Abstract:
A tendon or riser connector has a separate lock-down device that overrides the connector&#39;s ability to unlock if the riser or tendon goes slack. The locking device has blocks that are radially actuated through a hole in a receptacle to engage a profile in the connector. When the blocks are pushed in, they prevent the connector from moving downward, and thus prevent any unlocking of the connector. The blocks are secured with pivotable gates that engage and retain the blocks in both positions.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates in general to tendon or riser mooring connectors and, in particular, to an improved system, method, and apparatus for locking down a tendon or riser mooring. 
   2. Description of the Related Art 
   In the prior art, one type of tendon or riser mooring connector for platforms typically operates with vertical motion only. At the sea floor, the connector is lowered a short distance into a receptacle mounted to the sea floor, lifted vertically, and locks into a profile in the receptacle. If lowered a longer distance into the receptacle, such as when the riser or tendon goes slack, an unlocking mechanism allows the connector to release from the receptacle. Under extreme operating conditions, such as hurricanes, the connector can be accidentally unlocked due to motion of the platform at the surface and severely jeopardize the safety of personnel and equipment. Thus, an improved solution for securing the connections between tendon or riser moorings and receptacles would be desirable. 
   SUMMARY OF THE INVENTION 
   One embodiment of a system, method, and apparatus for locking down a tendon or riser mooring incorporates a separate lock-down device that overrides the connector&#39;s ability to unlock if the riser or tendon goes slack. The locking device is carried on the outside of the receptacle or on a separate sleeve. It comprises one or more pins or blocks that are radially actuated by a diver, remotely-operated vehicle (ROV), a hydraulic drive mechanism, or the like, and extends through a hole in the receptacle. A profile on the end of the block interfaces with a mating turned profile on the guide sleeve below the mooring connector. When the block is pushed in, it prevents the connector from moving downward, and thus prevents any unlocking of the connector. 
   In one embodiment, the block is located inside a box and is restrained in the inward or locked and outward or unlocked positions by one or more locating pins. The locating pin is inserted into the block vertically. In another embodiment, the block is carried in a cradle on the exterior of the receptacle or a separate sleeve. To lock the device, the diver or ROV lifts the block out of the cradle and places it into the hole in the receptacle and pushes it into engagement with a grooved guide on the mooring connector. To prevent accidental loss of the block or locating pin, they may be attached to the receptacle or sleeve by a cable or chain. Alternatively, a pivotable gate may be used to engage and retain the block in either position via a lock down groove in the guide sleeve. 
   The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
       FIG. 1  is a sectional side view of one embodiment of a bottom mooring and is constructed in accordance with the present invention; 
       FIG. 2  is an isometric view of one embodiment of a sleeve for the bottom mooring of  FIG. 1  and is constructed in accordance with the present invention; 
       FIG. 3  is a side view of one embodiment of a receptacle for the bottom mooring of  FIG. 1  and is constructed in accordance with the present invention; 
       FIG. 4  is an isometric view of one embodiment of a radially-movable member for the bottom mooring of  FIG. 1  and is constructed in accordance with the present invention; 
       FIGS. 5   a  and  5   b  are isometric views of one embodiment of securing means for the radially-movable member of  FIGS. 4 and 6 , showing engaged and disengaged positions, respectively, and is constructed in accordance with the present invention; 
       FIG. 6  is a sectional side view of the securing means of  FIG. 5   a  in the engaged position and is constructed in accordance with the present invention; 
       FIGS. 7   a  and  7   b  are isometric views of another embodiment of securing means for the radially-movable member of  FIGS. 4 and 6 , showing engaged and disengaged positions, respectively, and is constructed in accordance with the present invention; and 
       FIG. 8  is a high level flow diagram of one embodiment of a method constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1-3 , one embodiment of a system, method, and apparatus for securing a mooring connection for a tendon or riser is disclosed. A mooring receptacle  11  is located on the sea floor  13  and has an interior locking profile  15 . A bottom connector  17  has a tubular member  18  (e.g., a tendon or riser) extending therefrom to a platform at a sea surface (not shown). The bottom connector  17  is secured to the interior profile  15  in the receptacle  11 . 
   In the embodiment shown, the bottom connector  17  may be connected to and disconnected from the receptacle  11  strictly via vertical motion. In this way, the bottom connector  17  locks into the receptacle  11  by being lowered into the receptacle for a limited distance, past a locked position, but not enough to engage an unlocked position, and then raised back up to the locked position. The bottom connector  17  is unlocked from the receptacle  11  by being lowered beyond the locked position to the unlocked position, after which the bottom connector  17  may be removed from the receptacle  11 . An optional sleeve  19  (e.g., anode sleeve) may be lowered onto and secured to an exterior of the receptacle  11  to provide cathodic protection for the installation. 
   The invention also comprises securing means  21  for preventing the bottom connector  17  from being lowered to the unlocked position and so that it cannot be unlocked from the receptacle  11 . In one embodiment, the securing means  21  is separate and spaced apart from the bottom connector  17 . The securing means  21  may be mounted to an exterior of the receptacle  11 , or anode sleeve  19  (if present). In this disclosure, the phrase “exterior to the receptacle” or “exterior surface of the receptacle” may include the exterior or exterior surface of the optional sleeve  19 , if present. The securing means  21  extends radially through holes  24 ,  26  ( FIG. 6 ) in the anode sleeve  19  and the receptacle  11 , respectively, into engagement with the bottom connector  17 . 
   In the embodiment shown, the securing means  21  comprises a plurality of radially movable members  23  ( FIG. 4 ) having an engaged position ( FIGS. 1 ,  2 , and  5   a ) wherein the radially movable members  23  restrain the bottom connector  17  from vertical motion relative to the receptacle  11 . The radially movable members  23  also have a disengaged position ( FIG. 5   b ) wherein the radially movable members  23  permit vertical motion of the bottom connector  17  relative to the receptacle  11 . The radially movable members  23  may be independently actuated by a device such as a diver, remotely-operated vehicle (ROV), or a hydraulic drive mechanism. 
   In one embodiment, each of the radially movable members  23  comprises a block  25  ( FIGS. 4 and 6 ) having a profile  27  that extends through hole  26  in the receptacle  11 . The profile  27  on the block  25  interfaces with a mating profile  29  on the bottom connector  17  and, in the engaged position ( FIGS. 1 ,  2 , and  5   a ), prevents the bottom connector  17  from moving downward to prevent unlocking of the bottom connector  17  relative to the receptacle  11 . In the embodiment shown, each block  25  is located inside a box  31  mounted exterior to the receptacle  11  (or, e.g., on the sleeve  19 ). The blocks  25  are restrained from removal from the boxes  31  in both the engaged and disengaged positions by, for example, locating pins  33  ( FIGS. 7   a  and  7   b ). The locating pins  33  may be attached to the receptacle via chains or cables. The locating pins  33  may be independently actuated as described above for radially movable members  23 . 
   Alternatively ( FIGS. 5   a  and  5   b ), a pivotable gate  41  is mounted exterior to the receptacle  11  (or, e.g., sleeve  19 ) for each radially movable member  23  (e.g., block  25 ). The pivotable gates  41  selectively retain the radially movable members  23  in both the engaged and disengaged positions via a pair of spaced-part grooves  43 ,  45 , respectively ( FIG. 5   b ), by engaging the pivotable gates  41 . For illustration purposes in  FIG. 5   b , the gate  41  is shown in a lifted position, but readily seats in groove  45  to retain block  25  in the disengaged position. In one embodiment, a pivotable redundant pin  47  may be used for each of the pivotable gates  41  for engaging and securing the pivotable gates  41  in both the engaged and disengaged positions of block  25 . The redundant pins  47  seat in notches formed in the gates  41  for positive retention thereof. Redundant pins  47  provide an additional level of security to maintain the gates  41  engaged with blocks  25  in both the engaged and disengaged positions. The pivotable gates  41  and redundant pins  47  may be independently actuated as described above for radially movable members  23 . 
   In one embodiment ( FIG. 4 ), each block  25  has an elliptical body  51  that is complementary to the elliptical hole  26  ( FIG. 3 ) in the receptacle  11 . The block profile  27  comprises a radial tooth having a downward-sloping upper surface  53  (e.g., approximately 3°) and an upward sloping lower surface  55  (e.g., approximately 45°) that exceeds an angle of inclination of the downward-sloping upper surface  53 . Again, the shape of block profile  27  is complementary to mating profile  29  ( FIG. 6 ) in bottom connector  17 . 
   In one embodiment, a sufficient gap  54  ( FIG. 5   b ) between block  25  and box  31  is incorporated to allow adjustment for vertical and lateral mismatch between the assembly of block  25 , box  31 , and the hole  26 . A sufficient vertical gap between profile  53  and profile  29  is provided for vertical mismatch between block  25 /box  31  and connector  17 . 
   A key  61  ( FIG. 3 ) may be formed on and extend radially from an exterior surface of the receptacle  11 . A stripe  63  (e.g., painted) may be formed on the exterior surface of the receptacle  11  and extend vertically downward from the key  61 . An aperture  65  ( FIG. 2 ) formed in the sleeve  19  has a guide member  67  for receiving the key  61  to assist in rotationally aligning the sleeve  19  relative to the receptacle  11 . The stripe  63  facilitates rotational alignment with the aperture  65  by being visible below the sleeve  19  as the sleeve  19  is lowered onto the receptacle  11 . In this way, the stripe  63  provides visual reference to position the key  61  in the guide member  67  of the aperture  65 . 
   Referring now to  FIG. 8 , one embodiment of a method of securing a mooring connection according to the invention is shown. The method begins as indicated at step  101 , and may comprise providing a receptacle on a sea floor and a bottom connector having a tubular member (step  103 ); lowering the bottom connector into the receptacle such that the bottom connector connects to the receptacle in a locked position via vertical motion (step  105 ); unlocking the bottom connector from the receptacle by lowering the bottom connector beyond the locked position to an unlocked position (step  107 ); securing the bottom connector to the receptacle in the locked position by preventing the bottom connector from being lowered to the unlocked position of the previous step and unlocking from the receptacle (step  109 ); before ending as indicated at step  111 . 
   One embodiment of the method also may comprise providing the tubular member of the bottom connector as one of a tendon and a riser. Step  109  may comprise extending radial members through the receptacle into engagement with the bottom connector, and/or moving the radial members to an engaged position that restrains the bottom connector from vertical motion relative to the receptacle; while further comprising moving the radial members to a disengaged position that permits vertical motion of the bottom connector relative to the receptacle in step  107 . 
   The method may further comprise independently actuating the radial members with a device selected from the group consisting of a diver, remotely-operated vehicle (ROV), and a hydraulic drive mechanism. In another embodiment, the radial members comprise blocks having profiles, and extending the profiles through holes in the receptacle, such that the profiles on the blocks interface with mating profiles on the bottom connector that, in the engaged position, prevent the bottom connector from moving downward to prevent unlocking of the bottom connector relative to the receptacle. 
   The method may still further comprise mounting the blocks in boxes mounted exterior to the receptacle, and restraining the blocks from removal from the boxes in both the engaged and disengaged positions by locating pins that are attached to the receptacle; and/or using a pivotable gate mounted exterior to the receptacle for each radial member to selectively retain the radial members in both the engaged and disengaged positions; and/or using redundant pins on the pivotable gates for engaging and securing the pivotable gates in both the engaged and disengaged positions. 
   In addition, the method may further comprise positioning a sleeve on an exterior of the receptacle, and providing a key extending radially from an exterior surface of the receptacle and a stripe on the exterior surface of the receptacle and extending vertically downward from the key, forming an aperture in the sleeve and having a guide member for receiving the key and rotationally aligning the sleeve relative to the receptacle, facilitating rotational alignment with the stripe as the aperture is visible below the sleeve when the sleeve is lowered onto the receptacle, and the stripe providing visual reference to position the key in the guide member of the aperture. 
   While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.