Flexible pipe for conveying a fluid having a smooth inner surface, and associated manufacturing method
Patent Information
- Application Number
- AU2025258223
- Authority / Receiving Office
- AU · AU
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-04-16
- Filing Date
- 2025-04-16
- Publication Date
- 2026-10-29
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The present invention relates to a flexible pipe for transporting fluid, comprising: - a polymer inner sheath delimiting a fluid circulation passage having a central axis, the fluid circulation passage having an inside diameter; - at least one armor layer arranged outside the inner sheath; - an internal carcass, arranged in the inner sheath, the internal carcass comprising a folded first strip delimiting a helical gap opening toward the central axis, the first strip being formed of a first material; - a helical insert closing off the helical gap toward the inside, the helical insert comprising a folded second strip, formed of 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 protruding from the radial region, the axial inner region at least partially closing off the helical gap. The pipe is preferably a flexible pipe of the unbonded type, intended for transporting hydrocarbons across a body of water, such as an ocean, a sea, a lake or a river. Such a flexible pipe is, for example, produced in accordance with the normative documents published by the American Petroleum Institute (API), API 17J, 4th edition - May 2014 and API RP 17B, 5th edition - May 2014. The pipe is generally formed of a set of concentric and superimposed layers. It is considered “unbonded” within the meaning of the present invention when 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 unbonded pipe is a pipe devoid of bonding materials connecting layers forming the pipe. The pipe is generally arranged across a body of water, between a bottom assembly, intended to collect the fluid extracted from 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 semisubmersible platform, an FPSO or another floating assembly. In certain cases, the flexible pipe comprises an internal carcass arranged inside the pressure sheath, in order to prevent the crushing of the pressure sheath under the effect of the external pressure, for example during depressurization of the internal fluid circulation passage delimited by the pressure sheath. The internal carcass is generally formed of a profiled metal strip, wound in a spiral. The turns of the strip are interlocked with one another. The turns delimit between them a helical gap (referred to by the term “corrugation”). The gap opens radially inward into the central fluid circulation passage. The internal surface of the carcass therefore presents axially a succession of recesses and flat portions. The pipe is then generally described by the term “rough bore”. In certain cases, particularly when transporting pressurized gas, the circulation of the fluid along the carcass is disturbed by the surface features defined on the carcass by the helical gap. This disturbance of the flow is sometimes considered to be the cause 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”). To overcome this problem, it is known to manufacture flexible pipes devoid of an internal carcass and therefore having a smooth surface (“smooth bore”). In cases where resistance to crushing is desired, it is also known to manufacture flexible pipes whose internal carcass has a smooth internal surface in that the helical gaps are obstructed by the addition of a structural element formed of a helical insert. An example of a pipe having a helical insert with an S-shaped section is disclosed in WO 2021 / 074192. In this example, an outer region of the section of the insert 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. Such a pipe is not, however, entirely satisfactory. Indeed, to meet the operating constraints and particularly the requirements for resistance to crushing, the carcass must be made with a material that has high mechanical properties, particularly in terms of elasticity to ensure the rigidity of the pipe. During manufacture of the pipe, the carcass and the insert are spirally wound together. The helical insert inserted into the gaps of the carcass undergoes a bending step when the successive turns of the carcass interlock with one another. This bending and / or the differences in winding radius between different zones of the section of the insert (particularly between the free edge and the zone anchored in the carcass) can generate high compressive stresses and lead to the appearance of local deformations in the insert, typically buckling phenomena. A local radial deformation of the turns of the insert toward the axis of the pipe is then created. This local phenomenon, once it has appeared, is furthermore liable 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. Moreover, 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 observed that this buckling phenomenon, possibly accompanied by radial depressions, occurs mainly during manufacture of the carcass of the pipe. All these phenomena produce surface features on the internal surface of the insert that may be problematic for reducing linear pressure losses and also for eliminating vibrations and pulsations induced by the circulation of the fluid. Furthermore, the presence of these undesirable surface features makes it difficult, or even compromises any possibility of checking the integrity of the inside of the carcass during occasional inspection operations by “pigging”. An aim of the invention is therefore to produce, by simple and inexpensive means, a flexible pipe in which the risk of undesirable surface features is limited, even in cases where the mechanical properties of the internal carcass are high. To this end, the invention relates to a flexible pipe of the aforementioned type, characterized in that the second material has a yield strength lower than the yield strength of the first material, the ratio of the thickness of the second strip to the inside diameter being between 0.10% and 1%. The flexible pipe according to the invention may comprise one or more of the following features, taken individually or in any technically possible combination: - the ratio of the thickness of the second strip to the inside diameter is between 0.33% and 1%; - the yield strength of the second material is less than or equal to 350 MPa, the yield strength of the first material being strictly greater than 350 MPa, particularly strictly greater than 400 MPa; - the section of the helical insert is L-shaped; - the radial region of each L-shaped section defines a free edge of the helical insert, the free edge of the helical insert being arranged freely in the helical gap without being pinched by the internal carcass; - the difference in open-circuit potential between the first material and the second material is less than 0.2 V; - the first material is selected from a lean 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; - the second material is selected from an austenitic stainless steel, a super-austenitic steel or a nickel-based alloy; - the first material is selected from a steel of UNS S32101, UNS S32205,UNS S32304 or UNS S32750 grade, the second material being selected from a steel of UNS 31600,UNS 31603, UNS S30400 or UNS S30403 grade; - the internal carcass comprises a plurality of interlocked turns, each turn of the internal carcass having an inner portion, an intermediate portion, the inner portion having a U shape folded toward the intermediate portion and an outer portion, the outer portion having a U shape folded toward the intermediate portion, the radial region of the helical insert being pressed against the intermediate portion, the axial inner region of the helical insert advantageously protruding axially beyond the inner portion; - the ratio of the thickness of the second strip to the inside 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%; - the ratio of the thickness of the second strip to the inside 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%; - the ratio of the thickness of the second strip to the inside 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: - forming an internal carcass, the internal carcass comprising a folded first strip delimiting a helical gap opening toward the central axis, the first strip being formed of a first material; - producing a polymer inner sheath delimiting a fluid circulation passage having a central axis, the fluid circulation passage having an inside diameter, the internal carcass being arranged in the inner sheath; - arranging at least one outer armor layer outside the inner sheath; - the method comprising placing a helical insert in the helical gap, the helical insert comprising a folded second strip formed of a second material; - the helical insert having a cross-section, taken in a median axial plane, comprising a radial region arranged in the helical gap and an axial inner region protruding from the radial region, the axial inner region at least partially closing off the helical gap, characterized in that the second material has a yield strength lower than the yield strength of the first material, the ratio of the thickness of the second strip to the inside diameter being between 0.10% and 1%. The method according to the invention may comprise one or more of the following features, taken individually or in any technically possible combination: - the cross-section of the helical insert is L-shaped, the radial region of each L-shaped crosssection 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. The invention will be better understood on reading the description that follows, given solely by way of example, and made with reference to the appended drawings, in which: - [Fig.1] Figure 1 is a partially cutaway perspective view of a central segment of a first flexible pipe according to the invention; - [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; - [Fig. 3] Figure 3 is a view of a detail of Figure 2, illustrating an L-shaped cross-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; - [Fig.5] Figure 5 is a schematic view of another example of a station for manufacturing and installing the carcass and the insert; - [Fig.6] Figure 6 is a view analogous to Figure 2 of a variant of a flexible pipe according to the invention. A first flexible pipe 10 according to the invention is partially illustrated by Figure 1. The flexible pipe 10 comprises a central segment 12. It comprises, at each of the axial ends of the central segment 12, an end fitting (not visible). 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. The flexible pipe 10 is intended to be arranged across a body of water (not shown) in a fluid production installation, in particular a hydrocarbon production installation. The body of water is, for example, a sea, a lake or an ocean. The depth of the body of water at the fluid production installation is, for example, between 500 m and 4000 m. The fluid production installation comprises a surface assembly, in particular a floating one, and a bottom assembly (not shown) which are generally connected to each other by the flexible pipe 10. The flexible pipe 10 is preferably an “unbonded” pipe. 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. Such a pipe is, for example, described in the standards documents published by the American Petroleum Institute (API), API 17J, 4th edition - May 2014 and API RP 17B, 5th edition -May 2014. Furthermore, in all that follows, the terms “outer” and “inner” are generally understood radially relative to the central axis A-A’ of the pipe, the term “outer” being understood as relatively farther radially from the axis A- A’ and the term “inner” extending as relatively closer radially to the axis A-A’ of the pipe. As illustrated by Figure 1, the pipe 10 defines a plurality of concentric layers around the A-A’ axis, which extend continuously along the central segment 12 to the end fittings located at the ends of the pipe. According to the invention, the pipe 10 comprises at least one first tubular sheath 20 based on polymer material advantageously constituting a pressure sheath. The pipe 10 further comprises at least one tensile armor layer 24, 25 arranged externally relative to the first sheath 20 forming a pressure sheath. The pipe 10 further comprises an internal carcass 26 arranged inside the pressure sheath 20, optionally a pressure vault 27 interposed between the pressure sheath 20 and the tensile armor layer or layers 24, 25, and an outer sheath 30, intended for protecting 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 bearing contact with the internal carcass 26. In a known manner, the pressure sheath 20 is intended to confine in a leak-tight manner the fluid transported in the passage 16. The pressure sheath 20 is advantageously formed of 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). Alternatively, the pressure sheath 20 is formed based on 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), polyphenylene ether (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. The thickness of the pressure sheath 20 is, for example, between 5 mm and 20 mm. With reference to Figure 2, the central passage 16 defined by the pressure sheath 20 has an inside diameter ID 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 profiled metal first strip 31, wound helically. The successive turns of the strip 31 are interlocked with one another. The main function of the carcass 26 is to withstand radial crushing forces. The radial crushing forces are, for example, the hydrostatic pressure of the body of water. 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 defined by the pressure sheath 20. The first strip 31 is advantageously formed from a first material that is a steel or a nickel alloy. The first material has high mechanical characteristics, in particular a yield strength strictly greater than 350 MPa (for example greater than 355 MPa), notably strictly greater than 400 MPa, in particular between 410 MPa and 900 MPa. The yield strength YS is measured by the method described in the NF EN ISO 6892-1 Standard (2019). The first material is notably selected from lean duplex steels, duplex steels, superduplex steels and hyperduplex steels. Examples of lean 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). Examples of duplex steel are grade 2205 (UNS S31803, YS = 450MPa), or grade 2205 H (UNS S32205, YS = 450MPa). 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). Alternatively, the first material is selected from austenitic or super-austenitic stainless steels or work-hardened austenitic stainless steels, for example according to the EN 10088-2 Standard. Examples of super-austenitic stainless steels are grade 4565 (UNS S32565, YS = 420MPa), or grade 654 SMO (UNS S32654, YS = 425MPa). Examples of work-hardened austenitic stainless steels are grade 301LN (UNS S30153, CW1 according to the C850 Standard, YS = 552MPa), grade 301 (UNS30100, CW1 according to the C850 Standard, YS = 557 MPa, or CW2 according to the C850+ Standard, Y = 660MPa, or CW3 according to the C1000 Standard, YS= 877MPa) or grade 316L (UNS S31603, CW2 according to the C850+ Standard, Y = 678MPa, or CW3 according to the C1000 Standard, YS= 895MPa). In a further alternative, the first material is an austenitic nickel alloy, for example inconel® 625 (UNS N06625, YS= 414 MPa). The helical winding of the profiled first strip 31 forming the carcass 26 is short-pitch, that is, it has a helix angle with an absolute value close to 90° relative to the central A-A’ axis, typically between 75° and 90°. The first strip 31 has two edges folded longitudinally over a central region. It defines a plurality of interlocked turns with a closed and flattened S-shaped cross section, as illustrated by Figure 2 and by Figure 6. The first strip 31 has a substantially constant thickness e1. The closed S-shaped cross section of each turn of the carcass 26 comprises successively, parallel to the A-A’ axis from right to left in Figure 2, an inner portion 32 of generally U shape, an inclined intermediate portion 34 and an outer portion 36 of generally U shape having, near its free end, a bearing wave 38, commonly referred to by the term “stud” or “hook” or “seal groove” in the technical field of the invention. The inner portion 32 of each turn of the first strip 31 is folded toward the intermediate portion 34 away from the central A-A’ axis, externally relative to the inclined portion 34. It defines a U-shaped cross section extending parallel to the A-A’ axis and opening toward the inclined portion 34. The outer portion 36 of an adjacent turn is partially engaged in the inner portion 32, the bearing wave 38 being interposed between the branches of the U. The inner portion 32 defines an inner surface 39 located on a cylindrical envelope having the A-A’ axis. The outer portion 36 also defines a U-shaped cross section extending parallel to the A-A’ axis and opening toward the inclined portion 34. The outer portion 36 of each turn is folded toward the intermediate portion 34, toward the central A-A’ axis, internally relative to the inclined portion 34. The outer portion 36 and the bearing wave 38 of the cross section are received in the inner portion 32 of an adjacent cross section, and partially cover, toward the outside, the inner portion 32 of the adjacent cross section. For each turn, the intermediate portion 34, the outer portion 36 and the inner portion 32 of an adjacent cross section delimit an inner gap 40, partially or totally defining the axial play of the carcass 26. The gap 40 opens radially toward the central A-A’ axis. For each turn, it opens internally toward the A-A’ axis between the inner surfaces 39 of the inner portions 32 of two adjacent turns. It is closed externally by the outer portion 36 and laterally by the intermediate portion 34 of one turn and by the inner portion 32 of an adjacent turn. The gap 40 thus extends continuously in the shape of a helix having an A-A’ axis with a pitch P1 along the carcass 26. The outer branch of the U of the inner portion 32 of one turn is in direct contact with the outer branch of the U of the outer portion 36 of an adjacent turn. The gap 40 is therefore closed laterally on one side by this contact. Each turn of the carcass 26 has a width advantageously between 5 mm and 100 mm and preferably between 5 mm and 50 mm. The carcass 26 has, between each pair of interlocked turns, a first axial clearance defined by the axial travel of relative sliding of the outer portion 36 of one turn in the inner portion 32 of an adjacent turn in which it is engaged. The insert 28 is arranged partially in the gap 40 and closes off the gap 40 toward the A-A’ axis. The insert 28 thus advantageously has a helical shape around the A-A’ axis, with a pitch P1 similar to the pitch of the gap 40. In the example illustrated by Figure 3, the insert 28 has a cross section, taken in a median axial plane, of generally L-shaped form. The insert 28 is made in one piece by folding a second strip 48. The second strip 48 is advantageously formed from a second material that is a steel or a nickel alloy. The second material has lower mechanical properties than the first material, in particular a yield strength less than or equal to 350 MPa, notably between 150 MPa and 350 MPa. The yield strength YS is measured by the method described in the NF EN ISO 6892-1 Standard (2019). The second material is, for example, selected from austenitic or super-austenitic stainless steels. 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). 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, notably when the first material of the first strip 31 is formed from an austenitic nickel alloy. 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). In an advantageous example, the first material forming the strip 31 of the carcass 26 is a duplex steel having a yield strength strictly greater than 350 MPa. The second material forming the strip 48 of the insert 28 is an austenitic steel having a yield strength less than 350 MPa. 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). Generally, the difference in open-circuit potential 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 the ASTM G71-81 (2019) and ASTM G82-98 (2021) Standards. More generally, the second strip 48 advantageously has a constant thickness e2. According to the invention, the ratio of the thickness e2 of the second strip to the inside diameter ID is between 0.10 % and 1%, notably between 0.10 % and 0.70%, notably between 0.10 % and 0.60 % and notably between 0.10 % and 0.50 %. Advantageously, notably between 0.10 % and 0.40 %, notably between 0.10 % and 0.35 %, notably between 0.15 % and 0.30 % notably between 0.15 % and 0.25 % and notably between 0.15 % and 0.22 %. Advantageously, the ratio of the thickness e2 of the second strip to the inside diameter ID is between 0.10 % and 0.21 %, notably between 0.10 % and 0.20% or between 0.26% and 0.33%, notably between 0.27% and 0.33%. The thickness e2 of the second strip 48 is preferably less than the thickness e1 of the first strip 31. The thickness e2 is, for example, between 0.3 mm and 2 mm, notably between 0.4 mm and 1.5 mm, preferably between 0.5 mm and 1 mm. Indeed, surprisingly, the fact of combining a first material having higher mechanical properties to form the strip 31 of the carcass 26 with a second material having lower mechanical properties to form the strip 48 of the insert 28 and of observing a certain ratio of the thickness e2 of the second strip to the inside diameter ID is particularly suited to preventing the occurrence of local buckling phenomena of the insert 28 along the flexible pipe 10. This beneficial effect with respect to the absence of occurrence of local buckling is reinforced by the L shape of the cross section of the insert 28 described in French patent FR 3 097 612. Thus, a flexible pipe 10 according to the invention, even provided with an internal carcass 26 formed with materials having high mechanical properties (notably a yield strength greater than 350MPa) and an insert 28 closing off the helical gap of the internal carcass 26 exhibits fewer defects by reducing the risk of radial depression, of local buckling of the insert 28 and the risk that they propagate. 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 occasional inspection by pigging of the internal passage 16 of the flexible pipe 10. It is therefore possible to broaden the design range of internal carcasses 26 to use materials having high properties, with larger inside diameters and smaller carcass thicknesses while reducing the risk of buckling of the insert. Furthermore, the combinations of first material and second material described above reduce the risk of galvanic corrosion. As illustrated by Figure 3, the insert 28 comprises an outer radial region 44 for anchoring in the gap 40 and an axial inner region 46 protruding from the radial region 44. The axial inner region 46 at least partially closes off the gap 40. Advantageously, the axial inner region 46 completely closes off the gap 40. The radial region 44 comprises, in this example, a curved outer segment 50. It comprises a linear intermediate segment 52, and a curved inner segment 54 connecting to the inner region 46. The outer segment 50 here defines the outer free edge 51 of the insert 28 that is arranged in the helical gap 40. The outer segment 50, when present, has a curvature with a convexity directed outward. The radius of curvature of the outer segment 50 is advantageously greater than the thickness e2 of the second strip 48. The outer segment 50 protrudes axially relative to the intermediate segment 52, opposite to the axial inner region 46. The length L1 of the outer segment 50, taken in projection onto the A-A’ axis, 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 onto the A-A’ axis. Furthermore, the length L1 of the outer segment 50, taken in projection onto the A-A’ axis, is less than or equal to 40% of the outer portion 36 of the carcass 26. Advantageously, the insert 28 and in particular its outer free edge 51, especially the radial region 44 and the outer segment 50 when present, are free to move in the gap 40 of the carcass. The helical insert 28 is furthermore capable of being disengaged from the carcass 26, without interference with the interlocking of the turns of the carcass 26. The outer free edge 51 and, more generally, the entire outer segment 50 are located in the gap 40, and are therefore not engaged between the outer branch of the U of the inner portion 32 of a section of the carcass 26 and the outer branch of the U of the outer portion 36 of an adjacent section of the carcass 26. The insert 28 is free to move axially and radially in the gap 40 of the carcass 26. The small length L1 allows such an arrangement in which the insert 28 can move within the clearance 40 of the carcass. The intermediate segment 52 extends at an incline relative to an axis perpendicular to the central A-A’ axis while being located axially away from the inner region 46. The inner segment 54 has a curvature with a convexity directed inward, opposite to the convexity of the curvature of the outer segment 50. It has a radius of curvature greater than the radius of curvature of the outer segment 50. Alternatively, the intermediate segment 52 extends parallel to an axis perpendicular to the central A-A’ axis. The radial region 44 is arranged 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. The inner region 46 protrudes axially from the inner segment 54 of the radial region 44. The inner region 46 extends axially along the A-A’ axis, on a cylindrical envelope having the A-A’ axis or at an angle of 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 segment 54 to its free edge 55. In section in a median axial plane, the inner region 46 preferably extends along a continuously differentiable curve from the inner segment 54 to its free edge 55, constituting the inner free edge 55 of the insert 28. The length L2 of the inner region 46, taken in projection onto the A-A’ axis, is greater than the length L4 of the radial region 44, taken in projection onto the A-A’ axis. Preferably, the length L2 is greater than 3 times, in particular than 4 times the length L4 and preferably greater than 6 times the length L4. Furthermore, the length L2 of the inner region 46, taken along the A-A’ axis, is greater than the length L3 of the inner portion 32, taken along the A-A’ axis. The radial extent ER of the radial region 44, taken perpendicular to the A- A’ axis, is less than the length of the axial inner region 46, taken in projection along the central A-A’ axis, in particular is less than 50% of the length of the axial inner region 46, taken in projection along the A-A’ axis. Preferably, the length L2 of the axial inner region 46, taken in projection onto the A-A’ axis, is equal to or greater than 5 times the radial extent ER of the radial region 44 taken perpendicular to the A-A’ axis. 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. With reference to Figure 2, the inner region 46 of each turn of the insert 28 comprises a first axial segment 56 pressed against the inner surface 39 of the inner portion 32 of a turn of the carcass 26, an intermediate axial segment 58 closing off toward the inside the gap 40 delimited by the inner portion 32, and a second axial segment 60 pressed against an inner surface of the inner region 46 of an adjacent turn of the insert 28, at the first axial segment 56 of this inner region 46. 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 helical winding of the carcass 26. Thus, the successive turns of the insert 28 overlap one another by their inner regions 46, in order to close off the gap 40 toward the inside. The overlap width of each inner region 46, when the carcass 26 occupies an undeformed linear configuration, is greater than the axial clearance of the carcass 26. The inner assembly formed by the carcass 26 and the insert 28 is permeable to the passage of fluid. This allows the balancing of pressures on either side of this assembly. Such a configuration is therefore completely opposite to that of a completely leak-tight metal pipe as described in US 2002 / 195157, which aims to contain a fluid inside the pipe without fluid leakage. With reference to Figure 1, the pressure vault 27 is intended to withstand the forces associated with the pressure prevailing inside the pressure sheath 20. It is, for example, formed from a profiled metal wire 25 wound helically around the sheath 20. The profiled wire 25 generally has a complex geometry, in particular in the shape of a Z, a T, a U, a K, an X or an I. The metal material forming the profiled wire 25 is selected from carbon steel, in particular selected from carbon steel grades comprising between 0.01% and 0.8% carbon. In applications in a particularly corrosive environment, the metal material is selected from austenitic or austenitic-ferritic stainless steels or from nickel-based alloys, such as duplex steels. The pressure vault 27 is wound helically with a short pitch around the pressure sheath 20, that is to say, with a helix angle having an absolute value close to 90° relative to the central A-A’ axis, typically between 75° and 90°. The flexible pipe optionally comprises a hoop reinforcement (not shown). The hoop reinforcement, when present, consists of 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 thickness of hoop reinforcement. This increases the burst resistance of the flexible pipe 10. The winding of the at least one wire has a short pitch around the A-A’ axis of the flexible pipe 10, that is to say, with a helix angle having an absolute value close to 90° relative to the central A-A’ axis, typically between 75° and 90°. In an embodiment variant of the invention, the pressure vault 27 and the hoop reinforcement are replaced by a pressure vault 27 of greater thickness formed from a profiled metal wire having a geometry in the shape of a T, a U, a K, an X or an I, and / or from at least one high-mechanical-strength aramid tape (Technora® or Kevlar®), and / or from at least one composite tape comprising a thermoplastic matrix in which carbon fibers or glass fibers are embedded. The flexible pipe 10 according to the invention comprises at least one armor layer 24, formed by a helical winding of at least one elongated armor element 63. 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 A-A’ axis of the pipe. By “wound at a long pitch”, it is meant that the absolute value of the helix angle is less than 60°, and is typically between 10° and 60°, in particular between 25° and 55°. 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°. The armor elements 63 are, for example, formed by metal wires, in particular steel wires, or by strips of composite material, for example strips reinforced with carbon fibers. The metallic material forming the armor elements 28 is selected from carbon steel, in particular selected from carbon steel grades comprising between 0.01 % and 0.8% carbon. For applications in a particularly corrosive environment, the metallic material is selected from austenitic or austenitic-ferritic stainless steels or from nickel-based alloys, such as duplex steels. In this example, each tensile armor layer 24, 25 advantageously rests on at least one antiwear tape (not shown). The anti-wear tape 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. Advantageously, a retaining tape such as a high-mechanical-strength aramid tape (Technora® or Kevlar®) is wound around the second tensile armor layer that is outermost relative to the A-A’ axis, to mechanically retain the tensile armor layers 24, 25. Alternatively, the aramid fibers are replaced by glass fibers or carbon fibers. The outer sheath 30 is intended to prevent fluid permeation from the outside of the flexible pipe 10 toward 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 PA11 or PA12 The thickness of the outer sheath 30 is, for example, between 5 mm and 15 mm. The carcass 26 and the insert 28 are manufactured and are put in place simultaneously in a manufacturing and installing station 70, examples of which are illustrated schematically by Figures 4 and 5, respectively. In the example illustrated in Figure 4, the station 70 comprises a mandrel 72 rotatable about an A-A’ axis, intended to guide the winding of the carcass 26 and the insert 28. The station 70 comprises a support 73 rotatable about the A-A’ axis and relative to the mandrel 72, a first unwinder 74 (shown schematically) receiving the first strip 31, and a carcass strip profiling machine 76 arranged downstream of the first unwinder 74 between the first unwinder 74 and the mandrel 72. The station 70 further comprises a second unwinder 78 (shown schematically) receiving the second strip 48. In the example of Figure 4, the station 70 comprises an insert strip profiling machine 80, arranged downstream of the second unwinder 78 between the second unwinder 78 and the mandrel 72. In this same example, the station 70 comprises a system 81 for bringing together the strips 31, 48 at their exit from the profiling machines 76, 80. The station 70 further comprises members 82 for radially pressing the carcass 26 and the insert 28 against the mandrel 72, and advantageously, deflection members 83 for guiding the first strip 31 and the second strip 48 from each unwinder 74, 78 toward a respective profiling machine 76, 80. The rotating mandrel 72 protrudes axially relative to the support 73 along an A-A’ winding axis. It has an outer surface on which a first carcass profile 85, obtained from the first strip 31 deformed in the carcass profiling machine 76, and a second insert profile 87, obtained from the second strip 48 deformed in the insert profiling machine 80, are applied. In this example, the rotating mandrel 72 further comprises an assembly for lubricating the outer surface. The rotating mandrel 72 is capable of being driven in rotation about the A-A’ axis at a speed and in a direction of rotation different from those of the support 73. The support 73 comprises, for example, a plate driven in rotation about the A-A’ axis in the winding direction of the insert 28 and the carcass 26. The support 73 carries the unwinders 74, 78, and the profiling machines 76, 80. In this example, the profiling machines 76, 80 are arranged diametrically on the same side relative to a median axial plane passing through the A-A’ axis. The profiling machines 76, 80 are, for example, situated one above the other. Each profiling machine 76, 80 comprises a plurality of pairs of rollers 100 for deforming the strip 31, 48, which define a respective B-B’, C-C’ axis for feeding the carcass 26 and the insert 28, respectively, onto the mandrel 72. The profiling machines 76, 80 are movable in translation on the support 73 in a plane perpendicular to the A-A’ winding axis. The insert profiling machine 80 is capable of being pivoted about its C-C’ axis to adjust the angle of introduction of the insert profile 87 into the bringing-together system 81. The bringing-together system 81 advantageously comprises a profile guide 106 interposed between the insert profiling machine 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 profiling machine 80 and, on the other hand, the mandrel 72. These guiding means conform to 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. The radial pressing members 82 are arranged radially around the outer surface of the mandrel 72. They comprise, for example, wheels capable of being applied radially to the outside of the insert 28 and the carcass 26 to finalize the positioning of the insert 28 in the helical gap 40, and the interlocking of the carcass 26. In a variant, to facilitate the release of the insert 28 and the carcass 26 away from the mandrel 72, the radial pressing members 82 located on the mandrel 72 are capable of closing the carcass 26 only partially. A specific mandrel (not shown), associated with additional pressing members, is then provided downstream of the mandrel 72. A method for manufacturing the flexible pipe in the station 70 of Figure 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 into the profiling machines 76, 80, respectively. Simultaneously, the support 73 is driven in rotation about the A-A’ axis. In the carcass profiling machine 76, the first strip 31 is successively deformed to produce the first profile 85 comprising the inner portion 32, the intermediate portion 34 and the outer portion 36, without completely closing the inner portion 32 and the outer portion 36. In particular, the inner branch of the U of the outer portion 36 remains partially open, as does the outer branch of the U of the inner portion 32. In the insert profiling machine 80, the second strip 48 is deformed and folded 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 the connecting segments 50, 54. A second profile 87 having an L-shaped cross-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 formed in one operation, that is to say that the radial region 44 and the inner region 46 as well as the connecting segments 50, 54 are created at the same time. The second profile 87 is then guided by the profile guide 106. 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 toward the mandrel 72 with a lead angle of a few degrees relative to the first profile 85, for example between 8° and 12°. A combined profile forms and is pressed against the outer surface of the mandrel 72 before being wound helically, at the pitch desired for insertion into the gap 40, thus forming the insert 28 and the carcass 26. 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. Furthermore, the inner region 46 of each turn of the second profile 87 is applied against the inner region 46 of an adjacent turn to close off the gap 40 being formed. The radial pressing members 82 are then applied to the outside of the carcass 26 and the insert 28 to close and interlock the carcass 26, while ensuring the internal positioning of the insert 28 in the helical gap 40. The turns thus formed of the carcass 26 and the insert 28 are progressively released downstream, detaching from the mandrel 72 under the effect of the lubrication provided by the lubrication assembly, and of the difference in rotation between the support 73 and the mandrel 72 tending to expand the carcass 26. Once the carcass 26 has been produced, and the insert 28 arranged 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. The outer sheath 30 is then advantageously produced by extrusion, being arranged outside the armor layers 24, 25. The inner assembly formed by the carcass 26 and the insert 28 is permeable to the passage of fluid from the inside of the carcass 26 to the outside of the carcass 26. In a variant (not shown) of the manufacturing and installing station 70, the profiling machines 76, 80 are arranged diametrically opposite one another, on either side of a median axial plane 5 passing through the A-A’ axis. Figure 5 illustrates another variant of the manufacturing and installing station 70. In this example, the station 70 comprises a single profiling machine 76, intended to profile the first strip 31 and the second strip 48 jointly. The first strip 31 is fed upstream into the profiling machine 76 to be partially deformed by 10 upstream rollers 100, without deformation of the second strip 48. From the intermediate introduction of the undeformed second strip 48, transversely relative to the profiling machine 76, the first strip 31 and the second strip 48 deform jointly between the rollers 100 to form a combined profile 112. The combined profile 112 is then wound on the outer surface of the mandrel 72, as described previously. 15 In a variant (not shown), the insert has an S-shaped cross-section, in particular an extended S-shaped cross-section, as described in patent application WO2015 / 121424.
Claims
1. Flexible pipe (10) for transporting fluid, comprising:- a polymer inner sheath (20) delimiting a fluid circulation passage (16) having a central axis (A-A’), the fluid circulation passage (16) having an inside diameter (ID);- at least one armor layer (24, 25) arranged outside the inner sheath (20);- an internal carcass (26), arranged in the inner sheath (20), the internal carcass (26) comprising a folded first strip (31) delimiting a helical gap (40) opening toward the central axis (A-A’), the first strip (31) being formed from a first material;- a helical insert (28) closing off the helical gap (40) toward the inside, the helical insert (28) comprising a folded second strip (48), formed from a second material, the helical insert (28) having a cross-section, taken in a median axial plane, comprising a radial region (44) arranged in the helical gap (40) and an axial inner region (46) protruding from the radial region (44), the axial inner region (46) at least partially closing off the helical gap (40),characterized in that the second material has a yield strength (YS) lower than the yield strength (YS) of the first material, the ratio of the thickness (e2) of the second strip (48) to the inside diameter (ID) being between 0.10% and 1%.
2. Pipe (10) according to claim 1, wherein the ratio of the thickness (e2) of the second strip (48) to the inside diameter (ID) is between 0.33% and 1%.
3. Pipe (10) according to claim 1 or 2, wherein the yield strength (YS) of the second material is less than or equal to 350 MPa, the yield strength (YS) of the first material being strictly greater than 350 MPa, in particular strictly greater than 400 MPa.
4. Pipe (10) according to any one of the preceding claims, wherein the cross-section of the helical insert (40) is L-shaped.
5. Pipe (10) according to claim 4, wherein the radial region (44) of each L-shaped cross-section defines a free edge (51) of the helical insert (40), the free edge (51) of the helical insert (40) being arranged freely in the helical gap (40) without being pinched by the internal carcass (26).
6. Pipe (10) according to any one of the preceding claims, wherein the difference in open-circuit potential 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, wherein the first material is selected from a lean 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. Pipe (10) according to any one of the preceding claims, 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, wherein the first material is selected from a steel of grade UNS S32101, UNS S32205, UNS S32304 or UNS S32750, the second material being selected from a steel of grade UNS 31600, UNS 31603, UNS S30400 or UNS S30403.
10. Pipe (10) according to any one of the preceding claims, wherein the internal carcass (26) comprises a plurality of interlocked turns, each turn of the internal carcass (26) havingan inner portion (32), an intermediate portion (34), the inner portion (32) having a U shape folded back toward the intermediate portion (34) and an outer portion (36), the outer portion (36) having a U shape folded back toward 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 protruding axially beyond the inner portion (32).
11. Method for manufacturing a flexible pipe (10), comprising the following steps:- forming an internal carcass (26), the internal carcass (26) comprising a folded first strip (31) delimiting a helical gap (40) opening toward the central axis (A-A’), the first strip (31) being formed of a first material;- producing a polymer inner sheath (20) delimiting a fluid circulation passage (16) having a central axis (A-A’), the fluid circulation passage (16) having an inside diameter (ID), the internal carcass (26) being arranged in the inner sheath (20);- arranging at least one layer (24, 25) of external armors outside the inner sheath (20);the method comprising placing a helical insert (28) in the helical gap (40), the helical insert (28) comprising a folded second strip (48) formed of a second material,the helical insert (28) having a cross-section, taken in a median axial plane, comprising a radial region (44) arranged in the helical gap (40) and an axial inner region (46) protruding from the radial region (44), the axial inner region (46) at least partially closing off the helical gap (40), characterized in that the second material has a yield strength (YS) lower than the yield strength (YS) of the first material, the ratio of the thickness (e2) of the second strip (48) to the inside diameter (ID) being between 0.10% and 1%.
12. Method according to claim 11, wherein the cross-section of the helical insert (40) is L-shaped, the radial region (44) of each L-shaped cross-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 internal carcass (26).