WO2019129870A1

WO2019129870A1 - Flexible undersea pipeline comprising a multi-layered external sheath

Info

Publication number: WO2019129870A1
Application number: PCT/EP2018/097114
Authority: WO
Inventors: Emmanuelle QUEMENEUR
Original assignee: Technip France
Priority date: 2017-12-29
Filing date: 2018-12-28
Publication date: 2019-07-04
Also published as: FR3076337A1; FR3076337B1

Abstract

The invention relates to a flexible undersea pipeline for transporting hydrocarbons, comprising, from the outside to the inside of the pipeline: an external fluid-tight polymer sheath; at least one tensile armour layer as a reinforcement layer; an internal fluid-tight polymer sheath; and, optionally, a metal carcass, characterised in that the external fluid-tight polymer sheath comprises an external polymer layer (8) including a polymer Pe that covers an internal polymer layer (10) comprising a polymer Pi, the Young's modulus at 20°C of polymer Pe being lower than that of polymer Pi. The invention also relates to the method for producing said pipeline. This pipeline is particularly suitable for the dynamic transport of hydrocarbons.

Description

Flexible underwater line comprising a multilayer outer sheath

The present invention relates to an underwater flexible pipe for the transport of hydrocarbons in deep water.

These pipes are likely to be used under high pressures, above 100 bar, or even up to 1000 bar, and at high temperatures, above 130 ° C., or even 170 ° C., for long periods of time. that is to say, several years, typically 30 years.

Subsea flexible pipes for the transport of deep-sea hydrocarbons comprise an assembly of flexible sections or a single flexible section. These flexible pipes comprise a metal reinforcing layer around an internal polymeric sheath sealing, in which hydrocarbons circulate. They typically include, from the outside to the inside of the pipe:

an outer polymeric sheath for sealing,

at least one layer of tensile armor as a reinforcing layer, which is generally metallic,

an internal polymeric sheath for sealing,

- possibly a carcass.

Each tensile armor ply is formed of son, generally metallic, placed with a game which thus creates a free volume, called annular, between the outer polymeric sheath sealing and the inner polymeric sheath sealing. The annular can be filled with gases that are derived from the internal space of the pipe and which have passed through the polymeric inner sheath sealing permeability.

The polymeric outer sheath sealing must fulfill various functions which are in particular:

the mechanical protection of the tensile armor ply (s), in particular the impact and friction protection to which the flexible pipe could be confronted when it is installed or put into service, and the resistance to wear, especially in case of relative contact and displacement with the laying equipment,

the provision of stiffness / rigidity to the flexible pipe, especially in very dynamic zones to limit the curvature of the flexible pipe,

- the protection against the penetration of seawater within the annulus in order to prevent the corrosion of the metallic wires,

the ability to ensure the resistance to circumferential stresses ("hoop stress" in English) due to the pressure of the gases filling the ring finger, - Thermal insulation, because to facilitate the exploitation of deposits, the internal space must be at a temperature above the formation temperature of hydrates and paraffins.

There are two main applications for these flexible pipes that can be static or dynamic. The normative document API 17J, 4th edition, May 2014 defines the dynamic application and the static application.

By dynamic application, it is understood an application in which the flexible pipe is subjected to cyclic forces. Indeed, in certain configurations, the flexible pipe extends between a bottom structure such as a well head or a collector and a surface assembly such as a production, storage and unloading vessel ("FPSO"). Floating Production Storage and Offloading in English). Such conduct is called rising conduct ("riser" in English). In this configuration, the movement of the laying ship imposes broad cyclic constraints on the flexible driving characteristics of a dynamic application.

In contrast, a static application is characterized by the absence of broad cyclic constraints imposed on driving. Typically, the flexible pipe may extend over the seabed or be buried in the seabed. Such conduct is generally referred to as flowline. In this configuration, the mechanical stresses are not very cyclic.

Different materials have been selected to meet the various functions of the outer polymeric sheath sealing. These materials are mainly polyamides (PA), polyethylenes (PE) and thermoplastic elastomeric polymers (TPE). Depending on the application conditions of the flexible pipe, one material will be preferred over another for the desired performance such as stiffness, thermal insulation and seawater tightness.

Polyethylenes are susceptible to nicks formation. They are therefore generally not used for the outer sheath in contact with seawater for dynamic applications because of the risk of damage when handling the pipes.

For dynamic applications, outer sheaths are generally limited to thermoplastic elastomeric or polyamide polymer materials.

Polyamides are mainly used for specific requirements such as very good wear resistance.

As constituent material of the outermost layer in contact with seawater, preference is given to elastomeric thermoplastic polymers which have in particular better permeability properties than polyethylene, which makes it possible to de-energize the annular environment and better thermal insulation. For example, the application FR 2 837 898 describes a flexible pipe whose outer polymeric sheath sealing is elastomeric thermoplastic polymer (TPE). However, the use of an outer TPE sheath has limitations: the resistance to circumferential stresses of the TPE sheaths is significantly lower than that of the polyethylene. Also, the rigidity of the TPE sheaths is insufficient in the context of dynamic applications and sometimes leads to having to increase the thickness of the outer sheath only with respect to this aspect, which implies an additional cost. Finally, the wear resistance of TPE is lower than that of polyethylene.

The flexible underwater pipes may further comprise a protective sheath which covers the outer polymeric sheath sealing (the protective sheath is then the outermost layer, the one in contact with seawater). The function of the protective sheath is to protect the outer sheath polymeric sealing and / or to make the flexible pipe more rigid especially in very dynamic areas.

For example, the application WO 201 1/072690 discloses a flexible pipe comprising an outer polymeric sheath sealing coated with a stiffness improving layer ("stiffening cover" in English) and being based on a polymer whose flexural modulus is greater than that of the constituent material of the outer polymeric sheath sealing. In one embodiment, the material of this stiffness-improving layer may be a combination of a TPE and a thermovinyl thermoplastic polymer. In another embodiment, the material of the stiffness improving layer is identical to that of the outer polymeric sheath sealing. However, it can then be observed difficulties when mounting with the tip given the too intimate bonding between these two sheaths of the same nature. In addition, in case of damage to the stiffness-improving layer, there may be crack propagation ("cracks" in English) of the stiffness-improving layer through the outer polymeric sheath sealing. The protective sheaths and outer sheath no longer perform their sealing functions. It is therefore preferable to have materials in outer polymeric sheath sealing and protective sheath well distinct. In addition, in case of damage to the layer improving rigidity, the stiffness of the flexible pipe may become insufficient, especially for dynamic applications.

In addition, the presence of this additional protective sheath requires the addition of an additional step in the manufacture of flexible pipes.

This protective sheath also poses problems transmitting radial forces during installation. This point is particularly critical for applications strong depths where the hanging point is important when laying. This problematic concerns dynamic application structures as well as static ones.

The development of external polymeric sheath sealing alternative does not have these disadvantages and allows to use the flexible pipe, especially in dynamic applications, is sought.

For this purpose, according to a first object, the subject of the invention is an underwater pipe intended for the transport of hydrocarbons, comprising, from the outside to the inside of the pipe:

an outer polymeric sheath for sealing,

at least one layer of tensile armor as a reinforcing layer,

an internal polymeric sheath for sealing,

- possibly a metal carcass,

characterized in that the outer polymeric sealing sheath comprises an outer polymeric layer comprising a polymer P _e which has an inner polymeric layer comprising a polymer P, the Young's modulus at 20 ° C of the polymer P _e being lower than that of polymer P ,.

The outer polymeric layer protects the inner polymeric layer and thus preserve the tightness of the flexible pipe.

The inner polymeric layer improves:

- the rigidity of the flexible pipe,

the resistance to the circumferential stresses of the outer polymeric sheath sealing, and / or

- The wear resistance of the outer polymeric sheath sealing.

Thus, the mechanical properties of the outer polymeric sheath of sealing are improved in comparison with an outer polymeric sheath sealing consisting of a single layer, including a single layer of elastomeric thermoplastic polymer.

These properties make the flexible underwater pipe according to the invention particularly suitable for use in dynamic applications. It is preferably a rising pipe.

Typically the polymer P _e of the outer polymeric layer has a Young's modulus at 20 ° C. of less than 500 MPa, in particular less than 300 MPa, preferably of 200 MPa at 300 MPa, and the polymer P of the inner polymeric layer has a Young's modulus at 20 ° C greater than 500 MPa, especially greater than 700 MPa, preferably greater than 1000 MPa. Alternatively, the polymer P _e of the outer polymeric layer has a Young's modulus at 20 ° C. of less than 300 MPa, preferably of 200 MPa at 300 MPa, and the polymer P of the internal polymeric layer has a Young's modulus at 20. ° C greater than 300 MPa, especially greater than 500 MPa, preferably greater than 700 MPa, a modulus greater than 1000 MPa being particularly preferred.

The Young's modulus is measured according to ASTM D638-14 ("Standard test method for tensile properties of plastics") of 2014, typically taking into account the following test parameters:

Speed of the test machine: 50 mm / min,

Test sample: Type IV according to the ASTM D638 classification

- Characteristics of the test sample: 25 mm long, 6 mm wide and 2 mm thick.

Advantageously, the polymer P _e of the outer polymeric layer has a Young's modulus at 20 ° C. of 200 MPa at 300 MPa. The outer polymeric layer is thus sufficiently elastic to withstand external stresses and seal the pipe and sufficiently rigid to withstand the abrasion associated with the flexible pipe installation devices such as tensioners or hose clamps or clamping forces.

Given this minimal rigidity that advantageously has the polymer Pe, the outer polymeric layer exerts a force on the inner polymeric layer. This effort is likely to increase the phenomenon of propagation of cracks through the inner polymeric layer.

Preferably, the bonding strength ("bonding strength" in English) between the inner polymeric layer and the outer polymeric layer is from 1 N / m to 10 N / m, preferably from 2 N / m to 6 N / m. Bond strength can be measured according to ISO8510-2, 2nd edition, of 2006-12-01.

In fact, surprisingly, it has been demonstrated that a maximum bonding strength of 10 N / m advantageously makes it possible to limit the propagation of cracks and allows the use of a polymer P _e with sufficient rigidity.

It has also been discovered that insufficient bonding between the inner polymeric layer and the outer polymeric layer can cause difficulties during installation. Indeed, the radial clamping forces are not transmitted between the two layers and results in a sliding of the inner polymeric layer during the installation of the flexible pipe. To overcome this drawback, it has been demonstrated that the minimum adhesive strength between the inner polymeric layer and the outer polymeric layer is advantageously 1 N / m. Advantageously, such a bonding strength is sufficient for:

that the inner polymeric layer coated by the outer polymeric layer together form a single layer (ie the outer polymeric sheath sealing),

- Ensure good transmission of radial forces during the laying of the flexible pipe (and in particular a better transmission of radial forces during laying compared to an outer polymeric sealing sheath comprising two layers not bonded together) because adhesion of the inner polymeric layer and the outer polymeric layer is important,

but is weak enough that the inner polymeric layer and the outer polymeric layer are not intimately related. Thus, when cracks form in the outer polymeric layer, they do not propagate in the inner polymeric layer. The absence of cracks on the inner polymeric layer advantageously makes it possible to seal the pipe.

The outer polymeric sheath of sealing can be obtained by coextruding the inner polymeric layer and the outer polymeric layer under conditions to obtain such a resistance to sticking, in particular by choosing:

polymers P _e and P ,,

the coextrusion temperature, preferably between 140 ° C. and 220 ° C.,

the extrusion rate, preferably between 0.2 m / min and 0.6 m / min, and / or

- The cooling mode, including the cooling rate and / or the nature of the flow used to cool, preferably water.

Preferably, the flexible pipe does not comprise a binder between the outer polymeric layer and the inner polymeric layer in order to limit the costs.

Generally, the polymer P, of the inner polymeric layer is polyolefin, especially polyethylene homopolymer, polypropylene homopolymer, copolymer of polyethylene and polypropylene or a mixture thereof. The inner polymeric layer may comprise a single polyolefin or a mixture of polyolefins.

The polymer P _e of the outer polymeric layer is generally made of elastomeric thermoplastic polymer (TPE). The outer polymeric layer may comprise a single TPE or a mixture of TPEs. These TPEs are indeed particularly suitable for obtaining the aforementioned adhesive strength between the inner polymeric layer and the outer polymeric layer when layers comprising them are coextruded.

When the inner polymeric layer or the outer polymeric layer comprises several polymers, the Young's modulus to be considered is that of the mixture of polymers. For example, when the inner polymeric layer comprises a plurality of polymers P, and the outer polymeric layer comprises a plurality of polymers P _e , the Young's modulus at 20 ° C of the polymer blend P _e is lower than that of the polymer blend P 1. Elastomeric thermoplastic polymers generally have an elongation at the yield point of greater than 15%. TPEs are located between thermoplastic resins, easy to use and varied, but whose properties are limited in temperature or, in the dynamic domain and elastomers with remarkable elastic co-properties, but whose implementation is heavy, complex and often polluting. The structure of the TPEs always comprises two incompatible phases, one of them bringing together the thermoplastic blocks dispersed in the elastomer phase. There are usually five categories of TPEs:

thermoplastic olefinic elastomers (TPO), which are physical mixtures made from polyolefins. Those which contain more than 60% of olefin and those whose elastomer phase is predominant (more than 70%), which can be cross-linked or not, are distinguished.

block copolymers based on polystyrene, the rigid phase of which consists of polystyrene blocks, the flexible phase being for example formed of polybutadiene (SBS), polyisoprene (SIS) or poly (ethylene butylene) (SEBS) blocks;

polyurethane block copolymers (TPU) which can be obtained by the joint reaction of a high molecular weight diol which constitutes the crystallizable elastomer block of TPE on a diisocyanate and a low molecular weight diol which generate the rigid block .

polyester-based block copolymers such as those obtained by copolymerization of a polybutylene (PBT) or a polyethylene terephthalate (PET) which constitutes the rigid and crystalline blocks and of a low molecular weight glycol (butane diol, diethylene glycol) which combined with a polyalkylene ether glycol forms the crystallizable flexible block.

polyamide-based block copolymers whose rigid sequences consist of polyamide (PA) and the crystallizable flexible blocks of polyether, also called polyetheramides.

The TPEs may be chosen from ethylene-propylene-diene monomer (EPDM) rubbers, acrylonitrile-butadiene-styrene copolymers, methylmethacrylate-butadiene-styrene copolymers, ester-amide and ether-amide copolymers, thermoplastic copolyether-esters, copolymers polystyrene and polyisoprene elastomer-based sequences, polybutadiene, and the like. butadiene-styrene, ethylene-ethylacrylate, ethylene-ethylacetate and ethylene-vinyl acetate copolymers and their terpolymers, fluorinated elastomers, silicone elastomers, fluorinated silicone elastomers, polyurethanes.

The TPE may be crosslinked, uncrosslinked, or a crosslinked and uncrosslinked TPE blend.

The polyolefins used as polymer P, and the TPEs used as polymer P _e are commercially available or can be prepared by methods known to those skilled in the art.

Preferably, the inner polymeric layer and the outer polymeric layer do not have the same color. In the event of damage to the outer polymeric layer, the color difference makes it possible to have an indicator of wear of the outer polymeric sealing layer. This difference in color may especially be visible during an inspection by a remotely operated vehicle (ROV).

The polymeric outer sheath sealing is multilayer. In one embodiment, it consists of the inner polymeric layer and the outer polymeric layer. In another embodiment, it comprises one or more additional layers, in particular one or more layer (s) located between the inner polymeric layer and the traction armor layer (when the pipe comprises several layers). armor, this is the outermost armor tablecloth). Typically, the outer polymeric sheath sealing comprises an additional polymeric layer P _s polymer, the additional polymeric layer being coated by the inner polymeric layer.

Preferably, the bond strength between the inner polymeric layer and the additional polymeric layer is 1 N / m at 10 N / m, preferably 2 N / m at 6 N / m. Such bonding strength is sufficient for:

the additional polymeric layer coated by the inner polymeric layer coated by the outer polymeric layer together form one and the same outer polymeric sealing sheath,

- Ensure good transmission of radial forces during the laying of the flexible pipe, since the adhesion of the inner polymeric layer and the additional polymeric layer is important,

but low enough that the inner polymeric layer and the additional polymeric layer are not intimately related.

The outer polymeric sheath sealing can be obtained by coextruding the additional polymeric layer, the inner polymeric layer and the layer external polymer under conditions which make it possible to obtain the above-mentioned sticking strengths, in particular by choosing:

the polymers P _s , P _e and P,,

the coextrusion temperature,

the extrusion rate, preferably between 0.2 m / min and 0.6 m / min, and / or

Generally, the outer polymeric layer, the inner polymeric layer and the optional additional polymeric layer are obtained by coextrusion. Coextrusion is easy to implement. The preparation process according to the invention is thus simpler and less expensive than a process in which each layer of the outer polymeric sheath of sealing is extruded one after the other. Preferably, the conduit does not include a binder between the additional polymeric layer and the inner polymeric layer in order to limit costs.

The outer polymeric sheath sealing comprising coextruded layers advantageously simplifies the design of the end pieces because there is only one sheath to crimp, while at least two sheaths must be crimped into the ends when the pipe includes :

an outer polymeric sealing sheath comprising layers that are not bonded together, or

an outer polymeric sheath for sealing and a protective sheath.

Typically, the polymer P _s of the additional polymeric layer is elastomeric thermoplastic polymer, which may be the same or different from that of the outer polymeric layer. The TPE useful as polymer P _s is in particular as defined above. The additional polymeric layer may comprise a single TPE or a mixture of TPEs.

Each layer of the outer polymeric conduit sealing sheath typically comprises:

a polymeric matrix, and

- optionally discontinuously dispersed components in the polymer matrix.

"Polymeric matrix" means the continuous polymer phase which forms the layer of the outer polymeric sheath sealing. The polymeric matrix is a continuous matrix. Each layer of the outer polymeric sheath of sealing may optionally comprise components dispersed discontinuously in the polymeric matrix, but which are not part of the polymeric matrix. Such components may for example be fillers such as fibers, which may themselves be polymeric.

The outer polymeric sheath sealing is generally obtained by coextrusion of as many masterbatches as layers included in the outer polymeric sheath sealing (for example two masterbatches for an outer polymeric sheath sealing consisting of the inner polymeric layers and outer polymeric layer). Each masterbatch contains at least one polymer (which will form the polymeric matrix) and optionally one or more additives. During coextrusion, certain additives are incorporated in the polymer matrix, while others do not mix with the polymer (s) forming the polymeric matrix and disperse discontinuously in the polymer matrix, to form discontinuously dispersed components in the polymeric matrix.

Preferably, the polymeric matrix of the inner polymeric layer comprises a polymer P, and / or the polymeric matrix of the outer polymeric layer comprises a polymer P _e and / or the polymeric matrix of the additional polymeric layer comprises a polymer P _s .

Usually :

the mass proportion of polymer P, or of the polymer mixture P, in the inner polymeric layer is greater than 50% by weight, especially greater than 70% by weight, preferably greater than or equal to 80% by weight relative to the internal polymeric layer, and / or

the mass proportion of polymer P _e or of the polymer mixture P _e in the outer polymeric layer is greater than 50% by weight, in particular greater than 70% by weight, preferably greater than or equal to 80% by weight relative to the outer polymeric layer, and / or

the mass proportion of polymer P _s or of the polymer mixture P _s in the additional polymeric layer is greater than 50% by weight, in particular greater than 70% by weight, preferably greater than or equal to 80% by weight relative to the additional polymeric layer.

The inner polymeric layer and / or the outer polymeric layer and / or the additional polymeric layer may comprise additives, such as antioxidants, anti-UV, reinforcing fillers and / or manufacturing adjuvant.

Generally, the outer polymeric layer is likely to be in contact with seawater. By "external polymeric layer likely to be in contact with seawater", it is meant that the layer comes into contact with the seawater. seawater when the pipe is put into service. Thus, the pipe does not include a tubular layer external (that is to say seawater-resistant layer) that would oppose the contact between seawater and the outer polymeric layer. Typically, the outer polymeric layer of the pipe is not coated with a metal tube or a polymeric tubular layer. Preferably, the outer polymeric layer is thus the outermost layer of the pipe. Advantageous properties of the outer polymeric sheath of sealing reported above have the consequence that a protective sheath or overgaring are not necessary.

In addition to the outer polymeric sealing sheath, the pipe comprises at least one tensile armor ply, an inner polymeric sheath sealing, and optionally a metal carcass, these layers being generally as described in published normative documents by the American Petroleum Institute (API), API 17J (4th edition - May 2014) and API RP 17B (5th edition - May 2014).

If the pipe comprises a metal carcass, it is said to non-smooth passage ("rough-bore" in English). If the pipe is free of metal carcass, it is said to smooth passage ("smooth-bore" in English).

The main function of the metal carcass is to take radial forces directed from the outside to the inside of the pipe in order to avoid the collapse in English of all or part of the pipe under the effect of these efforts. These efforts are particularly related to hydrostatic pressure exerted by the seawater when the flexible pipe is immersed. Thus, the hydrostatic pressure can reach a very high level when the pipe is immersed at great depth, for example 200 bar when the pipe is submerged to a depth of 2000 m, so that it is often necessary to equip the flexible pipe. of a metal carcass.

The metal casing also has the function of preventing the collapse of the polymeric inner sheath sealing during rapid decompression of a flexible pipe having transported hydrocarbons. In fact, the gases contained in the hydrocarbons diffuse slowly through the internal polymeric sheath sealing and are found partly trapped in the annular space between the inner polymeric sheath sealing and the outer polymeric sheath. As a result, during a production stop resulting in rapid decompression of the inside of the flexible pipe, the pressure in this annular space can temporarily become significantly greater than the pressure inside the pipe, which in turn the absence of metal carcass would lead to the collapse of the polymeric inner sheath sealing.

As a result, generally, for the transport of hydrocarbons, a pipe comprising a metal carcass is preferred, while a pipe free of Metal carcass will be suitable for the transport of water and / or water vapor under pressure. In addition, when the pipe is intended both to carry hydrocarbons and to be immersed at great depth, then the metal carcass becomes indispensable in most applications.

The metal casing consists of longitudinal elements wound helically with a short pitch. These longitudinal elements are strips or stainless steel son arranged in turns stapled to each other. Advantageously, the metal carcass is made by profiling an S-shaped strip and then winding it in a helix so as to staple the adjacent turns together.

In the present application, the concept of short-pitch winding designates any helical winding at a helix angle close to 90 °, typically between 75 ° and 90 °. The concept of winding with a long pitch covers the propeller angles of less than 60 °, typically between 20 ° and 60 ° for armor plies.

In known manner, the internal polymeric sheath sealing is intended to seal the fluid transported within the flexible pipe. It is formed of a polymer material, for example based on a polyolefin such as polyethylene, based on a polyamide such as PA1 1 or PA12, or based on a fluorinated polymer such as polyvinylidene fluoride ( PVDF). The choice of the polymeric material is generally a function of the conditions of pressure, temperature and the composition of the fluid transported.

The tensile armor plies consist of metal or composite wire wound in long steps and their main function is to take up the axial forces related on the one hand to the internal pressure prevailing inside the flexible pipe and on the other hand the weight of the flexible pipe especially when it is suspended. The presence of an additional metallic reinforcing layer intended to take up the radial forces related to the internal pressure, in particular a so-called "pressure vault" layer, is not essential since the helix angles of the wires constituting the layers of tensile armor is close to 55 °. Indeed, this particular helix angle gives the traction armor plies the ability to resume, in addition to axial forces, the radial forces exerted on the flexible pipe and directed from the inside to the outside of the pipe.

In a preferred manner, and especially for deep applications, in addition to the tensile armor plies, the flexible pipe comprises a pressure vault interposed between the inner polymeric sheath and the tensile armor plies. In such a case, the radial forces exerted on the flexible pipe, in particular the radial forces directed from the inside towards the outside of the pipe are taken up by the pressure vault in order to avoid the bursting of the internal polymeric sheath under the effect of the pressure prevailing inside the pipe. The pressure vault consists of longitudinal elements wound at short pitch, for example Z-shaped (zeta), C, T (teta), U, K or X-shaped wire wires arranged in coils stapled to one another .

The nature, number, sizing and organization of the layers constituting the flexible pipes are essentially related to their conditions of use and installation. Of course, the pipe may comprise one or more tubular layers (metal and / or polymeric) in addition to the outer polymeric sheath sealing, the layer (s) of tensile armor, the inner polymeric sheath sealing and the possible metal carcass, for example:

a holding layer between the outer polymeric sheath and the layers of tensile armor,

- one or more layer (s) anti-wear.

The flexible pipes according to the invention are particularly suitable for transporting fluids, especially hydrocarbons in the seabed, and at great depths. Advantageously, the reinforcing layers of the flexible pipe such as the ply (s) of tensile armor and / or the pressure vault is (are) free (s) to move relative to the polymeric layers such that the polymeric inner sheath sealing and / or the outer polymeric sheath sealing and / or any tubular polymeric layer comprising the flexible pipe. Typically, the reinforcing layers of the flexible pipe according to the present invention are not embedded in an elastomeric sheath. Also, the reinforcing layers of the flexible pipe such as the tensile armor plies and / or the pressure vault are free to move relative to the polymeric layers such as the internal sealing sheath and / or the polymeric sheath. external sealing and / or any tubular layer constituting the flexible pipe.

Flexible pipes can be used at great depth, typically up to 3000 meters deep. They allow the transport of fluids, especially hydrocarbons, having a temperature typically reaching 130 ° C and may even exceed 150 ° C and an internal pressure of up to 1000 bar or 1500 bar.

The outer polymeric layer and the inner polymeric layer of the outer polymeric sheath seal generally have a thickness of 1 mm to 75 mm, preferably 2 mm to 7.5 mm. Their thicknesses may be identical or different.

The polymeric outer sheath of the flexible pipe is typically tubular, generally has a diameter of 50 mm to 600 mm, preferably 50 mm to 400 mm, and / or a thickness of 2 mm to 150 mm, preferably 4 mm to 15 mm and / or a length of 1 m to 10 km.

According to a second subject, the invention relates to a method for preparing a pipe as defined above comprising the steps of:

a) extrusion to form the internal polymeric sheath sealing, the extrusion possibly being performed on a metal carcass,

b) assembling the inner polymeric sheath obtained in step a) with at least one layer of tensile armor, and

c) coextruding the outer polymeric layer, the inner polymeric layer and the optional additional polymeric layer to form the outer polymeric sealing sheath.

If the extrusion of step a) is not performed on a carcass, but independently, the flexible pipe obtained is smooth-running ("Smooth Bore" in English). If the extrusion of step a) is performed on a carcass, the resulting flexible pipe is non-smooth passage ("rough boron" in English).

The steps a) of extrusion and c) of coextrusion may be carried out by any method known to those skilled in the art, for example using a single-screw or twin-screw extruder.

When one of the layers of the outer polymeric sheath seal comprises several polymers, the mixture of the two polymers can be made before or during coextrusion.

The layers are thus assembled to form a submarine flexible pipe in which the reinforcing layer (s), such as (the) layer (s) of tensile armor and / or the roof of pressure, is (are) free (s) to move relative to the polymeric layers such as the inner polymeric sheath sealing and / or the outer polymeric sheath sealing and / or any tubular polymeric layer component flexible pipe. Also, the layers are assembled to form an underwater flexible pipe in which the reinforcing layers such as the tensile armor plies and / or the pressure vault are free to move relative to the polymeric layers such as the sheath. internal sealing and / or the outer polymeric sheath sealing and / or any tubular layer forming the flexible pipe.

According to a third object, the subject of the invention is a submarine flexible pipe that can be obtained by the aforementioned method.

According to a fourth object, the subject of the invention is the use of the above-mentioned flexible underwater pipe for the transport of hydrocarbons, in particular for dynamic applications. Other features and advantages of the invention will become apparent on reading the following description of particular embodiments of the invention, given by way of indication but not limitation, with reference to Figures 1 and 2.

Figures 1 and 2 are partial schematic perspective views of flexible pipes according to the invention.

FIG. 1 illustrates an underwater flexible pipe according to the invention comprising, from the outside to the inside:

an outer polymeric sheath for sealing comprising an inner polymeric layer comprising a polymer P and being coated with an outer polymeric layer comprising a polymer P _e , the Young's modulus at 20 ° C. of the polymer P _e being lower than that of P, polymer

an outer layer of traction armor 12,

an internal ply of tensile armor 14 wound in the opposite direction of the outer ply 12,

a pressure vault 18 for taking up the radial forces generated by the pressure of the hydrocarbons transported,

an inner polymeric sheath 20, and

an internal carcass 22 for taking up the radial forces of crushing.

FIG. 2 illustrates a flexible pipe according to the invention comprising, from the outside to the inside:

an outer polymeric sheath for sealing comprising an additional polymeric layer 11 comprising a polymer P _s and being coated with an inner polymeric layer 10 comprising a polymer P, and being coated with an outer polymeric layer 8 comprising a polymer P _e , the Young's modulus at 20 ° C of the polymer P _e being lower than that of the polymer P ,,

an outer layer of traction armor 12,

an inner polymeric sheath 20, and

an internal carcass 22 for taking up the radial forces of crushing.

Due to the presence of the inner carcass 22, these pipes are said to non-smooth passage ("rough bore" in English). The invention could also apply to a so-called smooth-bore pipe in English, which does not include an internal carcass.

Similarly, it is not beyond the scope of the present invention by eliminating the pressure vault 18. Preferably, in the absence of pressure vault 18, the helix angles of the son constituting the layers of armor 12, 14 are close to 55 ° and in opposite directions.

The armor plies 12, 14 are obtained by long-pitch winding of a set of son of metal or composite material, of generally substantially rectangular section. The invention would also apply if these wires had a section of circular or complex geometry, of the type for example T auto-stapled. In Figure 1, only two armor plies 12 and 14 are shown, but the pipe could also include one or more additional pairs of armor. The armor ply 12 is called external because it is here the last, starting from the inside of the pipe, before the outer sealing sheath 10.

The flexible pipe may also comprise layers not shown in FIGS. 1 and 2, such as:

a holding layer between the outer polymeric sheath 10 and the tensile armor plies 12 and 14, or between two plies of tensile armor,

one or more anti-wear layers of polymeric material in contact either with the internal face of the aforementioned holding layer, or with its external face, or with both faces, this anti-wear layer; -usure to prevent the holding layer wears in contact with metal armor. Anti-wear layers, which are well known to those skilled in the art, are generally made by helical winding of one or more ribbons obtained by extrusion of a polymeric material based on polyamide, polyolefins, or PVDF (" polyvinylidene fluoride "). Reference can also be made to the document WO 2006/120320 which describes anti-wear layers consisting of polysulfone (PSU), polyethersulfone (PES), polyphenylsulfone (PPSU), polyetherimide (PEI), polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK) ribbons. ) or phenylene polysulfide (PPS).

The invention is illustrated by the following examples. EXAMPLES

EXAMPLE 1 Preparation of External Polymeric Sheaths by Coextrusion Sealing

External polymeric sheaths of sealing according to the invention were made by coextrusion, in the absence of binder between the layers. The sheaths had an internal diameter of 71.4 mm. They included, from the outside to the inside, an outer layer, an inner layer, and a possible additional layer (present in case 1, absent in cases 2 and 3).

The tests are summarized in Table 1 below:

(1) Thermoplastic elastomer type HD-Flex ^® having a Young modulus measured at 20 ° C of 388 MPa

(2) PE 80 medium density polyethylene according to the IS012162 classification, second edition (2009), and having a Young's modulus measured at 20 ° C. of 750 MPa

Table 1: Structure of the outer polymeric sheaths of sealing prepared by coextrusion

The layers are bound in extrusion outlets and no delamination between the layers is noted.

These sheaths were used in the tests of the examples which follow. Example 2: Crack propagation tests

The tests were carried out according to the ISO15850 standard "Plastics-Determination of tension-stress fatigue crack propagation - Linear elastic fracture mechanics (LEFM) approach" of 2014, with +/- 6.5% deformation at 27 ° C and at a frequency of 0.1 Hz, on rod type samples of dimension 9 ^* 10 ^* 100 mm.

The tests are summarized in Table 2 below:

Suppl. : additional layer

Table 2: Location of notches made in crack propagation tests

Crack propagation within the notched layer has been observed, but the propagation of the crack stops at the interface between the notched layer and the adjacent layer, and therefore does not propagate to the other (s) layer (s) of the outer sheath. This results in a stop of crack propagation within the outer sheath sealing. Example 3: Bending and bending tests

Bend and bend tests were performed on specimens from 200 ^* 20 mm samples cut in the longitudinal direction. The tests were carried out at 27 ° C. according to the following stages:

- bending + 90 °,

- counter-bending -90 °,

- bending + 180 °,

- counter-bending -180 °.

No detachment of the layers of the outer sheath was observed. The radial forces are therefore transmitted within the outer sheath during the tests.

Example 4: Traction tests

Tensile tests were also performed under the following conditions:

- Instron 10T1 175 and 1,185 traction machines,

- Instron temperature chamber 31 19007,

- test specimens D638-I taken from cases 1 to 3 of Table 2,

- test temperatures of 27 ° C, 80 ° C or 5 ° C and

- speed of 50 mm / min.

The results are provided in Table 3 below:

Table 3: Results of tensile tests

No detachment of the layers of the outer sheath was observed.

Claims

1 .- Underwater flexible pipe for the transport of hydrocarbons comprising, from the outside to the inside of the pipe:

an outer polymeric sheath for sealing,

at least one tensile armor ply (12, 14) as reinforcing layer,

an internal polymeric sheath for sealing (20),

- optionally a metal carcass (22),

characterized in that the outer polymeric sealing sheath comprises an outer polymeric layer (8) comprising a polymer P _e which has an inner polymeric layer (10) comprising a polymer P ,, the Young's modulus at 20 ° C of the polymer P _e being lower than that of the polymer P 1.

2. A pipe according to claim 1, wherein the polymer P _e of the outer polymeric layer (8) has a Young's modulus at 20 ° C of less than 500 MPa, in particular less than 300 MPa, and the polymer P, of the inner polymeric layer (10) has a Young's modulus at 20 ° C greater than 500 MPa, especially greater than 700 MPa, preferably greater than 1000 MPa.

3. A conduit according to claim 1 or 2, wherein the polymer P _e of the outer polymeric layer 8 has a Young's modulus at 20 ° C of 200 to 300 MPa.

4. Conduit according to any one of claims 1 to 3, wherein the bonding strength between the inner polymeric layer (10) and the outer polymeric layer (8) of 1 to 10 N / m, preferably 2 to 6 N / m.

5. A conduit according to any one of claims 1 to 4, comprising no binder between the outer polymeric layer (8) and the inner polymeric layer (10).

6. Conduit according to any one of claims 1 to 5, wherein the polymer P of the inner polymeric layer (10) is polyolefin, in particular polyethylene homopolymer, polypropylene homopolymer, copolymer of polyethylene and polypropylene or in a mixture of these.

7. Conduit according to any one of claims 1 to 6, wherein the polymer P _e of the outer polymeric layer (8) is elastomeric thermoplastic polymer.

8. Conduit according to any one of claims 1 to 7, wherein the outer polymeric layer (8) and the inner polymeric layer (10) are obtained by coextrusion.

9. A conduit according to any one of claims 1 to 8, wherein the outer polymeric layer (8) is likely to be in contact with seawater.

10. A process for preparing a pipe according to any one of claims 1 to 9 comprising the steps of:

a) extrusion to form the internal polymeric sheath sealing (20), the extrusion possibly being performed on a metal carcass (22),

b) assembling the internal polymeric sheath (20) obtained in step a) with at least one ply of tensile armor (12, 14), then

c) coextruding the outer polymeric layer (8) and the inner polymeric layer (10) to form the outer polymeric sealing sheath.

1 1.- Use of a pipe according to any one of claims 1 to 9 for the transport of hydrocarbons.