FR2832206A1 - Flotation device able to withstand pressures found in deep water, e.g. for ensuring flotation of pipeline or other equipment as it is positioned at great depth - Google Patents

Abstract

The device comprises at least one container (2) made of an assembly of rigid pieces (14) with one or more free spaces (5) between them and separated from each other by a layer (4) of plastically deformable material. The container is separated from the pipeline and connected to it by a linkage (11). The rigid pieces are made of a material with a high elastic limit, for example glass, steel, composite materials or aluminum (in particular glass) and have a symmetry of circular revolution, for example in the form of rings or conical sections. The rigid pieces may have an annular radial part (disc) attached to a side wall which is perpendicular or inclined to the radial part. The layer of plastically deformable material is an elasto-plastic material such as polyurethane, rubber or epoxy, or a relatively soft metal such as lead, annealed copper or annealed aluminum. The rigid pieces are placed in the middle of the elastoplastic layer, to form a seal with the rings, or the elastoplastic material is placed around the rigid pieces or inside them. The layer of elastoplastic material is between 0.5 and 20 mm thick. A sealant layer (15) such as polypropylene or polyethylene is applied to the external surface of the rigid pieces. This sealant layer is thermo-retractable. The linkage is formed by a fixing (12) and a band (13). The container has two side walls (17) and a collar (18) applied to each wall and fixed to the container. The collars at the two ends of the container are connected together by straps (19). The side walls are connected to the end of the container by gluing or welding to ensure a seal.

Description

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 The technical field of the present invention is that of flotation devices intended for pipelines for transporting hydrocarbons at sea.

 The depletion of offshore hydrocarbon reserves in conventional areas of exploitation has led to the emergence of installations at great depths (of the order of a kilometer). The term installation generally designates subsea well heads, platforms, etc.). We know that, in this case, the transport of fluids is very often ensured by steel or other tubes which are involved in all stages of oil extraction, and in particular by horizontal pipelines arranged at the bottom of the sea to connect the different parts of the same installation. These pipelines are named in English term flowlines. They are made from intermediate steel tubes of a length of around twelve meters and then assembled to form sections several kilometers long which come to rest at the bottom of the sea.

 Several methods are known for laying these pipelines at the bottom of the sea.

 One method consists in transporting the tubes on a barge and assembling them at sea either in an almost horizontal manner (so-called S-pose) or almost vertical (so-called J-pose).

 Another method consists in carrying out the pipeline on long land on land, then winding it on a wheel which is brought to the installation site using a barge and unrolling it at sea at wanted place on the bottom of the sea.

 Another method, known as pulling, is based on towing at sea to the offshore site of the pipeline after assembly on land of the elementary tubes over a great length (several kilometers). The mass of the pipeline in the water must therefore be low, for example less than 40 kg per linear meter, or it must be floating if the pipeline is drawn between two waters.

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 To obtain satisfactory flotation conditions, recourse is had to additional means. One can connect the pipeline to one or more floats to give sufficient buoyancy by Archimedes effect. If you are considering a significant depth (1000 meters for example), you must increase the thickness of the wall of the float or of the transport tube to allow it to resist the water pressure. It then becomes too heavy to perform its function as a float. To remedy this, it has been proposed to pressurize the float or the transport tube with nitrogen to balance the internal pressure with the hydrostatic pressure. We do not currently exceed depths of 1,000 meters with this system for practical reasons of safety and density of pressurized nitrogen.

 To replace the conveyor tube, it has been proposed to use syntactic foam bars or cylindrical reservoirs most often made of composite material in order to combine a low mass and good buckling resistance. These two solutions are very expensive.

 This is why the aim of the present invention is to provide a flotation device which can be used at very great depth, simple and economical, suitable for drawing or laying a pipeline and the flotation of which can be adjusted.

 We cited above the example of laying pipelines but it is obvious that the device according to the invention can be used when laying other subsea systems, belonging to the petroleum industry or 'other industrial sectors without any modification.

 The invention therefore relates to a flotation device for example to ensure the flotation of a submerged pipeline at great depth, characterized in that it comprises at least one enclosure made up of a set of rigid parts delimiting between them one or several free spaces separated from each other by a layer of plastically deformable material, said

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 enclosure being separated from the pipeline and connected to it by a connecting means.

 According to a first characteristic, the rigid parts are made of a material having a high elastic limit, chosen for example from the group consisting of glass, steel, composite materials or aluminum.

 According to another characteristic, the rigid parts have a symmetry of circular revolution, for example in the form of washers, truncated cones.

 According to yet another characteristic, the rigid parts have an annular radial part attached to a side wall.

 The side wall may be perpendicular or inclined with respect to the radial part.

 Advantageously, the rigid parts have a radial part in the form of a disc attached to a side wall.

 According to yet another characteristic, the layer of plastically deformable material consists of an elastoplastic material or a relatively soft metal.

 Advantageously, the elastoplastic material consists of polyurethane or rubber, or epoxy.

 According to another characteristic, the rigid parts are arranged within the layer of the elastoplastic material, said material making a sealed connection with the annular parts.

 According to yet another characteristic, the layer of elasto-plastic material is disposed around or inside the annular parts.

 Advantageously, the layer of elastoplastic material has a thickness of between approximately 0.5 and 20 mm.

 Advantageously also, the relatively soft metal consists of lead or annealed aluminum.

 According to yet another characteristic, the enclosure comprises a layer of waterproof material constituted by

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 polypropylene or polyethylene applied to the external surface of rigid parts.

 Advantageously, the layer of waterproof material is heat-shrinkable.

 According to yet another characteristic, the connecting means consists of a fastening clip and a strap.

 According to yet another characteristic, the enclosure is limited on either side by two side walls and a collar applied to this wall and secured to the enclosure.

 Advantageously, the collars of the two ends of the enclosure are interconnected by tie rods.

 According to yet another characteristic, the side walls are linked to the end of the enclosure by gluing or welding in order to ensure sealing.

 Advantageously, the rigid parts are made of glass.

 An application of the flotation device is particularly intended for the lightening of subsea pipeline systems.

 A very first advantage of the flotation device according to the invention lies in the fact that the hydrostatic pressure prevailing at the envisaged depths is no longer an obstacle to the use of the floats.

 Another advantage lies in the use of an assembly lighter than steel to make the enclosure.

 Another advantage lies in the possibility of using annular parts made of a material which does not allow the production of tubular parts of great length. The typical example consists of glass which does not lend itself to the production of parts with a unit mass greater than ten kg.

 Another advantage lies in the use of annular parts whose specific resistance (elastic limit / density) is high, such as for example glass and composites.

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 Other characteristics, details and advantages of the invention will emerge more clearly on reading the additional description given below for information only in relation to the drawings in which: - Figure 1 illustrates in section a first embodiment of the flotation device according to the invention, - Figure 2 illustrates various configurations of the annular parts of a flotation device, - Figures 3A and 3B illustrate in section another embodiment of the side wall of the enclosure of the device flotation according to the invention, - Figure 4 illustrates in section another embodiment of the wall of the enclosure according to the invention, - Figure 5 shows in section an embodiment of the flotation device according to the invention, - Figures 6 and 7 illustrate particular assemblies of rigid parts, - Figures 8 and 9 illustrate other embodiments of rigid parts, and - Figure 10 illustrates a disp buoyancy device with an assembly of rigid parts.

 As indicated above, the invention proposes a flotation device defining a new type of inexpensive float to be produced and offering flexibility of use in laying a pipeline at the bottom of the sea at great depth. This typically involves transporting crude oil from one point to another.

 As is apparent from the above, the rigid parts are of various shapes and embodiments. The advantage of the flotation device according to the invention lies in the fact that these assembled parts delimit an internal space filled with air or any gas, said space being continuous or discontinuous. When the parts are annular, they delimit a continuous internal space between all these annular parts. In this case, the shape of the annular parts can be very simple, for example a washer, or a more complex shape by including a perforated radial wall and a side wall connected to this wall.

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 radial. The side wall may have any regular shape, continuous or not. In this case the side wall can be connected in different ways to the radial wall. It can for example be fixed to the periphery of the radial wall extending on one side or on either side of said radial wall. It can also be fixed anywhere on the side wall. The side wall may also be in the form of a wing fixed on one side and another wing of different shape fixed on the other side, both on the radial wall. The float can also be made without departing from the scope of the invention of an assembly of rigid parts having a continuous solid radial wall connected to a side wall of any shape as explained above. These parts are assembled by connecting the end of the adjoining side walls using joints. In this case, two adjacent rooms delimit a closed internal space filled with air or any gas. Whatever the shape of the rigid parts, buoyancy is always ensured and it is adjusted according to the desired requirements.

 The rigid parts can be manufactured in a conventional manner, for example by molding. It suffices to make a mold in the desired shape to manufacture the parts by molding from molten material.

 In Figure 1, there is shown a partial section of the flotation device 1 according to the invention whose wall defines an enclosure 2, or float, consisting of an assembly of annular parts 3 connected together by annular layers 4 of material plastically deformable, for example an elastoplastic material. The parts 3 are symmetrical with respect to the longitudinal axis Dl. The connection between each part 3 and each layer 4 is obtained in a conventional manner, for example by in situ bonding or vulcanization or in situ molding. In this figure, the side walls closing the enclosure are not shown.

 The thicknesses dl, d2 and d3 of the annular parts 3

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 are chosen according to the nature of their constituent material and the depth at which the enclosure 2 must ensure the required buoyancy. A thickness dl of the order of 1 to 50 mm ensures good resistance to the envisaged depths. It is the same for the thickness d2 of the layer 4 which can be of the order of 1 to 10 mm. As shown in the figure, it is possible to choose a substantially equivalent thickness for the parts 3 and the layers 4.

 The thickness d3 of the enclosure can be of the order of 10 to 50 mm for an external diameter d4 of the order of 150 to 800 mm, which provides an internal diameter d5 of the order of 100 to 700 mm .

 The annular parts can be made of different materials having a high elastic limit. By high limit is meant a value of the order of 1000 MPa.

Examples include glass, steel, composite materials, aluminum. Glass will preferably be used.

 In the particular case of glass which has a density of approximately 2.5, it is possible to economically produce an enclosure having a very high resistance to hydrostatic pressure. It should be noted that glass finds a completely unexpected application in this technical field.

 The layers 4 of plastically deformable material can be produced in an elastoplastic material of the polyurethane, polyethylene, epoxy, polypropylene type or a rubber such as EPDM (ethylene propylene diene monomer).

 The layers 4 of plastically deformable material can also consist of a relatively soft metal such as lead, annealed copper or annealed aluminum. Sealing must then be ensured by an insulating layer as will be explained below.

 The float thus produced has a continuous internal free space 5 which may contain air or another gas after closure in order to improve its buoyancy.

 In Figure 2, different forms of

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 realization of the annular parts 3 having a symmetry with respect to the longitudinal axis D2. The part 3a has an annular shape, the production of which has been explained above. The part 3b has an I-shaped cross-section. An embodiment of this type offers a larger surface for attaching the layer 4 and greater rigidity. The part 3c has a frustoconical shape in section and offers the same advantages as the part 3b. The 3d part has an L-shaped section in section and the 3rd part has a Z shape. These shapes are given for information only and the enclosure according to FIG. 1 can include annular parts 3 having one or more of the shapes represented in the figure. 2.

 One can also use a part 3f as shown in Figure 6. The frustoconical geometry has a certain advantage for parts manufactured by molding where it is necessary to provide a slight flare to allow demolding. According to this embodiment, the parts are mounted head to tail. These parts are also symmetrical with respect to the axis D6. They are joined together by the seal 6 disposed at the level of the small base and the seal 7 disposed at the level of the large base.

They delimit the continuous internal space 5.

 To manufacture the pipe according to the invention, one can operate in different ways, for example by stacking or by using a mandrel which is removed later after assembly. The annular pieces 3 are placed or inserted alternately and to form the layer 4 a layer of plastically deformable material is poured, for example the elastoplastic material or else sheets of elastoplastic material are inserted between the pieces making sure good adhesion between them. One can also use in the same way a relatively soft metal deforming plastically such as lead or annealed aluminum.

 If an annular part is used according to FIG. 6, we proceed as indicated above but by interposing the seals 6 and 7 between each annular part. A layer of

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 elastoplastic material of the same kind as layer 4 can then be used to externally cover the parts 3f and the seals 6 and 7.

 In FIGS. 3A and 3B, two half-sections of an enclosure 2 have been shown according to which the layer 4 of elastoplastic material is produced in a different manner. In FIG. 3A, the layer 4 delimits the internal profile 8a of the enclosure whereas in FIG. 3B it delimits its external profile 8b. A combination of these two embodiments can be envisaged by those skilled in the art without any difficulty. Whatever the embodiment, the annular parts 3a joined together delimit the continuous free space 5.

 According to another embodiment of the enclosure 2 according to the invention shown in the half-section of Figure 4, the annular parts 3 are completely embedded in the layer 9 of elastoplastic material. In this configuration, good adhesion is ensured between the annular parts and total protection vis-à-vis the external environment. Of course, the annular part 3a can be replaced by one of the shapes shown in FIG. 2. It is also possible in this configuration to combine several different shapes of annular pieces. This embodiment offers the advantage of delimiting in a single operation the internal profile and the external profile of the enclosure 2.

 It is possible to manufacture a section of float in finite length, for example 10 m, provided with a connecting element at the two ends as will be described below in relation to FIG. 5.

 This FIG. 5 shows an example of an embodiment of the enclosure 2 having a substantially cylindrical shape. It is in the form of a generally cylindrical assembly fixed to a pipeline 10 by connection means 11. Each means consists of a fastening clip 12 in the form of a cable connecting the enclosure 2 to the pipeline 10 and a strap 13 arranged around the pipeline. We understand that

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 several enclosures 2 can be connected to the pipeline at the same point or at different points depending on the buoyancy that it is desired to provide. This achievement makes it possible to temporarily fix the speakers by detaching the ruts when the time comes. These speakers can therefore be reused. According to this figure, the enclosure is shown by separating according to an advantageous embodiment the functions of sealing and resumption of axial forces between the annular parts.

 The enclosure 2 consists of a set of annular parts 14, for example made of glass, spaced apart by layers 4 of plastically deformable material. The annular parts 14 are arranged in a regular pitch. Materials of the polypropylene or polyethylene or rubber or epoxy type are perfectly suitable for this use.

The assembly can be threaded into a sheath 15 ensuring sealing against the outside. It can also be produced in the form of a heat-shrinkable tubular element. It then suffices to heat it slightly to shrink it on the annular parts 14 and to hold them securely in place. The sheath 15 ensures protection of the enclosure against shocks which may in the case of glass be harmful.

The enclosure 2 can be used as such because it offers excellent performance in terms of resistance to hydrostatic pressure while keeping a reduced mass. Thus, if we compare steel and glass, we can make the glass work at high stress values. Glass typically reaches a compressive stress at break of 2,000 MPa, while steels hardly allow more than 4 to 500 MPa at the elastic limit, while having a density three times higher.

 The inner surface of the enclosure can be covered with a layer 16 of separate waterproof material, connected for example by gluing, of the same nature as the sheath 15 or which can be the elastoplastic material itself if it it is tightly connected to the annular parts.

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 The enclosure 2 is equipped with an end closure on either side constituted by two walls 17 which are, in the example illustrated, bearing against the terminal annular part 14a. Each wall 17 can be made of a material of the steel, aluminum or polymer type allowing a tight connection to be made with the sheath 15. The connection can be reinforced by the interposition of a collar 18 bearing on the wall 17 and on layer 15 of the enclosure. Optionally, the two collars 18 can be connected together using tie rods 19 screwed or welded. Of course, the collars 18 can be joined by a single piece so as to constitute a compact assembly.

 In Figure 7, there is shown in half-section a partial enclosure 2, of longitudinal axis D7, consisting of rigid parts 20 whose radial wall 21 is full, said wall being extended on one side by a side wall 22 at an obtuse angle. The parts 20 are arranged head to tail by interposing the seals 23 and 24.

Two consecutive pieces 20 delimit a closed space 25 which can be filled with air or any gas.

 In Figures 8 and 9, there is shown a part having the same general shape. The longitudinal section shown shows in Figure 8 that the enclosure can be made from parts 26 having a full radial wall 27 connected to a side wall 28 having a generally frustoconical shape. In FIG. 8, it can be seen that the radial wall 28 is connected substantially at the level of the middle part of the side wall 28 and at the edge of this radial wall. In FIG. 9, the longitudinal section shows an annular part 29 comprising a perforated radial wall 30 connected to a side wall 31.

This part 29 is substantially identical in its general shape to the rigid part 27.

 A float produced from an assembly of the parts 26 will generally conform to the float shown in FIG. 5, seals being arranged between these parts.

 In Figure 10, there is shown a float made at

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 starting from parts 29. In this float, there is no continuous free space but individual spaces delimited by two consecutive rigid parts. In this example, the parts 29a, 29b and 29c are adjusted head to tail via a seal 32. This seal can be produced as described above, for example from polyurethane, EPDM or soft metal. An outer tube 33 is applied to the outer surface of the side wall 31 of the parts in the form of a hoop obtained by thermoforming to obtain a constriction and a narrow application on the parts 29. This hoop is applied intimately on each side wall of the parts 29. In the figure, a free space has been left between the tube 33 and the walls 31 for reasons of clarity of the drawing. The rigid parts delimit closed or closed internal spaces, two of which are visible in the figure. The space 34 is delimited by the parts 29a and 29b and the space 35 by the parts 29b and 29c. These closed spaces are either filled with air or filled with a gas. These spaces are isolated from each other without communication between them. Preferably, the rigid parts 29 are made of glass. The structure of the float can be completed as described in relation to Figure 5 by the end walls. Alternatively, one could provide two end pieces whose radial walls seal the float. Finally, a layer of elastoplastic material can be placed between the tube 33 and the side wall 31 of the parts 29.

Claims (22)

1. Flotation device (1) for example to ensure the flotation of a submerged pipeline (10) at great depth, characterized in that it comprises at least one enclosure (2) consisting of a set of rigid parts (3 , 14,21, 26,29) delimiting between them one or more free spaces (5,25, 34,35) and separated from each other by a layer (4,6, 7,9, 23,24, 32) of plastically deformable material, said enclosure being separated from the pipeline and connected to the latter by a connecting means (11).  2. Flotation device (1) according to claim 1, characterized in that the rigid parts (3,14, 21,26, 29) are made of a material having a high elastic limit, chosen for example from the group consisting of glass, steel, composite materials or aluminum.  3. Flotation device according to claim 2, characterized in that the rigid parts (3,14, 21,26, 29) have a symmetry of circular revolution.  4. Flotation device according to claim 3, characterized in that the rigid parts (3,14, 21,26, 29) are in the form of washers.  5. Flotation device according to claim 2, characterized in that the rigid parts (3,14, 21,26, 29) are in the form of truncated cones.  6. Flotation device according to any one of the preceding claims, characterized in that the rigid parts (20, 26, 29) have an annular radial part attached to a side wall (22, 28, 31).  7. Flotation device according to claim 6, characterized in that the side wall (22,28, 31) is perpendicular or inclined relative to the radial part.  8. Flotation device according to any one of claims 1 to 5, characterized in that the rigid parts (26) have a radial part (27) in the form of a disc attached to a side wall (28). <Desc / Clms Page number 14>  9. Flotation device according to one of the preceding claims, characterized in that the layer (4,6,7,9,23,24,32) of plastically deformable material consists of an elastoplastic material or a relatively metal soft.  10. Flotation device according to claim 6 or 7, characterized in that the elastoplastic material consists of polyurethane or rubber, or epoxy.  11. Flotation device according to claim 6, 7 or 10, characterized in that the rigid parts (3.12) are disposed within the layer (4.13) of the elastoplastic material, said material providing a sealed connection with the annular parts.  12. Flotation device according to claim 6, 7 or 10, characterized in that the layer (4) of elastoplastic material is arranged around the annular parts (3,14) or inside them.  13. Flotation device according to any one of claims 9 to 12, characterized in that the layer (4) of elastoplastic material has a thickness of between approximately 0.5 and 20 mm.  14. Flotation device according to claim 9, characterized in that the relatively soft metal consists of lead, annealed copper or annealed aluminum.  15. Flotation device according to any one of the preceding claims, characterized in that it comprises a layer (15) of waterproof material constituted by polypropylene or polyethylene applied to the external surface of the rigid parts.  16. Flotation device according to claim 15, characterized in that the layer (15) of waterproof material is heat-shrinkable.  17. Flotation device according to any one of the preceding claims, characterized in that the connecting means (11) consists of a fixing clip (12) and a strap (13). <Desc / CRUD Page number 15>  18. Flotation device according to any one of the preceding claims, characterized in that the enclosure (2) is limited on either side by two side walls (17) and a collar (18) applied to this wall and integral with the enclosure.  19. Flotation device according to claim 17, characterized in that the collars (18) of the two ends of the enclosure are interconnected by tie rods (19).  20. Flotation device according to claim 17, characterized in that the side walls (17) are linked to the end of the enclosure (2) by bonding or welding in order to ensure sealing.  21. Flotation device according to any one of the preceding claims, characterized in that the rigid parts (3,14, 21,26, 29) are made of glass.  22. Application of the flotation device according to any one of the preceding claims to the reduction of underwater systems.