The present application is a 35 U.S.C. §§371 national phase conversion of PCT/FR2010/051447, filed Jul. 8, 2010, which claims priority of French Application No. 0903496, filed Jul. 16, 2009, the contents of which are incorporated by reference herein. The PCT International Application was published in the French language.
The present invention relates to an oil pipe suspension device for suspending an oil pipe on a float in order to establish a connection between a seabed and a sea surface to route a hydrocarbon therein. The present invention also relates to a method of installing such a suspension device.
Thus, the field of the invention is installations for transferring fluids, in this instance hydrocarbons, between a seabed and a sea surface that are not shown here. These installations are commonly referred to as “riser towers”. They comprise a tubular riser having a bottom end which is anchored to the seabed and having at the opposite end, a connection end that is connected to a float held a few tens of meters below the level of the sea surface. As a result, the float exerts traction on the riser to hold it vertically. A flexible pipe is then connected to the connection end and extends in a catenary from a surface installation. Accordingly, the hydrocarbon is routed from the seabed to the surface installation. The object of the invention relates precisely to the suspension device situated between the connection end of the riser and the float.
Known installations include devices for suspending oil pipes more commonly referred to as “risers”. The pipe has a bottom end adapted to be anchored to the seabed, for example at a well head, and at the opposite end a connection end that is connected to a float situated below the sea surface. The length of the pipe is predefined so that the float is situated well below the sea surface, in an area that is not perturbed by the swell, so that it is able to exert a substantially constant traction in an upward direction. Moreover, the volume of the float is also determined to obtain a sufficient traction force. The connection end of the pipe is then connected to a flexible pipe that extends in a catenary toward a surface installation. The suspension device adapted to suspend the riser precisely on the float comprises two hitching members connected together by a flexible longitudinal element. These hitching members comprise a respective connection end. To the two connection ends are connected the respective two opposite ends of the flexible longitudinal element, and the other end opposite the connection end is provided with a fastener. The hitching members are then respectively attached to the float and to the connection end of the oil pipe via their fastener.
Reference may be made to the document FR 2 809 136, which discloses one such suspension device.
Because of the effect of sea currents, relative movement of the float and the riser induces localized stresses on the suspension device. The above prior art document precisely aims to prevent this concentration of stresses by providing a flexible longitudinal element the inertia of which varies along its length. However, fracture of this longitudinal element generated by repeated movements of the float and the riser causes the latter element to sink to the seabed. It is then difficult and above all costly to raise the riser. Furthermore, it is equally difficult to predict imminent fracture of this longitudinal element in order to be able to replace it.
Thus a problem that arises and that the present invention aims to solve is to provide a suspension device enabling easy inspection of its condition in such a manner as to be able to intervene and to replace it before fracture occurs.
With the aim of solving this problem, and in accordance with a first object, the present invention proposes an oil pipe suspension device for suspending a riser on a submarine float between a seabed and a sea surface, said riser having a connection end and at the opposite end a bottom end, said bottom end being adapted to be anchored to said seabed, while said connection end is connected to said float to retain said connection end in the vicinity of said sea surface, said suspension device comprising two hitching members and flexible link means, said hitching members comprising a respective connection end and at the opposite end an end provided with a fastener, said two hitching members being respectively attached to said float and to said connection end of said pipe by their fastener, while said connection ends of said two hitching members are connected together by said flexible link means. According to the invention said connection end of each hitching member includes two hooks that extend radially away from each other and said connection means comprise two flexible links independent of each other adapted to be fitted substantially parallel to connect two by two the respective hooks of said two hitching members.
Thus one feature of the invention is the use of two flexible links independent of each other, adapted to absorb traction forces of the float on the connection end of the pipe in order that it may be suspended. As a result, if one of the flexible links deteriorates, or in an extreme situation fractures, it is easy to determine visually the condition of the suspension device. Moreover, thanks to the use of the hooks on the hitching members, it is easier to substitute a new flexible link in good condition for the defective flexible link.
In one particularly advantageous embodiment of the invention, said connection end of each hitching member further includes at least two additional hooks that extend radially and said connection means comprise two additional flexible links independent of each other adapted to be fitted substantially parallel to connect two by two the respective additional hooks of said two hitching members. As a result, the connection means comprise four flexible links independent of each other and thus, if one of the links is damaged, the traction forces of the float on the riser are absorbed by the other three links. Consequently, the risk of deterioration of the other three links is lower, pending replacement of the defective flexible link, as each takes only one third of the additional traction forces. If there are only two connections, as envisaged hereinabove, they must each be sufficiently strong to take half of the additional traction forces in the event of fracture of one of the two.
In a particularly advantageous variant, at least one of said hitching members includes two elements sliding axially one in the other, one of said sliding elements including said two hooks, while the other of said sliding elements includes said two additional hooks in such a manner as to be able to modify the relative tension of said two independent flexible links and said two independent additional flexible links. In fact, and as explained in more detail in the remainder of the description, by driving the sliding elements one relative to the other the choice may be made to relax two of the links, and in particular the one that is defective, while the other two take the entire load of the traction forces. As a result, it is easier to replace the defective link.
According to another preferred variant, said connection end of each hitching member includes a mooring element in which the end of a sling is adapted to be engaged and, as explained hereinafter, it is possible to pull on the sling to move the hitching members toward each other.
Each hook advantageously has a substantially cylindrical barrel terminated by a free end. It extends substantially perpendicularly to the axis of the hitching member intersecting its two ends. This cylindrical barrel has at the end opposite its free end a fixing end fastened to the hitching member. As explained hereinafter, the flexible link is thus installed around the cylindrical barrel and against the hitching member. Said barrel is preferably curved substantially toward said corresponding fastener, precisely to retain the flexible link against the hitching member.
Furthermore, each independent flexible link advantageously includes a cable having a loop at each of its ends, said loop being adapted to be engaged in said hooks. Thus when the links are taut, in a direction substantially perpendicular to the barrels of the hooks, the loop remains trapped therein.
In accordance with another object, the present invention proposes a method of installing cables of said suspension device as described above, said method comprising the following steps: at least one cable is provided having a loop at each of its ends, said hitching members are moved toward each other a distance substantially less than the length of said at least one cable, the loops of said at least one cable are engaged around respective corresponding hooks of said hitching members, and said hitching members are then released in such a manner as to transfer at least part of the traction force of said float to said connection end via said at least one cable.
Accordingly, thanks to the suspension device of the invention, it is easy to install the riser and the float and, moreover, it is even easier to carry out maintenance if one of the cables is defective.
According to a particularly advantageous variant, said elements described above sliding axially one in the other are driven in translation to move said hitching members toward each other. It is thereafter easier to replace defective cables.
According to another variant, the mooring elements of said hitching members as described above are connected together by a sling and winch means for moving them toward each other. The advantages of this variant are explained in more detail hereinafter.
Other features and advantages of the invention will emerge on reading the following description of particular embodiments of the invention, given by way of nonlimiting example, with reference to the appended drawings, in which:
The hitching members 16, 18 are described in more detail with reference to
The upper connection end 22 of the upper body 21 of the upper hitching member 16 has four upper faces disposed as opposite pairs 36, 38 and 40, 42 from which respectively extend radially four substantially cylindrical upper barrels 44, 46 and 48, 50 forming hooks. They define a median plane substantially perpendicular to the axis of symmetry AA of the upper hitching member 16 and are successively oriented at substantially 90° to each other.
These substantially cylindrical upper barrels 44, 46; 48, 50 have a length in the range 1.5 times to twice their diameter, for example, which is in the range 0.2 m to 0.8 m, and they are substantially curved towards the attachable upper end 24 precisely to form a hook. Moreover, they have a free end 52 having a retaining enlargement the function of which is explained in more detail in the remainder of the description.
The lower body 21′ of the lower hitching member 18 has, in the same fashion, four lower faces disposed in opposite pairs 36′, 38′ and 40′, 42′ from which respectively extend radially four substantially cylindrical lower barrels 44′, 46′ and 48′, 50′ forming hooks. These lower barrels 44′, 46′; 48′, 50′ have a length in the range 1.5 times to twice their diameter and are substantially curved, the opposite way to the upper barrels, toward the attachable lower end 24 and precisely to form hooks. Just like the upper barrels 44, 46; 48, 50, they have an enlarged lower free end 52′.
Referring again to
Regarding the mode of connection, the cables 20 are of identical lengths and each has at its ends a deformable loop 56 the maximum diameter of which is greater than the diameter of the upper cylindrical barrels 44, 46; 48, 50 and the lower cylindrical barrels 44′, 46′; 48′, 50′. Thus the cables 20 fit between the respective two hitching members 18, 16 in such a fashion that the two deformable loops 56 of each of the cables 20 are respectively engaged around the lower barrels 44′, 46′; 48′, 50′ and the upper barrels 44, 46; 48, 50 in corresponding relationship. As a result, a cable portion of each of the loops bears on a cylindrical barrel at the junction with its corresponding face.
The deformable loops 56 constituted by the end of the cables curved on itself and bound are relatively rigid. And when the cylindrical barrel is engaged inside them and the axial traction of the float 12 and the connection end 10 is exerted on the cables, the deformable loops 56 are trapped on the hitching member 16, 18 because the cylindrical barrels 44′, 46′; 48′, 50′ and 44, 46; 48, 50 are respectively substantially curved in the direction opposite the traction that is exerted on the loop. Moreover, the enlarged free end 52, 52′ forms a stop that prevents the deformable loop 56 escaping from the corresponding cylindrical barrel when the cables are taut.
Accordingly, the overall traction force F exerted by the float 12 is divided between the four cables 20 and therefore divided into four substantially equal fractions. The advantage of such a configuration lies notably in the secure connection between the float 12 and the connection end 10. In fact, if one of the cables 20 fractures, the other three are able to take the traction force. Moreover, thanks to the embodiment of the invention described hereinabove, the deterioration of the suspension device 14 may be seen and, additionally, may be remedied by a method of replacement or installation described next with reference to
To do this, it is necessary to overcome the upward traction forces exerted by the float 12 and to draw it a relatively short distance, of the order of one meter, toward the seabed. Accordingly, in the embodiment shown in
As a result, the cylindrical barrels 44, 44′ are easily engaged in the corresponding loops 72 without excessive deformation of the latter loops despite the enlarged free ends 52, 52′ forming stops. Because, in fact, no tension is being exerted on the cable, the loops retain their original shape in which they define a substantially maximum open area.
The submarine robot 67 is naturally then used to release the actuator means 66 and as relaxation proceeds the three cables 20 and the new cable 70 therefore take the tension exerted by the float 12.
In an embodiment of the invention that is not shown, the actuator means are constituted of a winch in which the sling 64 is engaged.
Refer now to
Accordingly, in this second embodiment, the lower hitching member includes a symmetrically cylindrical first element 76 with a straight generatrix and a second element 78 constituted of a U-shaped part installed so that it slides inside the first element 76. The first element 76 has a fixing end 80 articulated to the connection end, not shown, of the riser on which it is mounted and at the opposite end an open end 82 through which the second element 78 is engaged. The first element 76 also has an upper facial edge 84 from which projects one of the lower cylindrical barrels 44″. In symmetrical manner, and to the rear of the plane of the figure, one of the other lower cylindrical barrels 46″ extends from an opposite upper edge.
The second element 78 has a bottom wall 86 and two parallel flanges 88, 90 adapted to extend outside the symmetrically cylindrical first element 76. Moreover, the lower hitching member includes inside the two elements 76, 78 a hydraulic piston-and-cylinder actuator 92 including a body 94 fastened to the first element 76 at the level of its opening 82 and, at the opposite end, an actuator rod 96 fastened to the bottom wall 86 of the second element 78. Moreover, the first element 76 has two opposite lateral edges 98, 100 pierced by two respective coaxial orifices and the two flanges 88, 90 have, in the same fashion, two coaxial bores, so that the second element 78 may be retained and immobilized in translation inside the first element 76 by means of a locking rod 102 engaged in the coaxial orifices and also in the bores.
Moreover, the second element 78 supports at the free end of its two flanges 88, 90 the other two lower and opposite cylindrical drums 48″, 50″. It is seen that, in a vertical direction, these other two lower cylindrical barrels 48″, 50″ are spaced from one of said lower cylindrical barrels 44″ and one of the other lower cylindrical barrels 46″ and in an opposite direction to the fixing end 80 of the first element 76. Also, given that the upper hitching member, not shown here, is identical to that shown in
As a result, if one of the cables of the second pair of cables 108 is fractured, to replace it, first the locking rod 102 is withdrawn, then the piston-and-cylinder actuator 92 is commanded so as to extend it, as shown in
The piston-and-cylinder actuator 92 may then be commanded again to retract the actuation rod 96 in such a manner that the new cable is tensioned and the coaxial bores and orifices of the two elements 76, 78 may be realigned to be able to reengage the locking rod 102.
On the other hand, if it is one of the cables of the first pair of cables 104, 106 that is damaged and must be replaced, the piston-and-cylinder actuator 92 is no longer commanded to extend it but is retracted, its rod 96 being accommodated entirely within its body 94. In this configuration, the float and the connection end of the riser remain stationary with respect to each other. It is in fact the other two opposite lower cylindrical barrels 48″, 50″ respectively installed on the two flanges 88, 90 of the second element 78 that are moved in the direction of the arrow T toward the upper hitching member. Thus the load is taken entirely by the cables of the second pair of cables 108 and either of the cables of the first pair of cables 104, 106 may then be replaced.
According to a third embodiment, shown in
Number | Date | Country | Kind |
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09 03496 | Jul 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2010/051447 | 7/8/2010 | WO | 00 | 3/15/2012 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2011/007084 | 1/20/2011 | WO | A |
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2809136 | Nov 2001 | FR |
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Entry |
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Number | Date | Country | |
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20120168170 A1 | Jul 2012 | US |