FR2931099A1 - PROCESS FOR PRODUCING A FLEXIBLE TUBULAR STRUCTURE - Google Patents

Abstract

The invention relates to a flexible tubular pipe (10) for offshore oil exploitation and its method of production. Said pipe comprising, a sealed inner conduit and at least one sheath (20) of elastomeric thermoplastic polymer of a predetermined thickness around said inner conduit (18); according to the invention said elastomeric thermoplastic polymer comprises a thermoplastic polymer based on polypropylene and an elastomer based on ethylene-propylene-diene terpolymer, and it further comprises a compatibilizing agent for increasing the miscibility of said thermoplastic polymer based on polypropylene and said elastomer based on ethylene-propylene-diene terpolymer.

Description

f Method of manufacturing a flexible tubular structure

The present invention relates to a method of manufacturing a flexible tubular structure of great length for transporting fluids for offshore oil exploitation, and the structure obtained according to said method. It more specifically relates to certain sheaths of the structure made of polymer material. In the present application, the term flexible tubular structure refers to both subsea flexible pipes, submarine umbilicals and flexible tubular structures combining the functions of flexible pipes and submarine umbilicals. Subsea flexible pipes are mainly used to transport oil or gas extracted from an offshore field. They can also be used to convey pressurized seawater for injection into the reservoir to increase hydrocarbon production. These flexible pipes are formed of a set of different layers each intended to allow the pipe to support the constraints of service or offshore installation. These layers include, in particular, polymeric sheaths and reinforcing layers formed by windings of metal-shaped wires, strips or wires of composite material. The flexible tubular conduits generally comprise, from the inside to the outside, at least one internal sealing tube intended to convey the transported fluid, layers of reinforcements around the internal sealing tube, and a polymeric protective sheath. external around the reinforcement layers. The internal sealing tube is generally made of a polymeric material and is in this case referred to indifferently as the internal sealing sheath or pressure sheath. However, subsea flexible pipes exist in which the inner sealing tube is a thin-walled corrugated metal tube of the type described in WO98 / 25063. In some cases, an intermediate polymeric sheath is also provided between the inner sealing tube and the outer sheath, for example between two reinforcing layers. Such flexible pipes are described in the normative documents published by the American Petroleum Institute (API), API 17J Specification for Unbonded Flexible Pipe and API RP 17B Recommended Practice for Flexible Pipe. The submarine umbilicals are mainly used to transport fluids, power and signals to underwater equipment, such as valves, wellheads, collectors, pumps or separators, to supply power and remotely control and control the actuators of this equipment. The fluids transported for these applications are generally hydraulic control oils. The submarine umbilicals may also be used to transport various fluids for injection into a hydrocarbon main line so as to facilitate the flow of said hydrocarbon, for example by injection of agents. chemicals to prevent the formation of hydrate or methane plugs facilitating the rise of oil to the surface (gas lift method), or to ensure the maintenance of said main pipe, for example by injection of corrosion inhibitors. An underwater umbilical consists of an assembly of one or more internal sealing tubes, and optionally electric cables and / or optical fiber cables, said assembly being made by helical winding or S / Z of said tubes and cables, so that the umbilical is flexible, said assembly being able to be surrounded by reinforcing layers and an outer protective polymeric sheath. These internal sealing tubes, whose function is to transport the aforementioned fluids, generally have a diameter much smaller than the external diameter of the umbilical. An umbilical internal sealing tube generally consists of either a sealed metal tube or a sealed polymeric tube surrounded by one or more layers of reinforcement. Such submarine umbilicals are described in the normative documents published by the American Petroleum Institute API, API 17E Specification for Subsea Umbilicals.

US6102077 discloses a flexible tubular structure combining the functions of an underwater flexible pipe and an underwater umbilical. This structure comprises at its center a flexible pipe of large diameter used to transport hydrocarbons, said central flexible pipe being surrounded by a plurality of small diameter peripheral tubes assembled helically or in S / Z around the central flexible pipe, said peripheral tubes being used for functions similar to those of umbilicals, including hydraulic controls or fluid injection. Such flexible tubular structures are known to those skilled in the art as Integrated Subsea Umbilical and Integrated Production Bundle. These large diameter structures are generally surrounded by a polymeric outer sheath. In the present application, the term "internal sealing tube" includes either the internal polymeric sheath or the pressure sheath of an underwater flexible pipe or the metallic or polymeric fluid transport tubes of an underwater umbilical. The term internal sealed conduit means meanwhile a subset of the flexible tubular structure, said subassembly comprising at least one internal sealing tube. These definitions also apply to: flexible tubular structures combining the functions of an underwater flexible pipe and an underwater umbilical. The document W003083344 in the name of the applicant teaches the use of thermoplastic elastomeric polymer (TPE) for producing the outer sheath or the intermediate sheath of flexible underwater pipes. Indeed, these polymers are well suited to such applications, while being less expensive than the polyamides used previously. These polymers are also naturally suitable for producing outer or intermediate polymeric sheaths of submarine umbilicals, or flexible tubular structures combining the functions of an underwater flexible pipe and an underwater umbilical. The methods for producing these tubular conduits are well known, and as regards the abovementioned polymer material sheaths, and more specifically the outer sheath or the intermediate sheath, they are extruded directly around the reinforcing layers of the pipe. Thus, the internal pressure sheath is first surrounded with at least one tensile-resistant layer and most often with at least one other pressure-resistant layer. Then, a softened layer of an elastomeric thermoplastic polymer including an olefin polymer mixed with an elastomer is hot extruded and finally said layer is cooled to obtain at least a second polymeric sheath of a determined thickness around the layers of reinforcement. The extrusion is performed by means of an extruder equipped with a crosshead in English language. Until now, these polymeric sheaths had a relatively low thickness, typically less than 10 mm, and indeed, the method of implementation of the aforementioned thermoplastic elastomer polymer allowed to obtain inexpensive sheaths with good mechanical strength. However, because of the increase in water depths, the outer diameter of the flexible tubular structures, and also the thermal insulation requirements, it has naturally sought to increase, in particular, the thickness of the elastomeric thermoplastic polymer sheaths. Unfortunately, it turned out that, overall, the mechanical properties of the thick elastomer thermoplastic sheaths then obtained were insufficient. In particular, the elastomeric elastomeric sheath elongation at break of the prior art tends to decrease greatly when the sheath thickness is greater than 15 mm, which has the disadvantage of increasing the minimum radius the flexible pipe can be bent without risk of tearing said thick sheaths. Also, a technical problem which then arises, and which the present invention aims to solve, is to provide a flexible tubular structure and a method 25 for producing such a pipe, including at least the outer protective sheath or an intermediate sheath. , made of elastomeric thermoplastic polymer, withstands the constraints of use of the structure, although the thickness of this sheath is increased relative to the thickness of the sheaths made according to the prior art. For this purpose, and according to a first aspect, the present invention provides a method of manufacturing a flexible tubular structure for offshore oil exploitation, said method being of the type according to which: an inner conduit is first provided waterproof and an elastomeric thermoplastic polymer; a softened layer of said elastomeric thermoplastic polymer is then formed by hot extrusion around said sealed inner conduit; then cooling said softened layer to obtain at least one polymeric sheath of a predetermined thickness around said sealed inner conduit; and according to the invention, said elastomeric thermoplastic polymer comprises a polypropylene thermoplastic polymer (PP) and an ethylene-propylene-diene-monomeric terpolymer elastomer (EPDM), and a compatibilizing agent for mixing is further provided together said elastomeric thermoplastic polymer and said compatibilizer prior to said hot extrusion, so as to increase the miscibility of said polypropylene thermoplastic polymer and said ethylenepropylene-diene-monomeric terpolymer elastomer (EPDM) during extrusion, by wherein the elongation at break of said polymeric sheath is increased. Thus, a characteristic of the invention lies in the use of a compatibilizing agent capable of increasing the miscibility of the thermoplastic polymer and of the elastomer one in the other during the extrusion, one is to polypropylene base (PP) and the other based on ethylenepropylene-diene-monomer terpolymer (EPDM). In this way, it turns out that the mechanical properties of the sheath are more homogeneous throughout its thickness. Also, such a sheath is less prone to tearing and more generally is more resistant despite the more severe conditions of use. Such a benefit of the compatibilizing agent could not be observed so far, because the thin sheaths obtained according to the prior methods, had homogeneous mechanical properties throughout their thickness. In reality, the use of a thick sheath, for example greater than 15 mm, has brought to light a technical problem that did not arise in the past. Indeed, it has been discovered that the mechanical characteristics of the elastomeric thermoplastic polymer sheath depend greatly on its cooling conditions after the extrusion. Thus, the outermost sheath portions and therefore those which are cooled most rapidly, in air or in water, after the formation of the softened layer of elastomeric thermoplastic polymer around the sealed inner conduit, exhibit mechanical characteristics greater than the duct portions located in the vicinity of said sealed internal duct. These last portions of sheath, are of course cooled more slowly. Thus, a correlation has been established between the cooling rate of the softened polymer and the mechanical properties obtained after cooling. However, there is no economically feasible industrial means for cooling the softened layer after extrusion throughout its thickness homogeneously. Optical analysis showing the formation of large crystallites in outer skin and small size in inner skin, it was first tried to incorporate a nucleating agent to homogenize the crystal structure. However, against all odds, this solution did not significantly improve the mechanical properties of the sheath, despite homogenization of the crystalline structure. Also, and this is one of the merits of the invention, it was then imagined to incorporate in the elastomeric thermoplastic polymer, before extrusion, the compatibilizing agent which allows a better cohesion between the phases of the two types of polymer. and therefore a better mechanical strength of the cooled material. Advantageously, a polymer selected from polymers based on polyolefin or styrene-ethylene-butadiene-styrene (SEBS) is provided as compatibilizer. In this way, such a polymer which on the one hand has functional groups or chemical groups having an affinity for the elastomer, and on the other hand, functions or chemical groups having an affinity for the thermoplastic polymer, allows a more high miscibility of the two types of polymer together when they are extruded hot. Advantageously, the styrene-ethylene-butadiene-styrene chosen is, moreover, an ungrafted linear tri-block polymer. Further, a nucleating agent is also advantageously provided, and said nucleating agent, said compatibilizer, said polypropylene thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer are mixed together prior to said extrusion at hot, to increase the crystallization speed of said polymers and then to homogenize the crystalline structure in the thickness of said softened layer 3o and then the sheath. The nucleating agents make it possible to initiate the crystallization reactions of the polymers by promoting the formation of the crystallites as soon as the polymer is softened, at a temperature situated beyond its glass transition temperature. It will be observed that the cooling conditions of the elastomeric thermoplastic polymer after extrusion directly affect the size and density of the crystallized zones. However, the nucleating agent initiating very early crystallite formation, provides a relatively homogeneous distribution of these crystallized areas both in the thickness of the sheath and also at the circumference of said sheath.

According to a particularly advantageous embodiment of the invention, a nucleating agent comprising a phosphate salt and a dicarboxylate salt is provided so as to obtain a better distribution of the crystallized zones in the thickness of the sheath. According to one embodiment of the preferred invention, an elastomeric thermoplastic polymer having between 40% and 70% by weight of said thermoplastic polymer based on polypropylene is provided between 10% and 20% by weight of said elastomer based on ethylene terpolymer. propylene-diemonomer and between 1% and 20% by weight of said compatibilizer. In this way, a sheath is obtained whose mechanical properties, and in particular elongation at break, make it possible to avoid the risks of tearing the sheath. Indeed, as will be explained hereinafter in more detail, the material of the sheath obtained according to the aforementioned method has an elongation at break greater than 200% irrespective of its position in the thickness of the sheath. and whatever the value of this thickness, while the material of the sheaths 20 obtained according to the prior art, and in the vicinity of the sealed inner conduit when the sheath has a thickness of between 15 and 20 mm, has an elongation at break between 7% and 50% depending on its surface condition at the interface with the internal duct. According to the prior art, under these conditions, when the inner face of the sheath has a good surface state, the elongation at break is of the order of 50%. On the other hand, in areas where the inner face of the sheath has indentations related to the geometry of the underlying layer, the elongation at break can degrade and fall to around 7%. However, when the flexible tubular structure is bent to its minimum allowed radius, the polymeric outer sheath can undergo an elongation of the order of 5% to 7% along the most taut generatrix. Thus, the invention makes it possible to significantly increase the elongation at break and thus to move away from the risk zone.

In addition, there is provided a thermoplastic elastomer having between 0.1% and 1% by weight of said nucleating agent for initiating the crystallization reactions of the polymers during the implementation of the polymer. Advantageously, a softened layer of said elastomeric thermoplastic polymer is formed by hot extrusion around said sealed internal conduit so as to obtain a polymeric sheath with a thickness greater than 10 mm around said sealed internal conduit. Such a sheath, thanks to the compatibilizing agent and also to the nucleating agent, has homogeneous mechanical characteristics in the thickness of the sheath obtained, although the cooling rates of the extruded polymer layer are different. According to a second aspect, the invention relates to a flexible tubular structure intended for offshore oil exploitation, said flexible tubular structure comprising a sealed inner conduit, and at least one thermoplastic elastomeric polymer sheath of a determined thickness around said inner conduit sealed, said sheath being obtained by hot extruding a softened layer of said elastomeric thermoplastic polymer around said sealed inner conduit and cooling said softened layer; according to the invention, said elastomeric thermoplastic polymer comprises a polypropylene thermoplastic polymer and an ethylene-propylene-diene-monomer terpolymer elastomer, and it further comprises a compatibilizer to increase during extrusion, miscibility said polypropylene-based thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer, whereby the elongation at break of said sheath is increased. Thus, a feature of the invention lies in the use of a compatibilizing agent with the thermoplastic polymer and the elastomer during extrusion, so as to obtain an elastomeric thermoplastic polymer which, under the conditions of pressure and temperature of The use of the tubular structure has uniform mechanical characteristics throughout the sheath so as to withstand the stresses it undergoes. Advantageously, said compatibilizing agent is a polymer or a copolymer chosen from polymers based on polyolefin or styrene-ethylene-butadiene-styrene (SEBS). These polymers have the advantage of being widely produced in industry, so they are likely to be obtained at advantageous costs. In addition, said elastomeric thermoplastic polymer preferably comprises a nucleating agent intended to induce a homogeneous crystallite distribution according to said determined thickness, during the cooling phase and thus to obtain spherulites uniformly distributed both in the thickness of the sheath and according to the circumference of the sheath. Advantageously, said nucleating agent comprises a phosphate salt and a dicarboxylate salt. According to an advantageous characteristic, said elastomeric thermoplastic polymer comprises between 40% and 70% by weight of said thermoplastic polymer based on polypropylene, between 10% and 20% by weight of said elastomer based on ethylene-propylene-diene-monomer terpolymer, and between 1% and 20% by weight of said compatibilizer, so as to obtain satisfactory mechanical properties and to avoid the risk of tearing. In addition, said elastomeric thermoplastic polymer advantageously comprises between 0.1% and 1% by weight of nucleating agent. In addition, said polymeric sheath has a thickness greater than 10 mm around said sealed inner conduit and has identical mechanical properties in all respects. According to a particular embodiment of the invention, said sealed internal conduit comprises, from the inside to the outside of said tubular structure, an internal polymeric sheath for sealing, reinforcing threads wrapped around said internal polymeric sheath. In the present application, the term "reinforcing wire" is used to cover at least one reinforcing layer, so that a flexible tubular pipe commonly used for the offshore transport of hydrocarbons is used. for example glass or carbon fibers, and woven strips or reinforcing ropes made of metallic material or high-tenacity fiber of the type, for example aramids, etc. Other features and advantages of the invention will emerge on reading of the description given below of a particular embodiment of the invention, given for information but not limited If, with reference to the accompanying drawings in which: - Figure 1 is a partial schematic perspective view and severed of a flexible tubular pipe obtained by the method according to the invention; and - Figure 2 is a schematic view of an installation s implementation of the method according to the invention. Figure 1 partially illustrates a flexible tubular structure 10 which will be described first before describing its production method and for which protection is also sought. This tubular structure is a pipe intended specifically for the transport of hydrocarbons and it has, from the inside to the outside, a tight internal pressure sheath 12 inside which a hydrocarbon is likely to circulate. This internal pressure sheath 12 is surrounded by an armor layer 14 formed of a short-pitch winding of a metal wire stapled and intended to take up the internal pressure forces with the inner sheath 12. Around the 14 armor layer 14, two traction armor plies 16, 18 are wound with a long pitch and are intended to take up the longitudinal tensile forces to which the pipe is subjected. These two plies of tensile armor 16, 18 wrapped around the armor layer, itself located around the inner pressure sheath, together constitute a sealed inner conduit. The flexible tubular conduit 10 finally has an outer protective sheath 20 for protecting the aforementioned reinforcement layers 14, 16, 18. The object of the invention relates precisely to this outer protective sheath 20. It will be observed, however, that an intermediate sheath of the same type can be inserted between the reinforcing layers 14, 16, 18, and that it can be realized. with the same polymeric materials and according to the same manufacturing process as will be described hereinafter. With reference to FIG. 2, the installation for manufacturing a flexible tubular pipe of the aforementioned type, and more particularly the outer protective sheath 20, will be described first. Thus, the installation schematically comprises an extruder 22. having a drive screw 24, which has at one of its ends a loading hopper 26 and the other of its ends, the injection nozzle 28. Unlike extruders equipped with an injection mold , the extruder 22 here presented comprises a crosshead 30 adapted to be traversed by a pipeline during manufacture 32 and to be connected at the injection nozzle 28. The pipe is driven from the upstream 31 from the right-angle head 30 downstream 35. Conventionally, the granular polymers are introduced into the loading hopper 26, heated and softened inside the drive screw 24 and driven melting to the crosshead 30 which is adapted to form a cylindrical layer 33 of polymer softened on the outermost reinforcing layer 18 of the conduit being manufactured 32. This polymer layer is of a thickness greater than 15 mm. Beyond the downstream of the angle head 30, the pipe coated with the cylindrical layer 33 of softened polymer is then cooled, either in air or through a water bath. However, the passage of the extrusion temperature, which is greater than the glass transition temperature of the polymer and close to the melting temperature, at room temperature, is not instantaneous. Also, as soon as the pipe crosses the cooling zone, a radial thermal gradient is installed in the thickness of the outer sheath, the outside being colder than the inside. This gradient disappears of course after a while. Thus, the elastomeric thermoplastic polymer used to form the aforementioned outer sheath, comprises a first blend including a vulcanized elastomer based on ethylene-propylene-diene-monomer terpolymer (EPDM) and a polypropylene-based thermoplastic polymer (PP). Advantageously, this first mixture has been manufactured by a dynamic vulcanization process (dynamic vulcanization in English) making it possible to obtain a crosslinked elastomeric phase and distributed in the form of fine particles dispersed in the matrix of the thermoplastic polymer. In this way, the mechanical properties of the sheath 20 are improved. This process known to those skilled in the art is described in particular in US3037954. This first mixture comprises, by weight, approximately 60% of thermoplastic polymer and 15% of elastomer. The formulation of this first blend also includes plasticizers and fillers. It will be observed that this first mixture is especially sold under the trademark Santoprene 203-50 by the company ExxonMobil. To this first mixture is incorporated a second mixture including a compatibilizing agent and in this case styrene-ethylene-butadiene-styrene (SEBS). Advantageously, the SEBS chosen is a tri-block linear copolymer based on styrene and ethylene-butadiene marketed under the trademark Kraton G-1650 by Kraton Polymers. This second mixture is generally called master batch. This second mixture may also include a nucleating agent comprising a phosphate salt and a dicarboxylate salt. For example, this nucleating agent is a salt of bicyclo [2.2.1] heptane dicarboxylate. The latter is marketed by Milliken under the reference HPN-68. Thus, according to a preferred embodiment, there is provided a second mixture including, by weight, 46% of compatibilizer in the form of a styrene-ethylenebutadiene-styrene and 8% of nucleating agent, the bicyclo salt [ 2.2.1] heptane dicarboxylate. Then, the first mixture and the second mixture are mixed together at 100 parts by weight of the first mixture to 8 parts of the second mixture to form a third mixture. This operation can be done automatically upstream of the extruder using a known device called gravimetric mixer doser. The first and second mixtures are supplied in the form of granules which feed the two inlets of the mixing metering unit, said mixing metering device delivering at the outlet a homogeneous mixture of granules in the desired proportions. The output of the mixer dispenser is directly connected to the receiving hopper of the extruder. Thus, the compatibilizing agent, in the example given here, styrene-ethylene-butadiene-styrene (SEBS), will make it possible to increase the miscibility of the thermoplastic polymer based on polypropylene and the elastomer during the melting. of the two polymers together. Indeed, these two categories of polymer are very poorly miscible one in the other when they are melt. In this way, the first and second mixtures together constitute a third blend incorporating 55.5% polypropylene thermoplastic polymer, 14% ethylene-propylene-diene-monomer terpolymer, 3.4% compatibilizer. , styrene-ethylene-butadiene-styrene and 0.6% nucleating agents, the bicyclo [2.2.1] heptane dicarboxylate salt.

Note that the above formulation is an advantageous formulation, but that other formulations may be suitable. Also, the thermoplastic polymer composition is preferably between 40% and 70% by weight of the total formulation. As regards the elastomer, it is between 10% and 20%. The compatibilizing agent is between 1% and 20%. And the nucleating agent, if incorporated into the thermoplastic elastomer, is between 0.1% and 1%. Of course, the formulation also comprises conventional additives, and well known thermal stabilizer type, anti-oxidant, anti-UV, charges or plasticizers. Thus, the third mixture, or final formulation, which is in the form of a mixture of granules, is then introduced into the receiving hopper 26 of the plant shown in FIG. 2. In this way, extrusion is formed. while heating a softened and homogeneous layer of the third mixture is around the outermost reinforcing layer and then, this layer is cooled to obtain a polymeric sheath of a determined thickness around the reinforcing layer. This polymeric sheath thus extruded was analyzed. It has been verified that the mechanical characteristics, and in particular the elongation at break of the sheath portions located outwardly and in the vicinity of the reinforcing layer, which portions are spaced at least 10 mm, when the Sheath thickness is greater than 15 mm, were comparable. In theory, it would be more accurate to reason at the threshold elongation to classify and select suitable materials, but threshold elongation measurements are unreliable for these highly ductile polymers. Thus, it was established by forming test pieces in sheath portions located in the vicinity of the reinforcing layer that the elongation at break of the material was more than twice that of the materials used according to the prior art. In reality, it has been found by analyzing the aforementioned advantageous formulation, in comparison with the formulations according to the prior art, a certain degradation of the mechanical properties of the sheath portions situated in the vicinity of the reinforcing layer when the thickness of the sheath increases. Nevertheless, the elongation at break of these portions of sheaths for the aforementioned advantageous formulation is not only higher regardless of the thickness of the sheath, but moreover, the difference between the sheaths resulting from the two formulations increases with the thickness in favor of the sheath made with the advantageous formulation. Thus, for a sheath having a thickness of 5 mm, the elongation at break of the sheath portions situated in the vicinity of the reinforcing layer is 500% for the sheath obtained with the aforementioned advantageous formulation and 450% for the sheath obtained with the formulation according to the prior art. When the thickness of the sheath is 10 mm, these elongations at break are respectively 300% and 200%. When the thickness of the sheath is 20 mm, these elongations at break Io are respectively 200% and 50%. Thus, the elongation at break of the material according to the invention is at least 200% in the thickness of the sheath, for thicknesses of between 15 and 20 mm, which considerably improves the flexibility of the sheaths then produced. In addition, it has been verified that the measurement of the thickness of the elastomeric thermoplastic sheaths thus produced can be carried out accurately and reliably with conventional ultrasonic ultrasound non-destructive testing methods, which was not always the case with the elastomeric thermoplastic polymer of the prior art. Indeed, in the case of thick sheaths made according to the prior art, it was indeed difficult to obtain a reliable measurement of this thickness by these ultrasonic methods because the propagation speed of the ultrasound was not sufficiently homogeneous in the thickness of the sheath. On the other hand, thanks to the new material according to the invention, on the one hand, the speed of propagation of the ultrasounds is much more homogeneous in the thickness of the sheath, and on the other hand the ultrasonic attenuation is markedly reduced, although Ultrasonic ultrasound measurement is more reliable and accurate. This non-destructive control thus makes it possible to continuously measure the thickness of the thermoplastic elastomer sheath during the manufacture of the tubular structure. According to another example of formulation, the compatibilizing agent was increased to 15% in the third mixture. It was then found that the elongation properties at break of the sheath were increased. It will be observed, however, that, conversely, the thermal resistance of the sheath is substantially altered. However, it is necessary in some applications, to retain significant thermal insulation properties of the flexible pipe. Also, it has been shown that the formulation of the third mixture should advantageously include between 2% and 5% of styrene-ethylene-butadiene-styrene-based compatibilizer (SEBS). In this way, the thermal conductivity of the polymer of the sheath thus obtained is less than 0.2 W / m.K., which makes it possible to impart good thermal insulation to the flexible tubular pipe thus produced. In other circumstances, another compatibilizing agent may be incorporated into the formulation, replacing the styrene-ethylene-butadiene-styrene-based polymer (SEBS), and in particular a polyolefin-based polymer, and more specifically Polyethylene for example, the polyethylene marketed under the trade name Exceed 1018CA by Exxon was used. It is a hexene linear copolymer belonging to the family of linear low density polyethylenes (LLDPE for Polyethylene, Linear Low Density, in English).

It has been verified that in the limit of 20% by weight of the formulation, the more the proportion of this compatibilizing agent is increased, the more the mechanical properties and in particular the elongation of the polymer of the sheath obtained, are improved. According to a particular embodiment of the invention, a tubular structure of the umbilical type is produced. Also, we assemble an internal sealing tube, and electric cables. Said assembly is made by helically winding the tubes and cables so that the umbilical is flexible. The assembly which then forms a sealed inner conduit is surrounded by an outer thermoplastic polymer elastomeric sealing sheath 25 according to the method of the invention described above.

Claims (16)

REVENDICATIONS1. A method of manufacturing a flexible tubular structure (10) for offshore oil exploitation, said method being of the type in which: - a sealed internal conduit (12, 14, 16, 18) is provided; an elastomeric thermoplastic polymer is provided; a softened layer (33) of said elastomeric thermoplastic polymer is formed by hot extrusion around said sealed inner conduit (12,14,16,18); lo - said softened layer (33) is cooled to obtain at least one polymeric sheath (20) of a determined thickness around said sealed internal conduit (12, 14, 16, 18); characterized in that said elastomeric thermoplastic polymer comprises a polypropylene thermoplastic polymer (PP) and an ethylene-propylene-diene-monomer terpolymer elastomer (EPDM), and that a compatibilizing agent is further provided for mixing said elastomeric thermoplastic polymer and said compatibilizer together prior to said hot extrusion, so as to increase the miscibility of said polypropylene thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer (EPDM) during extrusion, whereby the elongation at break of said polymeric sheath (20) is increased. 2. Method according to claim 1, characterized in that a polymer selected from polyolefin-based polymers or styrene-ethylene-butadiene-styrene (SEBS) as compatibilizer. 3. Method according to claim 1 or 2, characterized in that one further provides a nucleating agent, and in that said nucleating agent, said compatibilizing agent, said thermoplastic polymer based on polypropylene and said elastomer are mixed together. based on ethylenepropylene-diene-monomer terpolymer prior to said hot extrusion. 4. Method according to claim 3, characterized in that provides a nucleating agent comprising a phosphate salt and a dicarboxylate salt. 5. Method according to any one of claims 1 to 4, characterized in that provides an elastomeric thermoplastic polymer comprising between 40% and 70% by weight of said thermoplastic polymer based on polypropylene, between 10% and 20% by weight said elastomer based on ethylene-propylene-diene terpolymer, and between 1% and 20% by weight of said compatibilizer. 6. Method according to claims 3 or 4 and 5, characterized in that provides an elastomeric thermoplastic polymer further comprising between 0.1% and 1% by weight of nucleating agent. io 7. Method according to any one of claims 1 to 6, characterized in that said elastomeric thermoplastic polymer is obtained by a dynamic vulcanization process. 8. Process according to any one of claims 1 to 7, characterized in that a softened layer of said elastomeric thermoplastic polymer is formed by hot extrusion around said sealed internal conduit (18) so as to obtain a polymeric sheath of a thickness greater than 10 mm around said sealed internal conduit (18). 9. flexible tubular structure; 10) for offshore oil exploitation, said flexible tubular structure comprising a sealed inner conduit (12, 14, 16, 18), and at least one sheath (20) of elastomeric thermoplastic polymer; a thickness determined around said sealed inner conduit (12, 14, 16, 18), said sheath (20) being obtained by hot extruding a softened layer (33) of said elastomeric thermoplastic polymer around said sealed inner conduit (12, 14, 16, 18) and cooling said softened layer (33); characterized in that said elastomeric thermoplastic polymer comprises a polypropylene thermoplastic polymer and an ethylene-propylene-diene-monomer terpolymer elastomer, and further comprising a compatibilizer for increasing during extrusion the miscibility of said polypropylene thermoplastic polymer and said ethylene-propylene-monomer terpolymer elastomer, whereby the elongation at break of said sheath (20) is increased. Flexible tubular structure according to claim 9, characterized in that said compatibilizing agent is: a polymer chosen from the group of polymers comprising polyolefin-based polymers and styrene-ethylene-butadiene-styrene-based polymers (SEBS) ), or a mixture of these polymers. Flexible tubular structure according to claim 9 or 10, characterized in that said elastomeric thermoplastic polymer comprises a nucleating agent for inducing a homogeneous distribution of crystallites according to said determined thickness. l0 Flexible tubular structure according to claim 11, characterized in that said nucleating agent comprises a phosphate salt and a dicarboxylate salt. Flexible tubular structure according to any one of claims 9 to 12, characterized in that said thermoplastic polymer is elastomeric comprises between 40% and 70% by weight of said thermoplastic polymer based on polypropylene, between 10% and 20% by weight said elastomer based on ethylene-propylene-diene-monomer terpolymer, and between 1% and 20% by weight of said compatibilizer. Flexible tubular structure according to claims 11 or 12 and 13, characterized in that said elastomeric thermoplastic polymer further comprises between 0.1% and 1% by weight of nucleating agent. Flexible tubular structure according to any one of claims 9 to 14, characterized in that said polymeric sheath (20) has a thickness greater than 10 mm around said sealed inner conduit (12, 14, 16, 18). 16. flexible tubular structure according to any one of claims 9 to 15, characterized in that said sealed inner conduit (12, 14, 16, 18) comprises from the inside to the outside of said pipe, an inner polymeric sheath (12) sealing, reinforcing son wound around said inner polymeric sheath sealing to form at least one reinforcing layer (14, 16, 18).