Abstract:
An open throat power tong  10  as commonly used for making up and/or breaking apart an oilfield tubular connection, comprising a tong body  20,  a tong door assembly  40,  a partial ring member  30  and a ring segment  150.  The partial ring member  30  and ring segment  150  may not be structurally connected and each may support one or more jaw members thereon for gripping a tubular  11.  The partial ring member  30  and ring segment  150  may rotate substantially in unison along a substantially common plane and about a common axis, along a defined rotation course through the tong body  20  and door  40.  The ring segment  150  may be substantially secured within the door when the door  40  is opened. An improved latch mechanism  100  is included for securing the door  40  to the tong body  20  to facilitate relatively easy closing and latching and unlatching of the door  40  with the tong body  20,  and to prevent expansion of the open throat  25  during application of high torque.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to power tongs of the type commonly used to make up and break apart oilfield tubular threaded connections. More particularly, this invention relates to an improved open throat power tong which may be laterally moved on and off a tubular string, and to an improved door for such a power tong which will extend across the open throat when in the closed position and will expose the open throat when in the opened position.  
         BACKGROUND OF THE INVENTION  
         [0002]    Power tongs have been used for decades to make up and break apart oilfield tubular connections. While such power tongs have a variety of configurations, and different mechanisms for both gripping and rotating an upper tubular pipe relative to a lower tubular pipe, such power tongs generally may be classified as being either the closed throat type or the open throat type. Closed throat power tongs provide a tong body which fully encircles the tubular string, so that repeated oilfield threaded connections pass axially through an opening in the closed throat power tong.  
           [0003]    The body of an open throat power tong, on the other hand, typically encircles a majority of the oilfield tubular connection, but an open throat is provided in the tong body to allow the tong to be laterally moved on and off the tubular string. Likewise, a majority of a rotary ring may typically encircle a majority of the tubular and may rotate around the tubular, within the tong body. Most open throat power tongs are provided with a door which accordingly is opened to expose the open throat of the power tong when the tong is not being operated. The door assembly of an open throat power tong is typically closed and latched when the power tong is operated to increase the reliable torque output of the power tong by preventing “spreading” of the open throat and/or to safely retain the tubular within the throat while rotating the tubular. The door assembly provides an open throat tong with the ability to fully encompass a tubular member to aid in safely and securely gripping and rotating the tubular. Also, closing the tong door may increase the safety of the power tong by preventing a tong operator from inadvertently engaging the power tong rotating ring prior to correct tong engagement with the pipe, and may prevent jamming of the rotating ring due to misalignment with the door assembly.  
           [0004]    Various types of latching mechanisms have been used in the power tong industry to retain the pivotal door in the closed position. The commonly used latching mechanism in an open throat power tong employs a heavy duty hammer latch mechanism which includes a latch arm pivotally connected to one of a pair of doors positioned on opposing sides of the open throat. Alternatively, a single door may extend across the open throat so that the latch arm on the door engages a lug on the tong body. In either case, a latch head at the end of the latch arm engages a latch lug or stop to retain the door or the pair of doors in the closed position. The latch head and the latch lug typically have planar surfaces which engage when the door or the pair of doors are in the closed position. The heavy duty latch mechanism and door are sufficient to withstand a substantial lateral force, and thus minimize spreading of the open throat of the power tong. To open the doors, the operator manually grasps a handle secured to the latch arm and pulls the latch arm away from the latch stop to disengage the mating surfaces. With the door or doors opened, a power tong may then be moved laterally on and off a tubular string.  
           [0005]    When the double door open throat power tong is positioned about the tubular string and prior to activating the partial ring, the door with the latch stop is first closed, then the door with the latch arm is manually closed. The latch arm conventionally includes a spring member which biases the latch arm to the closed position relative to its supporting door. By applying a considerable closing force to the door supporting the latch arm, a cam surface on a latch head engages a corresponding cam surface on the latch stop which causes the latch arm to pivot toward an opened position while the latch head moves radially outward from the latch stop. Once the latch arm is pivotally moved to the opened position, the latch head moves radially inward relative to the latch stop so that the planar surfaces on the latch head and the latch stop engage. The spring on the latch arm may serve to provide additional force which retains the doors closed.  
           [0006]    A significant disadvantage of the power tong door discussed above is that it typically requires a relatively large amount of closing force to shut the doors while the latch head moves radially outward with respect to the latch stop, so that the latch head will then be properly positioned so that it may move back radially inward relative to the latch stop and secure the doors closed. This large closing force requires that the door components be sized both for withstanding the spreading force discussed above, and also to ensure that components are sufficiently rugged to withstand the repeated substantially jarring force which these components endure during closing of the door.  
           [0007]    A related drawback of this prior art system is that a great deal of effort is required by a tong operator to close the door, which unfortunately increases the tendency for the operator to merely position the door in the partially closed position and not fully latch the door closed. Failure to latch the door closed creates a safety risk, as discussed above, and may also result in tong spreading when high torque is used to make up or break apart the threaded connection.  
           [0008]    A second generally distinguishing characteristic between tongs, (other than open/closed throat design), is design of the jaw system. Tongs may generally be classified as either the two jaw system or three jaw system. A two jaw tong system typically includes two sets of gripping jaws segments provided within the tong body, with both sets combining to provide a maximum gripping area of 360 degrees less the circumferential door area. A three jaw tong system typically includes a two jaw system plus a third jaw that is located within the tong door segment, thereby ideally affording substantially 360 degrees of jaw gripping surface to a tubular member.  
           [0009]    A drawback of prior art three jaw tongs is that gear pins were required to attach the body ring gear section with the door ring gear section. One gear pin was included on the hinge side of the gear door segment and a second pin was provided on the latch side of the ring gear door segment. A second set of pins or a pin and latch mechanism, were used to pivot and latch the door assembly to the tong body. Each time the door segment were opened or closed, the latch side of the door were unlatched and/or unpinned, as appropriate. In addition, at least one side of the ring gear door segment was also unpinned. Such operations were and are time consuming, and increase the complexity and reliability of the tongs. Additional problems include maintaining proper alignment of gear, door, pin, latch and housing components each time the tong door is closed. Pins typically require a tight fit and alignment between components can be critical to proper rotation of the gear and/or to proper tong operation. If improperly aligned or if the door is improperly closed or latched, the tong gear may seize and lock up the rotational tong components. Operation of a power tong with the door opened may be dangerous and is not recommended except under special circumstances and with appropriate safety precautions. If the tong is operated with the door opened, the rotational components may jam and require some tong disassembly to disengage the jammed components. Also, if operated with the door opened, there is a possibility of the ring segment coming partially or completely out of the tong.  
           [0010]    A prior art power tong is incorporated herein by reference, which was filed Jan. 13, 1999, as file number Eckel-71. Eckel-71 discloses a latch mechanism that may require a relatively lower force and effort to open and close the door and latch mechanism.  
           [0011]    The disadvantages of the prior art are overcome by the present invention. An improved open throat power tong is disclosed including a door that provides a non-pinned, rotating gear section and a rotating third gripping jaw, within the door section for the power tong. The door of the present invention may significantly increase the area over which the tong grips the tubular, such that an increased make up and/or break out torque may be applied without increasing risk of collapsing or damaging the tubular.  
         SUMMARY OF THE INVENTION  
         [0012]    An improved open throat power tong for making up and/or breaking apart an oilfield tubular connection includes a tong body having an open throat therein, and a partial ring member having an open throat. The partial ring member having an open throat may be rotatably supported on the tong body for rotating one tubular member relative to another during a connection make up and/or break out operation. At least two heads may be included on the partial ring member that are rotatable with the partial ring for gripping engagement with the upper oilfield tubular. A door is included which may be pivotally connected to the tong body adjacent a side of the open throat, wherein the door extends at least partially across the open throat when in the closed position, and when in the opened position exposes the open throat to enable the power tong to be moved laterally on and off the oilfield tubular. A ring segment is included which may be rotatably supported within the door for rotating in conjunction with the partial ring member. The ring segment may carry one or more heads for gripping engagement with the upper tubular. A hydraulic drive motor may be provided for powering rotation of the partial ring member, the ring segment and the first tubular.  
           [0013]    A rotational support mechanism, such as rollers and/or bearings, may be provided in the tong body to define the rotational path for the partial ring member and the ring segment. The support mechanism may also prevent spreading of the open throat in the partial ring member under high torque operations by confining radial movement or other deflection of the partial ring member or the ring segment.  
           [0014]    A latch mechanism may be provided to secure the door to the tong body when the door is in the closed position. The latch mechanism may be at least partially secured to the door. A latch arm is pivotally moveable between a latch arm closed position and a latch arm opened position. The latch mechanism may include a latch coupling and a pivotally mounted inner latch head, both for engaging a latch stop. The latch stop may be fixedly secured to the tong body, adjacent a side of the open throat. When the door and latch mechanism and are in the closed and latched positions respectively, the inner latch head and the latch coupling may engage the latch stop and the outer latch head may engage the inner latch head to lock the inner latch head in engagement with the latch stop.  
           [0015]    The improved open throat power tong provides for a simplified, reliable rotating mechanism in that the partial ring member and the ring segment are structurally independent from one another, both during door opening/closing, and while rotating the partial ring member and ring segment in unison to make up and/or break out a tubular connection. When the door is closed, the ring segment may substantially fill in the open throat portion of the partial ring member, essentially providing up to 360 degrees of gripping area around the tubular member. The partial ring member and ring segment substantially rotate along a common plane, at a common radius about a common axis.  
           [0016]    During rotation, a planar or configured end surface of the ring segment may engage a similar end surface configuration of the partial ring member, however, the ring segment and partial ring member may remain structurally independent from each other. To open the door of the power tong, rotation may be interrupted when the ring segment is substantially aligned with the door in the open throat of the tong body. The door may then be opened and in so doing the ring segment may pivot out of the open throat with the door. When the door is opened or unlatched, a retainer arm may engage the ring segment to secure the ring segment within the door and to prevent the ring segment from coming out of the door while the door is opened, until the door is closed and the latch is latched, wherein the retainer arm may disengage from the ring segment. As the ring segment may be structurally independent of the partial ring member during rotation, when the door is closed the ring segment may be immediately ready for rotational operation as no pins are required to connect or align the ring segment with the partial ring member.  
           [0017]    The present invention provides a power tong with an improved three or more jaw gripping mechanism to facilitate applying higher torque to make up and break out operations by distributing the rotational torque over a larger circumference on the tubular member than a two jaw gripping system. Such enhanced force distribution may reduce the risk of crushing the tubular while also facilitating the application of additional torque.  
           [0018]    It is an object of the present invention to provide a high torque power tong that may incorporate at least three gripping jaws with the tong having a reduced propensity for jamming or binding of the partial ring member and/or the ring segment, during rotation. The unsecured or “floating” ring segment of the preferred embodiment is not secured to the partial ring member. A rotational guide mechanism is provided which facilitates unison rotation of both the ring segment and the partial ring member about a substantially common plane and axis, in a torque range from low to high, without requiring critical alignment between the door, tong body, partial ring member and ring segment.  
           [0019]    It is also an object of the present invention to provide an open throat power tong with an improved door which will reliably latch the door in the closed position, and which may close with a relatively low closing force. A latch assembly is disclosed which closes reliably with relatively low closing force while also self latching in conjunction with the door closing, such that door latching is accomplished in the same operation as door closing. The preferred embodiment latch assembly increases the likelihood that the tong operator will reliably latch the door of an open throat power tong in the closed position before operating the power tong. The latching system disclosed herein is reliably self latching upon closing of the door. Alternatively, other latching mechanisms may be utilized with the ring segment and partial ring member combination.  
           [0020]    It is a feature of the present invention that the latching mechanism securely latches the door to the tong body when the door is in the closed position, and in addition may strengthen the power tong by preventing spreading of the open throat under high torque. The latch mechanism may support load and tong deformation forces in a plurality of orientations.  
           [0021]    It is a significant feature of the present invention that the power tong may save time and effort in opening and closing the door as the ring segment and partial ring member do not require pinning or otherwise connecting with each other. The ring segment is structurally independent from the partial ring member. The partial ring member and ring segment may be rotated in unison within the tong and door to make up or break out a connection from substantially the time the door is closed. In addition, the door may be opened substantially immediately after ceasing rotation and aligning the ring segment with the door.  
           [0022]    It is a feature of this invention that the partial ring member may be rotated while the door is opened and the ring segment non-rotationally contained within the door. Although it is recommended that the door be closed during normal operation of the power tong, the tong door does not have to be closed for the tong to operate, and the ring segment does not have to be engaged with the partial ring member for the tong to operate. The circumferential distance between two driving idler gears in the tong body that engage the partial ring member to rotate the partial ring member is thus greater than the circumferential gap in the partial ring member. During rotation of the partial ring member while in the absence of the ring segment, e.g., when the door is opened and the ring segment is not rotating, at least one idler gear may at all times engage and drive the partial ring member. Thereby, if necessary and under special safety measures, the tong may be briefly operated with the door opened.  
           [0023]    It is not recommended that the tong be normally operated with the door opened. The tong should only be operated with the door closed. Should special circumstances arise when may be necessary briefly to operate the tong with the door opened, extreme care, caution and special safety measures should be exercised to avoid injury.  
           [0024]    It is also a feature of the present invention that the rotational partial ring member and ring segment may not be as susceptible to binding and jamming as may occur when ring segments and partial ring members are structurally pinned or otherwise interconnected.  
           [0025]    Another feature of the invention is that the door for the power tong may include a single door which extends across the open throat of a power tong, or may include a pair of doors each pivotally connected to the tong body at opposing sides of the open throat of the power tong, with one of the doors supporting a latch stop thereon. In such embodiment, one of the doors may also support a head for gripping the tubular.  
           [0026]    An advantage of the present invention is that the fatigue on the operator is reduced by significantly reducing the effort required to both close the door and concurrently latch the door in the closed position in a single operation.  
           [0027]    Yet another advantage of the invention is that the door and the floating ring segment mechanism are reliable, simple and may be inexpensively manufactured. Binding, jamming and alignment problems may be reduced by allowing the ring segment to “flex,” “float,” move vertically or otherwise, relative to the partial ring member.  
           [0028]    These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to figures in the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 is a top view illustration of a power tong embodiment with the latch mechanism unlatched and the door opened, with the top cover partially removed.  
         [0030]    [0030]FIG. 2 is a top view illustration of the power tong illustrated in FIG. 1, with the door closed and latched.  
         [0031]    [0031]FIG. 3 is a bottom view of a section of the power tong with the door opened and the latch mechanism unlatched.  
         [0032]    [0032]FIG. 4 is a cross section view of section  4 - 4  in FIG. 3.  
         [0033]    [0033]FIG. 5 is a bottom view of the section of the door and latch illustrated in FIG. 3, with the door closed and the latch mechanism latched.  
         [0034]    [0034]FIG. 6 is a three dimensional isometric view of a power tong, generally.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    FIGS.  1 - 6  illustrate a generalized, suitable embodiment for an open throat high torque power tong  10  according to the present invention. A power tong door assembly  40  may be pivotally connected to a power tong body  20  by door hinge pin  44 . The door assembly  40  may be opened, as illustrated in FIG. 1, exposing an open throat  25  in the power tong body  20 . The power tong body  20  may include a substantial generally circular opening or central bore  27  near the back of the throat  25 , the circular opening having a central axis  15 . A lower end of a first tubular member  11 , such as an oil field tubular pipe which may be suspended near a second end from a rig derrick (not shown), may be laterally positioned through the open throat  25  and within the central bore  27 . Thereafter, the door  40  may be pivoted closed with the tong body  20  and latched by a latch mechanism  100 , thereby closing the open throat  25 . In such configuration, a central axis of the first tubular member  11  may be generally coaxial with the tong central axis  15 .  
         [0036]    Power may be applied to the power tong  10  to cause the power tong  10  to rotate the first tubular member  11  to make up or break out a threaded connection between first tubular member  11  and a second tubular member (not shown). The second tubular member may be typically suspended within a well bore (not shown), below the first tubular member  11 . The power tong door  40  may thereafter be opened to allow the power tong  10  to be laterally removed from engagement with the first tubular member  11 .  
         [0037]    High Torque Power Tong  
         [0038]    For a preferred embodiment as shown in FIGS.  1 - 6 , the power tong assembly  10  may be powered, hydraulically or otherwise, to impart torque upon and rotate the first tubular member  11 . A gear assembly  22  may be included in the transition of power through the tong  10 . Additional tong components may include a partial ring member  30  and a plurality of jaw members engaged thereto, for gripping the first tubular member  11 . The tong body  20  may provide an open throat for laterally moving the tong between engagement and disengagement with the tubular member  11 . A generally circular central bore  27  near the back of the open throat  25  may be included to position the tubular member during rotation of the tubular member  11 . The diameter of the circular opening  27  is large enough to accommodate the largest diameter tubular member  11  for which the particular power tong  10  is designed to rotate, plus some additional diameter to facilitate telescopic transmission of such tubular members  11  through the central bore  27  without binding the tubular  11  with the tong  10 .  
         [0039]    The tong body  20  may include an upper cage plate  17  which may substantially provide an upper cover on the tong body  20 , and a lower cage plate (not shown) which may substantially provide a lower cover on the tong body  20 , opposing the upper cage plate  17 . A tong frame  19  may generally encompass portions of the periphery of the tong body  20 , excepting for the open throat  25  and the central bore  27  portions of the tong body  20 . The tong frame  19  may enclose at least a portion of an interior of the tong body  20  between and at least partially supporting the upper  17  and lower tong plates. The tong frame  19  may also extend through portions of the interior of the tong body  20 .  
         [0040]    The partial ring member  30  is designed to rotate within the tong body  20 , about the central axis  15 . The partial ring member  30  may include a row of gear teeth  58  on a portion of an outer periphery of the partial ring member  30  to rotationally connect the partial ring member  30  with the gear assembly  22 . One or more roller guide surfaces  57  may also be provided on the partial ring member  30 , preferably near an outer periphery of the partial ring member  30 , to engage a plurality of tong body roller guides  52 . The plurality of tong body roller guides  52  may confine rotation of the partial ring member  30  within a rotational course that may be at least partially defined by and supported by the roller guides  52 . In addition, the roller guides  52  may aid in preventing spreading of the partial ring member  30  under applications of high torque by providing lateral support to the partial ring member  30 .  
         [0041]    An inner surface of the partial ring member  30  may support at least two heads  36  for selectively gripping the tubular member  11 . The heads  36  may partially move or pivot radially inward toward the central axis  15  during rotation of the partial ring member  30 , such that tong dies (not shown) or other tubular gripping components supported on the heads  36  may engage and grip the tubular  11 . The heads  36  may also be selectively retractable such that the heads  36  may move radially outward toward the partial ring member to release the tubular  11 .  
         [0042]    The tong body  20  may support the tong door  40 . The door  40  may be pivotally connected to the tong body  20  adjacent a side of the open throat  25  to extend at least partially across the open throat when the door  40  is in a closed position. When the door  40  is in an opened position the opened throat  25  is exposed, thereby enabling the power tong  10  to be moved laterally on and off tubular  11 . In the closed position, the hinged end of the door  40  may be secured to the tong body  20  by hinge pin  44 , while a latch end of the door  40  is secured to the tong body  20  with a latch mechanism  100  which is latched to a latch stop  114  that is secured to the tong body  20 .  
         [0043]    The door assembly  40  generally may securely close the open throat  25  and guide the partial ring member  30  and a ring segment  150 , during rotation. When the door  40  is in the opened position, the door  40  may support the ring segment  150 . The ring segment  150  may support at least one additional jaw member  160  for gripping the tubular  11 . When the door  40  is closed, the ring segment  150  and partial ring member  30  may rotate at least partially within each of the tong body  20  and the door  40 .  
         [0044]    The door assembly  40  may include an upper frame portion  154 , a lower portion  164  substantially opposing the upper frame portion  154 , and an outer wall  163 , generally forming a door interior. A door cage plate  148  may also be included to cover a portion of the interior of the door assembly  40 .  
         [0045]    The ring segment  150  may be designed to rotate about the central axis  15  along a defined rotational course within each of the tong body  20  and closed door assembly  40 . A radially outward surface of the ring segment  150  may include a row of gear teeth  168  to connect the ring segment  150  with the gear assembly  22 . One or more roller guide surfaces  157  may also be provided on the ring segment  150 , preferably on an outer periphery of the ring segment  150 , to engage a plurality of door roller guides  152 . The plurality of door roller guides  152  may confine and support rotation of the ring segment  150  and partial ring member  30  within the door assembly  40  and tong body  20  along a rotational course at least partially defined by and supported by roller guides  52  and  152 . In addition, the roller guides  152  may aid in preventing spreading of the partial ring member  30  under applications of high torque by providing lateral support to the partial ring member  30 .  
         [0046]    An inner surface of the ring segment  150  may support at least one head  160  for selectively gripping the tubular  11 . The head  160  may partially move or pivot radially inward toward the central axis  15  during rotation of the ring segment  150  and partial ring member  30 , such that tong dies (not shown) or other tubular gripping components supported on the heads  36  may engage and grip the tubular  11 . The head  160  may also be selectively retractable such that the head  160  may move radially outward toward the ring segment  150  to release the tubular  11 .  
         [0047]    The ring segment  150  may have a radius of curvature and a general configuration that is substantially the same as the partial ring member  30 , with a significant difference being that the arc length of the ring segment  150  may be less than the arc length of the partial ring member  30 . The ring segment  150  may have an arc length that extends across a portion of the open throat  25  wherein the partial ring member  30  may rotate. Consequently, when the door  40  is closed, the ring segment  150  and the partial ring member  30  may substantially encircle the tubular  11  with a 360 degree arc length.  
         [0048]    The open throat portion of the partial ring member  30  may include end surfaces  91  and  92 . The ring segment  150  may include ring segment end surfaces  81  and  82 . When the door  40  is closed, ring segment end surfaces  81  and  82  may substantially abut end surfaces  91  and  92  respectively. The ring segment  150  may also include ring segment end surfaces  83 ,  84 ,  85  and  86 . The partial ring member  30  may include end surfaces  93 ,  94 ,  95  and  96 . End surfaces  81  and  82  may be staggered from respective adjacent end surfaces  83  and  85 , and  84  and  86 , respectively. Likewise, end surfaces  91  and  92  may be staggered from respective adjacent end surfaces  93  and  95 , and  94  and  96 . A staggering arrangement of end surfaces, such as shown in FIGS. 1 and 2 or otherwise, may provide for interlocking the ring segment  150  and the partial ring member  30 , without structurally connecting the two components, such as with pins. Each end of the partial ring member  30  may be substantially coplanar with a respective mating end of the ring segment  30 . Consequently, as the ring segment  150  and partial ring member  30  rotate, the points of contact between end surfaces of the two components may provide for relative planar displacement and/or for “flexing” between the two components, at the interconnection points. Therefore, binding, jamming and misalignment problems may be reduced while providing a means for at least partial engagement between the two components.  
         [0049]    The arc length of the door section  25  of the power tong  10  is relatively small as compared to the outer circumferential arc length of the partial ring member  30 , such that with appropriate safety measures in place the tong  10  may be operated with the door  40  opened. A preferred embodiment of the power tong  10  includes at least two driving idler gears  23 ,  24 . The driving idler gears  23 ,  24  each may impart rotation to either or both of the partial ring member  30  and the ring segment  150 . The span or arc distance between two driving idler gears  23 ,  24  which engage the partial ring member  30  to rotate the partial ring member  30  is greater than the arc length of the gap or open throat  25  in the outer circumferential arc of the partial ring member  30 . Consequently, during rotation of the partial ring member  30  while in absence of the ring segment  150  in common rotation therewith, e.g., when the door  40  is opened and the ring segment  150  is not rotating, at least one driving idler gear  23 ,  24  may at all times engage and drive the partial ring member  30 . Thereby, under special circumstances and for brief periods, and with extra safety measures in place, the tong  10  may be briefly operated with the door  40  opened.  
         [0050]    In alternative embodiments, end surfaces  91 ,  93  and  95  of the partial ring member  30  may be coplanar or angular with respect to respective end surfaces  92 ,  94  and  96  of the partial ring member  30 . Likewise, end surfaces  81 ,  83  and  85  of the ring segment  30  may be coplanar or angular with respect to respective end surfaces  82 ,  84  and  86 . Those skilled in the art will appreciate that many variations may be conceived for relational door, body and ring structure and/or design.  
         [0051]    Latch Mechanism  
         [0052]    The power tong may  10  may include a latch mechanism  100  partially secured to the door assembly  40  to securely retain the door  40  in the closed position. The disclosed latch mechanism  100  may be simple, reliable and easily latched and unlatched. The latch mechanism  100  may include two portions, namely, a door portion and a tong body portion.  
         [0053]    The tong body end of the latch mechanism  100  may include a latch stop  114  which is securely affixed to the tong body  20 , substantially adjacent a side of the open throat. The latch stop  114  may preferably be a single component. The door  40  portion of the latch mechanism  100  may include a door hinge bracket  42  that is secured to the door  40  and which allows the door  40  to pivot on door hinge pin  44 . A latch coupling  122  may be secured to the opposing end of the door  40  to releasably engage the latch stop  114  when the door  40  is in the closed position. The latch coupling  122  may be pivotal secured to the door  40  by pin  124 . The latch coupling  122  may assist in preventing spreading of the open throat  25  during applications of high torque.  
         [0054]    A latch arm  132  may be included for latching and releasing the latch mechanism  100 . The latch arm  132  may be pivotally attached to latch arm hinge member  135 , by latch arm hinge pin  134 . A biasing device (not shown), such as a torsion spring, may be included to bias the latch mechanism, including latch arm  132 , in a closing position. Such biasing may assist and secure latching of the latch mechanism. The hinge member  135  may be immovably connected to the door body  154 . The latch arm  132  may be pivotally movable between a latch arm closed position and a latch arm opened position. The latch arm  132  may include an outer latch head  130  having an inner latch head engagement surface  136  for engagement with an offset portion  128  of an inner latch head  120  to latch the door  40  when the door  40  and latch mechanism  100  are in the closed position. A latch handle  146  may be immovably secured to the outer latch head  130  to facilitate opening the latch mechanism  100 .  
         [0055]    Inner latch head  120  may be included, which is pivotally connected to the door  40 . The inner latch head  120  may include a latch stop recess  125  for receiving the latch stop  114 . The inner latch head  120  may include an outer latch head engagement surface  126  for engagement with the inner latch head engagement surface  136  on the outer latch head  130  when the latch mechanism  100  is in the latched position.  
         [0056]    Prior to opening the door, the ring segment  150  may be rotated to where the ring segment  150  is substantially within the door  40 . The latch mechanism  100  may be released and the door  40  opened by pivoting the door  40  out of the open throat  25 . When the door  40  is in the opened position, the “floating” ring segment may be retained within the door  40  by a retainer arm  141  which may operate in conjunction with the latch mechanism  100 .  
         [0057]    Manipulation of the retainer arm  141  in conjunction with the latch mechanism may require additional components, including a retainer connector bracket  138 , which may be secured to the latch arm  132 . The retainer connector bracket  138  may pivot with the latch arm  132  between the latch arm opened position and the latch arm closed position. One or more retainer hinge pins  174 , or other linkage mechanism, may pivotally connect the retainer connector bracket  138  and a retainer arm  141 . A retainer guide  142  may be secured to the door  40  and may provide a channel to telescopically guide movement of the retainer arm  141 . A retainer arm engagement port  151  may be provided in the ring segment  150  for selectively receiving the retainer arm  141 .  
         [0058]    Power Tong Operation  
         [0059]    A high torque power tong  10  as disclosed in the preferred embodiment may preferably be hydraulically powered, including a hydraulic power source and hydraulic control system (not shown). In the door opened, open throat configuration the power tong may be laterally moved into engagement with a tubular  11 . The tubular  11  may be transmitted through the open throat  25  and into the central bore  27  near the back of the open throat  25 . The door  40  may be pivoted closed such that the ring segment  150  is circumferentially positioned adjacent an open throat  25  portion of the partial ring member  30 . A recessed opening  123  in the latch coupling  122  may engage the latch stop  114 , while a recessed opening  125  in the inner latch head  120  may engage the latch stop  114 .  
         [0060]    To secure engagement of the inner latch head  120  and the latch coupling  122  with the latch stop  114 , the latch arm  132  and outer latch head  130  may be pivoted from the opened position to the closed position. The outer latch head  130  may be pivoted into engagement with the offset portion  128  of the inner latch head  120 , such that the inner latch head engagement surface  136  on the outer latch head  130  may engage the outer latch head engagement surface  126  on the inner latch head  120 .  
         [0061]    As the latch arm  132  is pivoted to the closed position, the retainer connector bracket  138  which may be affixed to the latch arm  132 , may concurrently pivot with the latch arm  132 , wherein the retainer arm  141  may be telescopically disengaged from the recess  151  in the ring segment  150 . The retainer pin  174  may connect the retainer arm  141  and connector bracket  138 , and the retainer guide  142  may control movement of the retainer arm  141 .  
         [0062]    Hydraulic power may be applied to the power tong  10  to cause the engaged tubular member  11  to rotate relative to a second tubular (not shown), in a selected direction to make up or break out a threaded connection between the first tubular II and the second tubular. The power tong  10  may also be operated to rotate more than merely one joint of tubular member  11 ; for example, rotating a full string of connected tubulars such as when drilling, or manipulating downhole tools. Power may be transmitter through the gear assembly  22  preferably to one or more points near the radially outer periphery of the partial ring member  30  and the ring segment  150 , as the partial ring member  30  and ring segment  150  are rotated within the tong body  20  and door  40 . Rotational movement of the partial ring member  30  and ring segment  150  may cause the plurality of jaw members  36 ,  38 ,  160  to partially move radially inward to engage and grip the tubular member  11 , such that the tubular  11  is rotated in conjunction with the partial ring member  30  and ring segment  150 . Torque may be relaxed or rotation reversed, causing the jaws  36 ,  38 , and  160  to disengage from the tubular  11  and retract radially outward away from the tubular  11 . The tubular may then be moved telescopically up or down through the central bore  25 . Subsequent connections may be thereafter selectively made up, broken out and/or otherwise rotated.  
         [0063]    To laterally remove the power tong  10  out of engagement from a tubular  11  that is positioned with the central bore  27 , the partial ring member  30  and ring segment  150  may be rotated until the ring segment  150  is substantially positioned within the door  40  and the retainer arm engagement port  151  is aligned with the retainer arm  141 . The latch mechanism  100  may be unlatched, the door  40  opened and the tong  10  moved laterally out of engagement with the tubular II. To unlatch the latch mechanism  100 , an operator may pull laterally outward on the handle  146 , away from the door  40 , causing the outer latch head  130  to disengage from projection  128  on the inner latch head  120 . Concurrently, the retainer connector bracket  138  may cause the retainer arm  141  to partially telescopically penetrate into the retainer arm engagement port  151  to secure the ring segment  150  within the door  40  while the door  40  is in the opened position.  
         [0064]    The door  40  may thereafter be pivoted from the closed position within the tong throat  25  to an opened position, thereby exposing the open throat  25 . The power tong  25  may be laterally removed from engagement with the tubular  11 . Because the partial ring member  30  is not secured to the ring segment  150 , in lieu of or prior to removal of the power tong from engagement with the tubular  11  the partial ring member  30  and tubular  11  may be rotated with the door  40  opened and the ring segment removed. In such instance, the partial ring member  30  may traverse the open throat within the rotational course, without the presence or assistance of the door  40 . Normal tong operation with the door opened is not recommended. Injury may result from tong  10  operations with the door  40  opened, due to exposure of moving components within the tong  10 .  
         [0065]    In an alternative embodiment of an open throat power tong assembly  10  which provides for a floating ring segment  150  in the door  40 , the inner latch head  120  may be pivotally mounted on the latch coupling  122 . Also, in alternative embodiments, the retainer arm mechanism  138 ,  141 ,  142 ,  151 , and  174  may be of a mechanical configuration other than as disclosed above, such as a friction mechanism, a variation on the disclosed pin configuration, magnets, or a clamp mechanism. Some power tong  10  embodiments may completely eliminate the retainer mechanism and retain the ring segment  150  within the door  40  by close tolerance component fit, or otherwise.  
         [0066]    It may be appreciated that various changes to the details of the illustrated embodiments and systems disclosed herein may be made without departing from the spirit of the invention. While preferred embodiments of the present invention have been described and illustrated in detail, it is apparent that still further modifications and adaptations of the preferred and alternative embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, which is set forth in the following claims.