Abstract:
A tong assembly comprises a body and a center member slidable relative to the body. A pair of clamping arms is rotatably connected to the body. The clamping arms are connected to the center member such that as the center member slides relative to said body, the clamping arms rotate relative to the body. The assembly also comprises a plurality of die assemblies, wherein at least one die assembly is mounted to each clamping arm and at least one die assembly is mounted to the center member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   BACKGROUND 
   The present invention relates generally to methods and apparatus for gripping and manipulating pipe. More particularly, the present invention relates to methods and apparatus for facilitating the connection and disconnection of sections of drill pipe. 
   Drill strings used in rotary drilling are often constructed from individual lengths of drill pipe connected in series to form a drillstring. The individual lengths of drill pipe are commonly joined by threaded connections. Because of the loads incurred by the drillstring, the connections have to be pre-loaded with a certain amount of torque in order to maintain a satisfactory connection during use. 
   Pipe tongs are one tool used for facilitating the connection and disconnection, or making and breaking, of drill pipe connections. Pipe tongs are generally located at the drill floor and operate by gripping a connection between two adjacent lengths of pipe and applying torque to loosen or tighten the connection. Many pipe tongs operate by gripping above and below the junction between two adjacent pipe sections. The tongs then rotate the two sections of pipe relative to each other. This rotation often has a very limited rotational range but is performed with sufficient torque to properly make or break the connection. The torque applied to a given connection can be on the order of tens of thousands of foot-pounds. 
   Because of the high torque loads applied to the pipe, pipe tongs have been known to scar the outer diameter of the pipe, especially if the pipe slips within the tong. In order to minimize this slippage, as well as to ensure the proper torque requirements are met, the interface between the pipe and the tong is critical. In some cases, pipe tongs have been known to partially collapse the pipe with an excessive clamping force. Excessive damage to the pipe is often a result of the pipe not being centered within the pipe tong causing the gripping mechanism of the tong to apply uneven force to the pipe. 
   Thus, there remains a need to develop methods and apparatus for facilitating the connection and disconnection of pipe sections, which overcome some of the foregoing difficulties while providing more advantageous overall results. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   A tong assembly comprising a body and a center member slidable relative to said body. A pair of clamping arms are rotatably connected to said body. The clamping arms are connected to said center member such that as said center member slides relative to said body, said clamping arms rotate relative to said body. The assembly also comprises a plurality of die assemblies, wherein at least one die assembly is mounted to each clamping arm and at least one die assembly is mounted to said center slider. 
   One embodiment comprises a tong assembly comprising a body and a center member slidable relative to said body. A pair of clamping arms are rotatably connected to said body. The clamping arms are connected to said center member such that as said center member slides relative to said body, said clamping arms rotate relative to said body. The assembly includes a plurality of die assemblies, wherein at least one die assembly is mounted to each clamping arm and at least one die assembly is mounted to said center slider. In some embodiments, a hydraulic cylinder is operable to slide said center member relative to said body. 
   In certain embodiments, the die assemblies that are mounted to the clamping arms are rotatable relative to the clamping arms and the die assembly that is mounted to the center slider is not rotatable relative to the center slider. Each die assembly may comprise a die, a holder adapted to receive the die; and a retainer supporting the holder such that the holder is rotatable relative to the retainer, wherein the retainer is attached to one of the clamping arms. 
   The tong assembly may also comprises a pair of connecting links, wherein each of the connecting links is pivotally connected to the center member and one of the clamping arms by a pin connection that connects to one of the connecting links; and a pivot connection that connects to the body, wherein the clamping arm rotates about the pivot connection, wherein the distance from the pin connection to the pivot connection is equal to the distance from the pivot connection to the center of the die assembly. In some embodiments, the body is a unitary weldment having an open side and the center member and the clamping arms are installed in the body through the open side. 
   In another embodiment, the tong assembly may comprise an upper tong, a back-up tong aligned with and below the upper tong, a slider connected between the upper tong and the back-up tong, wherein the slider establishes a center point about which the upper tong and the back-up tong can rotate. A pair of first hydraulic cylinders operable to rotate the upper tong relative to the back-up tong, wherein the pair of first hydraulic cylinders have first ends connected at a single attachment to one of the tongs and second ends attached at separate points to the other of the tongs such that the tongs rotate relative to each other as one of the first cylinders retracts and the other of the first cylinders extends. 
   Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
       FIG. 1  is an elevation view of a tong assembly constructed in accordance with embodiments of the invention; 
       FIG. 2  is a plan view of the tong assembly of  FIG. 1 , with the upper tong removed; 
       FIG. 3  is a plan view of a tong assembly in an open position; 
       FIG. 4  is a plan view of the tong assembly of  FIG. 3  in a closed position; 
       FIG. 5  is a plan view of the operating components of the tong assembly of  FIGS. 3 and 4 ; 
       FIG. 6  is a partial plan view of one embodiment of a die assembly; 
       FIG. 7  is a cross-sectional elevation view of one embodiment of a die assembly; and 
       FIG. 8  is a partial sectional plan view of one embodiment of a die assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , tong assembly  100  includes top tong  102  and back-up tong  104  rotatably connected by slider  106  and torquing cylinders  108 .  FIG. 2  shows tong assembly  100  with top tong  102  removed. Cylinders  108  are connected to top tong  102  at pins  110  and to back-up tong  104  at pin  112 . Slider  106  allows cylinders  108  to rotate top tong  102  relative to back-up tong  104  while maintaining proper alignment between the tongs. 
   Tong assembly  100  transfers torque produced by cylinders  108  to a threaded connection between two adjacent tubular members that are engaged by clamping arms  111 . Cylinders  108  may be hydraulically linked to one another such that the piston (extend) side  114  of one cylinder is coupled to the rod (retract) side  116  of the other cylinder. In this manner, hydraulic pressure can be applied simultaneously from the same source to extend one cylinder and retract the other cylinder, thus optimizing the torque applied to the threaded connection. 
   Referring now to  FIG. 3 , a tong  200  is shown including body  202  with its top plate  204  partially cut away to show clamping assembly  206 . Body  202  is preferably formed from a unitary weldment substantially enclosed on all but one side, which is left open to accept clamping assembly  206 . Clamping assembly  206  comprises center slider  208 , clamping arms  210 , connecting links  212 , slider guides  214 , and die assemblies  216 A-C. Pins  218  and  220  pivotally attach connecting links  212  to center slider  208  and clamping arms  210 , respectively. Pins  222  provide a pivoting connection between clamping arms  210  and body  202 . Pins  222  also carry the load that is applied by the torquing cylinders from body  202  to clamping arms  210 . Clamping assembly  206  is actuated by hydraulic cylinders  224 , which preferably act in unison to actuate the clamping assembly. 
   Referring now to  FIG. 4 , as hydraulic cylinders  224  extend, center slider  208  is moved toward tubular member  226 . Center slider  208  pushes connecting links  212  and rotates clamping arms  210  about pins  222  until die assemblies  216 A and  216 B engage tubular member  226 . Die assembly  216 C moves toward tubular member  226  with center slider  208 . Slider guides  214  maintain alignment between center slider  208  and tubular member  226  to ensure proper operation of the tong assembly. In the preferred embodiments, all three die assemblies  216 A-C engage tubular member  226  at the same time and with equal amounts of force. 
   Referring now to  FIG. 5 , the actuating components of clamping assembly  206  are shown engaged with tubular member  228 . In the preferred embodiments, clamping assembly  206  operates such that, within a given size range, tubular member  228  is substantially centered, and evenly engaged by die assemblies  216 A-C. Therefore, clamping assembly  206  is arranged such that as die assembly  216 C moves toward the center of tubular member  228 , die assembles  216 A and  216 B also move toward the center of the tubular member at substantially the same rate. 
   Clamping arms  210  are arranged such that distance  232  from pin  222  to the center of die assembly  216 B is substantially equal to the distance  230  from pin  222  to pin  218 . Pin  218  moves in unison with, and in substantially the same direction as die assembly  216 C that is mounted on center slider  208 . Because pin  218  and die assembly  216 B rotate about pin  222  at the substantially the same diameter, the distance traveled by die assembly  216 B is substantially the same as the distance traveled by pin  218 . Therefore, during actuation of clamping assembly  206 , the distance traveled by die assembly  216 B (or  216 A) is substantially the same as the distance traveled by die assembly  216 C. Because dies  216 A–C have starting positions substantially the same distance from the center of tubular member  228 , the tubular member will always be substantially centered by the die assemblies. 
   In order to accommodate a wide range of tubular sizes and ensure that tong  200  contacts the pipe surface as close to perpendicular as possible, die assemblies  216 A and  216 B may be rotatable relative to clamping arms  210 . Die assembly  216 C is preferably stationary so to not allow a tubular member to move off-center. 
   Referring now to  FIG. 6 , one embodiment of a die assembly  300  is shown installed in clamping arm  210  and including die  302  and holder  304 . Die  302  is preferably constructed of a hardened material formed with teeth  308  for engaging the outside surface of a tubular member. Die also includes shoulders  310  configured to interface with grooves  312  in holder  304 . Holder  304  has a curved rear surface  314  and curved ridge  316  on both the top and the bottom of the holder. 
     FIG. 7  illustrates a cross-section of shows a section of a die assembly  300  assembled on a clamping arm  210 . Die  302  and holder  304  are retained in position by ridges  316  interfacing with grooves  320  on retainers  306 . Retainers  306  are fixed to clamping arm  210  by cap screws  328 . Gaps  322  ensure that as die  302  is compressed, the load is transferred into clamping arm  210  and not into retainers  306 . 
   Referring now to  FIG. 8 , a partial sectional view of die assembly  300  is shown so that the interface between ridge  316  and groove  320  can be seen. Groove  320  may be slightly longer than ridge  316  in order to allow holder  304  to rotate relative to the retainer. Each retainer  306  has a groove  320  for supporting rotation of holder  304 , but the grooves on the two retainers may be different. Retainer  306  is preferably arranged so as to facilitate easy assembly and disassembly of die assembly  300  to support fast changing of die  302 . 
   While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the pipe gripping and manipulating apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.