Abstract:
A connector for connecting sections of drilling riser pipe wherein a first riser contains a pin assembly with an external first grooved profile and a second riser contains a housing assembly. An internal split pivoting latch segment assembly carried by the housing assembly contains a second grooved profile adapted to mate to the first grooved profile and a split actuation ring movably carried by the housing assembly forces the second grooved profile of the latch segment assembly into engagement with the first grooved profile of the pin assembly. A plurality of retraction links engage an upper edge of the latch segment assembly to disengage the second grooved profile of the latch segment assembly from the first grooved profile of the pin assembly if the risers are to be disconnected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to provisional application 60/801,667, filed May 19, 2006. 

   FIELD OF THE INVENTION 
   This invention relates in general to high pressure riser systems with surface or near surface blowout preventers and more particularly to a high strength, high preload, rapid makeup connector for such riser systems. 
   DESCRIPTION OF THE PRIOR ART 
   A drilling riser is a large diameter pipe used in offshore drilling operations to guide the drill string from the offshore platform to and from the subsea wellhead and to provide means for circulation of drilling fluid. The drill string is lowered through the drilling riser. Drilling fluid circulates down from the platform through the drill string, out through the drill bit, and returns to the platform in the space between the inner diameter of the riser and outer diameter of the drill string. Environmental forces caused by waves, currents and the movement of the offshore platform as well as internal forces caused by the weight of the heavy drilling fluids all contribute to the substantial loads applied to the drilling riser. Additionally, high pressure drilling risers, utilizing surface blowout preventors, may be exposed to fill well bore pressure. The connection between each successive joint of drilling riser must be able to withstand such loads. 
   The prior art makes up the riser pipe or joint connections with bolted flange type connectors or with radially oriented screws that move dogs into and out of engagement with a profile on the riser pipe. Both of these methods require manipulation with a wrench or stud tensioning device, placing personnel in close proximity to the drilling slots for prolonged periods of time, and increasing the danger level of performing the task. 
   Normally, these connectors and the riser pipe need withstand only fairly low pressure, such as 2000 psi, because the blowout preventer is located subsea on top of the wellhead assembly. A recent approach is to mount the blowout preventer on the vessel and make the riser of sufficient strength to handle much higher internal pressure, such as 10,000 psi. The connection between the individual riser pipes must be able to withstand this high pressure. 
   Improvements to this prior art are desired which would allow for the connection between the riser pipes to be made rapidly and more safely, while at the same time generating high preload, able to withstand significant design separation loads. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a device for connecting risers which can withstand high pressure and provides both a high strength and low fatigue connection, such as drilling risers or completion risers. A connector having the features of the present invention would generally be used for riser systems that utilize a surface blowout preventer, but is also suitable for use on risers using subsea blowout preventors. 
   The connector of the present invention comprises a pin assembly that is attached to the end of a first riser pipe and a housing assembly that is attached to the end of a second riser pipe that is to be connected with the first riser pipe. The housing assembly contains an internal split pivoting latch segment assembly. One end of each latch segment contains a grooved profile that mates with a corresponding external profile on the pin assembly. The other end of the latch assembly engages an internal shoulder of the housing assembly The housing assembly has a sufficiently large cavity to allow the latch segments to pivot between the open and engaged positions. 
   In order to secure the first riser pipe to the second riser pipe, a split actuation ring is repositioned inside the cavity of the housing assembly, forcing the profile of latch segment into engagement with the profile of the pin assembly by rotating the latch segments. The actuation ring is positioned by a series of load transfer blocks that are moved axially by a drive sleeve, which resides on the outside of the housing assembly. Alternatively, the load transfer blocks may directly act on the latch segments. The load transfer blocks travel in slots or windows that are milled into the housing assembly. Split actuation ring retainers hold the actuation ring in place. Retaining screws attach both the actuation ring retainer and actuation ring to the load transfer block. The drive sleeve may be controlled by an actuation device built in to a riser spider system. Seals and gaskets of the connector prevent leakage of fluid between the interior of the riser and the surrounding environment, the entry of sea water into the connector, and prevent high pressure bore fluid from passing into the cavity within the housing assembly. 
   A retraction link is carried on the box, which rotates about a curved surface within the housing assembly and, contains a lip which engages an upper edge of latch segment. In order to release the first riser pipe from the second riser pipe, the actuation ring is repositioned by the load transfer blocks that are moved by a drive sleeve. When the split actuation actuation ring retainer makes contact with the retraction link, the retraction link rotates and engages the edge of the latch segment, moving the latch segment into the open position. As a result, the profile of the latch segment disengages from the profile of the pin. In an alternative configuration, the load transfer blocks directly engage the retraction link. 
   The connection is compressively preloaded by providing a relatively shallow load flank angle to the profile of the latch segment and to the corresponding profile of the pin. The magnitude of preloading should be sufficient such that if the maximum projected tensile load is applied to the first and second riser joint, the faces of the connecting parts do not separate from the gasket. The preload would thus he sufficient to maintain a sealed connection under expected working loads of the joint sections. 
   One embodiment of the present invention may also include an automatic connector actuation lock. This actuation lock ensures that the drive sleeve does not move unexpectedly during operations and can lock the drive sleeve in both the open or engaged position. In particular, the actuation lock will ensure that the drive sleeve remains in open position while bringing the riser joints together and in the engaged position during working conditions. The actuation lock is composed of two concentric split rings, a smaller diameter ratchet ring and a larger diameter back-up ring, both located within a cavity in the drive sleeve. The ratchet ring has a thread profile on its inner diameter that corresponds to a thread profile on the outside diameter of the housing assembly. The ratchet ring has a profile on its outer diameter that corresponds to a profile on the inner diameter of the back-up ring. When the spider engages the riser pipe, a handling tool engages the drive sleeve and depresses a series of radial pins in the drive sleeve, which force the back-up ring to reduce in diameter and to move upward. This in turn provides clearance for the ratchet ring to expand and move axially over the threads of the outer diameter on the housing assembly. When the spider is disengaged, the radial pins retract, the back-up ring returns to its larger diameter, and the ratchet ring is unable to move axially, thereby locking the sleeve in place. 
   The benefits of this connector over the prior art is that this connector is designed for rapid make-up while at the same time generating high preload which is able to withstand significant design separation loads. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view illustrating a riser constructed in accordance with this invention. 
       FIG. 2  is a sectional view of a connection system for a riser joint with a latch segment in the open position. 
       FIG. 3  is a sectional view of the connection system of  FIG. 1  with the latch segment in the closed position. 
       FIG. 4  is a schematic view illustrating a riser constructed in accordance with this invention, including the actuation lock. 
       FIG. 5  is a schematic view illustrating the actuation lock in the open position. 
       FIG. 6  is a schematic view illustrating the actuation lock in the locked position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a riser  11  is schematically shown extending from a floating platform  13 . Platform  13  is illustrated schematically and can be any type, such as a spar, tension leg platform, mobile offshore drilling unit, or the like. Riser  11  is a drilling riser used to drill offshore wells and is particularly for use in applications where the blowout preventer is located at the surface. The drilling riser may be submerged for several years at a time, such as for use on a spar platform. The drilling riser may also be recovered after drilling each well, such as on a tension leg platform. 
   Riser  11  is made up of a plurality of high pressure riser joints  15 , each approximately 60 feet in length. A blowout preventer  17  is shown schematically at the upper end of riser  11 . A subsea tieback assembly  19  is shown schematically at the lower end of riser  11  although blowout preventer  17  can also be at the lower end. Locating blowout preventer  17  at the platform or near the surface has significant advantages but in such a case riser  11  has to be able to withstand high internal pressure. Subsea tieback assembly  19  may incorporate a quick disconnect mechanism as well as a hydraulic connector on its lower end that connects it to a subsea wellhead assembly. Subsea tieback assembly  19  is not normally equipped to seal around drill pipe. 
   Referring to  FIG. 2 , a first high pressure drilling riser joint  21  is fitted with a housing assembly  23 , referred to as a box, and a second high pressure drilling riser joint  25  is fitted with a pin assembly  27 . Box  23  slides over pin  27 . Box  23  contains an internal split pivoting latch segment assembly. Preferably the latch ring assembly combines a plurality of separate segments  29 , for example twelve, spaced around box  23 . One end of each latch segment  29  contains a grooved profile  31  that mates with a corresponding profile  33  on pin assembly  27 . Profiles  31  and  33  may have a saw tooth pattern or an alternative pattern. A second end  35  of latch segment  29  engages a shoulder  37  of box  23 . Second end  35  is a curved, convex surface and shoulder  37  is a curved concave shoulder. This arrangement allows latch segment  29  to rock between the open position of  FIG. 2  and the engaged position of  FIG. 3 . 
   Turning to  FIG. 3 , in order to secure riser  21  to riser  25 , a split actuation ring  41  is repositioned inside cavity  39  of box  23 , forcing profile  31  of latch segment  29  into engagement with profile  33  of pin  27  by rotating latch segment  29  about end  35 . Actuation ring  41  has a curved convex inner side that slides along the convex outer surface of latch segment  29  as can be seen by comparing  FIGS. 2 and 3 . Actuation ring  41  may be fabricated in multiple segments that are then mated to create a full ring around the inner concave surface of cavity  39 . The curvature of the convex inner surface of actuation ring  41  and the curvature of convex outer surface of latch segment  29  are such that as actuation ring  41  slides along the outer surface of latch segment  29 , contact between the convex inner surface of actuation ring  41  and the convex outer surface of latch segment  29  is maintained. As latch segment  29  rotates about end  35 , the relative angle between the outer surface of latch segment  29  and the inner surface of actuation ring  41  will change. The design of the curvature of both the inner surface of actuation ring  41  and outer surface of latch segment  29  must take this relative change into account to allow the surfaces to remain in contact. 
   Actuation ring  41  moves axially between the upper unlocked position of  FIG. 2  and the lower locked position of  FIG. 3 . In this embodiment, actuation ring  41  is moved vertically by a series of load transfer blocks  43  that are moved axially by a drive sleeve  47 , which resides on the outside of box  23 . Drive sleeve  47  forms a complete ring around box  23 , with the inner cylindrical surface of drive sleeve  47  matching the outer cylindrical surface of box  23 . The number of load transfer blocks  43  corresponds to the number of latch segments  29  in this embodiment. The load transfer blocks  43  travel in slots or windows  44  that are milled into box  23 . Actuation ring retainer  55  secures actuation ring  41  to load transfer block  43 . Actuation ring retainer  55  is a split ring. A retaining screw  53  attaches actuation ring retainer  55  and the actuation ring  41  to each load transfer block  43 . In an alternate configuration, transfer blocks  43  directly engage latch segments  29 , and there is no need for the actuating ring or retainer. The drive sleeve  47  may be moved axially by an actuation device  85  built in to a riser spider system such as spider system  80  shown in  FIG. 4 . Spider system  80  is mounted on platform  13  and moves horizontally towards riser pipe  25  until upward facing surface  75  of vertical member  77  of spider system  80  is positioned such that it can support downward facing surface  79  of pin assembly  27 . A handling tool has piston assembly  83  which is supported by spider system  80 , and threaded adapter  87 , which is located on top of piston assembly  83 . Threaded adapter  87  contains actuation devise  85  which engages drive sleeve  47  and moves drive sleeve  47  axially by the action of piston assembly  83 . 
   Returning to  FIG. 3 , when connected, conical seal face  48  of joint  21  and seal face  49  of joint  25  are pressed against either side of gasket  51 . Gasket  51  prevents leakage of fluid between the interior of the riser and the surrounding environment. Seals  54  and  56  between box  23  and pin  27  seal cavity  39  against the entry of sea water. Seals  52 ,  54  additionally prevent high pressure bore fluid from passing into cavity  39 . Seals  58  and  60  between drive sleeve  47  and box  23  prevent the entry of sea water into seal cavity  39  via the space between drive sleeve  47  and box  23 . Box  23  contains a port  62  for testing seals  52  and  54 , and for allowing leakage of high pressure bore fluids to vent before passing into cavity  39 . 
   A plurality of retraction segments or links  45  are carried on pin  27  above profile  33 . Each retraction link  45  has an upward facing curved concave surface which engages a curved convex surface  46  depending from box  23 . This engagement allows retraction link  45  to pivot about the curved convex surface  46  of box  23 . A lower side of retraction link  45  contains a lip  50  which engages an upper edge of latch segment  29 . Actuation ring retainer  55  has a convex curved surface that engages the concave outer surface of each retraction link  45 . 
   Referring again to  FIG. 2 , in order to release the first riser  21  from second riser pipe  25 , actuation ring  41  is moved to the lower position by the load transfer blocks  43  that are moved axially by a drive sleeve  47 . When actuation ring retainer  55  makes contact with retraction link  45 , it causes retraction link  45  to rotate or pivot about convex surface  46 . Lip  50  engages the upper edge of latch segment  29 , pivoting latch segment  29  into the open position. As a result, profile  31  of latch segment  29  disengages from profile  33  of pin  27 . Box  23  contains a sufficiently large cavity  39  to allow latch segment  29  to pivot into the open position and fully disengage from pin  27 . In an alternative configuration, load transfer blocks  43  contact actuation rings  55  directly. 
   The curvature of the convex surface of actuation ring retainer  55  and the curvature of concave outer surface of retraction link  45  are such that as actuation ring retainer  55  slides along the outer surface of retraction link  45 , contact between the surfaces is maintained. As retraction link  45  rocks or pivots about convex surface  46 , the relative angle between the convex surface of actuation ring retainer  55  and the curvature of concave outer surface of retraction link  45  will change. The design of the curvature of both the convex surface of actuation ring retainer  55  and concave outer surface of retraction link  45  must take this relative change into account to allow the surfaces to remain in contact. 
   The connection is compressively preloaded by providing a relatively shallow load flank angle to profile  31  of latch segment  29  and to the corresponding profile  33  of pin  27 . The magnitude of preloading should be sufficient such that if the maximum projected tensile load is applied to riser joint  21  and  25 , face  48  of joint  21  and face  49  of joint  25  do not separate from gasket  51 . The preload would thus be sufficient to maintain the contact between faces  48  and  49  and gasket  51  under expected working loads of the joint sections. The preloading forces are transmitted from joint  21  through box  23  and transferred to pin assembly  27  of joint  25  via the profiles  31  and  33 . 
   In operation, when making up riser  11  for lowering into the sea, the operator makes sure that latch segment  29  is in the open position as shown in  FIG. 2 . The operator lowers a first riser joint  25  with the end of riser joint  25  containing pin assembly  27  pointed upwards and holds this riser joint in place with the riser spider system of platform  13 . The operator then lowers a second riser joint  21 , with box  23  pointed downward, landing box  23  of riser  21  over the pin assembly  27  of riser joint  25 . The operator then actuates drive sleeve  47  by an actuation device built into the riser spider of platform  13 , which moves load transfer blocks  43  downward, which in turn repositions actuation ring  41 , forcing profile  31  of latch segment  29  into engagement with profile  33  of pin  27 . When the operator is ready to install the next riser joint, he repeats this cycle. The operator can break out the riser joint of riser  11  by reversing the procedure. 
   Turning to  FIG. 4 , one embodiment of the present invention may also include an automatic connector actuation lock  64 . Actuation lock  64  ensures that drive sleeve  47  does not move unexpectedly during operations. Actuation lock  64  can lock drive sleeve  47  in both the open or engaged position. In particular, the actuation lock will ensure that drive sleeve  47  remains in the engaged position during working conditions, and the open position while bringing the joints together during installation. 
   Actuation lock  64  is composed of two concentric split rings, comprising a smaller diameter ratchet ring  66  and a larger diameter back-up ring  68 , both located within cavity  70  in drive sleeve  47 , as can be seen in  FIG. 5 . A threaded ring  71  secures to drive ring  47  to define the upper end of cavity  70 . Ratchet ring  66  has a groove profile  72  on its inner diameter that corresponds to groove profile  74  on the outside diameter of box  23 . Ratchet ring  66  is biased inward to engage profile  74 . Ratchet ring  66  has groove profile  76  on its outer diameter that corresponds to groove profile  78  on the inner diameter of back-up ring  68 . Back-up ring  68  is outwardly biased. 
   When riser actuation device  85  engages drive sleeve  47  ( FIG. 4 ), engagement member  81  of threaded adapter  87  engages peg member  89  of threaded adapter  87  depresses a plurality of pins  82  spaced radially around and carried on drive sleeve  47 , which force back-up ring  68  to reduce in diameter. Cavity  70  of drive sleeve  47  has a downward sloping shoulder  84  which remains in contact with the upward sloping surface  86  of back-up ring  68  such that as back-up ring  68  reduces in diameter, it also moves upward along downward facing shoulder  84 . The upward movement of back-up ring  68  aligns outer profile  76  with profile  78  on the inner diameter of back-up ring  68  such that the upward facing flanks  88  of profile  76  of ratchet ring  66  do not interfere with the downward facing flanks  90  of profile  78  of back-up ring  68 . This alignment of profiles  76  and  78  allows ratchet ring  68  to expand and contract and move axially over threads  74  of the outer diameter of box  23  as drive sleeve  47  is moved either upwards or downwards. 
   Groove profile  72  on ratchet ring  66  engages groove profile  74  on the outside diameter of box  23  when drive sleeve  47  is in the locked position ( FIG. 6 ). When drive sleeve  47  is in the unlocked position ( FIG. 5 ), groove profile  72  on ratchet ring  66  engages a profile  92  ( FIG. 4 ) on the outside diameter of box  23  spaced above profile  72 . While engaging profile  92 , ratchet ring  66  holds drive sleeve  47  in the unlocked position. 
   When threaded adapter  87  is removed, turning now to  FIG. 6 , pins  82  retract from cavity  70  causing back-up ring  68  to expand and take on a larger diameter. As back-up ring  68  moves outward, downward sloping shoulder  84  of cavity  70  remains in contact with the upward sloping surface  86  of back-up ring  68 , forcing back-up ring  68  to move downward. When back-up ring  68  is in the outer and lower position, face  94  of profile  78  lines up with face  96  of profile  76  and ratchet ring  66  is unable to expand. As a result, profile  74  of box  23  engages profile  72  of ratchet ring  66  and ratchet ring  66  unable to move axially, locking drive sleeve  47  in place. 
   The invention has significant advantages. The coupling provides a high preload which is necessary for long, high pressure riser strings. The coupling can be quickly made-up and broken out with an automated handling tool. Personnel are not placed in exposed positions while the riser is being made-up or broken out. The assembly and retrieval of a riser is less time consuming than in the prior art. 
   The present invention has been described with reference to several embodiments thereof. Those skilled in the art will appreciate that the invention is thus not limited, but is susceptible to variation and modification without departure from the scope and spirit thereof For example, box  23  and pin  27  could be connected with the pin facing upward or downward. The lock could be used with connectors other than one using a pivoting latch assembly.