FR2931098A1 - 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

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 transport pressurized seawater to be injected into the deposit 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 comprise 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 inner sealing tube is generally made of a polymeric material and is in this case referred to either as the internal sealing sheath or the pressure sheath.  However, there are subsea flexible conduits 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.  The flexible pipe may further comprise a thermal insulation layer disposed between the reinforcing layers and the outer protective sheath.  This thermal insulation layer is generally made by helical winding of syntactic foam strips.  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, in order to supply power and energy. remotely control and control the actuators of this equipment.  The fluids transported for these applications are generally hydraulic control oils.  Underwater umbilicals can 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) 25, 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 electrical cables and / or optical fiber cables, said assembly being made by helical winding 30 or in 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 reinforcing layers.  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 to combine 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 tubes peripherals 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 inner polymeric sheath or the pressure sheath of an underwater flexible pipe or the metal or polymeric fluid transport tubes of a submarine umbilical.  The term "sealed internal conduit" refers to 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.  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 the submarine flexible 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 aforementioned polymer material sheaths, and more specifically the outer sheath or the intermediate sheath, they are extruded directly around the reinforcement 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. 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 the water depths, the outer diameter of the flexible tubular structures, and also the thermal insulation needs, it has naturally sought to increase the thickness of the thermoplastic elastomer polymer sheaths.  Unfortunately, it turned out that, overall, the mechanical properties of the thick elastomer thermoplastic sheaths then obtained were insufficient.  In particular, the elongation at break of the elastomeric thermoplastic sheaths made according to prior practice tends to decrease sharply when the sheath thickness is greater than 15 mm, which has the disadvantage of increasing the minimum radius at which the flexible pipe can be bent without risk of tearing said thick sheaths.  EP1619218 teaches a solution to solve this problem.  This solution consists mainly in adding a nucleating agent to the thermoplastic elastomer polymer, and in addition ensuring that the extruded sheath does not have too much hardness.  However, the only test results presented on page 9 of this document concern samples of extruded strips 2 mm thick, that is to say thin, and therefore relate to cases that are not representative of those where the aforementioned problem arises.  In addition, the author deduces from these non-representative tests that this solution would solve the problem of fragility of outer sheaths thicker than 5 mm, or even 10 mm or even 15 mm.  Now, the Applicant has carried out full-scale tests of this solution, and found that the elongations at break of the thick outer sheaths thus produced remain insufficient, so that the risk of rupture of said sheaths is not avoided.  Also, a technical problem that arises, and that aims to solve the present invention is to provide a flexible tubular structure and a method of producing such a conduit, including at least the outer protective sheath or an intermediate sheath, made of thermoplastic elastomer 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 proposes a method for manufacturing a flexible tubular structure intended for offshore oil exploitation, said method being of the type in which: first of all, a tight internal conduit is provided; 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, whereby the elongation at break of said polymeric sheath is increased.  Thus, a feature of the invention lies in the implementation of a compatibilizer capable of increasing the miscibility of the thermoplastic polymer and the elastomer in one another 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 has not been observed until now, since the thin sheaths obtained according to the prior methods had homogeneous mechanical properties throughout their thickness.  In reality, the implementation of 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 greatly depend on its cooling conditions after 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 thermoplastic elastomer polymer around the sealed inner conduit, have characteristics mechanical upper portions of the sheath portions located in the vicinity of said sealed inner conduit.  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, contrary to all expectations, this solution, furthermore taught by document EP1619218, did not make it possible to 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.  This result is surprising because, in the absence of a nucleating agent, the extruded sheath exhibits strong crystalline heterogeneities, in particular when the thickness of said sheath is greater than 10 mm, and whereas these crystalline heterogeneities seem little affected by the presence the compatibilizer.  In addition, according to the prior art and in particular that disclosed in EP1619218, it was thought that the problem of fragility of these thick sheaths was essentially related to a too low cooling rate after extrusion, this cooling too slow causing excessive magnification of the crystallites .  The natural solution for solving what was thought to be the main problem was therefore to add a nucleating agent.  However, it has been discovered after tests that this problem of size and heterogeneity of the crystallites is in fact secondary, that another technical effect associated with another main problem conditions the quality of the sheath, and that the Adding a compatibilizer agent solves this other main problem.  This other main problem seems to be related to the significant thermal gradient in the thickness of the sheath 30 during the cooling of the latter just after the extrusion step.  In fact, the cooling of the sheath at the extrusion outlet takes place mainly from the outside, the calories being essentially removed by the air from the workshop and the water from the cooling tanks that the pipe passes through after leaving the the extrusion head.  In the case of a thick sheath, the thermal gradient resulting from this phenomenon has a high amplitude, the outer face of the sheath being cooled much faster than its inner face.  The molten polymer first solidifies rapidly in the vicinity of the outer face of the sheath, then the solidification front progresses to the inner face with a speed of increasingly slow.  In the mixture constituting the polymer of the sheath, the elastomer is in the form of solid nodules dispersed in a polypropylene thermoplastic matrix, said matrix being in the molten state during the extrusion and then progressively solidifying during cooling.  During the radial progression of the solidification front, the solid nodules of EPDM tend to move radially in the sheath to come to concentrate in the vicinity of the inner face of the sheath, that is to say is in the zone which solidifies last.  The reason for this displacement is not known, but it seems related to the combination of the strong thermal gradient and the low cooling rate in the vicinity of the inner face.  The result observed with the solutions of the prior art is a significant difference in the composition of the thermoplastic elastomer between the zones situated in the vicinity of the inner and outer faces.  For example, in the case of a thick sheath according to the prior art, respective mass concentrations of polypropylene and EPDM of 70% and 5% in the vicinity of the external face were observed, and 65% and 10% in the vicinity of the inner face, the concentration of polypropylene falling radially by 5% and that of EDPM increasing radially of the same order of magnitude.  These chemical gradients alone do not explain the reason for the problem, but they seem to be an indicator revealing another underlying problem probably related to the morphology and structure of the polymer.  In addition, it has been found that the addition of a compatibilizer of the SEBS or polyolefin type makes it possible to significantly reduce this chemical composition gradient in the thickness of the sheath, and that this reduction in the chemical composition gradient accompanied by an improvement in the mechanical characteristics of the sheath, in particular its elongation at break.  It appears that the presence of this compatibilizing agent has the effect of reducing the mobility of the EPDM nodules during the solidification phase, the compatibilizing agent acting as an anchor between the polypropylene molecules and the EPDM nodules.  Advantageously, there is provided a polymer selected from polyolefin-based polymers or styrene-ethylene-butadiene-styrene (SEBS) 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, makes it possible to greater miscibility of the two types of polymer together when they are hot extruded.  Advantageously, the styrene-ethylene-butadiene-styrene chosen is, moreover, an ungrafted linear tri-block polymer.  Moreover, a nucleating agent is also advantageously provided, and said nucleating agent, said compatibilizing agent, said polypropylene thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer are mixed together before said extrusion is carried out. hot, to increase the crystallization rate of said polymers and then to homogenize the crystalline structure in the thickness of said softened layer 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 areas.  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.  In addition, it has been found that once a compatibilizing agent has been added, the addition of a nucleating agent makes it possible to increase the elongation elongation even more rapidly while the same nucleating agent, without the presence of a compatibilizing agent does not lead to any improvement in the mechanical characteristics and in particular the elongation at break.  To our knowledge this is the first time that we observe this synergistic compatibilizing agent / nucleating agent in the field of thick sheaths.  According to a particularly advantageous embodiment of the invention, a nucleating agent comprising a phosphate salt and / or 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, there is provided an elastomeric thermoplastic polymer comprising between 40% and 70% by weight of said thermoplastic polymer based on polypropylene, between 10% and 20% by weight of said terpolymer elastomer. ethylene-propylene-diene-monomer 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 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 tensile 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 1s for offshore oil exploitation, said flexible tubular structure comprising a sealed inner conduit, and at least one elastomeric thermoplastic 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 thermoplastic elastomer polymer comprises a thermoplastic polymer based on polypropylene and an elastomer based on ethylene-propylene-diene-monomer terpolymer, and it further comprises a compatibilizing agent for increasing during extrusion, the miscibility of said Polypropylene thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer, whereby the elongation at break of said sheath is increased.  Thus, a characteristic of the invention lies in the use of a compatibilizing agent with the thermoplastic polymer and the elastomer during the extrusion, so as to obtain an elastomeric thermoplastic polymer which, under the conditions of pressure and temperature 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 distribution of crystallites according to said determined thickness, during the cooling phase ~ o and thus to obtain uniformly distributed spherulites both in the thickness of the sheath only according to the circumference of the sheath.  Advantageously, said nucleating agent comprises a phosphate salt and / or a dicarboxylate salt.  According to an advantageous characteristic, said elastomeric thermoplastic polymer comprises between 40% and 70% by weight of said thermoplastic polypropylene polymer, 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 one particular embodiment of the invention, said sealed internal conduit comprises, from the inside to the outside of said tubular structure, an internal polymeric sheath of sealing, reinforcing threads wrapped around said internal polymeric sheath. sealing to form at least one reinforcing layer.  Thus, there is provided a flexible tubular conduit commonly used for offshore hydrocarbon transportation.  In the present application, the term reinforcing wire covers indifferently metal or composite son based for example on glass or carbon fibers, and woven strips or reinforcing cables made of metallic material or high-tenacity fiber. type for example aramids.  Other features and advantages of the invention will appear on reading the following description of a particular embodiment of the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which: Figure 1 is a partial schematic perspective view and severed of a flexible tubular conduit obtained by the method according lo the invention; and - Figure 2 is a schematic view of an installation for implementing the method according to the invention.  Figure 1 partially illustrates a flexible tubular structure 10 which will be described first before describing its method of production 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 is likely to circulate a hydrocarbon.  This inner pressure sheath 12 is surrounded by an armor layer 14 formed of a short-pitch winding of a stapled wire and intended to take up the internal pressure forces with the inner sheath 12.  Around the armor layer 14, two traction armor plies 16, 18 are wound with a long pitch and are intended to take up the longitudinal traction forces to which the pipe is subjected.  These two plies of tensile armor 16, 18 wound around the armor layer, itself around the inner pressure sheath, together constitute a sealed inner conduit.  The flexible tubular conduit 10 finally has an outer protective sheath 20, intended to protect the reinforcing layers 14, 16, 18 above.  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 made with the same polymeric materials and according to the same manufacturing method as will describe below.  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 first be described.  Thus, the installation comprises schematically 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, ~ o the extruder 22 here presented has a crosshead 30 adapted to be traversed by a pipeline during manufacture 32 and to be connected at the nozzle Injection 28.  The pipe is driven from upstream 31 of the right angle head 30 towards its downstream 35.  Conventionally, the granular polymers are introduced into the loading hopper 26, heated and softened inside the drive screw 24 and melt to the crosshead 30, which itself is adapted to form a cylindrical layer 33 of softened polymer on the outermost reinforcing layer 18 of the pipeline during manufacture 32.  This polymer layer has a thickness greater than 15 mm.  Beyond the downstream 35 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 was manufactured by a dynamic vulcanization process (dynamic vulcanization in English) 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 mixture 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-ethylene-butadiene-styrene and 8% of nucleating agents, the salt of bicyclo [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 inputs of the mixer dispenser, said mixer dispenser providing 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 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 mixture incorporating 55.5% thermoplastic polymer based on polypropylene, 14% ethylene-propylene-diene-monomer terpolymer, 3.4% compatibilizer, the styrene-ethylene-butadiene-styrene and 0.6% of nucleating agents, bicyclo [2. 2. 1] heptane dicarboxylate.  It will be appreciated 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, antioxidant, anti-UV, fillers 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.  In this way, a softened and homogeneous layer of the third mixture is formed by hot extrusion around the outermost reinforcing layer and then this layer is cooled to obtain a polymeric sheath of a determined thickness around a reinforcing layer. .  

Tests have been made to verify the performance of this sheath and compare its properties with those of sheaths made according to the prior art. These tests consisted in extruding in real size an outer sheath of thickness varying between 10 mm and 20 mm around a flexible pipe core of diameter of the order of 225 mm. Said core comprises all the conventional layers of a flexible pipe with the exception of the outer sheath. Single-screw extruders with a diameter of 150 mm and 155 mm were used. The solutions of the prior art which have been tested are on the one hand the polypropylene / EPDM mixture without nucleating agent or compatibilizing agent, and on the other hand the polypropylene / EPDM mixture with a nucleating agent but without compatibilizing agent. The nucleating agent used was a salt of bicyclo [2.2.1] heptane dicarboxylate according to the teaching of EP1619218. Sheath samples were then collected and analyzed in the laboratory. It was first found that the sheaths made according to the present invention have satisfactory mechanical characteristics, even when the thickness of the sheath is greater than 15 mm. In theory, it would be more accurate to reason at the threshold elongation to classify and select appropriate materials, but threshold elongation measurements are unreliable for these highly ductile polymers. In addition, it has been established with the same method of sampling and testing that the sheaths made according to the present invention have an elongation at break higher than those produced according to the prior art, especially in cases where the sheath has thickness greater than 15 mm, typically 20 mm, and where the tensile specimens are taken near the inner face. In these most severe cases, the elongation at break of the material according to the present invention may be more than twice that of the materials according to the prior art. In fact, 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 ~ o the thickness of the sheath is 20 mm, these elongations at break are respectively 200% and 50%. In addition, the two aforementioned solutions of the prior art lead to elongations at break of the same order of magnitude, the addition of a nucleating agent does not seem to have a significant effect on the mechanical properties of the sheath, particularly in case 1s thick sheaths. 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. Tests were also carried out, under conditions similar to those described above, with, on the one hand, the polypropylene / EPDM mixture with a nucleating agent without a nucleating agent and, on the other hand, the polypropylene / EPDM mixture with a compatilizing agent and with nucleating agent. When the thickness of the sheath is 20 mm, the elongations at break are then respectively 200% and 250%. Thus, the elongation at break of the material according to the invention, via the combination of a compatibilizing agent and a nucleating agent, is at least 250% in the thickness of the sheath, for thicknesses between 15 and 20 mm, which considerably improves the flexibility of the sheaths then made. In addition, it has been verified that the measurement of the thickness of elastomeric thermoplastic sheaths thus produced can be carried out accurately and reliably with conventional ultrasonic ultrasound non-destructive testing methods, which was not possible. always the case with the elastomeric thermoplastic polymer of the prior art. Indeed, in the case of sheaths of high thicknesses made according to the prior art, it was indeed difficult to obtain a reliable measurement of this thickness by these ultrasonic methods because the speed of propagation of 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 ultrasound is much more homogeneous in the thickness of the sheath, and on the other hand the ultrasonic attenuation is significantly reduced, so that 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 in 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 sold 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 mode of implementation of the invention, a tubular structure of umbilical type is produced. Also, we assemble an internal sealing tube, and electric cables. Said assembly is made by winding ~ o helical tubes and cables so that the umbilical is flexible. The assembly which then forms a sealed inner conduit is surrounded by an outer sealing sheath of elastomeric thermoplastic polymer 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); 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 polypropylene-based thermoplastic polymer (PP) and an ethylene-propylene-diene-monomer terpolymer elastomer (EPDM), and in addition a compatibilizing agent is 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. 25 2. Method according to claim 1, characterized in that provides 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 further provides a nucleating agent, and in that said nucleating agent, said compatibilizing agent, said polypropylene thermoplastic polymer and said elastomer are mixed together. based on ethylene-propylene-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 / or a dicarboxylate salt. 5. Process according to any one of Claims 1 to 4, characterized in that an elastomeric thermoplastic polymer comprising between 40% and 70% by weight of said thermoplastic polymer based on polypropylene is provided, between 10% and 20% by weight. weight of 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. 7. Method according to any one of claims 1 to 6, characterized in that said elastomeric thermoplastic polymer is obtained according to 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 thickness greater than 10 mm around said sealed inner conduit (18). 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 of determined thickness about 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 to increase during extrusion the miscibility of said polypropylene thermoplastic polymer and said ethylene-propylene-diene-monomer terpolymer elastomer, whereby the elongation at break of said sheath (20) is increased. Flexible tubular structure according to Claim 9, characterized in that the 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. 11. flexible tubular structure according to claim 9 or 10, characterized in that said elastomeric thermoplastic polymer comprises a ~ o nucleating agent for inducing a homogeneous distribution of crystallites according to said determined thickness. Flexible tubular structure according to claim 11, characterized in that said nucleating agent comprises a phosphate salt and / or a dicarboxylate salt. 15 Flexible tubular structure according to any one of claims 9 to 12, characterized in that said thermoplastic elastomer polymer comprises between 40% and 70% by weight of said thermoplastic polymer based on polypropylene, between 10% and 20% by weight of said ethylene-propylene-diene-monomer terpolymer-based elastomer, 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). Flexible tubular structure according to any one of claims 9 to 15, characterized in that said sealed internal conduit (12, 14, 16, 18) comprises from the inside towards the outside of said conduit, a polymeric sheath internal seal (12), reinforcing threads wrapped around said inner polymeric sheath sealing to form at least one reinforcing layer (14, 16, 18).