Patent Application
20070181309
The present invention relates to a connector for securing a first generally cylindrical member, such as a production riser, to a second generally cylindrical member, such as a subsea wellhead. More particularly, the invention relates to a connector which comprises a locking mandrel that includes a stepped surface which engages a corresponding stepped surface on a lock ring to thereby force the lock ring into locking engagement with the second member.
Tieback connectors are commonly used to secure production risers to subsea wellheads. Since the production riser extends to a surface vessel which is located a considerable distance from the wellhead, the production riser is typically subjected to sizeable forces which give rise to substantial separation forces between the tieback connector and the wellhead. Thus, the tieback connector must be able to maintain a sealed connection to the wellhead in the presence of these separation forces. In the past, this was accomplished by making the locking mandrel and the lock ring sufficiently large to withstand the separation forces. However, this in turn required the overall diameter of the tieback connector to be relatively large, which is undesirable when working from certain types of surface vessels.
In accordance with the present invention, these and other limitations in the prior art are overcome by providing a connector for securing a first cylindrical member to a second cylindrical member, the connector comprising a cylindrical body which includes a first end that is attached to the first member and a second end that is positioned proximate the second member, a cylindrical housing sleeve which is positioned concentrically over the body and which includes an upper end portion that is secured to the body and a lower end portion that is disposed adjacent the second member, a cylindrical primary piston that is positioned between the body and the housing sleeve, a locking mandrel which is connected to or formed integrally with the primary piston and which includes at least first and second annular portions that have different diameters, and a split lock ring which is supported by the lower end portion adjacent a number of locking grooves in the second member and which includes at least first and second cylindrical portions that correspond to the first and second annular portions of the locking mandrel. In operation movement of the primary piston from a first position to a second position will force the first and second annular portions of the locking mandrel into engagement with the first and second cylindrical portions of the lock ring, respectively, and consequently force the lock ring into engagement with the locking grooves to thereby lock the connector to the second member.
Thus, when the connector is locked to the second member, the stepped interface between the locking mandrel and the lock ring provides two distinct bearing surfaces through which separation forces acting between the first and second members are transmitted. In addition, the provision of these two distinct bearing surfaces tends to distribute the separation forces more evenly among all the locking grooves compared to prior art designs. Consequently, for a given anticipated set of separation forces, the overall diameter of the connector can be reduced.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.
The slimline tieback connector of the present invention provides a simple yet effective means for remotely connecting two subsea hydrocarbon production members together. Although the slimline tieback connector can be used to connect any of a variety of subsea hydrocarbon production members, it is particularly useful for securing a first generally cylindrical member to a second generally cylindrical member in an end-to-end arrangement. For purposes of simplicity, however, the present invention will be described herein in the context of a connector for securing a production riser to a subsea welihead.
Referring to
The tieback connector 10 comprises a generally cylindrical body 30 and a flow bore 32 which extends generally axially through the body. The body 30 may be formed integrally with an end of the production riser 12 or attached thereto using any suitable means. In the illustrated embodiment of the invention, for example, the body 30 includes a top connection flange 34 which is attached to the bottom connection flange 20 by a number of conventional stud and nut assemblies 36. The body 30 is preferably also sealed to the production riser 12 using a suitable gasket 38 which is positioned between the top and bottom connection flanges 34, 20.
The body 30 also comprises a bottom end 40 and a frustoconical seal surface 42 which is formed in or adjacent the bottom end. When the body 30 is secured to the wellhead 14, a suitable seal, such as a conventional VX-type gasket 44, engages the seal surface 42 and a corresponding seal surface on the wellhead 14 to thereby form a pressure tight seal between the body 30 and the wellhead. Thus, when the tieback connector 10 is attached to the production riser 12 and then subsequently secured to the wellhead 14, the flow bore 32 in the body 30 will fluidly connect the production bore 18 in the production riser with the central bore 24 in the wellhead.
In accordance with one embodiment of the invention, the body 30 further comprises a radial flange portion 46 which is located below the top connection flange 34, a first reduced diameter portion 48 which is located below the flange portion, and a second reduced diameter portion 50 which is located below the first reduced diameter portion. In addition, a first shoulder 52 is formed between the flange portion 46 and the first reduced diameter portion 48, and a second shoulder 54 is formed between the first reduced diameter portion and the second reduced diameter portion 50.
Referring still to
Referring to
The tieback connector 10 also includes an optional ring-shaped secondary piston 84 which is located below the head portion 76, an annular seal sleeve 86 which is located below the secondary piston, and a lock ring 88 which is supported on the ledge 64. The secondary piston 84 is sealed to the body 30 with a third seal 90 and to the primary piston 72 by a fourth seal 92. In addition, the seal sleeve 86 is sealed to the body 30 by a fifth seal 94 and to the primary piston 72 by a sixth seal 96. As with the first and second seals 80, 82, the third through sixth seals 90 through 96 can be any suitable seals, such as non-metallic S-type face seals.
Referring still to
Referring to
In the unlocked condition of the tieback connector 10, which is shown in
Thus, in the locked condition of the tieback connector 10, the stepped interface between the locking mandrel 78 and the lock ring 88 provides two distinct bearing surfaces through which the separation forces acting on the tieback connector are transmitted. The first bearing surface is the interface between the first annular portion 130 of the locking mandrel 78 and the first cylindrical portion 122 of the lock ring 88. The second bearing surface is the interface between the second annular portion 132 of the locking mandrel 78 and the second cylindrical portion 124 of the lock ring 88.
The provision of these two distinct bearing surfaces provides the tieback connector 10 with a relatively high load bearing capability. The different diameters of the bearing surfaces, combined with the enhanced stiffness of the lower portion of the lock ring 88 due to its increased thickness, tends to distribute the separation forces more evenly among all the locking grooves. Consequently, for a given anticipated set of separation forces, the overall diameter of the tieback connector 10 can be reduced. This is particularly advantageous when the tieback connector 10 is intended to be used with a slimline production riser.
In accordance with one embodiment of the present invention, the primary piston 72 is actuated hydraulically to lock and unlock the tieback connector 10. Referring again to
Referring again to
In order to lock the tieback connector 10 to the wellhead 14, hydraulic fluid is supplied to the first piston chamber 138 to force the primary piston 72 downward into its lowered position. This in turn will move the locking mandrel 78 downward and thereby force the lock ring 88 into the locking grooves 28, as discussed above. In order to unlock the tieback connector 10 from the wellhead 14, hydraulic fluid is supplied to the second piston chamber 140 to force the primary piston 72 upward into its raised position. This in turn will raise the locking mandrel 78 and thereby allow the lock ring 88 to retract from the locking grooves 28.
In accordance with another embodiment of the present invention, the secondary piston 84 is actuated hydraulically to move the primary piston 72 from its lowered position to its raised position in order to unlock the tieback connector 10 in the event of a failure of the hydraulic circuit supplying the primary piston. Accordingly, the tieback connector 10 also comprises a third piston chamber 158 which is formed between the body 30 and the primary piston 72 by the third and fourth seals 90, 92 and the fifth and sixth seals 94, 96. Similar to the first and second piston chambers 138, 140, the third piston chamber 158 is fluidly connected to a port (not shown) which extends through the primary piston 72 to a third elongated nipple 160 that is connected to the source of hydraulic fluid. The third piston chamber 158 may also be fluidly connected to a corresponding compensation port in the primary piston 72 which in turn is connected to an accumulator by a respective nipple.
Thus, if under normal operation of the tieback connector 10 the primary piston 72 cannot be moved from its lowered position to its raised position, hydraulic fluid can be supplied to the third piston chamber 158 to move the secondary piston 84 upwards. As the secondary piston 84 rises, it will engage the head portion 76 of the primary piston 72 and push the primary piston into its raised position. In this position, the tieback connector 10 will be unlocked from the wellhead 14.
In accordance with yet another embodiment of the invention, the tieback connector 10 also includes mechanical means for moving the primary piston 72 from its lowered position to its raised position in the event of a failure of the hydraulic circuits supplying the primary and secondary pistons 72, 84. Referring to
Thus, as the release plate 162 is lifted, it will engage the lift nuts 170 and pull the lift rods 164 upwards. The lift rods 164 will in turn pull the primary piston 72 upwards into its raised position. In this regard, it should be noted that the lift rods 164 are sufficiently long to allow the primary piston 72 to move from its raised position to its lowered position without interference from the release plate 162. Also, the lift rods 164 and the lift nuts 170 will provide a visual indication of whether the primary piston 72 is in its raised or lowered position.
In operation, the tieback connector 10 is attached to an end of the production riser 12 at a surface facility, such as a floating production vessel, and then lowered on the production riser toward the subsea wellhead 14. Once the tieback connector 10 is landed on the wellhead 14, the primary piston 72 is actuated to lock the tieback connector to the wellhead. When it is desired to disconnect the production riser 12 from the wellhead 14, the primary piston is again actuated to unlock the tieback connector 10 from the wellhead. In the event of a failure of the hydraulic circuit supplying the primary piston 72, the tieback connector 10 can be unlocked from the wellhead 14 by either actuating the secondary piston 84 or lifting the release plate 162.
It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.
