WO2018046886A1

WO2018046886A1 - Flexible pipe design and manufacture

Info

Publication number: WO2018046886A1
Application number: PCT/GB2017/052477
Authority: WO
Inventors: Paul SNOWDON; Cathal CLANCY; Ashley CLACK; Peter Williams
Original assignee: Ge Oil & Gas Uk Limited
Priority date: 2016-09-09
Filing date: 2017-08-22
Publication date: 2018-03-15
Also published as: GB201615345D0

Abstract

A method for providing a flexible pipe 100 is disclosed. The method comprises the steps of receiving a nominal internal diameter as an indicated design parameter of project-specific design requirements for a flexible pipe, and responsive to the indicated design parameter, providing a fabrication specification for manufacturing flexible pipe body, including a carcass layer and at least one smoothing insert disposed between adjacent hoop-like elements of the carcass layer to smooth a radially inner surface of the carcass layer, having an effective internal diameter less than said nominal internal diameter.

Description

FLEXIBLE PIPE DESIGN AND MANUFACTURE

The present invention relates to a method for providing flexible pipe. In particular, but not exclusively, the present invention relates to a method for providing flexible pipe by designing flexible pipe body in a non-conventional manner so that an internal diameter of a resultant flexible pipe is reduced relative to a comparable conventional flexible pipe yet retains desired performance characteristics.

Traditionally flexible pipe is utilised to transport production fluids, such as oil and/or gas and/or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location (which may be deep underwater, say 1000 metres or more) to a sea level location. The pipe may have an internal diameter of typically up to around 0.6 metres (e.g. diameters may range from 0.05 m up to 0.6 m). Flexible pipe is generally formed as an assembly of flexible pipe body and one or more end fittings. The pipe body is typically formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses that impair the pipe's functionality over its lifetime. There are different types of flexible pipe such as unbonded flexible pipe which is manufactured in accordance with API 17J or composite type flexible pipe or the like. The pipe body is generally built up as a combined structure including polymer layers and/or composite layers and/or metallic layers. For example, pipe body may include polymer and metal layers, or polymer and composite layers, or polymer, metal and composite layers. Layers may be formed from a single piece such as an extruded tube or by helically winding one or more wires at a desired pitch or by connecting together multiple discrete hoops that are arranged concentrically side-by-side. Depending upon the layers of the flexible pipe used and the type of flexible pipe some of the pipe layers may be bonded together or remain unbonded.

Some flexible pipe has been used for deep water (less than 3,300 feet (1 ,005.84 metres)) and ultra-deep water (greater than 3,300 feet) developments. It is the increasing demand for oil which is causing exploration to occur at greater and greater depths (for example in excess of 8202 feet (2500 metres)) where environmental factors are more extreme. For example in such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature that may lead to pipe blockage. In practice flexible pipe conventionally is designed to perform at operating temperatures of -30°C to +130°C, and is being developed for even more extreme temperatures. Increased depths also increase the pressure associated with the environment in which the flexible pipe must operate. For example, a flexible pipe may be required to operate with external pressures ranging from 0.1 MPa to 30 MPa acting on the pipe. Equally, transporting oil, gas or water may well give rise to high pressures acting on the flexible pipe from within, for example with internal pressures ranging from zero to 140 MPa from bore fluid acting on the pipe. As a result the need for high levels of performance from certain layers such as a pipe carcass or the pressure armour and tensile armour layers of the flexible pipe body is increased. It is noted for the sake of completeness that flexible pipe may also be used for shallow water applications (for example less than around 500 metres depth) or even for shore (overland) applications.

Unbonded flexible pipe of the type to which the present invention relates is conventionally designed and subsequently manufactured according to the American Petroleum Institute (API) standard 17J with reference to an associated ISO standard IS013628. Conventionally as part of the standard process for providing a flexible pipe a purchaser, typically a nation state or nation owned oil company, requests manufacturers of flexible pipe to provide flexible pipe according to stipulated project-specific design requirements. A manufacturer of flexible pipe receives such project-specific design requirements, which include numerous indicated design parameters, and thereafter provides a proposed fabrication specification for manufacturing flexible pipe body. Thereafter flexible pipe body is manufactured in line with an agreed fabrication specification. A key indicated design parameter provided by a purchaser of flexible pipe according to conventional techniques is a nominal internal diameter of the to be manufactured flexible pipe. Often a nominal internal diameter is indicated to provide a sufficiently wide bore for the flexible pipe body to enable a resultant fluid flow and flow rate to satisfy predetermined criterion.

As a flexible pipe body internal diameter increases the thicknesses of constituent parts of the various layers of the flexible pipe body must also be increased. For example, tensile wire thickness, that is to say a thickness of wires forming tensile armour layers in the pipe generally increases in relation to the internal diameter. As a result as a pipe internal diameter increases extra material costs can be expected and the resultant flexible pipe becomes heavier which complicates installation and use.

Increasing internal diameter of flexible pipe body and flexible pipes incorporating such flexible pipe body also increases a risk of "birdcaging" and also increases collapse safety risk. - -

Furthermore, subsequent to manufacture of flexible pipe body and a flexible pipe incorporating such flexible pipe body the flexible pipe itself is typically kept ready for use wound on a drum. Flexible pipe body having a large internal diameter itself typically results in flexible pipe body having a relatively large outer diameter. As a result only limited lengths of flexible pipe can be kept on any single storage drum.

It is an aim of the present invention to mitigate at least one of the above-mentioned problems. It is an aim of certain embodiments of the present invention to provide a method of designing and manufacturing flexible pipe body in which an internal diameter of flexible pipe body can be reduced relative to conventional techniques whilst still satisfying specified project-specific requirements in terms of pipe performance. It is an aim of certain embodiments of the present invention to provide a flexible pipe including a carcass which presents a relatively smooth inner surface to fluid transported along the bore of the flexible pipe.

It is an aim of certain embodiments of the present invention to provide a method of designing and subsequently manufacturing flexible pipe in which a pressure drop per unit length of a rough bore flexible pipe is reduced relative to conventional techniques.

It is an aim of certain embodiments of the present invention to provide a manner for designing and subsequently manufacturing flexible pipe body in which an internal diameter of the flexible pipe can be reduced relative to conventional techniques, thus providing the advantages of a small bore pipe whilst still enabling the flexible pipe body to perform in terms of flow rate and pressure drop like a larger bore flexible pipe.

It is an aim of certain embodiments of the present invention to provide a method of designing and manufacturing flexible pipe body, and a flexible pipe utilising the flexible pipe body, that is made by helically winding elongate tapes to form a carcass layer or alternatively by interlocking adjacent discrete hoops arranged concentrically in a side-by-side relationship.

According to a first aspect of the present invention there is provided a method for providing a flexible pipe, comprising the steps of: - - receiving a nominal internal diameter as an indicated design parameter of project- specific design requirements for a flexible pipe; and

responsive to the indicated design parameter, providing a fabrication specification for manufacturing flexible pipe body, including a carcass layer and at least one smoothing insert disposed between adjacent hoop-like elements of the carcass layer to smooth a radially inner surface of the carcass layer, having an effective internal diameter less than said nominal internal diameter.

Aptly the method further comprises receiving the nominal internal diameter as a one of a plurality of general design parameters provided as flexible pipe purchasing guidelines for the flexible pipe.

Aptly the method further comprises providing a design premise including a plurality of internal fluid parameters associated with fluid flow along a pipe bore comprising said carcass layer and smoothing insert.

Aptly the method further comprises providing a minimum inlet pressure and required outlet pressure as two of said plurality of internal fluid parameters, a pressure drop between the inlet pressure and outlet pressure being less than a corresponding pressure drop associated with a flexible pipe manufactured without the smoothing insert and having said nominal internal diameter.

Aptly the method further comprises providing a design load report including analysis results of load cases set out in the design premise.

Aptly the method further comprises providing said fabrication specification as a specification for manufacturing flexible pipe body that includes a carcass layer formed by interlocking adjacent windings of a helically wound carcass tape and a smoothing insert formed by helically winding a smoothing insert tape between adjacent windings of the carcass tape.

Aptly the method further comprises providing a design report comprising an indication of a selected material and cross-section for both an elongate carcass tape element that provides carcass windings and an elongate smoothing insert tape element that provides the smoothing insert windings. - -

Aptly the method further comprises the cross-section of the insert tape element has a generally uniform cross-section and is generally T-shaped and comprises a central body portion and a first and further wing portion. Aptly the method further comprises providing said fabrication specification as a specification for manufacturing flexible pipe body that includes a carcass layer formed by interlocking adjacent discrete carcass hoops in a side-by-side configuration and locating a plurality of discrete smoothing inserts, each formed as a discrete hoop, between respective adjacent carcass hoops.

Aptly the method further comprises providing a design report comprising an indication of a selected material and cross section for both the discrete carcass hoops and the discrete smoothing inserts. Aptly the method further comprises manufacturing flexible pipe body according to said fabrication specification.

Aptly the method further comprises terminating each of two ends of the flexible pipe body with a respective end fitting.

According to a second aspect of the present invention there is provided apparatus constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings. According to a third aspect of the present invention there is provided a method substantially as hereinbefore described with reference to the accompanying drawings.

Certain embodiments of the present invention provide a method by which flexible pipe body including a carcass layer and a smoothing insert can be provided. As a result an effective internal diameter of the flexible pipe body is smaller than would otherwise be deemed necessary to achieve adequate performance relative to standard conventional design and manufacturing techniques.

Certain embodiments of the present invention provide the advantage that flexible pipe body can be manufactured with up to a 10% smaller inner diameter than with conventional - - techniques for a given pressure loss and/or flow rate or other such predetermined required pipe performance parameter.

Certain embodiments of the present invention provide a method for providing a flexible pipe which incorporates reduced stress allowing the use of smaller wires, providing better birdcaging performance and collapse safety factors.

Certain embodiments of the present invention reduce an expected minimum bend radius for a flexible pipe relative to conventional techniques. This allows for the use of smaller storage drums and provides for easier installation. Also reduced numbers of pipe sections are required resulting in multiple reel savings and end fitting savings relative to the provisioning of a pipeline according to conventional techniques.

Certain embodiments of the present invention provide for a way of designing and subsequently manufacturing flexible pipe which reduces stiffness in an end result flexible pipe and which enables easier onshore/offshore handling.

Certain embodiments of the present invention provide a method of designing and subsequently manufacturing flexible pipe body using either helically wound elements or interlocked discrete hoops arranged concentrically in a side-by-side arrangement.

Certain embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates flexible pipe body;

Figure 2 illustrates uses of a flexible pipe;

Figure 3 illustrates a carcass layer;

Figure 4 illustrates steps in the design and manufacture of flexible pipe body; and Figure 5 illustrates a Moody diagram. In the drawings like reference numerals refer to like parts. Throughout this description, reference will be made to a flexible pipe. It is to be appreciated that certain embodiments of the present invention are applicable to use with a wide variety of flexible pipe. For example certain embodiments of the present invention can be used with respect to flexible pipe and associated end fittings of the type which is manufactured according to API 17J. Such flexible pipe is often referred to as unbonded flexible pipe.

Turning to Figure 1 it will be understood that the illustrated flexible pipe is an assembly of a portion of pipe body and one or more end fittings (not shown) in each of which a respective end of the pipe body is terminated. Figure 1 illustrates how pipe body 100 is formed from a combination of layered materials that form a pressure-containing conduit. As noted above although a number of particular layers are illustrated in Figure 1 , it is to be understood that certain embodiments of the present invention are broadly applicable to coaxial pipe body structures including two or more layers manufactured from a variety of possible materials. The pipe body may include one or more layers comprising composite materials, forming a tubular composite layer. It is to be further noted that the layer thicknesses are shown for illustrative purposes only. As used herein, the term "composite" is used to broadly refer to a material that is formed from two or more different materials, for example a material formed from a matrix material and reinforcement fibres. A tubular composite layer is thus a layer having a generally tubular shape formed of composite material. Alternatively a tubular composite layer is a layer having a generally tubular shape formed from multiple components one or more of which is formed of a composite material. The layer or any element of the composite layer may be manufactured via an extrusion, pultrusion or deposition process or, by a winding process in which adjacent windings of tape which themselves have a composite structure are consolidated together with adjacent windings. The composite material, regardless of manufacturing technique used, may optionally include a matrix or body of material having a first characteristic in which further elements having different physical characteristics are embedded. That is to say elongate fibres which are aligned to some extent or smaller fibres randomly orientated can be set into a main body or spheres or other regular or irregular shaped particles can be embedded in a matrix material, or a combination of more than one of the above. Aptly the matrix material is a thermoplastic material, aptly the thermoplastic material is polyethylene or polypropylene or nylon or PVC or PVDF or PFA or PEEK or PTFE or alloys of such materials with reinforcing fibres manufactured from one or more of glass, ceramic, basalt, carbon, carbon nanotubes, polyester, nylon, aramid, steel, nickel alloy, titanium alloy, aluminium - - alloy or the like or fillers manufactured from glass, ceramic, carbon, metals, buckminsterfullerenes, metal silicates, carbides, carbonates, oxides or the like.

The pipe body 100 illustrated in Figure 1 includes an internal pressure sheath 1 10 which acts as a fluid retaining layer and comprises a polymer layer that ensures internal fluid integrity. The layer provides a boundary for any conveyed fluid. It is to be understood that this layer may itself comprise a number of sub-layers. It will be appreciated that when a carcass layer 120 is utilised the internal pressure sheath is often referred to by those skilled in the art as a barrier layer. In operation without such a carcass (so-called smooth bore operation) the internal pressure sheath may be referred to as a liner. A barrier layer 1 10 is illustrated in Figure 1 .

It is noted that a carcass layer 120 is a pressure resistant layer that provides an interlocked construction that can be used as the innermost layer to prevent, totally or partially, collapse of the internal pressure sheath 1 10 due to pipe decompression, external pressure, and tensile armour pressure and mechanical crushing loads. The carcass is a crush resistant layer. It will be appreciated that certain embodiments of the present invention are thus applicable to 'rough bore' applications (with a carcass). Aptly the carcass layer is a metallic layer. Aptly the carcass layer is formed from stainless steel, corrosion resistant nickel alloy or the like. Aptly the carcass layer is formed from a composite, polymer, or other material, or a combination of materials and components. A carcass layer is radially within the barrier layer.

A pressure armour layer 130 is a pressure resistant layer that provides a structural layer that increases the resistance of the flexible pipe to internal and external pressure and mechanical crushing loads. The layer also structurally supports the internal pressure sheath. Aptly as illustrated in Figure 1 the pressure armour layer is formed as a tubular layer. Aptly for unbonded type flexible pipe the pressure armour layer consists of an interlocked construction of wires with a lay angle close to 90 °. Aptly in this case the pressure armour layer is a metallic layer. Aptly the pressure armour layer is formed from carbon steel, aluminium alloy or the like. Aptly the pressure armour layer is formed from a pultruded composite interlocking layer. Aptly the pressure armour layer is formed from a composite formed by extrusion or pultrusion or deposition. A pressure armour layer is radially outside an underlying barrier layer. - -

The flexible pipe body also includes an optional first tensile armour layer 140 and optional second tensile armour layer 150. Each tensile armour layer is used to sustain tensile loads and optionally also internal pressure. Aptly for some flexible pipes the tensile armour windings are metal (for example steel, stainless steel or titanium or the like). For some composite flexible pipes the tensile armour windings may be polymer composite tape windings (for example provided with either thermoplastic, for instance nylon, matrix composite or thermoset, for instance epoxy, matrix composite). For unbonded flexible pipe the tensile armour layer is typically formed from a plurality of wires. (To impart strength to the layer) that are located over an inner layer and are helically wound along the length of the pipe at a lay angle typically between about 10° to 55°. Aptly the tensile armour layers are counter-wound in pairs. Aptly the tensile armour layers are metallic layers. Aptly the tensile armour layers are formed from carbon steel, stainless steel, titanium alloy, aluminium alloy or the like. Aptly the tensile armour layers are formed from a composite, polymer, or other material, or a combination of materials.

Aptly the flexible pipe body includes optional layers of tape 160 which help contain underlying layers and to some extent prevent abrasion between adjacent layers. The tape layer may optionally be a polymer or composite or a combination of materials, also optionally comprising a tubular composite layer. Tape layers can be used to help prevent metal-to- metal contact to help prevent wear. Tape layers over tensile armours can also help prevent "birdcaging".

The flexible pipe body also includes optional layers of insulation 165 and an outer sheath 170, which comprises a polymer layer used to protect the pipe against penetration of seawater and other external environments, corrosion, abrasion and mechanical damage. Any thermal insulation layer helps limit heat loss through the pipe wall to the surrounding environment.

Each flexible pipe comprises at least one portion, referred to as a segment or section, of pipe body 100 together with an end fitting located at at least one end of the flexible pipe. An end fitting provides a mechanical device which forms the transition between the flexible pipe body and a connector. The different pipe layers as shown, for example, in Figure 1 are terminated in the end fitting in such a way as to transfer the load between the flexible pipe and the connector. - -

Figure 2 illustrates a riser assembly 200 suitable for transporting production fluid such as oil and/or gas and/or water from a sub-sea location 221 to a floating facility 222. For example, in Figure 2 the sub-sea location 221 includes a sub-sea flow line 225. The flexible flow line 225 comprises a flexible pipe, wholly or in part, resting on the sea floor 230 or buried below the sea floor and used in a static application. The floating facility may be provided by a platform and/or buoy or, as illustrated in Figure 2, a ship. The riser assembly 200 is provided as a flexible riser, that is to say a flexible pipe 240 connecting the ship to the sea floor installation. The flexible pipe may be in segments of flexible pipe body with connecting end fittings.

It will be appreciated that there are different types of riser, as is well-known by those skilled in the art. Certain embodiments of the present invention may be used with any type of riser, such as a freely suspended (free-hanging, catenary riser), a riser restrained to some extent (buoys, chains), totally restrained riser or enclosed in a tube (I or J tubes). Some, though not all, examples of such configurations can be found in API 17J. Figure 2 also illustrates how portions of flexible pipe can be utilised as a jumper 250.

Figure 3 illustrates the carcass layer 120 in more detail. As shown in Figure 3 the carcass layer is a generally tubular structure formed by self-interlocked windings of a elongate tape having a generally S-shaped cross-section. Each winding 300i-₆ is formed from a folded strip and is manufactured by winding the profile strip over an underlying substantially cylindrical layer whereby each new winding will self-interlock with an immediately preceding winding. In this way each winding forms an effective hoop which resists collapse pressures exerted externally on a flexible pipe.

Figure 3 also helps illustrate how a smoothing insert 350 can be wound on the radially inner surface of the windings of the carcass layer. As illustrated in Figure 3 the smoothing insert is formed from a folded strip having a generally T-shaped cross-section. It will be appreciated that certain other embodiments of the present invention provide a smoothing insert wound between adjacent carcass windings that have other cross-sections and that are formed other than from folded strip. For example, as described hereinafter, the smoothing insert may have a V-shape or L-shape. Alternatively, moulded or composite bodies may be wound as a smoothing insert. As shown in Figure 3, the illustrated insert 350 has a cross-section which includes a first wing portion 360 which ends to a tip 365 formed from an edge of the folded strip and a further wing portion 370 which likewise has a tip 375 formed from another edge of the folded strip. At the centre of the cross-section of the insert strip is a generally U-shaped - - body portion 380 which extends radially outwardly away from the central bore B formed by the carcass layer and barrier layer. In use, as the flexible pipe body, which includes the carcass layer 120, bends and flexes the windings move nearer and further apart depending upon their position with respect to a bending site. The body portion 380 of the smoothing insert helps keep the insert duly located with respect to the adjacent windings of the carcass tape where the smoothing insert winding is positioned. The insert shown can be manufactured in a convenient manner from an initial flat strip. This makes it economically attractive. By virtue of the helically wound smoothing insert the gaps between adjacent windings of the carcass layer are entirely or at least significantly filled. That is to say a radially inner surface provided by the radially inner surface of the carcass windings together with the radially inner surface of the windings of the smoothing insert present a much smoother surface than would otherwise be provided by a rough bore flexible pipe without such a smoothing insert. Smoothing the surface of the carcass layer generally reduces turbulent flow of fluid transported along the bore of the pipe and tends to engender more laminar flow. As a result greater flow rates and thus more favourable flow characteristics can be provided.

Figure 4 helps illustrate a method for providing a flexible pipe. Figure 4 helps illustrate how flexible pipe body is first stipulated by a purchaser such as a nation state or state owned oil company and how subsequently a manufacturer of flexible pipe body responds to project- specific design requirements to design and subsequently manufacture flexible pipe body satisfying the desired requirements. The flexible pipe body is subsequently terminated at respective ends with an end fitting to thereby provide the flexible pipe.

In more detail Figure 4 helps illustrate how as a first step S100 guidelines for flexible pipe body are generated by purchaser. The generated guidelines are project-specific design requirements given as flexible pipe purchasing guidelines. The project-specific design requirements for a flexible pipe include various indicated design parameters. Aptly a length of pipe, tolerance required on length, fluid description (oil, gas, water), flow regime description, flow direction, flow rate, minimum inlet pressure (MPa), required outlet pressure (MPa), maximum operational depressurisation and pressurisation rates, design minimum temperature (centigrade) and design maximum temperature (centigrade) or the like as well as other factors may be stipulated. An internal diameter is provided as a nominal internal diameter for the flexible pipe. - -

The project-specific design requirements for the flexible pipe are provided to a manufacturer. As part of a method for providing flexible pipe at step S200 the manufacturer provides a design premise responsive to the received project-specific design requirements. According to certain embodiments of the present invention the design premise includes multiple parameters including, but not limited to, internal fluid parameters, external environments, system description, service life, design load case definition, design accidental events, design criteria, analysis parameters and the like. In particular according to certain embodiments of the present invention in contrast to conventional design and manufacturing standards for providing a rough bore unbonded flexible pipe and despite not being specifically requested by a purchaser and not being need for any prior known purposes the design premise is based upon a flexible pipe including a carcass layer which includes a bore smoothing insert of the type illustrated in Figure 3. Aptly other bore smoothing insert shapes and configurations could be used. Step S300 helps illustrate how subsequent to an agreement between the purchaser and manufacturer based upon the design premise associated with step S200, a design load report is provided. The design load report includes results from analysis of load cases defined in the agreed design premise. Calculated stresses and strains are reported for each design load case. A design report is prepared at step S400 which includes a detailed description, including drawings, of each component of the flexible pipe. The description includes a layer- by- layer description of the pipe including materials, any wire cross-section, lay angle, diameter, thickness, number of wires and the like. Aptly material specification and associated data is included in the design report. Aptly the design load report is incorporated into the design report.

At step S500 the manufacturer provides a quality plan for manufacturing. The manufacturing quality plan specifies quality control procedures including inspection points and test procedures. At step S600 the manufacturer provides a fabrication specification. The fabrication specification describes each step in a manufacturing process by which the flexible pipe body is manufactured. This includes detailing welding, heat treatment, type and extent of NDE and acceptance criteria, factory acceptance test (FAT) procedures, fabrication methods and allowable repair procedures. By utilising a smoothing insert helically wound between adjacent carcass windings to smooth the radially inner surface of the carcass layer the fabrication specification for manufacturing flexible pipe body can be based upon flexible pipe - - body having an effective internal diameter less than the nominal internal diameter stipulated in the project-specific design requirements. Aptly the manufacturing quality plan is included in the fabrication specification. At step S700 flexible pipe body is generated according to the fabrication specification.

Table 1 below illustrates how, according to certain embodiments of the present invention, use of a smoothing insert helically wound between adjacent carcass windings of a carcass layer in a flexible pipe means a flexible pipe can be provided having a reduced inner diameter relative to a conventional "rough bore" flexible pipe whilst retaining desired pipe performance characteristics. For example as shown in Table 1 for a desired volumetric flow rate along a flexible pipe, a flexible pipe with an effective internal diameter of 14 inches (around 356mm), if smoothed with the helically wound T-insert, can perform as per a conventional rough bore flexible pipe with a nominal internal diameter of 16 inches (around 406mm).

TABLE 1 - -

In the table the volumetric flow rate is the volume of fluid flowing through the pipe per unit time. The Reynolds number Re is a dimensionless number which encapsulates a relationship of friction loss in the pipe to shear stress between the pipe surface and the fluid flowing within it. This depends upon the conditions of the physical properties of the system. The value p is the density of the fluid (kg/m³), U is the mean fluid velocity, D is the effective diameter of the pipe and μ is the viscosity of the transported fluid (kg/m/s).

Likewise in Table 1 the effective roughness of the inner surface on the inner surface of the type is denoted by £. As indicated in Table 1 the value S/D is the relative roughness and Table 1 helps illustrate how the use of a smoothing wound insert helps substantively reduce the relative roughness of the pipe.

In fluid flow conditions along a bore of the flexible pipe friction loss is the loss of pressure or "head" that is experienced due to the effect of a transported fluid's viscosity near the radially inner surface of the pipe. The Darcy/Weisbach Equation relates the head loss, or pressure loss, due to friction along the given length of pipe to the average velocity of fluid flow for an incompressible fluid. The relationship between friction factor, relative pipe roughness and Reynolds number for various materials is shown in the Moody diagram of Figure 5.

Whilst certain embodiments of the present invention have thus been described in which flexible pipe body is designed and subsequently manufactured using a carcass layer formed by a helical winding of a carcass layer tape together with a helically wound smoothing insert tape, it will be appreciated that as an alternative, the carcass layer may be designed and manufactured to be formed from multiple discrete hoops arranged concentrically in a side- by-side configuration with corresponding discrete hoops that act as intervening smoothing inserts. By providing a smoothing insert as a helical winding or multiple discrete hoops fluid flow along a bore of a flexible pipe can be better controlled than via conventional techniques. As a result a smaller bore flexible pipe can be utilised relative to what otherwise would be needed according to conventional techniques and this provides a number of advantages.

One of many conventional flexible pipe design programs could be used to vary the parameters of flexible pipe body in order to meet project-specific design requirements. For example, the fluid flow properties along a portion of flexible pipe body could be simulated via a conventional program based on a flexible pipe including a carcass layer which includes a bore smoothing insert. If, when incorporating the bore smoothing insert, the simulated fluid - - flow properties indicate that the flexible pipe body performs above the required fluid flow criteria stipulated in the project-specific design requirements, the flexible pipe design program could optimise the required internal diameter of the flexible pipe body such that a given pressure loss and/or flow rate or other such predetermined required pipe performance parameter could still be met. This results in the provision of an effective internal diameter for flexible pipe body less than the nominal internal diameter stipulated in the project-specific design requirements.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to" and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive. The invention is not restricted to any details of any foregoing embodiments. The invention extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS:

1 . A method for providing a flexible pipe, comprising the steps of:

receiving a nominal internal diameter as an indicated design parameter of project-specific design requirements for a flexible pipe; and

2. The method as claimed in claim 1 , further comprising:

receiving the nominal internal diameter as a one of a plurality of general design parameters provided as flexible pipe purchasing guidelines for the flexible pipe.

3. The method as claimed in claim 1 or claim 2, further comprising:

providing a design premise including a plurality of internal fluid parameters associated with fluid flow along a pipe bore comprising said carcass layer and smoothing insert.

4. The method as claimed in claim 3, further comprising:

providing a minimum inlet pressure and required outlet pressure as two of said plurality of internal fluid parameters, a pressure drop between the inlet pressure and outlet pressure being less than a corresponding pressure drop associated with a flexible pipe manufactured without the smoothing insert and having said nominal internal diameter.

5. The method as claimed in claim 3 or claim 4, further comprising:

providing a design load report including analysis results of load cases set out in the design premise.

6. The method as claimed in any preceding claim, further comprising:

providing said fabrication specification as a specification for manufacturing flexible pipe body that includes a carcass layer formed by interlocking adjacent windings of a helically wound carcass tape and a smoothing insert formed by helically winding a smoothing insert tape between adjacent windings of the carcass tape.

7. The method as claimed in claim 6, further comprising:

providing a design report comprising an indication of a selected material and cross-section for both an elongate carcass tape element that provides carcass windings and an elongate smoothing insert tape element that provides the smoothing insert windings.

8. The method as claimed in claim 7, further comprising:

the cross-section of the insert tape element has a generally uniform cross- section and is generally T-shaped and comprises a central body portion and a first and further wing portion.

9. The method as claimed in any one of claims 1 to 5, further comprising:

providing said fabrication specification as a specification for manufacturing flexible pipe body that includes a carcass layer formed by interlocking adjacent discrete carcass hoops in a side-by-side configuration and locating a plurality of discrete smoothing inserts, each formed as a discrete hoop, between respective adjacent carcass hoops.

10. The method as claimed in claim 8, further comprising:

providing a design report comprising an indication of a selected material and cross section for both the discrete carcass hoops and the discrete smoothing inserts.

1 1 . The method as claimed in any preceding claim, further comprising:

manufacturing flexible pipe body according to said fabrication specification.

12. The method as claimed in claim 1 1 , further comprising:

terminating each of two ends of the flexible pipe body with a respective end fitting.