Flexible underwater pipe with a wear-resistant polypropylene homopolymer layer

Description

[0001] The present invention relates to an underwater pipeline intended for the transport of fluids, in particular hydrocarbons.

[0002] Most flexible pipelines used in the offshore oil industry are flexible pipelines that generally consist of, from the inside out: possibly a metal frame, an internal polymer sealing sheath, at least one reinforcing layer consisting of a helical winding of a longitudinal metallic or composite material element around the internal sealing sheath, an external polymer sealing sheath.

[0003] Typically, they include, from the inside out: possibly a metal frame, an internal polymer sealing sheath, possibly a pressure vault, at least one layer of tensile armor (usually two layers of tensile armor), an external polymer sealing sheath.

[0004] In all that follows, the terms "outside" or "external" and "inside" or "internal" are understood respectively as further radially from the axis of the flexible pipe and as closer radially to the axis of the flexible pipe.

[0005] These pipes are generally of the unbonded type. By "unbonded," we mean that the layers are free to move relative to each other. Typically, adjacent layers are not glued together, welded together, or embedded in a polymer or elastomeric sheath.

[0006] Such flexible pipelines are described in the API 17J standard, "Specification for Unbonded Flexible Pipe," 4th edition, May 2014, published by the American Petroleum Institute. They are used primarily in deepwater applications within the oil and gas industry. Typically, they are used for transporting fluids, particularly hydrocarbons, or for reinjecting carbon dioxide into a subsea reservoir. Oil pipelines generally extend across a body of water between a surface and a bottom assemblies. These pipelines can also extend between two surface assemblies or between two bottom assemblies.

[0007] The bottom system is designed to collect the extracted fluid from the bottom of the water body, monitor and control its flow, and distribute it to the surface system. The surface system is typically floating. It is designed to collect, potentially treat, and distribute the fluid on land. The surface system can be a semi-submersible platform, an FPSO, or another floating system.

[0008] In some cases, for the operation of fluids in deep water, the flexible pipeline has a length of more than 800 m, or even more than 1000 m or 2000 m for ultra-deep water applications.

[0009] For great depths, the flexible pipe is sized to withstand very high hydrostatic pressure, typically from 50 to 1000 bar, for example 200 bar for a pipe submerged at a depth of 2000 m and high temperatures, above 130°C, or even 170°C, for long periods of time, i.e. several years, typically 20 years.

[0010] Furthermore, flexible pipe is generally designed to withstand an axial tension greater than the total weight of the flexible pipe suspended from a surface assembly and extending underwater from the surface to the seabed. This is particularly relevant when the flexible pipe is used as a riser to provide a vertical connection between the seabed and the surface assembly during operation. The flexible pipe's ability to support its own weight when suspended in water facilitates its installation at sea from a pipe-laying vessel.

[0011] However, these flexible pipelines are generally heavy, making their installation in deep and ultra-deep water complex and expensive. Furthermore, riser pipes of this type typically require buoys for deep-water applications, resulting in additional costs. Finally, the metallic reinforcement layers are generally susceptible to corrosion, particularly corrosion under the influence of acidic gases such as H₂S and CO₂ present in hydrocarbons from certain reservoirs. Composite reinforcement layers are sometimes prone to degradation in the presence of water (particularly hydrolysis), a process that can be exacerbated by H₂S.

[0012] To overcome these problems, lightweight flexible pipes with a tubular reinforcement structure made of composite material comprising a thermoplastic matrix and reinforcing fibers embedded in the matrix have been developed, namely the so-called "hybrid" flexible pipes ("hybrid flexible pipe" HFP in English).

[0013] In so-called "hybrid" flexible pipes, the metal casing and internal polymer sealing sheath of the flexible pipe described above are replaced by a thermoplastic composite pipe ("Thermoplastic Composite Pipe" (TCP)), as described in the normative document DNVGL-ST-F119 "Thermoplastic Composite Pipe", September 2019 edition published by Det Norsk Veritas. These "hybrid" flexible pipes consist, from the inside out: an internal tubular polymer sheath, a tubular reinforcement structure made from a winding of several strips of composite material, this intermediate layer being linked to the internal tubular polymer sheath, a sealing polymer sheath, at least one reinforcement layer consisting of a helical winding of a longitudinal metallic or composite material element around the sealing polymer sheath, an external sealing polymer sheath.

[0014] By "bonded," we mean that the tubular reinforcement structure and the internal tubular polymer sheath are not free to move relative to each other. They can be bonded by gluing (using glue or an adhesive) or by welding.

[0015] The tubular reinforcement structure typically absorbs most of the radial forces applied to the hybrid flexible pipe. This tubular reinforcement structure, connected to the internal tubular polymer sealing liner, also acts as a gas barrier, protecting against acidic gases such as H₂S and CO₂ contained in hydrocarbons transported within the internal tubular polymer liner. This protects the metallic reinforcement elements of the flexible pipe from corrosion and / or the composite materials from degradation by hydrolysis.

[0016] The reinforcement layer(s), made of metallic or composite wires, are similar to those found in unbonded flexible hoses; that is, they consist of wires or strips wound helically, usually with a long pitch. They are generally not bonded to adjacent layers. These are typically tensile reinforcement layers.

[0017] In addition, these hybrid flexible pipes can optionally include an internal reinforcement located inside the inner tubular polymer sheath. This internal reinforcement serves to increase the pipe's collapse resistance. The internal reinforcement is formed, for example, from a profiled metal strip wound in a spiral. The spirals of the strip are advantageously stapled together, which allows them to withstand crushing forces.

[0018] These hybrid flexible pipes are described in particular in the article "Unbonded Flexible Pipe: Composite Reinforcement for Optimized Hybrid Design" written by N. Dodds, V. Jha, J. Latto and D. Finch, and published under reference OTC-25753 at the "Offshore Technology Conference" held in Houston from May 4 to 7, 2015, or in applications GB 2 504 065 and WO 2018 / 091693. These two applications describe hybrid flexible pipes in which the tubular reinforcement structure is made from a winding of several strips comprising a polymer matrix and in which reinforcing fibers are embedded.

[0019] Whether the flexible pipe is a "conventional" unbonded type or a hybrid flexible pipe, the various unbonded layers are, to a certain extent, mobile relative to each other, allowing the flexible pipe to flex. When the pipe includes several adjacent layers of metallic or composite reinforcement, this mobility induces friction between them and the adjacent layers, ultimately leading to their premature wear.

[0020] Also, in order to prevent at least two of these metallic or composite reinforcement layers from being in direct contact with each other, which would cause them to wear out, an intermediate layer of polymeric material, called an "anti-wear layer", can be interposed.

[0021] This intermediate wear-resistant layer can, however, deteriorate rapidly when the flexible pipe is subjected to severe stresses, such as those encountered in the operation of certain deep-sea oil fields where the hydrocarbon temperature exceeds 130°C, and / or in the case of severe dynamic conditions (variations in the pipe's curvature). Under such conditions, this intermediate wear-resistant layer can withstand temperatures approaching 110°C and contact pressures of 300 to 400 bar. One of the most common forms of deterioration is a loss of thickness in the wear-resistant layer due to creep, which can limit, or even eliminate, the protection provided by the wear-resistant layer to the adjacent reinforcing layers.

[0022] Application WO 2006 / 120320 describes a flexible pipeline for the transport of hydrocarbons comprising an anti-wear layer of amorphous polymer, preferably of polysulfone (PSU), polyethersulfone (PES), polyphenylsulfone (PPSU) or polyetherimide (PEI).

[0023] The use of thermoplastic materials in unbonded flexible pipes is summarized in the standards documents API RP 17B (2014) and API 17J (2014) published by the American Petroleum Institute.

[0024] The literature reports the use of polypropylene as a polymeric material for polymeric layers of a flexible pipe.

[0025] For example, application WO 2017 / 174660 describes a subsea pipeline for the transport of hydrocarbons comprising a metallic reinforcing layer around an internal polymer sealing liner that may come into contact with hydrocarbons and comprises a homopolymer polypropylene of specific density and melt flow index. However, the internal polymer sealing liner is not a wear-resistant layer (and vice versa). A wear-resistant layer does not come into contact with hydrocarbons when the pipeline is in service.

[0026] Application WO 2017 / 076412 describes a subsea pipeline for the transport of hydrocarbons comprising a polymer layer consisting of at least 50% by weight of polypropylene and at least 1% by weight of a plastomer formed from propylene and at least one comonomer other than propylene. However, this application does not suggest a homopolymer polypropylene having the flexural modulus and flow index defined below for that used in the present invention, nor does it suggest improved creep behavior making its use advantageous as a wear-resistant layer. Furthermore, the presence of the plastomer is required to give the layer the necessary strength and flexibility, and in significant proportions. Such a plastomer considerably increases the cost of the layer.

[0027] Application WO 2015 / 004597 describes a flexible pipeline for the transport of hydrocarbons comprising a carcass, an inner polymer sheath, an outer protective polymer layer, a mechanical armor layer comprising pressure-resistant armor and a protective armor layer, the mechanical armor layer comprising a plurality of elongated carbon steel elements covered with an aluminum sheath. Between the pressure-resistant armor and the protective armor layer, the pipeline may include a layer, preferably of polyamide or polypropylene. Furthermore, the protective armor layer preferably comprises a first and a second protective armor layer, and between these two armor layers, a polymer layer, preferably of polyamide or polypropylene, may be located.

[0028] Application WO 2018 / 149462 describes an assembly of an end fitting and a flexible, unbonded hose. The hose comprises a casing, an internal pressure sheath, a pressure arch, optionally an intermediate thermal and / or electrical insulation layer, at least one reinforcement layer, and optionally an external sheath. The intermediate thermal and / or electrical insulation layer may be made of various polymers, including polypropylene. It may also include a wear-resistant layer, preferably made of polyethylene, polyamide, polyaramid, polyurethane, polypropylene, or PVDF.

[0029] One of the objectives of the present invention is to provide a subsea pipeline for the transport of fluid, preferably hydrocarbons, whose anti-wear layer is less expensive and which has creep resistance such that the anti-wear layer slows down, preferably prevents the wear of the metallic or composite reinforcement layers surrounding it, and this over the entire life of the pipeline, typically 20 years.

[0030] To this end, according to a first object, the invention relates to a flexible underwater pipeline for the transport of fluid according to claim 1, preferably hydrocarbons, comprising at least two reinforcing layers separated by a wear-resistant layer made of polymeric material, each of said reinforcing layers being made by helical winding of a longitudinal metallic or composite material element, said wear-resistant layer being made by helical winding of at least one strip of said polymeric material, the polymeric material comprising a homopolymer polypropylene having: a flexural modulus measured at 23°C according to ISO 178 of 2019 greater than 1500 MPa, and a melt flow index (MI or MFI) measured according to ISO 1133 revised in 2011 at 230°C under a mass of 2.16 kg less than or equal to 4.0 g / 10 minutes.

[0031] The invention is based on the discovery that such a homopolymer polypropylene exhibits creep resistance that allows the wear-resistant layer formed from a strip containing it to maintain sufficient thickness so that the surrounding reinforcing layers do not come into contact with each other, and therefore do not wear against one another. The use of such a homopolymer polypropylene reduces the thickness loss of the wear-resistant layer, which is advantageous because the greater the thickness of the wear-resistant layer, the better it protects the surrounding reinforcing layers.

[0032] Furthermore, such a homopolymer polypropylene withstands the pressure and temperature conditions mentioned above. In addition, it exhibits chemical resistance compatible with its use as a polymer material for a layer in a flexible pipeline for transporting hydrocarbons. The annular space (the space between the inner and outer polymer sheaths of the pipeline seal) in which the wear-resistant layer is located contains gases and / or acids (CO₂ and H₂S in particular). Advantageously, homopolymer polypropylene is not susceptible to hydrolysis, unlike a polyamide-based wear-resistant layer. Moreover, homopolymer polypropylene is minimally, if at all, susceptible to CO₂-induced plasticization.

[0033] Another advantage of such an anti-wear layer is that homopolymer polypropylene has good permeability to CO2 and H2S, which allows the concentration of CO2 and H2S to decrease in the innermost layers of the anti-wear layer, and therefore reduces corrosion (especially for metallic layers) and / or degradation by hydrolysis (especially for polymeric or composite material layers) of these innermost layers.

[0034] Another advantage of such an anti-wear layer is its low cost.

[0035] The polymeric material of the helically wound strip to form the wear-resistant layer of the pipe comprises a homopolymer polypropylene or a mixture of homopolymer polypropylenes.

[0036] There are three main classes of polypropylene: homopolymers (PPH), block copolymers (also called impact copolymers) (PPB), and statistical copolymers (PPR) (designations according to ISO 15013 revised in 2015 and ISO 1873-2 revised in 2011). Typically, PPHs consist of at least 97%, in particular at least 98%, typically at least 99%, preferably at least 99.8%, and advantageously exclusively of a chain of propylene units relative to the total number of units. The proportion of propylene units can be determined, in particular, by Fourier transform infrared spectroscopy.

[0037] The homopolymer polypropylene of the polymeric material of the strip has a flexural modulus measured at 23°C according to ISO 178:2019 at a flexural strain rate of 1% min⁻¹ < 1500 MPa, in particular > or equal to 1550 MPa, preferably > or equal to 1600 MPa, and particularly preferably > or equal to 1700 MPa. The flexural modulus is generally less than 2500 MPa, in particular < 2300 MPa, and preferably < 2100 MPa. These flexural moduli are particularly suitable for ensuring that the wear-resistant layer has the required creep resistance to minimize the reduction in its thickness.

[0038] The homopolymer polypropylene of the polymeric material in the belt has a melt flow index measured according to ISO 1133 revised in 2011 at 230°C under a mass of 2.16 kg of 4.0 g / 10 minutes or less. The melt flow index is generally greater than 0.1 g / 10 minutes, in particular greater than 0.3 g / 10 minutes, and preferably greater than or equal to 2.0 g / 10 minutes. Such melt flow indices facilitate the preparation of a belt by extrusion. The use of homopolymer polypropylene with a higher melt flow index generally results in belts with insufficiently uniform thickness, which impairs the uniformity of the thickness of the resulting wear-resistant layer and therefore its performance.

[0039] When the polymeric material comprises a mixture of homopolymer polypropylenes, it is not mandatory for each homopolymer polypropylene it contains to have a flexural modulus and melt flow index as defined above. It is sufficient for the mixture as a whole to have these properties. In a particular embodiment, each homopolymer polypropylene in the mixture of homopolymer polypropylenes has a flexural modulus and melt flow index as defined in this application.

[0040] The homopolymer polypropylene of the polymeric material of the strip (or the mixture of homopolymer polypropylenes, or even each homopolymer polypropylene in the mixture of homopolymer polypropylenes) generally has: a density according to ISO 1183 of 2019 greater than or equal to 0.85 g / cm 3< , typically or equal to 0.88 g / cm 3< , in particular or equal to 0.905 g / cm 3< , a tensile yield stress measured at 23 ± 2 °C and with a travel speed of 50 mm / min according to ASTM D638 type IV of 2014 or ISO 527-2 of 2012 of between 30 and 45 MPa, and / or an elongation at yield (measured at 23 ± 2 °C and with a travel speed of 50 mm / min according to ASTM D638 of 2014 or ISO 527-2 of 2012) of 1 to 7%, preferably 3 to 5%.

[0041] The homopolymer polypropylene of the polymeric strip material (or each homopolymer polypropylene in the blend of homopolymer polypropylenes) generally has a melting point (considering the peak corresponding to the highest melting point in differential scanning calorimetry (DSC) according to ISO 11357-3:2018) of at least 150°C, in particular at least 200°C, preferably at least 220°C. Generally, there is a coexistence of alpha and beta crystal morphologies in homopolymer polypropylene, which can lead to two distinct melting points in DSC. In this case, the peak corresponding to the highest melting point is taken into consideration for the purposes of this application.

[0042] Homopolymer polypropylene (or a mixture of homopolymer polypropylenes, or even each individual homopolymer polypropylene within a mixture of homopolymer polypropylenes) generally has a degree of crystallinity of at least 40%, typically at least 50%. The degree of crystallinity can be calculated by dividing the heat of fusion of homopolymer polypropylene, as determined by differential scanning calorimetry, by the heat of fusion of 100% crystalline homopolymer polypropylene, usually estimated at 207 joules / gram.

[0043] Such density, yield stress, yield elongation, melting temperature and degree of crystallinity contribute to the fact that the polypropylene homopolymer exhibits improved creep resistance and is compatible with the use of the polymeric material strip comprising the polypropylene homopolymer as an anti-wear layer between two layers of metallic or composite reinforcement in a pipeline for the transport of fluids, preferably hydrocarbons.

[0044] Examples of homopolymer polypropylene exhibiting these properties include the following homopolymer polypropylenes: Repsol PP040C1E, Polychim HL10XF, LyondellBasell Moplen HP740J, Braskem Inspire 234, Total PPH4022 and Braskem H605.

[0045] The homopolymer polypropylene of the strip (or one of, or even each, homopolymer polypropylene of the mixture of homopolymer polypropylenes) can be crosslinked.

[0046] The homopolymer polypropylene of the strip (or one of, or even each, homopolymer polypropylene of the mixture of homopolymer polypropylenes) may be non-crosslinked.

[0047] Embodiments are described below for the band and the polymeric material. They apply to at least one band, preferably to each band, when the wear-resistant layer comprises several bands.

[0048] The strip comprising the homopolymer polypropylene defined above typically includes: a polymer matrix, and possibly components dispersed discontinuously in the polymer matrix.

[0049] The term "polymer matrix" refers to the continuous polymeric phase that forms the tape. The polymer matrix is ​​a continuous matrix. The polymeric material of the tape may optionally include components dispersed discontinuously within the polymer matrix, but which are not part of the polymer matrix itself. Such components may, for example, be fillers such as fibers.

[0050] The polymer matrix of the polymeric strip material is generally obtained by extruding one or more polymers (which will form the polymer matrix) and possibly additives (masterbatch). During extrusion, some additives are incorporated into the polymer matrix, while others do not mix with the polymers forming the polymer matrix and disperse discontinuously within the polymer matrix, forming discontinuously dispersed components.

[0051] According to a first alternative, the polymeric material of the strip has a polymeric matrix which includes a homopolymer polypropylene as defined above.

[0052] According to this alternative, the polymeric material of the strip whose polymeric matrix includes homopolymer polypropylene is generally obtained by extrusion of one or more polymers (which will form the polymeric matrix), at least one of them being the homopolymer polypropylene defined above, and possibly in the presence of additives.

[0053] The components dispersed discontinuously within the polymer matrix may include polymers, for example, a homopolymer polypropylene as defined above. That being said, a conduit: whose polymeric material of the anti-wear layer band comprises a component dispersed discontinuously in the polymeric matrix (in particular fillers such as fibers) comprising or consisting of homopolymer polypropylene as defined above, but whose polymeric matrix is ​​free of homopolymer polypropylene as defined above, does not meet the definition of a pipe comprising an anti-wear layer made by helical winding of at least one strip of polymeric material whose polymeric matrix comprises a homopolymer polypropylene as defined above, as defined in this first alternative.

[0054] According to a second alternative, the polymeric material of the strip comprises a component dispersed discontinuously in the polymeric matrix, said component comprising a homopolymer polypropylene as defined above.

[0055] According to this second alternative, a component dispersed discontinuously within the polymer matrix of the web material comprises a homopolymer polypropylene as defined above. The component may be a filler such as a fiber. The component comprising a homopolymer polypropylene as defined above is generally one of the additives in the masterbatch used during extrusion. According to this second alternative, the polymer matrix of the web material may be free of homopolymer polypropylene as defined above.

[0056] According to a third alternative, the polymeric material of the strip comprises a component dispersed discontinuously in the polymeric matrix, said component comprising a homopolymer polypropylene as defined above and its polymeric matrix comprising a homopolymer polypropylene as defined above.

[0057] According to this third alternative, homopolymer polypropylene as defined above is therefore present both in the polymer matrix and in a component dispersed discontinuously in the polymer matrix.

[0058] The polymeric material of each strip comprises at least 50% by weight, in particular at least 65% by weight, preferably at least 75% by weight, typically at least 85% by weight, for example at least 90% by weight, particularly preferably at least 95% by weight of homopolymer polypropylene as defined above, relative to the weight of the strip. Advantageously, the properties of homopolymer polypropylene as defined above allow for the use of little or no modifier.

[0059] The strip may include a plasticizer, which improves the performance of the cold-weather wear layer (by lowering the glass transition temperature by 10°C, or even 25°C, measurable by dynamic mechanical analysis (DMA)). The plasticizer can, for example, be chosen from the compounds defined in the publication. Handbook of Plasticizers edited by Georges Wypych. The plasticizer can for example be chosen from among liquid saturated hydrocarbons (such as ExxonMobil's Primol 542), isooctyl tallate monoester (such as Hallstar Industrial's PLASTHALL ®< 100), dioctyl sebacate, paraffin oil or a mixture of these.

[0060] For example, the polymeric material of the strip comprises 0% to 5% by weight of plasticizer.

[0061] The polymeric material of the tape may also include an impact modifier, which improves its cold-weather performance, particularly its resistance to cold brittleness. Thus, the polymeric material of the tape may contain 0 to 5% by weight, relative to the total weight of the tape, of an impact modifier, generally a polymer with a flexural modulus of less than 100 MPa measured according to ISO 178:2019. The impact modifier is preferably composed of one or more polyolefins.For example, the polyolefin is selected from: an elastomeric ethylene-propylene copolymer (EPR), an ethylene-butene copolymer (EBR), an ethylene-octene copolymer (EOR), an elastomeric ethylene-propylene-diene copolymer (EPDM), a styrene-butadiene copolymer (SBR) and an ethylene / (meth)acrylate alkyl copolymer, preferably selected from an ethylene-butene copolymer (EBR), an ethylene-octene copolymer (EOR), a styrene-butadiene copolymer (SBR) and an ethylene / (meth)acrylate alkyl copolymer.

[0062] Preferably, the polymeric material of the tape comprises less than 0.4%, and in particular less than 0.1% by weight of the tape, or even be free of, any plastomer formed from propylene and at least one comonomer other than propylene. In addition to homopolymer polypropylene (or a mixture of homopolymer polypropylenes), the polymeric material of the tape comprises less than 0.4%, and in particular less than 0.1% by weight of the tape, or even be free of, any copolymer of polypropylene and one or more other monomers. A polypropylene copolymer generally contains less than 95%, typically less than 90%, of propylene units relative to the total number of units in the polypropylene copolymer. The proportion of propylene units can be determined, in particular, by Fourier transform infrared spectroscopy.

[0063] The polymeric material of the tape may comprise less than 10%, and in particular less than 5% by weight of the tape, or even be free of any polyolefin other than homopolymer polypropylene (or a mixture of homopolymer polypropylenes).

[0064] The polymeric material of the tape may include one or more other additives, in particular selected from antioxidants, UV inhibitors, reinforcing fillers, manufacturing aids, heat stabilizers (for example, a stabilizer from the Brüggemann BRUGGOLEN®< H range), nucleating agents, and a mixture thereof, preferably selected from antioxidants, nucleating agents, and a mixture thereof. Thus, the polymeric material of the tape may comprise from 0 to 10% by weight, preferably from 0 to 5% by weight, of additives or mixtures thereof, relative to the total weight of the tape.

[0065] Typically, the polymeric material of the tape comprises, or is even made up of: 80 to 100% by weight, preferably 90 to 100% by weight, of homopolymer polypropylene as defined above or mixture thereof, 0 to 5% by weight of plasticizer, 0 to 5% by weight of shock modifier, 0 to 10% by weight of additives.

[0066] The tape can be multilayered, for example two- or three-layered. Preferably, the tape is single-layered.

[0067] In general, the belt has a rectangular or near-rectangular cross-section. Preferably, the belt has a thickness of 0.1 to 5.0 mm, preferably 0.5 to 3.0 mm, and / or a width of 30 to 200 mm, preferably 40 to 150 mm. The belt length is variable and can reach up to 5 km.

[0068] The pipe comprises at least two reinforcement layers, each formed by helical winding of a longitudinal metallic or composite element. The wear-resistant layer is surrounded by these two reinforcement layers. It may or may not be adjacent to them.

[0069] Generally, each of these two reinforcement layers is produced by helical winding of a longitudinal element with a long pitch. In this application, the term "short pitch winding" refers to any helical winding with a helix angle close to 90°, typically between 75° and 90°. The term "long pitch winding" covers helix angles less than 60°, typically between 20° and 60° for the reinforcement layers.

[0070] Generally, each of these two reinforcement layers is unbonded to the adjacent polymer layers. By "unbonded," we mean that the reinforcement layers are free to move relative to the adjacent polymer layers (especially the wear layer). Typically, the reinforcement layers of the flexible pipe are not embedded in a polymer or elastomeric sheath (especially the wear layer). Similarly, there is preferably no adhesive between the reinforcement layers and the adjacent polymer layer(s) (especially the wear layer).

[0071] According to one alternative, the flexible pipe includes an internal sealing polymer sheath through which the fluid to be transported flows. This sheath can be made of polyamide, PVDF, polyethylene (particularly high molecular weight polyethylene or high-strength polyethylene), or polypropylene (particularly homopolymer polypropylene or polypropylene copolymer). The internal sealing polymer sheath of the flexible pipe is typically tubular. It generally has a diameter of 50 mm to 600 mm, preferably 50 to 400 mm, and / or a thickness of 1 mm to 150 mm, preferably 4 to 15 mm, and / or a length of 1 m to 10 km.

[0072] The pipe may also include a metal casing. If the pipe includes a metal casing, it is said to have a rough bore. If the pipe does not have a metal casing, it is said to have a smooth bore.

[0073] The primary function of the metal casing is to resist radial forces directed from the outside to the inside of the pipeline in order to prevent the collapse of all or part of the pipeline under these forces. These forces are primarily related to the hydrostatic pressure exerted by seawater when the flexible pipeline is submerged. Thus, the hydrostatic pressure can reach very high levels when the pipeline is submerged at great depths, for example, 200 bar when the pipeline is submerged at a depth of 2000 m, making it often essential to equip the flexible pipeline with a metal casing.

[0074] When the flexible pipe includes an outer polymer sheath, the metal casing also serves to prevent the collapse of the inner polymer sealing sheath during rapid decompression of a flexible pipe that has transported hydrocarbons. Indeed, the gases contained in hydrocarbons diffuse slowly through the inner polymer sealing sheath and become partially trapped in the annular space between the inner and outer polymer sealing sheaths. Consequently, during a production shutdown resulting in rapid decompression of the inside of the flexible pipe, the pressure in this annular space can temporarily become significantly higher than the pressure inside the pipe, which, without a metal casing, would lead to the collapse of the inner polymer sealing sheath.

[0075] Consequently, for hydrocarbon transport, a pipeline with a metal casing is generally preferred, while a pipeline without a metal casing is suitable for transporting water and / or steam under pressure. Furthermore, when the pipeline is intended to both transport hydrocarbons and be submerged at great depths, a metal casing becomes essential in most applications.

[0076] The metal frame consists of longitudinal elements wound helically with a short pitch. These longitudinal elements are strips or profiled metal wires (generally stainless steel) arranged in turns stapled together. Typically, the metal frame is made by profiling a strip into an S-shape and then winding it helically so that adjacent turns are stapled together.

[0077] The metal casing is generally coated with the internal polymer sealing sheath. Since the metal casing is not adjacent to another reinforcing layer, it does not undergo wear from friction and is therefore preferably not coated with a wear-resistant layer.

[0078] At least one of the pipeline reinforcement layers is typically a layer of tensile armor. The main function of tensile armor layers is to resist axial forces related to both the internal pressure within the flexible pipeline and its weight, particularly when suspended. When the pipeline is free of pressure arches (for example, in the case of an OOL (Oil Offloading Line) flexible pipeline), the armor layer resists both axial and radial forces. Tensile armor layers are located on the outer edge of the pipeline. These layers are produced by winding metallic wires at long pitches. These wires generally have a roughly rectangular cross-section, but sometimes a circular or complex geometry, such as a self-stapled T-shaped wire.Alternatively, they can be obtained by winding a longitudinal element of composite material at a long pitch, for example as described in application FR 2 776 358. This composite material typically comprises a polymer matrix reinforced with carbon fibers, glass fibers, aramid fibers, metallic fibers or even mineral fibers (for example basalt).

[0079] Generally, the pipe comprises two layers of tensile armor, typically two: an inner layer (the one closest to the center of the pipe) and an outer layer (the one furthest from the outside of the pipe), with their longitudinal elements wound in opposite directions by helical windings. The pipe may comprise more than two layers of tensile armor, with the longitudinal elements of two successive layers of tensile armor wound in opposite directions by helical windings.

[0080] One of the reinforcement layers may be a pressure arch. This is designed to absorb the radial forces related to internal pressure, directed from the inside to the outside of the pipe, in order to prevent the internal polymer liner from bursting under the pressure inside the pipe. Usually, the pressure arch is located towards the inside of the pipe. It is a layer further inward than the tensile reinforcement layer(s). The pressure arch consists of longitudinally wound elements with a short pitch, for example, Z (zeta), C, T (theta), U, K, X, or I shaped metal wires, and / or at least one high-strength aramid strip (Technora® or Kevlar®), and / or at least one composite strip comprising a thermoplastic matrix in which reinforcing fibers, such as carbon or glass fibers, are embedded.

[0081] The presence of a pressure arch is not essential, particularly when the helix angles of the wires constituting the tensile reinforcement plies are close to 55°. This specific helix angle allows the tensile reinforcement plies to withstand not only axial forces but also radial forces exerted on the flexible pipe and directed from the inside to the outside of the pipe. Preferably, and especially for deep-well applications, the flexible pipe includes a pressure arch.

[0082] The flexible pipe generally includes an external polymer sealing sheath to prevent seawater from entering the pipe. This helps protect the tensile reinforcement layers from seawater and thus prevents seawater corrosion. The external polymer sealing sheath is advantageously made of a polymer material, particularly one based on a polyolefin, such as polyethylene; a polyamide, such as PA11 or PA12; a fluoropolymer, such as polyvinylidene fluoride (PVDF); or a thermoplastic elastomer comprising a polyolefin, such as polyethylene or polypropylene, combined with an elastomer of the type SBS (styrene butadiene styrene), SEBS (styrene ethylene butadiene styrene), EPDM (ethylene propylene diene monomer), polybutadiene, polyisoprene, or polyethylene butylene.

[0083] The flexible pipe may include, as a reinforcement layer, a reinforcing tape between the outer polymer sealing sheath and the reinforcement layer (the outermost layer when there are multiple layers of reinforcement). This reinforcing tape is formed, for example, of a high-strength anti-buckling layer to limit buckling of the tensile reinforcement layer(s) in the event that the pipe is subjected to the reverse bottoming effect. This anti-buckling layer is, for example, made of aramid. The reinforcing tape is wrapped around the outermost reinforcement layer, advantageously as specified in API 17J, 4th edition, May 2014.

[0084] The nature, number, dimensions, and arrangement of the layers constituting flexible conduits are essentially linked to their conditions of use and installation. Conduits may include additional layers beyond those mentioned above.

[0085] The wear-resistant layer can be adjacent to the two reinforcing layers between which it is located. In this case, the wear-resistant layer is the only layer between the two reinforcing layers.

[0086] Alternatively, there may be one or more additional layers between the two reinforcing layers. For example, in addition to the wear-resistant layer, there may be a support layer between the two reinforcing layers. The support layer is in contact either with the inner or outer face of the wear-resistant layer.

[0087] When the pipe comprises several wear-resistant layers, the two wear-resistant layers may be identical or different (for example, it may be two distinct homopolymer polypropylenes in each wear-resistant layer, or the dimensions of the strips may be identical or different).

[0088] The flexible hose is usually tubular.

[0089] Advantageously, the flexible pipe is of the unbonded type, that is to say that its reinforcing layers, such as the tensile reinforcement layer(s) and / or the pressure arch, are not bonded to the adjacent polymer layer(s), such as the wear-resistant layer(s) and / or the internal sealing polymer sheath and / or the external sealing polymer sheath and / or the anti-buckling sheath and / or any tubular polymer layer composing the flexible pipe.

[0090] Preferably, flexible driving is of the unbound type as described in API 17J (2014) and / or API RP 17B (2014).

[0091] Typically, driving involves (or even consists of) moving from the inside out: possibly a metal frame, an internal polymer sealing sheath, possibly a pressure vault as a reinforcing layer, an internal tensile reinforcement layer, an external tensile reinforcement layer, possibly a reinforcing tape as a reinforcing layer, an external polymer sealing sheath, the pipe comprising at least one wear-resistant layer as defined above between two reinforcing layers, i.e. it comprises a wear-resistant layer as defined above: between the internal tensile armor layer and the external tensile armor layer, and / or between the pressure vault and the internal tensile armor layer (it being understood that the pressure vault is then present), and / or, between the external tensile armor layer and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0092] In a first embodiment of this first alternative, the at least two reinforcement layers of the pipe comprise at least two layers of tensile armor, and the wear-resistant layer is located between two successive layers of tensile armor. The flexible pipe then typically comprises (or is even made up of), from the inside to the outside of the pipe: possibly a metal carcass, an internal polymer sealing sheath, possibly a pressure vault as a reinforcing layer, an internal tensile armor layer as a reinforcing layer, the wear-resistant layer as defined above, an external tensile armor layer as a reinforcing layer, possibly a reinforcing tape as a reinforcing layer, and an external polymer sealing sheath.

[0093] The flexible conduit may include one or more additional wear-resistant layers as defined above, in particular between the pressure arch and the internal tensile armor layer (it being understood that the pressure arch is then present) and / or between the external tensile armor layer and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0094] In a second embodiment of this first alternative, the at least two reinforcement layers of the pipe comprise at least one layer of tensile armor and one pressure arch, and the wear-resistant layer is located between the layer of tensile armor (the innermost layer when there are multiple layers of tensile armor) and the pressure arch. The flexible pipe then typically comprises (or is even made up of), from the inside to the outside of the pipe: possibly a metal carcass, an internal polymer sealing sheath, a pressure vault as a reinforcing layer, the wear-resistant layer as defined above, one, usually two, layers of tensile armor as a reinforcing layer(s), possibly a reinforcing tape as a reinforcing layer, and an external polymer sealing sheath.

[0095] The flexible conduit may include one or more additional wear-resistant layers as defined above, in particular between two successive layers of tensile armor and / or between the layer of tensile armor (the outermost one when there are several) and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0096] In a third embodiment of this first alternative, the at least two layers of reinforcement of the pipe include at least one layer of tensile armor and a reinforcing tape and the wear-resistant layer is located between the layer of tensile armor (the outermost one when there are several layers of tensile armor) and the reinforcing tape.

[0097] The flexible conduit then typically includes (or is made up of), from the inside to the outside of the conduit: possibly a metal carcass, the internal polymer sealing sheath, possibly a pressure vault as a reinforcing layer, one, usually two, layers of tensile armor as a reinforcing layer, a wear-resistant layer as defined above, a reinforcing tape as a reinforcing layer, and an external polymer sealing sheath.

[0098] The flexible pipe may include one or more additional wear-resistant layers as defined above, in particular between two successive layers of tensile armor and / or between the pressure arch and the layer of tensile armor (the innermost one when there are several) (it being understood that the pressure arch is then present).

[0099] In a second alternative, flexible driving is a so-called "hybrid" flexible driving. It includes (or is even made up of), from the inside out: an inner tubular sheath, a composite reinforcement structure as a reinforcement layer, the composite reinforcement structure being bonded to the inner tubular sheath, the composite reinforcement structure comprising a winding of at least one laminated reinforcement layer, each reinforcement layer having a fiber-reinforced thermoplastic matrix, at least one sealing layer of a thermoplastic material around the composite reinforcement structure, an internal tensile reinforcement layer as a reinforcement layer, the internal tensile reinforcement layer being unbonded to the sealing layer, an external tensile reinforcement layer as a reinforcement layer, optionally a reinforcing tape as a reinforcement layer, and optionally an external polymer sealing sheath, the pipe comprising at least one wear-resistant layer as defined above between two reinforcing layers, i.e. it comprises a wear-resistant layer as defined above: between the composite reinforcement structure and the internal tensile armor layer (the wear layer generally surrounding the sealing layer), and / or between the internal tensile armor layer and the external tensile armor layer, and / or between the external tensile armor layer and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0100] The inner tubular sheath is designed to contain, generally in a leak-proof manner, the transported fluid. It also serves to protect the composite reinforcement structure from abrasion caused by the presence of abrasive particles, such as sand, within the transported fluid.

[0101] The inner tubular sheath is made of polymer material, preferably thermoplastic.For example, the polymer forming the inner tubular sheath is chosen from a polyolefin such as polyethylene, a polyamide such as PA11 or PA12, or a fluoropolymer such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-polyhexafluoropropylene copolymers (PVDF-HFP), PEK (polyetherketone), PEEK (polyetheretherketone), PEEKK (polyetheretherketoneketone), PEKK (polyetherketoneketone), PEKEKK (polyetherketoneetherketoneketone), PAI (polyamide-imide), PEI (polyether-imide), PSU (polysulfone), PPSU (polyphenylsulfone), PES (polyethersulfone), PAS (polyarylsulfone), PPE (polyphenylene ether), PPS (polyphenylene sulfide), LCPs (low-crystal polymers) liquids), PPA (polyphthalamide), copolymers thereof, and / or mixtures thereof, or a mixture of one or more of these with a polysiloxane, PTFE (polytetrafluoroethylene) or PFPE (perfluoropolyether).

[0102] The tubular inner sheath is formed from a tube of polymer material, an assembled strip of polymer material, or an impregnated polymer mat.

[0103] When the tubular inner sheath is formed from a tube, it is advantageously obtained by extrusion of a thermoplastic tube chosen in particular from the polymers mentioned above.

[0104] When the inner tubular sheath is formed from a strip of assembled polymer material, it is advantageously produced by extruding and winding thermoplastic strips of a polymer as described above. Preferably, the turns of a first layer are contiguous (edge ​​to edge without overlap) and the turns of a higher layer are arranged so that two adjacent lower strips overlap, ensuring the sealing of the inner tubular sheath.

[0105] The thickness of the inner tubular sheath is, for example, between 1 mm and 20 mm.

[0106] The composite reinforcement structure comprises at least one, preferably a plurality of laminated reinforcement layers, and optionally, an anti-delamination layer interposed between at least two reinforcement layers.

[0107] Each laminated reinforcement layer consists of an overlay of composite reinforcement layers.

[0108] Each reinforcement layer consists of a polymer matrix and reinforcing fibers embedded in the polymer matrix.

[0109] The matrix polymer is preferably thermoplastic.For example, the polymer forming the matrix is ​​chosen from a polyolefin such as polyethylene, a polyamide such as PA11 or PA12, a fluoropolymer such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene (PVDF-HFP) copolymers, PEK (polyetherketone), PEEK (polyetheretherketone), PEEKK (polyetheretherketoneketone), PEKK (polyetherketoneketone), PEKEKK (polyetherketoneetherketoneketone), PAI (polyamide imide), PEI (polyetherimide), PSU (polysulfone), PPSU (polyphenylsulfone), PES (polyethersulfone), PAS (polyarylsulfone), PPE (polyphenylene ether), PPS (polyphenylene sulfide), LCPs (liquid crystal polymers), PPA (polyphthalamide), copolymers thereof and / or mixtures thereof or a mixture of one or more of these with a polysiloxane, PTFE (polytetrafluoroethylene) or PFPE (perfluoropolyether).

[0110] Reinforcing fibers include, for example, carbon fibers, glass fibers, aramid fibers, and / or basalt fibers.

[0111] For example, the reinforcing fibers are arranged unidirectionally within the matrix for each reinforcement layer. They are then parallel to each other. Alternatively, the reinforcing fibers are crossed in two orthogonal directions, or are arranged randomly within the matrix.

[0112] The length of the reinforcing fibers in each reinforcement layer is greater than 100 m, and is notably between 100 m and 4500 m.

[0113] The diameter of composite fibers is, for example, less than 100 microns, and is notably between 4 microns and 10 microns.

[0114] Preferably, each reinforcement layer is formed from a winding of at least one composite strip having several layers of fibers embedded in an elongated matrix, with a length greater than at least 10 times its width and at least 10 times its thickness.

[0115] For example, the length of each composite strip is greater than 100 m and is between 100 m and 4500 m. The width of each composite strip is between 6 mm and 50 mm. The thickness of each composite strip is between 0.1 mm and 1 mm.

[0116] During the production of each reinforcement layer, the composite strip or strips are helically wound around the inner tubular sheath and heated to cause partial melting of the matrix and bonding with successive turns of the composite strip and / or with adjacent layers, which may be other reinforcement layers, anti-delamination layers, or the inner tubular sheath.

[0117] The absolute value of the helix angle β of each composite strip relative to the pipe axis is, for example, between 55° and 85°. This ensures elongation of the composite under the effect of internal pressure, and adequate cooperation with the reinforcement layers.

[0118] The thickness of each reinforcement layer is generally between 0.10 mm and 10 mm, for example between 0.12 mm and 7 mm, or between 0.22 mm and 5 mm.

[0119] The sealing layer is designed to create a watertight seal around the composite reinforcement structure. In particular, in the event of water infiltration inside the flexible pipe, between the outer polymer sheath and the sealing layer, the layer's function is to limit, and preferably prevent, contact between the infiltrated water and the composite reinforcement structure.

[0120] The sealing layer preferably comprises a thermoplastic polymer. For example, the polymer forming the sealing layer is chosen from a polyolefin, possibly cross-linked, such as polyethylene or polypropylene; a thermoplastic elastomer (TPE) such as thermoplastic polyurethane (TPE-U or TPU) or styrenic copolymers (TPE-S or TPS) or vulcanized polypropylene and ethylene-propylene-diene (PP-EPDM) copolymers (TPE-V or TPV); a polyamide such as PA11 or PA12;or a fluoropolymer such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-polyhexafluoropropylene copolymers (PVDF-HFP), or it comprises a polymer selected from PEK (polyetherketone), PEEK (polyetheretherketone), PEEKK (polyetheretherketoneketone), PEKK (polyetherketoneketone), PEKEKK (polyetherketoneetherketoneketone), PAI (polyamide-imide), PEI (polyether-imide), PSU (polysulfone), PPSU (polyphenylsulfone), PES (polyethersulfone), PAS (polyarylsulfone), PPE (polyphenylene ether), PPS (polyphenylene sulfide), LCPs (liquid crystal polymers), PPA (polyphthalamide) and / or mixtures thereof, or a mixture of one or more of these with polysiloxane, PTFE (polytetrafluoroethylene) or PFPE (perfluoropolyether).

[0121] The sealing layer can be formed as a single piece of tubular sheath made of polymer material, typically by extruding a thermoplastic material around the reinforcing composite structure. Alternatively, the sealing layer is made from a discontinuous structure, for example, an assembled strip of polymer material. It is then typically produced by winding thermoplastic strips of a thermoplastic polymer, followed by a welding step. Preferably, the turns of a first layer are edge-to-edge without overlap, and the turns of a top layer are arranged so that two adjacent lower strips overlap, ensuring the sealing of the layer.

[0122] The sealing layer may be bonded or unbonded to the composite reinforcement structure.

[0123] The embodiments described above for the pipeline tensile armor layer(s) according to the first alternative are applicable to the pipeline tensile armor layers according to the second alternative.

[0124] The embodiments described above for the pipe reinforcement tape according to the first alternative are applicable to the pipe reinforcement tape according to the second alternative.

[0125] The embodiments described above for the external polymeric pipe sealing liner according to the first alternative are applicable for the external polymeric pipe sealing liner according to the second alternative.

[0126] The wear-resistant layer can be adjacent to the two reinforcing layers between which it is located. In this case, the wear-resistant layer is the only layer between the two reinforcing layers.

[0127] Alternatively, there may be one or more additional layers between the two reinforcing layers. For example, in addition to the wear-resistant layer, there may be a support layer between the two reinforcing layers. The support layer is in contact either with the inner or outer face of the wear-resistant layer.

[0128] In a first embodiment of this second alternative, the at least two reinforcement layers of the pipe comprise at least two layers of tensile armor, and the wear-resistant layer is located between two successive layers of tensile armor. The flexible pipe then typically comprises (or is even made up of), from the inside to the outside of the pipe: an inner tubular sheath, a composite reinforcement structure as a reinforcement layer, the composite reinforcement structure being bonded to the inner tubular sheath, the composite reinforcement structure comprising a winding of at least one laminated reinforcement layer, each reinforcement layer having a fiber-reinforced thermoplastic matrix, at least one sealing layer of a thermoplastic material around the composite reinforcement structure, an internal tensile armor layer as a reinforcement layer, the internal tensile armor layer being unbonded to the sealing layer, a wear-resistant layer as defined above, an external tensile armor layer as a reinforcement layer, optionally a reinforcing tape as a reinforcement layer, and optionally an external polymer sealing sheath,

[0129] The flexible conduit may include an additional wear-resistant layer as defined above, in particular between the composite reinforcement structure and the internal tensile armor layer and / or between the external tensile armor layer and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0130] In a second embodiment of this second alternative, the at least two reinforcement layers of the pipe comprise at least one layer of tensile armor and a reinforcing tape, and the wear-resistant layer is located between the layer of tensile armor (the outermost one when there are several layers of tensile armor) and the reinforcing tape.

[0131] The flexible conduit then typically includes (or is made up of), from the inside to the outside of the conduit: an inner tubular sheath, a composite reinforcement structure as a reinforcement layer, the composite reinforcement structure being bonded to the inner tubular sheath, the composite reinforcement structure comprising a winding of at least one laminated reinforcement layer, each reinforcement layer having a fiber-reinforced thermoplastic matrix, at least one sealing layer of a thermoplastic material around the composite reinforcement structure, an internal tensile armor layer as a reinforcement layer, the internal tensile armor layer being unbonded to the sealing layer, an external tensile armor layer as a reinforcement layer, a wear-resistant layer as defined above, a reinforcing tape as a reinforcement layer, and optionally an external polymer sealing sheath,

[0132] The flexible conduit may include an additional wear-resistant layer as defined above, in particular between the composite reinforcement structure and the internal tensile armor layer and / or between two successive tensile armor layers.

[0133] In a third embodiment of this second alternative, the at least two reinforcement layers of the pipeline comprise a composite reinforcement structure and at least one layer of tensile armor, and the wear-resistant layer is located between the reinforcement structure and the layer of tensile armor (the innermost one when there are several layers of tensile armor).

[0134] The flexible conduit then typically includes (or is made up of), from the inside to the outside of the conduit: an inner tubular sheath, a composite reinforcement structure as a reinforcement layer, the composite reinforcement structure being bonded to the inner tubular sheath, the composite reinforcement structure comprising a winding of at least one laminated reinforcement layer, each reinforcement layer having a fiber-reinforced thermoplastic matrix, at least one sealing layer of a thermoplastic material around the composite reinforcement structure, a wear-resistant layer as defined above, an internal tensile armor layer as a reinforcement layer, the internal tensile armor layer being unbonded to the sealing layer, an external tensile armor layer as a reinforcement layer, optionally a reinforcing tape as a reinforcement layer, and optionally an external polymer sealing sheath,

[0135] The flexible conduit may include an additional wear-resistant layer as defined above, in particular between two successive layers of tensile armor and / or between the outer layer of tensile armor and the reinforcing tape (it being understood that the reinforcing tape is then present).

[0136] According to a second object, the invention relates to a method for preparing a flexible subsea pipeline for the transport of fluid, preferably hydrocarbons, in particular as defined above, comprising the sequential helical winding of at least two longitudinal metallic or composite material elements to form at least two reinforcement layers, at least one strip of polymeric material being helically wound between said reinforcement layers to form a wear-resistant layer, the polymeric material comprising a homopolymer polypropylene having: a flexural modulus measured at 23°C according to ISO 178 of 2019 greater than 1500 MPa, and a melt flow index measured according to ISO 1133 revised in 2011 at 230°C under a mass of 2.16 kg less than or equal to 4.0 g / 10 minutes.

[0137] The embodiments defined above for the flexible conduit are of course applicable to the process. Preferably, the flexible conduit prepared by the process is that defined above.

[0138] The process may include a preliminary or concurrent step of preparing at least one strip by extrusion. The homopolymer polypropylene defined above has the advantage of being easily extruded. Generally, homopolymer polypropylene (or a blend thereof) is extruded into thin, long sheets, which are then slit to obtain strips of the desired width (from 30 to 200 mm, preferably from 40 to 150 mm, typically 40, 75, 100, or 126 mm). Alternatively, homopolymer polypropylene (or a blend thereof) is extruded directly into strips of the desired width. The strips are then packaged for installation on a pipe production device.

[0139] The strips can be butted together, typically by welding, including ultrasonic welding, laser welding, or by overlapping and then heating, for example in contact with a heating plate until melting, or by gluing (with glue, tape or adhesive).

[0140] According to a third object, the invention relates to an underwater conduit that can be obtained by the aforementioned process.

[0141] According to a fourth object, the invention relates to the use of the aforementioned underwater pipeline for the transport of fluid, preferably hydrocarbons.

[0142] The flexible pipeline can be used at great depths, typically up to 3000 meters. It allows the transport of fluids, preferably hydrocarbons, with a temperature above 90°C, typically reaching 130°C and even exceeding 150°C, and / or an internal pressure above 100 bar, reaching 1000 bar or even 1500 bar.

[0143] The use of a homopolymer polypropylene (or a mixture of homopolymer polypropylenes), where said homopolymer polypropylene (or said mixture) has: a flexural modulus measured at 23°C according to ISO 178 of 2019 greater than 1500 MPa, and a melt flow index measured according to ISO 1133 revised in 2011 at 230°C under a mass of 2.16 kg less than or equal to 4.0 g / 10 minutes, as a polymeric material of a helically wound strip to form a localized anti-wear layer between at least two reinforcement layers of a subsea pipeline intended for the transport of fluids, preferably hydrocarbons, each of said reinforcement layers being made by helical winding of a longitudinal metallic or composite material element, in order to improve the creep resistance of said anti-wear layer is described.

[0144] The invention also relates to a method for improving the creep resistance of a wear-resistant layer made of polymeric material which separates at least two reinforcement layers of a flexible subsea pipeline for the transport of fluids, preferably hydrocarbons, each of said reinforcement layers (12,16,20) being made by helical winding of a longitudinal metallic or composite material element, said wear-resistant layer being made by helical winding of at least one strip of said polymeric material, the method comprising the use of a homopolymer polypropylene as defined above within said polymeric material.

[0145] This improvement in creep resistance results in a small loss of thickness of the anti-wear layer, preferably less than 60%, in particular less than 50%, in particular less than 40%, after 20 years of use of the flexible pipe at a temperature of 90°C and a pressure of 200 bar, or at a temperature of 70°C and a pressure of 300 bar.

[0146] The implementation methods described above are of course applicable.

[0147] Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example but not limitation, with reference to the figure 1 .

[0148] [ Fig 1 ] There figure 1is a partial schematic perspective view of a flexible driving system according to the first alternative of the invention. It illustrates a driving system conforming to the invention comprising (or even consisting of), from the outside in: an external polymeric sealing sheath 10, an external layer of tensile reinforcement 12 produced by helical winding with a long pitch of a longitudinal metallic or composite material element, a first wear-resistant layer 14 produced by helical winding of at least one strip of a polymeric material comprising homopolymer polypropylene as defined above, an internal layer of tensile reinforcement 16 produced by helical winding with a long pitch of a longitudinal metallic or composite material element (in the opposite direction to the helical winding of the longitudinal element of the external layer of tensile reinforcement 12), a second wear-resistant layer 18 produced by helical winding of at least one strip of a polymeric material comprising homopolymer polypropylene as defined above, a pressure arch 20 produced by helical winding with a short pitch of a longitudinal element,an internal polymer sealing sheath 22, and an internal frame 24 for resisting radial crushing forces.

[0149] The pipe shown has a first helical winding of a strip of polymeric material comprising a homopolymer polypropylene as defined above to form a first wear-resistant layer 14 between the two layers of tensile reinforcement 12, 16 and a second helical winding of a strip of polymeric material comprising a homopolymer polypropylene as defined above to form a second wear-resistant layer 18 between the pressure arch 20 and the inner layer of tensile reinforcement 16.

[0150] Thanks to these two anti-wear layers, the tensile reinforcement layers 12, 16 and the pressure arch 20 are not in contact with each other, so that, when the flexible pipe is flexed, there is no wear due to friction between the reinforcement layers.

[0151] Due to the presence of the internal casing 24, this pipe is said to have a rough bore. The invention could also be applied to a pipe with a smooth bore, which does not have an internal casing.

[0152] The invention could be applied to a pipe not comprising the first wear-resistant layer 14 (the pipe then necessarily includes the wear-resistant layer 18). It could also be applied to a pipe not comprising the second wear-resistant layer 18 (the pipe then necessarily includes the first wear-resistant layer 14).

[0153] Similarly, removing the pressure vault 20 and the anti-wear layer 18 would not depart from the scope of the present invention.

[0154] On the figure 1Only two layers of tensile armor, 12 and 16, are shown, but the pipe could also include one or more additional pairs of tensile armor. The wear-resistant layer could then be present between two successive layers of armor. There could also be a wear-resistant layer between each of the armor layers. For example, if there are four armor layers, the pipe could comprise, from the outside in, an outermost armor layer, a first wear-resistant layer as defined above, an outer intermediate armor layer, a second wear-resistant layer as defined above, an inner intermediate armor layer, a third wear-resistant layer as defined above, and an innermost armor layer, with the first, second, and third wear-resistant layers being either identical or different.

[0155] Flexible conduit may also include layers not shown in the figure 1 , such as a retaining layer, for example between the outer polymer sheath 10 and the outer tensile armor layer 12, or between two tensile armor layers 12 and 16, or in contact either with the inner face of the wear-resistant layer 14, or with its outer face. Example Example 1: Preparation of polymer sheets by extrusion

[0156] Polymer samples were extruded at a speed of 3.3 to 3.9 m / min in the form of strips approximately 100 mm wide, approximately 1.5 mm thick and at least 20 meters long. [Table 1]

[0157] Table 1: Characteristics of polymers extruded in strip form. Polymer Supplier Grade MFI (g / 10 min) 230°C / 2.16 kg Modulus of elasticity (MPa) Flexion module at 23°C (MPa) (ISO 178) melting point (ISO 11357-3) (°C) Crystall inity rate (1 re< heating) Crystallization rate (2nd heating) Co mp. Copolym era of propylene e Total PPC 1645 0,3 1800 according to ISO 527-2; 1819 according to ASTM D 638 type IV - 228 57 64 Co mp. Copolym era of propylene e INEOS Eltex Tub 350-HM00 0,3 1520 according to ASTM D 638 type IV 185 0 227 55 63 Inv. Polyprop ylene homopol ymer Repsol PP040 C1E 3 1935 according to ASTM D 638 type IV 180 0 227 64 71 Inv. Polyprop ylene homopol ymer Total PPH4 022 3 1800 according to ISO 527-2; 1939 according to ASTM D 638 type IV 170 0 226 56 67 Inv. Polyprop ylene homopol ymer Polychi m HL10X F 3,9 1666 according to ASTM D 638 type IV 180 0 236 55 61 Co mp. Polyprop ylene homopol ymer SABIC 520P 10 1800 according to ASTM D 638 type IV - 200 ND ND Comparative: Comparative - Inventory: Homopolymer polypropylene as defined in the invention *rate calculated by dividing the heat of fusion of the polymer obtained by DSC with heating up to 200°C at 20°C / min by the heat of fusion of a 100% crystalline homopolymer polypropylene estimated at 207 joules / grams (Perkin Elmer documentation)

[0158] Because of its high melting index (10 g / 10 min), the extrusion of SABIC homopolymer polypropylene resulted in a strip of uneven thickness and width. Example 2 : Creep resistance tests

[0159] The creep tests consisted of placing a disc of polymer material (60 mm in diameter and the same thickness as the strip used on the flexible pipe: 0.8 mm, 1.5 mm, 2.5 mm, etc.) between two circular steel pieces of the same diameter as the strip. These steel pieces were machined to reproduce, on the face in contact with the strip, the dimensions and gaps of the wires in the pressure arches and reinforcement layers. For example, to simulate a reinforcement layer / reinforcement layer interface with wires 14 mm (width) x 6 mm (height), the gap was 0.7 mm. To simulate a reinforcement layer / pressure arch interface, a gap of 3.5 mm on one side and 0.7 mm on the other was used.

[0160] The steel part / polymer disc / steel part assembly was placed under pressure and temperature, and the thickness loss of the strip was measured. The test lasted from a few hours to several months, the aim being to observe the stabilization of the "creep rate" (i.e., the slope of the thickness loss of the polymer disc as a function of time).

[0161] The thickness loss results after 200 hours of testing are provided in Table 2 and correspond to a configuration with a 3.5 mm gap on one side and 0.7 mm on the other (simulating a web / pressure arch interface). Since almost all the thickness loss of a wear-resistant layer occurs at the very beginning of the flexible pipe's service life, 200 hours of testing is sufficient to assess creep resistance. [Table 2]

[0162] Table 2: Thickness loss after 200 hours of testing at 90°C and 200 bar depending on the polymer tested. Loss of thickness after 200 hours PP copolymer (Total PPC1645) (comparative) PVDF (CoflonXD) (comparison) PP homopolymer (Repsol PP040C1E) (invention) 90°C / 200 bar 80,3% 91,2% 49,6%

[0163] These results show that the thickness loss is significantly less for the polypropylene homopolymer with the required flexural modulus and melt flow index. The thickness loss with the copolymer PP is 62% greater than that observed with the homopolymer PP, and the thickness loss with PVDF is 84% ​​greater than that observed with the homopolymer PP.

Claims

1. A flexible underwater pipe for the transport of fluid comprising at least two reinforcement layers (12,16,20) separated by an anti-wear layer (14,18) of polymeric material, each of said reinforcement layers (12,16,20) being produced by helical winding of a longitudinal element of metal or of composite material, said anti-wear layer (14,18) being produced by helical winding of at least one strip of said polymeric material, the polymeric material comprising at least 50% by weight of a polypropylene homopolymer or of a mixture of polypropylene homopolymers, each polypropylene homopolymer having: - a flexural modulus measured at 23°C, according to the 2019 ISO 178 standard, greater than 1500 MPa, and - a melt flow index measured as per ISO 1133, revised in 2011, at 230°C under a weight of 2.16 kg less than or equal to 4.0 g / 10 minutes.

2. The flexible pipe according to Claim 1, wherein the polypropylene homopolymer has a flexural modulus measured at 23°C, as per the 2019 ISO 178 standard, of greater than or equal to 1550 MPa, preferentially greater than or equal to 1600 MPa, particularly preferentially greater than or equal to 1700 MPa.

3. The flexible pipe according to claim 1 or 2 wherein the polypropylene homopolymer has: - a density measured as per ISO 1183 of 2019 greater than or equal to 0.85 g / cm3, typically or equal to 0.88 g / cm3, in particular or equal to 0.905 g / cm3, - a tensile stress at the threshold measured at 23 ± 2 °C and with a displacement speed of 50 mm / minute according to ASTM D638 of 2014 or ISO 527-2 of 2012 comprised between 30 and 45 MPa, - an elongation at yield measured at 23 ± 2 °C as per ASTM D638 of 2014 or ISO 527-2 of 2012, of 1 to 7%, preferentially of 3 to 5%, - a melting temperature determined by differential scanning calorimetry as per the 2018 ISO 11357-3 standard at least equal to 150°C, in particular at least equal to 200°C, preferentially at least equal to 220°C, and / or - a degree of crystallinity determined by differential scanning calorimetry of at least 40%, typically at least 50%.

4. The flexible pipe according to any of claims 1 to 3, wherein the strip comprises less than 0.4%, in particular less than 0.1%, or is even free of plastomer formed from propylene and at least one comonomer other than propylene.

5. The flexible pipe according to according to any of claims 1 to 4, wherein the strip comprises, or even consists of: - 80 to 100% by weight of polypropylene homopolymer such as defined according to any of claims 1 to 3, - 0 to 5 % by weight of plasticizer, - 0 to 5% by weight of impact modifier, - 0 to 10% by weight of additives, in particular chosen from antioxidants, UV stabilizers, reinforcement fillers, manufacturing admixtures, heat stabilizers, nucleating agents and a mixture thereof.

6. The flexible pipe according to any of claims 1 to 5, which comprises from the inside to the outside: - if appropriate, a metal carcass (24), - an inner polymeric sealing sheath (22), - if appropriate, a pressure vault (20), - an inner tensile armor layer (16), - an outer tensile armor layer (12), - if appropriate, a reinforcement tape, - an outer polymeric sealing sheath (10), the pipe comprising an anti-wear layer (14.18) such as defined according to any of claims 1 to 5: - between the inner tensile armor layer (16) and the outer tensile armor layer (12) and / or - between the pressure vault (20) and the inner tensile armor layer (16) with the proviso that the pressure vault is then present, and / or - between the outer tensile armor layer (12) and the reinforcement tape, with the proviso that the reinforcement tape is then present.

7. The flexible pipe according to claim 6, the flexible pipe being of the unbonded type.

8. The flexible pipe according to any of claims 1 to 5, which comprises from the inside to the outside: - a tubular inner sheath, - a composite reinforcement structure bonded to the tubular inner sheath, the composite reinforcement structure comprising a winding of at least one laminated reinforcement layer, each reinforcement layer having a fiber-reinforced thermoplastic matrix, - at least one sealing layer of thermoplastic material applied around the composite reinforcement, - an inner tensile armor layer unbonded to the sealing layer, - an outer tensile armor layer, - if appropriate, a reinforcement tape, and - if appropriate, an outer polymeric sealing sheath, the pipe comprising at least an anti-wear layer such as defined according to any of claims 1 to 5: - between the composite reinforcement structure and the inner tensile armor layer, and / or - between the inner tensile armor layer and the outer tensile armor layer and / or - between the outer traction armor layer and the reinforcement tape, with the proviso that the reinforcement tape is then present.

9. A method of preparation of a flexible underwater pipe for the transport of fluid according to any one of claims 1 to 8, comprising the helical winding in sequence of at least two longitudinal elements of metal or of composite material, in order to form at least two reinforcement layers (12,16,20), at least one strip of polymeric material being helically wound between said reinforcement layers (12,16,20) in order to form an anti-wear layer (14,18), the polymeric material comprising a polypropylene homopolymer having: - a flexural modulus measured at 23°C, according to the 2019 ISO 178 standard, greater than 1500 MPa, and - a melt flow index measured as per ISO 1133, revised in 2011, at 230°C under a weight of 2.16 kg less than or equal to 4.0 g / 10 minutes.

10. The use of the submarine pipeline according to one of claims 1 to 8 or obtained according to the method according to claim 9 for the transport of fluids, preferentially of hydrocarbons.