AU2019408425A1 - Flexible pipe for conveying a fluid in a submarine environment, and associated method - Google Patents

Abstract

The invention relates to a flexible pipe (10) for conveying a fluid in a submarine environment, having a longitudinal axis (A) and a liquid-impermeable outer layer (20) with a thickness of between 1/125 and 1/75 of the internal diameter of said outer layer (20), and comprising at least one helically wound strip (22) forming a plurality of turns, said strip (22) being made of a polymer matrix (24) reinforced with a plurality of reinforcing elements (26).

Description

Flexible pipe for conveying a fluid in a submarine environment and associated method The invention relates to the technical field of flexible pipes for conveying a fluid in a submarine environment. More particularly, the invention relates to unbonded flexible pipes used for conveying hydrocarbons in a submarine environment. Flexible pipes for conveying a fluid in a submarine environment are immersed in a body of water at depths that can exceed 3000 m. They are particularly useful for conveying water and/or hydrocarbons between a bottom installation and a surface installation. They can also be used to connect two bottom installations. Some flexible pipes can also be used to connect two surface installations. The structure of a flexible pipe is described, for example, within the standard documents API RP 17B, 5th edition, published in May 2014 and API 17J, 4 h edition, published in May 2014 by the American Petroleum Institute. Typically, a flexible pipe comprises an inner sealing sheath referred to in the technical field of the invention as a "pressure sheath". The inner sealing sheath forms an internal passageway for the flow of fluid and thus ensures the sealed conveyance thereof. High tensile stresses can be exerted on the flexible pipe line particularly when it extends through deep bodies of water. A pair of tensile armor plies is arranged around the inner sheath to take up these tensile stresses. The pair of tensile armor plies is typically composed of wires helically wound at a long pitch, i.e. the absolute value of the helix angle is between 20 and 55°. In order to prevent the ingress of water from the water body into the flexible pipe, the latter typically comprises a protective polymeric outer sheath arranged around the pair of tensile armor plies. The outer sheath is typically 10 mm thick. The inner sheath and the outer sheath define a space called the annular space. The pair of tensile armor plies is arranged within the annular space. The fluid conveyed is generally composed of crude hydrocarbons. These hydrocarbons typically comprise a mixture of gases such as carbon dioxide, methane or hydrogen sulfide. The conveyed fluid also comprises water and possibly sand particles. The gases contained in the conveyed fluid diffuse through the inner sheath and accumulate within the annular space. The annular space also contains water which results from an accidental loss of seal of the outer sheath and/or from the diffusion and condensation of water contained in the conveyed fluid through the inner sheath. The presence of water and these gases within the annular space causes various corrosion phenomena of the metallic elements within the annular space. The armor wires may then be subjected to stress corrosion cracking (SCC), for example. In order to reduce the corrosion of the armor wires, increasing the thickness of the outer sheath is taught, for example, in the API 17B document mentioned above. This reduces the risk of tearing the outer sheath and thus reduces the probability of water entering the annular space and causing corrosion. However, this solution is not entirely satisfactory. Indeed, although the risks of tearing the outer sheath are reduced, the water contained in the conveyed fluid can still diffuse through the inner sheath and condense within the annular space. In the presence of gases that have diffused through the inner sheath, this can lead to corrosion of the armor wires. In addition, increasing the thickness of the outer sheath increases the cost of manufacturing the flexible pipe, since more raw material is required. Therefore, there is a need to provide a flexible pipe in which the metal elements are preserved from corrosion as well as a process for manufacturing such a flexible pipe that is simple to implement and inexpensive. To this end, the subject matter of the invention is a flexible pipe for conveying a fluid in a submarine environment having a longitudinal axis and, from the inside to the outside of the pipe, comprising: - an inner polymeric sheath, to form a passage for circulation of fluid, - at least one pair of tensile armor plies, to reinforce the flexible pipe against axial forces, - a liquid-impermeable outer layer, the inner sheath and the outer layer defining an annular space in which said at least one pair of tensile armor plies is arranged, - said outer layer having a thickness of between 1/125 and 1/75 of the internal diameter of the outer layer and comprising at least one helically wound strip forming a plurality of turns, said strip being made of a polymer matrix reinforced with a plurality of reinforcing elements. The thickness of the outer layer according to the invention promotes the diffusion of gases such as carbon dioxide, hydrogen sulfide and/or methane through the outer layer to the exterior of the flexible pipe. This reduces the gas concentration of within the annular space and protects the pair of tensile armor plies from corrosion. In contrast, it has been found that when winding the flexible pipe onto storage devices such as reels, the outer layer deforms and forms folds ("folding") due to the thinness of the outer layer. These folds can damage the outer layer irreversibly and cause it to break.

The present invention solves this problem by reinforcing the outer layer with a plurality of reinforcing elements. In contrast, in order to ensure their reinforcing function, the reinforcing elements must be oriented at a specific angle in relation to the longitudinal axis of the flexible pipe. This angle is close to 90, for example. However, the conventional outer layer extrusion process does not allow for such an orientation of the reinforcing elements. To solve this problem, it was discovered that the outer layer must be in the form of a reinforced polymeric strip. In fact, the strip can be helically wound, to orient the reinforcing elements at the desired angle in relation to the longitudinal axis of the flexible pipe. The polymer matrix ensures the sealing of the strip in relation to fluids as well as the flexibility of the outer layer and thus of the flexible pipe. The strip is further wound in such a way as to obtain a liquid-impermeable outer layer to prevent water penetration while promoting gas diffusion to the outside of the flexible pipe. Preferably, the thickness of the outer layer is between 3 mm and 5 mm for an internal diameter of the outer layer of between 250 mm and 600 mm. Advantageously, the turns of the strip are bonded together. The bonding of the turns of the strip reinforces the sealing of the outer layer in relation to liquids as well as its resistance to internal pressure in particular. Advantageously, the turns of the strip have an overlap. The overlap of the turns enables further improving the sealing of the outer layer in relation to liquids as compared to an outer layer in which the turns of the strip are only joined. Advantageously, the strip is wound at a helix angle of absolute value of between 60 and 90° in relation to the longitudinal axis of the flexible pipe. When the helix angle is within this range, the resistance of the outer layer to radial forces is improved. The outer layer then has a double function, which is to ensure the sealing of the flexible pipe in relation to liquids while allowing the diffusion of gases towards the outside, but also to prevent the bulging of the tensile armor plies under the effect of the reverse bottom effect. Indeed, when the flexible pipe, whatever its nature, is subjected to an outer pressure that is higher than the internal pressure, an axial compression can occur, which is known to the person skilled in the art as the "reverse end cap effect". The reverse end cap effect tends to axially compress the flexible pipe, shortening its length and increasing its diameter, which tends to cause the pair of tensile armor plies to bulge. In the case where the outer layer is sealed, the hydrostatic pressure outside the pipe effectively opposes the bulging of the tensile armor. However, if the outer layer is no longer sealed, due to an accidental tear, for example, the hydrostatic pressure no longer opposes the bulging of the pair of tensile armor plies. As a result, in the absence of an additional means having the function of limiting this bulging, the wires composing the tensile armor plies may buckle radially, which may cause an irreversible local deformation of the pair of armor plies having the shape of a "bird's cage", and thus lead to ruining the flexible pipe. The outer layer, according to this embodiment, limits this risk of local deformation of the pair of tensile armor plies. Preferably, the outer layer comprises a plurality of superimposed strips, preferably between 2 to 8 superimposed strips. The plurality of strips enables the use of thinner strips. Thus, when the turns of a strip overlap, the thickness of the overlap areas is less important and thus the possible mechanical problems of the outer layer caused by thickness variations are reduced. Advantageously, according to this embodiment, at least two strips are crossed. This improves the properties of the outer layer. According to one preferred embodiment, the reinforcing elements are fibers such as organic fibers, mineral fibers or metallic fibers. Advantageously, the reinforcing elements are oriented at an angle of absolute value of between 0 and 40 in relation to the longitudinal axis of the strip. Advantageously, the polymer matrix is selected from thermoplastic materials such as a polyethylene, a polypropylene, a polyamide, or elastomeric thermoplastic materials, such as a vulcanized thermoplastic, in particular a vulcanized thermoplastic silicone or thermosetting materials. According to one preferred embodiment, the reinforcing elements are embedded in the polymeric matrix. The invention also relates to a method of manufacturing a flexible pipe for conveying a fluid in a submarine environment comprising the following steps: (a) forming an inner polymeric sheath, forming a fluid flow passage, (b) forming at least one pair of tensile armor plies, to reinforce the flexible pipe against axial forces, (c) helically winding a strip forming a plurality of turns, said strip being made of a polymer matrix reinforced with a plurality of reinforcing elements, to form an outer layer impermeable to liquid compounds, having a thickness of between 1/125 and 1/75 of the internal diameter of the outer layer, the outer layer and the inner sheath defining an annular space in which said at least one pair of tensile armor plies is arranged. Advantageously, in step (c) the strip is wound with an overlap of turns. Advantageously, the method comprises a step of bonding the turns. Advantageously, the step of bonding the turns comprises a sub-step of heating the strip.

Advantageously, the method comprises a step in which pressure is applied to the strip.

Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of indication but not limiting, with reference to the attached drawings in which: - Figure 1 schematically represents a perspective view of an example embodiment of a flexible pipe according to the invention, - Figure 2 schematically represents a perspective view of another example embodiment of a flexible pipe according to the invention, - Figures 3a and 3b schematically represent a perspective view of example embodiments of a strip according to the invention, - Figures 4a and 4b schematically represent a cross-sectional view of example embodiments of an outer layer according to the invention, - Figure 5 schematically represents an installation for manufacturing a flexible pipe according to the invention, - Figure 6 schematically represents a device for manufacturing an outer layer of a flexible pipe according to the invention. Figure 1 shows an example of a flexible pipe (10) according to the invention. The flexible pipe (10) is intended to be immersed within a body of water. The body of water may be a lake, a sea or an ocean. Generally, the depth of the body of water is at least 100 m, and more particularly between 500 m and 3000 m. The flexible pipe (10) conveys a fluid through the body of water between a first installation and a second installation. The first installation is a subsea installation such as a wellhead or a manifold, for example. The second installation is a surface installation such as a Floating Production Storage and Offloading (FPSO) or a Tension Leg Platform (TLP), for example. The flexible pipe (10) conveys the fluid between two surface installations or between an underwater installation and a surface installation or between two underwater installations. The fluid conveyed by the flexible pipe (10) is water and/or an oil and/or liquid gas, for example. The oil and/or gas fluid is formed of a multiphase mixture comprising a liquid part formed mainly of linear and/or cyclic, saturated and/or unsaturated carbon compounds, of variable density, and water, a gaseous part composed of methane (CH4), carbon dioxide (C02), hydrogen sulfide (H2S) and other gases, for example, and finally, a solid part composed generally of sand particles. The temperature of the fluid within the flexible pipe

(10) is between 50 C and 200 C, more particularly between 50 C and 130 C. The temperature of the fluid varies during conveyance between the first and the second plant. The fluid has a carbon dioxide partial pressure of between 1 bar and 300 bar, for example and a hydrogen sulfide partial pressure of less than 1 bar. The partial pressure of each of the gases within the fluid depends in particular on the nature of the oil and/or gas field being exploited. As shown as an example in Figure 1, the flexible pipe (10) comprises a plurality of concentric layers arranged around a longitudinal axis (A). According to the invention, the flexible pipe (10) comprises an inner sheath (14), at least one pair of tensile armor plies (18) and an outer layer (20). The flexible pipe (10) is preferably an unbonded flexible pipe. Unbonded, for the purposes of the present invention, is understood as a flexible pipe (10) in which the pair of tensile armor plies (18) is free to move relative to the inner sheath (14) upon flexing the flexible pipe (10). Preferably, all layers of the pipe (10) are free to move relative to each other. This makes the flexible pipe (10) more flexible than a pipe in which the layers are bonded to each other. Preferably, the flexible pipe (10) also comprises an internal carcass (12) arranged within the inner sheath (14). Advantageously, the flexible layer (10) comprises a pressure vault (16) arranged around the inner sheath (14). The pressure vault (16) is arranged between the pair of tensile armor plies (18) and the inner sheath (14). The internal carcass (12) reinforces the flexible pipe (10) against external pressure forces. It limits the risk of collapse of the flexible pipe (10) when the pressure outside the flexible pipe (10) is higher than the pressure inside the flexible pipe (10). The internal carcass (12) comprises at least one profiled wire helically wound with a short pitch. For the purposes of this invention, a short pitch is understood as a helix angle with an absolute value of between 75 and 90. The cross-section of the profiled wire has an S-shaped geometry, for example. In order to increase the resistance of the carcass to external pressure forces, the turns of the metal wire are interlocked to each other. The metal material is stainless steel, for example. When the internal carcass (12) is present, the flexible pipe (10) is said to have a rough bore. When the flexible pipe (10) has no internal carcass (12), it is said to have a smooth bore. The internal carcass (12) is generally in contact with the fluid being conveyed. The innersheath (14) is arranged around the internal carcass (12)when it is present. The inner sheath (14) forms passage for circulation of fluid. It ensures that the fluid is conveyed through the body of water in a sealed way. The inner sheath (14) is polymeric, i.e. more than 50% of the material forming the inner sheath (14) is a polymer. The polymer is, for example, a polyolefin such as a polypropylene, polyethylene or polyamide or a fluorinated polymer such as a polyvinylidene fluoride (PVDF). The polymeric material is chosen according to the nature and temperature of the fluid being conveyed. The thickness of the inner sheath (14) is for example between 4 mm and 15 mm. The inner sheath (14) is made by extrusion around the internal carcass (12), for example. The pressure vault (16) reinforces the resistance of the flexible pipe (10) against the internal pressure. It limits the risks of bursting the flexible pipe (10), in particular when the pressure inside the flexible pipe (10) is higher than the pressure outside the flexible pipe (10). The pressure vault (16) is arranged around the inner sheath (14). The pressure vault (16) is formed of at least one profiled wire helically wound with a short pitch. The cross section of the profiled wire has an I-, K-, Z- or U-shaped geometry, for example. The material of the profiled wire is carbon steel, for example. The pair of tensile armor plies (18) is intended to reinforce the flexible pipe (10) against tensile forces. The pair of tensile armor plies (18) comprises an internal tensile armor ply (18a) and an outer tensile armor ply (18b). The pair of tensile armor plies (18) comprises a plurality of tensile armor wires wound at a long pitch. "Long pitch" is understood as a helix angle of absolute value of between 20 and 55°. The cross-section of the tensile armor wires is rectangular or circular, for example. The tensile reinforcement wires are metallic, for example. The metallic material is a carbon steel, for example. The tensile armor wires of the internal tensile armor ply (18a) are wound at a helix angle opposite to the helix angle of the tensile armor wires of the outer tensile armor ply (18b). The tensile armor wires of the same tensile armor ply (18a, 18b) are contiguous. The outer layer (20) is arranged around the pair of tensile armor plies (18). The outer layer (20) is arranged around the outer tensile armor ply (18b). "Around the outer tensile armor ply (18b)" in the sense of the present invention is understood as the outer layer (20) being arranged outside of the outer tensile armor ply (18b). Additional layers may be arranged between the outer layer (20) and the outer tensile armor ply (18b). The outer layer (20) is liquid-impermeable and forms a protective barrier against water penetration from the body of water within the flexible pipe (10). The outer layer (20) and the inner sheath (14) define an annular space between them. The annular space, according to the example shown in Figure 1, comprises the pressure vault (16) and the pair of tensile armor plies (18).

Gases such as carbon dioxide and/or methane and/or hydrogen sulfide and water contained in the fluid diffuse through the inner sheath (14) and accumulate within the annular space. These compounds can induce corrosion of the metal wires of the pair of tensile armor plies (18) and the profiled metal wires of the pressure vault (16). To reduce the gas concentration within the annular space, the outer layer (20) has a thickness of between 1/125 and 1/75 of the internal diameter of the outer layer (20). The internal diameter of the outer layer (20) is between 100 mm and 600 mm. Preferably, the thickness of the outer layer (20) is between 3 mm and 5 mm, for an internal diameter of the outer layer (20) of between 250 mm and 600 mm. According to the invention, the thickness of the outer layer (20) and the internal diameter of the outer layer (20) are measured in the same units, in millimeters. Such a thickness favors the diffusion of gases, in particular carbon dioxide and/or methane and/or hydrogen sulfide through the outer layer (20) and thus reduces the concentration of these gases within the annular space. Corrosion of the metal wires of the pair of tensile armor plies (18) and the pressure vault (16) is thereby reduced. According to the invention, the outer layer (20) is formed of at least one helically wound strip (22). In order to improve the resistance to radial forces, the strip (20) is wound at a helix angle of absolute value of between 60 and 90 in relation to the longitudinal axis (A) of the flexible pipe (10). According to one preferred embodiment of the invention shown in Figure 2, the outer layer (20) comprises a plurality of strips (22), for example an inner strip (22a) and an outer strip (22b). Preferably, the outer layer (20) comprises between 2 to 8 strips (22) stacked on top of each other. To improve the strength of the outer layer (20) when it comprises a plurality of strips (22), at least two strips are crossed. For example, the inner strip (22a) and the outer strip (22b) are crossed. Advantageously, in order to optimize the properties of the outer layer (20) in particular in relation to the pressure inside the flexible pipe (10), the strips (22) are wound at an opposite helix angle. According to one preferred embodiment, the strips (22) are bonded together. For example, the outer strip (22b) is bonded to the inner strip (22a). The bonding is achieved by fusing at least a portion of one strip (22) to another strip (22), for example, or by self vulcanization of the bands (22). They are advantageously bonded along the entire length of the flexible pipe (10) or at intervals of between 0.5 m and 2 m.

To improve the sealing of the outer layer (20), the turns of the strip (22) have an overlap. The width of the overlap between the turns of the strip (22) is for example between 5% and 70% of the width of the strip (22). To further improve the sealing of the outer layer (20), the turns of the strip (22) are bonded, for example, by gluing, fusing or any other suitable process. The fusion bonding of the strip (22) is preferred because it facilitates the assembly process and provides optimal bonding strength. The strip (22) is shown in Figures 3a and 3b, for example. The strip (22) has a width (L) of between 50 mm and 150 mm. The thickness of the strip (22) is between 0.4 mm and 2 mm. Preferably, the strip (22) has a tensile strength in the longitudinal direction of the strip (22) of between 100 daN/cm and 800 daN/cm as measured at 23 C according to ISO 527-1 (2012). The strip (22) is formed of a polymer matrix (24) reinforced by a plurality of reinforcing elements (26). The polymer matrix (24) is selected from among thermoplastic materials such as a polyethylene, polypropylene, polyamide or elastomeric thermoplastic materials such as a vulcanized thermoplastic, in particular a vulcanized thermoplastic silicone or thermosetting materials such as silicones or a mixture thereof. Preferably, the elongation at the threshold of the polymer matrix (24) is greater than or equal to 5%, advantageously greater than or equal to 7% and even more advantageously greater than or equal to 10%. The reinforcing elements (26) are fibers such as organic fibers, mineral fibers or metallic fibers for example. The organic fibers are aramid fibers or polyethylene terephthalate or high molecular weight polyethylene fibers for example. The mineral fibers are carbon or basalt or glass fibers, for example. The metallic fibers are formed of boron or alumina, for example, or other metallic material suitable for the present invention. Advantageously, the elasticity modulus of the reinforcing elements (26) is greater than or equal to 10 GPa, advantageously greater than 30 GPa, even more advantageously greater than or equal to 50 GPa and preferably between 50 GPa and 150 GPa. Advantageously, the reinforcing elements form a fabric, nonwoven or a mat. The reinforcing elements, such as the fibers, are oriented at an angle of absolute value of between 0° and 40° in relation to the longitudinal axis (B) of the strip (22). Thus, the strip (22) has anisotropic properties. The reinforcing elements (26) in combination with a wrap angle of the strip (22) of between 600 and 90°, provide the strip (22) sufficient resistance to limit the radial deformation of the outer layer (20) in relation to the axis of the flexible pipe (10). In addition, the polymer matrix (24) has an elongation at the threshold to maintain the flexibility of the outer layer (20) in the axial direction of the flexible pipe (10). According to a first embodiment of the strip (22) shown in Figure 3a, the reinforcing elements (26) are embedded in the polymer matrix (24). This protects the reinforcing elements from wear resulting from friction between the layers of the flexible pipe (10). "Embedded in the matrix" is understood as the reinforcing elements (26) being completely enveloped by the polymer matrix (24). According to a second embodiment of the strip (22) shown in Figure 3b, the reinforcing elements (26) are arranged on an outer surface of the strip (22). Advantageously, the reinforcing elements (26) are bonded to the polymer matrix (24). The bonding can be chemical, by gluing the reinforcing elements (24), for example, or mechanical. According to another embodiment (not shown), the reinforcing elements (26) are arranged on both surfaces of the strip (22). This increases the density of the reinforcing elements (26) within the strip (22). Figure 4a shows an example of an embodiment of the outer layer (20). The outer layer (20) comprises a strip (22) and an additional layer (23), for example. The strip (22) comprises the polymer matrix (24) and reinforcing elements (26) arranged on an outer surface of the strip (22) as described with reference to Figure 3b. Advantageously, the reinforcing elements (26) are arranged on the outer surface of the strip (22) radially closest to the additional layer (23). The strip (22) is helically wound with a short pitch. The turns of the strip (22) are joined together. The additional layer (23) is a sheath extruded around the strip (22), for example. The material of the additional layer (23) is selected from thermoplastic materials such as polyethylene, polypropylene, polyamide, for example, or elastomeric thermoplastic materials such as a vulcanized thermoplastic, in particular a vulcanized thermoplastic silicone or thermosetting thermoplastic materials such as silicones or a mixture thereof. Preferably, the material of the additional layer (23) is identical to the polymer matrix of the strip (22). Advantageously, the additional layer (23) is bonded to the strip (22). The bonding is achieved, for example, by melting the materials of the additional layer (23) and the strip (22) during the extrusion of the layer (23) onto the strip (22), for example. According to another example shown in Figure 4b, the outer layer comprises a plurality of strips (22), for example, including an inner strip (22a), a middle strip (22c) and an outer strip (22b). The strips (22) comprise the polymer matrix (24) and reinforcing elements (26) arranged on an outer surface of the strip (22) as described with reference to Figure 3b. The inner strip (22a) is helically wound at a short pitch. The reinforcing elements (26) of the inner strip (22a) are arranged on the outer surface of the inner strip (22a) furthest radially from the longitudinal axis (A) of the flexible pipe (10). The central strip (22c) is wound helically with a short pitch around the inner strip (22a). The reinforcing elements (26) of the central strip (22c) are arranged on the outer surface of the central strip (22c) furthest radially from the longitudinal axis (A) of the flexible pipe (10). This limits wear of the reinforcing elements (26) resulting from friction between the reinforcing elements (26) of the bands (22). The outer strip (22b) is wound helically around the center strip (22c). The reinforcing elements (26) of the outer strip (22b) are arranged on the outer surface of the outer strip (22b) radially closest to the longitudinal axis (A) of the flexible pipe (10). The matrix (24) of the outer strip (22b) thus protects the reinforcing elements (26) from UV attacks and from any external damage resulting from friction with storage or laying equipment, for example. The flexible pipe (10) may comprise additional layers such as anti-wear strips arranged between the pressure vault (16) and the internal tensile armor ply (18a) and/or between the internal tensile armor ply (18a) and the outer tensile armor ply (18b). The anti wear strips limit wear of the pressure vault (16) and the pair of tensile armor plies (18) due to friction. The flexible pipe (10) may comprise an additional pair of tensile armor plies when tensile forces are particularly high. Advantageously, the flexible pipe (10) comprises thermal insulation strips. For example, thermal insulation strips are wound at a short pitch between the outer layer (20) and the outer tensile armor ply (18b). The thermal insulation strips are formed of a polypropylene polymer matrix, for example. An installation for manufacturing the flexible pipe (10) will now be described with reference to Figure 5 and Figure 6. The installation comprises a station (120) for manufacturing the internal carcass (12), a station (140) for manufacturing the inner sheath (14), a station (160) for manufacturing the pressure vault (16), a station (180) for manufacturing the pair of tensile armor plies (18) and a station (200) for manufacturing the outer layer (20). The station (120) for manufacturing the internal carcass (12) comprises a turntable on which at least one wire profiling device is mounted and wire stapling means arranged downstream of the profiling device. The turntable further comprises a central passage of the internal carcass (12). The wire is stored and unwound from a spool arranged upstream of the turntable.

The carcass (12) is transferred to the station (140) for manufacturing the inner sheath (14). The station (140) for manufacturing the inner sheath (14) comprises an extruder for forming the inner sheath (14) around the internal carcass (12) and optionally a means for cooling the inner sheath (14) located downstream of the extruder, such as air or water nozzles to accelerate the cooling of the inner sheath (14). Theinnersheath (14)arranged around the internal carcass (12) is transferred to the station (160) for manufacturing the pressure vault (16). The station (160) for manufacturing the pressure vault (16) comprises means for winding the profiled metal wire. The assembly is transferred to the station (180) for manufacturing the pair of tensile armor plies (18). The station (180) for manufacturing the pair of tensile armor plies (18) comprises a plurality of spools from which the tensile armor wires are unwound. The outer layer (20) is manufactured around the pair of tensile armor plies (18) at the station (200) manufacturing the outer layer (20). Advantageously, the station (200) for manufacturing the outer layer (20) is arranged in line with the station (180) for manufacturing the pair of tensile armor plies (18). According to another example, the station (200) for manufacturing the outer layer (20) is not arranged in line with the station for manufacturing the pair of tensile armor plies (18). The installation then comprises a flexible pipe (10) storage device for storing and unwinding the flexible pipe (10) within the station (200) manufacturing the outer layer (20). The station (200) for manufacturing the outer layer (20) is shown in Figure 6, for example, and comprises a winding device (220) for the strips (22) mounted on a support (300) of a turntable (280), and optionally a heating device (240). The manufacturing station (200) optionally comprises at least one pressure roller (260). The winding device (220) comprises a reel on which the strip (22) is wound. It is mounted on the support (300) of the turntable (280) and is driven in rotation. The winding device (220) allows the strip (22) to be deposited on the outer tensile armor ply (18b) with a winding angle of absolute value between 60 and 90 in relation to the longitudinal axis (A) of the flexible pipe (10). Advantageously, the winding device (220) is motorized. Advantageously, the winding device (220) comprises a brake. The brake makes it possible to modulate the tension force to which the strip (22) is subjected during its winding around the outer tensile armor ply (18b). The heater (240) is configured to cause the polymer matrix (24) of the strip (22) to melt to bond the turns of the strip (22). The heating device (240) comprises, for example, a laser, a lamp such as an infrared lamp, an ultrasonic welding device and/or a hot air blower.

The heating device (240) is advantageously mounted on the support (300) of the turntable (280) to be rotated together with the winding device (220). The pressure roller (260) is arranged around the central passage of the turntable (280), at the point of contact between the strip (22) and the outer tensile armor ply (18b). The pressure roller (260) is intended to exert pressure on the strip (22) during winding around the outer tensile armor ply (18b) to promote bonding between the turns of the strip (22). According to a particular embodiment not shown, the station (200) comprises a plurality of coils (220) for depositing multiple strips (22) in an overlapping way. The heating device (240) and the pressure roller (260) then ensure an optimal connection between each strip (22). According to a particular embodiment not shown, the station (200) further comprises an extruder for forming the additional layer (23) around the strip (22). According to this mode, the heating device (240) and the pressure roller (260) advantageously make it possible to improve the bond between the additional layer (23) and the strip (22). The installation according to the invention thus allows the flexible pipe (10) to be manufactured continuously without interrupting the manufacturing process. Indeed, the manufacturing of the outer layer (20) is carried out simultaneously with the manufacturing of the pair of tensile armor plies (18), since the manufacturing stations can be arranged in line. Also, the manufacturing station (220) for the outer layer (20) implements conventional manufacturing means and does not require any special equipment or set-up. A method for manufacturing the flexible pipe (10) will now be described. According to an optional first step, an internal carcass (12) is provided. The process comprises the step (a) of forming the polymeric inner sheath (14) that forms the passage for circulation of fluid. It comprises extruding the inner sheath (14) and cooling the inner sheath (14). The inner sheath (14) is then moved to the station for manufacturing the pressure vault (16). The wires are helically wound at a short pitch around the inner sheath (14) to form the pressure vault (16). Next, the method comprises a step (b) in which the pair of tensile armor plies (18) are formed. In a sub-step, the internal tensile armor ply (18a) is formed by helically winding a plurality of wires at a long pitch. Then, in a further sub-step, the outer tensile armor ply (18b) is formed by helically winding a plurality of wires at an angle opposite to the helix angle of the wires of the internal tensile armor ply (18a).

In a final step (c), the outer layer (20) is formed. In this step, the strip (22) is helically wound, advantageously with an overlap between the turns. Advantageously, the strip (22) is wound with a short pitch. Advantageously, during this step, the strip (22) is heated. The heating is carried out before or after winding the strip (22) around the outer tensile armor ply (18b). Preferably, the strip (22) is heated at the point of contact between the strip (22) and the outer tensile armor ply (18b). Advantageously, according to this step, pressure is exerted on the overlap area between the turns of the strip (22). According to another embodiment, in step (c), the strip (22) is helically wound so that the turns of the strip (22) are joined. The strip (22) is then advantageously heated. Then, an additional layer (23) is formed around the strip (22) by extrusion, for example. Advantageously, pressure is applied to the additional layer (23) after extrusion. According to yet another embodiment, in step (c), a plurality of strips (22) are helically wound. In a first sub-step, an inner strip (22a) is wound at a short pitch with an overlap between the turns. In a further step, a central strip (22c) is wound with a short pitch. Then in a further step, an outer strip (22b) is wound with a short pitch. According to an embodiment, before step (c), the strip (22) is subjected to a calendering step. Preferably, the calendering of the strip (22) is performed at a temperature higher than the ambient temperature and lower than the melting temperature of the polymer matrix (24). For example, the calendering of the strip (22) is performed at 60 C, preferably at 80° C. This improves the temperature resistance of the strip (22) and thus the outer layer (20).

Claims (16)

1. A flexible pipe (10) for conveying a fluid in a submarine environment having a longitudinal axis (A) and comprising from the inside to the outside of the pipe (10): - an inner polymeric sheath (14), to form a passage for circulation of fluid, - at least one pair of tensile armor plies (18), to reinforce the flexible pipe (10) against axial forces; - a liquid-impermeable outer layer (20), the inner sheath (14) and the outer layer (20) defining an annular space in which said at least one pair of tensile armor plies (18) is arranged - said outer layer (20) having a thickness of between 1/125 and 1/75 of the internal diameter of the outer layer (20) and comprising at least one helically wound strip (22) forming a plurality of turns, said strip (22) being made of a polymer matrix (24) reinforced with a plurality of reinforcing elements (26).

2. The flexible pipe according to claim 1, characterized in that the thickness of the outer layer (20) is between 3 mm and 5 mm for an internal diameter of the outer layer (20) of between 250 mm and 600 mm.

3. The flexible pipe according to one of claims 1 or 2, characterized in that the turns of the strip (22) are bonded together.

4. The flexible pipe according to any one of claims 1 to 3, characterized in that the turns of the strip (22) have an overlap.

5. The flexible pipe according to any of the preceding claims, characterized in that the strip (22) is wound at a helix angle of absolute value of between 600 and 90 in relation to the longitudinal axis (A) of the flexible pipe (10).

6. The flexible pipe according to any one of the preceding claims, characterized in that the outer layer (20) comprises a plurality of superimposed strips (22), preferably between 2 and 8 superimposed strips (22).

7. The flexible pipe according to claim 6 characterized in that at least two strips (22) are crossed.

8. The flexible pipe according to any one of the preceding claims, characterized in that the reinforcing elements (26) are fibers such as organic fibers, mineral fibers or metallic fibers.

9. The flexible pipe according to any one of the preceding claims, characterized in that the reinforcing elements (26) are oriented at an angle of absolute value of between 0° and 40° in relation to the longitudinal axis of the strip (22).

10. The flexible pipe according to any one of the preceding claims, characterized in that the polymer matrix (24) is chosen from among thermoplastic materials such as a polyethylene, a polypropylene, a polyamide or elastomeric thermoplastic materials such as a vulcanized thermoplastic, in particular a vulcanized thermoplastic silicone, or thermosetting materials.

11. The flexible pipe according to any one of the preceding claims, characterized in that the reinforcing elements (26) are embedded in the polymer matrix (24).

12. A method of manufacturing a flexible pipe (10) for conveying a fluid in a submarine environment comprising the following steps: (a) forming a polymeric inner sheath (14) forming a passage for circulation of fluid, (b) forming at least one pair of tensile armor plies (18), to reinforce the flexible pipe (10) against axial forces (c) helically winding a strip (22) forming a plurality of turns, said strip (22) being made of a polymer matrix (24) reinforced with a plurality of reinforcing elements (26) to form a liquid-impermeable outer layer (20) compounds having a thickness of between 1/125 and 1/75 of the internal diameter of the outer layer (20), the outer layer (20) and the inner sheath (14) defining an annular space in which the at least one pair of tensile armor plies (18) is arranged.

13. The method according to claim 12, characterized in that in step (c) the strip (22) is wound with an overlap of the turns.

14. The method according to any of claims 12 or 13, characterized in that it comprises a step of bonding the turns.

15. The method according to claim 14, characterized in that the step of bonding the turns comprises a sub-step of heating the strip (22).

16. The method according to any one of claims 12 to 15, characterized in that it comprises a step in which pressure is applied to the strip (22).