that provides opposing reactive force to the torque of a power tong without rotating the back-up tong one-hundred eighty (180) degrees when the rotation of the power tong is reversed. 
   2. Related Art 
   To interconnect and disconnect tubing that is lowered into oil or gas production wells, two types of tongs are typically utilized to make or break the threaded joint connections between successive tubing sections. The ends of each tubing section are threaded with a male screw thread at one end and a female screw thread at an opposite end. As each tube section is lowered into the well bore, a successive section is screwed to its upper end. Power tongs apply torque to the upper tubing of the joint, while a back-up tong applies opposing torque to the lower tubing of the joint. In this manner, the back-up tong reacts against the torque applied by the power tong to the upper tubing of the joint, as such, the back-up tong keeps the bottom tubing of the joint from rotating when the power tong applies torque to the upper tubing to connect or disconnect threaded joint connections between tubing sections. 
   Today, power/back-up tong combination devices, such as the tong combination device  100  illustrated in prior art  FIG. 1 , are utilized to assemble and disassemble threaded joint connections between successive tubing sections that form the continuous tubing string extending through a well bore into underground deposits. As illustrated in  FIG. 1 , a back-up tong  102  is generally suspended from a power tong  104 , so that the reaction torque of one tong is cancelled by the other tong, which eliminates the need to anchor the tongs to the oil rig. Instead, the tong combination device  100  is suspended by a hoist over the well bore. In such arrangements, the tail end  106  of the back-up tong  102  attaches to a structural support  108  on the back end of the power tong  104 . 
   Current designs also feature a swivel and hinge mounting of the back-up tong  102  that allows the back-up tong  102  to be lowered away from the power tong  104  to permit rotation of the back-up tong  102  by one-hundred eighty (180) degrees in relation to the tubing being assembled. The jaws of current back-up tongs  102  only apply torque in one opposing rotational direction. To provide appropriate reactive force to the torque of the power tong  104 , the back-up tong  102  must be flipped over according to the direction of rotation of the power tong  104 . Accordingly, if rotation must be reversed, for example, from assembling tubing sections to disassembling the tubing sections, the power tong  104  and back-up tong  102  are removed from the tubing connection area and the power tong  104  is adjusted to perform the opposite rotation. The back-up tong  102  is then rotated upside down to react to the reversed torque of the power tong  104  on the tubing T. 
   An example of a current back-up tong  102  generally used in a power/back-up tong combination device  100 , such as the device illustrated in  FIG. 1 , is described in U.S. Pat. No. 5,823,074 and illustrated in  FIG. 2 .  FIG. 2  illustrates a top view of an open-head Foster-style back-up tong  200  having three pivoting jaws  202  in mesh connection with a ring gear  204 . A drive cylinder  206  powered by a hydraulic motor engages the outer circumference of the ring gear  204 . As illustrated in  FIG. 3 , rotation of the ring gear  204  in one direction causes each of the jaws  202  to pivot toward the center of the ring gear  204  and grip any tubing placed in the center opening of the back-up tong  200 . 
   While the open-head Foster-style back-up tongs  200  work well, such back-up tongs still require more than one individual to operate. The current open-head Foster-style back-up tongs, of the type illustrated in  FIGS. 2-3 , only apply torque in one opposing rotational direction. Thus, current back-up tongs still require rotation to provide appropriate reactive force to the torque of the power tong when the rotation of the power tong is reversed. 
   Accordingly, a need exists for a back-up tong that can provide reactive force to the torque of the power tong when rotation of the power tong is reversed without requiring the back-up tong to be rotated one-hundred and eighty (180) degrees. In other words, a need exists for a back-up tong capable of gripping a pipe for assembling and disassembling pipe joints without rotating the back-up tong (i.e., reversing the back-up tong by turning the back-up tong upside down). 
   SUMMARY 
   A back-up tong for assembling or disassembling threaded joints of tubing for use in oil and gas wells is provided. The back-up tong has both a first and second gripping mechanism. The first gripping mechanism has a plurality of jaws for engaging the tubing to prevent rotation of the tubing in a clockwise direction and the second gripping mechanism has a plurality of jaws for engaging the tubing to prevent rotation of the tubing in a counter-clockwise direction. Accordingly, a back-up tong is provided that is capable of providing opposing reactive forces to the torque of a power tong without requiring rotation of the back-up tong one-hundred eighty (180) degrees when the rotation of the power tong is reversed. 
   Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 


   
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention may be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
       FIG. 1  is a perspective view of a typical prior art power/back-up tong combination device, with tubing captive in both tongs indicated in phantom lining. 
       FIG. 2  is a top view of a typical prior art open-head Foster-style back-up tong with the top plate of the housing removed to expose the jaws of the tube gripping mechanism in the disengaged position. 
       FIG. 3  is a top view of the prior art back-up tong in  FIG. 2  illustrating the jaws of the tube gripping mechanism in the engaged or gripping position. 
       FIG. 4  is a perspective view of one example of an implementation of a reversible torque open head back-up tong. 
       FIG. 5  is an exploded view of the reversible torque open head back-up tong of  FIG. 4 . 
       FIG. 6  is a top view of the reversible torque open head back-up tong of  FIG. 4 . 
       FIG. 7  is a cross-sectional view of the reversible torque open head back-up tong taken along line A-A of  FIG. 6 . 
       FIG. 8  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate removed exposing the upper jaws of the upper gripping mechanism in the disengaged position and the lower jaws of the lower gripping mechanism in the engaged position. 
       FIG. 9  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate removed exposing the upper jaws of the upper gripping mechanism in the disengaged position, the lower jaws of the lower gripping mechanism in the engaged position and further illustrating the lower jaws of the lower gripping mechanism in phantom lining. 
       FIG. 10  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate removed exposing the upper jaws of the upper gripping mechanism in the engaged position, the lower jaws of the lower gripping mechanism in the disengaged position and further illustrating the lower jaws of the lower gripping mechanism in phantom lining. 
   


   DETAILED DESCRIPTION 
     FIGS. 4-10  illustrate one example of an implementation of a back-up tong  400  that is capable of reversing the direction of the torque applied by the back-up tong  400  without physically rotating the back-up tong  400 . In particular,  FIG. 4  is a perspective view of one example of an implementation of a reversible torque open head back-up tong  400 . As illustrated in  FIG. 4 , the back-up tong  400  has a through bore  402  and a tong head  404  that contains two sets, i.e., an upper set and a lower set, of actuated gripping mechanisms  406  and  408 . The back-up tong  400  is of an open head configuration, having a radial slot  410  extending from the through bore  402  to the outside of the tong head  404 . The radial slot  410  permits tubing T to be admitted laterally, i.e. in a radial direction, into the through bore  402 . A hinged latch  412  closes the radial slot  410  for safety. 
   Further, the back-up tong  400  has three generally planar plates: a top plate  414 , an intermediate plate  416  and a bottom plate  418 . The plates  414 ,  416  and  418  are spaced apart in substantially parallel relationship to one another, where the upper gripping mechanism  406  is positioned between the top plate  414  and the intermediate plate  416 , and the lower gripping mechanism  408  is positioned between the intermediate plate  416  and the bottom plate  418 . 
     FIG. 5  is an exploded view of the reversible torque open head back-up tong  400  of  FIG. 4 .  FIG. 5  better illustrates the construction of the reversible torque open head back-up tong  400 , including the upper and lower gripping mechanisms  406 ,  408 . The upper, lower and intermediate plates  414 ,  416  and  418  are spaced apart by four radial spacers,  502 ,  504 ,  506 ,  508 . The upper radial spacers  502  and  504  are positioned on opposing sides of the back-up tong  400  between the top plate  414  and intermediate plate  416 , and the lower radial spacers  506  and  508  are similarly positioned on opposing sides of the back-up tong  400  between the intermediate plate  416  and the bottom plate  418 . All four spacers are held in compression between the three plates  414 ,  416  and  418  by bolts  510  extending through aligning holes in the plates  414 ,  416  and  418  and radial spacers  502 ,  504 ,  506  and  508 . 
   The upper gripping mechanism  406  includes an upper circular ring gear  512  having a gap for alignment with the radial slot  410  in the tong head  404  (see  FIG. 1 ) to allow the back-up tong  400  to receive the tubing through the radial slot  410 . The upper ring gear  512  has an outer circumference that slides tangentially along the upper radial spacers  502  and  504 , whereas the inner circumference of the upper ring gear  512  includes teeth  802  for engagement of the toothed end  804  of upper jaws  514  (as illustrated in  FIGS. 8-10  below). 
   Similarly, the lower gripping mechanism  408  includes a lower circular ring gear  516  having a gap for alignment with the radial slot  410  in the tong head  404  (see  FIG. 1 ) to allow the back-up tong  400  to receive the tubing through the radial slot  410 . The lower ring gear  516  has an outer circumference that slides tangentially along the lower radial spacers  506  and  508 , whereas the inner circumference of the lower ring gear  516  includes teeth  802  for engagement of the toothed end  804  of lower jaws  518  (as illustrated in  FIGS. 8-10  below). 
   Both the upper and lower jaws  514  and  518  are mounted through aligning holes in the upper and lower jaws  514  and  518  by pivot rods  520 . The aligning holes in the upper jaws  514  are offset from the aligning holes in the lower jaws  518 , as shown in the intermediate plate  416 . Each ring gear  512  and  516  turns freely about its center in sliding contact with the radial spacers  502 ,  504  and  506 ,  508  respectively. Each ring gear  512  and  516  is driven by a hydraulically or pneumatically actuated cylinder  522 ,  524 . Each cylinder  522 ,  524  is pivotally connected to its respective ring gear  512 ,  516 , and upon actuation of the cylinders  522 ,  524  the respective ring gears  512 ,  516  are rotated, causing the respectively engaged jaws,  514 ,  518  to extend outward and grip a centrally located tube or pipe T, as will be further described in connection with  FIGS. 8-10  below. 
   In operation, the back-up tong  400  is suspended underneath a power tong, similar to the power tong  104  illustrated in  FIG. 1 .  FIG. 5  includes illustrations of the structures utilized to suspend the back-up tong  400  underneath the power tong. For example, front suspension supports  526  are provided for attachment underneath the power tong for supporting the tong head  404 . The front suspension supports  526  are attached to axially align the through bore  402  of the back-up tong  400  with the through bore of the power tong. Further, the power tong and back-up tong  400  are fixed at their ends by connecting support  528 . The back-up tong  400  is secured to the connecting support  528  via a suspension block  530  that is bolted to the stem  532  of the back-up tong  400  as well as the connecting support  528 . 
     FIG. 6  is a top view of the reversible torque open head back-up tong  400  of  FIG. 4 . The structure of the top plate  414  of the tong head  404 , hinged latch  412  and stem  532  are all clearly illustrated in this view. The intermediate plate  416  is also illustrated protruding from under the left side of the top plate  414 . The upper jaws  514  are also visible, as well as the upper pivot rods  520  pivotally securing the upper jaws  514  between the top plate  414  and the intermediate plate  416 . The bolts  510  that hold the top, intermediate and bottom plates  414 ,  416  and  418  in compression with the radial spacers  502 ,  504 ,  506  and  508  are also illustrated. 
     FIG. 7  is a cross-sectional view of the reversible torque open head back-up tong  400  taken along line A-A of  FIG. 6 .  FIG. 7  clearly illustrates the separation of the upper gripping mechanism  406  from the lower gripping mechanism  408  by the intermediate plate  416 . Two of the upper jaws  514  of the upper gripping mechanism  406  are shown positioned between the top plate  414  and intermediate plate  416 . Two additional lower jaws  518  are also shown positioned between the intermediate plate  416  and the bottom plate  418 . The upper ring gear  512  is also shown driven by pivotal attachment to the upper cylinder  522  and the lower ring gear  516  is shown driven by the pivotal attachment to the lower cylinder  524 . Pivot rods  520 , hinged latch  412 , the stem  532  and suspension block  530  are also illustrated in this cross-sectional view. 
     FIGS. 8-10  illustrate the operation of the reversible torque open head back-up tong  400  shown in  FIGS. 4-7 . In particular,  FIGS. 8 and 9  illustrate the lower jaws  518  of the lower gripping mechanism  408  in the engaged position and the upper jaws  514  of the upper gripping mechanism  406  in the disengaged position.  FIG. 10 , on the other hand, illustrates the upper jaws  514  of the upper gripping mechanism  406  in the engaged position and the lower jaws  518  of the lower gripping mechanism  408  in the disengaged position. 
     FIGS. 8-10  further illustrate the upper and lower jaws  514  and  518  and engagement of the jaws  514  and  518  by the upper and lower ring gears  512  and  516 . Each jaw  514  and  518  has a toothed end  804  that is in mesh with the teeth  802  on the inner circumference of the respective ring gears  512  and  516 . The opposite end of each jaw  514  and  518  includes a jaw insert  806  having a circularly curved jaw face. Each jaw insert  806  is removably secured to the jaws  514  and  518  by, for example, bolts  808 . 
   The angular movement of the ring gears  512  and  516  is guided by the radial spacers  502 ,  504 ,  506  and  508 . Further, the ring gears  512  and  516  are circumferentially contained against spreading at their free ends by the radial spacers  502 ,  504 ,  506  and  508 . Each radial spacer  502 ,  504 ,  506  and  508  acts against the radially outward reactive force acting on the ring gears  512  and  516  upon engagement of the jaws  514  or  518  with a tube T. In this regard, the radial spacers  502 ,  504 ,  506  and  508 , acting in cooperation with the bolts  510  serve to join the plates  414 ,  416 ,  418 , maintain the positioning of the ring gears  512  and  516  about a center of rotation concentric with the radial slot  410 , and providing structural back-up to prevent the ring gears  512  and  516  from spreading under operating stress. 
     FIG. 8  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate  414  removed exposing the upper jaws  514  of the upper gripping mechanism  406  in the disengaged position and the lower jaws  518  of the lower gripping mechanism  408  in the engaged position. As illustrated in  FIG. 8 , with the top plate  414  removed, the intermediate plate  416 , the upper jaws  514 , the upper ring gear  512  and the upper radial spacers  502  and  504  are exposed. An actuating rod  812  of the pneumatic or hydraulically powered upper cylinder  522  is pivotally attached to the upper ring gear  512  at an upper ring tab  810  extending from the upper ring gear  512 . Similarly, actuating rod  812  of the pneumatic or hydraulically powered lower cylinder  524  is pivotally attached at a lower ring tab  810  extending from the lower ring gear  516 , as illustrated by phantom lines. 
   As shown in  FIG. 8 , when the lower cylinder  524  is actuated, the actuating rod  812  extends from the lower cylinder  524 . The lower ring gear  516  responds to the torque from the lower cylinder  524  by rotating relative to the plates  414 ,  416 ,  418  to a position illustrated in  FIG. 8 . As the lower ring gear  516  rotates, it causes each of the lower jaws  518  to turn in a counter-clockwise direction about their respective pivots, moving the lower jaws  518  from a retracted position, as illustrated in  FIG. 4  and  FIG. 10 , to a gripping position shown in  FIG. 8 . A tube T placed in the radial slot  410  of the tong head  404  and positioned concentrically with the ring gears  512  and  516  is engaged at three circumferentially spaced locations by the three jaw faces  806  of the lower jaws  518 . 
     FIG. 9  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate  414  removed exposing the upper jaws  514  of the upper gripping mechanism  406  in the disengaged position, the lower jaws  518  of the lower gripping mechanism  408  in the engaged position and further illustrating the lower jaws  518  of the lower gripping mechanism  408  in phantom lining.  FIG. 9  shows the same operational position of the jaws  514  and  518  in  FIG. 8 , except that the lower gripping mechanism  408  is visible in phantom lines under the intermediate plate  416 . 
     FIG. 10  is a top view of the reversible torque open head back-up tong of  FIG. 6  with the top plate  414  removed exposing the upper jaws  514  of the upper gripping mechanism  406  in the engaged position, the lower jaws  518  of the lower gripping mechanism  408  in the disengaged position and further illustrating the lower jaws  518  of the lower gripping mechanism  408  in phantom lining. As shown in  FIG. 10 , when the upper cylinder  522  is actuated, the actuating rod  812  of the upper cylinder  522  extends from the upper cylinder  522 . The upper ring gear  512  responds to the torque from the cylinder  522  by rotating relative to the plates  414 ,  416 ,  418  to a position illustrated in  FIG. 10 . As the upper ring gear  512  rotates, it causes each of the upper jaws  514  to turn in a clockwise direction about their respective pivots (which is the opposing direction of the lower jaws  518  when actuated), moving the upper jaws  514  from a retracted position, as illustrated in  FIGS. 4 ,  8  and  9 , to a gripping position shown in  FIG. 10 . A tube T placed in the radial slot  410  of the tong head  404  and positioned concentrically with the ring gears  512  and  516  is engaged at three circumferentially spaced locations by the three jaw faces  806  of the upper jaws  514 . 
   In one example implementation of the invention, the jaws  514  and  518  may be removable and more than one set of jaws  514  and  518  may be provided that are sized and configured for gripping a range of tube diameters. For example, one set of jaws  514  and  518  may be shaped to extend further in a radially inward direction towards the center of the ring gears  512  and  516  for engaging a range of smaller diameter tubes. Various jaw inserts can also be provided to cover substantially the entire range of tube diameters normally encountered in oil and gas well bores. 
   Although  FIGS. 4-10  illustrate an implementation of a back-up tong  400  actuated by pneumatic or hydraulic cylinders  522  and  524 , an implementation of the back-up tong can be constructed for manual operation by eliminating the drive cylinders  522  and  524 , associated hoses and fluid conduits, and adding gear handles for manually rotating the ring gears  512  and  516 . Optionally, return springs may also be provided to bias the ring gears  512  and  516  to their retracted positions. Further, although  FIGS. 4-10  illustrate an open faced back-up tong, the back-up tong  400  may be a closed faced tong without departing from the invention. 
   Using pneumatic or hydraulic cylinders  522  and  524  to move a gripping mechanism such as the gripping mechanism shown in prior art  FIGS. 2 and 3  are known in the art. Thus, the connection of the back-up tong  400  and associated cylinders  522  and  524  to a pressurized pump and associated control valves via external hoses need not be discussed in any detail. 
   The foregoing description of implementations has been presented for purposes of illustration and description. It is not exhaustive and does not limit the claimed inventions to the precise form disclosed. Modifications and variations are possible in light of the above description or may be acquired from practicing the invention. The claims and their equivalents define the scope of the invention.