GB2315530A

GB2315530A - Mechanical riser pin and box coupling and method

Info

Publication number: GB2315530A
Application number: GB9715658A
Authority: GB
Inventors: Bryce A Levett
Original assignee: Varco Shaffer Inc
Current assignee: Varco LP
Priority date: 1996-07-25
Filing date: 1997-07-24
Publication date: 1998-02-04
Also published as: BR9704078A; GB9715658D0

Abstract

The coupling 10 is provided with an external annular pin shoulder 45 that engages the annular end 44 of the box 12 when the coupling is initially engaged. The coupling 10 is suitable for tubular riser sections extending from a drilling structure above the water surface to the seabed. Dogs 22 carried on the box 12 are adjusted radially to engage and lock the box to the pin. Tapered bearing surfaces - formed on the dogs 22 and on the pin 11 engage and force the pin and box together as the dogs are adjusted radially. Engagement of the box 12 and external pin shoulder 45 stops movement of the pin and box toward each other so that continued adjustment of the dogs 22 provides an increasing pre-load bearing pressure between the pin and box. Full engagement of the box end 44 and the pin shoulder 45 permit the application of large pre-loading force, prevent the dogs from distorting the box, protect the overlap area between the pin and box from contamination and provide positive visual confirmation of shoulder engagement.

Description

DESCRIPTION OF INVENTION MEa1ANICAL RISER COUPLING AND METhOD Field of the Invention The present invention relates generally to the interconnection of tubular bodies. More specifically, rhe present invention relates to a coupling and method for connecting together segments of a tubular nser conduit used in the drilling of offshore oil and gas wells.

Backeround of the Invention Marine riser pipes are used to connect a wellbore drilled in the earth below a body of water to tbe drilling structure positioned above the water surface. The distance from the water bottom to the drilling structure may be significant, and often exceed 100 meters. Typically, the riser pipe is formed from a number of segments that are coupled at their ends to form a continuous string that extends from the water bottom to the drilling structure. Riser pipes in this environment are subjected to very large cyclical axial and lateral forces imposed by the pipe weight. water currents.

wave action, platform or drill ship movement, and other causes.

The cyclical action of the forces acting on the riser pipe tend to promote leakage, metal fatigue failure, and mechanical disconnection. The effects of these forces are offset to a degrec by connecting the riser pipe segments together with connectors that are secured to each other with very large holding forces. The effects of tensile forces tending to separate the segments at the connectors are reduced by preloading the connectors to clamp them together with an axial force that exceeds anticipated separating forces causcd by the string weight and external forces acting on the string.

In one prior art device, this pre-loading of force on the connectors is accomplished with the use of locking dogs that extend from the box into the pin of the riser. Tlle dogs are equipped with tapered bearing surfaces that draw the pin and box together as the dogs are adjusted radially. An internal shoulder within the box engages the pin end to limit the travel of the pin into the box. Adjustment of the locking dogs forces the pin end against the internal box shoulder to provide the desired preloading of the connection. An elastomeric O-ring seal disposed between the pin and box adjacent the pin end is employed to provide a leak-proof seal for the connection. A second Wring seal is provided near the box end to prevent contaminants from entering the seal area from outside the riser pipe. Riser connectors using dogs are sold by Vetco Gray under the MR-6C and MR-6D designations.

One of the shortcomings associated with the described prior art connector is that the large axial preload forces imposed by the dogs cause the box to be distorted.

The distortion and resulting stress concentration in the box contribute to the possibility of leakage and mechanical failure of the connector.

It has been proposed to correct the above-descnbed problem by increasing the dimensions and strength of the box and incrcasing the circumferential dimensions of the locking dogs. This proposed design. while minimizing the distortion in the box when the riser is subject to large axial loads, does not eliminate the problem.

Moreover, the increased dimensions of the "beefed-up" connection increase both the cost and the weight of the connection.

The present invention seeks to provide an improved mechanical riser coupling which is capable of reliably handling large axial forces imposed on a connection without resulting leakage or failure of the connection.

According to one aspect of this invention there is provided a coupling connection for interconnecting two tubular bodies, comprising a pin connection and a box connection carried respectively by the tubular bodies and being adapted to be placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, the overlap region of the pin connection including a pin end surface and a pin external tapered bearing surface, the box connection including a stop surface thereon, a locking dog mechanism carried by and axially fixed relative to the box connection and radially movable into engagement with the pin connection for interconnecting the pin connection and the box connection, a dog tapered bearing surface on the locking dog mechanism for engagement with the pin tapered bearing surface whereby radial movement of the locking dog mechanism causes the dog tapered bearing surface to ride against the pin tapered bearing surface and force the pin connection and the box connection axially toward each other, and an external shoulder on the pin connection for engagement with the stop surface on the box connection to limit axial movement of the pin connection toward the box connection and thereby axially preload the coupling connection when the dog tapered bearing surface rides against the pin tapered bearing surface.

According to another aspect of this invention there is provided a coupling connection for interconnecting tubular bodies, comprising a pin connection and a box connection carried respectively by the tubular bodies and being adapted to be placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, the overlap region of the pin connection including a pin end surface and a pin external tapered bearing surface, the box connection including a stop surface thereon, a plurality of locking dog mechanisms circumferentially spaced about the box connection, each of the plurality of locking dog mechanisms being carried by and axially fixed relative to the box connection and radially movable into engagement with the pin connection for interconnecting the pin connection and the box, a dog tapered bearing surface on each of the plurality of the locking dog mechanisms for engagement with the pin tapered bearing surface whereby radial movement of each of the locking dog mechanisms causes the respective dog tapered bearing surface to ride against the pin tapered bearing surface and force the pin connection and the box connection axially toward each other, and an external shoulder on the pin connection axially opposite the pin end surface with respect to the pin external tapered bearing surface for engagement with the stop surface to limit axial movement of the pin connection toward the box connection and thereby axially preload the connection when the dog tapered bearing surface rides against the pin tapered bearing surface.

Preferably the connection further comprises an external annular frustoconical surface on the overlap region of the pin connection for engagement with an internal annular frustoconical surface on the overlap region of the box connection to align the pin connection with the box connection when coupling the connection.

Advantageously the connection further comprises an elastomeric annular seal interposed on the box connection for sealing with the external surface on the pin connection.

Conveniently the external shoulder on the pin connection and the stop surface on the box connection are circumferentially aligned with the locking dog mechanism whereby axial forces exerted by radial movement of the locking dog mechanism are transmitted through the box connection shoulder and against the pin connection shoulder to prevent deformation of the box connection.

Advantageously the external shoulder on the pin connection and the stop surface on the box connection are each an annular surface lying within a plane substantially perpendicular to a central axis of the coupling connection.

Preferably the annular external shoulder on the pin connection engages the annular stop surface on the box connection in annular planar engagement.

Conveniently the locking dog mechanism comprises a plurality of locking dog mechanisms equally spaced circumferentially about the box connection.

The invention also provides a method of interconnecting tubular forming bodies, comprising forming a pin connection and a box connection carried respectively by the tubular bodies, the connections being adapted for being placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, forming a pin end surface and a pin external tapered bearing surface on the overlap region of the pin connection, forming a stop surface on the box connection, axially fixing a locking dog mechanism on the box connection, the locking dog mechanism having a dog tapered bearing surface thereon, and radially moving the locking dog mechanism such that the dog tapered bearing surface rides against the pin tapered bearing surface and forces the pin connection and the box connection axially toward each other while the stop surface limits axial movement of the pin connection toward the box connection and thereby axially preloads the connection.

The method may further comprise providing an elastomeric annular seal on the box connection for sealing with the external sealing surface on the pin connection.

The method may additionally comprise circumferentially aligning the external shoulder on the pin connection with the stop surface on the box connection such that axial forces exerted by radial movement of the locking dog mechanism are transmitted through the box connection shoulder and against the pin connection shoulder to prevent deformation of the box connection.

The method may further comprise forming the external shoulder on the pin connection and the stop surface on the box connection each as an annular surface lying within a plane substantially perpendicular to a central axis of the coupling connection.

The method may additionally comprise axially fixing a plurality of locking dog mechanisms on the box connection equally spaced circumferentially about the box connection.

In a preferred embodiment of the invention an external annular shoulder, provided on the radially outer surface adjacent the pin end of a riser connection, engages the axial end of the box end of the connection to limit the travel of the pin into the box and to serve as a reaction shoulder for the pretensioning of the connection. Radially adjustable dogs carried by the box are adjusted into engagement with the pin to lock the pin and box connection together. Tapered bearing surface engaging between the pin and dogs force the box toward the pin as the dogs are adjusted radially.

The annular axial end of the box engages the external annular pin shoulder to form a continuous bearing surface that uniformly distributes the bearing forces around the connection. The engagement of the box end with the pin shoulder reinforces the box to prevent it from distorting as the locking dogs are adjusted to pretension the connection. the external should engagement also provides positive visual verification that the pin and box shoulders are engaged.

The continuous engagement of the pin shoulder and box end isolates the overlap area from the area externally of the riser pipe to protect the overlap area from contamination and eliminate the necessity for a separate barrier sealing. An elastomeric seal near the pin end provides a leak-proof barrier between the pin and box.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a vertical elevation, partially in section, illustrating the riser connector of the present invention, and FIGURE 2 is an enlarged, vertical sectional view illustrating details in the construction and operation of the locking dogs employed in the riser connector of the present invention.

The riser coupling connection of the present invention is indicated generally at 10 in Fig. 1 The coupling conncction 10 is comprised of a tubular pin end connection 11 that is received within a closely fitting tubuhr box end connection 12.

Thc two connections mcei along 2 frustoconical overlap region 13. The pin end connection 11 is welded at 14 to a tubular riser pipe 15 that extends down to a box end connection (not illustrated) similar to the connection 12. The box end connection 12 is welded at 16 to a tubular riser pipe 17 that extends upwardly to a pin end connection (not illustrated) similar to the connection 11. In a tvpical construction, a number of riser pipe segments having pin connectors at one end and box connectors at the other end are connected together, as illustrated in Fig. 1, to form a continuous, elongate riser pipe that extends from the water bottom to the drilling structure for use in drilling a well below the body of water.

An annular ring 18 extending circumferentially about the box end connection 12 cooperates with a similar ring 19 extending about the pin end connection 11 to contain and support auxiliary lines and controls (not illustrated) that extend longitudinally along the side of the riser pipe. Axially extending openings 20 and 21 formed in the nngs 18 and 19, respectively, are aligned longitudinally to receive the auxiliary lines.

The pin and box end connections 11 and 12 are lodked together by arcuateshaped locking dogs 22 that are adapted to be moved radially from the box end connection into the pin end connection. In the embodiment of Fig. 1, six such dogs are disposed equidistant from each other about the circumference of the box end connection 12. The dogs 22 are radially movable in closely fitting radial window openings 23 extending through the box cnd connection. An actuating screw 24 engages the locking dog 22 to drive the dog through the window openings 23 into and out of engagement with the pin end connection.

As fnay best be described with reference to Fig. 2, the radially inner end of the actuating screw 24 is providcd with a circular bearing disk 25 that is received in a conforming recessed area 26 formed at the radially outer end of the locking dog 22.

The disk 25 is free to rotate within the recessed area 26. A lip 27 extending from the rear of the recessed area 26 traps the disk section 25 to force the dog 22 to follow the radially outward movement of the actuating screw 24.

The screw 24 is provided with external threads 28 that mate with internal threads 29 formed centrally through a bonnet 30. With reference to Fig. 1, each bonnet 30 is securely fastened to the box end connection 12 by bolts 31 extending through the bonnet and into the connection 12. As will be understood, rotation of the actuating screw 24 advances the scrcw threads 28 through the bonnet threads 29 to move the screw 24 radially through the bonnet 30.

The radially outer end of the actuating screw 24 is provided with a hexagonal drive head 31 that is adapted to be engaged by a conforming wrench (not illustrated) to rotate the screw. An anti-rotation plate 32 is positioned over a bonnet recess 34 to prevent the actuating screw 24 from rotating once the conforming wrench has been disengaged. The plate 32 is held in place by the engagement of a snap ring 33, which is fitted within an internal groove 36 formed in the bonnet 30. Springs 51 located in the bonnet recess 34 push the plate 32 against the snap ring 33. The plate 32 has a central opening that conforms to the hexagonal drive head 31 to prevent movement of the screw 24. The central opening of the plate 32 can be disengaged from the hexagonal drive head 31 by pushing the plate against the springs 51. The plate 32 is moved to a position with respect to the screw 24 by the wrench, such that a groove 52 cut between the hexagonal drive head 3] and the screw threads 28 permits roration of the screw within the bonnet. Grease or other protective material may be used as needed to protect the actuating screw from corrosion and exposure to contaminants.

The radially inner end of the locldng dog 22 is equipped with dog tapered bearing surfaces 38 and 39 that are adapted to engage and bear against oppositely tapered pin bearing surfaces 40 and 41, respectively, formed annularly about the pin end connection 11.

As will be described, engagement of the belting dog and pin connection bearing surfaces is employed to force the pin and box connections together. An annular, elastomeric O-ring seal 42 carried in an 0-ring groove 43 formed internally of the box end connection 12 engages and seals against the external pin surface immediately above the conical overlap area 13. The seal ring 42 provides a leak proof, sturdy seal between the mating connections.

When the pin and box connections are engaged, the axial end 44 of the box connection 12 engages an external annular shoulder 45 formed on the radially outer surface of the pin connection. The box end 44 functions as a stop surface and provides an annular shoulder that forms a continuous annular planar engagement with the pin shoulder 45. As illustrated in Fig. 1, the annular pin shoulder 45 is radially outward of the overlap region 13.

In the assembly of the riser connection 10, the box connection 12 is telescoped over the pin connection 11 with the dogs 22 in their retracted position as illustrated in Fig. 1. The frustoconical form of the pin and box in the overlap area 13 cooperates to center and properly align the two connections. Once the two components are in the position illustrated in Fig. 1, the actuating screws 24 are rotated with an appropriate wrench (not illustrated) to advance the screws through the bonnet 30. The bearing disk 25 at the base of the actuating screw rotates within the locking dog recess 26 and pushes the dog 22 radially inwardly as the screw advances.

The locking dogs 22 are advanced until the dog bearing surfaces 35 and 39 are engaged with the annular pin bearing surfaces 40 and 41, respectively. Once engaged, the bearing surfaces force the pin connection against the box connection as the actuating screw 24 is advanced radially inwardly.

The engagement of the outer box and pin connection shoulders 44 and 45 limit the travel of the two connections toward each other so that the axially directed forces produced in dnving the tapered locking dog and pin bearing surfaces toward each other are exerted along the shoulder contact areas. As will be appreciated, the axially directed forces acting through the dogs 22 are transferred directly to the box connection immediately below the window recess area 23 and are then transmitted to the underlying pin shoulder 45. The pin shoulder 45 is thus circumferentially positioned relative to the dogs 22 and provides a reinforcing structure at the point of the force application in the box connection to prevent deformation and reduce stress concentration in the box connection.

It will be understood that the provision of the external shoulders 44 and 45 permit visual confirmation of shoulder engagement. The shoulders provide a seal that prevents the ingress of debris.

It will be appreciated that the described connector 10 may be modified without departing from the present invention. For example, it will be understood that the continuous annular pin shoulder 45 may be replaced with a number of smaller, arcuate pin shoulders that are aligned circumferentially with the locking dogs 22. Similarly, while a connector using six locking dogs has been described, it will be appreciated that the connector may be fabricated with a lesser or greater number of locking dogs.

It will also be appreciated that the mechanical actuating screws 24 may be replaced by hydraulically driven pistons or other force applying mechanisms that will drive the dogs radially.

On one embodiment of the coupling 10 manufactured for connecting together 53.3 cm (21 inch), OD. riser piper sections having 158 cm (0.625 inch) wall, six locking dog 22 assemblies were employed to secure the pin and box connectors. The bonnet bolts 31 were connected with 474.5 Nm (350 foot pounds) torque. The connector 10, exclusive of the pipe sections 15 and 17, had a eight of approximately 793 kg (1,750 pounds).

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. It will be appreciated by those skilled in the art that various changes in the six, shape and materials, as well as in the details of the illustrated construction, combinations of features and the method steps discussed herein may be made without departing from the invention.

From the foregoing, it will be appreciated that preferred embodiments of the present invention provide a riser pipe connector and method of connecting pipe sections that improves the distribution of connection stresses within the connector resulting from the prestressing of the connection.

The preferred embodiments of the present invention provide a riser connector having a stronger stress receiving area structure that functions to better resist fatigue failure than prior proposals.

In a preferred embodiment of the invention the preload and operational stresses of the riser connector is preloaded over a large structural area to reduce metal fatigue in the connection.

A significant feature of the invention is a riser connector that maintains its shape without significant distortion when the connector is prestressed to hold two riser pipe segments together.

Still another feature of the present invention is a riser pipe connector that has external shouldering surfaces for permitting visual confirmation of proper shoulder engagement.

Yet another feature of the invention is a simple riser connector in which the external debris seal for the connection is provided by shouldering contact between the pin and box of the connection.

The preferred embodiment of the present invention is a simple riser pipe connector having only a single elastomeric O-ring seal.

The preferred embodiment of the invention is a high strength riser connector that has a comparatively light weight and is not expensive to manufacture or maintain.

Claims

CLAIMS:

1. A coupling connection for interconnecting two tubular bodies, comprising a pin connection and a box connection carried respectively by the tubular bodies and being adapted to be placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, the overlap region of the pin connection including a pin end surface and a pin external tapered bearing surface, the box connection including a stop surface thereon, a locking dog mechanism carried by and axially fixed relative to the box connection and radially movable into engagement with the pin connection for interconnecting the pin connection and the box connection, a dog tapered bearing surface on the locking dog mechanism for engagement with the pin tapered bearing surface whereby radial movement of the locking dog mechanism causes the dog tapered bearing surface to ride against the pin tapered bearing surface and force the pin connection and the box connection axially toward each other, and an external shoulder on the pin connection for engagement with the stop surface on the box connection to limit axial movement of the pin connection toward the box connection and thereby axially preload the coupling connection when the dog tapered bearing surface rides against the pin tapered bearing surface.

2. A coupling connection for interconnecting tubular bodies, comprising a pin connection and a box connection carried respectively by the tubular bodies and being adapted to be placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, the overlap region of the pin connection including a pin end surface and a pin external tapered bearing surface, the box connection including a stop surface thereon, a plurality of locking dog mechanisms circumferentially spaced about the box connection, each of the plurality of locking dog mechanisms being carried by and axially fixed relative to the box connection and radially movable into engagement with the pin connection for interconnecting the pin connection and the box, a dog tapered bearing surface on each of the plurality of the locking dog mechanisms for engagement with the pin tapered bearing surface whereby radial movement of each of the locking dog mechanisms causes the respective dog tapered bearing surface to ride against the pin tapered bearing surface and force the pin connection and the box connection axially toward each other, and an external shoulder on the pin connection axially opposite the pin end surface with respect to the pin external tapered bearing surface for engagement with the stop surface to limit axial movement of the pin connection toward the box connection and thereby axially preload the connection when the dog tapered bearing surface rides against the pin tapered bearing surface.

3. The coupling connection as defined in Claim 1 or 2 further comprising an external annular frustoconical surface on the overlap region of the pin connection for engagement with an internal annular frustoconical surface on the overlap region of the box connection to align the pin connection with the box connection when coupling the connection.

4. The coupling connection as defined in any one of the preceding Claims further comprising an elastomeric annular seal interposed on the box connection for sealing with the external surface on the pin connection.

5. The coupling connection as defined in any one of the preceding Claims where the external shoulder on the pin connection and the stop surface on the box connection are circumferentially aligned with the locking dog mechanism whereby axial forces exerted by radial movement of the locking dog mechanism are transmitted through the box connection shoulder and against the pin connection shoulder to prevent deformation of the box connection.

6. The coupling connection as defined in any one of the preceding Claims wherein the external shoulder on the pin connection and the stop surface on the box connection are each an annular surface lying within a plane substantially perpendicular to a central axis of the coupling connection.

7. The coupling connection as defined in Claim 6, wherein the annular external shoulder on the pin connection engages the annular stop surface on the box connection in annular planar engagement.

8. The coupling connection as defined in any one of the preceding Claims wherein the locking dog mechanism comprises a plurality of locking dog mechanisms equally spaced circumferentially about the box connection.

9. A method of interconnecting tubular forming bodies, comprising forming a pin connection and a box connection carried respectively by the tubular bodies, the connections being adapted for being placed together in an overlapping connection defining an overlap region of the pin connection which is radially inward of an overlap region of the box connection, forming a pin end surface and a pin external tapered bearing surface on the overlap region of the pin connection, forming a stop surface on the box connection, axially fixing a locking dog mechanism on the box connection, the locking dog mechanism having a dog tapered bearing surface thereon, and radially moving the locking dog mechanism such that the dog tapered bearing surface rides against the pin tapered bearing surface and forces the pin connection and the box connection axially toward each other while the stop surface limits axial movement of the pin connection toward the box connection and thereby axially preloads the connection.

10. The method as defined in Claim 9 further comprising forming an external annular frustoconical surface on the overlap region of the pin connection, forming an internal annular frustoconical surface on the overlap region of the box connection, and engaging the frustoconical surfaces to align the pin connection with the box connection when coupling the connection.

11. The method as defined in Claim 9 or 10 further comprising providing an elastomeric annular seal on the box connection for sealing with the external sealing surface on the pin connection.

12. The method as defined in Claim 9, 10 or 11 further comprising circumferentially aligning the external shoulder on the pin connection with the stop surface on the box connection such that axial forces exerted by radial movement of the locking dog mechanism are transmitted through the box connection shoulder and against the pin connection shoulder to prevent deformation of the box connection.

13. The method as defined in any one of Claims 9 to 12 forming the external shoulder on the pin connection and the stop surface on the box connection each as an annular surface lying within a plane substantially perpendicular to a central axis of the coupling connection.

14. The method as defined in any one of Claims 9 to 13 axially fixing a plurality of locking dog mechanisms on the box connection equally spaced circumferentially about the box connection.

15. A coupling connection substantially as herein described with reference to and as shown in the accompanying drawings.

16. A method interconnecting tubular bodies substantially as herein described with reference to the accompanying drawings.

17. Any novel feature or combination of features disclosed herein.