Flexible tube body

Abstract

The present disclosure relates to a flexible pipe body for delivering high pressure fluids. The flexible tube body includes a tubular fluid sealing layer, a pressure maintaining armor layer positioned on the tubular fluid sealing layer, and a tensile armor layer positioned on the pressure maintaining armor layer. The tubular fluid sealing layer comprises a composition comprising a plasticizer and a homopolymer of vinylidene fluoride, and wherein the plasticizer is present in an amount of 0.3 wt% to 2.0 wt% based on the total weight of the polymer composition.

Description

Technical Field

[0001] The present invention relates to a flexible pipe body for use, for example, in conveying high pressure fluids to and from a subsea location. Background Art

[0002] Flexible pipe can be used to transport produced fluids such as oil and / or gas and / or water from one location to another. Flexible pipe can be used to connect a seafloor location (which can be deep sea) to a sea level location in particular. The pipe can have an inner diameter of generally up to about 0.6 meters (for example, the diameter can be in the range of 0.05m to up to 0.6m). Flexible pipe is generally formed as an assembly of a flexible pipe body and one or more end fittings. The pipe body is generally formed as a combination of layered materials, which form a pressure-bearing conduit. The pipe structure allows large flexures without causing bending stresses that would impair the function of the pipe during its service life. The pipe body is generally constructed as a combined structure including a polymer layer and / or a metal layer and / or a composite material layer. For example, the pipe body may include a polymer layer and a metal layer, or a polymer layer and a composite material layer, or a polymer layer, a metal layer and a composite material layer.

[0003] API Recommended Practice 17B provides guidance for the design, analysis, manufacture, testing, installation, and operation of flexible pipe and flexible pipe systems for onshore, subsea, and offshore applications.

[0004] In many flexible pipe designs, the pipe body includes one or more armor layers positioned on a tubular polymer layer. The primary load on such armor layers is formed by radial forces. The armor layers typically have a specific cross-sectional profile to interlock so as to be able to hold and absorb the radial forces generated by external or internal pressure on the pipe. The cross-sectional profile of the winding wire that thus prevents the pipe from collapsing or rupturing due to pressure is sometimes referred to as a pressure-resistant profile. When the armor layer is formed by a helically wound wire forming a hoop component, the radial forces on the pipe from external or internal pressure cause the hoop component to expand or contract, thereby applying a tensile load on the wire.

[0005] The polymer layer of flexible pipe body can be formed by extrusion.For at least some polymers (comprising the polymer of vinylidene fluoride), plasticizer is usually used as processing aid to ensure that tubular layer can be extruded and the extruded pipe is flexible enough, thereby providing a kind of pipe, this pipe keeps required storage and operation bending radius and can not damage this pipe or make this pipe too hard.For the homopolymer of vinylidene fluoride, usually use 3 weight % or larger plasticizer amount to provide the desired processability of the tubular fluid sealing layer forming flexible pipe to the polymer composition obtained.The example of suitable plasticizer is dibutyl sebacate.

[0006] Applying internal pressure to the pipe (i.e., pressure from within the hole) produces radial expansion in the fluid seal and the layers outside it. This occurs when the polymer layer can undergo deformation and creep into the gap of the overlying armor layer. Under high pressure (about 8000psi / 55MPa or higher), the resulting strain distribution in the polymer fluid sealing layer can be highly localized at the area around the gap. This can cause the strain distribution through the polymer thickness to produce high stress areas between the peak strain areas at the outer diameter of the layer at or near the inner surface of the polymer fluid barrier sealing layer, and at these locations of enhanced stress, the polymer material can be deformed by cavitation rather than plastic flow. This in turn leads to the formation of microcracks or microcracks at those radial inner surface locations of the polymer fluid barrier sealing layer. During any subsequent load period (such as the load experienced during normal use of transporting produced fluids), such microcracks can then extend to form longer and / or deeper cracks throughout the polymer layer. This can increase the risk of failure of the polymer layer and can ultimately lead to the loss of pressure sealing, thereby having an adverse effect on the life of the flexible pipe. Additionally, the life of the pipe may be limited by the fatigue life of the layers within the pipe structure. The polymer layer is critical to the sealing of the fluid in the pipe, so fatigue resistance must be ensured, but this may be adversely affected by aging of the polymer layer, as over time plasticizers can leach out of the polymer and hydrocarbons can enter the polymer, causing the polymer to swell. These physical changes in the polymer can lead to reduced flexibility and therefore reduced fatigue life. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 A flexible pipe body according to an embodiment of the present invention is shown;

[0008] Figure 2 An example of a riser assembly suitable for transporting produced fluids such as oil and / or gas and / or water from a subsea location to a floating facility is shown; and

[0009] Figure 3 A comparison of plasticizer removal from Grade 3 and Grade 4 over time is shown. DETAILED DESCRIPTION

[0010] According to one aspect of the present invention, a flexible pipe body for conveying high pressure fluid is provided. The flexible pipe body comprises a tubular fluid sealing layer, a pressure retaining armor layer positioned on the tubular fluid layer, and a tensile armor layer positioned on the pressure retaining armor layer. The tubular fluid sealing layer comprises a polyvinylidene fluoride (PVDF) polymer composition, and the PVDF polymer composition comprises a homopolymer of a plasticizer and vinylidene fluoride. The plasticizer is present in an amount of 0.3 wt % to 2 wt % based on the total weight of the polymer composition.

[0011] According to another aspect of the present invention, a method for manufacturing a flexible pipe body is provided. The method includes extruding a tubular fluid sealing layer from a PVDF polymer composition, the PVDF polymer composition comprising a homopolymer of vinylidene fluoride and a plasticizer, wherein the plasticizer is present in an amount of 0.3 wt % to 2 wt % based on the total weight of the polymer composition. The method also includes positioning a pressure retaining armor layer on the tubular fluid sealing layer, and positioning a tensile armor layer on the pressure retaining armor layer.

[0012] Plasticizers (e.g., dibutyl sebacate) are typically incorporated into polymer compositions for forming tubular fluid sealing layers of flexible pipe bodies. Typically, the content of plasticizers (e.g., dibutyl sebacate) is 3 wt % or more to provide the polymer composition with the processability required for extrusion to form a tubular sealing layer. Some polymer compositions may not contain plasticizers. However, in order to provide the required processability, such compositions typically contain a significant amount of low viscosity polymer components, which can affect other mechanical properties of the polymer composition.

[0013] The inventors have found that the plasticizer level can be optimized to 0.3 wt % to 2 wt %. Surprisingly, when the plasticizer level is reduced from known levels to a level of 0.3 wt % to 2 wt %, the cracking and / or fatigue performance of the flexible pipe body can be maintained. This is unexpected because higher amounts of plasticizers are expected to improve the flexibility and flow characteristics of the polymer composition, making it less likely to crack. It has been found that by using a plasticizer in an amount of 0.3 wt % to 2 wt %, the polymer composition can still be provided with the processability required, for example, for an extruded tubular fluid sealing layer, while maintaining the cracking and fatigue performance of the resulting layer and improving aging performance.

[0014] It has also been found that, in the case of long-term use, plasticizers can be removed from the tubular fluid sealing layer by interaction with, for example, hydrocarbons flowing through the flexible pipe body. The loss of plasticizer can result in a loss of volume of the tubular fluid sealing layer and hardening of the polymer. This can have an adverse effect on the performance of the tubular fluid sealing layer and can also compromise the secure retention of the end fitting to the flexible pipe body, as the polymer can shrink away from the sealing ring, thereby reducing the seal or even causing a loss of seal. Reducing the amount of plasticizer can reduce the extent of volume loss while improving long-term performance, such as the above-mentioned crack resistance and fatigue performance.

[0015] The plasticizer can be present in an amount of 0.5 wt % to 1.9 wt % based on the total weight of the polymer composition. For example, the plasticizer can be present in an amount of 1.0 wt % to 1.9 wt %, preferably 1.3 wt % to 1.8 wt %, more preferably 1.5 wt % to 1.7 wt %.

[0016] Any suitable plasticizer may be used. One example may be dibutyl sebacate.

[0017] The polymer composition may include 50 wt % to 85 wt % of a homopolymer of vinylidene fluoride. In some examples, the homopolymer of vinylidene fluoride may be present in an amount of 60 wt % to 80 wt % based on the total weight of the polymer composition.

[0018] Homopolymers of vinylidene fluoride may include ultra-high molecular weight polymer chains, such as materials having molecular weights greater than 3,000,000 g / mol.

[0019] The homopolymer of vinylidene fluoride can have a melt flow index according to ISO 1133 (230° C., 12.5 kg) of less than or equal to 15 g / min, eg, less than 10 g / min or less than 5 g / min.

[0020] The polymer composition may also include a copolymer of vinylidene fluoride. The copolymer of vinylidene fluoride may be a copolymer of vinylidene fluoride and a comonomer. The comonomer may be selected from at least one of the following: vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ether; such as perfluoro(methyl vinyl) ether (PMVE); perfluoro(ethyl vinyl) ether (PEVE) or perfluoro(propyl vinyl) ether (PPVE); perfluoro(2,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); a fluorocarbon of formula CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 X comonomer, where X is SO 2 F.CO 2 H, CH 2 OH, CH 2 OCN or CH 2 OPO 3 H; Formula CF 2 =CFOCF 2 CF 2 SO 2 F comonomer; formula F(CF 2 ) n CH 2 OCF=CF2 comonomer, wherein n is 1, 2, 3, 4 or 5; formula R 1 CH 2 OCF=CF 2 The comonomer, R 1 is hydrogen or F(CF 2 )z , and z has a value of 1, 2, 3 or 4; Formula R 3 OCF=CH 2 The comonomer, R 3 is F(CF 2 )z, and z has a value of 1, 2, 3 or 4; perfluorobutylethylene (PFBE); fluorinated ethylene propylene (FEP); 3,3,3-trifluoropropyl; 2-trifluoromethyl-3,3,3-trifluoro-1-propene; 2,3,3,3-tetrafluoropropene or HFO-1234yf; E-1,3,3,3-tetrafluoropropene or HFO-1234zeE; Z-1,3,3,3-tetrafluoropropene or HFO-1234zeZ; 1,1,2,3-tetrafluoropropene or HFO-1234yc; 1,2,3,3-tetrafluoropropene or HFO-1234ye; 1,1,3,3-tetrafluoropropene or HFO-1234zc; and chlorotetrafluoropropene or HCFO-1224.

[0021] According to a preferred embodiment, the comonomer is hexafluoropropylene (HFP).

[0022] The copolymer can be present in the composition in a weight proportion of greater than 10% to 40% based on the total weight of the polymer composition. The copolymer can be present in an amount of 15% to 40%, preferably 17% to 35%. In some examples, the comonomer can be present in the copolymer composition in an amount of 25% to 40% by weight.

[0023] The weight proportion of the comonomer in the vinylidene fluoride copolymer is greater than 25%, advantageously greater than or equal to 26%, and / or less than or equal to 40%, preferably less than or equal to 37%.

[0024] The polymer composition may further include a second homopolymer of vinylidene fluoride, the second homopolymer of vinylidene fluoride exhibiting different properties from the first homopolymer of vinylidene fluoride, for example, when heated at a temperature of 230° C. and 100 s -1 Different viscosities in Pa.s when measured in the molten state using a capillary rheometer under shear.

[0025] The second homopolymer of vinylidene fluoride may be present at 1 to 20 wt %, specifically 5 to 20 wt %, and preferably 5 to 15 wt %.

[0026] When a second homopolymer of vinylidene fluoride is present, the ratio of the apparent melt viscosity of the first homopolymer to the second homopolymer may be greater than or equal to 5, such as greater than or equal to 10 or greater than or equal to 50. The apparent melt viscosity may be expressed as Pa.s and measured on a capillary rheometer at a temperature of 230°C and 100 s -1 Measured at a shear rate of .

[0027] The polymer composition can be formed using any suitable method, for example, by blending the polymer components in the molten or dry state.

[0028] The polymer composition may have a carbon content of at least 1.65 gcm as measured according to ISO 1183 or ASTM D792. -3 In some examples, the polymer composition may have a density of 1.70 gcm as measured according to ISO 1183. -3 Up to 1.75gcm -3 density.

[0029] The polymer composition may have a melting point of at least 160° C. as determined by ISO 11357-2. In some examples, the polymer composition of the tubular layer may have a melting point of 165° C. to 170° C. as determined by ISO 11357-2.

[0030] The polymer composition may have a tensile strength at yield of at least 30 MPa at 23°C, 50 mm / min according to ASTM D 638. The polymer composition may have a tensile strength at break of at least 30 MPa at 23°C, 50 mm / min according to ASTM D 638.

[0031] The polymer composition may contain fillers (e.g., carbon fibers, glass fibers, basalt fibers, or particles such as clays / silicates, carbonates, metal oxides). Where the polymer composition containing fillers contains fibers, these fibers can be provided in the form of a tape containing long fibers oriented in the length direction of the tape; the tape also contains a matrix of the polymer composition, which can be spirally wound around the pipe body and subsequently consolidated using heat and / or pressure to form a composite pipe layer. The filler can reduce the permeability of the polymer layer to gases, and / or strengthen the layer.

[0032] The maximum operating temperature of the tubular fluid sealing layer may be greater than 130°C, for example greater than 140°C. This is determined by creep testing and aging data, where a polymer sample is immersed in a hydrocarbon medium (e.g., diesel) for a period of time to simulate use; this can remove plasticizers and cause hydrocarbons to be absorbed into the polymer, thereby changing its physical and mechanical properties. These properties can be determined according to normal test standards such as those cited in API 17J.

[0033] It has been discovered that by using a plasticizer in an amount of 0.3 wt % to 2 wt %, a tubular fluid sealing layer can be produced having a higher maximum operating temperature than most PVDF materials while maintaining crack and fatigue performance, and improving aging performance.

[0034] It has also been discovered that the selected plasticizer content can be reduced from higher levels (eg, 3 wt %) to 0.3 wt % to 2 wt % while maintaining the permeability characteristics of the polymer, as can be seen in the examples below.

[0035] The tubular fluid sealing layer may have a diameter of 50 mm to 600 mm, for example 50 mm to 400 mm. The thickness of the tubular sealing layer may be 1 mm to 50 mm, for example 5 mm to 20 mm. The length of the tubular sealing layer may be 10 m to 10 km or more.

[0036] In use, the tubular fluid sealing layer contacts the fluid flowing through the flexible pipe body. For example, the tubular fluid sealing layer can be an internal pressure sheath of the flexible pipe body. In some examples, a carcass layer (e.g., a metal carcass layer) can be positioned within the tubular fluid sealing layer so that the flexible pipe body has a rough hole. However, even with a carcass layer, when the fluid penetrates the joint in the carcass layer, the fluid flowing through the flexible pipe body contacts the tubular fluid sealing layer.

[0037] The pressure retaining armor layer is positioned on the tubular fluid sealing layer. The pressure retaining armor layer can be arranged around the tubular sealing layer by winding. The pressure retaining armor layer can surround the tubular fluid sealing layer. The pressure retaining armor layer can be in direct contact with the tubular fluid sealing layer.

[0038] Applying internal pressure to the pipe (i.e., pressure from within the hole) produces radial expansion in all layers. This occurs when the tubular fluid-sealing layer may be subjected to deformation and creep into the gap of the overlying pressure-maintaining armor layer. Under high pressure (about 8000psi / 55MPa or higher), the resulting strain distribution within the tubular fluid-sealing polymer layer may be in the area around the gap, and the polymer composition of the tubular fluid-sealing layer may be deformed by cavitation rather than plastic flow. This in turn leads to the formation of microcracks or microcracks on the radial inner surface of the polymer layer. During any subsequent load period (such as the load experienced during normal use of transporting produced fluids), such microcracks may then extend to form longer and / or deeper cracks throughout the polymer layer. This may increase the risk of failure of the polymer layer and may ultimately lead to the loss of pressure sealing, thereby having an adverse effect on the life of the flexible pipe. By using a plasticizer in an amount of 0.3 wt % to 2 wt %, the risk of cracking and cracking is unexpectedly reduced. Thus, the polymer compositions employed in the present invention can be used to provide tubular fluid sealing layers having improved crack resistance compared to prior art tubular fluid sealing layers employing higher amounts of plasticizers.

[0039] The pressure retaining armor layer may include at least one wire, such as at least one metal wire. Optionally, the pressure retaining armor layer may include a composite structure of fiber elements and a polymer matrix. In some examples, the pressure retaining armor layer may include at least one layer of wound composite tape. The composite tape may be at least partially bonded to the underlying fluid sealing layer. The composite tape may include a polymer matrix comprising a homopolymer of vinylidene fluoride according to the present invention.

[0040] The pressure retaining armor layer may be a structural layer. The layer may be formed of a metal wire or composite tape wound around the tubular fluid-tight layer. The pressure retaining armor layer may be wound, for example, at a lay angle close to 90°. This may increase the resistance of the flexible pipe to internal and external pressures and mechanical breaking loads. The pressure retaining armor layer may also structurally support the tubular fluid-tight layer. The pressure retaining armor layer may have an interlocking construction.

[0041] The tensile armor layer is positioned over the pressure retaining armor layer. The tensile armor layer may be disposed around the pressure retaining armor layer by winding. The pressure retaining armor layer may surround the pressure retaining armor layer. The tensile armor layer may be in direct contact with the pressure retaining armor layer. In some examples, at least one intermediate layer may be disposed between the tensile armor layer and the pressure retaining armor layer. The intermediate layer may serve as a sacrificial wear layer to help prevent wear between adjacent layers.

[0042] The tensile armor layer comprises a plurality of helically wound tendons. The tendons may comprise metal wires or composite fiber elements. In some examples, more than one tensile armor layer may be provided. For example, the flexible pipe body may comprise a first tensile armor layer and a second tensile armor layer. Each tensile armor layer may be a structural layer. The lay angle of the tensile armor layers may typically be between 10° and 55°. Each layer may be used to maintain tensile loads and internal pressure. The tensile armor layers may be counter-wound in pairs.

[0043] The flexible pipe body may include a thermal insulation layer. The flexible pipe body may also include an outer jacket. The outer jacket may include a polymer layer for protecting the pipe from penetration, corrosion, abrasion and mechanical damage by seawater and other external environments.

[0044] Flexible pipes can be used to transport produced fluids such as oil and / or gas and / or water from one location to another. In some examples, the flexible pipe body is used to transport fluids to and from a subsea location. The subsea location can be deep sea, such as 1000 meters or more, or just below sea level. The flexible pipe body can have an inner diameter of typically up to about 0.6 meters.

[0045] The flexible pipe body may be provided with one or more end fittings to form a flexible pipe. The end fittings of the flexible pipe may be used to connect sections of the flexible pipe body together or to connect it to terminal equipment, such as a rigid subsea structure or a floating facility. Thus, among other different uses, the flexible pipe may be used to provide a riser assembly for conveying fluid from a subsea flow line to a floating structure. In such a riser assembly, a first section of the flexible pipe may be connected to one or more further sections of the flexible pipe. Each section of the flexible pipe comprises at least one end fitting.

[0046] The flexible pipe body can be used to form an unbonded flexible pipe. In an unbonded pipe, the layers are not bonded together during the manufacturing process. Thus, for example, the tubular fluid-tight layer is not bonded to the pressure-retaining armor layer during the manufacturing process. API Specification 17J, entitled "Specification for Unbonded Flexible Pipe," defines the technical requirements for safe, dimensionally and functionally interchangeable flexible pipes that are designed and manufactured to uniform standards and criteria.

[0047] In certain embodiments, the flexible pipe body conveys fluid under pressure. The pressure may exceed 100 psi (-700 kPa) and / or be up to 24,000 psi (-165 MPa). Additionally or alternatively, the method may include the step of maintaining the pressure in the fluid for a predetermined period of time to secure the radial motion of the fluid sealing layer. Maintaining the pressure in the fluid may include maintaining a pressure in excess of 100 psi (-700 kPa) and / or up to 24,000 psi (-165 MPa).

[0048] The features of all the above-described embodiments are intended to be combinable with each other unless mutually exclusive.

[0049] Figure 1 It is shown how a flexible pipe body 100 may be formed from a combination of layered materials according to one embodiment of the invention. It should be noted that the layer thicknesses are shown for schematic illustration purposes only.

[0050] like Figure 1 As shown, the flexible pipe body may include an optional innermost carcass layer 101. The carcass provides an interlocking construction that can be used as an innermost layer to completely or partially prevent the tubular fluid-tight layer 102 (or internal pressure sheath) from collapsing due to pipe decompression, external pressure, and tensile armor pressure and mechanical breaking loads. It should be understood that certain embodiments of the present invention are suitable for "smooth hole" operations (i.e., without a carcass) as well as such "rough hole" applications (with a carcass).

[0051] The tubular fluid-sealing layer 102 can be used as a fluid-retaining layer and is formed of a polymer layer that ensures the integrity of the internal fluid. It should be understood that this layer itself may include multiple sublayers. It should be understood that when an optional carcass layer is used, the tubular fluid-sealing layer is generally referred to as a barrier layer by those skilled in the art. In operations without such a carcass (so-called smooth-bore operations), the tubular fluid-sealing layer may be referred to as a liner.

[0052] A pressure retaining armor layer 103 is disposed around the tubular fluid sealing layer 102. The pressure retaining armor layer may be a structural layer that increases the resistance of the flexible pipe to internal and external pressures and mechanical breaking loads, having, for example, a lay angle close to 90°. The layer may also structurally support the tubular fluid sealing layer. The pressure retaining armor layer 103 may have an interlocking construction, or include helically wound composite tape layers that are consolidated to form a composite pressure armor layer.

[0053] The flexible pipe body also includes a tensile armour layer located on the pressure retaining armour layer 103. Figure 1 As shown, the flexible pipe body may include a first tensile armor layer 105 and a second tensile armor layer 106. Each tensile armor layer may be a structural layer having a lay angle typically between 10° and 55°. Each layer may be used to maintain tensile loads and internal pressure. The tensile armor layers may be reverse wound in pairs.

[0054] The flexible pipe body shown also includes an optional tape layer 104 that contains underlying layers and may serve as a sacrificial wear layer to prevent wear between adjacent layers.

[0055] The flexible pipe body may also include an optional insulation layer 107 and an outer jacket 108 comprising a polymer layer for protecting the pipe from penetration by seawater and other external environments, corrosion, abrasion and mechanical damage.

[0056] Each flexible pipe includes at least one portion (sometimes referred to as a segment or section of the pipe body 100) and an end fitting located at at least one end of the flexible pipe. The end fitting provides a mechanical device that forms a transition between the flexible pipe body and the connector. For example, Figure 1 The different pipe layers shown terminate in end fittings so that loads are transferred between the flexible pipe and the connector.

[0057] Figure 2 An example of a riser assembly 200 suitable for transporting produced fluids such as oil and / or gas and / or water from a subsea location 201 to a floating facility is shown. Figure 2 In the embodiment of the present invention, the seabed location 201 includes a seabed flow line. The flexible flow line 205 includes a flexible pipe that is fully or partially resting on the seabed 204 or buried below the seabed and is used for static applications. The floating facility can be composed of a platform and / or a buoy or a floating structure such as a floating structure. Figure 2 The vessel 200 is shown provided. The riser assembly 200 is provided in the form of a flexible riser, ie a flexible pipe 203 connecting the vessel to a seabed facility. The flexible pipe may be located in a section of a flexible pipe body having connecting end fittings.

[0058] It should be understood that there are different types of risers, as is well known to those skilled in the art. Embodiments may be used with any type of riser, such as a freely suspended riser (free catenary riser), a riser constrained to some extent (buoy, chain), a fully constrained riser or enclosed in a tube (I-tube or J-tube).

[0059] Figure 2 It is also shown how sections of flexible tubing can be used as flow lines 205 or jumpers 206 .

[0060] Various modifications to the detailed arrangements described above are possible. For example, the polymer layer may be any layer of the pipe body, and is not limited to a liner or barrier layer. Similarly, the strength layer may be any layer of the flexible pipe body, such as a pressure armour layer, a tensile armour layer, etc. The polymer layer need not be directly adjacent to the strength layer; there may be intermediate layers, such as sacrificial tape layers. For flexible pipe bodies having more than one polymer layer, the above method may be used more than once, in order to treat each polymer layer in turn or simultaneously. This treatment stage may be performed on a barrier layer with a carcass layer, as the carcass layer is not fluid tight and will allow pressurized fluid to flow therebetween to enter the polymer barrier layer.

[0061] Rather than carbon steel wire as described above, the strength layer may be made of stainless steel wire or strip, reinforced polymer composite material or other such suitable material and have any suitable cross-section.

[0062] The invention is not limited to the details of any of the foregoing embodiments. A person skilled in the art will appreciate that several variations of the foregoing embodiments may be envisaged without departing from the scope of the invention, for example, the pressurized fluid may be supplied between a sleeve and another sleeve through a single inlet.

[0063] The invention extends to any novel feature or any novel combination of features disclosed herein, including those of the appended claims and drawings. The claims should not be interpreted as covering only the aforementioned embodiments, but also any embodiments falling within the scope of the claims.

[0064] All features disclosed herein (including those of the attached claims and drawings) can be combined in any combination, except combinations where at least some of such features are mutually exclusive. Furthermore, each feature disclosed herein (including those of the attached claims and drawings) may be replaced by an alternative feature serving the same, equivalent or similar purpose, unless expressly stated otherwise. Therefore, unless expressly stated otherwise, each feature disclosed is merely an example of a general series of equivalent or similar features.

[0065] Example

[0066] As can be seen from Tables 1 and 2 below, the PVDF polymer material with lower plasticizer (Grade 4) exhibits improvements in fatigue and cracking performance compared to many PVDF materials (Grades 1 and 2), and does not suffer any degradation in properties compared to similar PVDF materials with higher plasticizer content (Grade 3), while maintaining permeation and fatigue performance. Figure 3 A comparison of the removal of plasticizer from Grade 3 and Grade 4 over time is also shown for comparative purposes to show the benefit of reducing the plasticizer content of the polymer.

[0067] The performance of the polymer sealing layer of the flexible pipe body can be evaluated through a number of test protocols to understand its physical and mechanical properties. These properties include permeation, ductile-brittle transition temperature and fatigue performance. The first two of these properties can be seen relative to four commercial grades of PVDF polymers in Table 1; the maximum operating temperature, fatigue performance and cracking performance of the same four PVDF polymers can be seen in Table 2.

[0068] Table 1 :

[0069]

[0070] Table 2

[0071]

[0072] *Fatigue performance based on small scale testing of polymer samples extruded from a tube, including all tube features inherent in this layer. Fatigue testing was performed using a setup based on ASTM D6272-10 and a strain controlled method using a four point bend test to form fatigue sn curves as described in conference papers OTC-27260 presented at the Offshore Technology Conference in Houston in May 2016 and OMAE-23573 presented at the International Conference on Offshore Mechanics and Arctic Engineering in San Francisco in June 2014. 1 / 10 means that the material did not reach 10 million load cycles at a strain range below 0.5%; 10 / 10 means that the material reached more than 10 million load cycles at a strain range below 0.5%.

[0073] **Crack performance is based on pressure testing of a cross section of an extruded fluid sealant layer constrained by a simulated pressure armor layer up to at least 24,000 psi using water as the pressurizing medium, confirmed by pressure testing of the pipe (all layers) using full scale. This has been described, for example, in a presentation by Dr. Upul Fernando at the MCE Deepwater Development conference in London in March 2015, "Challenges and Solutions in Developing Ultra-high Pressure Flexibles for Ultra-deep water Applications". 5 / 10 means only minor cracks are visible when the test is applied to the pipe for a design pressure of 10,000 psi; 10 / 10 means no cracks when the test is applied to the pipe for a design pressure in excess of 10,000 psi.

Claims

1. A flexible pipe body for conveying high-pressure fluid, the flexible pipe body comprising Tubular fluid sealing layer, a pressure retaining armor layer positioned over the tubular fluid sealing layer, and a tensile armor layer positioned over the pressure retaining armor layer; wherein the tubular fluid sealing layer comprises a composition comprising a plasticizer and a homopolymer of vinylidene fluoride, and wherein the plasticizer is present in an amount of 0.3 wt % to 2.0 wt % based on the total weight of the polymer composition.

2. The flexible pipe body of claim 1, wherein the polymer composition comprises from 1.5 wt% to 1.9 wt% based on the total weight of the polymer composition.

3. The flexible pipe body according to claim 1 or 2, wherein the polymer composition further comprises a copolymer of vinylidene fluoride.

4. The flexible pipe body according to claim 3, wherein the copolymer of vinylidene fluoride is a copolymer of vinylidene fluoride and hexafluoropropylene.

5. Flexible pipe body according to claim 3 or 4, wherein the copolymer of vinylidene fluoride is present in an amount of 10 to 40 wt% based on the total weight of the polymer composition.

6. A flexible pipe body according to any one of the preceding claims, wherein the polymer composition has a thermal conductivity as measured according to ISO 1183 or ASTM D792 of at least 1.65 gcm -3 density.

7. A flexible pipe body according to claim 6, wherein the polymer composition has a thermal conductivity of 1.70 gcm / s as measured according to ISO 1183 or ASTM D792. -3 Up to 1.75gcm -3 density.

8. Flexible pipe body according to any one of the preceding claims, wherein the polymer composition of the tubular layer has a melting point of at least 160°C as determined by ISO 11357-2.

9. The flexible pipe body according to claim 8, wherein the polymer composition of the tubular layer has a melting point of 165 to 170°C as determined by ISO 11357-2.

10. Flexible pipe body according to any one of the preceding claims, wherein the polymer composition has a tensile strength at yield according to ASTM D 638 at 23°C, 50 mm / min of at least 30 MPa.

11. Flexible pipe body according to any one of the preceding claims, wherein the polymer composition has a tensile strength at break according to ASTM D 638 at 23°C, 50 mm / min of at least 30 MPa.

12. Flexible pipe body according to any one of the preceding claims, wherein the amount of plasticiser is from 1.6 to 1.8 wt% based on the total weight of the polymer composition.

13. The flexible pipe body according to any one of the preceding claims, wherein the pressure retaining armour layer comprises at least one metal wire.

14. The flexible pipe body according to any one of claims 1 to 13, wherein the pressure retaining armour layer comprises a composite structure of fibre elements and a polymer matrix.

15. The flexible pipe body of claim 14, wherein the pressure retaining armour layer comprises at least one layer of helically wound composite tape at least partially bonded to an underlying fluid sealing layer, and wherein the polymer matrix comprises a homopolymer of vinylidene fluoride.

16. A flexible pipe body as claimed in any preceding claim wherein the tensile armour layer comprises a plurality of helically wound tendons, optionally comprising metal wire or composite fibre elements.

17. A method of manufacturing a flexible pipe body according to any one of the preceding claims, the method comprising extruding a tubular fluid sealing layer from a polymer composition comprising a homopolymer of vinylidene fluoride and a plasticizer, wherein the plasticizer is present in an amount of 0.3 wt % to 2 wt % based on the total weight of the polymer composition; positioning a pressure retaining armour layer on the tubular fluid sealing layer; and positioning a tensile armour layer on the pressure retaining armour layer.

Images