Flexible duct for conveying hydrocarbons and having a reinforced maintain layer

(54) Title: SUBMARINE FLEXIBLE CONDUCT (57) Summary:

FOR THE TRANSPORT OF

HYDROCARBONS.

(30) Unionist Priority: 3/21/2007 fr 0702065,

21/03/2007 FR 0702066 (73) Owner (s): Technip France (72) Inventor (s): Alain Coutarei, Anh Tuan Do, Patrice Joêl Louis Jung (74) Attorney (s): Momsen, Leonardos & Cia.

(86) International Application: PCT FR2008000383 of 21/03/2008 (87) International Publication: WO 2oos / i35663de 13/11/2008

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“SUBMARINE FLEXIBLE CONDUCT FOR HYDROCARBON TRANSPORT”

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

The flexible conduits for the transport of hydrocarbons are already well known, and they generally comprise from the inside to the outside of the conduit, a metal housing, an internal tightness sheath made of polymer, a pressure vault, traction reinforcement blankets and a sheath outer shell made of polymer to protect the duct assembly and notably to prevent sea water from penetrating its thickness. The metal housing and the pressure vault are made up of longitudinal elements rolled up with a short pitch, and they give the conduit its resistance to radial efforts while the tensile armor sheets are made up of metal wires wound in accordance with long steps to compensate for axial forces. The nature, number, dimensioning and organization of the layers that make up the flexible ducts are essentially linked to their conditions of use and installation. In the present application, the notion of short pitch winding designates any helical winding according to a helix angle close to 90 °, typically comprised between 75 ° and 90 °. The notion of winding with long pitch covers with respect to the helix angles below 55 °, typically between 25 ° and 55 °, for the reinforcement blankets.

These flexible conduits are intended for the transportation of hydrocarbons, notably on the seabed and this, at great depths. More precisely, they are said to be unbonded in English and they are described in the normative documents published by the American Petroleum Institute (API), API 17J and APIRP 17B.

When the flexible conduit, whatever its nature, is subjected to an external pressure that is greater than the internal pressure, an axial compression that is known to the professional can be produced under the name of reverse end effect cap effect ”in English). The inverse bottom effect tends to axially compress the flexible conduit, shorten its length and increase its diameter, which tends to cause inflation of the tensile reinforcement sheets. In the case where the external conduit sheath is watertight, the hydrostatic pressure that exists outside the conduit is effectively opposed to the inflation of the traction reinforcement. On the other hand, if the outer sheath is no longer watertight, for example as a result of accidental tearing, the hydrostatic pressure is no longer opposed to the inflation of the tensile reinforcement sheets. In the sequence, in the absence of an additional means that has the function of limiting this inflation, the wires that compose the traction reinforcement blankets can be buckled according to a radial mode, which can cause an irreversible local deformation of the said blankets. armor that is in the shape of a “bird cage”, and thus cause the conduit to collapse.

A known solution that reduces this risk of radial buckling in a “bird cage” consists of wrapping with a short pitch, around the blankets of traction armor, reinforced aramid fiber tapes, and more precisely fibers marketed under the brand Kevlar® DuPont de Nemours. Such tapes present a great mechanical resistance in traction according to their longitudinal axis, what allows to limit the inflation of the reinforcement sheets of traction. On the other hand, they have great flexibility in flexion, which facilitates the handling and winding operations around the reinforcement sheets. Finally, with equal mechanical characteristics, they are much lighter than metallic tapes, which allows to reduce the weight of the flexible conduit. It will be possible notably to refer to document FR 2 837 899 in which such a conduit is disclosed.

These reinforcement tapes are in the form of bundles of fiber strands or filamentary strands made of Kevlar® oriented parallel to the longitudinal axis of the tape. These strands of longitudinal fibers can be joined together in the form of a relatively flat bundle having a substantially rectangular section like that of a ribbon or strip. It is also possible to use a reinforcement strip consisting of a substantially rectangular central section and two thinner longitudinal edges than the central section as described in EP 1419338. The means of joining and containing these strands of fibers or filament strands, they generally comprise transverse elements which are shaped so as to encircle and tighten said wicks together to form a relatively flat bundle. In current configurations, these transverse elements are assimilable to weft threads, the filament strands forming the warp, and the ribbon can then be considered as a woven material. Different embodiments of these reinforcement tapes are described in WO97 / 12753 and WO9713091.

However, it was found nonetheless, that under extreme conditions of use, these reinforcement tapes could deteriorate. These extreme conditions are found mainly when the flexible conduit is on the one hand immersed in great depth, typically more than 2000 m, and on the other hand simultaneously subjected to dynamic stresses in flexion, which generates a fatigue phenomenon of the reinforcement tapes. These conditions can be gathered at the level of the lower part of the flexible risers (“flexible risers” in English) arranged in catenary, and that ensure the connection between the seabed and a support that floats on the surface. Due to movements of the floating support, the lower part of the catenary can be subjected to wide variations in curvature. In addition, this dynamic zone is located close to the point of contact with the seabed (“touch down point” in English), which means potentially at great depth.

Likewise, a problem that presents itself and that the present invention aims to solve is to provide a submarine flexible conduit that can withstand these extreme conditions of depth and dynamic stresses in flexion, and for which the inflation of the traction reinforcements can be contained durably for avoid radial buckling in “bird cage”.

In order to solve this problem, the present invention proposes a submarine flexible conduit for the transportation of hydrocarbons, said flexible conduit comprising, from the inside to the outside, an internal watertightness sheath, at least one layer of traction armatures wrapped around about said internal sealing sheath, a deformable retaining layer comprising at least one flexible retaining tape wrapped around said tensile reinforcement mat, and at least one tubular structure surrounding said retaining layer, said retaining tape comprising strands of fibers, said strands being oriented substantially according to the longitudinal direction of said retaining tape, and according to said invention retention tape is coated with a reinforcement layer made of polymeric material to increase the deformation resistance of said retention layer.

Thus, a feature of the invention resides in the use of the retention strip, and the reinforcing layer made of polymeric material, allowing joints increase the overall stiffness in bending of the retention strip coated and therefore, the resistance to deformation of the retention layer. In fact, it has been found that this characteristic allows to significantly increase the life span of the flexible conduit retention layer, when the latter is immersed in great depth and simultaneously subjected to dynamic bending stresses.

Long and thorough tests were necessary to understand the deterioration phenomena of the retention layer and to develop the present invention. These tests were technically difficult to perform, since it was necessary to test segments of flexible conduit in real size, simultaneously subjecting them to a very large external pressure and to variations in curvature.

This invention has a surprising character and goes against several prejudices of the professional. In fact, the latter naturally considered that the greater the depth, the greater the inverse bottom effect and, as a result, the more resilient the means must be designed to prevent inflation of the tensile armor sheets. Now, when the retention layer exerts its function of limiting the inflation of the tension reinforcement blankets, the retention tape is mainly requested in tension according to a direction substantially parallel to its longitudinal axis, that is to say of the fiber strands. As a result, the professional had previously sought to maximize the tensile strength of the retaining tapes. In addition, in order to facilitate the fabrication of the retaining layer, he had also sought to minimize the flexural rigidity of the retaining tape, which allowed the winding operation to be carried out with a low-power tape dispenser. Now, the present invention goes against these two practices, since the fact of covering the retaining tape with a reinforcement layer made of polymeric material leads on the one hand to a decrease in its mechanical strength in tension with an equal cross section ( increase in the section with an equal amount of fiber strands), and on the other hand to an increase in its flexural rigidity.

Thus, the reinforcement layer made of polymeric material increases the flexural stiffness of the retaining tape, which surprisingly limits the preceding phenomenon of fatigue.

The reinforcement layer made of polymeric material is advantageously made of polyamide, polyethylene or polypropylene or polyester; fluorinated polymers such as PVDFs may also suit. The adapted polymers are preferably thermoplastic polymers.

For the rest, the retaining tape is advantageously oriented so that the reinforcement layer is directly in contact with the reinforcement. Thus, the fibers of the wicks are preserved from wear by their friction against the reinforcement.

According to a special embodiment of the invention, said reinforcement layer and said retaining tape are at least partially interpenetrated in each other, in order to obtain a perfect cohesion of the reinforcement layer and the retaining tape. In this way, the mechanical properties of the retaining tape, in terms of tensile strength, are preserved so that the reinforcement layer is preserved from the tensile forces that are exerted on it, and that same reinforcement layer can then play its role stiffening the retaining tape.

Furthermore, said fibers have an elasticity modulus, preferably greater than 50 GPa, at room temperature. The modulus of elasticity is measured by a tensile test in accordance with ASTM D885-04. This test is done not on an individual fiber, but on a thread made up of 500 to 2500 identical fibers or filaments of the same length. The twist of the wire used for the test is less than 100 turns per meter and, for example, on the order of 60 turns per meter, which allows to improve the reproducibility and accuracy of measurements, in accordance with the recommendations of the standard mentioned. The distance between claws at the beginning of the tensile test is about 400 mm. The traction speed is of the order of 50 mm / min. The ambient temperature at which these tests are carried out is in the range of 18 ° C to 23 ° C.

As a result, thanks to this elasticity module, the fiber strands and therefore the coated retaining tape, compensate without stretching too much, the traction efforts that are exerted substantially tangentially to the retaining tape and prevent inflation of the blankets. armor. The fibers adapted for making such wicks are organic fibers, for example aramid fibers, or high performance polyethylene or polyester. Such fibers have, on the other hand, advantageously an elongation at break greater than 2%, for example 2.5%. The measurement of this elongation at rupture is performed by tensile testing in accordance with the ASTM D885-04 standard mentioned.

On the other hand, said fiber strands comprise core fibers surrounded by surface fibers, a portion of said surface fibers is advantageously embedded within said polymeric material of said reinforcement layer to bond said reinforcement layer and the said retaining tape. In this way, the reinforcement layer made of polymeric material adheres to the retention tape a lot more thanks to a mechanical bond by the fiber bonding than to a chemical bond. The polymeric material extends more or less deeply into the fiber and holds at least the surface fibers.

On the other hand, the retaining tape further comprises, and in a particularly advantageous manner, containment means for holding said strands of fibers together. For example, said retaining tape is a woven material and the containment means intended to hold together the different strands of fibers then comprise at least one weft yarn woven with said strands which themselves constitute the warp elements. Such weft yarns not being subjected to the tensioning stresses applied to the strip, can advantageously be made with a slightly resistant material different from that of the fiber wicks.

On the other hand, said fibers are held together, preferably pressed against each other, in order to increase their coefficient of friction in relation to each other and to increase the strength of the fiber strand in tension.

Advantageously, said retaining tape comprises two faces opposite each other, each of said faces is covered by said reinforcement layer, in order to further increase the rigidity of the flexing maintenance layer and also to preserve the retaining tape abrasion on both sides. In addition, and according to another embodiment, said reinforcement layer forms a sheath around said retaining tape, for this purpose and preserving it not only on the two opposite faces but also in thickness.

Moreover, the reinforcement layer is obtained by extruding said polymeric material. This reinforcement layer is then either directly extruded onto the retaining tape, or extruded independently and then adapted and calendered with the retaining tape. It will be explained in more detail, in the sequence of the description, how to carry out the reinforcement layer on the retaining tape.

Furthermore, advantageously, a textile layer, for example a textile layer that forms a mat, is interspersed between the fiber strands and the reinforcement layer. The term mat designates a membrane of short non-woven fibers, usually joined by mechanical compaction and / or gluing. In this way, the adhesion between the fiber strands and the reinforcement layer is improved.

Other particularities and advantages of the invention will be highlighted by reading the description made below of special embodiments of the invention, given as an indicative but not limiting title, with reference to the attached drawings in which:

Figure 1 is a partial schematic view in perspective of a flexible conduit according to the invention;

Figure 2 is a partial schematic view in perspective of an element of the flexible conduit shown in Figure 1;

- Figure 3 is a schematic view of an installation that allows the element shown in Figure 2 to be covered with a reinforcement layer;

- Figure 4 is a schematic view in straight section of the element partially shown in Figure 2 and coated, according to a first embodiment;

Figure 5 is a schematic cross-sectional view of the element partially shown in Figure 2 and coated, according to a second embodiment;

- Figure 6 is a schematic view in straight section of the element partially shown in Figure 2 and coated, according to a third embodiment; and

Figure 7 is a schematic cross-sectional view of the element partially shown in Figure 2 and coated, according to a fourth embodiment.

Figure 1 illustrates a conduit according to the invention comprising, from the outside to the inside, an external polymeric waterproofing sheath 10 (called an external sheath), a retention layer 12 which will be detailed below wrapped around an external blanket of traction armatures 14, an internal traction armature mat 16 rolled in the opposite direction of the outer mat 14, a pressure vault 20 to compensate for the radial stresses generated by the rush of the transported fluid, an internal polymeric sheath 18 and an internal housing 17 to compensate for radial crushing forces. Due to the presence of the internal carcass 17, this conduit is said to be a non-smooth passage (“rough bore” in English). The invention could also be applied to a so-called smooth bore conduit (“smooth bore” in English) that does not include an internal housing. Likewise, one would not leave the field of the present invention by suppressing the pressure vault 20, provided that the helix angles of the wires that constitute the reinforcement webs 14, 16 are close to 55 ° and in the opposite direction. Reinforcement webs 14, 16 are obtained by winding with a long pitch a set of wires made of metallic or composite material, of generally substantially rectangular section. The invention would also apply if these wires had a section of circular or complex geometry, of the type for example autogramped T. In Figure 1, only two reinforcement mats 14 and 16 are represented, but the conduit could also comprise one or more supplementary pairs of reinforcements. The armor sheet 14 is said to be external because it is the last one here, starting from the inside of the duct, before the external waterproofing sheath 10. The retaining layer 12 is generally wound around the outer mat 14, but the invention would also apply to the case of a retaining layer interspersed between two layers of tensile reinforcement. Such a configuration is disclosed in FR 2 837 899. The retaining layer 12 can be made up of several strips, small strips, retaining tapes or unitary elements rolled with a short pitch around the outer reinforcement mat 14. This winding is usually joined or covered so as to increase the ability to compensate for radial inflation efforts. The unitary elements of the retention layer present not only a great resistance in longitudinal traction, according to its longitudinal axis, but also a great flexural stiffness that increases the resistance to deformation of the retention layer.

Thus, the unitary retaining elements are made of appropriate materials, in this case on a retaining tape made of fibers, coated with a reinforcement layer made of polymeric material. The retaining tape is made by woven or non-woven joining of said fibers.

This retaining layer 12 is designed to block the radial expansion of said reinforcement mat when it is subjected to radial efforts. And this is the case when the flexible duct, extended on a deep seabed, is subjected to a large inverse bottom effect, and that the traction armor sheets 14, 16 tend to inflate radially under the effect of compression axial.

In order to realize this retention layer, a retention tape 22 shown partially in perspective in Figure 2 is provided. This retention tape 22 is suitable for extending longitudinally according to an axis A. Retention tape 22 comprises several wicks and in that case six strands 24 of fibers 26, the strands 24 being oriented longitudinally according to the A axis of the tape. The wicks 24 are thus constituted by the union of fibers 26, yarns or filaments made of a high tenacity organic material, of the aramid type, high performance polyethylene or aromatic polyester. Among the aramids, those sold under the brand Kevlar® by the company Du Pont de Nemours, and those sold under the brands Twaron® and Technora® by the company Teijin can be mentioned. Advantageously, Kevlar® 49 is chosen, whose fibers have an elasticity modulus of the order of 110 GPa measured according to the ASTM D885-04 standard mentioned. They are juxtaposed and held together by containment means 28 oriented transversely to the A axis of the retaining tape 22. These containment means may comprise strands surrounding the assembly, or weft threads woven with wicks 24, the latter then constituting the warp elements. The containment means do not have the function of compensating the longitudinal forces of traction, they can be made with less resistant polymers than those used for the wicks 24.

A method of carrying out, according to a first variant and thanks to an adapted installation, a retaining tape coated with a reinforcement layer made of polymeric material will be described below with reference to figure 3. In order to do this, a retaining tape 30 of the type specified is provided, with a width between 50 mm and 250 mm and for example here 75 mm, and with a thickness between 0.5 mm and 5 mm and for example 1 mm, and wound on a storage coil 32. The retaining tape 30 passes through a square extrusion head 34 in which it is coated with a reinforcement layer 35, and then passes through a calender 36 so that the retaining tape 30 and the reinforcement layer 35 interpenetrate one in the another; the retention tape 30 thus coated is then cooled in a heat exchanger 33 and finally wound on a receiving coil 40. The extrusion head 34 extends a die 42 which allows a polymeric material to be brought in the vicinity of a melting temperature. On the other hand, simultaneously, two intermediate layers formed by two fiber membranes 44, 46, or mats, supplied by rollers 48, 50, are applied over the two opposite faces of the retaining tape 30 before entering the extrusion head 34 .

The polymeric materials considered are preferably thermoplastic polymers whose tensile modulus is greater than 300 MPa. Advantageously, the tensile modulus of the polymer is on the other hand less than 3000 MPa, and preferably less than 1200 MPa. This range of modules between 300 MPa and 1200 MPa allows in practice to obtain a retaining tape that has sufficient flexural stiffness to solve the problem of fatigue, while avoiding excessive stiffness that would have an unfavorable effect. winding the said tape is difficult. Thus, polyamides, polypropylenes, polyethylenes, polyesters or fluorinated polymers of the PVDF type may be suitable. Among the polyamides, the following may apply: polyamide 11, polyamide 12, polyamide 6, polyamide 6-6, polyamide 613

12; is chosen here polyamide 11.

Thus, the melted polyamide is extruded around the retaining tape 30 and in particular on the two fiber membranes 44, 46 as it unfolds. In this way, the two fiber membranes 44, 46 made up of short non-woven fibers and joined by mechanical compaction and with a thickness comprised between 0.1 and 0.5 mm, allow to increase at the same time the impregnation of the melting polymer and the adhesion. In fact, the fiber membranes 44, 46 absorb the melting polyamide playing the role of blotter and consequently increase the impregnation of the fibers of the wicks. On the other hand, they also prevent the polymer from flowing into the core of the retaining tape 30. Thus, despite the pressure induced by the extrusion of the polymer around the retaining tape 30 and thanks to the absorption effect of the fiber membranes, the polymer in the melt precisely tends to uniformly cover the two opposite faces of the retaining tape 30. And then, the calendering through the calender 36, which exerts a normal pressure on the coated retaining tape, allows the viscous polymer in the cooling phase to penetrate slightly inside the retaining tape 30, so that afterwards, after cooling in the heat exchanger 38 , hold the fibers.

Reference will be made to Figure 4, which illustrates in straight section, the retaining tape 430 coated with reinforcement layer 435. In this Figure, the strands 424 of circular straight section and made up of fibers 426 are found. The retaining tape 430 has a original thickness 4E1 that corresponds substantially to the diameter of the strands 424 and the order of millimeter and a width 4L1 of about 75 mm. On the other hand, the two fiber membranes 444, 446, of a thickness 4E mat of about 0.2 mm, are applied on the two opposite faces of the retaining tape 430 and covered with the reinforcement layer 435 made of polyamide. Likewise, this reinforcement layer 435, of thickness 4E21 = 4E22, forms a sheath that also covers the thickness of the retaining tape 430. Preferably, the cumulative thickness of the reinforcement layer 435 on the two opposite faces of the retaining tape 430 is greater than one third of its thickness 4E1. Advantageously, this cumulative thickness 4E21 + 4E22 is greater than half of the thickness 4E1. This feature gives the retaining tape sufficient flexural stiffness to solve the aforementioned fatigue problem.

Fiber membranes are made up of short fibers of a few millimeters made of polymeric material such as that of fibers 426 of strands 424. Thus, when fibers 426 of strands 424 are, for example, made of Kevlar® 49, fiber membranes 444, 446 are made of aramid fibers.

On the other hand, still according to this first variant, but in another embodiment, the fiber membranes 444, 446 are previously fixed by stitching on the retaining tape 430. Thus, it is in no way necessary to employ both rolls 48, 50 shown in Figure 3 and which provide the fiber membranes. This frees you from the side feed guide in fiber membranes which is difficult to use simultaneously with the guide of the retaining tape 430.

Table I below illustrates the dimensions of examples of coated 430 retaining tape.

Table I

<td>4L1</td><td>50 mm</td><td>100 mm</td><td>200 mm</td>

<td>4L2</td><td>51 mm</td><td>102 mm</td><td>204 mm</td>

<td>4E1</td><td>0.5 mm</td><td>1 mm</td><td>2 mm</td>

<td>4E21</td><td>0.2 mm</td><td>0.2 mm</td><td>0.5 mm</td>

<td>4E22</td><td>0.2 mm</td><td>0.2 mm</td><td>0.5 mm</td>

<td>4E21 + 4E22</td><td>0.4 mm</td><td>0.4 mm</td><td>1 mm</td>

<td>4Treadmill</td><td>0.1 mm</td><td>0.1 mm</td><td>0.5 mm</td>

The thicknesses 4E21 and 4E22 of the reinforcement layer 435 on the two opposite faces of the retaining tape 430 are both advantageously between 0.2 mm and 2 mm, and preferably between 0.3 mm and 1.5 mm.

According to yet another embodiment, not shown, and according to this first variant, the two opposite thicknesses of the retaining tape 430 are free, and the two opposite faces are respectively covered by a fiber membrane and a layer reinforcement.

Reference will now be made to figure 5, which illustrates in straight section, a retaining tape 530 coated with a reinforcement layer 534 made of polymeric material and carried out by carrying out the method described in reference to Figure 3, according to a second variant. According to this second variant, fiber membranes are not applied between the reinforcement layer 535 and the strands 524 of the retaining tape 530. Thus, the reinforcement layer 535 also forms a flap around the retaining tape 530 and it is obtained by directly applying the extruded polymer on the retaining tape.

To do this, the temperature of the polymer extruded by the extrusion head 34 is adjusted so that its viscosity is substantially higher than that which is considered to coat a 530 retention tape covered with fiber membranes, such as illustrated in Figure 4, in order to prevent this polymer from flowing completely through the retaining tape 530, and in order that it can form a coherent layer on the surface. Of course, the nature of the polymeric material can also be adapted as a result.

Reference will now be made to Figure 6 which represents, in a straight section and according to a third embodiment, a retaining tape 630 coated with a reinforcement layer 635 on one side. Such a coated retention tape 630 is liable to be made according to the method described above with reference to the installation illustrated in Figure 3. However, said installation is modified substantially in such a way as to directly extrude the polymeric material intended to form reinforcement layer 635 directly on one side only of the retaining tape 630. On the other hand, it is necessary, as shown in Figure 6, for the polymeric material to flow slightly between the wicks 624 in order to impregnate a greater number of fibers 626 and also to provide means for containing the wicks 624, in order to obtain a better bonding of reinforcement layer 635 and retaining tape 630. In addition, the temperature of the extruded polymer is increased in order to decrease the viscosity of that polymer, so that it also penetrates inside the fibers 624 636. The mechanical connections between the reinforcement layer 635 and the retaining tape 630 will only be reinforced for this, after the polymer has cooled. The reinforcement layer 635 is centered on the retaining tape 630 and it extends in a width 6L2 substantially less than the width 6L1 of the retaining tape 630. Advantageously, the thickness 6E2 of the reinforcement layer 635 is greater than one third of the thickness 6E1 of the retaining tape 630 and preferably more than half. Thus, this thickness criterion, which indirectly conditions the overall inertia of the coated retention layer 630, therefore determines the flexural strength. On the other hand, the modulus of elasticity (Young's modulus) of the polymeric material, here polyamide 11, is greater than 300 MPa at room temperature.

However, according to a special embodiment, according to that third embodiment, it is provided to coat the two opposite faces of the retaining tape 630 with a reinforcement layer 635. In this way, the two opposite faces of the retaining tape retention 630 are likely to be preserved from friction wear. In addition, the 630 retaining tape has greater flexural rigidity and, as a result, greater resistance to fatigue.

According to a fourth embodiment illustrated in Figure 7, a retaining tape 730 consists of several overlapping layers and in this case two overlapping layers of strands 724 of fibers 726 joined together by appropriate containment means 728. Thus, the Mechanical tensile strength of the retaining tape 730 is increased in relation to the monolayer retaining tapes of the preceding embodiments.

Retention tape 730 is coated with a reinforcement layer 735 substantially similar to reinforcement layer 635 that covers the monolayer retention tape 630 shown in Figure 6.

On the other hand, advantageously, an anti-wear layer ("anti-wear layer" in English) made of polymeric material can be inserted between the outer layer of tensile reinforcement 14 and the retention layer 12. This solution allows to increase the life span of the retention layer 12, on the one hand suppressing the phenomenon of wear in contact with the metallic reinforcements, and on the other hand reducing the phenomenon of fatigue. The anti-wear layers, which are well known to the professional, are generally made by helically winding one or more tapes obtained by extruding a polymeric material based on polyamide, polyolefins, or PVDF ("polyvinylidene fluoride" in English). It will also be possible to refer to document W02006 / 120320 which describes anti-wear layers consisting of tapes made of polysulfone (PSU), polyethersulfone (PES), polyphenylsulfone (PPSU), polyetherimide (PEI), polytetrafluoroethylene (PTFE), polyetherethercetone (PEEK) or polysulfide phenylene (PPS). In the variants not shown in which a retaining layer is placed between the two layers of tension reinforcement 14, 16, it would be advantageous to insert two anti-wear layers in contact respectively with the inner and outer faces of this retaining layer, in order to prevent polymer fibers in this retention layer may be in direct contact with one of these two armor sheets.

As for the production methods for coated retention tapes, three other methods not shown can be used.

According to a first of the other methods of realization, and resuming the installation illustrated in Figure 3, the polymeric material is extruded directly into the retaining tape, on the two opposite surfaces, and then they are applied successively and in each of its two opposite faces, a fiber membrane and a film made of thermoplastic polyamide. The five-layer set is then calendered and then cooled. In this way, the fiber membranes are sandwiched between the extruded polymeric material, during hardening and the thermoplastic polyamide film; and when the set is hot-rolled, the polyamide film softens and, under the effect of the pressure exerted by the calender, it crosses at least partially the fiber membrane to reach the polymeric material. Thus, the polymeric material and the polyamide of the film tend to form a single phase and therefore hold the fiber membrane. This complex structure, allows to obtain a great flexural rigidity of the coated retention tape.

According to the second other embodiment, on each of the two opposite faces of the retaining tape, a fiber membrane and a film made of polyamide are successively applied, the whole being then hot rolled. In this way, through the calender and by means of an adapted regulation of the calendering temperature, the polyamide films soften to form a single phase that crosses the fiber membranes but also that flows through the fibers of the strands of the retaining tape. Such a method has the advantage of freeing itself from relatively expensive and bulky extrusion means.

According to the third other embodiment, the polymeric coating of the retaining tape is carried out by a process of laying thermoplastic powder followed by a hot calendering step. The tape previously charged with static electricity is first immersed in an enclosure containing a fluidized bed of fine polymer particles suspended in compressed air. During this stage, due to the attraction force due to electrostatic charges, the tape is coated with a layer of said fine particles. During the next step of hot calendering, the layer of fine polymeric particles is softened, melted and thus solidified with the fiber strands of the ribbon. This method also has the advantage of freeing itself from extrusion media.