Device for transferring fluid from a marine mounting

Abstract

A device for transferring fluid from a support installed at sea and fitted with a device for storing flexible pipes having the first ends of a plurality of flexible pipes fastened thereto, the pipes preferably extending between said support and an offloading ship. The pipe device having a first connection and valve device, the pipes being connected to one another at their seconds ends by a the first connection and valve device having n first pipe portions and suitable for being connected to a second connection and valve device, preferably installed on board an offloading ship.

Claims

1. A fluid transfer device for transferring fluid from a support installed at sea, in grounded or floating manner, to a ship which is arranged alongside said support or in tandem adjacent to said support, said fluid transfer device comprising a plurality, n, of flexible pipes that are suitable for being stored on said support by means of a flexible pipe storage device to which a first end of each of said flexible pipes is suitable for being fastened, said flexible pipes being suitable for extending between said support and said ship arranged alongside or in tandem adjacent to said support, the fluid transfer device comprises a first connection and valve device, said flexible pipes being connected together at their second ends by said first connection and valve device, said first connection and valve device having n first pipe portions held in fixed positions relative to one another, n being an integer not less than 3, each said first pipe portion comprising: at a first end, a first pipe coupling element; at a second end, a second coupling element, assembled to the second end of one of said flexible pipes; each of said first pipe portions including, between its two ends, a number (n1) of branch connections enabling said first pipe portion to communicate with respective ones of the n1 other ones of said first pipe portions, each of said branch connections including a first communication valve; a first connection valve situated between said first pipe coupling element and one of said branch connections; said first pipe portions being held by a first rigid support to which said first pipe portions are secured; wherein said support is installed at sea, fitted on a surface of said support with a storage device for storing and guiding flexible pipes and which said flexible pipe storage device is suitable for storing and guiding a plurality of said flexible pipes, said flexible pipe storage device comprising: a first carrier structure resting on or secured to a deck of said support close to a side of said support, said first carrier structure supporting a plurality of circular turntables arranged one above another; and each of said turntables being suitable for being driven in rotation in powered manner by a first motor about a vertical central axis ZZ independently of one another, each turntable having a central orifice surmounted by a central cylinder against and around which at least one of said flexible pipes can be wound in concentric juxtaposed spiral turns of increasing diameter resting on the top face of said turntable, said central orifice of said turntable being fitted with a rotary joint coupling suitable for providing coupling between firstly a first end that is closest to said central cylinder of a flexible pipe wound around said flexible cylinder, said first pipe end being suitable for being driven in rotation together with said turntable, and secondly an end of a stationary transfer pipe having an other end of said stationary transfer pipe in communication with at least one first tank within said support.

2. The device according to claim 1, wherein said support is installed at sea, in a grounded or a floating manner, and said ship is arranged alongside said support or in tandem adjacent to said support; and said flexible pipe storage device is arranged on said support; and said flexible pipes that are fastened at said first end to said flexible pipe storage device extend between said floating support and said ship.

3. The device according to claim 1, wherein at least one of said flexible pipes is wound, at least in part, against and around said central cylinder in concentric juxtaposed spiral turns of increasing diameters resting on said turntable, said central cylinder presenting a radius greater than the minimum radius of curvature of said flexible pipe.

4. The device according to claim 1, further comprising a plurality of guide means, wherein each guide means is arranged at a different height facing a respective one of each of said turntables so as to be suitable for supporting an intermediate curved pipe portion between a downstream portion of said pipe in a substantially vertical position beside said side and said upstream pipe portion leaving the turntable in continuity with the wound pipe portion resting on said turntable, said upstream pipe portion leaving the turntable extending on a virtual plane P that is substantially tangential to the surface of the top face of said turntable on which said wound pipe portion is wound, the various downstream pipe portions in substantially vertical positions beside said side being arranged in positions that are offset relative to one another in a direction Y2Y2 parallel to said side on leaving said sheaves.

5. The device according to claim 4, wherein: each said guide means comprises a sheave mounted to revolve about a horizontal first axis of rotation Y.sub.1Y.sub.1, said sheave also being suitable for swiveling about a vertical second axis of rotation Z.sub.1Z.sub.1 extending along a diameter of the sheave; the various sheaves are arranged offset side by side relative to one another in said horizontal direction Y.sub.1Y.sub.1 parallel to said side at different heights; and wherein each sheave is supported by a second carrier structure arranged outside said floating support and fastened to a common side at a different position in said horizontal direction Y.sub.1Y.sub.1 parallel to said side, each sheave being mounted to swivel about said vertical second axis of rotation Z.sub.1Z.sub.1 relative to a portion of its second carrier structure fastened to said side.

6. The device according to claim 4, wherein each said guide means being suitable for guiding the portion of said pipe leaving a respective one of each of said turntables in continuity with the portion of pipe wound on said turntable such that the various ones of said pipe portions leaving the various turntables are arranged in straight lines, being offset in different positions along a horizontal direction Y1Y1 parallel to said side, at different heights, and capable of adopting different orientations for vertical axial planes of said pipe portions relative to said horizontal direction Y1Y1parallel to said side.

7. The device according to claim 1, wherein each said turntable includes or co-operates on its under face with wheels suitable for co-operating with or respectively supported by elements of said first carrier structure, and each said turntable including a bearing at said central orifice, the bearing being secured to said first carrier structure and being suitable for enabling said turntable to rotate relative to said first carrier structure.

8. The device according to claim 1, wherein at least one said turntable presents a top face that is plane and horizontal.

9. The device according to claim 1, wherein at least one said turntable presents a top face of convex frustoconical shape.

10. The device according to claim 1, wherein at least one said turntable presents a top face of concave frustoconical shape.

11. The device of claim 1, wherein said first communication valves are butterfly valves and said second connection valves are ball valves.

12. The device of claim 1, wherein said first and second pipe portions are rigid and each of them is held parallel to one another by said respective first and second rigid supports.

13. The device according to claim 1, comprising a second connection and valve device suitable for being arranged on board said ship, said first connection and valve device being connected to said second connection and valve device, said second connection and valve device comprising: n rigid second pipe portions; each said second pipe portion communicating or being suitable for communicating at one of its ends with a second tank inside said ship, and including at its other end a first complementary pipe coupling element, said first complementary pipe coupling element being suitable for co-operating in reversible coupling with said first pipe coupling element, said first complementary pipe coupling element being a female or male automatic connector portion; said second pipe portions being held in positions relative to one another so as to enable said first complementary coupling element to be coupled with said first coupling element; each said second pipe portion having a second connection valve suitable for allowing or preventing fluid from flowing in said second pipe portion towards or from said first complementary coupling element when open or closed, respectively; said second pipe portions being held by a second rigid support to which said second pipe portions are secured.

14. The device according to claim 13, wherein: said support is installed at sea, in a grounded or a floating manner, and said ship is arranged alongside or in tandem adjacent to said support; and said flexible pipe storage device is arranged on said support; and said flexible pipes are fastened at a first end to said flexible pipe storage device, said flexible pipes extending between said floating support and said ship.

15. The device according to claim 13, comprising said support, said storage device, and at least two said flexible pipes, extending between said support and said ship, arranged alongside or in tandem adjacent to said floating support, at least some of said flexible pipes being stored with the help of said flexible pipe storage device, said flexible pipes being fitted with said first connection and valve device, connected to said second connection and valve device arranged or suitable for being arranged on board said ship.

16. The device according to claim 15, wherein said flexible pipes are floating pipes, floating on the surface over at least a fraction of the distance between said support and said ship.

17. The device of claim 13, wherein said first communication valves are butterfly valves and said second connection valves are ball valves.

18. The device of claim 13, wherein said first and second pipe portions are rigid and each of them is held parallel to one another by said respective first and second rigid supports.

19. A method of transferring a liquid petroleum fluid from a support installed at sea, in grounded or floating manner, between said support and a ship, arranged alongside said support or in tandem adjacent to said support by means of a fluid transfer device and a plurality, n, of flexible pipes that are stored on said support by means of a flexible pipe storage device to which a first end of each of said flexible pipes is fastened, said flexible pipes extending between said support and said ship, wherein the fluid transfer device comprises: a first connection and valve device, said flexible pipes being connected together at their second ends by said first connection and valve device, said first connection and valve device having n first pipe portions held in fixed positions relative to one another, n being an integer not less than 3, each said first pipe portion comprising: at a first end, a first pipe coupling element, which is a male or a female portion of an automatic connector; at a second end, a second coupling element, assembled to the second end of one of said flexible pipes; each said first pipe portion including, between its two ends n1 branch connections enabling said first pipe portion to communicate with respective ones of the n1 other said first pipe portions, each of said branch connections including a first communication valve; a first connection valve situated between said first pipe coupling element and said branch connection; said first pipe portions being held by a first rigid support to which said first pipe portions are secured; and a second connection and valve device arranged on board said ship, said first connection and valve device being connected to said second connection and valve device, said second connection and valve device comprising: n rigid second pipe portions; each said second pipe portion communicating at one of its ends with a second tank inside said ship, and including at its other end a first complementary pipe coupling element, said first complementary pipe coupling element being suitable for co-operating in reversible coupling with said first pipe coupling element, said first complementary pipe coupling element being a female or male automatic connector portion; said second pipe portions being held in positions relative to one another so as to enable said first complementary coupling element to be coupled with said first coupling element; each said second pipe portion having a second connection valve suitable for allowing or preventing fluid from flowing in said second pipe portion towards or from said first complementary pipe coupling element when open or closed, respectively; said second pipe portions being held by a second rigid support to which said second pipe portions are secured; wherein said liquid petroleum fluid is transferred in two said flexible pipes comprising a first flexible pipe and a second flexible pipes, and then said first and second flexible pipes used for transferring the liquid petroleum fluid are purged by performing the following successive steps: a. closing said first and second connection valves, and disconnecting said first and second connection and valve devices from each other; b. injecting a purge gas into the first end of said first flexible pipe from said support and opening at least one said first communication valve between said first flexible pipe and said second flexible pipe assembled to the same said first connection and valve device, the other said first communication valves being closed; and then c. closing said first communication valve between said first flexible pipe and said second flexible pipe when said first flexible pipe has been emptied at least in part.

20. The method according to claim 19, wherein said flexible pipes comprise at least two said first and second flexible pipes for transferring liquefied gas therein between said floating support and at least one second tank of said ship, and a third flexible pipe, within which gas corresponding to the gas ceiling of the second tank is transferred from said second tank to a first tank within said floating support or to a liquefaction unit on said support prior to the gas being transferred to said first tank.

21. The method according to claim 19, wherein after step c), said second flexible pipe is completely by performing the following successive steps: d. injecting said purge gas from the support into said first end of said second flexible pipe and opening said first communication valve between said second flexible pipe and a third flexible pipe of smaller diameter than said second flexible pipe so that the flow rate of purge gas is such that the speed of said gas is greater than 1.5 m/s, said other first communication valves being closed; and e. closing said first communication valve between said second and third flexible pipes when said second flexible pipe has been emptied at least in part.

22. The method according to claim 19, wherein said flexible pipe storage device comprises a plurality of turntables arranged one above another on which, when all of said flexible pipes have been purged sufficiently, said flexible pipes are rewound until the second ends of all of said flexible pipes are above water.

23. The method according to claim 22, wherein said first flexible pipe is wound on said turntable having a top face of convex frustoconical shape.

24. The method according to claim 22, wherein at least one of said second flexible pipes used for transferring liquid, is wound on said frustoconical turntable of concave shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear better in the light of the following detailed description made by way of non-limiting illustration and with reference to the drawings, in which:

(2) FIG. 1A is a side view of a floating support 1, 1-1 of the FPSO type for producing and storing LNG shown while offloading to a ship, referred to herein as an offloading ship 2 of the methane tanker type, in a so-called tandem configuration, the FPSO being fitted with a flexible pipe storage and guide device 4 of the invention;

(3) FIG. 1B is a side view of a support 1, 1-2 of the FSRU type grounded on the sea bottom 21 and including a regasification and electricity production unit 1d together with a transformer station for delivering electricity to land, shown while offloading from a methane tanker type ship referred to as a supply ship in a tandem configuration, said floating support being fitted with a flexible pipe storage and guide device 4 of the invention;

(4) FIG. 1C is a side view of a floating support 1-1 of the FPSO type for producing and storing LNG, shown while offloading to an offloading ship 2 of the methane tanker type in a configuration referred to as an alongside configuration, the FPSO being fitted with a flexible pipe storage and guide device 4 of the invention;

(5) FIG. 1D is a side view of a floating support in which said flexible pipes are rewound onto a storage and guide device 4 by means of a said first connection device 13-1 that is above water;

(6) FIG. 2 is a side view, partially in section, showing the storage and guide device 4 of the invention having three superposed turntables 4-1, with FIG. 2 showing only one single flexible pipe guide means 10 with a sheave facing the central turntable so that the various elements making up said guide means can be seen more clearly;

(7) FIG. 3 is a plan view of the FIG. 2 storage and guide device fitted with three guide means 10-1a, 10-1b, and 10-1c that are offset from one another in the horizontal direction Y.sub.1Y.sub.1 parallel to the side 1d on which they are fastened; said top turntable 4-1a being shown without the pipe portion that is normally spiral-wound thereon in continuity with the pipe portion 3-2 leaving the turntable, in order to show the various possible angles of orientation of the pipe portions 3-2 leaving the turntables;

(8) FIG. 3A is a plan view of a turntable of the FIG. 3 device having a spiral-wound flexible pipe portion 3 shown thereon, the sheave 10-1 being shown in section on AA of FIG. 2;

(9) FIGS. 4A, 4B, and 4C are side views of a turntable having a top face of frustoconical shape that is concave (FIG. 4A), of frustoconical shape that is convex (FIG. 4B), or of plane shape (FIG. 4C), with a flexible pipe spiral-wound thereon and bent around guide means 10 at the outlet from said storage turntable;

(10) FIGS. 5A and 5B are plan views of a connection and valve device 13-1 for a set of three flexible pipes, comprising a first connection and valve device 13-1 at the ends of the three flexible pipes connected to a second connection device 13-2 arranged on board the offloading ship 2 (FIG. 5A); said first and second connection and valve devices 13-1 and 13-2 being disconnected in order to purge said pipe (FIG. 5B);

(11) FIG. 6 is a face view in section on BB in FIG. 5A showing said first connection and valve device;

(12) FIGS. 7A, 7B, 7C, and 7D are diagrammatic views showing various possible arrangements for fluid flow between the flexible pipes when the various valves of the first connection and valve device 13-1 are closed, in order to purge said flexible pipes; and

(13) FIGS. 8A and 8B show a flexible pipe 3b, 3c for transferring LNG from a turntable of convex shape to an offloading ship 2 while purging said pipe (FIG. 8A) and a flexible pipe 3a for returning gas co-operating with a turntable of concave shape while it is being purged (FIG. 8B).

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(14) FIG. 1A is a side view of a floating support 1 of the invention of FPSO type 1-1 anchored 1a on a gas production field in open sea.

(15) Said FPSO possesses equipment 1b for processing and liquefying gas together with first tanks 11 for storing LNG incorporated within its hull.

(16) A methane tanker type offloading ship 2 is positioned in tandem substantially on the axis of said FPSO and is connected thereto by a set of three flexible pipes 3A, 3B, and 3C that are handled by means of a storage and guide device 4 of the invention for storing and guiding flexible pipes 3, which device is described in greater detail below.

(17) Said flexible pipes 3 are floating flexible pipes of the type manufactured and sold by the supplier Trelleborg (France), being constituted essentially by metal or composite reinforcement together with thermoplastics or vulcanized elastomers.

(18) Such pipes for offload transfer of liquefied gas conventionally presents inside diameters lying in the range 250 millimeters (mm) to 600 mm, and outside diameters in the range 400 mm to 1000 mm. They are generally manufactured in lengths of 12 m and they are assembled together via their ends that are fitted with flanges so as to obtain lengths lying in the range 120 m to 250 m. In the same manner, the pipes for return transfer of gas in the gaseous state between the offloading ship 2 and the floating support 1 in a manner that is explained below, present the same total lengths but are advantageously of smaller diameter, having an inside diameter lying in the range 150 mm to 400 mm.

(19) Under certain circumstances, it is preferable for gas return to have pipes that are identical to the LNG transfer pipes, thereby presenting an advantage in terms of storing spare parts, since all of the elements are then identical.

(20) FIG. 2 is a side view partially in section of the device 4 for storing and guiding flexible pipes 3. The storage device is constituted by a plurality, three in this example, of turntables 4-1, 4a, 4b, 4c arranged one above another, preferably on a common vertical axis of rotation ZZ.

(21) The three turntables 4-1 are supported by a first carrier structure 5 resting on the deck 1c of the floating support 1 close to a side 1d and at one of its longitudinal ends.

(22) As shown in FIG. 3, the first carrier structure 5 in this example has eight vertical posts 5b that are connected together by first horizontal beams 5c at different heights, and by second horizontal beams 5a arranged radially and diametrically between the diametrically opposite vertical posts 5b. Said horizontal beams 5a constitute horizontal carrier structures at three different heights, each suitable for supporting one of the three turntables 4-1.

(23) At its center, each of said turntables presents an orifice 4-2 together with a bearing 4-4, e.g. a roller bearing, said bearing being secured in part to a said horizontal carrier structure 5a and enabling said rotation of the turntable about its central axis of rotation ZZ with the help of a first motor 6 and of wheels 4-5 that are described below.

(24) Each turntable 4-1 is supported at its periphery and via its bottom face by a series of wheels 4-5, that are preferably uniformly distributed around its periphery, the supports 4-5a of said wheels 4-5 being secured to a said horizontal carrier structure 5a.

(25) Each turntable 4-1 is set into rotation about its vertical axis ZZ by means of a first motor 6, preferably a hydraulic motor, that imparts rotary drive to an outlet shaft carrying a gear that co-operates with a toothed wheel 6-1 secured to said turntable 4-1, thereby driving said turntable in rotation when said outlet shaft is itself driven in rotation.

(26) A central cylinder 4-3 is arranged on top of said orifice 4-2 in each of said turntables. The outside radius of said central cylinder 4-3 is greater than the minimum radius of curvature of said flexible pipe that is to be wound with concentric touching spiral turns resting side by side on said turntable. Said central cylinder 4-3 is secured to said turntable 4-1.

(27) As shown in FIG. 4, a rotary joint coupling 7 of type known to the person skilled in the art is installed on the axis ZZ of each said turntable 4-1.

(28) It is constituted by a rotary joint proper 7-1 having a top portion fitted with a top bend 7-2 with its end coming against the wall of said central cylinder 4-3. The end of the top bend 7-2 is connected in leaktight manner at 7a to a first end 3-1 of a flexible pipe 3 that is to be spiral-wound against and around said central cylinder 4-3 when said turntable 4-1 is driven in rotation. The bottom portion of the rotary joint 7-1 comprises a bottom 7-3 that remains stationary while said top bend 7-2 is driven in rotating by rotation of said turntable 4-1. The bottom bend 7-3 is itself connected in leaktight manner to an end 8-1 of a transfer pipe 8 having its other end connected either to a first tank 11 of the FPSO 1, thereby enabling LNG coming from said first tank 11 to be taken to the FPSO 1, or else to a reliquefaction unit on board the FPSO, thereby enabling gas coming from said offloading ship 2 to be returned to said reliquefaction unit.

(29) All of the various transfer pipes 8 pass through respective central orifices 4-2 of the various turntables 4-1.

(30) Each flexible pipe 3, 3a-3b-3c is guided by guide means 10, only one of which is shown in FIG. 2, each guide means 10 comprising a sheave 10-1 arranged in a substantially vertical axial plane and suitable for revolving fast about a horizontal first axis of rotation Y.sub.1Y.sub.1.

(31) The sheave 10-1 presents a radius that is greater than the minimum radius of curvature of said flexible pipe 3 that is to be wound around said sheave.

(32) Said sheaves 10-1, 10-1a, 10-1b, 10-1c are arranged close to and facing respective ones of said turntables 4-1 in such a manner that the groove in each of said sheaves has its highest point substantially level with a virtual plane P that is tangential to the top face 4-1a, which virtual plane P has resting thereon the pipe portion 3-2 that leaves said turntable.

(33) In other words, the generator line for the surface of revolution constituting the top face 4-1a of said circular turntable 4-1 is tangential to the groove of said sheave at its highest point.

(34) In this way, the flexible pipe portion 3-2 leaving said turntable 4-1, i.e. that is in continuity with the last turn wound on said turntable 4-1, is guided more accurately during operations of winding and unwinding said pipe during rotation of said turntable 4-1 and during rotation of said sheave 10-1 about its horizontal axis X.sub.1X.sub.1.

(35) Each sheave 10-1 is secured to a second carrier structure 10-1 comprising a vertical support 10-3 terminated at its top end by a fork supporting the horizontal hub arranged on the first axis of rotation Y.sub.1Y.sub.1 about which the sheave 10-1a of FIG. 3 revolves, said vertical support 10-3 being hinged to swivel about a vertical second axis of rotation Z.sub.1Z.sub.1 at the top of a stationary pylon 10-4 resting on a structure 10-5 that is itself secured to the hull of the FPSO 1 on said side 1d. Because said vertical support 10-3 can be hinged to swivel freely about its vertical axis Z.sub.1Z.sub.1, said sheave 10-1 is suitable for swiveling about said vertical second axis of rotation Z.sub.1Z.sub.1.

(36) Furthermore, the vertical support 10-3 supporting the sheave 10-1 is suitable for being moved vertically in order to adjust the position of the top of the sheave relative to the plane tangential to the top face of the turntable 4-1 in front of which it is arranged.

(37) As shown in FIG. 3, such swiveling about the second axis of rotation Z.sub.1Z.sub.1 of said sheave 10-1 takes place progressively as the last point of contact of the last turn of the pipe wound on said turntable moves away from the center of the turntable between two limit points O and M, O being the point closest to the cylinder 4-3 (pipe fully unwound) and M being the point closest to the periphery of the turntable (pipe fully wound), as shown in FIG. 3.

(38) Also in FIG. 3, the three sheaves 10-1: 10-1a, 10-1b, and 10-1c are offset from one another in the horizontal direction Y.sub.1Y.sub.1 parallel to the side 1d. Furthermore, the substantially vertical axial planes P1, P2, and P3 of the three sheaves 10-1a, 10-1b, and 10-1c respectively may present variable angles of orientation 1, 2, and 3 respectively relative to said direction Y.sub.1Y.sub.1. Said substantially vertical axial planes P1, P2, and P3 of the three sheaves can swivel about said second axes of rotation through respective angles .sub.1, .sub.2, and .sub.3 between: a first limit position in which said pipe portion 3-2 leaving said turntable 4-1 for passing over the inlet of said sheave 10-1 is level with the last wound turn at the periphery of said turntable 4-1 at M; and a second limit position for said swiveling of each of the sheaves 10-1 in which the pipe portion 3-2 leaving the turntable is level with the point O corresponding to the position of said first flexible pipe end 3-1 close to the central cylinder 4-3.

(39) Said axial planes P1, P2, and P3 of the three sheaves also correspond to the substantially vertical axial planes of the three upstream pipe portions extending between each of said turntables and each of said sheaves, respectively.

(40) Each sheave 10-1 is preferably motor driven by a second motor 10-6, preferably a hydraulic motor, co-operating with a toothed ring (not shown) secured to said sheave and enabling each of said sheaves 10-1 to be driven to revolve about its own horizontal said first axis of revolution Y.sub.1Y.sub.1.

(41) The fact that the various sheaves 10-1 are arranged at different heights corresponding to the heights of said turntable 4-1 that it serves, and the fact that said sheaves 10-1 are arranged one beside another in a manner that is offset in the direction Y.sub.1Y.sub.1, in spite of the swivel angles 1, 2, and 3 of each of the three sheaves 10-1a, 10-1b, 10-1c, there is no risk of said sheaves interfering with one another.

(42) As shown in FIG. 2, curved intermediate portions 3-3 of flexible pipe 3 bent around a sheave 10-1 are followed by respective downstream pipe portions 3-4 in substantially vertical positions that reach the surface 20 of the sea on which the pipes float over respective fractions 3-5 of their length on going towards the ship 2.

(43) As shown in FIG. 3, the vertical downstream portions 3-4 of the various pipes 3, 3a, 3b, 3c are offset in a direction Y.sub.1Y.sub.1, but they remain in axial planes that are substantially vertical and substantially parallel in spite of said swiveling of said sheaves 10-1a, 10-1b, 10-1c about their second axes of rotation Z.sub.1Z.sub.1.

(44) In FIG. 1C, there can be seen a variant implementation in which the methane tanker 2 is arranged alongside the floating support 1, with the floating support 1-1 and the ship 2 in this implementation being arranged parallel and side by side along their respective longitudinal sides extending in their longitudinal directions XX, and the flexible pipes 3 connecting the device 4 on board the support 1-2 to the ship 2 are located above the level of the sea 20. More particularly, the flexible pipes 3 adopt a catenary-shaped configuration above the level of the sea 20 from the outlets of the sheaves 10-1 level with the storage and guide devices 4 of the floating support 1 and extending to the common valve device 13 on board the offloading methane tanker ship 2.

(45) By way of illustration, a turntable 4-1 presents a diameter of about 20 m. The height of the storage device 4, i.e. the height of the various posts 5b is about 15 m to 20 m for three turntables 4-1 that are spaced apart from one another vertically by 4 m to 5 m. A central cylinder 4-3 typically presents a diameter lying in the range 5 m to 8 m.

(46) Such a device 4 is particularly suitable for receiving flexible pipes having a diameter lying in the range 120 mm to 600 mm and presenting a length lying in the range 120 m to 250 m.

(47) Each of said turntables 4-1 can be set into rotation about its axis ZZ independently of any of the others. The same applies to the motor drive for said rotary movement of said sheaves 10-1 about their first axis of rotation. It is thus possible to adjust the tension and the length of each of said flexible pipes 3a, 3b, and 3c independently of any of the others so that said flexible pipes extend between the vertical portions 3-4 at the outlet from the sheaves 10-1 and a common valve device 13, also known as a connection and purge device, that is located on board the offloading ship 2 and to which the various second ends of the various flexible pipes 3a, 3b, and 3c are connected, with the tensions and lengths of said pipes being adjusted to be substantially equal throughout all winding and unwinding operations of said flexible pipe. Generally speaking, since the respective diameters of each said flexible pipes may be different, it is necessary to have different numbers of revolutions of the turntables for each of said flexible pipes 3a, 3b, and 3c in order to store the same length for each flexible pipe.

(48) Once the pipes are rewound onto their respective turntables 4-1, it is advantageous to use a turntable having a top face 4-1a that is of frustoconical shape that is concave 4-1b or convex 4-1c, as shown in FIGS. 4A and 4B respectively, in order to fully purge the residual LNG from within said wound pipe that has been used for transferring LNG from the floating support 1 to the methane tanker 2, and as a function of conditions of use for said pipes during purging as described below.

(49) The flexible pipes 3b, 3c conveying LNG stored in a first tank 11 of the support 1 to the ship 2 are of very large diameter in order to optimize the rate at which LNG is transferred, whereas the returning gas can be conveyed using a single pipe, generally a pipe of smaller diameter, since head losses are much smaller for gas than for LNG.

(50) It should be recalled that LNG is essentially constituted by liquid methane at 165 C., and that the offloading ships are constituted by methane tankers, i.e. by ships that transport LNG in tanks that, when empty, are in fact full of gaseous methane, possibly together with some nitrogen, coming from the regasification of LNG. The use of gas return pipes is intended firstly to remove the gas ceilings from the second tanks progressively as they are being filled with LNG coming from the first tanks, and secondly to remove LNG that has become regassified while it is being transported as a result of relative heating. Once the gas has been returned to the support 1, it is reliquefied to become LNG.

(51) There follows a description of the connection and valve device 13 together with the method of purging flexible pipes before they are rewound on their turntables. This purging is necessary firstly to lighten the flexible pipes and make them easier to rewind, and also to avoid damaging said flexible pipes while they are being rewound on said turntables, where such damage could arise as a result of the pipes being excessively heavy when full of liquid, and because of the presence of sea water ice on the surface of the pipes or on the connection elements.

(52) The connection and valve device 13 shown in FIGS. 5A, 5B, and 6 comprises:

(53) a) a first valve and connection device 13-1 arranged at the ends of said flexible pipes 3a, 3b, and 3c, and comprising: i. three first rigid pipe portions 21a, 21b, and 21c held in stationary positions relative to one another and in parallel; and ii. each said first rigid pipe portion 21a, 21b, and 21c comprising: at a first end, a first pipe coupling element 23-1a, 23-1b, 23-1c constituted by a male or female portion of an automatic connector; at its second end 3-6, an assembly flange 31 assembled to said second end 3-6 of the corresponding flexible pipe 3a, 3b, 3c; between the two ends of each said first rigid pipe portion, each of said first rigid pipe portions has two communication branch connections 30 each having a first communication valve 30ab, 30ac, 30bc, said branch connection 30 enabling each said first rigid pipe portion to communicate with one of the other two first rigid pipe portions of said device 13-1; and a first connection valve 22a, 22b, 22c situated between said first coupling element 23-1a, 23-1b, 23-1c and said branch connection 30 that is the closest to said first end of said first device 13-1; and

(54) b) a second connection and valve device 13-2 arranged on board said offloading ship 2 and comprising: three second rigid pipe portions 26a, 26b, 26c held in stationary positions relative to one another and in parallel; each said second rigid pipe portion 26a, 26b, 26c communicating at one of its ends with a said second tank 12 of the ship 2 and having at its other end a first complementary pipe coupling element 23-2a, 23-2b, 23-2c, said first complementary coupling elements being constituted by a female and/or respectively male portion of an automatic connector, i.e. a portion that is complementary to a said first coupling element 23 specifically so as to enable said first device 13-1 and said second device 13-2 to be coupled together; and each said second rigid pipe portion further including a second connection valve 27a, 27b, 27c. Said first rigid pipe portions being held together in a mutually parallel assembly by a first rigid support 24 to which they are secured at 24a, 24b, and 24c. Likewise, said second rigid pipe portions 26a, 26b, 26c are held together as a mutually parallel assembly by a second rigid support 25 to which they are secured at 25a, 25b, and 25c.

(55) Advantageously, the various valves are ball valves or butterfly valves.

(56) Because said first coupling elements are held together securely at constant distances from one another by said first support 24 to which they are secured at 24a, 24b, and 24c, and because said first complementary coupling elements are likewise held firstly at constant distances from one another that are identical to the distances between said first coupling elements, said first and second devices 13-1 and 13-2 can be connected together automatically by remotely controlled actuators (not shown), with it being possible for this to be done in a single sequence.

(57) FIG. 5B is a plan view showing the connectors during an approach stage prior to connection, with all of the valves 22a, 22b, and 22c of the devices 13-1 and 13-2 being closed.

(58) In FIG. 5A, the automatic connectors 23-1/23-2 are locked in leaktight manner and the valves 22a-22b-22c and also the valves 27a-27b-27c are in the open position, thus allowing LNG to pass from left to right in the two pipes 3b and 3c from the support 4 to the offloading ship 2, and allowing methane gas to pass in the return direction, from right to left, in the central pipe 3a from the offloading ship 2 to the FPSO 1.

(59) For clarity of explanations with reference to FIGS. 5A-5B, 7A-7B-7C-7D, and 8A-8B, transfers of LNG are represented by a two-line arrow and transfers of gas are represented by a single-line arrow, with the length of such an arrow being proportional to the flow rate in the corresponding pipe.

(60) The first valve device 13-1 is provided with a third series of communication valves between said first pipe portions 21a-21b-21c that are arranged as follows: a valve 30ac connects together the first pipe portions 21a and 21c; a valve 30ab connects together the first pipe portions 21a and 21b; and a valve 30bc connects together the first pipe portions 21b and 21c.

(61) During operations of transferring LNG from the offloading ship 2, said three vales 30ab, 30ac, and 30bc are in the closed position, as shown in FIG. 5A.

(62) In order not to leave the flexible pipes 3a, 3b, 3c floating on the sea between two transfers of LNG, which might represent a duration of several weeks, the flexible pipes are rewound on the turntables 4-1, preferably after they have been purged as follows: the valves 22a-22b-22c of the first common valve device 13-1 and also the valves 27a, 27b, 27c of the second common valve device 13-2 on board the offloading ship 2 are all closed; then said coupling elements 23 of the first and second valve devices 13-1 and 13-2 are disconnected; then the flexible pipes 3a, 3b, 3c together with their first connection device 13-1 are let go, which flexible pipes then float on the surface of the water 20; then a communication valve 30bc between the two first rigid pipe portions 21b and 21c communicating with the flexible pipes 3b and 3c respectively as shown in FIG. 7A are opened; then a first pipe, e.g. the pipe 3b, is pressurized from the FPSO 1 to a pressure P with the help of gas, generally methane or a mixture of nitrogen and methane so as to be able to push the LNG; the gas pressure pushes the LNG within said pipe 3b and the plane of separation between the liquid and gas phases moves progressively downwards in said pipe 3b as the LNG rises towards the FPSO via the second pipe 3c. Once said plane of separation reaches the pipe portion 3-5 at sea level, the flexible pipe 3b is then substantially horizontal and the gas continues to push, but a two-phase mixture then forms under pressure that travels towards the first valve device 13-1, and then passes through said valve 30bc and returns therefrom towards the FPSO via the flexible pipe 3c. The two-phase mixture has bubbles of small diameter at the level of the surface of the sea, but as soon as they reach the vertical portion 3-4 of said pipe 3c, given that hydrostatic pressure decreases on rising towards the deck of the FPSO, the bubbles become larger and the apparent density of the mixture decreases, thereby correspondingly accelerating the speed of the rising two-phase column, and as a result improving the entrainment of the liquid phase; and then when the horizontal portions 3-5 of the two flexible pipes 3b and 3c are substantially emptied, i.e. are substantially full of gas, the flow rate of gas from the FPSO in the pipe 3b is accelerated so as to greatly increase the disturbance to the two-phase flow in the substantially vertical portion 3-4 of the second pipe 3c, thereby having the effect of optimally entraining particles of LNG and thus enabling at least 85% and in practice 85% to 95% of the inside volume of both pipes 3b and 3c.

(63) More particularly, and as a general rule, the pipe 3b is empty while liquid remains in the pipe 3c occupying 10% to 20% of the inside volume of the pipe 3c, in particular in its substantially vertical portion 3-4, as shown in FIG. 8B.

(64) The purge process described above with reference to FIG. 7A is relatively fast and purging can thus be performed on pipes having a length of 100 m to 150 m in a duration of half an hour to 1 hour (h), whereas more than 24 h would be required for the LNG contained in the pipes to heat up and become gaseous.

(65) FIGS. 7B and 7C show a technique for purging the flexible pipes 3b and 3c more completely, in which a first flexible pipe 3c is purged by injecting gas from the gas return pipe 3a. For this purpose, the valve 30ac is opened while the valves 30ab and 30bc are closed, as shown in FIG. 7B. Purging is stopped when substantially all of the LNG, i.e. at least 85% of the LNG in the pipe 3c has been recovered on board the FPSO. Thereafter, the valve 30ac is closed and the valve 30ab is opened, thereby having the effect of purging the second flexible pipe 3b in the same manner, until at least 85% of the LNG in the pipe 3b has been recovered on board the FPSO. Finally, as shown in FIG. 7C, the direction of gas injection is reversed, with gas being injected directly into the two flexible pipes 3b and 3c, and with the LNG then returning via the pipe 3a. This arrangement presents a major advantage when said gas return pipe 3a is of smaller diameter. In order to cause the two-phase mixture to rise in the vertical portion 3-4 of the pipe 3a, the flow rate of gas needed in the pipes 3b and 3c is considerably smaller than in the situation described above with reference to FIG. 5A in which the two flexible pipes 3b and 3c are generally of the same diameter for the purpose of optimizing the rate at which LNG is transferred.

(66) In order to optimize emptying of the rising vertical pipe portion, it is appropriate to create a purge gas speed greater than 1.5 m/s, preferably greater than 3 m/s, and more preferably greater than 5 m/s. Thus, giving consideration to a pipe of small diameter, the gas flow rate needed to obtain such a speed decreases with the square of the ratio of the diameters, thus illustrating the advantageous nature of having a gas return pipe that is of smaller diameter.

(67) To further improve this stage of purging the pipes 3b and 3c, it is advantageous to proceed sequentially as shown in FIG. 7D in order to purge the pipe 3c completely by closing the valve 30ab in order to finalize the purging of the flexible pipe 3c, and then by opening the same valve 30ab while closing the valve 30ac in order to finalize purging of the flexible pipe 3c by injecting gas into the pipe 3c so to evacuate the residual LNG via the pipe 3a.

(68) FIG. 8A is a side view of the flexible pipe 3b from its storage turntable down to sea level. The convex storage turntable 4-1b presents a convex frustoconical top face with a negative angle , which is advantageous for the stage of purging flexible pipes, since in the description of the invention as given with reference to FIG. 7A, it is via this pipe that the purge gas is injected, and because of the conical shape of the storage turntable, the pipe naturally empties downwards.

(69) FIG. 8B is a side view of the flexible pipe 3b from its storage turntable down to sea level. The concave storage turntable 4-1c presents a concave frustoconical top face with a positive angle , which is advantageous for the stage of purging the flexible pipes, since in the description of the invention as given with reference to FIGS. 7A and 7B, it is via this pipe that the two-phase mixture rises towards the FPSO, and it is via the conical shape of the storage turntable that the pipe stored as a spiral winding on said conical turntable empties naturally towards the rotary joint 7 situated on the axis ZZ of the turntable. This FIG. 8B also shows that pipes practically empty in its horizontal portion 3-5, with the two-phase mixture in the substantially cylindrical portion 3-4 presenting bubbles of small diameter towards the bottom and of diameter that increases as the mixture rises along the pipe towards the storage turntable.

(70) For the pipe portion 3-4 having a height lying in the range 30 m to 35 m, corresponding to a pressure difference of 1.5 bars to 2 bars, the bubbles in the bottom portion will have a diameter lying in the range 5 mm to 10 mm, while the bubbles in the top portion will have a much larger diameter as a result of the pressure difference, lying in the range several centimeters to several decimeters, thereby having the effect of reducing the density of the two-phase mixture in the fluid column and thus encouraging its entrainment and offload at the level of the turntable: with this phenomenon being referred to as gas-lift.

(71) In the purging technique described with reference to FIGS. 7C and 7D, the turntable for storing the gas return pipe (FIG. 7C) 3a (FIG. 7D) is advantageously of the concave conical type with a positive angle .

(72) When the gas return pipe presents an inside diameter that is smaller than the inside diameter of the LNG pipes, the preferred purging method comprises the following two purging steps: a first step of purging a pipe 3b by injecting gas into the pipe 3b leading to the pipe 3b being purged completely while purging the pipe 3c only partially given the residual LNG gas, in particular in the portion 3-4 of the pipe 3c when the various valves are operated as described with reference to FIG. 7A. At the end of this first step, the pipe 3c still retains about 15% of its inside volume filled with LNG; then the valve 30bc is closed and the valve 30ac is open; and the second purging step is performed by injecting gas into the pipe 3c and discharging it via the gas return pipe 3a of smaller diameter by setting the various valves in the manner described with reference to FIG. 7C. Because the gas is exhausted via the smaller-diameter pipe 3a, the flow rate of gas needed in the pipe 3c is considerably reduced so as to obtain an optimum speed for the two-phase fluid, corresponding to a gas speed greater than 1.5 m/s, preferably greater than 3 m/s, and more preferably greater than 5 m/s. Because the section of the pipe 3a is smaller, the transfer of liquid takes place more slowly, but purging is greatly improved thereby in terms of the ultimate percentage of two-phase liquid that is purged and in terms of overall duration.

(73) After the three pipes 3a, 3b, and 3c have been purged, they are rewound onto their respective turntables until said first connection device 13-1 comes above the level of the water, and more particularly substantially just below the lowest turntable of the flexible pipes held together by the device 13-1, as shown in FIG. 1D, it thus being possible for the first connection device 13-1 to remain permanently connected to said second end 3-6 of said pipes 3a, 3b, and 3c that are connected together by said first device 13-1.

(74) By way of example, a transfer device of the invention comprises: two LNG flexible pipes having an inside diameter of 500 mm and an outside diameter of 900 mm, each of these pipes being 216 m long and being made up of 18 identical 12 m long segments assembled together by flanges, and weighing 300 kilograms per meter (kg/m) when empty; a flexible gas return pipe with an inside diameter of 250 mm and an outside diameter of 400 mm, the pipes being 216 m long and being made up of 18 identical 12 m long segments assembled together by flanges and weighing 125 kg/m when empty; a connection and valve device 13 fitted with ball valves 22 with an inside diameter of 500 mm for LNG and of 250 mm for gas return, the valves 30ab-30ac-30bc being butterfly valves with a flow-passing diameter of 250 mm, and weighing about 20 (metric) tonnes (t); and three motor-driven storage turntables 4 having an outside diameter of 23 m and a cylinder of diameter of 5 m, three motor-driven sheaves with a grooved diameter of 5 m, and their supporting structure, the entire assembly weighing about 1000 t.

(75) The procedure of purging the pipes is performed at a gas speed of 4 m/s under such conditions and occupies a total duration of 30 minutes (min) to 45 min so as to obtain an overall residue of LNG that is less than 1% of the overall volume of a pipe, which represents about 425 liters (L) of residual LNG that then produce 250 cubic meters (m.sup.3) of gaseous methane that will thus ultimately be reliquefied on board the FPSO.