FR2986599A1 - Flexible tubular pipe for use in oil layers exploitation structure, for transporting hydrocarbons in marine environment, has internal layer in contact with hydrocarbon flowing inside zone and carried out in semi-aromatic co-polyamide - Google Patents

Abstract

The invention relates to a flexible tubular pipe (10) for transporting hydrocarbons in a marine environment, said flexible tubular pipe comprising a waterproof sheath (14) of polymer material, and firstly a flow zone (24) for hydrocarbons. located inside said sealed sheath and on the other hand metal layers (16, 18, 20) wound on the outside around said sealed sheath (14) to allow said flexible tubular pipe to withstand radial stresses and longitudinally, said sealed sheath (14) having an outwardly facing outer layer (28) and an inner layer (26) independent of said outer layer inwardly of said sheath (14) for isolating said outer layer ( 28) with respect to said flow zone, said inner layer being intended to be in contact with the hydrocarbon flowing inside said flow zone (24). Said inner layer (26) is made of semi-aromatic copolyamide so as to preserve said outer layer (28) of the hydrolysis.

Description

The present invention relates to a flexible tubular pipe for transporting hydrocarbons in a marine environment.

One area of application envisaged is notably, but not exclusively, the extraction of hydrocarbons in the deep sea. Under these conditions, the pipes are not only subjected to high pressures, but also to unusual thermal conditions where the hydrocarbon is generally hot.

The known flexible tubular pipes comprise, from the inside towards the outside of the pipe, a tight sheath, also called pressure sheath, made of a polymeric material and layers of armor wound on the outside around the sheath for ability to withstand radial pressure stresses and longitudinal extension stresses. More specifically, these two functions are dissociated and at least a first layer of a weave wire wound short pitch on the waterproof sheath allows to form contiguous turns constituting a pressure vault. It is intended to take over the radial pressure stresses. In addition, at least a second layer of armor son wound with a long pitch around the pressure vault makes it possible to take up the longitudinal stresses. Usually, a protective sheath covers this second layer of armor wires. Inside the waterproof sheath is a hydrocarbon flow zone. Generally, the waterproof sheath is supported inwardly on a flexible conduit, or inner carcass, made of a rolled section whose turns are stapled to each other. The flow zone thus extends inside the inner carcass. The waterproof sheaths are made of various polymeric materials depending on the constraints they have to undergo. Polyethylenes, for example, are commonly used to produce sealed sheaths.

However, they are sensitive to heat and the liquid hydrocarbons naturally diffuse through, which results in their swelling. Polyamide-11 and polyamide-12 are more resistant to heat and pressure as well as swelling due to hydrocarbons. On the other hand, they hydrolyze and thus lose their mechanical properties. In addition, when plasticized, the plasticizer tends to exude into the hydrocarbon and their mechanical properties change. The polymers of vinylidene fluoride, whose acronym is PVDF, are appreciated for their resistance to heat and pressure, and especially for their great chemical inertness vis-à-vis the hydrocarbon. On the other hand they are more expensive. The operating conditions of hydrocarbons becoming more severe, the waterproof sheath undergone by the same, higher stresses and is likely to degrade then more quickly. Thus, the combined action of temperature and pressure first of all, tends to cause the creep of the sheath outwardly in the gaps, or interstices, of the pressure vault. This not only decreases the flexibility of the pipe, but can also cause fracture primers in the waterproof sheath. The temperature and pressure parameters can also contribute to causing blistering, or "blistering" in the English language, during the depressurization phases of the flexible tubular pipe. In addition, the action of temperature alone on the chemical reactions that can occur at the level of the sheath, accelerates its degradation. Also, it has been imagined to install in the conduit a sealed sheath consisting of two independent layers, on the one hand an inner layer not including a so-called external plasticizer, which could exude, but a plasticizer grafted into the polymer, said internal plasticizer, and secondly an outer layer plasticized with an external plasticizer. In this way, the chemical inertness of the inner layer is improved, while its mechanical properties fall because of the internal plasticizer, while the chemical inertia of the outer layer remains low, but its mechanical properties are intact. Reference can be made to document FR 2 772 108, which discloses such a double-layer sheath. However, it is observed that the inner layer of the impervious sheath degrades more rapidly than the outer layer, especially when the hydrocarbon contains water, and thus the outer layer is more rapidly reached in its turn.

Also, a problem that arises and that aims to solve the present invention is to provide a flexible tubular conduit, the sealing sheath more resistant to hydrolysis in particular. For this purpose the present invention proposes, according to a first object, a flexible tubular pipe for transporting hydrocarbons in a marine environment, said flexible tubular pipe comprising a tight sheath of polymer material, and firstly a hydrocarbon flow zone. located inside said sealed sheath and secondly layers of metal armor wound on the outside around said sealed sheath to allow said flexible tubular pipe to withstand radial and longitudinal stresses, said sheath having a seal an outwardly facing outer layer and an inner layer independent of said outer layer inwardly of said sealed sheath for isolating said outer layer from said flow region, said inner layer being intended to be in contact with said outer layer; contact with the hydrocarbon flowing within said flow zone. According to the invention, said inner layer is made of semi-aromatic copolyamide so as to preserve said outer layer of hydrolysis. Thus, a feature of the invention lies in the implementation of a semi-aromatic copolyamide to form the inner layer of the sealed sheath. By semi-aromatic copolyamide is meant a polymer resulting from the copolymerization of at least two polyamides, at least one of which is semi-aromatic. Preferably, said semi-aromatic copolyamide is made from a homopolymeric aliphatic polyamide and a semiaromatic polyamide. For example, said homopolymeric aliphatic polyamide is chosen from polycaprolactam or PA-6, polyundecanamide or PA-11, polylauroamide or PA-12, polyhexamethylene adipamide or PA-6-6, polyhexamethylene sebacamide or PA-6-10. and polyhexamethylene dodecanediamide or PA-6-12.

Such a polymer is, for example, the result of the use of polyhexamethylene dodecanediamide, also known as polyamide-6-12, with a semi-aromatic polyamide, for example polyamide PA 6 -T resulting from the polycondensation of hexamethylenediamine, or hexane-1,6-diamine, and terephthalic acid, or benzene-1,4-dicarboxylic acid. Polyamide-6-12 results from a polycondensation reaction of hexamethylenediamine and 1,12-dodecanedioic acid. While polyamides were known to be less resistant to hydrolysis than other polymers, and their properties inside the pipe were likely to degrade under extreme temperature and pressure conditions, it is surprisingly, the implementation of an inner layer of semi-aromatic copolyamide, preserves the outer layer over a longer period of time.

Preferably, the outer layer is all the better preserved when the inner layer is made of polyhéxamethylene dodecanediamide and a semi-aromatic polyamide. Thus, instead of replacing the double-layer sheath with a more resistant, but also more expensive, polyvinylidene sheath, the production of an inner layer based on polyhexamethylene dodecanediamide and a semi-aromatic polyamide allows, at an advantageous cost, to preserve the outer layer and to avoid any risk of incompatibility with the additives of a polyvinylidene fluoride. The consequences of the hydrolysis on the mechanical properties of the polymer will be explained in greater detail in the remainder of the description. Notwithstanding, the internal layer undergoes degradation over time and acts as a sacrificial layer with respect to the outer layer which remains less affected and remains watertight, at least during a period corresponding substantially to that during which the inner layer degraded. In addition, such an inner layer makes it possible to form a heat shield vis-à-vis the outer layer of the sealing sheath, and thereby reduce the phenomenon of deplastification of the outer layer and improve the insulation. In this way, the flow of the hydrocarbon fluid is guaranteed according to the properties of "flow assurance". According to a particularly advantageous embodiment of the invention, said outer layer of said sealed sheath is made of polyamide. In this way, the mechanical properties of the two layers can be relatively homogeneous, and thus the movements of the sheath do not cause any mechanical deterioration of one of the layers by the other. In addition, advantageously, said outer layer of said sealed sheath is also made of semi-aromatic copolyamide, which not only reduces the costs of producing the sheath, but also to obtain a total homogeneity of the mechanical properties of the sheath. the sheath in its thickness. It will be observed that the production of two layers of the same material has an advantage in comparison with a single layer of the same material.

Indeed, as will be explained in more detail in the following description, the interface between the two layers is a discontinuity blocking the road, in particular, the crack initiators that are born in the inner layer because of its degradation, or due to the propagation of a surface defect, particularly related to the extrusion of the inner layer on a carcass with gaps. In addition, said inner layer of said sealed sheath is preferably produced by extrusion, which makes it possible to obtain, from the polyamide in powder form or granules transformed in an extrusion screw, a continuous cylindrical surface. In addition, the outer layer of said sealed sheath is advantageously made by extrusion also on said inner layer, is advantageously by tandem extrusion. That is to say that said inner layer and said outer layer of said sealed sheath are made one after the other by extrusion and coaxially. According to an advantageous embodiment of the invention, said outer layer has a thickness greater than the thickness of said inner layer, in order to meet the normative requirements of API 17J or API RP 17B, established by the American Petroleum Institute. (API) creep in the gaps of the pressure vault of the tubular structure described above. In this way, the overall service life of the sheath, that is to say the total period during which it is sealed, is optimal. Advantageously, the thicknesses of the outer and inner layers are greater than three millimeters and for example, the inner layer has a thickness of three point five millimeters while the thickness of the outer layer is greater than or equal to three point five millimeters. According to another embodiment of the invention, said waterproof sheath further comprises an intermediate layer made of semi-aromatic copolyamide, for example based on polyhexamethylene dodecanediamide, and located between said inner layer and said outer layer. In this way, the outer layer is better preserved and the overall service life of the sealed sheath is increased. According to a second object, the present invention relates to the use of a flexible tubular pipe as described above, in a structure for operating oil deposits. According to a mode of use of said pipe of the invention, the operating structure extracts a marine deposit whose production crude has a temperature substantially greater than or equal to 70 ° C, advantageously 90 ° C and preferentially 110 ° C since the seabed to the surface. Favorably, the use of flexible pipes comprising a waterproof sheath having an inner layer and an outer layer made of semi-aromatic copolyamide, for example based on polyhexamethylene dodecanediamide, and an outer layer of polyamide, can convey 20 hydrocarbon fluids whose temperature is higher than those usually encountered with single-layer or single-sheath structures of polyamide. In the context of using a pipe according to the invention for high pressure and high temperature applications (HP / HT), it is possible to improve the holding thereof in several ways, including two cases. are described below. A first case consists in producing a multilayered waterproof sheath, that is to say that it comprises at least two polyamide 6-12 layers comprising at least one aromatic ring. Advantageously, the extrusion of three or even four layers of the same nature will have a beneficial effect on the behavior of the pipe. A second case consists in positioning between the metal carcass and the waterproof sheath, a heat shield having mechanical, chemical and thermal qualities effective and to improve the behavior of the pipe. More specifically, said heat shield, described in international application WO 2005/038327 is for example implemented by winding helical strips of a thermoplastic polymer material such as polytetrafluoroethylene (PTFE) or PTFE modified with n-perfluoropropylene -vinyl ether (PPVE). Other features and advantages of the invention will appear on reading the following description of particular embodiments of the invention, given by way of indication but not limitation, with reference to the accompanying drawings, in which: FIG. 1 is a partial diagrammatic view in cutaway of a flexible tubular conduit according to the invention; and - Figure 2 is a view of a diagram illustrating the evolution over time of the characteristics of an element of the flexible tubular conduit according to the invention. Figure 1 shows in perspective the structure of a flexible tubular conduit 10 according to the invention. From inside to outside it comprises, a metal casing 12, a sealed pressure sheath 14, a pressure vault 16, a first pair of successive tension armor layers 18, 20, and a second pair The second pair of armor layers 18 ', 20' is optional and is used for high pressure applications as will be described hereinafter. The embodiment of the flexible tubular conduit 10 and then the advantages of its leaktight pressure sheath 14 will firstly be explained in detail. The metal carcass 12 defines a flow zone 24 within which is adapted to come to flow a hydrocarbon. This metal carcass 12 is made by winding at short pitch, a section where the turns thus formed are stapled to each other so as to produce a flexible metal conduit not sealed. Then, on this metal carcass 12 is extruded the sealed pressure sheath 14. The latter has two layers on top of each other, an inner layer 26 and an outer layer 28, both made of a thermoplastic polymer. According to the invention, the inner layer 26 of the sealed pressure sheath 14 is made of polyamide and, according to a preferred embodiment of the invention, said inner layer 26 is made of polyhexamethylene dodecanediamide or polyamide-6-12 comprising at least an aromatic cycle. The polyamide-6-12 comprising at least one aromatic ring is for example supplied under the trade name Pipelon® HT by the company Pont de Nemours. As for the outer layer 28 it is advantageously made of polyamide and preferably of the same material as the inner layer 26.

These two layers 26, 28 are applied during two extrusion operations on the metal carcass 12. In this way, at the outlet of the extrusion head, the inner layer 26, such as a sleeve, is applied directly to the metal carcass 12, while the outer layer 28 is applied to the inner layer 26. The inner layer 26 has a minimum thickness of 3.5 mm, while the thickness of the upper layer 28 is equal to or greater than 3.5 mm and can be worn for example to 15 mm. It will be observed that the tandem extrusion of the two layers 26, 28 of the same polymer does not result in the fusion of the two layers together. Once the inner layer 26 has been extruded, the polymer material is cooled then the outer layer 28 of the impervious sheath is in turn extruded onto the carcass assembly and inner layer 26. After the tight pressure sheath has been made around the metal carcass 12, a steel-shaped wire 32 is wound with short pitch, to form contiguous turns constituting the pressure vault 16. The steel form wire 32 is for example shaped to allow the formation of stapled turns one to other. This pressure vault 16 makes it possible to take up the radial forces exerted on the pipe, either from the inside towards the outside when the hydrocarbon flows under pressure in the flow zone 24, or from the outside inward when the hydrostatic pressure is greater than the pressure of the hydrocarbon. This is a fortiori the case, when no hydrocarbon flows inside the pipe 10, and especially during the maintenance phases independently of the flexible tubular pipe 10.

On the pressure vault 16 are wound with a long pitch the crossed weave son of the two layers 18, 20. These two layers 18, 20 can also be crossed at an angle substantially equal to 55 ° on the sealed pressure sheath 14 when using a balanced structure (not shown). The layers 18, 20 allow the flexible tubular conduit 10 to withstand the tensile forces exerted on it between these two opposite ends. For high pressure (HP) applications, the structure of the flexible tubular pipe has the second pair of armor layers 18 ', 20', and as described in patent EP 0 937 932, the pipe may comprise a first pair layers 18, 20 of weave threads wound and wound in a long pitch at an armature angle of greater than 35 ° and less than 55 ° and a second pair of layers 18 ', 20' of crossed armor threads and also wound at a long pitch at an arming angle of less than 30 °. Another pair of layers 18, 20; 18 ', 20' may be rolled up over said second pair of layers 18 ', 20'. Finally, the protective sheath 22 is made of a polymeric material extruded around the two layers of tension armor 18, 20; 18 ', 20'. We will return more specifically to the tight pressure sheath 14, and in particular on its inner layer 26 made of semi-aromatic copolyamide, which, in a preferred embodiment of the invention is made from polyhexamethylene dodecanediamide and polyamide obtained from hexamethylenediamine and terephthalic acid. The problems generally encountered with pipes comprising a pressure-tight polyamide sheath are in particular due to the hydrolysis which causes irreversible aging of the polyamide over time. Indeed, while the condensation of an amine function and an acid function with elimination of a molecule of water makes it possible to constitute the amide bond, conversely hydrolysis is the reaction of water with the amide function, leading to cut the chains of the polymer. As these chains become shorter, the molecular weight decreases and the polymer loses its mechanical properties to a point where the mechanical stresses that the sheath undergoes lead to its rupture.

To follow the hydrolysis phenomenon, a simple way is to proceed to at least one measurement of the subsequently corrected inherent viscosity (noted CIV), method applied to evaluate the degradation by hydrolysis of amide group, described below as well as in " Durability of polyamide 11 for offshore flexible pipe applications ", publication written for the MERL conference (Material Engineering Research Laboratory) Oilfield Engineering with Polymers (1998). Inherent viscosity is a characteristic directly proportional to molecular weight, measured by dissolving a piece of polymer within a functional isomer, for example meta-cresol and recording the passage time of the meta-cresol / polymer solution. in a calibrated capillary tube. When the flexible tubular conduit 10 in accordance with the invention is in operation, the two layers 26, 28 are held in contact under pressure against each other since on one side, on the inside, the hydrocarbon is under pressure and on the other side, on the outside, the hydrostatic pressure tends to coerce the layers radially against each other. The hydrocarbon which flows under pressure in the flow zone 24, inside the metal carcass 12, tends to leak through the turns of the carcass 12 and come into contact with the inner layer 26 of the waterproof pressure sheath 14.

Also, when the hydrocarbon contains hydrogen sulphide or carbon dioxide and water, the medium is then relatively acidic at the inner layer 26, its pH is less than 7, and its hydrolysis is even more important. It will be observed that the higher the temperature of the hydrocarbon, the greater the chemical decomposition of the polyamide will be, simply under the Arrhenius laws. The water present in the hydrocarbons diffuse in the form of steam in the two layers 26, 28 constituting the sealing sheath 14 and is therefore in contact with the outer layer 28 causing its hydrolysis but in a less active manner than if the water were in liquid form. The outer layer 28 constituting the sealing sheath 14 therefore degrades from the beginning of the use of the flexible tubular pipe 10 but with a much slower kinetics than that of the inner layer 26 which is in contact with the fluid transported and which is also subject to a higher temperature.

When the pipe 10 is no longer in normal operation for reasons of maintenance, the two layers 26, 28 in semiaromatic copolyamide, preferably made from polyhexamethylene dodecanediamide and polyamide obtained from hexamethylenediamine and terephthalic acid , are no longer intimately in contact because the pressure of the transported fluid no longer applies to them. During these periods, a very slight gap is created between the layers 26, 28. The size of this gap depends on the degree of deplastification of the two layers 26, 28. The greater the displacement, the more layers 26, 28 undergo loss of thickness. During production shutdowns, part of the water that has diffused through the inner layer 26 and outer layer 28 condenses in the interstice and the outer layer 28 is thus in contact with liquid water but at a lower temperature to that of the transported fluid. During these time intervals, the hydrolysis of the outer layer 28 of the sealed pressure sheath is more active. The interstice created between the two layers 26,28 of the sealed sheath 14 during maintenance periods of the pipe 10 is partly occupied by condensed water. Following the evolution of the hydrolysis phenomenon occurring at this interstice, more precisely the evolution of the formation of condensed water, can be envisaged and the use of a pressure measuring device, not shown, such that a manometer, would allow to follow the variation of the differential pressure between the saturating vapor pressure prevailing at the gap and the partial pressure prevailing in the flow zone 24.

The inner and outer layers 26,28 are, at each end of the pipe 10, crimped into a connecting piece. The inner layer 26 is crimped independently of the outer layer 28, radially separated by a cannula (not shown), preferably a pierced cannula. At the first end of the pipe, the pierced cannula is provided with a drainage system comprising at least one axial drainage channel connecting the gap to at least one evacuation passage leading to an outlet orifice, to the outside of driving. And, at the second end of the pipe, the pierced cannula is provided with a drainage system comprising at least one axial drainage channel connecting the gap to the flow zone. Said outlet and the flow zone 24 can thus be connected to said pressure measuring device. The pressure measuring device may be provided with a visual indicator allowing the reading of the pressure values. In addition, said device can also be connected to a system, not shown, for recording and continuously processing the pressure measurements.

The use of the inner layer 26 of semi-aromatic copolyamide, preferably made from polyhexamethylene dodecanediamide and polyamide obtained from hexamethylenediamine and terephthalic acid, according to the preferred embodiment of the invention, makes it possible overall to preserve the integrity of the mechanical properties of the pressure sheath 14 for a period of time at least equal to the required service life of the flexible tubular conduit 10. The hydrolysis kinetics of the layers 26 and 28 forming the sheath The seal 14 described above is illustrated by way of example in FIG. 2. The curve 36 illustrates the degradation of the outer layer 28 during the production phases where the water is present in the form of water vapor as well as the maintenance phases where the condensed water is in the liquid state. Curve 38 illustrates the faster degradation of the inner layer 26. Said layer 26 is subjected to a higher temperature and is in contact with acidified water due to the presence of carbon dioxide (CO2) and sulfide. hydrogen (H2S) in the hydrocarbon fluid transported inside the metal carcass 12. Once the curve 38 reaches the ultimate CIV criterion, it is estimated that the inner layer 26 loses its seal and that from of this instant, the outer layer 28 undergoes more severe conditions, that is to say those undergone by the inner layer 26. Advantageously the criterion of CIV retained for the inner layer 26 may not take into account the margins of safety usually used to fix this criterion which makes it possible to guarantee the non-rupture of a polymeric sheath. However, since the inner layer 26 is a sacrificial layer, it is assumed that it degrades to failure. According to the preferred embodiment of the invention, even if the polyamide-6-12 used has good resistance to hydrolysis, nevertheless it degrades during the period of operation of the pipe, but it degrades less quickly than the polyamides usually used. In this way, the inner layer 26 constitutes a sacrificial layer preferentially degrading to the outer layer 28. The temperature of the hydrocarbon fluid transported is compared to the maximum acceptable temperature by the flexible tubular pipe 10, temperature depending on the service life the required pipe and the acidity of the water contained in the transported fluid. This maximum acceptable temperature must make it possible to guarantee that the final CIV of the outer layer 28 of polyamide, preferably of polyamide-6-12, is greater than or equal to the end criterion, depending on the final CIV of the inner layer 26, expressed as CIV units, or 0.95 dl / g. Thus, it is observed that the inner layer 26 plays the role of sacrificial layer, since it degrades more rapidly than the outer layer 28, during a period less than the life required for the flexible tubular conduit 10. In the example of Figure 2, after 15 years, when the inner layer 26 is completely degraded, it is the outer layer 28 which degrades faster because it is then in direct contact with the hydrocarbon fluid transported. It is estimated that after 20 years, although the outer layer 28 is partially degraded, the sealed pressure sheath 14, retains its overall mechanical and sealing properties, to ensure the transport of the hydrocarbon. Moreover, in addition to its good resistance to hydrolysis, the inner layer 26 forms a good heat shield. Indeed, if the temperature of the flow zone 24 is close to 100 ° C, it is only about 60 ° at the pressure vault 16. It also preserves the outer layer 28 of the heat. In addition, its heat shield capabilities are advantageous when the hydrocarbon suddenly stops flowing in the flow zone 24. Indeed, when the flexible tubular pipe 10 is immersed at depths of more than one thousand meters, the temperature water is only a few degrees, and the initially hot hydrocarbon cools rapidly and paraffin plugs or hydrates appear. Also, thanks to the heat shield effect of the inner layer 26, the dissipation of heat is attenuated, and the appearance of paraffin plugs is delayed. In addition to the aging phenomena due in particular to hydrolysis, the sealed pressure sheath 14, in two independent layers 26, 28 with an interface 30, has an advantage in terms of crack propagation. Indeed, the movements of the flexible tubular conduit 10 during operation, coupled with the gradual deterioration of the inner layer 26 of the pressure sheath 14, reveal cracks in the inner layer 26 at the level of the metal carcass 12. These cracks tend to propagate radially towards the outer layer 28. Thanks to the interface 30, the propagation of these cracks is stopped.

Claims (14)

REVENDICATIONS1. Flexible tubular pipe (10) for transporting hydrocarbons in a marine environment, said flexible tubular pipe comprising a waterproof sheath (14) of polymer material, and firstly a hydrocarbon flow zone (24) located inside said sealed sheath and secondly layers of metal armor (16, 18, 20) wound on the outside around said sealed sheath (14) to allow said flexible tubular pipe to withstand radial and longitudinal stresses, said impervious sheath (14) having an outwardly facing outer layer (28) and an inner layer (26) independent of said outer layer inwardly of said impervious sheath (14) for isolating said outer layer (28) with respect to said flow zone, said inner layer (26) being intended to be in contact with the hydrocarbon flowing inside said flow zone (24); characterized in that said inner layer (26) is made of semi-aromatic copolyamide so as to preserve said outer layer (28) of the hydrolysis. 2. Flexible tubular pipe according to claim 1, characterized in that said semi-aromatic copolyamide is made from a homopolymeric aliphatic polyamide and a semi-aromatic polyamide. Flexible tubular pipe according to claim 2, characterized in that said homopolymeric aliphatic polyamide is chosen from polycaprolactam, polyundecanamide, polylauroamide, polyhexamethylene adipamide, polyhexamethylene sebacamide and polyhexamethylene dodecanediamide. 4. Flexible tubular pipe according to claim 1, characterized in that said semi-aromatic copolyamide is made from polyhexamethylene dodecanediamide and polyamide obtained from hexamethylenediamine and terephthalic acid. 5. Flexible tubular pipe according to any one of claims 1 to 4, characterized in that said outer layer (28) of said waterproof sheath is made of polyamide. 6. flexible tubular pipe according to claim 5, characterized in that said outer layer (28) of said waterproof sheath is made of semi-aromatic copolyamide from one part of a homopolymeric aliphatic polyamide selected from polycaprolactam, polyundecanamide , polylauroamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, and polyhexamethylene dodecanediamide, and on the other hand a semi-aromatic polyamide obtained from hexamethylenediamine and terephthalic acid. 7. Flexible tubular pipe according to any one of claims 1 to 6, characterized in that said inner layer (26) of said sealed sheath (14) is made by extrusion. 8. Flexible tubular pipe according to any one of claims 1 to 7, characterized in that said outer layer (28) of said waterproof sheath (14) is made by extrusion on said inner layer (26). 9. Flexible tubular pipe according to claims 7 and 8, characterized in that said inner layer (26) and said outer layer (28) of said waterproof sheath are made by tandem extrusion. 10. Flexible tubular pipe according to any one of claims 1 to 9, characterized in that said outer layer (28) has a thickness greater than the thickness of said inner layer (26). Flexible tubular pipe according to claim 10, characterized in that the thicknesses of the outer (28) and inner (26) layers are greater than three millimeters. Flexible tubular pipe according to any one of claims 1 to 11, characterized in that said waterproof sheath (14) further comprises an intermediate layer made of semiaromatic copolyamide and located between said inner layer (26) and said outer layer. (28). Flexible tubular pipe according to claim 12, characterized in that said intermediate layer of said waterproof sheath is made of semi-aromatic copolyamide from one part of an aliphatic polyamide homopolymer chosen from polycaprolactam, polyundecanamide, polylauroamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, and polyhexamethylene dodecanediamide, and on the other hand a semi-aromatic polyamide obtained from hexamethylenediamine and terephthalic acid. 14. Operating structure of petroleum deposits comprising at least one flexible tubular pipe according to any one of claims 1 to 13, characterized in that it extracts a marine field whose production crude has a temperature substantially greater than or equal to 70 ° C, preferably 90 ° C and preferably 110 ° C from the seabed to the surface.