Universal Joint for Multiple Conduit System

1. Field of the Invention

This invention relates to new and improved articulated joint for flowlines and more particularly relates to a universal joint assembly of the type for a multiple conduit system used in underwater oil or gas production.

2. Description of the Prior Art

Production of crude oil from deep water areas remote from land poses significant problems. For example, in very deep water it is not economically feasible to install rigid ocean floor supported platforms of the type used to support production operations in shallow water. Also, the laying of large diameter pipelines in deep water is often impractical and unattractive economically. One promising approach for overcoming these difficulties involves the use of a production system comprising a production manifold positioned on or near the ocean floor and a riser assembly extending from the production manifold to an overlying moored floating vessel. The floating vessel is provided with conventional processing equipment and a storage area for crude oil. The riser assembly includes multiple flexible flowlines interconnecting the vessel with the subsea wellheads and manifold systems.

Development of a riser assembly that will withstand the forces encountered in typical floating production operations poses severe design problems. The riser system must have sufficient flexibility and structural strength to accommodate motions and withstand forces resulting from vessel excursions and from wave and current action. The riser must also have sufficient flow lines to conduct fluids from the sea bottom to the vessel, to conduct separated water or gas back to the sea bottom and to conduct flowline tools between the vessel and the wellheads.

A number of riser systems have been suggested for subsea petroleum production. One such riser system, commonly designated a "rigid self-standing riser", has a rigid connection at the wellhead or manifold and a flowline housing tensioned by a suitable buoyancy chamber at a distance of about 200 feet (61 meters) below the water surface. The steel flowlines in the flowline housing are then connected from the top of the buoyancy chamber to a moored floating vessel through a bundle of flexible floating hoses. This arrangement requires no special multiline flexible joint to provide flexibility riser but has the disadvantage that it requires heavy ballast and pile anchors to overcome the high tension and bending loads from riser buoyancy and current drag. Another disadvantage is that the flexible hoses are exposed to severe environmental conditions and are vulnerable to damage by surface vessels.

Another more suitable type of production riser, commonly designated a "tension leg riser", uses a single buoy, one multiline universal joint directly below the buoy, a riser stem housing, a second multiline universal joint directly above the base at the ocean floor and a multiple number of flow lines extending from the buoy to the ocean floor. The riser moors the production and storage vessel through a multiline swivel and articulated arm arrangement that permits the vessel to rotate or "weathervane" around the buoy in response to wave, wind and current action. This type of riser can be constructed using rigid flow lines to avoid the problems associated with the use of flexible flowlines. The multiline universal joints form a vital part of the production riser in that they provide the riser system with the requisite flexibility and structural strength to enable it to withstand the severe environmental conditions encountered in deep water operations.

In designing articulated joints, such as universal joints for riser systems having rigid flowlines, a number of factors must be taken into consideration, including for example, environmental conditions, water depth and the number and sizes of the flow lines. A significant economic and operational consideration is the size of the universal joint. In prior multiline universal joints, only two of the rigid flow lines could pass through the universal joint on the axes of pivot. The remaining rigid flow lines were positioned along the side of the universal joint. Each of the flow lines positioned along the side of the universal joint was provided with fluid swivels at the pivot axes of the universal joint. Because the fluid swivels were required to be located in end to end relation along the axes of pivot, the universal joints for a riser having a large number of flowlines had, by necessity, the fluid swivels extending a substantial distance outside the universal joint. Each additional flow line required an additional fluid swivel on each axis of pivot thereby increasing the overall size of the universal joint. Unfortunately, the larger sized universal joints are more expensive, heavier, more difficult to install, and are more susceptible to greater environmental loading. Further, it is difficult to maintain all of the fluid swivels in alignment with the pivot axes of the universal joint. Misalignment causes high stresses in the swivel bearings and results in early fatigue failure of the swivel. Further, in order to replace a fluid swivel immediately adjacent to the universal joint, it was necessary to first remove each of the outer fluid swivels on the axes of pivot. Since the number and sizes of the flow lines are controlled by operating conditions, it is apparent that a need exists for a multiline universal joint that will minimize the stresses imposed on the fluid swivels and provide a relatively compact flexible connection between multiple rigid flow lines to minimize environmental loading and reduce the cost.

A riser system for production of oil and gas from subsea wells includes a riser pipe extending between the bottom of the sea and a floating vessel and a plurality of rigid fluid conduits supported by the riser pipe to transport fluids between the floating vessel and the bottom of the sea. The riser system normally includes at least one multiline articulated joint, such as a universal joint of the present invention, to provide flexibility for the riser pipe. The universal joint may be positioned at the ocean floor or at various points along the length of the riser. The articulated joint connects a pair of riser members that support the conduits and provides pivotal movement of the riser members about two axes that are perpendicular to each other. The universal joint of the present invention enables all the fluid conduits to pass through the interior of the joint. Each of the plurality of conduits extending along the riser has a first portion extending generally along the longitudinal axis of one riser member and a second portion extending generally along the longitudinal axis of the other riser member. The first and second portions of two of the conduits extending along the riser are connected to each other by elbow conduits that pass through the universal joint on the pivot axes of the joint. The first and second portions of the remaining conduits are connected to each other by elbow conduits that pass through the universal joint on axes offset from and substantially parallel to the pivot axes of the joint. Each of the offset elbow conduits is provided with a first pivot means at each end. These first pivot means enable pivotal movement between the offset elbow conduits and the corresponding first and second conduit portions. Each of the first and second conduit portions, which are connected to the offset elbow conduits, is also provided with a second pivot means. The second pivot means enables rotational movement of the first pivot means around the pivot axes of the universal joint when the universal joint is flexed. Preferably the first and second pivot means comprise fluid swivels. In another embodiment of the present invention one or more (up to four) of the offset conduit may have a first portion which is offset and generally parallel to the pivot axis of one joint and a second portion which is on the pivot axis of the other joint. In this embodiment only the first portion of the offset conduit is provided with both the first and second pivot means.

Another type of universal joint means comprises the combination of a pivot means and a compensating means. This type of universal joint means is the subject of a separate patent application, Ser. No. 105,679, filed even date herewith in the names of John E. Ortloff, Clarence F. Stelzer Jr., and Donald R. Hays.

The advantages of the universal joint assembly of this invention over universal joint assemblies used in the past include: a reduction in the stresses imposed on the fluid swivels when the joint is flexed; a reduction in the size and weight of the universal joint; and an improved ability to replace various components of the conduits in the event of equipment failure.

A more thorough disclosure of the advantages of the present invention is presented in a detailed description which follows and from the accompanying drawings in which;

FIG. 1 is an elevation view illustrating a floating vessel positioned over a location wherein a manifold assembly is positioned on the ocean floor and a production riser extends between the manifold assembly and the surface vessel and is provided with universal joints of this invention;

FIG. 2 is a perspective view of one of the universal joints of this invention;

FIG. 3 is a schematic view of the universal joint of FIG. 2;

FIG. 4 is a schematic view of the universal joint of FIG. 3 in a flexed position;

FIG. 5 is a section view taken on line 5--5 of FIG. 3;

FIG. 6 is a view of an alternative embodiment of the universal joint of the present invention;

FIG. 7 is a view of the universal joint of FIG. 6 in a flexed position; and

FIG. 8 is a detail view, in longitudinal section, and slightly enlarged, of a suitable swivel member for use in the universal joint shown in FIG. 2.

Referring to FIG. 1, a vessel 10 is illustrated as floating on the surface of a body of water 11 while being positioned in a substantially fixed position over a preselected site. This site can be a wellhead, a production manifold, or a gathering point for lines from many wells. The vessel may be used for storage or production and may be any suitable floating or floatable vessel. At the wellhead site, generally designated 12, a riser system 13 comprises a housing 14 for supporting a plurality of rigid lines or conduits which are connected to a production manifold by means of a universal joint 15a which provides a flexible universal connection. Riser 13 is connected at its upper end through another universal joint 15b to buoyant conductor or conduit 16 which is in turn connected to rigid mooring arm 17 on the ship or vessel 10. The riser system may be maintained under tension by the buoyant conduit 16 and reserve buoyancy chamber 18. The riser system as shown is flexible at the upper and lower universal joints 15b and 15a and thereby permits flexing of the riser as a result of currents, environmental forces, drift of the vessel, etc. The universal joints 15a and 15b of this invention may be used in any flexible or articulated riser system requiring a universal joint.

FIGS. 2, 3, 4 and 5 illustrate one preferred embodiment of the universal joint of this invention. FIG. 2 shows a perspective view of the universal joint 15b as shown in FIG. 1. The universal joint 15b comprises a first longitudinal housing member 19 and a second longitudinal housing member 20 which are connected to riser housing 14 and buoyant conduit 16, respectively. Housing member 19 has a bifurcated end portion or yoke comprising a pair of arms 21 and 22 (see FIG. 5) which have smooth apertures therein which function as bearings. Housing member 20 has a bifurcated end portion or yoke comprising a pair of arms 24 and 25 having smooth apertures therein which function as bearings. A cross member 29 (see FIG. 5) is provided as a connector between the yokes of housing members 19 and 20 to provide universal movement of the joint. Cross member 29 has a plurality of trunnions 30, 31, 32 and 33. Each trunnion has a bore or passage extending completely therethrough so that the cross member is completely hollow. Cross member 29 is positioned with trunnion 30 in the bearing aperture of yoke arm 21 on housing member 19. The oppositely extending trunnion 32 is positioned in bearing aperture on yoke arm 22. The trunnions 31 and 33 of cross member 29 are positioned in apertures of yoke arms 25 and 24, respectively, on housing member 20.

The universal joint 15b is designed to carry a plurality of conduits or pipelines (this particular joint carries six rigid lines or conduits, three lines, 34, 35 and 36 are shown in FIG. 2 and the other three are hidden from view. It should be noted that the arrangement of conduits and connections on housing member 19 and the connections into cross member 29 is identical to that of the conduits and connections from housing member 20 except that they are rotated 90.degree. to fit the trunnions of the cross on which housing member 19 is pivoted. Conduits 34 and 36 may be larger conduits or pipelines for carrying crude oil, gas, or water and conduit 35 may be a smaller conduit for handling pumpdown tools.

Referring to FIG. 5, the cross member 29 is provided with a plurality of elbow conduits 38, 40, 42 44, 46 and 48, which extend therethrough. The elbow conduits connect the flowlines extending along housing member 19 to the corresponding flowlines extending along housing member 20. For example, elbow conduits 38, 40, and 42 enter the crossmember through trunnion 30 and exit the cross member through trunnion 33. The ends of these elbow conduits, which enter through trunnion 30, are connected to pivot means 50, 52 and 54 respectively. Pivot means 50, 52 and 54 are in turn connected to flow lines 34, 35 and 36 respectively. Elbow conduits 40 and 46 extend through the cross member 29 on the pivot axes of the universal joint. The remaining elbow conduits 38, 42, 44, and 48 are offset conduits and extend through the cross member on axes offset from and substantially parallel to the pivot axes of the universal joint. Flow lines 34 and 36 which are connected to the offset elbow conduit 38 and 42 respectively are further provided with pivot means 56 and 58. Pivot means 56 and 58 enable rotational movement of pivot means 50 and 54 around the pivot axis of the universal joint when the joint is flexed. Pivot means 50, 52, 54, 56 and 58 preferably comprise fluid swivels.

Referring to FIGS. 3 and 4, the pivoting of the housing member 20 with respect to the housing member 19 results in a corresponding rotation of cross member 29 about the axis extending through trunnions 30 and 32. Pivot means 50, 52, and 54 enable pivotal movement between flow lines 34, 35 and 36 and elbow conduit 38, 40 and 42 respectively which remain fixed within cross 29 (see FIG. 5). Swivels 56 and 58 disposed in flow lines 34 and 36 which are connected to offset elbow conduits 38 and 42 respectively, enable pivot means 50 and 54 to rotate around one pivot axis of the universal joint in a plane parallel to the plane of yoke arm 24. Flow line 35 is not provided with a second pivot means because it is positioned on the axis of rotation of housing member 20 which is also a pivot axis of the universal joint, and therefore pivot means 52 does not revolve around a pivot axis when the universal joint is flexed.

The system of conduits and pivot means connected through the universal joint 15b has been described for three (3) fluid conduits. For a system of six (6) conduits, the other three (3) conduits have this same connecting arrangement but pass through the other two trunnions. In operation, this multline, multiconduit universal joint is capable of a substantial degree of flexure along both pivotal axes and accommodates a substantial number of flow lines or conduits in a compact manner. As shown above, when the universal joint is flexed, the system of pivot means accommodates this pivotal movement.

In the embodiment of the universal joint shown in FIGS. 2, 3, 4 and 5, the pivot means disposed between the flow lines and the elbow conduits are aligned in a plane normal to the axes of housing members 19 and 20 when the universal joint is in the unflexed position.

Referring to FIGS. 6 and 7, there is shown an alternative embodiment wherein like numbers refers to like parts. In FIGS. 6 and 7, the pivot means of the elbow conduits are aligned in planes normal to the plane of the axes of the cross member 29. The connecting arrangement is the same as that shown in FIGS. 2, 3, 4, and 5. When housing member 20 is pivoted with respect to housing member 19, pivot means 56 and 58 enable pivot means 50 and 54 to rotate around one pivot axis of the universal joint in a plane parallel to the plane of yoke arm 21. In both the embodiments shown in FIGS. 2-4 and FIGS. 6-7, it may be desirable in some cases to provide each of conduits 34 and 36 which are connected to the offset elbow conduits with a third pivot means, 60 and 62 respectively, to reduce any stress in the flow lines occurring upon the flexing of the universal joint.

At this point, attention is directed to FIG. 8 for a more complete understanding of one type of suitable pivot means that can be used in the apparatus of this invention. FIG. 8 shows an enlarged longitudinal cross section of fluid swivel member 50 which connects conduit 34 to elbow conduit 38. Swivel member 50 is shown in a sectional view from its center line to the outer edge. Swivel member 50 has an inner cylindrical member 68 having a flange 68A that provides resistance to thrust loads caused by internal pressure. Member 68 is welded as at 69 to flange 70 which is connected to the end flange 71 on conduit 34. Outer cylindrical member 72 of swivel member 50 is welded as at 73 to end flange 74 which is connected to flange 75 on conduit 38. An annular end plate 76 is secured on cylindrical portion or sleeve 72 by a plurality of bolts 77. In the annular space between sleeves 68 and 72 there are positioned bearing members 78 and 78A of a very hard highly polymerized polyethylene or other suitable bearing material. These bearings resist both thrust and radial loads imposed on the swivel by internal and external pressure and by loads applied normal to the axis. There is also positioned a sleeve 79 of an oil resistant synthetic rubber such as acrylonitrile rubber. The rubber sleeve 79 is bonded to the outer surface of swivel sleeve 68 and is movable therewith. The outer surface of rubber sleeve 79 is slidable relative to the inner surface of swivel sleeve 72. The inner surface of sleeve 72 is preferably coated with a thin layer 72A of polymer such as polytetrafluoroethylene (Teflon). This swivel is capable of rotary motion and is fully sealed to prevent leakage of the fluid passing through the conduit. For small degrees of swivel rotation or oscillation, the relative motion between sleeves 68 and 72 is accommodated by deflection of rubber sleeve 79. At higher degrees of rotation, i.e. above about 5.degree., the sleeve 79 slips on the thin layer of Teflon 72A on the inner surface of swivel sleeve 72. This swivel construction is fully sealed and can handle fully rotary movement. The swivel just described is merely illustrative of the type of swivel that can be used in this invention. Another type of swivel suitable for use in the present invention is the swivel manufactured and sold by FMC Corporation under the trade name Chiksan swivel. Other types of antifriction bearing swivels may also be used in the apparatus of the present invention such as the roller bearing swivels available from Sealol Inc., Continental-Emsco Inc. and National Supply Company. It should be understood that any type of conduit swivel that will permit rotary motion of a fluid-carrying conduit may be used.

The universal joint of this invention may be used in any multiline system requiring the universal flexing movement. This joint, however, is particularly designed for and advantageous in underwater riser systems for production of crude oil and gas as described above.

This multiline universal joint has substantial advantages over universal joints known in the prior art. One advantage is that this universal joint utilizes the simplest of flexible components (fluid swivels). The fluid swivels can be readily replaced without having to remove them sequentially or in a specific order. Therefore, it is not necessary to remove a stack or series of swivels to replace one defective swivel. The practical limit for the number of flow lines that can be accommodated is the space in the hollow cross member. The overall arrangement substantially reduces weight and costs. The ability to individually replace one component eliminates the need for a complete shutdown of the equipment in the event of equipment failure.

The invention has been described fully and completely with respect to two embodiments thereof. It should be understood that equivalent components and equivalent modes of construction and assembly may be used without departing from the inventive concept. For example, The Engineers Illustrated Thesaurius, Herbert Herkimer, Chemical Publishing Company, Inc., 1952, P. 258-263, discloses a variety of articulated joints other than the yoke and cross type. The inventive concept of this invention as defined by the claims which follow can be applied in universal joints of a variety of types and also to other types of articulated joints. The invention, therefore, is not to be restricted except as is necessary by the prior art and by the lawful scope of the claims which follow.