Flexible pipe for conveying a fluid having a smooth inner surface, and associated manufacturing method

Abstract

The invention relates to a pipe having an inner sheath (20), which defines a fluid-circulation passage (16), and an inner casing (26), which is arranged in the inner sheath (20), the inner casing (26) comprising a first folded strip (31) defining a helical gap (40) made of a first material. The pipe comprises a helical insert (28) which inwardly seals the helical gap (40), the helical insert (28) comprising a second folded strip (48) made of a second material, the helical insert (28) having a radial region (44), which is arranged in the helical gap (40), and an axial inner region (46), which at least partly seals the helical gap (40). The second material has a yield strength which is lower than the yield strength of the first material, the ratio of the thickness of the second strip (48) to the inner diameter (DI) of the passage (16) being between 0.10% and 1%.

Description

[0001] DESCRIPTION

[0002] TITLE: Flexible fluid transport pipe having a smooth internal surface and associated manufacturing method

[0003] The present invention relates to a flexible fluid transport pipe, comprising:

[0004] - an internal polymer sheath delimiting a fluid circulation passage with a central axis, the fluid circulation passage having an internal diameter;

[0005] - at least one layer of armor arranged outside the internal sheath;

[0006] - an internal carcass, arranged in the internal sheath, the internal carcass comprising a first folded strip delimiting a helical gap opening towards the central axis, the first strip being formed from a first material;

[0007] - a helical insert closing the helical gap inwards, the helical insert comprising a second folded strip, formed from a second material, the helical insert having a section, taken in a median axial plane, comprising a radial region arranged in the helical gap and an axial inner region projecting from the radial region, the axial inner region at least partially closing the helical gap.

[0008] The pipeline is preferably an unbonded flexible pipeline intended for the transport of hydrocarbons across a body of water, such as an ocean, sea, lake or river.

[0009] Such a flexible pipe is for example produced according to the normative documents published by the American Petroleum Institute (API), API 17J, 4th edition - May 2014 and API RP 17B, 5th edition - May 2014.

[0010] The pipe is generally formed from a set of concentric and superimposed layers. It is considered to be “unbound” within the meaning of the present invention since at least one of the layers of the pipe is capable of moving longitudinally relative to the adjacent layers during bending of the pipe. In particular, an unbound pipe is a pipe devoid of binding materials connecting layers forming the pipe.

[0011] The pipeline is typically laid across a body of water, between a bottom assembly, intended to collect the fluid exploited in the bottom of the body of water and a floating or fixed surface assembly, intended to collect and distribute the fluid. The surface assembly may be a semi-submersible platform, an FPSO or another floating assembly.

[0012] In some cases, the flexible pipe comprises an internal carcass arranged inside the pressure sheath, in order to prevent the pressure sheath from being crushed under the effect of external pressure, for example during depressurization of the internal fluid circulation passage delimited by the pressure sheath.

[0013] The inner carcass is generally formed from a profiled metal strip, wound into a spiral. The turns of the strip are stapled together. The turns define a helical gap between them (referred to as "corrugation" in English). The gap opens radially inwards into the central fluid circulation passage.

[0014] The internal surface of the carcass therefore presents axially a succession of hollows and flats. The conduct is then generally described by the English term "rough bore".

[0015] In certain cases, particularly when transporting gas under pressure, the circulation of the fluid along the carcass is disturbed by the reliefs defined on the carcass by the helical gap.

[0016] This flow disturbance is sometimes considered to be the origin of vibration phenomena within the flexible pipe, or even, when resonance is reached, of pulsations induced by the circulation of fluid ("flow induced pulsations" or "singing" in English).

[0017] To overcome this problem, it is known to manufacture flexible pipes without an internal carcass and therefore having a smooth surface (“smooth bore” in English).

[0018] In the case where crush resistance is desired, it is also known to manufacture flexible pipes whose internal carcass has a smooth internal surface in that the helical interstices are obstructed by the addition of a structural element formed by a helical insert. An example of a pipe having a helical insert having an S-shaped section is disclosed in WO 2021 / 074192. In this example, an outer region of the insert section is anchored between two successive turns of the carcass in order to ensure the relative positioning between the insert and the carcass. Furthermore, WO 2021 / 074192 indicates that it is preferable for the carcass and the insert to be made from the same material.

[0019] However, such a ride is not entirely satisfactory. In fact, to meet the constraints of use and in particular crush resistance, the carcass must be made of a material which has high mechanical characteristics, in particular in terms of elasticity to ensure the rigidity of the ride.

[0020] During pipe manufacturing, the carcass and insert are spirally wound together. The helical insert inserted into the gaps in the carcass undergoes a bending step when the successive turns of the carcass are interlocked together. This bending and / or the differences in winding radius between different areas of the insert section (particularly between the free edge and the area anchored in the carcass) can generate high compressive stresses and lead to the appearance of local deformations at the insert level, typically buckling phenomena. A local radial deformation of the turns of the insert towards the axis of the pipe is then created.

[0021] This local phenomenon, once it has appeared, is also likely to propagate along the pipe, over significant lengths, for example during its manufacture or later when the pipe is in production, under the effect of movements of the pipe and / or under the effect of the internal pressure of the transported fluid and the external pressure exerted by the body of water in which the pipe is installed.

[0022] Furthermore, the radial buckling phenomenon is sometimes accompanied by the appearance of radial depressions along the circumference of the successive turns of the insert. It has been noted that this buckling phenomenon, possibly accompanied by radial depressions, occurs mainly during the manufacture of the pipe frame.

[0023] All these phenomena produce reliefs on the internal surface of the insert which can be problematic for the reduction of linear load losses and also in the elimination of vibrations and pulsations induced by the circulation of the fluid.

[0024] Furthermore, the presence of these undesirable reliefs makes it difficult, or even compromises, any possibility of controlling the integrity of the interior of the carcass during one-off inspection operations by "scraping" (or "pigging" in English).

[0025] An aim of the invention is therefore to produce, by simple and inexpensive means, a flexible pipe in which the risk of undesirable reliefs is limited, even in the case where the mechanical characteristics of the internal carcass are high.

[0026] To this end, the invention relates to a flexible pipe of the aforementioned type, characterized in that the second material has an elastic limit lower than the elastic limit of the first material, the ratio of the thickness of the second strip to the internal diameter being between 0.10% and 1%.

[0027] The flexible pipe according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination: - the ratio of the thickness of the second strip to the internal diameter is between 0.33% and 1%;

[0028] - the elastic limit of the second material is less than or equal to 350 MPa, the elastic limit of the first material being strictly greater than 350 MPa, in particular strictly greater than 400 MPa;

[0029] - the section of the helical insert (40) is L-shaped;

[0030] - the radial region of each L-shaped section defines a free edge of the helical insert, the free edge of the helical insert being freely disposed in the helical gap without being pinched by the internal carcass;

[0031] - the dropout potential difference between the first material and the second material is less than 0.2 V;

[0032] - the first material is chosen from a lightweight duplex steel, a duplex steel, a superduplex steel, a hyperduplex steel, an austenitic stainless steel which may be work-hardened, a super-austenitic steel or a nickel-based alloy;

[0033] - the second material is chosen from an austenitic stainless steel, a super-austenitic steel or a nickel-based alloy;

[0034] - the first material is chosen from a steel of grade UNS S32101, UNS S32205, UNS S32304 or UNS S32750, the second material being chosen from a steel of grade UNS 31600, UNS 31603, UNS S30400 or UNS S30403;

[0035] - the internal carcass comprises a plurality of stapled turns, each turn of the internal carcass having an inner part, an intermediate part, the inner part having a U shape folded towards the intermediate part and an outer part, the outer part having a U shape folded towards the intermediate part, the radial region of the helical insert being pressed against the intermediate part, the axial inner region of the helical insert advantageously projecting axially beyond the inner part;

[0036] - the ratio of the thickness of the second strip to the internal diameter is between 0.10% and 1%, in particular between 0.10% and 0.70%, in particular between 0.10% and 0.60% and in particular between 0.10% and 0.50%;

[0037] - the ratio of the thickness of the second strip to the internal diameter is between 0.10% and 0.40%, in particular between 0.10% and 0.35%, in particular between 0.15% and 0.30%, in particular between 0.15% and 0.25% and in particular between 0.15% and 0.22%;

[0038] - the ratio of the thickness of the second strip to the internal diameter is between 0.10% and 0.21%, in particular between 0.10% and 0.20% or between 0.26% and 0.33%, in particular between 0.27% and 0.33%. The invention also relates to a method for manufacturing a flexible pipe, comprising the following steps:

[0039] - formation of an internal carcass, the internal carcass comprising a first folded strip delimiting a helical gap opening towards the central axis, the first strip being formed from a first material;

[0040] - production of an internal polymer sheath delimiting a fluid circulation passage with a central axis, the fluid circulation passage having an internal diameter, the internal carcass being arranged in the internal sheath;

[0041] - provision of at least one layer of external armor outside the internal sheath;

[0042] - the method comprising placing a helical insert in the helical gap, the helical insert comprising a second folded strip formed from a second material;

[0043] - the helical insert having a section, taken in a median axial plane, comprising a radial region arranged in the helical gap and an axial inner region projecting from the radial region, the axial inner region at least partially closing the helical gap, characterized in that the second material has an elastic limit lower than the elastic limit of the first material, the ratio of the thickness of the second strip to the inner diameter being between 0.10% and 1%.

[0044] The method according to the invention may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:

[0045] - the section of the helical insert is L-shaped, the radial region of each L-shaped section defining a free edge of the helical insert, the method comprising freely arranging the free edge of the helical insert in the helical gap without being pinched by the internal carcass.

[0046] The invention will be better understood by reading the following description, given solely by way of example, and made with reference to the appended drawings, in which:

[0047] - [Fig.1] Figure 1 is a partially cutaway perspective view of a central section of a first flexible pipe according to the invention;

[0048] - [Fig. 2] Figure 2 is a partial view, taken in section along a median axial plane, of a detail of the pipe of Figure 1, illustrating the carcass and the insert arranged in the helical gap of the carcass;

[0049] - [Fig. 3] Figure 3 is a view of a detail of Figure 2, illustrating an L-shaped section of the insert; - [Fig.4] Figure 4 is a schematic view of an example of a station for manufacturing and installing the carcass and the insert;

[0050] - [Fig.5] Figure 5 is a schematic view of another example of a station for manufacturing and installing the carcass and the insert;

[0051] - [Fig.6] Figure 6 is a view similar to Figure 2 of a variant of flexible pipe according to the invention.

[0052] A first flexible pipe 10 according to the invention is partially illustrated in FIG. 1.

[0053] The flexible pipe 10 comprises a central section 12. It comprises, at each of the axial ends of the central section 12, an end piece (not visible).

[0054] With reference to Figure 1, the pipe 10 delimits a central passage 16 for circulation of a fluid, advantageously a petroleum fluid. The central passage 16 extends along a central axis A-A', between the upstream end and the downstream end of the pipe 10.

[0055] The flexible pipe 10 is intended to be arranged across a body of water (not shown) in a fluid exploitation installation, in particular hydrocarbons.

[0056] The body of water is, for example, a sea, a lake or an ocean. The depth of the body of water at the fluid exploitation facility is, for example, between 500 m and 4000 m.

[0057] The fluid exploitation installation comprises a surface assembly, in particular floating, and a bottom assembly (not shown) which are generally connected to each other by the flexible pipe 10.

[0058] The flexible conduit 10 is preferably an “unbonded” conduit.

[0059] At least two adjacent layers of the flexible pipe 10 are free to move longitudinally relative to each other during bending of the pipe. Advantageously, all the layers of the flexible pipe 10 are each free to move relative to each other.

[0060] Such conduct is for example described in the normative documents published by the American Petroleum Institute (API), API 17J, 4th edition - May 2014 and API RP 17B, 5th edition - May 2014.

[0061] Furthermore, in all that follows, the terms "exterior" and "interior" are generally understood to be radially relative to the central axis A-A' of the pipe, the term "exterior" being understood to be relatively further radially from the axis A-A' and the term "interior" extending as relatively closer radially to the axis A-A' of the pipe. As illustrated by FIG. 1, the pipe 10 delimits a plurality of concentric layers around the axis A-A', which extend continuously along the central section 12 to the end pieces located at the ends of the pipe.

[0062] According to the invention, the pipe 10 comprises at least one first tubular sheath 20 based on polymer material advantageously constituting a pressure sheath.

[0063] The pipe 10 further comprises at least one layer of tensile armor 24, 25 arranged externally relative to the first sheath 20 forming a pressure sheath.

[0064] The pipe 10 further comprises an internal carcass 26 arranged inside the pressure sheath 20, possibly a pressure vault 27 interposed between the pressure sheath 20 and the tensile armor layer(s) 24, 25, and an external sheath 30, intended for the protection of the pipe 10. The pipe 10 further comprises an insert 28 which in this example has an L-shaped cross-section, the insert 28 being arranged in internal support on the internal carcass 26.

[0065] In a known manner, the pressure sheath 20 is intended to confine in a sealed manner the fluid transported in the passage 16. The pressure sheath 20 is advantageously formed from a polymer material, for example based on a polyolefin such as polyethylene or polypropylene, based on a polyamide such as PA11 or PA12, or based on a fluorinated polymer such as polyvinylidene fluoride (PVDF).

[0066] Alternatively, the pressure sheath 20 is formed from a high-performance polymer such as a polyaryletherketone (PAEK) such as polyetherketone (PEK), polyetheretherketone (PEEK), polyetheretherketoneketone (PEEKK), polyetherketoneketone (PEKK) or polyetherketoneetherketoneketone (PEKEKK), polyamide-imide (PAI), polyether-imide (PEI), polysulfone (PSU), polyphenylsulfone (PPSU), polyethersulfone (PES), polyarylsulfone (PAS), polyphenyleneether (PPE), polyphenylene sulfide (PPS), liquid crystal polymers (LCP), polyphthalamide (PPA), fluorinated derivatives such as polytetrafluoroethylene (PTFE), perfluoropolyether (PFPE), perfluoroalkoxy (PFA) or ethylene chlorotrifloroethylene (ECTFE) and / or mixtures thereof.

[0067] The thickness of the pressure sheath 20 is for example between 5 mm and 20 mm.

[0068] With reference to Figure 2, the internal passage 16 delimited by the pressure sheath 20 has an internal diameter DI greater than 40 mm and generally between 50 mm and 600 mm. As illustrated by Figures 2 and 6, the carcass 26 is formed here from a first profiled metal strip 31, wound in a helix. The successive turns of the strip 31 are stapled to each other.

[0069] The main function of the carcass 26 is to absorb radial crushing forces. Radial crushing forces are, for example, the hydrostatic pressure of the body of water.

[0070] The carcass 26 is arranged inside the pressure sheath 20. It is capable of coming into contact with the fluid circulating in the central passage 16 delimited by the pressure sheath 20.

[0071] The first strip 31 is advantageously formed from a first material which is a steel or a nickel alloy. The first material has high mechanical characteristics, in particular an elastic limit strictly greater than 350 MPa (for example greater than 355 MPa), in particular strictly greater than 400 MPa, in particular between 410 MPa and 900 MPa.

[0072] The elastic limit YS is measured by the method described in Standard NF EN ISO 6892-1 (2019).

[0073] The first material is chosen from among lean duplex steels, duplex steels, superduplex steels and hyperduplex steels.

[0074] Examples of lightened duplex steels are grade 2101 (UNS S32101, YS = 480MPa), grade 2001 (UNS S32001, YS = 450MPa), grade 2202 (UNS S32202, YS = 550MPa), grade ATI2003 (UNS S32003, YS = 515MPa), grade 2304 FE08 (UNS S32304, YS = 450MPa), or grade 2404 (UNS S82441, YS = 640MPa).

[0075] Examples of duplex steel are grade 2205 (UNS S31803, YS = 450MPa), or grade 2205 H (UNS S32205, YS = 450MPa).

[0076] An example of superduplex steel is grade 2507 (UNS S32750, YS = 550MPa), and an example of hyperduplex steel is grade 3207 (UNS S33207, YS = 700MPa).

[0077] Alternatively, the first material is chosen from austenitic or super-austenitic stainless steels or work-hardened austenitic stainless steels, for example according to Standard EN 10088-2.

[0078] Examples of super-austenitic stainless steels are grade 4565 (UNS S32565, YS = 420MPa), or grade 654 SMO (UNS S32654, YS = 425MPa).

[0079] Examples of cold-worked austenitic stainless steels are grade 301 LN (UNS S30153, CW1 according to C850 Standard, YS = 552 MPa), grade 301 (UNS30100, CW1 according to C850 Standard, YS = 557 MPa, or CW2 according to C850+ Standard, Y = 660 MPa, or CW3 according to C1000 Standard, YS = 877 MPa) or grade 316L (UNS S31603, CW2 according to C850+ Standard, Y = 678 MPa, or CW3 according to C1000 Standard, YS = 895 MPa). Alternatively, the first material is an austenitic nickel alloy, for example Inconel® 625 (UNS N06625, YS= 414 MPa).

[0080] The helical winding of the first profiled strip 31 forming the carcass 26 has a short pitch, that is to say it has a helix angle of absolute value close to 90° relative to the central axis A-A', typically between 75° and 90°.

[0081] The first strip 31 has two edges folded longitudinally over a central region. It defines a plurality of stapled turns of closed and flattened S-shaped section, as illustrated in Figure 2 and Figure 6.

[0082] The first strip 31 has a substantially constant thickness e1.

[0083] The closed S-shaped section of each turn of the carcass 26 successively comprises, parallel to the axis A-A' from right to left in Figure 2, an inner part 32 in the general shape of a U, an inclined intermediate part 34 and an outer part 36 in the general shape of a U having, in the vicinity of its free end, a support wave 38, commonly designated by the term "nipple" or "hook" or "joint groove" in the technical field of the invention.

[0084] The inner part 32 of each turn of the first strip 31 is folded towards the intermediate part 34 away from the central axis A-A', externally with respect to the inclined part 34. It defines a U-shaped section extending parallel to the axis A-A' and opening opposite the inclined part 34.

[0085] The outer part 36 of an adjacent turn is partially engaged in the inner part 32, the support wave 38 being interposed between the branches of the U. The inner part 32 defines an inner surface 39 located on a cylindrical envelope of axis A-A'.

[0086] The outer portion 36 also defines a U-shaped section extending parallel to the axis A-A' and opening opposite the inclined portion 34.

[0087] The outer part 36 of each turn is folded towards the intermediate part 34, towards the central axis A-A', inwardly relative to the inclined part 34. The outer part 36 and the support wave 38 of the section are received in the inner part 32 of an adjacent section, and partially cover outwardly the inner part 32 of the adjacent section.

[0088] For each turn, the intermediate part 34, the outer part 36 and the inner part 32 of an adjacent section delimit an internal gap 40, partially or totally defining the axial play of the carcass 26.

[0089] The gap 40 opens radially towards the central axis A-A'. For each turn, it opens internally towards the axis A-A' between the inner surfaces 39 of the inner parts 32 of two adjacent turns. It is closed externally by the outer part 36 and laterally by the intermediate part 34 of a turn and by the inner part 32 of an adjacent turn.

[0090] The gap 40 thus extends continuously in the form of a helix with axis A-A' following a pitch P1 along the carcass 26.

[0091] The outer branch of the U of the inner part 32 of a turn is in direct contact with the outer branch of the U of the outer part 36 of an adjacent turn. The gap 40 is therefore closed laterally on one side by this contact.

[0092] Each turn of the carcass 26 has a width advantageously between 5 mm and 100 mm and preferably between 5 mm and 50 mm.

[0093] The carcass 26 has, between each pair of stapled turns, a first axial clearance defined by the axial travel of relative sliding of the outer part 36 of one turn in the inner part 32 of an adjacent turn in which it is engaged.

[0094] The insert 28 is partially disposed in the gap 40 and closes the gap 40 towards the axis A-A'.

[0095] The insert 28 thus advantageously has a helical shape with axis A-A', with pitch P1 similar to the pitch of the gap 40.

[0096] In the example illustrated by figure 3, the insert 28 has a section, taken in a median axial plane, in the general shape of an L.

[0097] The insert 28 is made in one piece by folding a second strip 48.

[0098] The second strip 48 is advantageously formed from a second material which is a steel or a nickel alloy. The second material has lower mechanical characteristics than the first material, in particular an elastic limit less than or equal to 350 MPa, in particular between 150 MPa and 350 MPa.

[0099] The elastic limit YS is measured by the method described in Standard NF EN ISO 6892-1 (2019).

[0100] The second material is, for example, chosen from austenitic or super-austenitic stainless steels.

[0101] Examples of austenitic stainless steels are grade 304 (UNS S30400, YS = 250MPa), grade 304L (UNS S30403, YS = 250MPa), grade 316 (UNS S31600, YS= 270MPa), grade 316L (UNS S31603, YS = 270 MPa) or grade 904L (UNS N08904, YS = 215MPa).

[0102] Examples of super-austenitic stainless steels are grade 926 (UNS N08926, YS = 295MPa), grade 254SMo (UNS S31254, YS = 310MPa), grade AL6XN (UNS N08367, YS = 310MPa), or grade 3127 hMo (UNS N08031, Y = 280MPa). Alternatively, the second material is selected from nickel alloys, in particular when the first material of the first strip 31 is formed from an austenitic nickel alloy.

[0103] Examples of austenitic nickel alloys are grade 825 (UNS N08825, YS = 180MPa), grade C276 (UNS N10276, YS = 350MPa), grade Alloy 59 (UNS N06059, YS = 340MPa), or grade C22 (UNS N06022, YS = 310MPa).

[0104] In an advantageous example, the first material forming the strip 31 of the carcass 26 is a duplex steel having an elastic limit strictly greater than 350 MPa. The second material forming the strip 48 of the insert 28 is an austenitic steel with an elastic limit less than 350 MPa.

[0105] In particular, the first material forming the strip 31 of the carcass 26 is a duplex steel of grade 2205 (UNS S31803). The second material forming the strip 48 of the insert 28 is an austenitic steel of grade 316L (UNS S31603).

[0106] Typically, the dropout potential difference between the first material and the second material is less than 0.2 Volts. This characteristic can be verified using a ZRA test (for "Zero Resistance Ammeter"). This test is for example according to ASTM G71-81 (2019) and ASTM G82-98 (2021) standards.

[0107] More generally, the second strip 48 advantageously has a constant thickness e2.

[0108] According to the invention, the ratio of the thickness e2 of the second strip to the internal diameter DI is between 0.10% and 1%, in particular between 0.10% and 0.70%, in particular between 0.10% and 0.60% and in particular between 0.10% and 0.50%. Advantageously, in particular between 0.10% and 0.40%, in particular between 0.10% and 0.35%, in particular between 0.15% and 0.30%, in particular between 0.15% and 0.25% and in particular between 0.15% and 0.22%.

[0109] Advantageously, the ratio of the thickness e2 of the second strip to the internal diameter DI is between 0.10% and 0.21%, in particular between 0.10% and 0.20% or between 0.26% and 0.33%, in particular between 0.27% and 0.33%.

[0110] The thickness e2 of the second strip 48 is preferably less than the thickness e1 of the first strip 31.

[0111] The thickness e2 is for example between 0.3 mm and 2 mm, in particular between 0.4 mm and 1.5 mm, preferably between 0.5 mm and 1 mm.

[0112] Indeed, surprisingly, the fact of associating a first material with higher mechanical characteristics to form the strip 31 of the carcass 26 with a second material with lower mechanical characteristics to form the strip 48 of the insert 28 and of respecting a certain ratio of the thickness e2 of the second strip to the internal diameter DI, is particularly suitable for preventing the appearance of local buckling phenomena of the insert 28 along the flexible pipe 10.

[0113] This beneficial effect with regard to the absence of the appearance of local buckling is reinforced by the L shape of the section of the insert 28 described in French patent FR 3 097 612.

[0114] Thus, a flexible pipe 10 according to the invention, even provided with an internal carcass 26 formed with materials with high mechanical characteristics (in particular with an elastic limit greater than 350 MPa) and an insert 28 closing the helical gap 40 of the internal carcass 26, presents fewer defects by reducing the risk of radial depression, local buckling of the insert 28 and the risk of them propagating.

[0115] The internal surface exposed to the fluid therefore remains smooth, which reduces linear pressure losses and eliminates the risk of vibrations and pulsations, and thus allows for the occasional inspection by pigging of the internal passage 16 of the flexible pipe 10.

[0116] It is therefore possible to expand the design scope of internal carcasses 26 to use materials with high characteristics, with larger internal diameters and lower carcass thicknesses, reducing the risk of insert buckling.

[0117] Furthermore, the combinations of first material and second material described above reduce the risk of galvanic corrosion.

[0118] As illustrated in FIG. 3, the insert 28 comprises a radial outer region 44 for anchoring in the gap 40 and an axial inner region 46 projecting from the radial region 44. The axial inner region 46 at least partially closes the gap 40. Advantageously, the axial inner region 46 completely closes the gap 40.

[0119] In this example, the radial region 44 comprises a curved outer section 50. It comprises a linear intermediate section 52, and a curved inner section 54 connecting with the inner region 46.

[0120] The outer section 50 here defines the outer free edge 51 of the insert 28 which is arranged in the helical gap 40.

[0121] The outer section 50, when present, has a convexity curvature directed outwards. The radius of curvature of the outer section 50 is advantageously greater than the thickness e2 of the second strip 48.

[0122] The outer section 50 projects axially relative to the intermediate section 52, opposite the axial inner region 46.

[0123] The length L1 of the outer section 50, taken in projection on the axis A-A', is very small in the example of figure 2. It remains small in the example of figure 6. This length L1 is for example less than 20%, in particular less than 10%, advantageously less than 5% of the length L2 of the axial inner region 46, taken in projection on the axis A-A'.

[0124] Furthermore, the length L1 of the outer section 50, taken in projection on the axis A-A' is less than or equal to 40% of the outer part 36 of the carcass 26.

[0125] Advantageously, the insert 28 and in particular its outer free edge 51, in particular the radial region 44 and the outer section 50 when it is present, are free to move in the gap 40 of the carcass.

[0126] The helical insert 28 is further capable of being disengaged from the carcass 26, without interference with the stapling of the turns of the carcass 26.

[0127] The outer free edge 51 and more generally the entire outer section 50 are located in the gap 40, and are therefore not engaged between the outer branch of the U of the inner part 32 of a section of the carcass 26 and the outer branch of the U of the outer part 36 of an adjacent section of the carcass 26.

[0128] The insert 28 is free to move axially and radially in the gap 40 of the carcass 26.

[0129] The short length L1 allows such an arrangement in which the insert 28 can move within the clearance 40 of the carcass.

[0130] The intermediate section 52 extends in an inclined manner relative to an axis perpendicular to the central axis A-A' while being located axially away from the interior region 46.

[0131] The inner section 54 has a curvature of convexity directed inwards, opposite the convexity of the curvature of the outer section 50. It has a radius of curvature greater than the radius of curvature of the outer section 50. Alternatively, the intermediate section 52 extends parallel to an axis perpendicular to the central axis A-A'.

[0132] The radial region 44 is disposed in the gap 40 between the intermediate portion 34 and the outer portion 36 of a turn of the carcass 26, and the inner portion 32 of an adjacent turn of the carcass 26.

[0133] The inner region 46 projects axially from the inner section 54 of the radial region 44.

[0134] The inner region 46 extends axially along the axis A-A', on a cylindrical envelope of axis A-A' or with an angle less than 10° relative to this envelope and preferably between 1° and 2.5°. Its section in a median axial plane extends linearly from the inner section 54 to its free edge 55. In section in a median axial plane, the inner region 46 preferably extends along a continuously derivable curve from the inner section 54 to its free edge 55, constituting the inner free edge 55 of the insert 28.

[0135] The length L2 of the inner region 46, taken in projection on the axis A-A', is greater than the length L4 of the radial region 44, taken in projection on the axis A-A'. Preferably, the length L2 is greater than 3 times, in particular 4 times, the length L4 and preferably greater than 6 times the length L4.

[0136] Furthermore, the length L2 of the inner region 46, taken along the axis A-A' is greater than the length L3 of the inner part 32, taken along the axis A-A'.

[0137] The radial extent ER of the radial region 44, taken perpendicular to the axis A-A', is less than the length of the axial interior region 46, taken in projection along the central axis A-A', in particular is less than 50% of the length of the axial interior region 46, taken in projection along the axis A-A'. Preferably, the length L2 of the axial interior region 46, taken in projection on the axis A-A' is equal to or greater than 5 times the radial extent ER of the radial region 44 taken perpendicular to the axis A-A'.

[0138] The radial extent ER of the radial region 44 is advantageously greater than or equal to 4 times the thickness e1 of the first strip 31.

[0139] With reference to Figure 2, the inner region 46 of each turn of the insert 28 comprises a first axial section 56 pressed against the inner surface 39 of the inner part 32 of a turn of the carcass 26, an intermediate axial section 58 closing inwards the gap 40 delimited by the inner part 32, and a second axial section 60 pressed against an inner surface of the inner region 46 of an adjacent turn of the insert 28, at the level of the first axial section 56 of this inner region 46.

[0140] The inner region 46 of each turn of the insert 28 is advantageously kept pressed against the inner surface of the inner region 46 of a turn of the insert 28, by the elastic return of the inner region 46 resulting from the spiraling of the carcass 26.

[0141] Thus, the successive turns of the insert 28 overlap each other by their interior regions 46, in order to close the gap 40 towards the inside.

[0142] The overlap width of each interior region 46, when the carcass 26 occupies an undeformed linear configuration, is greater than the axial clearance of the carcass 26.

[0143] The inner assembly formed by the carcass 26 and the insert 28 is permeable to the passage of fluid. This allows the pressures to be balanced on either side of this assembly. Such a configuration is therefore completely opposite to that of a completely sealed metal pipe as described in US 2002 / 195157 which aims to contain a fluid inside the pipe without fluid leakage.

[0144] With reference to figure 1, the pressure vault 27 is intended to take up the forces linked to the pressure prevailing inside the pressure sheath 20. It is for example formed of a profiled metal wire 25 wrapped in a helix around the sheath 20. The profiled wire 25 generally has a complex geometry, in particular in the shape of a Z, T, U, K, X or I.

[0145] The metallic material forming the profiled wire 25 is chosen from a carbon steel, in particular chosen from carbon steel grades comprising between 0.01% and 0.8% carbon. During applications in a particularly corrosive environment, the metallic material is chosen from austenitic or austenitic-ferritic stainless steels or from nickel-based alloys, such as duplex steels.

[0146] The pressure vault 27 is wound in a short-pitch helix around the pressure sheath 20, i.e. with a helix angle of absolute value close to 90° relative to the central axis A-A', typically between 75° and 90°.

[0147] The flexible pipe 10 optionally includes a collar (not shown).

[0148] The hoop, when present, is constituted by a spiral winding of at least one wire advantageously of rectangular cross-section around the pressure vault 27. The superposition of several wires wound around the pressure vault 27 can advantageously replace a given total hoop thickness. This increases the burst strength of the flexible pipe 10. The winding of the at least one wire is short-pitch around the axis A-A' of the flexible pipe 10, that is to say with a helix angle of absolute value close to 90° relative to the central axis A-A', typically between 75° and 90°.

[0149] In an alternative embodiment of the invention, the pressure vault 27 and the hoop are replaced by a pressure vault 27 of greater thickness formed from a profiled metal wire having a T-, U-, K-, X- or I-shaped geometry, and / or from at least one aramid strip with high mechanical strength (Technora® or Kevlar®), and / or from at least one composite strip comprising a thermoplastic matrix in which carbon fibers or glass fibers are embedded.

[0150] The flexible pipe 10 according to the invention comprises at least one layer of armor 24, 25 formed from a helical winding of at least one elongated armor element 63.

[0151] In the example shown in Figure 1, the flexible pipe 10 comprises a plurality of armor layers 24, 25, in particular an inner armor layer 24, applied to the pressure vault 27 and an outer armor layer 25 around which the outer sheath 30 is arranged. Each armor layer 24, 25 comprises longitudinal armor elements 63 wound at a long pitch around the axis A-A' of the pipe.

[0152] By "long pitch wound" we mean that the absolute value of the helix angle is less than 60°, and is typically between 10° and 60°, especially between 25° and 55°.

[0153] The armor elements 63 of a first layer 24 are generally wound at an opposite angle relative to the armor elements 63 of a second layer 25. Thus, if the winding angle of the armor elements 63 of the first layer 24 is equal to + a, a being between 10° and 60°, the winding angle of the armor elements 63 of the second armor layer 25 arranged in contact with the first armor layer 24 is for example equal to - a°.

[0154] The armor elements 63 are for example formed by metal wires, in particular steel wires, or by ribbons made of composite material, for example ribbons reinforced with carbon fibers.

[0155] The metallic material forming the armor elements 28 is chosen from a carbon steel, in particular chosen from carbon steel grades comprising between 0.01% and 0.8% carbon. During applications in a particularly corrosive environment, the metallic material is chosen from austenitic or austenitic-ferritic stainless steels or from nickel-based alloys, such as duplex steels.

[0156] In this example, each layer of tensile armor 24, 25 advantageously rests on at least one anti-wear strip (not shown). The anti-wear strip is for example made of plastic, in particular based on a polyamide or a polyvinylidene fluoride (PVDF). It has a thickness less than the thickness of each sheath.

[0157] Advantageously, a retaining tape such as a high mechanical strength aramid tape (Technora® or Kevlar®) is wound around the second outermost tensile armor layer 25 relative to the axis A-A', to ensure mechanical retention of the tensile armor layers 24, 25. Alternatively, the aramid fibers are replaced by glass fibers or carbon fibers.

[0158] The outer sheath 30 is intended to prevent the permeation of fluid from the outside of the flexible pipe 10 to the inside. It is advantageously made of a polymer material, in particular based on a polyolefin, such as polyethylene, or based on a polyamide, such as PA1 1 or PA12.

[0159] The thickness of the outer sheath 30 is for example between 5 mm and 15 mm.

[0160] The carcass 26 and the insert 28 are manufactured and are placed in place simultaneously in a manufacturing and installation station 70, examples of which are illustrated schematically respectively in Figures 4 and 5. In the example illustrated in Figure 4, the station 70 comprises a mandrel 72 rotating around an axis A-A', intended to guide the winding of the carcass 26 and the insert 28.

[0161] The station 70 comprises a support 73 rotating around the axis A-A' and relative to the mandrel 72, a first unwinder 74 (shown schematically) receiving the first strip 31, and a profiler of the strip of the carcass 76 arranged downstream of the first unwinder 74 between the first unwinder 74 and the mandrel 72.

[0162] The station 70 further comprises a second unwinder 78 (shown schematically) receiving the second strip 48. In the example of FIG. 4, the station 70 comprises a profiler for the strip of the insert 80, arranged downstream of the second unwinder 78 between the second unwinder 78 and the mandrel 72.

[0163] In this same example, station 70 includes a system 81 for joining the strips 31, 48 as they exit the profilers 76, 80.

[0164] The station 70 further comprises members 82 for radially pressing the carcass 26 and the insert 28 against the mandrel 72, and advantageously, return members 83 for guiding the first strip 31 and the second strip 48 from each unwinder 74, 78 towards a respective profiler 76, 80.

[0165] The rotating mandrel 72 projects axially relative to the support 73 along a winding axis A-A'.

[0166] It has an outer surface on which a first carcass profile 85, obtained from the first strip 31 deformed in the carcass profiler 76 and a second insert profile 87, obtained from the second strip 48 deformed in the insert profiler 80 are applied.

[0167] In this example, the rotating mandrel 72 further comprises an outer surface lubrication assembly.

[0168] The rotating mandrel 72 is capable of being driven in rotation around the axis A-A' with a speed and direction of rotation different from those of the support 73.

[0169] The support 73 comprises, for example, a plate driven in rotation around the axis A-A' in the direction of winding of the insert 28 and the carcass 26.

[0170] The support 73 carries the unwinders 74, 78, and the profilers 76, 80. In this example, the profilers 76, 80 are arranged diametrically on the same side relative to a median axial plane passing through the axis A-A'.

[0171] The profilers 76, 80 are for example located one on top of the other.

[0172] Each profiler 76, 80 comprises a plurality of pairs of rollers 100 for deforming the strip 31, 48, which define a respective axis B-B', C-C' for feeding the carcass 26 and the insert 28 onto the mandrel 72. The profilers 76, 80 are movable in translation on the support 73 in a plane perpendicular to the winding axis A-A'. The insert profiler 80 is capable of being pivoted about its axis C-C' to adjust the angle of introduction of the insert profile 87 into the joining system 81.

[0173] The joining system 81 advantageously comprises a profile guide 106 interposed between the insert profiler 80 and the mandrel 72. The profile guide 106 comprises means for guiding the insert 28 between, on the one hand, the downstream side of the insert profiler 80 and, on the other hand, the mandrel 72.

[0174] These guide means match the geometry of the insert 28 and comprise a set of guide rollers and / or one or more guide ramps having a low coefficient of friction.

[0175] The radial plating members 82 are arranged radially around the outer surface of the mandrel 72. They comprise, for example, knurled wheels suitable for being applied radially to the outside of the insert 28 and the carcass 26 to finalize the arrangement of the insert 28 in the helical gap 40, and the stapling of the carcass 26.

[0176] In a variant, to facilitate the release of the insert 28 and the carcass 26 away from the mandrel 72, the radial plating members 82 located on the mandrel 72 are capable of only partially closing the carcass 26. A specific mandrel (not shown), associated with additional plating members, is then provided downstream of the mandrel 72.

[0177] A method of manufacturing the flexible pipe 10 in the station 70 of FIG. 4 will now be described. Initially, the strips 31, 48 are loaded onto the unwinders 74, 78. Then, the strips 31, 48 are unwound to be introduced respectively into the profilers 76, 80. Simultaneously, the support 73 is rotated about the axis A-A'.

[0178] In the carcass profiler 76, the first strip 31 deforms successively to produce the first profile 85 comprising the inner part 32, the intermediate part 34 and the outer part 36, without completely closing the inner part 32 and the outer part 36.

[0179] In particular, the inner branch of the U of the outer part 36 remains partially open, as does the outer branch of the U of the inner part 32.

[0180] In the insert profiler 80, the second strip 48 is deformed and bent along an intermediate axis located away from the central axis of the strip 48 to form the radial region 44, and the inner region 46. The deformation continues by curving connecting sections 50, 54

[0181] A second profile 87 of L-shaped section comprising an axial inner region 46 and a radial region 44 is then obtained, to form the insert 28. According to a variant of the invention, the second strip 48 of the insert 28 is shaped in one operation, that is to say that the radial 44 and inner 46 regions as well as the connecting sections 50, 54 are created at the same time.

[0182] The second profile 87 is then guided by the profile guide 106.

[0183] Then, the second profile 87 is combined with the first profile 85 to form the carcass 26 according to the invention on the mandrel 72. The second profile 87 converges tangentially towards the mandrel 72 with a few degrees of advance angle relative to the first profile 85, for example between 8° and 12°.

[0184] A combined profile is formed and pressed against the outer surface of the mandrel 72 before being wound helically, at the desired pitch for insertion into the gap 40, thereby forming the insert 28 and the carcass 26.

[0185] Simultaneously, the partially open outer portion 36 of each turn of the first profile 85 is inserted into the inner portion 32 of an adjacent turn.

[0186] Furthermore, the inner region 46 of each turn of the second profile 87 is applied to the inner region 46 of an adjacent turn to close the gap 40 being formed.

[0187] The radial plating members 82 are then applied to the outside of the carcass 26 and the insert 28 to close and staple the carcass 26, while ensuring the internal wedging of the insert 28 in the helical gap 40.

[0188] The turns thus formed of the carcass 26 and the insert 28 gradually disengage downstream, detaching themselves from the mandrel 72 under the effect of the lubrication provided by the lubrication assembly, and of the rotation differential between the support 73 and the mandrel 72 tending to inflate the carcass 26.

[0189] Once the carcass 26 has been produced, and the insert 28 has been placed in the carcass 26, the inner sheath 20 is formed around the carcass 26, for example by extrusion. The pressure vault 27 and the armor layers 24, 25 are then wound around the inner sheath 20.

[0190] The outer sheath 30 is then advantageously produced by extrusion, being arranged outside the armor layers 24, 25.

[0191] The interior assembly formed by the carcass 26 and the insert 28 is permeable to the passage of fluid from the interior of the carcass 26 to the exterior of the carcass 26.

[0192] In a variant (not shown) of manufacturing and installation station 70, the profilers 76, 80 are arranged diametrically opposite one another, on either side of a median axial plane passing through the axis A-A'.

[0193] Figure 5 illustrates another variant of manufacturing and installation station 70.

[0194] In this example, the station 70 comprises a single profiling machine 76, intended to jointly profile the first strip 31 and the second strip 48. The first strip 31 is fed upstream into the profiling machine 76 to be partially deformed by upstream rollers 100, without deformation of the second strip 48. From the intermediate introduction of the second undeformed strip 48, transversely relative to the profiling machine 76, the first strip 31 and the second strip 48 are jointly deformed between the rollers 100 to form a combined profile 112.

[0195] The combined profile 112 is then wound onto the outer surface of the mandrel 72, as previously described.

[0196] In one variant (not shown), the insert has an S-shaped section, in particular an extended S-shaped section, as described in patent application WO2015 / 121424.

Claims

CLAIMS 1. Flexible fluid transport pipe (10), comprising: - an internal polymer sheath (20) delimiting a fluid circulation passage (16) with a central axis (A-A'), the fluid circulation passage (16) having an internal diameter (DI); - at least one layer of armor (24, 25) arranged outside the internal sheath (20); - an internal carcass (26), arranged in the internal sheath (20), the internal carcass (26) comprising a first folded strip (31) delimiting a helical gap (40) opening towards the central axis (A-A'), the first strip (31) being formed from a first material; - a helical insert (28) closing inwards the helical gap (40), the helical insert (28) comprising a second folded strip (48), formed of a second material, the helical insert (28) having a section, taken in a median axial plane, comprising a radial region (44) arranged in the helical gap (40) and an axial inner region (46) projecting from the radial region (44), the axial inner region (46) at least partially closing the helical gap (40), characterized in that the second material has an elastic limit (YS) lower than the elastic limit (YS) of the first material, the ratio of the thickness (e2) of the second strip (48) to the inner diameter (DI) being between 0.10% and 1%.

2. Pipe (10) according to claim 1, in which the ratio of the thickness (e2) of the second strip (48) to the internal diameter (DI) is between 0.33% and 1%.

3. Pipe (10) according to claim 1 or 2, in which the elastic limit (YS) of the second material is less than or equal to 350 MPa, the elastic limit (YS) of the first material being strictly greater than 350 MPa, in particular strictly greater than 400 MPa.

4. Conduit (10) according to any one of the preceding claims in which the section of the helical insert (40) is L-shaped.

5. A conduit (10) according to claim 4, wherein the radial region (44) of each L-shaped section defines a free edge (51) of the helical insert (40), the free edge (51) of the helical insert (40) being freely disposed in the helical gap (40) without being pinched by the inner casing (26).

6. A conduit (10) according to any preceding claim, wherein the dropout potential difference between the first material and the second material is less than 0.2 V.

7. Pipe (10) according to any one of the preceding claims, in which the first material is chosen from a lightened duplex steel, a duplex steel, a superduplex steel, a hyperduplex steel, an optionally work-hardened austenitic stainless steel, a super-austenitic steel or a nickel-based alloy.

8. A pipe (10) according to any preceding claim, wherein the second material is selected from an austenitic stainless steel, a super-austenitic steel or a nickel-based alloy.

9. Pipe (10) according to claims 7 and 8, in which the first material is chosen from a steel of grade UNS S32101, UNS S32205, UNS S32304 or UNS S32750, the second material being chosen from a steel of grade UNS 31600, UNS 31603, UNS S30400 or UNS S30403.

10. A pipe (10) according to any one of the preceding claims, wherein the inner carcass (26) comprises a plurality of stapled turns, each turn of the inner carcass (26) having an inner portion (32), an intermediate portion (34), the inner portion (32) having a U-shape folded towards the intermediate portion (34) and an outer portion (36), the outer portion (36) having a U-shape folded towards the intermediate portion (34), the radial region (44) of the helical insert (28) being pressed against the intermediate portion (34), the axial inner region (46) of the helical insert (28) advantageously projecting axially beyond the inner portion (32).

11. Method for manufacturing a flexible pipe (10), comprising the following steps: - formation of an internal carcass (26), the internal carcass (26) comprising a first folded strip (31) delimiting a helical gap (40) opening towards the central axis (A-A'), the first strip (31) being formed from a first material; - production of an internal sheath (20) made of polymer delimiting a fluid circulation passage (16) with a central axis (A-A'), the fluid circulation passage (16) having an internal diameter (DI), the internal carcass (26) being arranged in the internal sheath (20); - provision of at least one layer (24, 25) of external armor outside the internal sheath (20); the method comprising placing a helical insert (28) in the helical gap (40), the helical insert (28) comprising a second folded strip (48) formed of a second material, the helical insert (28) having a section, taken in a median axial plane, comprising a radial region (44) arranged in the helical gap (40) and an axial inner region (46) projecting from the radial region (44), the axial inner region (46) at least partially closing the helical gap (40), characterized in that the second material has an elastic limit (YS) lower than the elastic limit (YS) of the first material, the ratio of the thickness (e2) of the second strip (48) to the inner diameter (DI) being between 0.10% and 1%.

12. A method according to claim 11, wherein the section of the helical insert (40) is L-shaped, the radial region (44) of each L-shaped section defining a free edge (51) of the helical insert (28), the method comprising freely arranging the free edge (51) of the helical insert (28) in the helical gap (40) without being pinched by the inner carcass (26).

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