Abstract:
A subsea connection assembly comprises a stab plate a first stab plate which carries a first plurality of couplers and a second stab platewhich carries a second plurality of couplers for mating engagement with the couplers in the first plurality as the stab plates are moved together. The assembly includes a mounting plate, a support which is disposed for lateral movement in at least one direction relative to the mounting plate, and a pivot which allows tilting movement of the first stab plate relative to the support. The tilting and translational features accommodate many different possible trajectories of a pulling unit. In particular the assembly tolerates a separating action which is oblique to the normal mating and demating direction.

Description:
PRIORITY 
       [0001]    This application claims priority from GB patent application No. 1022065.5 filed Dec. 29, 2010, the disclosure of which is incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to stab plates such as are in use in subsea installations, particularly although not necessarily exclusively in conjunction with equipment for the control of extraction of fluid hydrocarbons. 
       BACKGROUND TO THE INVENTION 
       [0003]    Stab plates for this purpose normally come in pairs, one stab plate carrying a plurality of couplers (which may be hydraulic or electrical) which can be mated with respective coupler on the other stab plate as the plates are moved together. 
         [0004]    The invention particularly concerns a stab plate which has a much improved tolerance for initial mis-alignment and/or obliquity of approach of the stab plates and also for the effects of separating forces oblique to the direction in which the couplers mate. One preferred form of the invention is a load bearing stab plate assembly which should be able to separate without damage following an emergency failure of a nearby unit that it controls. As will be explained, it incorporates tilting and translational features to accommodate many different possible trajectories of a pulling unit. In particular the stab plate is adapted to allow a pulling action which is oblique to the normal mating and demating direction. The stab plate assembly preferably has capture features permitting an accurate alignment of mating parts for remote make up, separation and remake after separation. 
       SUMMARY OF THE INVENTION 
       [0005]    In one aspect the invention provides a stab plate assembly comprising a stab plate which carries a plurality of couplers for cooperation with respective couplers on a complementary plate The assembly includes a mount, a support which is disposed for lateral movement in at least one direction relative to the mount, and a pivot which allows limited tilting movement of the stab plate relative to the support. 
         [0006]    Preferably the support is disposed for lateral movement in two mutually perpendicular directions relative to the mount. The assembly may for this purpose include a first track provided on the mount, a second track, perpendicular to the first track, provided on a tracked member secured to said support, and an intermediate guide member disposed between the tracked member and the mount and engaging the tracks to allow the said lateral movement in said two mutually perpendicular directions. A securing member may extend from a cavity in the support through an aperture in the mount to said tracked member, which is disposed on the opposite side of the mount from the support. Preferably the said support is slidably disposed relative to the mount. 
         [0007]    The stab plate preferably includes docking members disposed to cooperate with datum members on the complementary plate so as cause tilting and/or lateral movement of the stab plate whereby to orient the couplers in the plurality thereof relative to their respective couplers as the stab plates are moved together. The pivot preferably comprises a ball joint. The ball joint may includes means for inhibiting rotation of the stab plate about an axis corresponding to the direction in which the couplers on the stab plate move to mate with the said respective couplers. 
         [0008]    The invention also provides subsea connection equipment comprising a stab plate assembly comprising a first stab plate which carries a first plurality of couplers, and a second stab plate which carries a second plurality of couplers for mating engagement with the couplers in the first plurality as the stab plates are moved together and being releasable as the stab plates are separated. The stab plate assembly comprises a mounting plate, a support which is disposed for lateral movement in at least one direction relative to the mounting plate, and a pivot which allows tilting movement of the first stab plate relative to the support. 
         [0009]    The equipment preferably includes a heavy duty ball tilting unit mounted on a central ball post which is held on tracks permitting horizontal motion in at least one and preferably two mutually perpendicular axes (X and Y) relative to a fixed mount. It may used in situations where a pair of stab plates containing hydraulic self sealing couplings and/or electrical connections is to be made up by thrusting the stab plates together and, in an emergency, rapidly separated. 
         [0010]    One emergency situation which may be envisaged is of a remote subsea connection of two stab plates in the control system to special equipment. If the special equipment is suddenly displaced (it could be remotely decoupled) it is required that the control system&#39;s stab plates should also separate without damage. 
     
    
     
       INTRODUCTION TO THE DRAWINGS 
         [0011]    One example of the invention will be described with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a schematic drawing of a stab plate according to the invention; 
           [0013]      FIG. 2  is a schematic drawing of the stab plate approaching engagement with a complementary stab plate in an assembly according to the invention; and 
           [0014]      FIGS. 3 to 7  are drawings of various parts of the stab plate shown in  FIG. 1  and also shown in the assembly shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  illustrates a first stab plate  1 , called herein ‘lower’ stab plate, which intended to cooperate with a second, or ‘upper’ stab plate  2 , which is shown in  FIG. 2 . The stab plate  1  is populated with couplers  3 , which project forwardly of the stab plate  1  in a direction normal to the general plane of the stab plate  1 . 
         [0016]    Only two couplers  3  are shown for the sake of simplicity. These couplers may be self-sealing hydraulic couplers as for example described in GB-2463966. Such couplers are employed in pairs, a ‘male’ or probe coupler on one stab plate being positioned to mate with a ‘female’ or socket coupler on the other stab plate. In this example the ‘male’ couplers are disposed on the lower stab plate and the female couplers  4  (see  FIG. 2 ) are disposed on the upper stab plate  2 . 
         [0017]    However, the invention is not limited to such a disposition. The couplers may be electrical couplers and the stab plates may in general carry both hydraulic and electrical couplers. 
         [0018]    In remote subsea use the stab plates are preferably pushed towards each other by a hydraulic ram with the aid of docking guides which orientate and align the respective couplers exactly before the couplings constituted by the pairs of couplers are fully engaged. Couplings in subsea use require large forces to engage and separate them. A make-up force of 25 tonnes and a demating force of 5 tonnes are common. 
         [0019]    As shown in  FIG. 1 , each coupler  3  is associated with a line (in this example a hydraulic line)  5 . These lead away from a post  6  on which the lower stab plate  1  is mounted. 
         [0020]    At each side of the lower stab plate is a respective docking guide  7 . This is in the form of a cone  8  which narrows to a throat  9 . These guides  7  each cooperate with a respective datum member comprising a guide post  10  disposed on the upper guide; the cones capture the posts  10  and ensure proper alignment of the couplers before final engagement thereof occurs. 
         [0021]    The lower stab plate  1  is as previously indicated pivotally mounted for limited tilting movement, preferably up to about 20° about any axis which is in or parallel to the general plane of the stab plate  1 . For this purpose the support, i.e. the post  6 , carries a ball  11  which has an upper annular bearing  12  and a lower annular bearing  13  disposed within a housing  14  secured within a central aperture  15  in the stab plate  1 . The ball is secured to the post  6  by means of a bolt  16 . The lower part of the housing has an annular flange  17  which extends around the post  6  and allows limited titling of the stab plate  1  relative to its support, the tilting being limited by engagement of the flange  17  with the post  6 . 
         [0022]    The ball  11  has equatorially located radially extending pins  18  which inhibit rotation of the stab plate about the axis of the post, i.e. about an axis generally normal to the plane of the stab plate and parallel to the direction in which final mating engagement (or initial demating) of the couplers occurs. 
         [0023]    An important feature of the assembly shown in  FIG. 1  is the mounting of the support post  6  such that it and thereby the stab plate  1  can move laterally (during a make up or releasing action) laterally relative to its mount in at least one and preferably two orthogonal directions (and thereby any direction). The post  6  has a broad base which is located on the upper surface  19  of a mounting plate  20  and can slide relative to the mounting plate  20 . 
         [0024]    Moreover, the assembly includes two tracks, extending in the two orthogonal directions, which allow the lateral movements of the post  6  relative to the mounting plate  20 . 
         [0025]    One of the tracks is provided on the mounting plate  20 . With reference to  FIG. 3 , in this example this track is in the form of parallel slots  21  in the underside  22  of the mounting plate  20 . 
         [0026]    A second track is provided by a member  23  fixed to the post  6 . The member  23  is in this example a plate which is secured to the post by a bolt  24  which extends from a cavity  25  in the post through a central aperture  26  in the mounting plate, the plate  23  being disposed in this example on the opposite side of the mounting plate from the post  6 . The plate  23 , as shown in  FIG. 4 , has two parallel slots  27 , extending in a direction perpendicular to the direction of the slots  21  in the underside of the mounting plate. 
         [0027]    Between the plate  23  and the mounting plate  20  is an intermediate plate  28 .  FIG. 5  is a top view,  FIG. 6  is a side view and  FIG. 7  is an underneath view of the intermediate plate  28 . On its top side the intermediate plate has a set of pins which engage the track slots  21 , two pins engaging each slot, and on its underside the intermediate plate has pins  30  engaging the track slots  27 , two pins engaging each slot to maintain alignment. Low friction strips  31  and  32  may be provided between the mounting plate and the intermediate plate  28  and between the intermediate plate  28  and the tracked plate  23  respectively. 
         [0028]    The ‘female’ stab plate (i.e. the stab plate  2  holding the female couplers  4 ) is moved into engagement with the male plate  1  by (for example) a hydraulic ram (not shown). As the ram nears the male plate a docking guide  7  on the stab plate  1  engages the top of a guide post  10  mounted on the stab plate. The guide post  10  is pushed downwards by further motion of the ram until a similar pin  10  on the opposite side of the plate  2  engages its respective docking guide  7 . This action has brought the two plates substantially parallel. Further motion of the ram causes the posts  10  to move the stab plate assembly along the tracks  21  and  27  so that the posts  10  are aligned with the capture bores  8 . Further motion of the ram motion the couplings, now in correct alignment, to be fully made up. 
         [0029]    After make up the ram can be pressurized to ensure that the high separation forces from unbalanced hydraulic couplings do not force the plates apart. A controlled demate of the stab plates may performed by lowering the ram pressure but removal of all mating pressure will not in practice separate the plates because normally (in the case of self-sealing hydraulic couplings) a vacuum is formed on closure of the couplers and the high separating pull referred to above is required. 
         [0030]    A real need for the tilting and planar motions of the lower stab plate relative to the mounting plate occurs when the stab plates are in their normal made up working situation controlling special equipment which is designed so that in an emergency the special equipment is designed to unlatch from the structure and to be pulled clear. In these circumstances the stab plate  2  and the ram mechanism are fixed to the special equipment and must also break clear of the structure. Because the tie to the special equipment is from the side the mated stab plates have to tilt to an angle normal to the direction of pull. After this action the female stab plate and ram mechanism will remain hanging from the special equipment remotely and totally separate from the stab plate  1 , which remains on the ball and track mounting on the structure. The mechanism suffers no damage in such separation and on refitting the special equipment the connection unit may be made up again.