Coupling arrangement for components in subsea structures and a remotely operated tool unit for handling such components
BACKGROUND OF THE INVENTION 
     This invention in general relates to an arrangement for interfacing retrievable subsea components particularly for hydrocarbon production, and a remotely operated tool unit (ROT) intended to cooperate with such components for performing operations thereon, for example locking or unlocking to/from the subsea structure and carrying a component between the surface and its subsea location. 
     The components of interest in this regard may be of various types, such as valves, control units or other types of separate retrievable units. During operations these components are mounted in fixed positions and in such a manner that they may be retrieved by means of a remotely operated tool unit (ROT). 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An important aspect of this invention is a common interface to several or all components concerned. The common interface has been devised in order to limit the number of different installation tools for the various components. 
     The invention also comprises features related to the ROT as such, as well as mechanisms belonging to some types of components, since the interface arrangement to some extent will influence the structure and functions incorporated in both the ROT and the components concerned 
     Essentially this invention is directed to the task of making it possible for an ROT to access and interface a subsea structure with equipment modules installed therein, comprising retrievable components or units as mentioned above. A particularly important aspect in this regard is the ability of an ROT to provide locking and unlocking forces to mechanical connectors fixing the retrievable components or units to mating connector means on the subsea structure. However, also other operations on subsea installed components may be contemplated here. 
     A basic principle behind the solutions to be presented in the following description, and in particular in the claims, may be seen in the generally vertical application of forces or vertical movements involved, this being related to the orientation of the components or units concerned, these being mounted for retrieval in a substantially vertical direction from a fixed position on the subsea structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the drawings, in which: 
     FIG. 1 somewhat simplified and in elevation shows a remotely operated tool unit (ROT) embodying aspects of this invention 
     FIG. 2 shows the ROT of FIG. 1 from below, 
     FIG. 3 shows details on the same ROT as in FIGS. 1 and 2, landed on a subsea structure and interfaced with a subsea structure component for effecting an operation on or with that component. 
     FIG. 4 is a vertical section showing the interface arrangement between the ROT and the component in FIG. 3 
     FIG. 5 shows the ROT on FIGS. 1 and 2 handling another type of component, 
     FIG 6 is a vertical section through the interface arrangement between the ROT and the component shown in FIG. 5, 
     FIG. 7 in elevation and partial section shows another example of component having an interface arrangement according to an embodiment of this invention, and 
     FIG. 8 in plan view shows a device for securing a component in an ROT during transportation or retrieval. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The subsea ROT illustrated in the drawings, is a self-contained unit serving primarily as a manipulating and transport tool for the installation and recovery of subsea components. The ROT is usually deployed on a lift wire, or a drill pipe from a surface vessel, and is built up within a support and protection frame more or less shaped as a cage. Guidance and landing of such an ROT on a subsea structure will generally be by the conventional haul-down method, but a guideline system or full thruster positioning may be used during deployment from a surface vessel. 
     As seen particularly in FIGS. 1 and 2, the illustrated embodiment of the ROT has a cage-like support and protection frame 1 within which a manipulating tool comprising an interface arrangement is mounted. FIG. 2 specifically shows haul-down winches 5 and 5A to assist in location and landing of the ROT on a subsea structure or a part thereof. The haul-down winches cooperate with a heave compensator on the surface vessel to eliminate the ROT heave motions. The ROT is also provided with a hydraulic power unit (not shown) for necessary hydraulic functions. As will be understood the ROT should further incorporate control and monitoring equipment connected to an installation or vessel at the surface by an electrical umbilical cable which includes a power supply for the hydraulic power units just mentioned, and including signal cables. 
     At the base of the supporting, structural frame or cage 1 there are integrated two soft landing shock absorbers 23 and two hydraulically operated lockdown mechanisms 24 for securing the ROT to a landing platform or the like on the subsea structure. Externally on the frame 1 there are provided two guide posts or guide funnels 2A and 2B which may be retractable for handling purposes. At the top of the ROT there are mounted one or more hydraulically or electrically powered thrusters 3, 4 for guidance of the ROT. For the possible use of guideline based installation procedures, there are included two wire guides 6A, 6B (FIG. 2). 
     On top of the cage 1 there is a transverse frame member 8 with a central anchoring member or joint 9 from which there is suspended an elevator assembly arranged to be moved in a longitudinal or height direction within the frame 1 guided by guide rods 11 and 12 along which can slide wing bearings 14 and 15 respectively, incorporated in the supporting or main structure constituting the elevator. This structure also comprises a transverse member 13. A hydraulic cylinder unit, shown at 10A in FIG. 3, is connected to transverse frame member 8 and to the elevator transverse member 13 for moving the elevator within frame 1. In FIG. 1 the elevator or hydraulic cylinder is generally indicated at 10. A locking device 8A with cooperating parts on the respective transverse members 8 and 13, is provided for securing the elevator in its upper position when carrying a component and also to restrict movement of bearings or the like during transportation. 
     An essential feature of the interface arrangement incorporated in the tool carried by the elevator is a handling connector 16 aligned with the vertical or central axis AX of the ROT and elevator, and dimensioned for lifting and transporting any one of the components concerned, in particular for retrieving such a component from the subsea structure to the surface. For such operations the handling connector 16 is connected to mating handling means in the form of a handling hub on the top of the component. 
     The interface arrangement also comprises one or more coupling members or smaller connectors 18A, 18B and 18C with associated hydraulic cylinders 17A, 17B and 17C respectively, for moving connectors 18A-C up or down with the central handling connector 16 remaining stationary. The smaller coupling connectors 18A-C with their respective hydraulic cylinders are used to connect to and operate mating coupling members in a complementary interface arrangement on each of the components to be interfaced with the ROT. 
     FIG. 3 illustrates a situation in which the central handling connector 16 and the coupling connector members 18A, 18B and 18C have been connected to mating means and members at the top of a component generally indicated at 40. This component is for example a choke valve the stationary valve body of which is incorporated in a piping system of the subsea system concerned, through connecting conduits shown at 40A and 40B with flange connections to the valve 40. At 44 there is generally indicated a level or plane at which the completed interface arrangement between the ROT and the component may be considered to be located. It should be noted however, that this interface will not generally comprise means or members all lying in the same plane. In fact, the interface arrangement comprises members being adapted to move in a direction normal to the interface &#34;plane&#34;, i.e. vertically in FIGS. 1 and 3. Further details of the interface arrangement will appear from the description of FIG. 4. 
     FIG. 3 also illustrates how the ROT is landed on a sort of platform 30 having guide funnels 32A and 32B for the guide posts 2A and 2B respectively, on the ROT. When referring to the landing area, the miniposts to which the ROT is secured and locked are not described nor shown on the figure, The locking arrangement is shown on FIG. 1,24. Moreover there is an elevator access area defined by a wall 31 underneath the platform 30, the top portion of valve component 40 being accessible through this area. Possibly the landing platform 30 with necessary associated structure may be arranged on a fixed or removable roof element for a subsea structure as described in the applicant&#39;s simultaneous, U.S. patent application Ser. No. 07/684,942. Also as an alternative, the landing platform 30 could normally be covered by a small removable roof element as described in the application just mentioned, preferably with a roof element of such design that it can be removed by means of the ROT itself. 
     Guide funnels 32A,B and posts 2A,B provide for a first step of coarse guidance for landing the ROT. A second and more exact guide function is obtained by means of two small posts projecting from platform 30 to cooperate with funnels associated with lockdown mechanisms 24 shown schematically in FIG. 1. One small post 24A is depicted below mechanism 24 in FIG. 1. At 34 in FIG. 3 there is shown a post 34 entered into a funnel or mechanism corresponding to mechanisms 24 in FIG. 1. A locking pin is hydraulically operated to enter a transverse hole in the small post, thereby locking and securing the ROT to the platform 30. 
     Obviously, the arrangement of guide funnels and posts can be inverted from what is just described. Thus, for example guide funnels 32A,B could belong to the ROT, with posts 2A,B projecting from platform 30, the former arrangement, however, being preferred. 
     In spite of the two guidance steps explained, there may still be a need for further accuracy when installing a component on a subsea structure with an ROT. Therefore, as will appear in particular from FIGS. 4 and 6, the component is also provided with guide means, such as guide pins for a third and final alignment step with respect to the housing or socket in which the component shall be mounted. In order to make this final alignment possible, taking into account unavoidable tolerances in landing and component arrangements as well in the ROT structure itself, the ROT elevator 10 with interface connectors 16 and 18A-C is suspended with some degree of play or float laterally. This is provided for (see FIG. 1) by bearings 14, 15 sliding on rods 11, 12, and supporting members 9,13. 
     At the top of the ROT in FIG. 3 there is shown a wire or cable 7 extended to the surface, for hoisting the ROT and possibly for electrical connections therewith. The dry weight of the complete ROT will for example be approximately 4 tons with a height of perhaps 4 meters, whereas the width may be from 1,5 to 2,0 meters. These dimensions of course depend on the size and weight of the components to be handled and retrieved. 
     Turning now to FIG. 4 the valve 40 is seen to comprise a valve body or housing 41 into which a retrievable valve insert assembly generally indicated at 42, can be mounted. This can for example be a choke valve, the critical parts of which from time to time must be retrieved to the surface for maintenance and the like. Thus, strictly speaking, the &#34;component&#34; referred to above (FIG. 3), in this example is represented by the retrievable insert assembly 42, substantial parts of which are located outside the valve cavity within body housing 41, i.e. above this housing. 
     At the top of this component there is provided a handling hub 49 having a shape and dimensions adapted to be engaged by the handling connector 16 of the ROT. In addition to handling hub 49 the interface arrangement of the component comprises three coupling members or mandrels 48, of which one is shown in engagement with a respective coupling connector member 18A in FIG. 4. The connections 16,49 and 18A,48 may be of more or less conventional designs, which makes possible the transfer of both push- and pull forces thereby. What is of particular interest in the present context is the essentially axial or vertical movements and force directions involved, which is of significance in view of the retrieval of the components in a substantially vertical direction from a fixed position on the subsea structure, as mentioned above. 
     Before studying further details of the interface arrangements illustrated in FIG. 4, it should be noted that the left-hand part of the drawing illustrates the mechanism in a position in which the valve insert or ccmponent is unlocked from the valve housing 41, whereas in the right hand part of the drawing there is established a lock between the valve insert 42 and the housing 41. This locking is provided for by a connector assembly 43 comprising movable locking pieces 43A designed for cooperation with corresponding locking abutments 41A at the upper part of housing 41. Locking is obtained by pushing down a sleeve 45 which by means of inclined internal camming surfaces 45B therein engaging surfaces 43B on the locking pieces 43A, move these into the position illustrated at 43A as shown in the right-hand part of FIG. 4. 
     The necessary push-down force for moving the sleeve 45 from the upper (or left-hand) position in FIG. 4 to the lower (or right-hand) position is exerted by the hydraulic cylinders 17A-C through the coupling connector members 18A-C. The mandrels 48 are mounted on a common yoke or annular plate 44 at the underside cf which the above sleeve 45 is mounted. The yoke or plate 44 is referred to above in connection with FIG. 3, as the level or &#34;plane&#34; of the interface arrangement. 
     For releasing locking pieces 43A when the sleeve 45 has been retracted upwards as shown in the left-hand part of FIG. 4, unlocking is provided for by cooperating inclined surfaces 45A and 43C bringing about a rocking motion of locking piece 43A, thereby displacing the lower end thereof to be disengaged from abutment 41A. 
     On the top surface of handling hub 49 there are shown ports or connectors 36B and 37B forming a significant part of the interface arrangement belonging to the removable or retrievable component 42 including the connector mechanism 43. For cooperation with ports or connectors 36B, 37B, the handling connector 16 of the ROT on mating surface is provided with corresponding ports or connectors 36A and 37A, for example in the form of stabs adapted to enter into respective ports in the handling hub 49. Whereas such handling hubs may have a different number and arrangement of such ports or connectors, depending on the requirements of the component concerned, the handling connector 16 must have a complete or full number and arrangement of such ports and connectors to enable it to interface the various components which it may be of interest to handle. 
     FIG. 5 shows the ROT as described above with respect to FIGS. 1, 2 and 3, having retracted component 60 by means of the elevator, completely within the supporting frame 1, for example in order to retrieve the component to the surface from a subsea station. Component 60 may be a retrievable valve insert as described in simultaneous U.S. patent application Ser. No. 07/684,941. The mating or common interface arrangements, as generally indicated at 55 in FIG. 5, in this case also comprises the central ROT handling connector 16 engaging a handling hub at the top of component 60, and coupling connector members 18A-C engaging coupling members or mandrels projecting upwards from an annular yoke similar to the one shown at 44 on FIG. 4. Further details with respect to component 60 in FIG. 5, will be described below with reference to FIG. 6. 
     For securing ccmponent 60 during transportation and retrieval to the surface by means of the ROT, there are provided supporting or clamping devices 90A and 90B mounted on the frame 1 and adapted to laterally engage and secure component 60 when suspended from the elevator. FIG. 8 shows more in detail an embodiment of such devices. Thus, in FIG. 8 one device 90A is shown as a whole, whereas device 90B is only partly includes in the drawing. The plan view of FIG. 8 schematically shows ccmponent 91 which is engaged by two clamping shoes 92A and 92B, preferably engaging component 91 from opposite sides. As indicated at 93 these shoes may have a resilient padding or cushion so as to avoid damage to component 91. Clamping shoe 92A is pivotably attached to a lever arm 94 being journalled at 95 and having an opposite end 96 connected to the piston rod of an actuator cylinder 97, thus providing for the necessary clamping movement cf shoe 92A against component 91. A supporting plate or frame 98 may be adjustably mounted within the ROT frame 1 to adapt the device to different component diameters. 
     Component 60 (FIG. 5) shall now be described somewhat more in detail referring to FIG. 6. Main parts of this component are valve insert 62 for a ball valve, connector means 63 for locking to a valve housing, and a valve actuator 64. The same main parts are illustrated and further described in the above simultaneous patent application. 
     Connector 63 is joined to valve insert 62 by bolts 67. A guide pin 69 is adapted to cooperate with a corresponding guide hole in the valve housing. The interface arrangement here is composed of handling hub 89 and three mandrels 68 spaced 120° around the periphery of an annular yoke 66, which is in turn being movable in a vertical direction in FIG. 6, in relation to handling hub 89. 
     A number of push-pull rods 81 have their upper ends connected to yoke 66 and are slidable in bores 80 to bring about lateral movement of locking pieces 84 having teeth or grooves in the external surface intended for engagement with correspondingly shaped locking means inside the valve housing into which the component or valve insert is to be mounted. In the position illustrated in FIG. 6, yoke 66 and therefore rod 81 has been pushed down and accordingly locking piece 84 assumes its locking position. This transformation of the axial or vertical movement of rod 81 to the lateral movement of locking piece 84 is brought about by interengaging inclined surfaces as indicated at 83 at the lower end portion 82 of rod 81 and at the inner side of locking piece 84 respectively. These inclined surfaces 83 may be in the form of a grooved profile enabling positive outward as well as inward displacement of locking piece 84. Thus, a pulling force applied to mandrels 68 from an ROT interface, moving push-pull rod 81 upwards, results in inward movement of locking piece 84 so that unlocking cf the component is obtained. 
     The connector means briefly described above is more fully covered by the simultaneous U.S. patent application Ser. No. 07/684,943. 
     At the top surface of handling hub 89 there are indicated ports or connectors 86, 87 which interface with mating ports or connectors arranged in a bottom surface of the ROT handling connector. 
     Turning now to FIG. 7, a further type of component 70 is schematically shown. This may be a control unit or control pod containing necessary parts and equipment for various control functions pertaining to a subsea station or subsea station module. This component, like the above described components, is provided with a handling hub 79 the axis of which is also a central axis of the complete component 70. To the left of axis AX there is shown a yoke member 77 with a connector mandrel 78B in a lower position, whereas at the right-hand side of axis there is shown a mandrel 78A in an upper position. It will be realized that mandrels 78A and 78B, as well as one or more additional mandrels in this interface arrangement, may all be constrained to move in unison by being mounted on the common yoke 77. Push-pull rod 76 is provided for transferring push-pull movements or forces into component 70, possibly for performing locking or unlocking thereof with respect to the subsea station.