WO2012168671A1

WO2012168671A1 - Assembly and method for manufacturing a tubular sheath

Info

Publication number: WO2012168671A1
Application number: PCT/FR2012/051305
Authority: WO
Inventors: Michel Paul Morand
Original assignee: Technip France
Priority date: 2011-06-09
Filing date: 2012-06-11
Publication date: 2012-12-13
Also published as: FR2976210A1; FR2976209A1; FR2976210B1; FR2976209B1

Abstract

The invention relates to an assembly and method for manufacturing a tubular sheath, including an extrusion head (12) and screw (14). The latter includes a barrel (16) connected to said extrusion head (12) and a screw shaft (20) mounted inside said barrel (16), which has an input end (22) for receiving a mixture of a polymer material and flow additive, and an output end (26) connected to the extrusion head (12), while said screw shaft (20) has a free end (21) located near said output end (26), said screw shaft (20) being intended to drive said mixture, while said flow additive migrates towards said screw shaft (20). According to the invention, said screw shaft (20) includes an axial passageway (38) leading to the surface of said free end (21), so as to be capable of extracting the polymer material which is molten and in which the flow additive is concentrated.

Description

Assembly and method of manufacturing a tubular sheath

The present invention relates to an assembly and method for manufacturing a flexible tubular conduit for the transportation of offshore petroleum products.

Such flexible tubular pipes are particularly intended for offshore oil exploitation. These pipes can be immersed at great depths and must therefore withstand high pressures and voltages. They are notably described in the normative documents API 17J "Specification for Unbonded Flexible Pipe" and API RP17B "Recommended Practice for Flexible Pipe" prepared by the American Petroleum Institute.

The flexible tubular conduits usually comprise an internal pressure sheath of polymer material sealing against the transported fluid, and reinforcing layers surrounding the pressure sheath and

15 ensuring in particular the recovery of forces related to the pressure of the transported fluid and the axial tension applied to the pipe. The pipe may also comprise other tubular sheaths of polymeric material, including an outer protective sheath, and one or more intermediate sheaths surrounding the inner pressure sheath. The pressure sheath, the intermediate sheaths and the outer sheath are generally made by hot extrusion of a thermoplastic polymer material.

Known flexible tubular pipe assembly assemblies comprise a tubular sheath extrusion plant of polymeric material, and a metal wire wrapping plant around said tubular sheath. The extrusion plant comprises an extrusion head and an extrusion screw comprising a sleeve mounted at right angles to the extrusion head. The extrusion head has an annular chamber adapted to axially receive the pipe portion to be covered with a tubular sheath. It has an open downstream end and a closed upstream end having a radial inlet opening.

The extrusion screw also comprises a screw shaft rotatably mounted inside the sleeve and the latter has an inlet end surmounted by a hopper adapted to receive a mixture of polymer material and an end outlet capable of opening into the annular chamber. The screw shaft extends from the inlet end of the sleeve to the outlet end where it has a free end. In addition, the sheath is equipped with heating pads. Thus, is the polymer mixture driven from the inlet end of the sheath to the outlet end by means of the screw shaft, and as it is advanced it is brought to a molten state to finally be injected under pressure into the annular chamber. Inside the latter is formed a sleeve of molten polymer material, which sleeve is applied by cooling on the pipe portion to be covered as it moves in translation in the axis of the annular chamber .

It is constantly necessary to increase the mechanical and thermal performance of the tubular sheaths of subsea flexible pipes and to do this, polymer materials of increasingly high molecular weights are used. However, the higher the molecular weight of the materials, the higher their viscosity increases for a given temperature, and more particularly the extrusion temperature. And consequently, the mechanical means of transformation of these high-viscosity polymers require greater powers, in particular to increase the injection pressures, and therefore it is necessary to modify the production tools.

This difficulty of manufacture concerns in particular the pressure sheath of flexible pipes intended to convey hydrocarbons at high temperature, typically between 100 ° C. and 130 ° C., or even 150 ° C. and higher. Indeed, such sheaths are generally made with a high-viscosity polymer, for example PVDF ("Polyvinylidene Fluoride" in English) as described for example in US4706713 and EP1717271, or PPS ("Polyphenylenesulfide" in the language English) as described in WO2007 / 096589, or PEEK ("Polyetheretherketone" in English) as described in WO2008 / 119677.

However, it is possible to facilitate the extrusion of such materials by introducing into the polymer material a flow additive generally called "process additive" or "processing aid", which makes it possible to lower the viscosity apparent of the polymeric material and thereby lowering the injection pressure without reducing the productivity of the existing extrusion plant.

However, such a possibility induces negative effects, especially when the proportion of flow additive introduced represents more than 1% of the mass of the polymer material. Indeed, these flow additives that play a role at the interface between the melt polymer material and the walls along which it flows, can generate unacceptable defects in the tubular sheath of the flexible pipe.

Also, a problem that arises and that aims to solve the present invention is to provide, in a first object, a manufacturing assembly of a flexible tubular conduit for manufacturing pipes having a tubular sheath of high molecular weight polymer material , free from defects.

For this purpose, the present invention proposes a manufacturing assembly of a flexible tubular conduit comprising a tubular sheath extrusion installation of polymer material, and a winding installation of metal elements around said tubular sheath, said installation of extrusion comprising an extrusion head having an annular chamber and an extrusion screw comprising a sleeve connected at right angles to said extrusion head and a screw shaft mounted longitudinally rotatable within said sleeve, said annular chamber comprising an open downstream end and a closed upstream end having a radial inlet opening, said sheath having an inlet end for receiving a mixture of polymer material and flow additive and an outlet end opening into said opening; radial inlet, while said screw shaft has a free end located in the vicinity of said outlet end of said sheath, said screw shaft being intended to drive said mixture of polymer material and flow additive towards said outlet end, whereas said polymer is melt-connected between said two ends of said end-piece; sheath for injecting said polymer in the molten state through said radial inlet opening, while said flow additive migrates into the polymeric material to the surface of said screw shaft. According to the invention, said screw shaft comprises an axial passageway extending inside said screw shaft, said axial flow path opening at the surface of said free end so as to extract through said passageway the melt polymer material concentrated flow additive flowing to the surface of said free end of said screw shaft.

Thus, a feature of the invention lies in the implementation of an axial passage way in the screw shaft so as to extract at the surface of the free end of the screw shaft, the polymer material in the molten state concentrated in flow additive flowing therein. The flow additive is a material of low molecular weight immiscible in the polymeric material and which during the transformation of the polymer material, between the inlet end of the sheath and its outlet end, migrates in particular at the interface with the screw shaft so as to facilitate the flow inside the sheath. In this way, as the melt polymer material is driven towards the outlet end of the sheath, part of the flow additive radially reaches the screw shaft and the concentration of the polymer material in flow additive along the screw shaft is maximum at its free end, Also, through the axial flow path that opens to the surface of the free end, the polymer material concentrated in the additive d The flow flows through the axial passageway in the opposite direction to the driving of the polymer material inside the sheath. In this way, a fraction of the flow additive polymer material is extracted from the mass of polymeric material which will flow through the outlet end of the sleeve and then into the annular chamber. Therefore, this corresponding flow additive fraction which has served to promote the flow of molten polymer material along the screw shaft is recovered and will not then form aggregates or nodules in the thickness of the the tubular sheath formed. It is in fact these aggregates or nodules of polymer material concentrated in flow additive which escape from the free end of the screw shaft which then locally weaken the mass of polymer material of the sheath after it has been removed. has been extruded and cooled. It will be observed that the pressure of the polymer material in the molten state is such, at the free end of the screw shaft, for example a few hundred bars, that the flow through the axial passageway does not require any particular suction or pumping means.

According to a particularly advantageous embodiment of the invention, said surface of said free end has a cylindrical portion, and said axial flow path opens into said cylindrical portion. Thus, a fraction of the flow additive-concentrated polymer material, which flows in a longitudinal direction along the screw shaft, is extracted substantially radially from the free end surface of the screw shaft. to flow inside the axial passageway. As a result, this fraction of polymer material concentrated in flow additive is diverted to the axial flow path without causing excessive pressure losses within the sheath.

Advantageously, said free end has slots extending between said cylindrical surface portion and said axial passageway for

Opening said axial passageway in said cylindrical surface portion. And these slits are preferably uniformly distributed around the free end of the screw shaft, without weakening it, and so as to extract the concentrated polymer material uniformly around the screw shaft. Preferably, said slots are arranged inclined 0 with respect to said axial passageway. And more particularly, they are inclined towards the inlet end of the sleeve, so as to reduce the angle between the flow along the free end of the screw shaft and the direction of the slots to precisely promote the flow through the slits.

According to another mode of implementation, independently or in addition to the embodiment described above, said surface of said free end has a convex portion, and said passageway opens axially in said convex portion. Thus, the concentrated polymeric flow additive material flows longitudinally along the surface of the free end of the screw shaft, and then curves along the convex portion 0 to enter the opposite direction in the way of passage. This mode of implementation does not involve any additional pressure drop inside the sheath. Moreover, said screw shaft advantageously has a discharge end opposite said free end, for discharging said melt-polymer material concentrated into flow additive, while said sleeve further comprises an upstream portion located in upstream of said inlet end of said sleeve with respect to said outlet end, said discharge end extending inside said upstream portion of said sleeve. In this way, the discharge end is maintained in thermal conditions equivalent to those of the sheath and therefore, the polymer material concentrated in flow additive is kept in a molten state until the end of 'evacuation.

In addition, the installation further comprises a receptacle connected to said upstream portion of said sleeve for receiving said melt polymer material concentrated in flow additive. Advantageously, the installation also comprises a cooling device mounted between said portion

Upstream of said sheath and said receptacle for cooling said melt polymer material concentrated in flow additive. In this way, the polymeric material flows from the upstream portion to the receptacle inside which it settles and becomes solid again. It can then be evacuated for possible recycling.

According to a particularly advantageous embodiment of the invention, the annular chamber has a junction zone opposite to said radial inlet opening, and two channels which extend in opposite circular directions from said inlet opening. radial to said opposite junction zone. With the prior art extrusion plants, the aggregates or nodules tended to accumulate in the junction zone, thereby weakening the tubular sheath in the resealing portion. Thanks to the extrusion plant, the aggregates or nodules no longer accumulate in the junction zone, and the tubular sheath is then more resistant in the pipe.

According to another object, the present invention proposes a method of manufacturing a flexible tubular conduit of the type according to which extrusion step is extruded a tubular sheath of polymeric material, and metal elements are wound around said tubular sheath. , said step extrusion process comprising the following steps. First of all, an extrusion installation is provided comprising an extrusion head having an annular chamber and an extrusion screw comprising a sleeve connected at right angles to said extrusion head and a screw shaft mounted longitudinally to rotate at an angle of inside said sleeve, said sheath having an inlet end and an outlet end opening into said radial inlet opening, whereas said screw shaft has a free end located in the vicinity of said outlet end of said sheath, said chamber annulus comprising an open downstream end and a closed upstream end having a radial inlet opening. Then a mixture of polymeric material and flow additive is introduced into said inlet end, said screw shaft being adapted to drive said mixture of polymeric material and flow additive to said outlet end; and, said polymer is brought to the molten state between said two ends of said sleeve in order to be able to inject said polymer in the molten state through said radial inlet opening, whereas said flow additive migrates into the polymer material towards the surface of said screw shaft. According to the invention, there is provided a screw shaft having an axial flow path extending inside said screw shaft, said axial passage path opening on the surface of said free end, and is extracted through said path axial passage the concentrated melt polymer material into a flow additive flowing over the surface of said free end of said screw shaft.

Advantageously, a polymer material consisting of a homopolymer and / or a copolymer of vinylidene fluoride is provided.

Preferably, a polymer material based on polyetheretherketone, acronym PEEK, is provided.

Other features and advantages of the invention will become apparent on reading the following description of particular embodiments of the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which:

- Figure 1 is a schematic sectional view of a manufacturing assembly of a flexible tubular conduit according to the invention; - Figure 2 is a schematic axial sectional view of an element of the installation shown in Figure 1 according to a first embodiment;

Figure 3 is a schematic detail view of the element shown in Figure 2;

- Figure 4 is a schematic axial sectional view of a detail of an element of the installation shown in Figure 1 according to a second embodiment; and,

- Figure 5 and a schematic perspective view of a cutaway flexible tubular pipe according to the invention.

Figure 1 illustrates an extrusion installation 10 forming part of a flexible tubular pipe manufacturing assembly also comprising a not shown installation, winding of metal elements. According to the invention, the extrusion plant 10 has an extrusion head 12 to which is connected an extrusion screw 14. The extrusion head 12 is shown in cross-section while the extrusion screw is shown in axial section. Also, the extrusion screw 14 is connected at right angles to the extrusion head 12.

The extrusion screw 14 comprises a sleeve 16 surrounded by heating elements 18 in the form of a collar, and inside a screw shaft 20 mounted in rotation and having a free end 21. The sleeve 16 has an inlet end 22 surmounted by a feed hopper 24, and opposite an outlet end 26 connected to the extrusion head 12. The screw shaft 20 further has a receiving zone 23 located at the end of the end 22 of the sleeve 16. The extrusion screw 14 further comprises a drive device 28 installed upstream of the inlet end 22 relative to the outlet end 26 of the sleeve 16, having a motorization electrical 30 and a gear 32 so as to drive in rotation the screw shaft 20.

Thus, the feed hopper 24 is loaded with a polymer material in powder form or granules, so as to be able to feed the inlet end 22. The screw shaft 20 is rotated, while the packing heaters 18 are activated. In this way, the polymer material softens and is brought to the molten state as it is translated into the sleeve 16 towards the outlet end 26 and then injected under pressure into an annular chamber 34 of the extrusion head 12 through a radial inlet opening.

The extrusion head 12 comprises a mandrel and a head sleeve coaxially cap the mandrel forming, in the gap, the annular chamber 34 of generally frustoconical shape. The mandrel and the head sleeve are secured to one another at a base. The annular chamber has a circular closed upstream end located towards the base, where the head sleeve and the mandrel are connected together tightly, and an open downstream end extended by a constriction and terminated by two coaxial lips. The radial inlet opening is then formed radially in the closed upstream end.

The extrusion head 12 has an axial recess 36, located inside the mandrel, and adapted to be traversed by a tubular structure, for example a curved spiral section with a short pitch and stapled to form a carcass. There is thus formed around the carcass a sealing sheath.

The polymer materials used to form the tubular sheaths have increasingly high molecular weights. These are, for example, polymeric materials consisting of a homopolymer and / or a copolymer of vinylidene fluoride. Or again, these polymeric materials are based on polyetheretherketone. Also, it is necessary to mix them with a flow additive to allow the extrusion of the polymeric material through the extrusion plants as described above. Indeed, the higher the molecular weight of the polymers, the higher their viscosity at the extrusion temperature. Also, their apparent viscosity and frictional forces with the surfaces on which they flow by means of flow additives are reduced. These are compounds of low molecular weight which are immiscible with the polymeric material and which migrate in particular at the contact surface with the inner wall of the sheath 16 and the outer wall of the screw shaft 20,

When the polymeric material is mixed with the flow additive at a concentration of more than 1% by weight, defects may appear in the thickness of the tubular sheath formed in the extrusion head. Indeed, a part of the flow additive migrates into the polymer material towards the surface of the screw shaft 20 and tends to accumulate on the surface of the free end 21 of the screw shaft 20. Also, in the extreme, this polymeric material enriched in flow additive tends to form a new phase which causes the appearance of nodules or aggregates that escape the free end 21 and are injected inside the chamber annular 34 via the outlet end 26.

A characteristic of the invention shown in detail in FIG. 2 consists in providing an axial passageway 38 in the axis of the screw shaft 20 so as to be able to recover and extract this fraction of polymeric material enriched in additive flow so as to avoid the formation of these nodules or aggregates.

FIG. 2 shows the free end 21 of the screw shaft 20 and its receiving zone 23 opposite. The surface of the free end 21 has a cylindrical portion 37 with a substantially circular guide and a convex portion. 39 defining a mean plane substantially perpendicular to the axis of the screw shaft 40. Thus, when the extrusion plant 10 is in operation, the screw shaft 20 is rotated, while the material mixture polymer and flow additive flowing by gravity around the receiving zone 23 is driven in translation along the arrow F towards the free end 21. As the translational movement, the polymer material becomes softened to form a mass of molten polymeric material, while the flow additive partially migrates radially along the arrow R to the surface 40 of the screw shaft 20. In this way, a layer of material polymer enriched with additi flow flowing on the surface of the free end 21 of the screw shaft 20, and more precisely in a direction of the generatrices of the cylindrical portion 37, and then radially to the surface of the convex portion 39 to enter an inlet orifice 42 of the axial passageway 38.

FIG. 3 shows in more detail the free end 21 of the screw shaft 20 and its cylindrical portion 37 as well as its convex portion 39. The inlet orifice 42 opens axially into the convex portion 39 in a manner direction substantially perpendicular to the latter. In addition, the axial passageway 38 has a frustoconical widening 44 at the inlet orifice 42. In the vicinity of the free end 21 of the screw shaft 20, the pressure of the polymer material is relatively large, of the order of one hundred bar, such that the layer of polymeric material enriched in flow additive flowing over the surface of the free end 21 is naturally driven to the inlet port 42 of the passageway 38 which is in depression relative to the environment of the free end 21. In this way, the polymer material enriched with flow additive then escapes through the passageway 38 against the current relative to the molten polymer material flowing in the sleeve 16 along arrow F and around the screw shaft. It will be explained in the following description, how this polymer material enriched in flow additive is recovered.

According to a second variant embodiment illustrated in FIG. 4, on which there is found the free end 21 of the screw shaft 20, and where the other references of substantially identical elements are assigned a sign "", the path axial passage 38 'no longer opens axially in the convex portion 39' but radially in the cylindrical portion 37 'through slots 46 forming gills. These slots 46 are inclined relative to a cross section of the free end 21 of the screw shaft 20 opposite the convex portion 39 '. They have an inlet lip 48 opening into the surface of the cylindrical portion 37 'and an opposite outlet lip 50 opening into the axial passageway 38'. In addition, they are offset both in the axial direction of the screw shaft 20 and angularly around the axial flow path 38 'so as to be able to provide an inlet for the flow additive enriched polymer layer which is flows along the free end 21 over 360 °, while keeping this free end 21 in one piece. In this way, a fraction of this layer of polymer enriched in flow additive, and more precisely that which is in contact with the free end 21 of the screw shaft 20 and which is therefore the most concentrated in additive of flow, is driven along the arrow F to the outlet end 26 shown in Figure 1, and enters the inlet lips 48 and flows into the axial passageway 38 '. In this way, the rest of the layer The flow additive-enriched polymer, which by nature is less concentrated, leaves the free end 21, while the flow additive is diluted in the bulk of the molten polymer material. In this way, no aggregate or nodule is formed when the layer of polymeric material flowing on the surface of the free end 21 deviates to reach the outlet end 26 of the sheath 6,

Advantageously, the thickness of the slots, their number and their width are adjusted so as to collect a predefined percentage of mixture of polymer material and flow additive, for example between 1% and 10%, or more precisely between 2% and 5%. In this range, the tubular sheath formed has no defect due to aggregates of polymer material enriched in flow additive.

Furthermore, the screw shaft 20 of the extrusion plant 10 shown in FIG. 1 has a not shown discharge end located behind the drive device 28 of the extrusion screw 14 to discharge the polymer material. in the molten state concentrated in flow additive. Furthermore, the sleeve 16 extends behind the inlet end 22 and the drive device 28 around the aforementioned discharge end. This upstream portion of the sleeve 16 is also equipped with heating inserts so as to maintain the melt polymer material concentrated in temperature flow additive. The upstream portion opens into a receptacle that collects this polymeric material and between the upstream portion and the receptacle, a cooling device is installed so that the polymer material cools faster and returns to a solid form in the receptacle.

The present invention also relates to a method of manufacturing a flexible tubular pipe of the type in which the tubular sheath of polymer material is extruded by means of the extrusion installation 10 described above, and metal elements are wound around said tubular sheath through the winding installation of metal elements. As will be described in more detail below, with reference to FIG. 5, a short stitched wire is wound around the tubular sheath after it has been formed. To do this, the mixture of polymer material and flow additive is introduced into the inlet end 22, and is then melt between the two ends of the sleeve 16, while the shaft screw 20 causes the mixing of polymer material and flow additive to the outlet end 26. According to the invention, the melt polymer material concentrated in the additive is extracted through the axial flow path 38. flow. This portion of molten polymer material concentrated in flow additive then forms aggregates or nodules. In this way, these aggregates or nodules are extracted before being injected into the annular chamber, and consequently, the sealing sheath formed, for example around the carcass through which the axial recess passes, is devoid of it. This gives a sheath free of defects that would weaken.

Figure 5 partially illustrates a flexible tubular conduit 52 obtained through the manufacturing assembly object of the invention. This tubular pipe is a pipe intended specifically for the transport of hydrocarbons, and here it is devoid of internal carcass. It comprises, from the inside to the outside, a sealed inner pressure sheath 54 inside which is likely to circulate a hydrocarbon. This inner pressure sheath 54 is surrounded by an armor layer 56 formed of a short-pitch winding of a wire of stapled metal shape and intended to take up the internal pressure forces with the inner sheath 54. Around the armor layer 56, two traction armor plies 58 60 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 58, 60 wrapped around the armor layer 56, itself located around the inner pressure sheath 54, together constitute a sealed inner conduit. The flexible tubular conduit 52 finally has an outer protective sheath 62, intended to protect the reinforcement layers 58, 60 mentioned above.

Thus, the internal pressure sheath and tight 54 is directly achieved through the extrusion installation 10 described above, and then the armor is wound through the winding installation. As for the outer protective sheath 62, it is extruded directly on the inner conduit mentioned above, which comes through axial reversion 36 of the extrusion head

Claims

1. A flexible tubular pipe production assembly comprising an extrusion installation (10) of tubular sheath of polymer material, and a winding installation of metal elements around said tubular sheath, said extrusion installation comprising a extrusion head (12) having an annular chamber (34) and an extrusion screw (14) comprising a sleeve (16) connected at right angles to said extrusion head (12) and a screw shaft (20) mounted longitudinally rotatable within said sleeve (16), said annular chamber comprising an open downstream end and a closed upstream end having a radial inlet opening, said sleeve having an inlet end (22) for receiving a mixture of polymeric material and flow additive and an outlet end (26) opening into said radial inlet opening, while said screw shaft (20) has a free end (21) located e in the vicinity of said outlet end (26) of said sheath (16), said screw shaft (20) being adapted to drive said mixture of polymeric material and flow additive to said outlet end (26), while said polymer is melt between said two ends of said sleeve (16) to be able to inject said polymer in the molten state through said radial inlet opening, while said flow additive migrates into the polymer material to the surface of said screw shaft (20);

characterized in that said screw shaft (20) comprises an axial flow path (38) extending inside said screw shaft (20), said axial flow path (38) opening at the surface of said end free (21) so as to extract through said axial passageway (38) the melt-flow polymer material concentrated in flow additive which flows to the surface of said free end (21) of said flow shaft. screw (20).

2. Manufacturing assembly according to claim 1, characterized in that said surface of said free end (21) has a cylindrical portion

(37 '), and in that said axial passage path (38') opens into said cylindrical portion.

3. Manufacturing assembly according to claim 2, characterized in that said free end (21) has slots (46) extending between said cylindrical portion (37 ') of surface and said axial passageway (38') for flowing said axial passageway (38 ') into said cylindrical portion (37') of surface.

4. Manufacturing assembly according to claim 3, characterized in that said slots (46) are arranged inclined with respect to said axial passage path (38 ').

5. Manufacturing assembly according to any one of claims 1 to 4, characterized in that said surface of said free end (21) has a convex portion (39), and in that said axial passageway (38) opens axially in said convex portion (39).

6. Manufacturing assembly according to any one of claims 1 to 5, characterized in that said screw shaft (20) has a discharge end opposite said free end (21) for discharging said polymer material to the concentrated melt state in flow additive, while said sheath (16) further comprises an upstream portion located upstream of said inlet end (22) of said sheath with respect to said outlet end, said discharge end s extending inside said upstream portion of said sheath.

7. Manufacturing assembly according to claim 6, characterized in that it further comprises a receptacle connected to said upstream portion of said sleeve (16) for receiving said melt polymer material concentrated in flow additive.

8. Manufacturing assembly according to claim 7, characterized in that it comprises a cooling device mounted between said upstream portion of said sleeve (16) and said receptacle for cooling said melt polymer material concentrated in flow additive .

9. Manufacturing assembly according to any one of claims 1 to 8, characterized in that said annular chamber has a junction zone opposite to said radial inlet opening, and two channels which extend in opposite circular directions to from said radial inlet opening to said opposite junction zone.

10. A method of manufacturing a flexible tubular pipe of the type according to which extrusion step is extruded a tubular sheath of polymeric material, and metal elements are wound around said tubular sheath, said extrusion step comprising the steps following:

an extrusion installation is provided that includes an extrusion head

(12) having an annular chamber (34) and an extrusion screw (14) comprising a sleeve (16) angled to said extrusion head (12) and a screw shaft (20) longitudinally rotatably mounted to the inside of said sheath (16), said sheath having an inlet end (22) and an outlet end (26) opening into said radial inlet opening, whereas said screw shaft (20) has a free end (21) located in the vicinity of said outlet end (26) of said sheath (16), said annular chamber comprising an open downstream end and a closed upstream end having a radial inlet opening,

a mixture of polymer material and flow additive is introduced into said inlet end (22), said screw shaft (20) being intended to drive said mixture of polymer material and flow additive to said outlet end (26); and,

said polymer is brought to the molten state between said two ends of said sleeve (16) in order to be able to inject said polymer in the molten state through said radial inlet opening, whereas said flow additive migrates into the polymer material; to the surface of said screw shaft (20);

characterized by providing a screw shaft (20) having an axial passageway (38) extending within said screw shaft (20), said axial flowpath (38) opening to the surface of said free end (21), and in that through said axial flow path (38) is extracted the melt polymer material concentrated in flow additive which flows on the surface of said free end (21) of said screw shaft (20).

11. Method of manufacture according to claim 10, characterized in that a polymer material is provided consisting of a homopolymer and / or a copolymer of vinylidene fluoride.

12. Method of manufacture according to claim 10, characterized in that provides a polymeric material based on polyetheretherketone.