Abstract:
Disclosed is a tubular pipe string element having a pin connector and a box connector complementary to the pin connector. The pin and box connectors are rotationally engageable with the respective box and pin connectors of another pipe string element and have complementary anti-rotation devices that cooperate to prevent unintentional relative rotation between the connectors. The anti-rotation devices may include saw-tooth profiled, radially extending teeth and a steep trailing tooth flank angle for the pin member, and at least one detent member formed on the pipe string element for the box connector. When securing the pin and box connectors, the leading flanks of the teeth engage with the detent members while allowing the connectors to rotate into a fully connected position. The steep trailing tooth flank is trapped by the detent member when in the fully connected position to prevent unintentional release of the connection.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to anti-rotation devices for pipe string couplings used in the oil industry and more particularly to pipe strings which incorporate such anti-rotation devices. 
       BACKGROUND 
       [0002]    During oil exploration and extraction, long tubular members, known are pipe strings, are run from a drill rig into the ground through bore holes so as to extend underground ultimately to an underground oil reservoir. These pipe strings are not continuous, but instead are formed of separate lengths which are connected together. This is not only because of the distances involved making a continuous length of pipe impractical, but also because different operating tools are normally connected within the pipe string to suit requirements—for example if a branch bore need to be drilled or the like. Each pipe string element is therefore usually formed with a male connector on one end and a making female connector on the other end (typically a male and female thread), so that next pipe string element is connected to the end of the previous one by simply inserting one end into the other and then rotating to connect them together. 
         [0003]    In practice, however, it is found that, during use, adjacent pipe string elements can rotate relative to each other. For example, for off-shore operations, the pipe string will extend from the drilling rig to the sea bed through the sea and the wave action and vibration in the pipe string resulting therefrom can cause the connected male and female connectors to rotate relative to each other in a release send. A relatively small amount of rotation can, then, cause the whole connection to fail. 
         [0004]    It is therefore the practice in the art to impose some sort of rotation lock on the connection between pipe string elements which prevents relative rotation between the connected male and female connectors, thereby preventing unintentional release of the joint. For example, one known approach is to deform the joint once the connection is made so that the concentric male and female parts are deformed into an eccentric shape and hence are prevented from relative rotation. Another approach is to form radially extending apertures in the walls of the male and female members which align with each other when the connector is fully made, a pin, screw or the like then being inserted through both holes to prevent rotation between the two connector parts. Other solutions are also known. However, none give a satisfactory solution for a variety of reasons. For example, deforming (crimping) requires additional tools to be used during the connection process, extending the time associated with completing the operation and also taking up valuable space of the rig. Use of locking screws/pins requires very precise manufacturing in order to ensure that the radial apertures are properly aligned when the connection is fully made, thereby increasing cost. 
         [0005]    According to the present invention there is provided a tubular pipe string element having: a first end with a male connector formed thereon, a second end having a female connector formed thereon which is complementary to the male connector, said male and female connectors being of the rotational connector type such that, in use, the male connector is engageable in a female connector of another pipe string element and rotatable relative thereto in a first direction in order to secure the connection and in a second direction in order to release the connection, and complementary anti-rotation devices associated with said male and female connectors which anti-rotation devices cooperate to prevent unintentional relative rotation between male and female connectors in the second direction; wherein said anti-rotation devices comprises: at least one saw-tooth profiled, radially extending tooth having a shallow leading tooth flank angle facing in one of said first and second direction and a steep trailing tooth flank angle facing in the other of said first and second directions formed on the pipe string element proximate one end thereof in association with one of the male and female connectors, and at least one detent member formed on the pipe string element proximate the other end thereof in association with the other of the male and female connectors, said at least one saw-tooth profiled tooth and said at least one detent member being rotationally and axially fast, with the pipe string element wherein, in use upon relative rotation in the first direction between engaged male and female connectors, the leading flank of the at least one saw-tooth profiled tooth engages with the at least one detent member, urging it to retract against a biasing member and allowing the connectors to rotate into a fully connected position, the steep trailing tooth flank being trapped by the detent member when in the fully connected position so as to prevent unintentional release of the connection. 
         [0006]    A pipe string element in accordance with the invention has the advantage that the anti-rotation elements operate to prevent unintentional disconnection of the male and female connectors without requiring any additional tooling during the making up of the tool string and also without causing any permanent damage or deformation to either of the pipe string components, making the components more easily reused. 
         [0007]    Preferably, each detent member comprises a cantilever spring arm provided on the relevant surface of the male or female connector with a locking member thereon which is urged by the spring force of the spring arm into the rotational path of the saw-tooth profiled tooth but which is retractable out of said path against the spring force upon engagement with the leading flank of the at least one tooth. In a particularly preferred embodiment, a through opening is formed in the wall of the tubular member in which the locking member engages. This can be achieved particularly effectively by forming the spring arm integrally with the pipe string element by cut outs in the wall of the pipe string element. This has the advantage that the locking member and/or spring arm is accessible from the side of the pipe string element remote from the mating connectors, thereby facilitating manual retraction of the locking member in order to release the connectors. 
         [0008]    The male and female connectors are preferably threaded connectors but other types of rotational connector are also possible such as bayonet connectors. 
         [0009]    The anti-rotation elements are preferably located proximate a tip end of the female connector and proximate the root end of the male connector. In the preferred embodiment, the at least one tooth is provided on the outer surface of the male connector and the at least one locking member and associated spring arm is provided in the tubular wall of the female connector. In this way, the manual release of the locking member can be achieved from outside of the pipe string element using a specially designed release tool. 
         [0010]    Preferably, a plurality of spring arms and associated locking members are provided, which may be equi-angularly distributed around the pipe string element but may also be distributed otherwise there-around, with a corresponding plurality of teeth also being provided. The teeth may then be provided around the entire periphery of the string element of may be provided in distinct groups, the groups being distributed around the pipe string element to match the distribution of the locking members. 
         [0011]    In a particularly preferred embodiment, the trailing edge of each saw-tooth profiled tooth is inclined backwards to form an undercut, and the trailing face of the locking member which engages against the trailing flank to prevent release is similarly undercut in a complementary manner so that the surfaces hook into each other to provide a particularly secure block against unintentional release. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    In order that the invention may be well understood, there will now be described an embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a sectional view through a box connector end of a pipe string element according to the invention; 
           [0014]      FIG. 2  is a sectional view on a second plane through the box connector of  FIG. 1 ; 
           [0015]      FIG. 3  is a perspective view of the box connector of  FIG. 1 ; 
           [0016]      FIG. 4  is a perspective view of a pin connector end of a pipe string element according to the invention; 
           [0017]      FIG. 5  is a sectional view on a first plane through the pin connector of  FIG. 4 ; 
           [0018]      FIG. 6  is a sectional view on a second plane through the pin connector of  FIG. 4 ; 
           [0019]      FIG. 7  is an enlarged view of an anti-rotation ligament which is formed as part of the box connector; 
           [0020]      FIG. 8  is an enlarged view showing the profile of one of the teeth carried on the locking member formed on the end of the ligament; 
           [0021]      FIG. 9  is a perspective view of the box and pin connectors connected together; 
           [0022]      FIG. 10  is a perspective view of the assembled connectors with a release collar mounted on the box connector; 
           [0023]      FIG. 11  is a perspective view of a box connector of a pipe string element according to a second embodiment of the invention; and 
           [0024]      FIG. 12  is a perspective view of the box connector of  FIG. 11  screwed together with the pin connector of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Referring first to  FIG. 1 , there is shown a section through a box connector  1 , being the female part of a threaded connector carried on one end of a pipe string element according to the invention. The box connector  1  is tubular and has an internal, inwardly tapering inner surface  2  extending away from an open end  3  on which is formed a female thread  4  into which is screwingly engageable a complementary male thread carried on the mating end of another pipe spring element. 
         [0026]    Between the outer end  4   a  of the thread  4  and the open end  3  of the box connector  1  four ligaments  5  are formed in the tubular wall  6  of the box connector  1 . The four ligaments are equi-angularly distributed about the circumference of the box connector  1  as shown more clearly in  FIG. 3 , but other distributions area also permissible within the scope of the invention. Each ligament  5  is formed by three through cuts  5   a,    5   b,    5   c  in the wall of the box connector  1  which bound three sides of the ligament  5 . The ligaments are thereby both rotationally and axially fast with the box connector  1 , so as to be constrained against axial or rotational movement relative to the box connector  1 . 
         [0027]    The stiffness of the metal of the ligament  5  biases the ligament into a position in which it lies substantially in line with the wall  6  of the box connector  1  as shown in  FIG. 7 . A cut-out  7  in the outer surface of each ligament  5  reduces the thickness of the ligament and makes it more resiliently deformable so as to allow the ligaments to deflect outwards as described below. 
         [0028]    As shown in  FIG. 7 , a number of saw-tooth profiled teeth  8  are formed on the inner surface of the end of the ligament  5 , which teeth  8  project inwardly of the inner wall of the box connector and are oriented in the circumferential direction. The term “saw-tooth profiled” is used to describe teeth which have a shallower inclined leading flank  8   a  and a steeply inclined trailing flank  8   b,  as shown in more detail in  FIG. 8 . During operation as described below, the shallow incline of the leading flank  8   a  enables a camming action to be developed through interaction with teeth on a pin member so as to cause the ligaments to deflect outwards and hence allow the teeth of the pin member to rotate past the teeth of the ligaments, whereas the steep trailing flank lockingly engages with the teeth of the pin member when rotated in the opposite direction and prevents such rotation. As shown in  FIG. 8 , the trailing flank  8   b  of the teeth  8  of the ligaments  5  have an undercut of approximately 2 degrees. 
         [0029]    A radially extending threaded hole  9  is also formed near the free end of each ligament  5  for screwing in a tool for manually retracting the ligaments to enable manual release of the connection as described below. 
         [0030]      FIG. 5  is a section through a pin connector  10  which complements the box connector  1  described above and which is formed the other end of pipe string element of the invention so as to enable multiple such elements to be connected end to end. The pin connector  10  has a frusto-conical outer surface  11  which tapers inwardly towards to the end  12  of the connector and has a male thread  13  formed thereon which complements the female thread  4  formed on the inner surface of the box connector such that the pin connector  10  may be screwed into the box connector  1  to couple neighbouring pipe string elements together. 
         [0031]    A series of circumferentially extending saw-tooth profiled teeth  14  are formed on the other surface of the pin connector  10  proximate the end of the thread  13  remote from the end  12  of the connector  10  as shown in  FIG. 6 . The teeth  14  may extend around the entire periphery of the pin connector  10 , as shown in the illustrated embodiment. The teeth may alternatively be arranged into groups of teeth  14   a,  the groups  14   a  being distributed around the periphery of the pin connector  10  in positions which correspond with the positions of the ligaments  5  on the box member so that, when the pin member  10  is fully screwed into the box member, each group of teeth  14  on the pin member aligns with and engages the teeth  8  on one of the ligaments. The teeth  14  are formed directly on or fastened directly to the pin connector  10  so as to be constrained against both axial and rotational mount relative to the pin connector  10 . 
         [0032]    The teeth  14  on the pin connector are sized so that they project beyond the outer periphery of the pin connector and are a clearance fit with the inner periphery of the box member  1  so that the pin member  10  can easily be engaged into the box member  1  and rotated in a first direction in order to screw the threads  4 ,  13  together. 
         [0033]    As the pin connector  10  approaches its fully engaged position, the teeth  14  on the pin connector come into alignment with the teeth  8  on the ligaments, the teeth  8  on the ligaments projecting inwardly of the inner surface of the box connector  1  so that they are engaged by the teeth  14  on the pin connector  10 , the shallow inclined flanks of the two sets of teeth  8 ,  14  contacting each other. The resulting camming action imparts a radially outward force on the ligaments  5 , causing them to move radially outwards against the biasing force of the canti-lever arms of the ligaments and hence allowing the two sets of teeth  8 ,  14  to ratchet over each other as the connectors  1 ,  10  rotate to their fully engaged position. 
         [0034]    The teeth  14  or groups of teeth  14   a  on the pin connector  10  are positioned to ensure that, in the fully engaged position, at least some of the teeth thereof are overlapped with the teeth  8  of the ligaments  5 . If the connectors  1 ,  10  are then rotated in the opposite/release direction relative to each other, the steep flanks  8   b  of the teeth  8 ,  14  abut against each other and the under-cuts thereof hook the teeth together, preventing relative radial movement therebetween and blocking further rotation of the connectors in the release direction. 
         [0035]    In order to release the connectors, a manual release tool is used in conjunction with threaded pegs which are screwed into the holes  9  formed in the ligaments  5  from the outer surface of the box connector  1  to that heads of the pegs sit proud of the outer surface of the box connector  1 . The release tool takes the form of a sleeve which is engageable over the outside of the box connector  1  and has axially extending ramped slots formed on its inner surface. As the release tool is slid onto the box connector  1 , the head of each peg is engaged into one of the ramped slots, the ramping of the slots developing a camming action which pulls the peg radially outwards as the tool is slid further forward, which, in turn, pulls the ligament radially outwards against the biasing loading of the spring arm. The teeth  8  on the ligaments are thereby disengaged from the teeth  4  on the pin member, freeing the two connectors  1 ,  10  to be rotated relative to each other in the second direction in to release the connection. It will, of course, be understood that the release tool may be configured for rotational rather than axial operation by orienting the ramped slots to extend circumferentially rather than axially. 
         [0036]    It will be understood that whilst the invention has been description in connection with a screw coupling, other forms of rotation coupling may also be used, such as a bayonet-type coupling. Also, whilst it is preferable to have saw-tooth profiled teeth on both connectors, the invention may also be achieved with teeth on just one of the connectors which engage with a simple block or the like. 
         [0037]    The exact position of the ligaments and mating teeth on the pin connector are also not essential to the invention. Whilst it is advantageous to locate the ligaments proximate the open end of the box member  1  since the thickness of the wall here is lower and hence the loading afforded by the ligaments easier to set and adjust, they may also be located within the threads or at the end of the threads remote from the open end, as long as the teeth  8 ,  14  on the two connectors  1 ,  10  are positions relative to each other to ensure engagement when the connectors are fully screwed together. 
         [0038]    Referring now to  FIG. 11 , there is shown a second embodiment of a box connector  40  of the invention. This is identical with the box connector according to the first embodiment except that instead of the teeth of the box connector  40  being carried on cantilevered ligaments, each set of teeth  41  is support by a pair of ligaments  42   a,    42   b,  the two ligaments  42   a,    42   b  in each case deflecting outwards together to allow the teeth  41 ,  14  of the pin and box connectors  10 ,  40  to ratchet over each other. It will also be seen that in this embodiment, 6 detents are provided equi-angularly distributed around the box connector as compared with 4 on the first embodiment. It will be understood from this that the exact number is not important, although it is preferable that they be evenly distributed around the box member to help balance loading.