Abstract:
An offshore fluid transfer system comprising a boom ( 2100 ) and at least one movable fluid conveying pipe ( 3000 ) attached to the boom, said movable pipe ( 3000 ) comprising, starting from its anchorage point, a length for extension, then an outer valve ( 3210 ) for coupling to a third party loading pipe, a maneuvering cable called outer maneuvering cable ( 4100 ) maneuvered from the boom ( 2100 ) being furthermore linked to the free end of the movable pipe at a point referred to as cable anchorage point, characterized in that the anchorage point is rigidly connected to the outer valve ( 3210 ). The invention also relates to the corresponding method.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an off-shore fluid transfer system and to an associated transfer method. The fluid may be liquefied natural gas for example and the transfer may be made between two ships on the open sea. 
     The first of the two ships may be a production ship known by the name LNGP (for “Liquefied Natural Gas Producer”), LNG-FPSO (for “Liquefied Natural Gas Floating Production Storage and Offloading”) or FLNG (for “Floating Liquid Natural Gas Unit”), a reliquefaction ship (FSRU for “Floating Storage and Regasification Unit”), a GBS (for “Gravity Base Structure”) or lastly a platform. 
     The second of the two ships may be a ship adapted to receive the gas for its transport, such as a tanker or an LNG-C (for “Liquefied Natural Gas Carrier”, for example a methane tanker). 
     Systems are known with rigid piping articulated to two successive arms and other flexible piping systems such as cryogenic hoses. One of the two structures, often the FLNG, possesses such movable piping extending over several meters outside the perimeter of its hull, a few meters above the level of the sea, and being adapted to be connected to ducts fixed to the second structure, within the perimeter of the hull thereof, in vertical alignment with the hull, or at a slight horizontal distance therefrom. Thanks to the flexibility in three dimensions given either by the two articulations controlling the arms, or by the flexible character of the piping, the transfer of fluid may be carried out successfully on a rough sea. 
     Systems are known, for example from the document EP0947464, using a coupling in which the movable piping, which is articulated, comprises a fastening flange which, disposed vertically, couples by a descending movement with a connector of the second structure which is open upwardly. A complex system of counterweights or cables raised from a support structure ensures, in case of disconnection, by leverage, the spontaneous rotation upwardly of the distal part of the articulated piping around an articulation disposed at mid-length of the piping, so as to avoid striking between that distal part and the second structure. During the connection, an additional cable provides for the positioning of the fastening flange relative to the connector of the second structure. This cable is fastened to the movable piping before a final assembly of swivel joints or rotations, which results in the opening of the piping being spontaneously oriented downwards, due to gravity. The connection is complicated by this configuration, since the approach of the fastening flange in the presence of motion due to the waves is delicate. 
     By contrast, patent application FR 2 941 434 describes a transfer system using, for the connection of the articulated tube that comes from the first ship to the piping of the second ship, an acquisition cable (also called LNGC cable or methane tanker cable) fastened to the free end of the tube and maneuvered by a winch disposed on the second ship. This solution enables the coupling of the ducts to be carried out by a movement of the free end of the articulated tube having a rising main component, the free end then being received by a connector on the second ship the opening of which is substantially downwardly directed. Such a solution enables shocks during the connection to be avoided simply, and to establish a coupling requiring no guidance other than that given by the acquisition cable. 
     Nevertheless, despite the solutions proposed until now, certain situations may still be difficult to manage during maneuvers. In particular, in a situation of emergency disconnection, it is desired to avoid plunging of the free end of the movable piping into the water. Furthermore, given the fast rates necessitated by the use of the structures, it is desired to enable the two ships to connect their ducting rapidly, and to move apart from each other as fast as possible after the disconnection, whatever the circumstances thereof. 
     SUMMARY OF THE INVENTION 
     The present invention thus relates to a system and a method enabling fluid transfer to be carried out even more simply, quickly and safely, by simplifying in particular the steps of connecting and disconnecting the piping of the two ships. 
     To that end there is provided an offshore fluid transfer system comprising a boom and at least one movable fluid conveying pipe attached to a point on the boom, said movable pipe comprising, starting from its anchorage point, a length for extension, then, at its free end, an outer valve for coupling to a third party loading pipe, a maneuvering cable called outer maneuvering cable maneuvered from the boom being furthermore linked to the free end of the movable pipe at a point referred to as anchorage point, characterized in that the anchorage point is rigidly connected (with no degree of freedom) to the outer valve. 
     Thanks to this device, it is possible to extend the movable conveying pipe prior to any connection with a third party floating unit, while having the advantage, once that unit is present, of a fast connection by means for coupling by rising movement, such as those referred to in FR 2 941 434. 
     Furthermore, it is possible, during disconnection, to have the advantage of a fast and simplified disconnection by the coupling means. This disconnection is then carried out by decoupling by descending movement. It is followed by an action of removing the links with the third party floating unit, which may therefore go away, before retracting the movable conveying pipe. 
     Lastly, in all the configurations and in all the sequences, including in case of emergency disconnection, the touching of the water by the free end of the movable pipe may be avoided by virtue of the outer maneuvering cable installed between the free end of the movable pipe and a point on the boom. 
     In an embodiment, on the movable pipe, on the approach to the free end, there has been disposed a set of swivel joints disposed such that the set of swivel joints is included between the length for extension and the anchorage point. The swivel joints are in particular necessary to enable the system to tolerate the movements imposed by the outer environment (waves, wind, current, etc.). In addition, however, the fact that the outer maneuvering cable is positioned after the last swivel joint enables the opening of the outer valve to be maneuvered upwardly, contrary to what is presented in EP0947464. 
     According to an advantageous feature, there is provided a safety device configured to maintain a constant unwound length of the outer maneuvering cable in case of emergency disconnection between the movable pipe and the third party loading pipe. 
     According to one embodiment, the movable pipe is constituted by at least two successive articulated arms. Alternatively, it is constituted by at least one flexible pipe. 
     According to particular features, the means for coupling by rising movement comprises at least one centering cone, male or female, and/or an anchorage point for an acquisition cable. The anchorage point may be on a transverse holding structure joining at least two movable fluid conveying pipes parallel to each other in the vicinity of their free end. 
     There is also provided a method for offshore fluid transfer by at least one movable fluid conveying pipe attached to a boom and comprising, starting from its anchorage point, a length for extension then an outer valve for coupling to a third party loading pipe, the general maneuver for coupling or for decoupling comprising a step of extending, or respectively of retracting, the movable pipe using an outer maneuvering cable maneuvered from the boom and linked to the movable pipe at a point referred to as anchorage point, characterized in that the anchorage point is rigidly connected (with no degree of freedom) to the outer valve. 
     Thanks to this method, it is possible to extend the movable conveying pipe prior to any connection with a third party floating unit, which may then approach even though the pipe is already extended, while having the advantage, once the third party floating unit is present, of a fast connection by means for coupling by a rising movement, such as those presented in FR 2 941 434. 
     Furthermore, it is possible, during disconnection, to have the advantage of a fast and simplified disconnection by the coupling means. This disconnection is then carried out by decoupling by descending movement. It is followed by an action of removing the links with the third party floating unit before retracting the movable conveying pipe. 
     According to a feature of implementation, the step of extending, or respectively of retracting, is carried out with the use of a second maneuvering cable, referred to as inner maneuvering cable, linking an intermediate point of the movable pipe to the boom. By virtue of this feature, the tension in the outer maneuvering cable is reduced relative to the prior art. 
     According to an advantageous feature, the coupling or uncoupling is carried out by maneuvering the free end also using an acquisition cable linking said free end to a point on a third party floating unit. 
     According to a feature of implementation, the coupling or the uncoupling is carried out in at least two steps, the outer maneuvering cable being wound or unwound during at least one step and the acquisition cable being wound or unwound during at least the other step. 
     According to a feature of implementation, a safety cable links a point on the third party floating unit and a structure fastened to the free end of the movable pipe during the fluid transfer, said safety cable being configured to unwind at a speed lower than a maximum speed of safety in case of emergency disconnection. This feature makes it possible to widen the perimeter of the conditions for use of the system in complete safety, the movable pipe being progressively released by the third party floating unit during the emergency disconnection process. 
     The structure fastened to the free end of the movable pipe during the transfer of the fluid is for example a lower valve of a valve-coupler of the third party loading pipe, said valve-coupler comprising a lower valve and an upper valve separated by an emergency decoupling system. 
     According to a feature of implementation, the coupling or the decoupling is carried out in at least two steps, centering cones entering into contact and into abutment during a first step, and a coupler, for example a hydraulic and/or automatic coupler, engaging a connection such that the fastening flanges are in contact and are centered, during a second step. 
     Other features and advantages of the invention will appear in the light of the following description, which is non-limiting and made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 5  present different successive steps of a method of connecting the piping of the two ships using the transfer system according to the invention. 
         FIG. 6  presents a three quarters view of the connection members of the piping of the two ships. 
         FIGS. 7 and 8  represent the side view of the connection members of the piping of the two ships, in connected and disconnected position, respectively. 
         FIGS. 9 to 12  present different successive steps of a procedure for disconnection of the transfer piping of the two ships using a transfer system according to the invention. 
         FIGS. 13 to 16  present different successive steps of a method of emergency disconnection of the piping of the two ships using a transfer system according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , a methane tanker  1000  has been represented close to a production ship  2000 . A support structure  2100  is fastened to the production ship  2000 . This support structure  2100  is essentially constituted by metal beams and it comprises a first rising segment  2150  fastened to the ship followed by a second horizontal segment  2160 . The assembly of the two segments constitutes a boom which extends outside the area of the production ship  2000  above the water, and whose rising segment constitutes the leg. Furthermore, the horizontal segment is extended by a pointed segment  2170  culminating at a slightly greater height than that of the horizontal segment at the distance of several meters from the hull of the production ship  2000 . As the drawing constitutes a side view, there may in reality be several of the members represented singly, disposed in line with each other perpendicularly to the plane of the view. 
     An articulated tube  3000  is fastened to the support structure  2100  at the junction between the horizontal segment  2160  and the pointed segment  2170  on the lower part of the support structure  2100 . Although the articulated tube  3000  is single in the view of the drawing, several tubes may be used, in particular three tubes, disposed in line with each other perpendicularly to the plane of the view. 
     The articulated tube  3000  is composed of two successive segments, the first being a proximal segment  3100  and the second a distal segment  3200 . The first end of the proximal segment  3100  is articulated to the horizontal segment  2160  by a series  3110  of three double swivel joints known as “rotations”. Such a combination of rotations enables movements of the structure in three planes (movements of “sway”, “surge” and “heave”). Each of these rotations is double, and comprises both a product rotation and a mechanical rotation. 
     In the vicinity of the junction between the proximal and distal segments  3100  and  3200 , the articulated tube is retained in the position of  FIG. 1  by a locking system  2180  holding the distal structure  3200  of the articulated tube  3000  to the horizontal segment  2160  of the support structure  2100 . This locking system  2180  is completed by a system which holds the proximal segment  3100  in place in the boom  2100 . 
     The proximal and distal segments  3100  and  3200  are linked together by a single rotation  3120  similar to those already referred to. Lastly, at the free end of the distal segment  3200 , a series  3230  of three rotations connects the distal segment  3200  to an outer valve  3210  fastened to a male centering cone  3220 . 
     The articulated tube  3000  constitutes a movable pipe for conveying fluid. Its point of fastening to the boom is offset by several meters horizontally relative to the leg thereof, to a point overhanging the sea. 
     As mentioned above, as  FIG. 1  is a side view, only one articulated tube  3000  is represented, but the invention may be implemented with several articulated tubes offset from each other perpendicularly to the plane of the Figure, or otherwise disposed. The invention may also be implemented with one or more external cables, the number of which may or may not be equal to the number of lines of articulated tubes. The invention may also be implemented with one or more outer cables, and one or more acquisition cables. The fact of having several lines or several cables may be advantageous to enable sharing of the loads applied to the different members, to ensure their redundancy or to balance the lines. 
     At its edge the methane tanker  1000  comprises a support structure  1100  presenting towards the sea a downwardly oriented female centering cone  1110  with its opening centered on an axis forming an angle with the vertical. In the vicinity of that cone  1110  there is a valve-coupler  1120 , oriented parallel to the cone  1110 . 
     In  FIG. 1 , an outer cable  4100  has been represented, linking the end of the pointed segment  2170  to the centering cone  3220 . This outer cable  4100  is presented here in dashes indicating that it is held with a minimum constant tension so as to avoid it slackening. A so-called acquisition cable  4200  of the methane tanker  1000  has also been represented which links the support structure  1100  of the methane tanker  1000  to the centering cone  3220 . 
     The acquisition cable  4200  was put into place in advance using a light messenger cable and a winch. This is also the case for the outer cable  4100 . The outer cable  4100  is a maneuvering cable the object of which is the maneuvering of the free end of the distal segment  3200  during operations of connection and disconnection. 
     In  FIG. 2 , the start of the process of connecting the articulated tube  3000  to the ducts of the methane tanker  1000  has been represented. 
     The locking system  2180  having been disengaged, the movement and the position of the articulated tube  3000  are controlled by the outer cable  4100  which is progressively wound via a pulley  2171  present at the end of the pointed segment  2170  by a winch  2172  placed at the rear of the boom  2100  in the leg  2150  of the boom and are also controlled by an inner cable  4300  linking a point of the proximal segment  3100  in the vicinity of the junction between the proximal and distal segments  3100  and  3200  and a point in the vicinity of the middle of the horizontal segment  2160  of the support structure  2100 . This inner cable  4300  is maneuvered by a winch  2161 . Both cables  4100  and  4300  are presented in  FIG. 2  in continuous line indicating a cable under tension undergoing controlled winding or unwinding. By contrast, the acquisition cable  4200  is, as in  FIG. 1 , still manipulated under minimum constant tension the object of which is not the movement or control of the articulated tube  3000 . 
     During the movement presented in  FIG. 2 , rotation is imparted to the proximal segment  3100  about its point of attachment to the support structure  2100  which progressively brings it from a substantially horizontal disposition to a vertical disposition represented in  FIG. 3 . The distal segment  3200  which, initially, was disposed at approximately 90° to the proximal segment  3100 , comes closer thereto until an angle of approximately 60° is formed with the proximal segment  3100 . 
     Because the movement continues, the position represented in  FIG. 3  is attained. The cable  4300  is then slackened such that only a minimum constant tension is applied to it. The position of  FIG. 3  is qualified as equilibrium position since in that position the change of tension in the cable  4300  has no effect on the position of the two parts of the articulated tube  3000 . In that position, the outer cable  4100  is substantially vertical. 
     At this stage, a winch  1130  of the support structure  1100  of the methane tanker  1000  is activated so as to wind the acquisition cable  4200 . A few moments later, the winding winch  2172  controlling the outer cable  4100  turning round the pulley  2171  is deactivated and only a minimum constant tension is then applied to the outer cable  4100 . Because the movement continues, the male cone  3220  engages in the female cone  1110  and the outer valve  3210  connects to the lower valve of the valve-coupler  1120 . The winch  1130  is then deactivated, or the acquisition cable  4200  is disconnected and the acquisition cable sheaths are disconnected using hydraulic pincers enabling the sheaths to be freed in case of emergency. Physically, the sheaths crimped on the cables remain in their housing but are no longer locked. 
     After the connection, only a minimum constant tension is applied to the outer cable  4100  and the inner cable  4300 . 
     In  FIG. 6 , the junction between the ducts coming from the production ship  2000  and the ducts from the methane tanker  1000  in the position of  FIG. 5  is shown. 
     This three quarters view shows the presence of three articulated tubes of the same kind as articulated tube  3000  presented in the preceding Figures, parallel to each other, as well as two acquisition cables, of the same kind as the acquisition cable  4200  presented in the preceding Figures, also parallel to each other. The articulated tubes respectively bear the references  3001 ,  3002  and  3003 , and the acquisition cables respectively bear the references  4201  and  4203 . 
     The articulated tubes  3001 ,  3002  and  3003  are joined to each other by a transverse holding structure  3020 . Two male centering cones  3221  and  3223  are fastened upwardly on that transverse holding structure  3020 . Two female centering cones  1111  and  1113  of the same kind as the female centering cone  1110  are fastened downwardly on the on the support structure  1100 . The male centering cones  3221  and  3223  are, in the configuration represented, engaged in the female centering cones  1111  and  1113 , respectively. 
     The acquisition cables  4201  and  4203  are controlled, via pulleys, by winches  1131  and  1133  of the same kind as the winch  1130  presented in the previous Figures. Each acquisition cable passes through a pair of centering cones to meet the transverse holding structure  3020  to which it is connected by sheaths and pincers. 
     The winch  1131 , the cable  4201 , the cones  1111  and  3221 , the tube  3001  and the valve-coupler and the outer valve for its connection are in a first plane, and the winch  1133 , the cable  4203 , the cones  1113  and  3223 , the tube  3003  and the valve-coupler and the outer valve for its connection are in a second plane parallel to the first plane. Between these two planes are situated the tube  3002  and the valve-coupler and the outer valve for its connection. 
     A winch  1200  controlling a safety cable  1210  (not visible) can also be seen. The safety cable  1210  is constantly attached to the lower part of one of the three valve-couplers of the methane tanker (see following paragraph for the structure of the valve-couplers). 
     As can be seen in  FIG. 7 , which is a side view in which one of the valve-couplers is referenced  1120 , the latter is constituted by a lower valve  1121  and upper valve  1122 . The valve-coupler  1120  is furthermore provided with an emergency release system  1128  (ERS for Emergency Release System or PERC for Powered Emergency Release Coupler), by which the lower valve  1121  is detached from the upper valve  1122  in case of emergency disconnection, while remaining connected to the outer valve  3210  of the hinged line. The winch  1200  ( FIG. 6 ) then constitutes a brake for the unwinding of the safety cable  1210  (not visible) which slows the drop of the free end of the distal segment  3200  of the articulated line (scenario described in  FIGS. 13 to 16 ). 
     The articulated tubes  3001 ,  3002  and  3003  are held fast to each other overall independently of the cables, in particular by the transverse holding structure  3020 . Thus, when there are three articulated tubes, only two acquisition cables  4201  and  4203  are used. Also, it is possible to use only two pairs of guide cones. In the same way, only two outer cables  4100  are used (not shown in  FIG. 6 ) and only two inner cables  4300  are used (not shown in  FIGS. 6 to 8 ). As for the safety cable  1210 , this is single and is linked to the valve-coupler placed in central position by a rigid structure in which the three valve-couplers are incorporated. 
       FIG. 7  shows one of the two articulated tubes  3000  which are positioned facing an acquisition cable and an engagement cone (in  FIG. 6 , either tube  3001  or tube  3003  is concerned). The tube is linked by the series  3230  of three successive rotations to the outer valve  3210  engaged in the lower valve  1121  of the valve-coupler, parallel to the female cone  1110  engaged with the male centering cone  3220 . The outer cable  4100  connected onto a structure adjacent to the male centering cone  3220  and rigidly connected thereto can also be seen. Reference  1125  designates the hydraulic coupling members used in a normal situation of connection and disconnection which contrary to the emergency release system  1128  does not require manual operation for the coupling. 
       FIG. 8  represents the same structure, the ducts being disconnected. The male centering cone  3220  is more visible than in  FIG. 7 . 
     Importantly, as the cable  4100  is fastened, relative to the articulated tube  3000  beyond the series of rotations  3220 , the mouth of the outer valve  3210  is directed upwardly in all circumstances. 
     It is to be noted that in other embodiments, the ducting could be constituted by flexible hoses, and in that case, the series of three rotations  3220  could be absent. The invention then still provides for the cable  4100  to be fastened rigidly to the outer valve  3210 , so as to enable the control of the presentation of its mouth upwardly. Rotations may be present above the valve-coupler  1120 , that is to say in the methane tanker  1000 . 
     Further to the movement for initiating disconnection represented in  FIG. 8 , starting from the position in  FIG. 7 , a complete disconnection procedure is implemented, as represented in  FIG. 9 . The acquisition cables  4200  are first of all re-connected. 
     Thus, once the valve-coupler  1120  and the outer valve  3210  have been unlocked from each other, the winch  1130  is activated to unwind the acquisition cable  4200 . Such unwinding is carried out at constant speed over a few meters. The outer  4100  and inner  4300  cables are, at this stage, held under minimum constant tension to avoid them going slack. In  FIG. 10 , the winch  2172  is then locked so as to provide a constant length for the outer cable  4100 . The acquisition cable  4200  is unwound at constant speed by the winch  1200  while the inner cable  4300  is held at minimum constant tension. 
     The movement is continued until the articulated tube  3000  attains its position of equilibrium represented in  FIG. 11 . This equilibrium position is defined by the fact that, in that position, a slackening of the acquisition cable  4200  has no impact on the movement or the position of the articulated tube  3000 . The acquisition cable  4200  is then detached from the free end of the articulated tube  3000  and simultaneously or slightly later, the inner cable  4300  starts to be wound by the winch  2161 . Also, in the configuration of  FIG. 11 , the winch  2172  is unlocked and the length of the outer cable  4100  is controlled so as to bring the whole of the articulated tube  3000  towards its parking position. 
     Thus, in  FIG. 12 , the proximal segment  3100  returns to a practically horizontal position and the distal segment  3200  to a practically vertical position, such that the locking system  2180  is able to act on the distal segment  3200 , the inner cable  4300  being reduced to practically zero length and the outer cable  4100  being controlled under minimum constant tension. 
     Once the articulated tube  3000  has been placed in parking position or resting position, the outer cable is wound in and a simple messenger cable is held between the pulley  2171  and the free end of the articulated tube  3000 . 
     A description will now be made of an emergency disconnection of the ducts of the production ship  2000  and of the ducts of the methane tanker  1000 , these latter being connected as was seen with reference to  FIGS. 5, 6 and 7 . Such an emergency disconnection is launched automatically or manually, for example, when the methane tanker  1000  moves too far away from the production ship  2000  as is represented in  FIG. 13 . 
     As of the start of a procedure for emergency disconnection, the winch  2172  actuating the outer cable  4100  is locked so as to maintain a constant length in that cable, which ensures that the free end of the distal segment  3200  does not fall into the water. Thus, the length of the outer cable or cables  4100  is fixed by actuating a locking device or brake a few fractions of seconds after the start of an emergency disconnection so as to keep the free end of the distal segment  3200  (called Style  80 ) out of the water. The inner cable  4300  continues to be kept at a minimum constant tension so as to avoid it slackening. The PERC (Powered Emergency Release Coupler)  1128  is disconnected, the valves  1121  and  1122  (see  FIGS. 7 and 8 ) are thus separated and the cones  1110  and  3220  move apart from each other. The safety cable  1210  unwinds at a maximum speed which may be chosen equal to 3 m/s, as can be seen in  FIG. 14 , on account of the braking action. It is to be noted that the acquisition cable  4200  (not represented) was disconnected beforehand, as of the end of the initial connection procedure, at the free end of the distal segment  3200 . 
     After a few moments, the entire length of the safety cable  1210  is unwound and it detaches by itself from the drum of the winch  1200 , as can be seen in  FIG. 15 . At this stage, the outer cable  4100  returns to a substantially vertical position, the proximal segment  3100  also resuming a substantially vertical position whereas the distal segment  3200  adopts a substantially horizontal disposition. 
     Under the effect of the movement adopted during the disconnection, the whole of the articulated tube  3000  approaches the production ship  2000  as can be seen in  FIG. 16 . As the acquired speed was particularly low due to the braking action of the winch  1200 , the movement is controlled. A brake is applied to the winch  2161  of the inner cable  4300 , then that brake is released. The inner cable  4300  is then subjected to winding at constant speed. The outer cable  4100  is also subjected to unwinding at constant speed. The two cables  4300  and  4100  are maneuvered so as to bring the articulated tube into its parking position, the following part of the maneuver being similar to a conventional disconnection procedure. 
     The invention is not limited to the disclosed embodiment and covers all the variants within the capability of the person skilled in the art, within the scope of the claims.