FR3161255A1 - Flexible fluid transport pipe having a smooth internal surface and associated manufacturing method - Google Patents

Abstract

Flexible fluid transport pipe comprising a smooth internal surface and associated manufacturing method The pipe comprises an inner sheath (20) delimiting a fluid circulation passage (16), and an inner carcass (26), arranged in the inner sheath (20), the inner carcass (26) comprising a first folded strip (31) delimiting a helical gap (40) formed of a first material. The pipe comprises 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 radial region (44) arranged in the helical gap (40) and an axial inner region (46) at least partially closing the helical gap (40). 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 (48) to the inside diameter (ID) of the passage (16) being between 0.10% and 1%. Figure for abstract: figure 2

Description

Flexible fluid transport conduit having a smooth internal surface and associated manufacturing process

The present invention relates to a flexible fluid transport conduit, comprising:

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

- at least one layer of armor arranged on the outside of the inner sheath;

- an internal frame, arranged in the internal sheath, the internal frame comprising a first folded strip delimiting a helical gap opening towards the central axis, the first strip being formed of a first material;

- a helical insert closing the helical gap inwards, the helical insert comprising a second folded strip, formed of a second material, the helical insert having a section, taken in a median axial plane, comprising a radial region disposed 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.

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

Such flexible management is for example carried out 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.

The pipe is generally formed from a series of concentric and superimposed layers. It is considered "unbonded" within the meaning of the present invention when at least one of the pipe layers is capable of moving longitudinally relative to the adjacent layers during pipe bending. In particular, an unbonded pipe is a pipe lacking bonding materials connecting the layers forming the pipe.

The pipeline is typically laid across a body of water, between a bottom assembly, designed to collect the extracted fluid from the bottom of the body of water, and a floating or fixed surface assembly, designed to collect and distribute the fluid. The surface assembly may be a semi-submersible platform, an FPSO, or another floating assembly.

In some cases, the flexible hose includes an internal casing arranged inside the pressure sheath, in order to prevent the pressure sheath from being crushed under the effect of external pressure, for example during a depressurization of the internal fluid circulation passage delimited by the pressure sheath.

The internal casing is generally made of a profiled metal strip, wound in a spiral. The coils of the strip are stapled together. The coils define a helical space between them (referred to as "corrugation" in English). This space opens radially inwards into the central fluid circulation passage.

The internal surface of the casing therefore presents an axial succession of hollows and flats. The pipe is then generally described by the English term "rough bore".

In some cases, particularly during the transport of pressurized gas, the circulation of the fluid along the frame is disrupted by the reliefs defined on the frame by the helical gap.

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

To overcome this problem, it is known to manufacture flexible pipes without an internal casing and therefore presenting a smooth surface ("smooth bore" in English).

In cases where crush resistance is required, it is also known to manufacture flexible pipes with a smooth inner surface on the inner casing, where the helical gaps are filled by the addition of a structural element consisting of a helical insert. An example of a pipe with an S-shaped helical insert is described in WO 2021/074192. In this example, an outer region of the insert's cross-section is anchored between two successive turns of the casing to ensure the correct relative positioning between the insert and the casing. Furthermore, WO 2021/074192 indicates that it is preferable for the casing and the insert to be made from the same material.

However, such a pipe does not provide complete satisfaction. Indeed, to meet the constraints of use and in particular resistance to crushing, the casing must be made with a material that has high mechanical characteristics, particularly in terms of elasticity to ensure the rigidity of the pipe.

During pipe manufacturing, the casing and insert are spirally wound together. The helical insert, placed within the casing's interstices, undergoes a bending process as successive turns of the casing interlock. This bending, and/or differences in winding radius between various areas of the insert's cross-section (particularly between the free edge and the area anchored in the casing), can generate high compressive stresses and lead to local deformations in the insert, typically buckling. This results in a local radial deformation of the insert's turns toward the pipe axis.

This local phenomenon, once it has appeared, is also likely to propagate along the pipeline, over significant lengths, for example during its manufacture or later when the pipeline is in production, under the effect of the movements of the pipeline 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 pipeline is installed.

Furthermore, the radial buckling phenomenon is sometimes accompanied by the appearance of radial depressions along the circumference of successive turns of the insert. It has been observed that this buckling phenomenon, possibly accompanied by radial depressions, occurs mainly during the manufacturing of the pipe casing.

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

Furthermore, the presence of these undesirable reliefs makes it difficult, or even compromises, any possibility of checking the integrity of the inside of the carcass during occasional inspection operations by "scraping" (or "pigging" in English).

One aim of the invention is therefore to produce, by simple and inexpensive means, a flexible conduit in which the risk of undesirable reliefs is limited, even in the case where the mechanical characteristics of the internal casing are high.

To this end, the invention relates to a flexible conduit of the aforementioned type, characterized in that the second material has a lower elastic limit 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%.

The flexible conduit according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination:

- the ratio of the thickness of the second strip to the inner diameter is between 0.33% and 1%;

- 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;

- the section of the helical insert (40) 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 freely disposed in the helical gap without being pinched by the internal frame;

- the potential difference at the point of abandonment between the first material and the second material is less than 0.2 V;

- the first material is chosen from a lightweight duplex steel, a duplex steel, a superduplex steel, a hyperduplex steel, an austenitic stainless steel possibly work-hardened, a super-austenitic steel or a nickel-based alloy;

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

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

- the internal frame comprises a plurality of stapled turns, each turn of the internal frame 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;

- 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%;

- 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%;

- 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:

- formation of an internal frame, the internal frame comprising a first folded strip delimiting a helical gap opening towards the central axis, the first strip being formed of a first material;

- fabrication of an internal polymer sheath delimiting a central axis fluid circulation passage, the fluid circulation passage having an internal diameter, the internal frame being disposed in the internal sheath;

- provision of at least one outer armor layer on the outside of the inner sheath;

- the process involving the placement of a helical insert in the helical gap, the helical insert comprising a second folded strip formed of a second material;

- the helical insert having a section, taken in a median axial plane, comprising a radial region disposed in the helical gap and an axial inner region protruding from the radial region, the axial inner region at least partially closing the helical gap, characterized in that the second material has a lower elastic limit 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%.

The method according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination:

- the helical insert section is L-shaped, the radial region of each L-shaped section defining a free edge of the helical insert, the method comprising the free arrangement of the free edge of the helical insert in the helical gap without being pinched by the internal frame.

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

- FIG. 1 there FIG. 1 is a partially cutaway perspective view of a central section of a first flexible conduit according to the invention;

- FIG. 2 there FIG. 2 is a partial view, taken in cross-section along a median axial plane, of a detail of the conduit of the FIG. 1 illustrating the carcass and the insert arranged in the helical gap of the carcass;

- FIG. 3 there FIG. 3 is a view of a detail of the FIG. 2 illustrating an L-shaped section of the insert;

- FIG. 4 there FIG. 4 is a schematic view of an example of a manufacturing and installation station for the carcass and insert;

- FIG. 5 there FIG. 5 is a schematic view of another example of a manufacturing and installation station for the frame and insert;

- FIG. 6 there FIG. 6 is a view analogous to the FIG. 2 of a flexible driving variant according to the invention.

A first flexible conduit 10 according to the invention is partially illustrated by the FIG. 1 .

The flexible conduit 10 has a central section 12. It has, at each of the axial ends of the central section 12, an end fitting (not visible).

With reference to the FIG. 1 The pipe 10 defines a central passage 16 for the 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 laid across a body of water (not shown) in a fluid handling facility, particularly for hydrocarbons.

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

The fluid handling installation comprises a surface assembly, including a floating assembly, and a bottom assembly (not shown), which are generally connected to each other by the flexible pipe 10.

Flexible driving 10 is preferably "unbonded" driving (designated by the English term "unbonded").

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

Such conduct is described for example 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.

Furthermore, in all that follows, the terms "outside" and "inside" are generally understood radially with respect to the central axis A-A' of the pipe, the term "outside" being understood as relatively further radially away from the axis A-A' and the term "inside" extending as relatively closer radially to the axis A-A' of the pipe.

As illustrated by the FIG. 1 , the conduit 10 delimits a plurality of concentric layers around the axis A-A', which extend continuously along the central section 12 to the end fittings located at the ends of the conduit.

According to the invention, the conduit 10 comprises at least a first tubular sheath 20 made of polymer material advantageously constituting a pressure sheath.

The conduit 10 also includes at least one layer of tensile armor 24, 25 arranged externally with respect to the first sheath 20 forming a pressure sheath.

The pipe 10 further comprises an inner carcass 26 arranged inside the pressure sheath 20, optionally a pressure arch 27 interposed between the pressure sheath 20 and the tensile armor layer(s) 24, 25, and an outer 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 inner carcass 26.

As is known, the pressure sleeve 20 is intended to hermetically seal the fluid transported in the passage 16. The pressure sleeve 20 is advantageously formed from 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 from a high-performance polymer such as a polyaryletherketone (PAEK) like 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 the FIG. 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 frame 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.

The main function of the frame 26 is to resist radial crushing forces. Radial crushing forces include, for example, the hydrostatic pressure of the body of water.

The carcass 26 is arranged inside the pressure sheath 20. It is suitable for coming into contact with the fluid circulating in the central passage 16 delimited by the pressure sheath 20.

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 properties, in particular a yield strength 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.

The yield strength YS is measured by the method described in Standard NF EN ISO 6892-1 (2019).

The first material is chosen in particular from among lean duplex steels, duplex steels, superduplex steels and hyperduplex steels.

Examples of lightweight 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 chosen from austenitic or super-austenitic stainless steels or work-hardened austenitic stainless steels, for example according to Standard EN 10088-2.

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 Standard C850, YS = 552MPa), grade 301 (UNS30100, CW1 according to Standard C850, YS = 557 MPa, or CW2 according to Standard C850+, Y = 660MPa, or CW3 according to Standard C1000, YS = 877MPa) or grade 316L (UNS S31603, CW2 according to Standard C850+, Y = 678MPa, or CW3 according to Standard C1000, YS = 895MPa).

Alternatively, the first material is an austenitic nickel alloy, for example inconel® 625 (UNS N06625, YS= 414 MPa).

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° with respect to the central axis A-A’, typically between 75° and 90°.

The first strip 31 has two edges folded longitudinally over a central region. It defines a plurality of interlocking turns with a closed and flattened S-shaped cross-section, as illustrated by the FIG. 2 and by the FIG. 6 .

The first strip 31 has a thickness e1 that is substantially constant.

The closed S-shaped section of each turn of the frame 26 comprises successively, parallel to the axis A-A' from right to left on the FIG. 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.

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.

The outer part 36 of an adjacent turn is partially engaged in the inner part 32, the support wave 38 being intercalated between the arms of the U. The inner part 32 defines an inner surface 39 located on a cylindrical envelope with axis A-A’.

The outer part 36 also defines a U-shaped section extending parallel to the axis A-A’ and opening opposite the inclined part 34.

The outer part 36 of each turn is folded towards the intermediate part 34, towards the central axis A-A', internally with respect 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 outwards the inner part 32 of the adjacent section.

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

The gap 40 opens radially towards the central axis A-A’. For each turn, it opens internally towards the axis A-A’ between the internal surfaces 39 of the internal 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.

The gap 40 thus extends continuously in the shape of a helix with axis A-A’ following a pitch P1 along the frame 26.

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

Each coil of the carcass 26 has a width advantageously between 5 mm and 100 mm and preferably between 5 mm and 50 mm.

The frame 26 has, between each pair of stapled turns, a first axial play defined by the axial stroke of relative sliding of the outer part 36 of a turn in the inner part 32 of an adjacent turn in which it is engaged.

The insert 28 is partially disposed in the gap 40 and closes the gap 40 towards the axis A-A’.

The insert 28 thus advantageously presents a helical shape with axis A-A’, of pitch P1 analogous to the pitch of the gap 40.

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

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, which is steel or a nickel alloy. The second material has weaker mechanical properties than the first material, in particular a yield strength less than or equal to 350 MPa, specifically between 150 MPa and 350 MPa.

The yield strength YS is measured by the method described in Standard NF EN ISO 6892-1 (2019).

The second material is, for example, chosen 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 = 270MPa) 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 chosen from nickel alloys, in particular 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 frame 26 is a duplex steel with a yield strength strictly greater than 350 MPa. The second material forming the strip 48 of the insert 28 is an austenitic steel with a yield strength less than 350 MPa.

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

Generally, the potential difference at the point of termination between the first and second materials is less than 0.2 volts. This characteristic can be verified using a ZRA (Zero Resistance Ammeter) test. This test is, for example, in accordance with 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 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%.

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%.

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, in particular between 0.4 mm and 1.5 mm, preferably between 0.5 mm and 1 mm.

Indeed, surprisingly, combining a first material with higher mechanical characteristics to form the band 31 of the carcass 26 with a second material with lower mechanical characteristics to form the band 48 of the insert 28 and respecting a certain ratio of the thickness e2 of the second band to the internal diameter DI, is particularly suitable to prevent the occurrence of local buckling phenomena of the insert 28 along the flexible pipe 10.

This beneficial effect regarding the absence of local buckling is reinforced by the L-shape of the section of the insert 28 described in French patent FR 3 097 612.

Thus, a flexible conduit 10 according to the invention, even equipped with an internal carcass 26 formed with materials with high mechanical characteristics (in particular with an elastic limit greater than 350MPa) and an insert 28 sealing 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.

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 spot inspection by pigging of the internal passage 16 of the flexible pipe 10.

It is therefore possible to extend the design range of internal carcasses 26 to use high-character materials, with higher internal diameters and lower carcass thicknesses, reducing the risk of insert buckling.

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

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

The radial region 44 in this example comprises an outer curved section 50. It includes an intermediate linear section 52, and an inner curved section 54 connecting to the inner region 46.

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

The outer section 50, when present, has an outward convex curvature. The radius of curvature of the outer section 50 is advantageously greater than the thickness e2 of the second strip 48.

The outer section 50 protrudes axially relative to the intermediate section 52, opposite the axial inner region 46.

The length L1 of the outer section 50, taken in projection onto the axis A-A', is very small in the example of the FIG. 2 It remains weak in the example of the FIG. 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 internal axial region 46, taken in projection on the axis A-A’.

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 frame 26.

Advantageously, the insert 28 and in particular its outer free edge 51, in particular the radial region 44 and the outer section 50 when present, are free to move in the gap 40 of the frame.

The helical insert 28 is also able to be disengaged from the carcass 26, without interfering with the stapling of the coils of the carcass 26.

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 frame 26 and the outer branch of the U of the outer part 36 of an adjacent section of the frame 26.

The insert 28 is free to move axially and radially in the gap 40 of the frame 26.

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

The intermediate section 52 extends at an angle to an axis perpendicular to the central axis A-A’, being located axially away from the inner region 46.

The inner section 54 has a convex curvature directed inwards, opposite to the convexity of the curvature of the outer section 50. It has a greater radius of curvature 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’.

The radial region 44 is arranged in the gap 40 between the intermediate part 34 and the outer part 36 of a turn of the frame 26, and the inner part 32 of an adjacent turn of the frame 26.

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

The inner region 46 extends axially along the axis A-A’, on a cylindrical envelope with axis A-A’ or at an angle of less than 10° 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 internal region 46, taken in projection onto the axis A-A', is greater than the length L4 of the radial region 44, taken in projection onto 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.

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’.

The radial extent ER of the radial region 44, taken perpendicular to the axis A-A', is less than the length of the internal axial region 46, taken in projection along the central axis A-A', and in particular is less than 50% of the length of the internal axial region 46, taken in projection along the axis A-A'. Preferably, the length L2 of the internal axial region 46, taken in projection onto 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'.

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 the FIG. 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 frame 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.

The inner region 46 of each turn of the insert 28 is advantageously held 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 frame 26.

Thus, the successive turns of the insert 28 overlap each other by their inner regions 46, in order to close the gap 40 inwards.

The overlap width of each internal region 46, when the frame 26 occupies an undeformed linear configuration, is greater than the axial clearance of the frame 26.

The internal assembly formed by the casing 26 and the insert 28 is permeable to the passage of fluid. This allows for pressure equalization on both sides of this assembly. Such a configuration is therefore completely opposite to that of a fully sealed metal pipe as described in US 2002/195157, which aims to contain a fluid inside the pipe without any fluid leakage.

With reference to the FIG. 1 The pressure arch 27 is designed to absorb the forces related to the pressure within the pressure sheath 20. It is, for example, formed of a profiled metal wire 25 wrapped helix around the sheath 20. The profiled wire 25 generally has a complex geometry, notably in the shape of a Z, T, U, K, X or I.

The metallic material forming the profile wire 25 is selected from carbon steel, specifically from grades of carbon steel containing between 0.01% and 0.8% carbon. For applications in particularly corrosive environments, the metallic 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 in a short-pitch helix around the pressure sheath 20, that is to say with a helix angle of absolute value close to 90° with respect to the central axis A-A’, typically between 75° and 90°.

The flexible conduit 10 optionally includes a ferrule (not shown).

The reinforcement, when present, consists of a spiral winding of at least one wire, advantageously with a rectangular cross-section, around the pressure arch 27. The superposition of several wires wound around the pressure arch 27 can advantageously replace a given total reinforcement thickness. This increases the burst resistance of the flexible pipe 10. The winding of the at least one wire has a 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° with respect to the central axis A-A', typically between 75° and 90°.

In one embodiment of the invention, the pressure arch 27 and the fret are replaced by a pressure arch 27 of greater thickness formed from a profiled metal wire having a geometry in the shape of a T, U, K, X or I, and/or from at least one strip of aramid 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.

The flexible conduit 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.

In the example shown on the FIG. 1 The flexible conduit 10 comprises a plurality of armor layers 24, 25, including an inner armor layer 24, applied over the pressure arch 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 long pitch around the axis A-A' of the conduit.

By "long pitch winding", 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°.

The armor elements 63 of a first layer 24 are generally wound at an opposite angle 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 layer of armor 25 arranged in contact with the first layer of armor 24 is for example equal to - a°.

The 63 armor elements are for example formed by metallic wires, in particular steel wires, or by tapes of composite material, for example carbon fiber reinforced tapes.

The metallic material forming the armor elements 28 is selected from carbon steel, in particular from grades of carbon steel containing between 0.01% and 0.8% carbon. For applications in particularly corrosive environments, 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 layer of tensile armor 24, 25 advantageously rests on at least one wear-resistant strip (not shown). The wear-resistant strip is, for example, made of plastic, particularly polyamide or 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 wrapped around the second outermost tensile armor layer 25 relative to the A-A' axis, to provide mechanical support for the tensile armor layers 24, 25. Alternatively, the aramid fibers are replaced by glass fibers or carbon fibers.

The outer sheath 30 is designed to prevent fluid permeation from the outside of the flexible hose 10 to the inside. It is advantageously made of 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 installed simultaneously in a manufacturing and installation station 70, examples of which are schematically illustrated respectively by figures 4 and 5.

In the example shown on the FIG. 4 , station 70 includes a mandrel 72 rotating around an axis A-A', intended to guide the winding of the carcass 26 and the insert 28.

The station 70 includes a support 73 rotating around the axis A-A’ and relative to the mandrel 72, a first uncoiler 74 (shown schematically) receiving the first strip 31, and a profiling machine for the carcass strip 76 arranged downstream of the first uncoiler 74 between the first uncoiler 74 and the mandrel 72.

Station 70 also includes a second unwinder 78 (shown schematically) which receives the second strip 48. In the example of the FIG. 4 , station 70 includes a profiling machine for the strip of insert 80, located downstream of the second uncoiler 78 between the second uncoiler 78 and the mandrel 72.

In this same example, station 70 includes a system 81 for joining the strips 31, 48 as they exit the profiling machines 76, 80.

The station 70 further includes radial plating elements 82 for the carcass 26 and the insert 28 against the mandrel 72, and advantageously, return elements 83 for guiding the first strip 31 and the second strip 48 from each uncoiler 74, 78 to a respective profiler 76, 80.

The rotating mandrel 72 protrudes axially relative to the support 73 along a winding axis A-A’.

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

In this example, the rotary chuck 72 also includes an external surface lubrication assembly.

The rotating chuck 72 is suitable for being driven in rotation around the axis A-A’ with a speed and direction of rotation different from those of the support 73.

The support 73 includes, for example, a plate driven in rotation around the axis A-A’ in the winding direction of the insert 28 and the frame 26.

The support 73 carries the uncoilers 74, 78, and the profilers 76, 80. In this example, the profilers 76, 80 are arranged diametrically on the same side with respect to a median axial plane passing through the axis A-A’.

For example, the profiling machines 76 and 80 are located one on top of the other.

Each profiling machine 76, 80 includes a plurality of pairs of rollers 100 for deforming the strip 31, 48, which define a respective axis B-B’, C-C’ for feeding respectively the frame 26 and the insert 28 onto the mandrel 72.

The roll forming machines 76 and 80 are movable in translation on the support 73 in a plane perpendicular to the winding axis A-A'. The insert roll forming machine 80 is able to be pivoted around its axis C-C' to adjust the angle of insertion of the insert profile 87 into the joining system 81.

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

These guiding means follow the geometry of the insert 28 and include a set of guide rollers and/or one or more guide ramps with a low coefficient of friction.

The radial plating elements 82 are arranged radially around the outer surface of the mandrel 72. They include, for example, rollers designed to be applied radially to the outside of the insert 28 and the frame 26 to finalize the arrangement of the insert 28 in the helical gap 40, and the stapling of the frame 26.

In one variant, to facilitate the release of the insert 28 and the frame 26 away from the mandrel 72, the radial clamping members 82 located on the mandrel 72 are able to only partially close the frame 26. A specific mandrel (not shown), associated with additional clamping members, is then provided downstream of the mandrel 72.

A manufacturing process for flexible conduit 10 in station 70 of the FIG. 4 will now be described. Initially, the strips 31, 48 are loaded onto the uncoils 74, 78. Then, the strips 31, 48 are uncoiled to be introduced respectively into the roll formers 76, 80. Simultaneously, the support 73 is driven in rotation around the axis A-A'.

In the carcass profiling machine 76, the first strip 31 is successively deformed to produce the first profile 85 comprising the inner part 32, the intermediate part 34 and the outer part 36, without totally closing the inner part 32 and the outer part 36.

In particular, the inner arm of the U of the outer part 36 remains partially open, as does the outer arm of the U of the inner part 32.

In the insert roll forming machine 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 bending connecting sections 50, 54

A second L-shaped profile 87 comprising an axial inner region 46 and a radial region 44 is then obtained, to form the insert 28.

According to one variant of the invention, the second strip 48 of the insert 28 is formed in one operation, i.e. the radial region 44 and inner region 46 as well as the connecting sections 50, 54 are created at the same time.

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

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

A combined profile is formed and pressed onto the outer surface of the mandrel 72 before winding into a helix, at the desired pitch for insertion into the gap 40, thus forming the insert 28 and the frame 26.

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

Furthermore, the inner region 46 of each turn of the second profile 87 applies to the inner region 46 of an adjacent turn to close the gap 40 being formed.

The radial plating elements 82 are then applied to the outside of the frame 26 and the insert 28 to close and staple the frame 26, while ensuring the internal positioning of the insert 28 in the helical gap 40.

The coils thus formed of the carcass 26 and the insert 28 gradually move away downstream, detaching from the mandrel 72 under the effect of the lubrication provided by the lubrication assembly, and the differential of rotation between the support 73 and the mandrel 72 tending to inflate the carcass 26.

Once the frame 26 is formed, and the insert 28 is placed within the frame 26, the inner sheath 20 is formed around the frame 26, for example by extrusion. The pressure arch 27 and the reinforcement layers 24, 25 are then wound around the inner sheath 20.

The outer sheath 30 is then advantageously produced by extrusion, being placed outside the armor layers 24, 25.

The internal 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 manufacturing and installation station 70, the profiling machines 76, 80 are arranged diametrically opposite each other, on either side of a median axial plane passing through the axis A-A’.

There FIG. 5 illustrates another variant of station 70 for manufacturing and installation.

In this example, station 70 includes 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 roll forming 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 with respect to the roll forming machine 76, the first strip 31 and the second strip 48 are deformed jointly between the rollers 100 to form a combined profile 112.

The combined profile 112 is then wrapped around the outer surface of the mandrel 72, as described previously.

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 (12)

Flexible fluid transport conduit (10), comprising:
- an internal polymer sheath (20) delimiting a central axis (A-A') fluid circulation passage (16), the fluid circulation passage (16) having an internal diameter (DI);
- at least one layer of armor (24, 25) arranged outside the inner sheath (20);
- an internal frame (26), arranged in the internal sheath (20), the internal frame (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 of 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 cross-section, taken in a median axial plane, comprising a radial region (44) disposed in the helical gap (40) and an internal axial region (46) projecting from the radial region (44), the internal axial region (46) at least partially closing 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 (DI) being between 0.10% and 1%. Conduit (10) according to claim 1, wherein the ratio of the thickness (e2) of the second strip (48) to the inner diameter (ID) is between 0.33% and 1%. Conduct (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. Conduit (10) according to any one of the preceding claims wherein the section of the helical insert (40) is L-shaped. 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 disposed freely in the helical gap (40) without being pinched by the internal frame (26). Conducting (10) according to any one of the preceding claims, wherein the dropout potential difference between the first material and the second material is less than 0.2 V. Conducting (10) according to any one of the preceding claims, wherein the first material is selected from a lightweight duplex steel, a duplex steel, a superduplex steel, a hyperduplex steel, an austenitic stainless steel optionally work-hardened, a super-austenitic steel or a nickel-based alloy. Conducting (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. Conduit (10) according to claims 7 and 8, wherein the first material is selected from a steel grade UNS S32101, UNS S32205, UNS S32304 or UNS S32750, the second material being selected from a steel grade UNS 31600, UNS 31603, UNS S30400 or UNS S30403. Conduit (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 part (32), an intermediate part (34), the inner part (32) having a U-shape folded towards the intermediate part (34) and an outer part (36), the outer part (36) having a U-shape folded towards the intermediate part (34), the radial region (44) of the helical insert (28) being pressed against the intermediate part (34), the axial inner region (46) of the helical insert (28) advantageously projecting axially beyond the inner part (32). A method for manufacturing a flexible pipe (10), comprising the following steps:
- formation of an internal frame (26), the internal frame (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 of a first material;
- fabrication of 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), the internal frame (26) being disposed in the internal sheath (20);
- arrangement of at least one layer (24, 25) of external armor outside the internal sheath (20);
the method comprising the placement of 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) disposed in the helical gap (40) and an internal axial region (46) projecting from the radial region (44), the internal axial region (46) at least partially closing 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 (DI) being between 0.10% and 1%. 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 the free disposition of the free edge (51) of the helical insert (28) in the helical gap (40) without being pinched by the internal frame (26).