GB2336382A

GB2336382A - Hang-off connector for marine riser

Info

Publication number: GB2336382A
Application number: GB9908266A
Authority: GB
Inventors: Steven Alexander Barras; Derek James Button
Original assignee: Coflexip SA; Coflexip Stena Offshore Ltd
Current assignee: Technip Energies France SAS; Technip UK Ltd
Priority date: 1998-04-16
Filing date: 1999-04-13
Publication date: 1999-10-20
Also published as: GB9807968D0; GB9908266D0

Abstract

A support for a marine riser comprising a first body or bearing (10) and a second body or cartridge (12), the first body (10) containing a fluid passage (14) extending through the length of the first body (10) whereby a marine riser (24) may be connected to a first end of the fluid passage (14) and a further fluid conduit may be attached to a second end of the passage. The external surface of the first body (10) is at least part-spherical (Figure 1) and the passage (16) contained in the second body (12) has an inner surface having a corresponding part-spherical configuration providing the seat for the first body (10). The configuration of the first and second bodies allows the fluid passage (14) to rotate about three orthogonal axes relative to the fixed, second body (12). This freedom of rotation reduces the moments and torsion applied to the marine riser (24) to low values at the connection point, hence reducing stresses and improving the fatigue life of the riser.

Description

2336382 1 1 nConnector for Marine Risers" The present invention relates to

connector devices for use in "hanging off,' marine production and/or export risers from fixed or floating production and offloading facilities (FPOs) (or fixed or floating production and storage facilities (FPS0s)) as employed in offshore production systems for the recovery, storage and distribution/transportation of oil and other hydrocarbon fluid products. The term FPSO will be used herein to indicate any type of fixed or floating vessel, platform or the like to which a production or export riser may be required to be connected as part of an offshore production system.

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Production and export risers provide fluid conduits between subsea production and distribution installations (such as subsea wellheads, distribution manifolds and the like) and FPS0s. The upper end of the riser is normally connected to some type of turret or other hang-off structure on the FPSO, in such a manner that wave and weather induced movements of the FPSO and/or the riser may be accommodated without damaging the riser. Conventionally, the upper ends of risers are fixedly connected to the hang-off structure 2 1 2 3 4 5 6 7 8 9 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 31 32 33 34 36 by means of welding or flange connections. Additional conduits or pipework on the FPSO are then connected to the upper end of the riser, typically by means of a flexible conduit, to establish fluid communication between the riser and whatever storage or distribution facilities are provided by the FPSO. Both the riser and the FPSO conduit are effectively connected to the hang-off structure in a rigid manner. This requires the use of stiffeners and/or bend restrictors on the upper end of the riser and/or the lower end of the FPSO conduit with which it communicates to prevent the riser and conduit being damaged by movements of the FPSO and/or the riser.

It is an object of the present invention to provide an improved riser hang-off connector which obviates or mitigates the need for such stiffeners or bend restrictors and which reduces the possibility of risers or FPSO conduits being damaged by FPSO/riser movements.

In accordance with the present invention, there is provided a support for a marine riser comprising a spherical or part-spherical bearing arrangement in which means are provided defining a fluid passage extending from a first side of the bearing to which a riser may be connected, in use, and a second side of the bearing, to which a further fluid conduit may be connected, in use, such that the fluid passage is free to rotate about three orthogonal axes relative to a fixed portion of the bearing.

Preferably, the support consists of a marine riser connector device comprising: a first body including means for establishing said fluid passage therethrough having a first end and a second end, whereby a marine riser may be connected to 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 said first end of said fluid passage and a further fluid conduit may be connected to said second end thereof; and a second body having a second passage extending therethrough from a first side of the second body to a second side thereof, said second passage being configured to provide a seat for said first body, such that said fluid passage extends from said first side to said second side of said second body; wherein the external surface of said first body is at least part-spherical and said second passage includes an inner surface having a corresponding part-spherical configuration providing said seat for said first body, whereby said first body may rotate about three orthogonal axes relative to said second body.

In certain embodiments of the invention, the fluid passage through the first body is provided by a fluid conduit formed integrally with the first body. In other embodiments, the first body has a through bore adapted to receive a length of fluid conduit extending therethrough and secured to the first body. In either case, the respective ends of the fluid conduit may be adapted to be connected to said marine riser and said further conduit by welding, by means of annular flange connectors, or by any other suitable means.

Preferably, the co-operating spherical or part spherical surfaces of either or both of the first and second bodies are formed from or coated with low friction material.

In addition, the first and/or second bodies may be provided with fluid paths to allow the injection of a lubricating medium to the interface between the bodies.

4 1 2 3 4 5 6 7 8 9 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Preferably also, the second body is split along at least one plane extending through said second passage, allowing the second body to be separated into at least two parts and assembled around the first body portion.

Preferably also, the second body has an outer surface configured to be seated in a corresponding socket provided in a hang-off structure of an FPSO such that the fluid passage extends from an upper side to a lower side of said hang-off structure and is free to rotate in said three orthogonal axes relative thereto.

The fluid passage through the connector is preferably of constant internal bore.

If required, the fluid passage may be configured to incorporate or to cooperate with pipe stiffening means or bend-restricting means.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a sectional side view of a first embodiment of a marine riser connector embodying the invention; Fig. 2 is a sectional side view of a second embodiment of a marine riser connector embodying the invention; Fig. 3 is a sectional side view of a third embodiment of a marine riser connector embodying the invention; Fig. 4 is a sectional side view of a fourth 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 embodiment of a marine riser connector embodying the invention; Fig. 5 is a sectional side view of a typical hangoff structure of an FPSO illustrating the use of connectors embodying the invention; Fig. 6 is a plan view of a chain stop portion of the structure of Fig. 5; Fig. 7 is a plan view of a lower bearing portion of the structure of Fig. 5; Figs. 8(a) to 8(d) are partial sectional side and plan views of the lower part of the structure of Fig. 5, taken on line B-B of Fig. 9, illustrating the manner in which connectors embodying the invention located the lower bearing portion of Fig. 7; Fig. 9 is a plan view similar to Fig. 7 of the lower bearing portion of the structure of Fig. S; Fig. 10 is an enlarged plan view of part of the lower bearing portion of Fig. 9 with a connector embodying the invention located therein; and Fig. 11 is a sectional side view on line A-A of Fig. 10.

Referring firstly to Figs. 1 to 4 of the drawings, the illustrated embodiments of the invention each include a first body or "bearing" 10 and a second body or "cartridge" 12. In each case the bearing 10 has an outer surface portion which is part-spherical (Figs. 1 and 3) or "fully" spherical (Figs. 2 and 4). The 6 2 3 4 6 7 8 9 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 31 32 33 34 35 36 1 cartridges 12 each include a passage 16 extending vertically therethrough, the passages 16 having inner surfaces including part-spherical portions corresponding to the spherical/part-spherical portions of the bearings 10 and providing a seat for supporting the bearings 10. The bearings are thus able to rotate about three orthogonal axes relative to the cartridges.

Each of the bearings 10 includes a through bore 14 extending along a diameter of the spherical/partspherical portions of the bearings 10 and used in providing a fluid passage through each bearing. In the embodiments of Figs. 1 and 2, the bearings 10 include integrally formed tubular stubs 18 and 20 extending from either end of their through bores 14, so that the bores 14 and stubs 18 and 20 themselves provide the required fluid passage. In the ernbodiments of Figs. 3 and 4, the through bores 14 are intended to have separate lengths of conduit inserted therethrough so as to provide the required fluid passage with stubs projecting from either end of the through bores 14, similar to the integral stubs 18 and 20 of Figs. 1 and 2. Fig. 4 shows such a conduit 22 in broken lines.

In the case of either of Figs. 1 and 2 or 3 and 4, the ends of the stubs 18 and 20 or of the conduit 22 are adapted for a riser to be connected to the lowermost stub 20 or conduit end and for a further conduit to be connected to the uppermost stub 18 or conduit end by any suitable means. Such connection is most likely to be effected by means of welding or by the use of annular flange connections (such flanges 24 are shown in broken lines in Figs. 2 and 4).

The either or both of the co-operating spherical/partspherical surfaces of the bearings 10 and cartridges 12 7 1 2 3 4 6 7 8 9 12 13 14 is 16 17 18 19 20 21 22 23 24 26 27 28 29 30 31 32 33 34 36 are preferably formed from or coated with low friction materials 26, 28.

The cartridge bodies 10 are adapted to be seated in a socket or the like formed in a hang-off support 30 forming part of a hangoff structure of an FPSO, as shall be discussed further below. A passage 34 extends through the socket, allowing the fluid path to extend through the support 30. The configuration of the outer surface of the cartridges 10 corresponds to that of the socket so that the device is positively located and seated therein. In the present examples, the cartridges and sockets may suitably have a substantially cylindrical configuration.

The connector devices will be retained in their sockets primarily by gravity (i.e. the weight of the riser). If they are required to be secured against upward loads, they may be secured by mechanical means such as a retaining ring 32 as seen in Figs. 2 and 4.

The cartridge bodies 12 may be split into sections to facilitate the fitting and removal of the bearing bodies 10. Preferably, they are split along a vertical plane extending through the passages 16. If the partspherical seat provided by the cartridges 12 is less than hemispherical, then the bearings 10 could be inserted and removed without splitting the cartridges. However, it is preferred that the seat is greater than hemispherical, so that the bearing is positively enclosed and retained therein.

The possible range of movement of the bearings 10 within the cartridges 12 depends on the size of the exit apertures of the passages 16 and 34 relative to the size of the stubs 18, 20 or conduit 22, the 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 dimensions of the passages 16 and 34 being selected to suit the diameter of the riser with which the device is to be used and the range of movements expected to be encountered in use. The proportion of a complete sphere provided by the bearings 10 and cartridges 12 is also selected to suit the range of directions of forces to be transmitted via the bearing and the rotations to be accommodated.

If necessary, the bearings and/or cartridge bodies may be provided with fluid paths to allow the injection of a lubricating medium to the interface between the bearing and the cartridge.

Fig. 5 illustrates a typical example of a hang-off turret of an FPSO, including a lower bearing member 50 corresponding to the hang-off support 30 of Figs. 1 to 4. A connector device 52 in accordance with the invention is shown located in one of a plurality of sockets 54 formed in the bearing member 50, which is i the form of a planar, annular ring as seen in Fig. 7. The sockets 54 are formed adjacent the inner circumference of the ring 50. Slots 56 extend from the inner circumference of the ring 50 to the sockets 54 to facilitate the installation of risers, as shall be described below. The sockets 54 are of different sizes to suit risers of different diameters. The slots 56 are wider than the corresponding risers but narrower than the associated connectors. Fig. 5 shows the connector 52 in position with a riser 58 connected to its lowermost end and a flexible jumper conduit 60 connecting its uppermost end to the permanent pipework of the FPSO. The drawing shows the connector bearing rotated so that the riser extends at an angle to the vertical. Fig. 6 shows a chain stop portion 62 of the turret in the form of a ring located below the bearing 9 1 2 3 4 6 7 8 9 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 36 ring 50 with an array of anchor chains 64 extending therefrom.

Figs. 8(a) to 8(d) and 9 to 11 illustrate the installation of the riser 58 in the bearing member 50. Each of Figs. 8(a) to 8(d) shows a partial side view of the structure of Fig. 5, and a fragmentary top view illustrating the position of the connector 52 relative to the socket 54 in which it is to be seated. The riser 58, with the connector 52 attached to its uppermost end, is pulled up from below the anchor stop 62 (Fig. 8(aH through the central aperture of the bearing ring 54 until the connector 52 is above the bearing ring 52 (Fig. 8(b)). The riser is then pulled sideways so that the riser 58 enters the slot 56 leading to the socket 54 (Fig. 8(c)). Once the riser is pulled through the slot 56 to extend through the socket 54, it can be lowered to seat the connector 52 in the socket 54. Figs. 10 and 11 show the connector 52 seated in the socket 54.

The methods and apparatus by means of which the riser 58 is raised, lowered and otherwise manipulated are well known in the art and will not be described herein.

The invention is advantageous in that it allows the connection point between the riser 58 and the jumper conduit 60 to rotate in the three orthogonal axes within limits set by the design of the bearing 10, cartridge 12 and hang-off support 30/50. This freedom of rotation reduces the moments and torsion applied to the riser 58 to very low values at the connection point, hence reducing stresses and improving the fatigue life of the riser at the connection point.

All rotation is achieved without compromising the fluid 1 2 3 4 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 flow path; i.e. the flow path is continuous and comprises only rigid or flexible flowlines, the bearing 10 effectively providing a rigid flowline of constant bore with a locally thickened and shaped wall. There are no weak points which could offer the potential for loss of fluid containment.

The hang-off connection is primarily gravity based and is very simple to connect. The cartridge/bearing system of the connector allows easy replacement of the cartridge sliding surfaces as required. The connector may be used above or below sea level depending on the choice of bearing/sliding materials for the bearing section and the cartridge.

The connector may be usefully employed with risers of any type, including flexible risers and steel catenary risers.

The invention will, in many cases, obviate the need for the use of any type of pipe stiffeners or bend restrictors on either side of the connection point as required in conventional riser connector systems. Stiffeners and/or bend restrictors may be necessary or desirable in some cases, however these may generally be of a lower specification than would otherwise be necessary in the absence of the present invention. Stiffeners and bend restrictors are well known in the art and will not be described in detail herein.

Where required, the stubs of the fluid conduit extending through the bearing can be configured as stiffeners, with local thickening of the conduit wall section adjacent the bearing, tapering to the wall section of the riser at the ends, while maintaining a constant internal bore, as is known in the art. The 1 2 3 4 inclusion of such stiffeners would allow for excessive loadings/displacements to be applied, as might be encountered during excessive storms (i.e. to provide 111000 year survivabilityll) or to permit greater loading and during installation procedures. Non-integrated stiffeners or bend restrictors may also be used, normally with suitably adapted flange connectors, particularly for flexible risers. The upper stub connection is less likely to require a stiffener or restrictor but, where required, this could again be generally much smaller and cheaper than would otherwise be needed.

6 7 8 9 10 11 12 13 14 Improvements and modifications may be incorporated without departing from the scope of the invention.

is 16 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Claims

1. A support for a marine riser comprising a spherical or part-spherical bearing arrangement in which means are provided defining a fluid passage extending from a first side of the bearing to which a riser may be connected, in use, and a second side of the bearing, to which a further fluid conduit may be connected, in use, such that the fluid passage is free to rotate about three orthogonal axes relative to a fixed portion of the bearing.

2. A support as claimed in Claim 1, wherein said support consists of a marine riser connector device comprising: a first body including means for establishing said fluid passage therethrough having a first end and a second end, whereby a marine riser may be connected to said first end of said fluid passage and a further fluid conduit may be connected to said second end thereof; and a second body having a second passage extending therethrough from a first side of the second body to a second side thereof, said second passage being configured to provide a seat for said first body, such that said fluid passage extends from said first side to said second side of said second body; wherein the external surface of said first body is at least part-spherical and said second passage includes an inner surface having a corresponding part-spherical configuration providing said seat for said first body, whereby said first body may rotate about three orthogonal axes relative to said second body.

3. A support as claimed 'n Claim 2, wherein the fluid L passage through the first body is provided by a fluid 13 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 conduit formed integrally with the first body.

4. A support as claimed in Claim 2, wherein the first body has a through bore adapted to receive a length of fluid conduit extending therethrough and secured to the first body.

5. A support as claimed in Claim 3 or Claim 4, wherein the respective ends of the fluid conduit are adapted to be connected to said marine riser and said further conduit by welding, by means of annular flange connectors, or by any other suitable means.

6. A support as claimed in any one of Claims 2 to 5, wherein. the cooperating spherical or part spherical surfaces of either or both of the first and second bodies are formed from or coated with low friction material.

7. A support as claimed in any one of Claims 2 to 6 wherein the first and/or second body is provided with fluid paths used to allow the injection of a lubricating medium to the interface between said first and second bodies.

8. A support as claimed in any one of Claims 2 to 7, wherein the second body is split along at least one plane extending through said second passage, allowing the second body to be separated into at least two parts and assembled around the first body portion.

9. A support as claimed in any one of Claims 2 to 8, wherein the second body has an outer surface configured to be seated in a corresponding socket provided in a hang-off structure of an FPSO such that the fluid passage extends from an upper side to a lower side of 14 1 2 3 4 5 said hang-off structure and is free to rotate in said three orthogonal axes relative thereto.

10. A support as claimed in any one of Claims 2 to 9, wherein the fluid passage through the connector is of constant internal bore.

6 7 8

11. A support as claimed in any one of Claims 2 to 10, wherein the fluid passage is configured to incorporate or to cooperate with pipe stiffening means or bendrestricting means.

11 12 13 14 is 16

12. A support for a marine riser substantially as hereinbefore described with reference to the accompanying drawings.