Abstract:
A pipe system comprises a metallic pipe section having a wall comprising a metal material, and a deformation absorber coupled to the first pipe section in end-to-end relation. The deformation absorber comprises a composite pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix. The composite pipe section is configured to sustain a greater level of strain than the metallic pipe section when the pipe system is subject to deformation by a load event.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT Patent Application No. PCT/GB2011/001684 filed on 5 Dec. 2011, which claims priority to United Kingdom Patent Application No. GB1020504.5 filed on 3 Dec. 2010, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Pipe systems are used in a wide variety of industries for the confined transportation of fluids and/or equipment. In the oil and gas industry, for example, pipe systems may be used to transport hydrocarbons and/or equipment from a subterranean formation to surface. To give an example, in order to recover hydrocarbons from a subsea formation, a well may be created which extends from a wellhead located on the sea floor to the hydrocarbon-bearing rock of the formation. A pipe, generally known as a riser, may be used to couple or “tie” the wellhead to a vessel located on the surface. In some cases, the riser may be coupled to a single wellhead. In other cases, a more complex arrangement may be provided which involves a number of other pipes, such as flow lines or jumpers, to couple a number of wellheads to a common riser. In use, hydrocarbons may be transported from the formation to a wellhead, and thereafter to the surface vessel via the flow lines and riser. Risers, and other pipe systems, may also be used to accommodate deployment and retrieval of equipment, such as wellbore equipment. For example, risers, and other pipe systems may be used to accommodate wellbore drilling equipment, completion equipment, intervention or workover equipment or the like. 
         [0003]    In subsea applications, pipe systems used in the construction of risers, flow lines, jumpers and the like are typically subject to a range of forces, stresses and strains, including for example those forces resulting from applied pressures and temperatures during operation. For example, the outer wall of a given flow line may be subject to high pressure and low temperatures from the subsea environment while the inner wall of the flow line may be subject to high temperatures and pressures from the hydrocarbons being transported. Such forces and the like may establish significant deformations within a pipe system, which may result in uncontrolled or undesired movement of the pipe system. 
         [0004]    Moreover, pipe systems may also be subject to significant variations in forces, stresses and strains. In some instances, operation of a given flow line may be intermittent, this resulting in significant variation in the forces acting on the flow line during its life. This may establish cyclic application of strains within the pipe line, which may result in material fatigue, the requirement to use complex architecture or the like. 
         [0005]    Variations in temperature, for example, may result in repeated axial expansion and/or contraction of a pipe line. These variations are typically too great for conventional steel pipes to absorb axially. Therefore, it is common to introduce specific architecture within a pipe line, typically called “flow line buckle” regions which are arranged to focus and to accommodate axial expansion and contraction within the pipe system. These flow line buckle regions are typically established by locally reducing the restraining forces within the pipe line in these regions. This may be achieved by means of floatation (or reduction in mass to increase floatation) to reduce the restraint on the pipe by the seabed. Such a known arrangement is shown in  FIG. 6  of the accompanying drawings, wherein  FIG. 6A  is a side view of a continuous steel pipe line  450  which includes buoyant portions  452  provided within a flow line buckle regions  454 . The buoyant portions  452  reduce the restrain on the pipe line  450  within the flow line buckle portion  454  which permits this region to flex, for example in an s-shape, as shown in the side view in  FIG. 6B  to accommodate expansion and contraction along the pipe line. 
         [0006]    In another known arrangement, such as shown in  FIG. 7A , a pipe line  460  is passed over another pipe  462  arranged perpendicular to the pipe line  460  to raise a portion clear of the sea bed  464  and form a flow line buckle region  466 . When the pipe line  460  expands, for example due to thermal effects, the flow line buckle region deforms perpendicular to the axial direction of the pipe line  460 , as shown in the sectional end view in  FIG. 7B . 
         [0007]    However, pipe or flow lines are also subject to multiphase flow, such as slug flow, and intermittent operation (switching on and off). Due to the non-axial arrangement of known integrated buckle regions, such as that shown in  FIGS. 6 and 7 , this multiphase flow or intermittent operation, for example, induces unpredictable dynamic loads in these sections that can lead to deformations that exceed the tensile strength of the section of pipe or create excessive fatigue loads due to repeated flexing. 
       SUMMARY 
       [0008]    An aspect of the present invention relates to a pipeline or a pipe system which includes a metallic pipe section and a deformation absorber formed of a composite pipe section which functions to absorb deformation within the pipeline or system, thus protecting the metallic pipe section. 
         [0009]    An aspect of the present invention may relate to a pipeline or pipe system comprising: 
         [0010]    a metallic pipe section having a wall comprising a metallic material; and 
         [0011]    a deformation absorber coupled to the metallic pipe section and comprising a composite pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix, wherein the composite material is constructed to cause the deformation absorber to sustain a greater level of strain than the metallic pipe section when the pipeline is subject to deformation by a load event such that a larger proportion of deformation within the pipeline caused by a load event is focussed within the deformation absorber. 
         [0012]    The metallic pipe section may be defined as a first pipe section, and the composite pipe section may be defined as a second pipe section. 
         [0013]    The deformation absorber may be directly coupled to the metallic pipe section. The deformation absorber may be indirectly coupled to the metallic pipe section, for example via an interface component. The deformation absorber may be interposed within the metallic pipe section. The pipeline or pipe system may comprise a connector arrangement interposed between the metallic pipe section and the deformation absorber to permit coupling therebetween. 
         [0014]    An aspect of the present invention may relate to a pipeline or pipe system, comprising: 
         [0015]    a first pipe section having a wall comprising a metal material; and 
         [0016]    a second pipe section coupled to the first pipe section in end-to-end relation and having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix, 
         [0017]    wherein the second pipe section is configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by a load event such that a larger proportion of deformation within the pipeline caused by a load event is focussed within the second pipe section. 
         [0018]    The first pipe section may be defined as a metallic pipe section, and the second pipe section may be defined as a composite pipe section. 
         [0019]    Accordingly, in any of the aspects defined above, during deformation of the pipeline or system caused by a load event, a greater proportion of strain will be sustained by the composite or second pipe section. This may assist in minimising the level of strain applied within the metallic or first pipe section, to the extent that a greater proportion of the strain induced within the pipeline or system during a load event will be sustained within the composite or second pipe section. As such, the second pipe section may function to protect the first pipe section during a deformation and load event applied to the pipe system. For example, the second pipe section may be configured to prevent or substantially minimise the risk of strains and/or stresses being applied within the first pipe section which may cause yield limits of the metal material of said first pipe section to be exceeded. The second pipe section may be configured to minimise the risk of failure, material fatigue, adverse or undesired elastic or plastic deformation, or the like, of the first pipe section. 
         [0020]    The pipe system may be configured such that a larger proportion of deformation within said system caused by a load event is focussed within the second pipe section. Accordingly, the second pipe section may be configured to accommodate a relatively greater proportion of deformation than the first pipe section. In embodiments of the present invention the second pipe section is configured to accommodate or absorb substantially all deformation of the pipe system during a load event. 
         [0021]    The second pipe section may be configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by a cyclical load event. Such a cyclical load event may be established during intermittent flow through the pipe system, during multi phase flow through the pipe system, during vortex shedding events when the pipe system is immersed in a flowing fluid, or the like. 
         [0022]    The second pipe section may be configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by an applied axial load. Accordingly, in this arrangement the second pipe section may be configured to accommodate a larger relative degree of axial expansion and/or contraction. In embodiments of the present invention, where an axial load is applied to the pipe system substantially all resulting axial deformation is absorbed by or restricted to the second pipe section. 
         [0023]    The second pipe section may be configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by an applied radial load. 
         [0024]    The second pipe section may be configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by a bending moment. Accordingly, in this arrangement the second pipe section may be configured to accommodate a larger relative degree of longitudinal bending. In embodiments of the present invention, where a bending moment is applied to the pipe system substantially all longitudinal bending is absorbed by or restricted to the second pipe section. 
         [0025]    The second pipe section may be configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by an applied torsional load. Accordingly, in this arrangement the second pipe section may be configured to accommodate a larger relative degree of twisting. In embodiments of the present invention, where a torsional load is applied to the pipe system substantially all resulting twisting deformation is absorbed by or restricted to the second pipe section. 
         [0026]    A load event may be considered to be any event which applies a load or stress to or within the pipe system. 
         [0027]    In one embodiment a load event may be established by thermal properties of the pipe system, for example thermal properties of one or both of the first and second pipe sections. A load event may be established by thermal expansion and/or contraction of the pipe system. In such an arrangement, deformation caused by thermal expansion and/or contraction may be accommodated, for example substantially entirely accommodated, by the second pipe section. For example, thermal expansion of one or both of the first and second pipe sections may generate a compressive axial load or stress within the pipe system. In such an arrangement or eventuality the second pipe section may be configured to sustain a greater level of compressive strain than the first pipe section. Further, thermal contraction of one or both of the first and second pipe sections may generate a tensile axial load or stress within the pipe system. In this arrangement or eventuality the second pipe section may be configured to sustain a greater level of tensile strain than the first pipe section. 
         [0028]    A load event may be established by exposure of the pipe system to a service environment. For example external equipment or the like may engage the pipe system to generate an applied load. Further, an environmental condition may establish an applied load, such as internal or external fluid pressure, for example during submergence of the pipe system, fluid drag, vortex induced vibration, for example during submergence in a flowing fluid, or the like. 
         [0029]    The second pipe section may define a greater resistance to one or more failure modes under load than the first pipe section. For example, the second pipe section may define a greater resistance to a buckling failure mode than the first pipe section. In such an arrangement the second pipe section may be configured to accommodate a greater degree of axial compressive loading or stress than the first pipe section prior to a buckling event. The second pipe section may be configured to accommodate a greater degree of axial compressive strain than the first pipe section prior to a buckling event. Accordingly, the second pipe section may sustain a greater level of strain than the first pipe section while retaining a substantially straight configuration. 
         [0030]    The second pipe section may define a greater resistance to a tensile failure mode than the first pipe section. In such an arrangement the second pipe section may be configured to accommodate a greater degree of axial tensile loading or stress than the first pipe section prior to a failure event. 
         [0031]    As defined above, the composite material of the composite or second pipe section may be constructed to permit said pipe section to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by an applied load. For example, the composite material may comprise desirable constructional properties, such as matrix type, fibre type, fibre alignment angle, composite material pre-stress, fibre packing density or the like. 
         [0032]    The second pipe section may define a substantially straight pipe section. The substantially straight second pipe section may be configured to remain substantially straight during deformation of the pipe system caused by an axial load. 
         [0033]    The second pipe section may be configured to be deformed laterally during deformation of the pipe system caused by an axial load. In such an arrangement deformation of the pipe system may be accommodated in a controlled manner by lateral deflection of the second pipe section. 
         [0034]    The second pipe section may define a bent pipe section, wherein said bent pipe section may be configured to absorb deformation within the pipe system caused by an applied load. In such an arrangement, the composite material of the second pipe section may permit effects of cyclical loading to be minimised. For example, material fatigue is not of particular concern in composite material. 
         [0035]    The second pipe section may comprise a homogeneous pipe construction. For example, the second pipe section may be formed or otherwise configured to have consistent properties in at least one of axially, circumferentially or radially of the pipe. 
         [0036]    Alternatively, the second pipe section may be formed or configured to have a localised constructional variation. 
         [0037]    The localised constructional variation may comprise a variation in construction of the second pipe section wall, or part of the second pipe section wall. 
         [0038]    In particular embodiments, the localised constructional variation may comprise a circumferential variation in construction of the second pipe section wall, such as in a circumferential segment of pipe section wall. 
         [0039]    The localised constructional variation may comprise an axial and/or longitudinal variation in construction of the second pipe section wall. 
         [0040]    The localised constructional variation may comprise a radial variation in construction of the second pipe section wall. 
         [0041]    Accordingly, the second pipe section may comprise at least two wall sections, segments and/or layers having different constructional properties. 
         [0042]    The localised constructional variation may be selected from at least one of: modulus of elasticity; second moment of area; coefficient of thermal expansion; thermal conductivity; strength such as for example, tensile strength, compressive strength, hoop strength, flexural strength or the like. 
         [0043]    The local constructional variation in at least one longitudinal portion may be selected to accommodate or absorb an anticipated movement, deformation or the like within the pipe, such as a longitudinal expansion movement or deformation. In such an arrangement the local constructional variation may be selected to provide a desired compression property or characteristic to permit axial expansion of the pipe to be accommodated within the associated longitudinal portion without any, or at least without any significant lateral deflection or deformation. 
         [0044]    The localised constructional variation may comprise a variation in the composite material. For example, the localised constructional variation may comprise a variation in one or both of a matrix material and reinforcing fibres of the second pipe section. The localised constructional variation may comprise a variation in the type and/or volume of the matrix material. Alternatively or additionally, the localised constructional variation may comprise one or more of a variation in the distribution density of the reinforcing fibres within the matrix material, the type of fibre within the composite material, fibre alignment angle within the composite material, fibre tension, and fibre stress. 
         [0045]    In particular embodiments, the fibre tension or stress may be considered to be the tension or stress applied to a fibre during manufacture of the pipe section, which tension or stress may be at least partially retained as a pre-tension or pre-stress within the manufactured pipe section. Thus, a localised constructional variation in fibre tension or stress in the second pipe section may permit a desired characteristic of the pipe system to be achieved, such as a desired bending characteristic. In use, this may assist in the positioning and/or manipulation of the pipe system, for example during installation, retrieval, coiling or the like. Furthermore, a localised constructional variation in fibre tension or stress in the second pipe section may assist to shift a neutral position of strain within the pipe section wall, which may assist in providing a more even or level strain distribution when the pipe system is in use, and/or for example is stored, such as in a coiled configuration. 
         [0046]    The localised constructional variation may be achieved by use of at least one insert. An insert may be installed within the second pipe section wall during manufacture or following manufacture of the second pipe section. 
         [0047]    The localised constructional variation may comprise a variation in geometry. 
         [0048]    The localised constructional variation may remain constant along a length of the pipe. 
         [0049]    The localised constructional variation may vary along a length of the pipe. 
         [0050]    The matrix material may comprise a polymer. The matrix material may comprise a thermoplastic component. The matrix material may comprise a thermoset component. The matrix material may comprise a polyaryl ether ketone, a polyaryl ketone, a polyether ketone, a polyether ether ketone, a polycarbonate or the like, or any suitable combination thereof. The matrix material may comprise a resin, such as an epoxy resin or the like. 
         [0051]    Accordingly, it will be recognised that a second pipe section having a wall comprising a composite material, and which provides a local variation in a property of the pipe system along the length of the pipe system facilitates greater control or certainty over the behaviour of the pipe system. Moreover, the risk that the pipe system and associated couplings and equipment will be deformed or damaged is reduced. 
         [0052]    The pipeline or pipe system may comprise one or a plurality of deformation absorbers. The pipeline or pipe system may comprise a single second pipe section or may comprise two or more second pipe sections. 
         [0053]    The pipe system may also comprise a single first pipe section or two or more first pipe sections. 
         [0054]    The first pipe section may be of any suitable form or construction. In particular embodiments, the first pipe section may comprise steel pipe. In subsea oil and gas recovery applications, for example, the first pipe section may comprise pipe as may be used for conventional risers, flow line, jumpers and the like. In alternative embodiments and arrangements, aluminium, titanium, metal alloys, ceramics, plastics, composites, concrete or other suitable materials may be used in the construction of the first pipe section. 
         [0055]    The second pipe section may be configured for coupling to the first pipe section. 
         [0056]    The pipeline or pipe system may comprise a connector arrangement interposed between the first and second pipe sections to permit coupling therebetween. 
         [0057]    The second pipe section may be coupled to the first pipe section by any suitable means. For example, the second pipe section may be coupled to the first pipe section by a flange connection. Alternatively, the second pipe section may be bonded, welded, cast or otherwise secured to the first pipe section to form the pipe system. 
         [0058]    As noted above, the second pipe section may be coupled to an end of a first pipe section. Thus, the first and second pipe sections may be abutted together and coupled together to form a continuous bore for transport of fluid, such as hydrocarbons, and equipment. 
         [0059]    The pipe system may be configured for use above the ground. The pipe system may be configured for use at least partially buried. The pipe system may be configured for use in a subterranean environment. The pipe system may be configured for use in a subsea location. 
         [0060]    The pipe system may be configured for use as part of, for example, a riser, a flow line, a jumper or the like, or any combination thereof. The pipe system may be configured for use in transporting a fluid, providing a confined conduit for tooling or the like, such as may be used in subterranean wellbore drilling operations, completion operations, intervention operations and the like. 
         [0061]    The pipe system may be configured for use in transporting product associated with the extraction of hydrocarbons from subsea reservoirs, including accommodating the flow of hydrocarbons, carbon dioxide, water, other chemicals, solid matter, fluid and gas mixes and the like. The pipe system may be configured for use in carbon dioxide or other gas sequestration. 
         [0062]    Another aspect of the present invention relates to a method of manufacturing a pipeline or pipe system, comprising: 
         [0063]    coupling a deformation absorber to a metallic pipe section which has a wall comprising a metallic material, 
         [0064]    wherein the deformation absorber comprises a composite pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix, wherein the composite material is constructed to cause the deformation absorber to sustain a greater level of strain than the metallic pipe section when the pipeline is subject to deformation by a load event such that a larger proportion of deformation within the pipeline caused by a load event is focussed within the deformation absorber. 
         [0065]    Another aspect of the present invention relates to a method of manufacturing a pipeline or pipe system, comprising: 
         [0066]    providing a first pipe section having a wall comprising a metal material; and 
         [0067]    coupling a second pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix to an end of the first pipe section, wherein the second pipe section is configured to sustain a greater level of strain than the first pipe section when the pipe system is subject to deformation by a load event. 
         [0068]    Embodiments of the present invention may permit a preferential control over the behaviour of the pipeline or pipe system to be achieved, which may assist when in a service condition, storage configuration, deployment/retrieval configuration or the like. For example, the pipe system may be arranged to permit a controlled deformation to be achieved within the composite second pipe section, and in some embodiments to be substantially restricted to this composite second pipe section. Such deformation may include buckling, longitudinal expansion and contraction, radial expansion and contraction, torsional deformation, bending or the like. Such deformation may include catastrophic failure, such as axial tensile failure, hoop tensile failure or the like. 
         [0069]    Embodiments of the present invention may also or alternatively permit multiple pipe systems to be arranged in proximity to each other, wherein the composite second pipe section in each pipe system facilitates a desired behavioural characteristic, such as controlled longitudinal bending, at a common location. This may prevent or substantially minimise interference between each pipe system, facilitate more compact installations and the like. This arrangement may be of application where, for example, multiple pipe systems are bundled in a common location, extend along a common path or course, converge to a common restricted location from various directions or the like, such as convergence towards a common floating vessel, for example a FPSO vessel used in the oil and gas industry. 
         [0070]    Another aspect of the present invention relates to a pipe system comprising: 
         [0071]    a first pipe section having a wall comprising a metal material; and 
         [0072]    a second pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix, wherein the second pipe section is coupled to the first pipe section in end-to-end relation and is configured to provide a local variation in a property of the pipe system along the length thereof. 
         [0073]    A pipe system according to embodiments of the present invention may define a hybrid pipe construction. 
         [0074]    In use, the local variation in a property of the pipe system may establish one or more preferential characteristic in the pipe system. Such a preferential characteristic may beneficially differ from that in a pipe of uniform construction, as may be found in the prior art. 
         [0075]    The pipe system may be configured to provide any selected preferential characteristic. 
         [0076]    In particular embodiments, the local variation or preferential characteristic may provide for absorption of axial loading and/or deformation, such as cyclic axial loading, and, in use, the pipe system may be configured to absorb axial expansion or compression loads which may otherwise result in fatigue, undesired lateral movement or buckling of the pipe system or associated components, couplings, adjacent pipe systems or the like. 
         [0077]    Alternatively or additionally, the local variation or preferential characteristic may provide for absorption of bending loads which may otherwise exceed the design limit of conventional uniform metal pipe systems. 
         [0078]    Alternatively or additionally, the local variation or preferential characteristic may provide for focussing of lateral buckling, deflection or deformation within the composite pipe section. This may permit a buckling event, for example by application of a critical buckling load, to be restricted within the composite pipe section. Restricting buckling to the composite pipe section may assist in protection of the overall pipe system or adjacent pipe systems. 
         [0079]    The local variation achieved in the pipe system may be selected to provide a desired longitudinal bending characteristic along the pipe system. 
         [0080]    The local variation may be selected to provide a desired deformation characteristic, such as bending, buckling or the like, within the pipe system when under load, such as when exposed to internal pressure, external pressure, torsional loading, radial loading, axial loading or the like. For example, the pipe section may be formed to permit bending or deformation to be restricted to a particular direction or plane. 
         [0081]    The local variation may be selected to provide a desired longitudinal twist characteristic of the pipe system. 
         [0082]    The local variation may be selected to provide a desired thermal expansion characteristic of the pipe system. 
         [0083]    The local variation may be selected to provide a desired thermal insulation characteristic of the pipe system. 
         [0084]    A preferential mechanical characteristic may be achieved, such as a selected strength, stiffness, flexural rigidity, bending, resonant characteristic or the like. A preferential thermal characteristic may be achieved, such as a selected thermal expansion characteristic, selected thermal insulation characteristic or the like. 
         [0085]    Another aspect of the present invention relates to a method of protecting a pipeline or pipe system, comprising: 
         [0086]    coupling a deformation absorber to a metallic pipe section, 
         [0087]    wherein the deformation absorber comprises a composite pipe section having a wall comprising a composite material formed of at least a matrix and a plurality of reinforcing fibres embedded within the matrix, the composite material constructed to cause the deformation absorber to sustain a greater level of strain than the metallic pipe section when the pipeline is subject to deformation by a load event such that a larger proportion of deformation within the pipeline caused by a load event is focussed within the deformation absorber. 
         [0088]    It should be understood that the features defined above in accordance with any aspect of the present invention may be utilised, either alone or in combination with any other defined feature, in any other aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0089]      FIG. 1  is a diagrammatic view of a subsea environment comprising a pipeline or pipe system according to an embodiment of the present invention; 
           [0090]      FIG. 2  is a diagrammatic side view of a pipe system for use in the subsea environment shown in  FIG. 1 ; 
           [0091]      FIGS. 3A and 3B  are diagrammatic side views of a pipeline or pipe system according to an embodiment of the present invention, wherein the pipe system includes a deformation absorber in the form of a composite pipe section configured to focus longitudinal expansion/contraction within said composite section; 
           [0092]      FIG. 4  is a diagrammatic side view of a further embodiment of the present invention, wherein the pipeline or pipe system includes a deformation absorber in the form of a composite pipe section configured to focus lateral buckling or deformation with said section; 
           [0093]      FIG. 5  is a diagrammatic perspective view of a pipeline or pipe system with three flow lines according to an embodiment of the present invention; 
           [0094]      FIGS. 6A and 6B  are side and top views, respectively, of a known flow line buckle arrangement; and 
           [0095]      FIGS. 7A and 7B  are side and sectional end views, respectively of a further known flow line buckle arrangement. 
       
    
    
     DETAILED DESCRIPTION 
       [0096]      FIG. 1  shows a subsea production system  400  for use in recovering hydrocarbons from a subsea hydrocarbon-bearing formation. As shown in  FIG. 1 , a riser  402  extends from a surface vessel  404  to a manifold  406  located on the floor of a body of water, such as the sea floor  408 . A number of pipelines or pipe systems  410  according to an embodiment of the present invention extend from the manifold  408  to wellheads  412  (three wellheads  412  are shown in  FIG. 1 ). The pipe systems  410  form flow lines for transport of hydrocarbons and/or equipment between wells  413  (shown in dotted line in  FIG. 1 ), the wellheads  402  and the manifold  406 . Each pipe system  410  is shown as a single flow line for clarity, however it will be understood that each pipe system  410  may comprise a plurality of flow lines. 
         [0097]      FIG. 2  shows a diagrammatic side view of one of the pipe systems  410  shown in  FIG. 1 . The pipe system  410  comprises two longitudinal steel wall pipe sections  414  and a longitudinal composite wall pipe section  416 , wherein as noted below the composite pipe section  416  defines a deformation absorber. The pipe sections  414 , 416  are abutted end-to-end and the composite pipe section  416  is coupled between the steel wall pipe sections  414  so that a contiguous pipe bore  418  is created for the passage of fluid or equipment through the pipe system  410 . In the embodiment shown, the pipe sections  414 , 416  are coupled by a flange connection  420 , although it will be understood that any suitable means for coupling the pipe sections  414 , 416  may be used. 
         [0098]    The composite pipe section  416  is configured to sustain a greater level of strain than the metal pipe sections  414  when the pipe system  410  is subject to deformation by a load event. This arrangement, in the embodiments shown, functions to focus the deformation of the pipe system substantially entirely within the composite pipe section  416 , thus acting to protect the metal pipe sections  414  from excessive strains and/or stresses, material fatigue or the like. 
         [0099]    In use, the composite pipe section  416  provides a local variation in a property of the pipe system  410  along the length of the pipe system  410 . In the case of the subsea production system  400  shown in  FIG. 1 , the composite pipe section  416  is configured to provide a local variation in the tensile strength, compressive strength and/or other property of the pipe system  410  in order that the pipe system  410  will absorb axial loads, which may be cyclic axial loads, acting on the pipe system  410  as a result of the environmental and/or operational conditions. The composite pipe section  416  may also be configured to provide a local variation in the second moment of area or other property in order to provide a local variation in the bending stiffness of the pipe system  410 . 
         [0100]    In use, the composite pipe section  416  may provide for local expansion, contraction, or bending to absorb the axial loads and reduce or eliminate the occurrence of fatigue, buckling, as may otherwise occur in a pipe system of uniform metal construction. In the embodiment shown the composite material is configured to focus longitudinal expansion and contraction within the composite pipe section  416 , for example from longitudinal expansion and contraction as a result of mechanical applied forces, thermal expansion/contraction and the like. 
         [0101]      FIG. 3A  illustrates a pipe system  410  in a contracted configuration.  FIG. 3B  illustrates a pipe system  410  in an expanded configuration. 
         [0102]    Referring to  FIGS. 3A and 3B , a composite pipe section  416  of the pipe system  410  defines a length  1  when in a contracted state, and an extended length L when in an expanded state. The composite pipe section  416  in the present embodiment is configured to absorb axial extension and contraction in the pipe, such as caused by thermal variations or cycles with minimal lateral deflection or deformation. In this embodiment, the composite pipe section  416  may be provided to remove or reduce any expansion and contraction effects in other longitudinal portions of the pipe, such as adjacent pipe sections  414 . 
         [0103]    A further alternative, or supplementary embodiment is shown in  FIG. 4 . In this embodiment the pipe, the composite pipe section  416  is configured to focus lateral buckling, deflection or deformation within said composite pipe section  416 , as illustrated in broken outline. This may permit a bucking event, for example by application of a critical buckling load, to be restricted within composite pipe section  416 . A critical buckling load may originate from a service condition of the pipe system  410 , such as axial thermal expansion or the like. 
         [0104]    In this present embodiment restricting buckling to the composite pipe section  416  may assist in protection of other pipe sections, such as adjacent sections  414 . Furthermore, by limiting lateral deviation or deformation of the pipe system to the composite pipe section, the effects of a dynamic service condition, such as caused by intermittent operation, multiphase flow or the like is minimised. For example, the composite pipe section  416 , by virtue of the composite material, will not be affected by material fatigue issues, and may be able to accommodate increased dynamic operational cycles or the like while maintaining sufficient integrity. Furthermore, restricting deviation or deformation within the pipe system to within the composite pipe section may permit absorption of such movement to be achieved by shorter pipe lengths which may otherwise be required in continuous metal pipe systems. 
         [0105]    Thus, in the present embodiment the composite pipe section  416  may be configured to firstly focus buckling at this point, and secondly to accommodate the lateral buckling deformation without resulting in exceeding the yield point of the material. Further, the composite pipe section  416  may permit multiple buckling cycles to be accommodated, while minimising effects of material fatigue and the like. 
         [0106]    The provision of a composite pipe section  416  having distinct properties from those of the steel wall pipe sections  414  also has the benefit of permitting control over the behaviour of the whole pipe section  410 . 
         [0107]    With reference now also to  FIG. 5  of the drawings, there is shown a pipe system  410  according to an embodiment of the present invention and which has three flow lines. As noted above, the composite pipe section  416  is formed or configured to provide a local variation in a property or properties of the pipe system  410 . A number of possible variations according to the present invention may be possible and in this embodiment the local variation of a property of the pipe system  410  is established by a localised constructional variation in the composite pipe section  416 . 
         [0108]    By providing said localised constructional variation, the bending characteristics of the pipe system  410  may be better controlled, such that the three flow lines shown in  FIG. 3  may be formed and arranged so that movement of the respective flow lines, for example due to fluid flow therethrough, is resisted or directed in a desired direction. 
         [0109]    It should be understood that the embodiments described herein are merely exemplary, and that various modifications may be made thereto without departing from the scope of the invention. 
         [0110]    For example, it should be understood that although the terms such as “circumferential” and “radial” are used herein, these are not intended to limit the pipe sections to being circular in cross-section. Instead, the pipe sections may be of any cross-sectional shape, such as oval, rectilinear or the like, and references to a circumferential segment may be considered to be a segment or sector of a perimeter of the pipe section.