WO2011073904A2

WO2011073904A2 - A high-pressure flexible pipe

Info

Publication number: WO2011073904A2
Application number: PCT/IB2010/055804
Authority: WO
Inventors: Keith Dixon-Roche
Original assignee: Pipeflex Manufacturing Ltd
Priority date: 2009-12-14
Filing date: 2010-12-14
Publication date: 2011-06-23
Also published as: GB0921792D0; WO2011073904A3

Abstract

Deep-sea oil and gas high-pressure pipes are required which are relatively light-weight yet strong and able to withstand cyclical collapse and reinflation without undue damage. A fully bonded high-pressure flexible pipe (10) having a pipe wall (20) of composite construction including pressure retaining reinforcement members (60) located within the pipe wall (20) is provided for this purpose.

Description

Title of Invention: A high-pressure flexible pipe

[0001] The present invention relates generally to a high-pressure flexible pipe and a method of manufacture of such a pipe and finds particular, although not exclusive, utility in sub-sea oil and gas exploration and production.

[0002] The pipe may be used for the transportation of hydrocarbon fossil fuels in deep water environments.

[0003] Given that the continental shelf has been exploited to the extent that the world's

remaining available reserves of fossil fuels is limited and rapidly diminishing, and that the continental shelf (shallow water areas) constitutes a small percentage of the total area of the world's oceans, it is considered reasonable to assume that the floor of the world's deepwater oceans will yield a much higher volume of oil and gas than has been recovered to date. It is therefore considered prudent to plan for cost effective deep water (>2000m) fossil fuel recovery.

[0004] The pipe described herein enables the recovery of oil and gas from subterranean

reservoirs in deep water (offshore) locations without incurring substantial additional cost. It is a high-pressure flexible pipe for deep water applications where the pipe may repeatedly flatten and recover without suffering damage.

[0005] Although collapsible high-pressure pipes for use in sub-sea oil and gas applications are known, they suffer from the following limitations.

[0006] Such known pipes are not fully bonded (or are non-bonded) and use relatively stiff reinforcement components, which means that when the pipe flattens due to pressure differentials between the bore and the surrounding environment (which is inevitable in deep water), damage to the pipe occurs as the different layers comprising the pipe wall will not move in synchronicity leading to such effects as "bird-caging" or relative displacement of the pipe component materials. Accordingly, to prevent damage these pipes must remain round (substantially circular) under external hydrostatic pressure. As such, the deeper the water into which the pipe is installed the stronger, heavier and more expensive it becomes. The increased weight and physical size of the product also increases the cost and difficulty of its installation.

[0007] In US2003/0116216-A1, flat and profiled steel wires are used as reinforcement

within the pipe wall. These "wires" have a thickness of approximately 1 mm or greater. This leads to permanent deformation (structural disruption and failure) of the pipe after any partial or complete collapse leading to the possibility that re-inflation is impeded or even impossible.

[0008] In the same application and in WO2004/044469-A2 longitudinal ribs internal to the bore of the pipe are provided to minimise over-flattening of the pipe. However, all such high-pressure flexible pipes manufactured using opposed helically wound reinforcement wires will flatten in the form of a long-pitch helix, the configuration of which is very difficult to predict. Accordingly, it is virtually impossible to ensure that flattening would automatically occur between the ribs along the total length of the pipe.

[0009] Furthermore, any additional member provided within the bore will impede fluid flow and possibly prevent re-inflation.

[0010] It is therefore desirable to provide an improved high-pressure flexible pipe for deep water applications where the pipe may repeatedly flatten and recover without suffering damage. It is an aim to provide a high-pressure flexible pipe that can repeatedly fully or partially collapse in an uncontrolled manner under external hydrostatic pressure and inflate without damage.

[0011] In a first aspect, the invention provides a fully bonded high-pressure flexible pipe having a pipe wall of composite construction including pressure retaining reinforcement members located within the pipe wall being sufficiently flexible to enable the pipe to collapse and re-inflate with substantially no damage or disruption to the wall structure.

[0012] In this regard, the term"composite construction" may mean a structure comprising more than one component material (one of which may be a polymer and another of which may be a high-tensile, flexible steel cord) which shall be enjoined (bonded and/ or interlocked) to the extent that recovery from repeated deformation (more than 1000 cycles) in all three degrees of freedom shall limit strain in the outer and inner surfaces of the composite structure to less than 5% with respect to their fully inflated condition and shall not significantly alter the pipes structure or physical properties during its design life (10 to 20 years). It may further be regarded as meaning that there is no substantial relative movement between the various elements after returning to a rest state after the pipe is deformed.

[0013] The pipe may comprise no rectilinear components, whether within or without the pipe wall or inside the pipe bore, located parallel to the longitudinal axis of the pipe, for controlling the collapse configuration of the pipe wall.

[0014] The pressure retaining reinforcement members located within the pipe wall may be sufficiently flexible to enable the pipe to collapse and re-inflate with substantially no damage or disruption to the wall structure. These pressure containment reinforcement members (possibly included within one or more plies) may be applied sufficiently close together to prevent extrusion of the pipe wall material (such as polymers). They may readily deflect with the pipe wall body (be flexible). They may allow maximum penetration and bonding of the polymer body material into their structure, which may be regarded as relatively open. [0015] The pressure retaining reinforcement members may be wrapped around and within the body of the pipe in alternately opposite directions, the combined helical angle of which averages to a neutral angle balancing hoop and longitudinal forces and growth.

[0016] The pipe may comprise at least one longitudinal reinforcement member embedded in and fully bonded to the pipe wall. The longitudinal reinforcement member(s) may support axial tensile loads applied to the pipe. This is because where such significant axial tensile forces are applied to high-pressure flexible pipes, in the absence of internal pressure and with no internal radial support (which would not be possible in a pipe that is expected to collapse under external hydrostatic pressure), the structure would separate (pull apart) longitudinally without such reinforcement. These longitudinal reinforcement members may not provide any control over the collapse configuration of the pipe wall. The longitudinal reinforcement member may have a tensile stiffness significantly greater than its compressional stiffness.

[0017] The pipe may comprise a plurality of longitudinal reinforcement members arranged equiangularly around the circumference of the pipe wall.

[0018] The pipe may comprise a plurality of longitudinal reinforcement members arranged substantially closely spaced in two substantially diametrically opposite groups around the circumference of the pipe wall.

[0019] The longitudinal reinforcement member(s) may be located outside the internal

pressure retaining reinforcement plies. Alternatively, the longitudinal reinforcement member(s) may be located inside the internal pressure retaining reinforcement plies. Another possibility is that the longitudinal reinforcement member(s) may be located both inside and outside the internal pressure retaining reinforcement plies.

[0020] The longitudinal reinforcement members may be axially compressible to allow

bending of the pipe whilst containing tensile extension to less than 5%, possibly less than 0.5%.

[0021] Thus the pipe may compress axially without damage to the pipe wall. The pipe may be described as a longitudinally compressible high-pressure pipe.

[0022] The reinforcement members (either or both of the pressure retaining members and the longitudinal reinforcement members) may comprise polymers and a flexible steel cord wherein the steel cord has an open structure such that the polymer has at least partially, or substantially totally, penetrated and bonded around and within it.

[0023] The flexible steel cord may be, at least partially, replaced with a flexible carbon fibre cord.

[0024] The open structures of the steel or carbon fibre cord may allow sufficient penetration and bonding to/into them by the polymer body material so as to be able to withstand repeated deformation of the pipe without tearing or dislocation of the cord from the other materials in the pipe wall. [0025] The steel/carbon fibre cord may have a fill density of less than 65%.

[0026] The pipe may comprise elastomers and/or plastics (collectively described herein as polymers), and a flexible steel cord, wherein the steel cord has an open structure such that the polymer has at least partially penetrated and bonded around and within it.

[0027] The polymers may accommodate maximum deflection strain and allow rapid

permeation of entrained gas. The elastomers may be selected from one or more of the nitrile materials such as NBR (nitrile butadiene rubber) or HNBR (hydrogenated NBR), or silicon for extreme (high or low) temperature conditions.

[0028] The open structure of the steel cord or carbon fibre cord may have a linear density of less than 65%. It may be less than 55% or even less than 50%. In this respect, linear density may mean the total cross-sectional area occupied by materials (as opposed to voids) divided by the total cross-sectional area of the cord. The total cross-sectional area of the cord may be equivalent to an imaginary circle drawn around the strands making up the cord such that it touches the outermost radial portion of each strand. The open structure may have a core of polymers. By comparison steel cord used in known high pressure pipes have a reinforcement of steel cord as will be explained in more detail below.

[0029] The term "reinforcement" may mean the provision of elongated high-strength

flexible wires or cords manufactured from materials such as steel in the form of a multi-strand wire cord (herein referred to as steel cord), or carbon fibre in similar (multi- strand) or in single rod form. The application of this reinforcement may be such that extrusion of the body filler polymer material is prevented or otherwise damaged.

[0030] The pipe may include a polyethylene film bonded to its exterior surface. This film may have a thickness of less than 0.2mm. The film may minimise water permeation, allow gas permeation and provide good abrasion resistance. The film may be melted into the surface of the pipe and may be punctured to improve permeability of entrained gases.

[0031] The pipe may be arranged to have a compressional shortening (axially) far greater than a tensional extension, when under load.

[0032] The pressure retaining members (or plies) may be formed using a calendaring

process.

[0033] The weight per metre of the pipe may lie in the range 20kg/m to 200kg/m.

[0034] Whilst all materials within the pipe wall may have substantially different stiffness, their construction is such that they all demonstrate similar bending characteristics in all

3 degrees of freedom.

[0035] The stiffness of the pipe wall may lie in the range 0.4 to 3.3 N.mm² for a two-ply wall and in the range 32 to 403 N.mm² for a ten-ply wall.

[0036] The pipe may comprise no fabric as this may initiate tearing in the pipe body/wall material under repeated deformation and recovery. This is due to fabric material not having similar bending characteristics in all three degrees of freedom.

[0037] The pipe may include a liner comprising plastics on the interior of the pipe wall. This liner may be a fully-fluorinated fluoropolymer plastic such that it may accommodate/ withstand the maximum variation in chemical and temperature conditions and reduce the gas permeation rate into the body/pipe wall of the pipe. Alternatively, this liner may be comprised of a partially fluorinated fluoropolymer plastic material. Another possibility is that the liner is comprised of PVDF (polyvinylidene fluoride). A yet further possibility is that the liner is comprised of polyethylene. In any case, the liner may be selected from the PTFE (Polytetrafluoroethylene) group of plastics such as FEP (Fluorinated Ethylene Propylene) or PFA (Per-Fluoro Alkoxy).

[0038] The pipe is intended for use in harsh deep water environments and preferably has a construction including a fully bonded composite structure comprising steel (or carbon fibre) and polymer materials that deform in unison under such conditions. The pipe wall materials may comprise an elastomeric body fully encapsulating and bonded to a similarly flexible reinforcement material of a relatively open and flexible structure all of which may be sandwiched between a fully fluorinated fluoropolymer plastic internal liner and a plastic outer skin.

[0039] For the purposes of this specification, the words "hose" and "flexible pipe" are

mutually synonymous. A flexible pipe is an elongated tubular conductor (or conduit) for the transportation of fluids. Furthermore, a high-pressure flexible pipe relies on its high-strength pressure retaining reinforcement members to contain internal pressure, whereas a low pressure flexible pipe relies on its polymeric body material to contain internal pressure. High-pressure is a relative term and varies inversely with internal diameter. For the purposes of this specification, high-pressure may be approximately in accordance with the relationship; lOOOpsi (70bar) and above for a 3 inch internal diameter down to lOOpsi (7bar) and above for a 20inch internal diameter.

[0040] The pressure retaining reinforcement members (or plies) in a high-pressure flexible pipe may be laid in contra-rotating helical coils of two or more plies with the helical pitch length of each cord in each ply being approximately equal. Whilst the lay angle of each ply may vary dependent upon its diameter of application, the average of all lay angles may be a neutral angle such that end cap and dilation forces are balanced.

[0041] When a high pressure pipe collapses due to an external pressure it may flatten.

Depending on the construction of the pipe wall two bulbs may be formed by the pipe wall, in the bore of the pipe substantially diametrically opposite one another in a radial sense. The stiffness of the pipe wall may control the degree of flattening (and the size of the bulbs) protecting the internal liner from being over compressed. The natural collapse condition of a correctly designed high-pressure pipe will generate allowable strain values in all materials from which the composite body has been constructed but will prevent excessive strain in any component material in any given water depth. Such a collapse may be allowed to occur naturally with no separate or integral longitudinal pipe wall bend controlling components of any kind. This is necessary due to the unpredictability of the natural helix formed by the flattened region along the length of the pipe. The natural helix will occur due to the discrepancy between lay angle and lay diameter of the helical pressure retaining reinforcement in each ply.

[0042] The sectional stiffness of the composite pipe wall may be modifiable by varying the stiffness and number of pressure retaining reinforcement members to allow for greater or lesser bulb size. The appropriate wall stiffness may be determined using the formula I=∑I+Ad², where given I is the total second moment of area of the composite structure, ∑I is the sum of the individual second moments of area of each component or material section, A is the area of the component or material section in question, and d is the distance from the centre of the area A to the neutral axis, in conjunction with the formula Stiffness=E.I, where E is Young's/tensile modulus of the material.

[0043] The high-pressure pipes may have a diameter in the range 2 to 20 inches. The pipes may have a minimum bend radius of 0.5m in an axial/longitudinal sense.

[0044] In a second aspect, the invention provides a method of manufacture of a fully bonded high-pressure flexible pipe having a pipe wall of composite construction including the steps of: forming a sheet of composite material comprising polymers and an embedded steel cord, wherein the polymers have been forced into the interstices of the open structure of the steel cord; forming a pipe from said sheet; wrapping a shrinkable tape around the pipe; and autoclaving the pipe such that the elastomer is vulcanised.

[0045] The method may further comprise the step of including at least one longitudinal reinforcement member in the longitudinal length of the pipe wall for controlling length and stiffness and not a collapse configuration of the pipe. In this respect, the at least one longitudinal reinforcement member may only help control the axial length and the stiffness of the pipe.

[0046] The method may include the step of providing an internal liner and/or an external cover.

[0047] The method may include other steps to produce a pipe according to the first aspect and/or as described herein. For instance it may include the step of locating the longitudinal reinforcement member radially inward, radially outward, or both, of the sheet comprising the embedded steel cord.

[0048] The term "steel cord" also encompasses the use of carbon fibre cord.

[0049] In a third aspect, the invention provides a multi-strand cord, each strand being constructed from multi-filament wires whereby a central axially orientated space is filled with a polymer material, this material being fully bonded to all surrounding filaments. [0050] In this regard, the multi-strand cord may be an OTR variant, as described herein. The cord may be used in any of the arrangements described herein and include any of the features and aspects described herein.

[0051] The strands may comprise steel and/or carbon fibre. The strands may be arranged in a radial pattern when viewed axially. The cord may have an axial compressive modulus significantly less than its tensile modulus, this relationship prevailing for at least 3% of the length of the cord.

[0052] In one embodiment, the cord may experience a reduction in length of 3-5% before "locking up". The cord may comprise planetary strands, each alternate strand being rotated such that its arrangement of filaments is different to its immediate neighbours so as to maximise packing density.

[0053] The longitudinal growth under axial tension of the cord may be minimised.

[0054] Radial slippage of the strands may be allowed to aid compressibility.

[0055] All strands may be coiled at a pitch providing approximately 0.5% helical clearance between each strand. This may relate to the planetary strands.

[0056] All of the features described and recited herein relating to the cord(s) may also relate to the OTR variant cord described above in relation to the flexible pipe.

[0057] The maximum arc length differential in longitudinal reinforcing members in the body of a bent high-pressure flexible pipe will vary between the inside and the outside of a given bend radius by between 1% and 4% dependent upon pipe diameter (2" to 20" bore). Moreover, the greater the tension in a bent pipe without interference from end terminations or external objects the greater the bend radius and the smallest bend radius occurs at the point of lowest tension.

[0058] The high-pressure pipe described in this specification may be able to collapse in any plane or axis without incurring damage, without any predefined collapse pattern/ orientation and without any additional element or feature to control the collapse located anywhere within the pipe.

[0059] Given that the pipe must ideally remain within 0.5% of its manufactured length under axial tension when straight (otherwise there is a risk of extruding the pipe body material between the reinforcement cords under internal pressure) it is required that the tensile force in each of the longitudinal reinforcement members may be such that maximum growth in the pipe at the neutral axis will not exceed 0.5%.

[0060] Given that an OTR cord will extend by approximately 5% at break, it may be

necessary to ensure maximum utilisation in each longitudinal reinforcement member of 0.5/5 = l/lO"¹ under maximum axial tension when straight in order not to exceed 0.5% growth in the pipe. These criteria may define the number of longitudinal reinforcement members required in the construction to support a given external axial tension in the pipe. [0061] As it is reasonable to assume that an OTR cord has a higher axial stiffness under tension than under compression, it is also reasonable therefore to assume that when a pipe constructed as shown in Figure 11 is bent, its neutral axis will shift towards the outside of the bend. Thus the cords inside the neutral axis must compress to a greater extent than the extension experienced in the cords outside the neutral axis.

[0062] It is a requirement for this specification that compression in any longitudinal reinforcement member may not disrupt the polymer body in which it is embedded. That is, it shall not significantly deform out-of-line under axial compression. Therefore it may be a requirement for the cords used for longitudinal reinforcement members in Figures 11 and 12 to be able to compress axially up to 3% of their length with considerably lower axial compressive modulus than when under tension. It may also be a requirement of this specification that the longitudinal reinforcement members shall demonstrate similar tensile modulus behaviour to conventional OTR cord (20000 < E < 30000 N/mm²) under tension.

[0063] Traditional steel cord constructions do not naturally compress under axial loads without deforming globally (bending the axis of the cord out of line). If global deformation occurs in a longitudinal reinforcement member when embedded in the polymer body of a high-pressure flexible pipe it may result in tearing of the polymer material.

[0064] For the purposes of this specification, a compressible steel cord may be a multi- strand wire comprising numerous small diameter (<0.25mm) wire filaments coiled or woven in an organised manner that together constitute a single cord or braid that will axially collapse by up to 3% with minimal axial compression but which behaves like a conventional steel cord in tension.

[0065] In a fourth aspect, the invention provides a fully bonded high-pressure flexible pipe having a pipe wall of composite construction including a multi-strand cord according to the third aspect.

[0066] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0067] Figure 1 is a cross-sectional view of a pipe in fully inflated condition;

[0068] Figure 2 is a cross-sectional view of the pipe of Figure 1 having been partially

compressed radially;

[0069] Figure 3 is a cross-sectional view of the pipe of Figure 1 having been further

compressed (flattened) radially; [0070] Figure 4 is a cross-sectional view of one end of pipe having been fully flattened;

[0071] Figure 5 is a series of two cross-sectional views of part of any section undergoing bending;

[0072] Figure 6 is a series of two cross-sectional views of part of a pipe wall undergoing bending;

[0073] Figure 7 is a cross-sectional view of a prior art steel cord;

[0074] Figure 8 is a cross-sectional view of another prior art steel cord;

[0075] Figure 9 is a cross-sectional view of a steel cord according to one embodiment of the invention;

[0076] Figure 10 is a cross-sectional view of a steel cord according to another embodiment of the invention;

[0077] Figure 11 is a cross-sectional view of a pipe with longitudinal reinforcement

members equiangularly spaced around the circumference;

[0078] Figure 12 is a cross-sectional view of a pipe with longitudinal reinforcement

members located in two discrete places around the circumference;

[0079] Figure 13 is a cross-sectional view of a pipe undergoing bending and incorporating longitudinal reinforcement members;

[0080] Figure 14 is an edge (in-plane) view of Figure 13;

[0081] Figure 15 is a sectional view of a steel cord showing linear strand locations;

[0082] Figure 16 is a sectional view of another steel cord showing non-linear strand

locations; and

[0083] Figure 17 is a series of two cross-sectional views of three filaments in the steel cords of Figure 16 under axial compression where certain filaments are able to displace radially thus allowing axial compression to occur.

[0084] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0085] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0086] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

[0087] It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0088] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments. Furthermore, the particular features, structures or characteristics of any embodiment or aspect of the invention may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0089] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0090] Furthermore, while some embodiments described herein include some features

included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0091] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0092] The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

[0093] In Figure 1 a pipe 10 is shown in fully inflated condition (no collapse). The pipe 10 comprises a pipe wall 20 having a radially outer surface 21, an inner radial surface 30 defining a bore 22 and a neutral axis shown as a broken line 25. The radius of this neutral axis is indicated "R ". A portion of wall 40a is outlined.

[0094] Figure 2 shows the pipe 10 having been partially compressed, due to a pressure differential between the bore 24 and the exterior of the pipe. The top and bottom portions 15 of the wall have been partially compressed radially. The pipe has an approximate figure of "8" shape (on its side). The portion of wall 40b outlined has a reduced radius compared to that shown 40a in Figure 1.

[0095] Figure 3 shows the pipe 10 having two bulbs 35a, 35b separated by a mid-portion where the pipe walls 16 have been compressed radially inward to such an extent that they meet in the middle. These bulbs may be self-supporting and ungoverned in that they may freely occur in any plane or axis and can "bend" along their axial length, possibly in a "slow" helix. The overall shape could be perceived as a "dog bone". The two bulbs allow for fluid to flow freely through the pipe and facilitate reinflation. The portion of wall 40c outlined has a still further reduced radius compared to that shown in Figures 1 and 2. The pipe may be viewed as having completely collapsed and/or be at the limit of flattening/collapse.

[0096] The neutral angle may be approximately 54°, 44', 8.2".

[0097] The view in Figure 4 is the same as the right hand end of the pipe 10 shown in Figure 3. It shows half a fully collapsed pipe. The bulb defining the bore 35b will occur naturally under external hydrostatic pressure 50 reducing the bend radius of the neutral axis 25 to R₂. The size of the bulb 35b will depend on a combination of the magnitude of the external hydrostatic pressure 50 and the resistance to bending (stiffness) of the pipe wall 20. It is normal and expected that a pipe with a relatively 'stiff wall section (calculated using the formula I=∑I+Ad², discussed in more detail below, to establish the contribution to effective stiffness of each reinforcement ply that has flattened under external hydrostatic pressure) will form a shape similar to that shown in Figure 4. The shape of the bulb will be defined by the resistance in the wall to deformation under external pressure. The distance "r" may illustrate the position of the neutral axis. If r=0 there will be no strain in the pipe wall.

[0098] Figure 5 shows a section of pipe wall 20 in both straight and bent configurations. The bend radius R may be used to determine strain in the composite materials making up the pipe wall 20. The strain in the composite materials in the bent pipe is equal to Ri - R₂, Ri and R₂ being shown in Figures 1 and 4. The maximum strain in the outer surface of the pipe wall is equal to r/R, where r is the distance of the neutral axis 25 a from the pipe wall radial surface, and R is the radius of curvature of the neutral axis 25b of the bent pipe wall.

[0099] Figure 6 shows in closer detail the sections of pipe wall 20 referenced "40a" and

"40c" shown in Figures 1 and 3. The pipe wall 20 includes steel cord 60. The less bent pipe section 40a has a neutral axis referenced "25 a"; the more bent pipe section 40c has a neutral axis referenced "25b". The radius of curvature of the less bent pipe section 40a is referenced "Ri", whereas the radius of curvature of the more bent pipe section 40c is referenced "R₂". The stiffness of the pipe wall section 40c is based upon a solid structure manufactured from various materials and may be calculated using the formula I=∑I+Ad², where given I is the total second moment of area,∑I is the sum of the individual second moments of area, A is the area of the material in question, and d is the distance from the centre of the area A to the neutral axis, in conjunction with the formula; Stiffness = EI (where E is Young's/tensile modulus of the material).

[0100] The effect on stiffness from any longitudinal reinforcement members may be ignored for this calculation.

[0101] Figure 7 is a cross-sectional view of a known steel cord strand 90. It has a perimeter approximately defined by a circle 100 enclosing all nineteen steel filaments 110 which are arranged in 5 rows. In the top row there are three filaments, the next row down has four filaments, the next one five, the next four and the bottom row has three filaments. There is a central wire or filament in the strand and the various filaments are relatively closely packed. This strand 90 is the basic structure for a Hosecord (1x19 Warrington construction). It is relatively very stiff and has a relatively small surface area for bonding. It is therefore considered unsuitable for a collapsible pipe.

[0102] A different strand 120 is shown in on the left of Figure 8. It has only seven filaments 110, a central one and six surrounding it in an approximate circle. The various filaments are relatively closely packed. This strand 120 is the basic structure for an OTR (7x7 off-the-road tyre) cord 92 shown on the right of the Figure. This cord 92 has seven strands 120 comprising a central strand and six other strands surrounding it in an approximate circle. The perimeter of the cord 92 is defined by an approximate circle 140. This structure is more flexible than Hosecord (i.e. OTR cord has less than 5% of Hosecord' s stiffness) and therefore considered suitable for use in a collapsible pipe where a relatively stiff pipe wall is necessary to protect the inner plastic liner from excessive strain.

[0103] Another different strand 150 is shown in on the right of Figure 9. It has thirteen

filaments 110, a central one, an intermediate layer of six filaments immediately surrounding the central one in an approximate circle, and then an outer "layer" comprising another six equiangularly spaced filaments. This strand 150 is the basic structure for an OTR variant cord 94, shown on the left of the Figure, that may provide maximum strength and flexibility that may be used in all collapsible pipe structures. The cord 94 has seven strands 150; a central one and six others surrounding it circularly in close relationship. All the strands have the same orientation as one another.

[0104] Figure 10 shows yet another different strand 180 on the left of the Figure. It

comprises twelve filaments having six filaments 110 arranged in a circle and then an outer "layer" comprising another six equiangularly spaced filaments. It is similar to the strand 150 shown and described in relation to Figure 9. However, one difference is that it comprises no central filament in the form of a steel wire of carbon fibre, rather it comprises a polymers core 200. This may completely fill the void between the surrounding six filaments and therefore may not be truly circular in cross-section but instead be an approximate star shape. The polymer may additionally or alternatively extend outside radially of the core at least partially filling the voids between the radially outer filaments. A cord 96, shown on the right of the Figure, is comprised of seven such strands 180; having a central strand 180 and six other strands 180 surrounding it in a closely spaced and circular arrangement. It is to be noted that three of the six surrounding (planetary) strands (every other one) have been rotated about their centres by approximately 30° to maximise packing and thereby limit the axial extension of the cord under tension. This is not necessarily an essential feature. It is expected that this strand rotation may result in the lifting of the outermost filament in these rotated strands (refer to Figures 16 and 17) which may assist axial compressibility. Alternatively, or additionally, it may be that one or more (possibly alternate) strands move radially out when the pipe is subjected to compression.

[0105] The polymer material in the core may be bonded to the surrounding filaments. The polymer core may allow the strand to expand radially under axial compression but not compress radially under axial tension. This may allow the compressible steel cord, and thus the pipe, to compress axially but minimise axial extension.

[0106] In any of the embodiments described herein, the cord 94, 96 may have a diameter of greater than 2.0mm. The filaments 110 may have a diameter of less then 0.025mm.

[0107] Another possible further variant to the design shown in Figures 9 and 10 is where smaller strands having fewer filaments or smaller diameter filaments are used to surround the central strand of the cord 94, 96.

[0108] It is known to use Hosecord (Figure 7) to produce high-pressure bonded flexible pipes for the pressure containment reinforcing plies. However, this makes the pipes relatively inflexible as the Hosecord has a relatively closed structure and its filaments are greater than 0.7mm diameter thereby making the cord relatively stiff. By way of illustration, the three types of steel cord available today are tyre cord, Hosecord (Figure 7) and OTR (Figure 8). Tyre cord is generally manufactured in diameters of 1mm and below and therefore too small to be of practical use with high-pressure pipes. It is possible, however, to use OTR Variants such as that shown in Figures 9 and 10 to provide pipes with improved properties over and above the principal alternatives. By way of illustration, the properties of alternative cord constructions of a similar diameter are compared in the following Table;

[0109] [Table 0001]

Table 1

[0110] As can be seen from the above Table, OTR Variants provide more strength per unit weight and considerably lower stiffness. For the purposes of this specification, the OTR or OTR Variants may be used for pressure containment reinforcing plies. Carbon fibre cords or rods may be used where reduced strength and some increased stiffness permit.

[0111] Figure 11 shows a possible configuration of longitudinal reinforcing members 290 in a collapsible high-pressure pipe 220. The pipe 220 comprises an outer radial surface 230 and an inner radial surface 240 defining a bore 250. It also comprises at least one ply 270, including, or being, pressure retaining reinforcement members such as cord (steel or otherwise), and layers of polymers 260, 280 sandwiching said ply 270. The longitudinal reinforcing members are arranged equiangularly spaced around the circumference on the pipe wall in eight radial positions. Each radial position has two reinforcing members 290, one radially outward of the ply 270 and one radially inward of the ply 270. Other arrangements and number of reinforcing members are possible selected as appropriate and according to the magnitude of the axial load likely to be applied to the pipe in use. The arrangement shown in Figure 11 may be for a straight section of pipe having externally applied axial loads.

[0112] Pipes that are expected/required to bend in more than one plane may use specially constructed longitudinal reinforcement members that may collapse axially with minimal resistance but that will essentially behave similar to a traditional steel cord under tensile axial loads (refer to Figures 10, 15 and 16). These reinforcement members may be referred to as "compressible steel cord".

[0113] The longitudinal reinforcement members may not impede the pressure containment characteristics of the pipe, but may readily deflect with the polymer flexible body (pipe wall). They may allow maximum penetration and bonding of the polymer body material into their structure, during manufacture, which may be a relatively open structure.

[0114] Figure 12 shows another possible configuration of longitudinal reinforcing members 390 in a collapsible high-pressure pipe 320. The pipe 320 comprises an outer radial surface 330 and an inner radial surface 340 defining a bore 350. It also comprises at least one ply 370 including pressure retaining reinforcement members such as cord (steel or otherwise), and layers of polymers 360, 380 sandwiching said ply 370. The longitudinal reinforcing members are arranged in two discrete areas 391, 392, substantially diametrically opposite one another in a radial sense. Each radial position 391, 392 has ten reinforcing members 390, five arranged radially outward of the ply 370 and five arranged radially inward of the ply 370. Other arrangements and number of reinforcing members are possible selected as appropriate and according to the magnitude of the axial load likely to be applied to the pipe in use. The arrangement shown in Figure 12 may be for a pipe in a bent arrangement expecting to have externally applied axial loads.

[0115] The amount and configuration of the longitudinal elements may be determined on the basis of application. For example, the number and strength of longitudinal reinforcement members may be selected to accommodate the axial load. The combined axial stiffness of the longitudinal reinforcement members may be selected such that growth under axial loads does not compromise pipe integrity but may accommodate natural growth of the pipe under pressure. Location of the members inside or outside the pressure carrying reinforcement plies may be a matter of preference for the designer.

[0116] Where axial loads are applied to straight pipe, the longitudinal reinforcement

members may be situated evenly around the body of the pipe (Figure 11). For pipes bent in-plane (e.g. risers or jumpers), the longitudinal reinforcement members may be spaced closely together either side of the centreline of the body of the pipe (Figure 12) at 90° to the plane of the pipe bend (Figures 13 & 14). For example they may be located either side of the pipe body in a riser.

[0117] For pipes bent out-of-plane (e.g. tie-in spool-pieces), the longitudinal reinforcement members may be spaced as described above for straight pipes, but selected such that axial stiffness of the longitudinal reinforcement members allows for greater length variation but also accommodate external axial loading (as opposed to internal pressure induced end-cap loading).

[0118] The wall of a high-pressure flexible pipe under full or partial collapse will induce strain in its constituent parts. As can be seen in Figures 1, 4 and 6, the wall of the pipe will be deformed due to its reduced bend radius from R j to R ₂ . The amount of strain in the component or material will depend upon its distance from the neutral axis (d in Figure 6). In order to ensure that the pipe wall retains sufficient stiffness to prevent excessive strain in any component material of the pipe wall (for example the fully flu- orinated fluoropolymer plastic liner) the reinforcement material may be selected and located within the wall such that the correct composite stiffness is achieved. The resulting stiffness can be determined by using the formula provided herein which is only valid for fully bonded composite structures.

[0119] Figure 13 shows a pipe bent under axial load associated with the configuration of longitudinal reinforcement members as shown in Figure 12. These longitudinal reinforcement members allow the imposition of axial loads without disruption of the pipe body. The axial stiffness of the longitudinal reinforcement members may be designed or applied such that they preferentially allow axial loads in both a straight pipe and a bent pipe.

[0120] Figure 14 shows the end view of the bent pipe shown in Figure 13 showing the longitudinal reinforcement members either side of the pipe in-plane of the bending radius.

[0121] Figure 15 shows a section through a conventional OTR cord 500 having helically wound strands wherein the outer filaments of the strands are in a substantially linear configuration which may inhibit longitudinal compression. The filaments 530 forming the strands lie in a uniform axial direction having equal radial distances from the axial centre of the cord. However, in Figure 16 (a section through a new steel cord 600), the filaments 630 include some 650 which are radially further away from the axial centre of the cord than others 640. In Figure 17 filaments at rest are shown on the left and filaments under compression are shown on the right. It is seen that the centre filament has moved further radially outward allowing axial compression of the cord without damage thereto.

[0122] It is possible that in one embodiment it is the strands that move radially outward relative to adjacent strands in the cords.

[0123] Below is a table of possible bending stiffness values for high-pressure pipe walls according to any of the aspects described herein.

[0124] [Table 0002]

Table 2

[0125]

[0126] Below is a table of possible multipliers for bending stiffness (being the number of times greater the pipe wall bending stiffness according to any of the aspects described herein may be as compared to a plain elastomer pipe wall).

[0127] [Table 0003]

Table 3

[0128] With regard to high-pressure pipes described herein the use of high-strength steel cord means that there is less steel in a pipe of equivalent pressure carrying capacity. Refer to table below. The new high-pressure pipes being the ones relating to the various aspects described herein. The bonded and un-bonded pipes being prior art pipes.

[0129] [Table 0004]

Table 4

Bonded and un-bonded pipes today must remain round under external pressure meaning that the deeper the water into which they are installed the heavier they get. The pipes of the present invention, however, may be designed for pressure differential only. For example, a 5,000psi 20" diameter surface pipe may weigh 242kg/m.

However, the external pressure in a water depth of 2,500m is 3,600psi meaning this pipe needs only be designed for a pressure differential of l,400psi resulting in a pipe weighing only 84kg/m. An equivalent non-bonded pipe (today's bonded pipes are not capable of being installed in deep water) may weigh well over 550kg/m. This therefore means that the installation vessel can carry many times the length of the new pipes compared to the known un-bonded pipe. This may lead to a significant reduction in the number of load outs and therefore the time and cost of deep water pipeline installations.

Claims

A fully bonded high-pressure flexible pipe having a pipe wall of composite construction including pressure retaining reinforcement members located within the pipe wall being sufficiently flexible to enable the pipe to collapse and re-inflate with substantially no damage or disruption to the wall structure.

The pipe of claim 1, comprising no rectilinear components, located parallel to the longitudinal axis of the pipe, for controlling the collapse configuration of the pipe wall.

The pipe of any preceding claim, comprising at least one longitudinal reinforcement member embedded in and fully bonded to the pipe wall. The pipe of claim 3 wherein the at least one longitudinal reinforcement member has a tensile stiffness significantly greater than its com- pressional stiffness.

The pipe of either one of claims 3 and 4, comprising a plurality of longitudinal members arranged equiangularly around the circumference of the pipe wall.

The pipe of either one of claims 3 and 4, comprising a plurality of longitudinal members arranged substantially closely spaced in two substantially diametrically opposite groups around the circumference of the pipe wall.

The pipe of any one of claims 3 to 6, wherein the longitudinal reinforcement member(s) is/are located outside the internal pressure retaining reinforcement plies.

The pipe of any one of claims 3 to 7, wherein the longitudinal reinforcement member(s) is/are located inside the internal pressure retaining reinforcement plies.

The pipe of any one of claims 3 to 8, wherein the longitudinal reinforcement member(s) is/are located both inside and outside the internal pressure retaining reinforcement plies.

The pipe of any one of claim 3 to 9, wherein the longitudinal reinforcement member(s) is/are axially compressible to allow bending of the pipe whilst containing tensile extension to less than 5%.

The pipe of any preceding claim, wherein the reinforcement members comprise polymers and a flexible steel cord, wherein the steel cord has an open structure such that the polymer has at least partially penetrated and bonded around and within it. [Claim 0012] The pipe of any one of claims 1 to 10, wherein the reinforcement

members comprise polymers and a flexible carbon fibre cord, wherein the carbon fibre cord has an open structure such that the polymer has at least partially penetrated and bonded around and within it.

Claim 0013] The pipe of either one of claims 11 and 12, wherein the open structure has a linear density of less than 65%.

Claim 0014] The pipe of any one of claims 11 to 13, wherein the open structure has a polymer core.

Claim 0015] The pipe of any preceding claim, including a polyethylene film bonded to its exterior surface.

Claim 0016] The pipe of any preceding claim, wherein the pipe is arranged to have a compressional shortening far greater than a tensional extension, when under load.

Claim 0017] The pipe of any preceding claim, wherein the weight per metre lies in the range 20 kg/m to 200 kg/m.

Claim 0018] The pipe of any preceding claim, wherein all materials demonstrate similar bending characteristics and behaviour in all three degrees of freedom.

Claim 0019] The pipe of any preceding claim, wherein the bending stiffness of the pipe wall lies in the range 0.4 to 3.3 N.mm²for a two-ply wall and in the range 32 to 403 N.mm² for a ten-ply wall.

Claim 0020] The pipe of any preceding claim, comprising no fabric.

Claim 0021] The pipe of any preceding claim, including a liner comprising plastics on the interior of the pipe wall.

Claim 0022] The pipe of claim 21, wherein the liner is a fully-fluorinated

fluoropolymer plastic.

Claim 0023] The pipe of claim 21, wherein the liner is comprised of a partially flu- orinated fluoropolymer plastic material.

Claim 0024] The pipe of claim 23, wherein the liner is comprised of PVDF

(polyvinylidene fluoride).

Claim 0025] The pipe of claim 21, wherein the liner is comprised of polyethylene. Claim 0026] A method of manufacture of a fully bonded high-pressure flexible pipe having a pipe wall of composite construction including the steps of: forming a sheet of composite material comprising polymers and an embedded steel cord, wherein the polymers have been forced into the interstices of the open structure of the steel cord; forming a pipe from said sheet; wrapping a shrinkable tape around the pipe; and autoclaving the pipe such that the elastomer is vulcanised. The method of claim 26, further comprising the step of including at least one longitudinal reinforcement member in the longitudinal length of the pipe wall for controlling length and stiffness and not a collapse configuration.

The method of either one of claims 26 and 27, including the step of providing an internal liner and/or an external cover.

A multi-strand cord, each strand being constructed from multi-filament wires whereby a central axially orientated space is filled with a polymer material, this material being fully bonded to all surrounding filaments. The multi- strand cord of claim 29, wherein the strands comprise steel and/or carbon fibre.

The multi-strand cord of either one of claims 29 and 30, wherein the strands are arranged in a substantial radial pattern.

The multi- strand cord of any one of claims 29 to 31, wherein the cord has an axial compressive modulus significantly less than its tensile modulus, this relationship prevailing for at least 3% of the length of the cord.

The multi-strand cord of any one of claims 29 to 32, wherein the cord comprises planetary strands and each alternate strand is rotated such that its arrangement of filaments is different to its immediate neighbours so as to maximise packing density.

The multi- strand cord of claim 33, wherein the longitudinal extension under axial tension is minimised and radial slippage of the strands may be permitted to aid compressibility.

The multi-strand cord of any one of claims 29 to 34, wherein all strands are coiled at a pitch providing approximately 0.5% helical clearance between each strand.