A carcass, a flexible pipe and methods for production thereof

Abstract

Carcass for a flexible pipe and production method thereof. The carcass has a profile structure comprising a plurality of consecutive helical windings of at least one first metallic strip (31) having a first (31a) and a second (31b) interlocked fold and with an inwards facing helicoidal interstice (33) between the first fold (31a) and the second fold (31b). The profile structure has a helically wound cover metallic strip (32) having a first width section (32a), a transition width section (32b) and a cover width section (32c). The first width section (32a) extends into the helicoidal interstice (33), the cover width section (32c) at least partially covers the inwards facing helicoidal interstice (33) in adjacent windings. The cover width section (32c) has at least one stiffening width portion (35) with a thickness larger than the thickness of at least one of the first width section (32a) and the transition width section (32b).

Description

[0001] A CARCASS, A FLEXIBLE PIPE AND METHODS FOR PRODUCTION THEREOF

[0002] TECHNICAL FIELD

[0003] The present invention relates to a carcass suitable for use in a flexible pipe, such an unbonded flexible pipe. The invention also relates to a flexible pipe as well as production of the carcass and the flexible pipe.

[0004] BACKGROUND ART

[0005] Flexible offshore pipes are widely used for transport of hydrocarbons such as oil and gas. Basically, a flexible pipe comprises a pressure sheath defining a bore through which a fluid, such as hydrocarbons may be transported. The pressure sheath is in most cases produced from polymer material which is extruded to form a tubular sheath, which has a high degree of impermeability in respect of the fluids to be transported. The pressure sheath may be supported and reinforced by several other layers, such as pressure armors and tensile armors. These layers are normally applied on the outer surface of the pressure sheath. However, due to external pressure it may be necessary to support the pressure sheath on the inner surface against collapse, e.g. where the flexible pipe is adapted for use at deep water e.g. as a riser and / or where there may be a risk of a pressure drop in the bore of the pipe. Normally, such a support is a metal structure known as a carcass. A carcass is conventionally made from one or more elongate strips of metal, which is / are wound to form a tubular structure. The one or more strips of metal may be wound with overlaps between consecutive windings to form the tube. Moreover, the wound one or more strips may be interlocked e.g. wherein the edge parts the metal strip(s) may be provided with bends which may engage in consecutive windings and thereby "lock" the windings to each other and provide additional strength to the resulting tube.

[0006] Consequently, flexible offshore pipes, hereafter referred to as flexible pipes, are for example used in the oil industry for raising or transporting hydrocarbons from a subsea well head to a platform or floating equipment such as a Floating Production and Storage Offloading unit known by the abbreviation FPSO. Such flexible pipes are for example described in "Recommended Practice for Flexible Pipe "API Recommended Practice 17 B", fifth edition 2014 published by the American Petroleum Institute. Moreover, flexible pipes are also described in "Specification for unbonded flexible pipe" API 17J, fourth edition 2014" or "Specification for Bonded Flexible Pipe"; API 17K, 2017, also published by the American Petroleum Institute.

[0007] However, these traditional carcasses typically have a helicoidal interstice (sometimes called a gap) between adjacent interlocked windings. When oil or gas is flowing in the flexible pipe, the oil or gas will be in contact with the carcass. Thus, when the flow reaches a certain velocity, and in particular where the fluid comprises gas, the helicoidal interstice between the adjacent windings may cause formation of vortexes in the flow, and the formation of these vortexes may again cause vibrations in the flowing gas as well as in the entire carcass structure and hence the flexible pipe. This phenomenon is known as "singing carcasses" and is highly undesirable as the vibrations may result in fatigue damage, which may be detrimental to the flexible pipe. When such vibrations appear, the vibrations may also spread to the connected structure comprising parts such as end fittings and connectors and cause severe damage to those parts and the whole installation.

[0008] Consequently, attempts have been made to reduce or eliminate the formation of the vortexes. One very simple way to eliminate the formation of vortexes in the flow is to reduce the velocity of the flow of oil or gases in the flexible pipe. However, this solution will also reduce the capacity of the flexible pipe. Thus, alternative attempts have been made to avoid vortex formation at high flow velocities of oil and gas.

[0009] French patent application FR2930622 Al discloses a method for eliminating vibrations by providing the strips from which the carcass is made with holes in the surface.

[0010] International patent application WO 2014 / 000816 Al suggests a solution in which the gaps are provided with an insert profile, which at least partly closes the gaps between adjacent windings.

[0011] International patent application WO 2014 / 135906 Al discloses a flexible metal pipe made from a layered strip. One of the layers in the strip may be un-folded and cover crevices in the flexible metal pipe. The structure makes it very difficult to achieve a pipe having a uniform diameter. To achieve a uniform diameter the layered strip needs to be modified by twisting or further bending, which complicates the manufacture of the metal pipe. However, generally the prior art solutions require use of relative large amounts of metal to ensure a stable reduction or elimination of vortex formation. Such use of relatively large amounts of metal is undesired both in respect of cost and in respect of weight of the carcass.

[0012] DISCLOSURE OF INVENTION

[0013] An objective of the present invention is to provide a carcass which effectively reduces or even fully avoids formation of vortex.

[0014] In an embodiment it is an objective to provide a carcass which is very effective against generation of vortexes and / or vibrations and which requires a relatively small amount of metal.

[0015] In an embodiment it is an objective to provide a carcass which ensures a very stable coverage of a helicoidal interstice of the carcass to reduce or even avoid formation and / or building up of undesired vibrations and which requires a relatively small amount of metal.

[0016] In an embodiment it is an objective to provide a flexible pipe, preferably for use as a riser pipe, and which flexible pipe has a very low risk of formation of and / or building up of undesired vortexes and / or vibrations, without this requires excess amounts of metal.

[0017] In an embodiment it is an objective to provide a carcass and / or a flexible pipe comprising a carcass which exhibits improved properties in respect of reducing vibrations even where the transported fluid comprises gas, such as a mixture of gas and liquid hydrocarbons.

[0018] In an embodiment it is an objective to provide a method of producing a carcass, which method is relatively simple and cost-effective.

[0019] These and other objectives have been solved by the invention or embodiments thereof as defined in the claims and / or as described herein below.

[0020] It has been found that the invention or embodiments thereof have a number of additional advantages which will be clear to the skilled person from the following description. The inventor of the present invention has found that by providing the carcass to comprise a cover width section of a cover metallic strip helically wound, wherein the cover width section comprises at least one stiffening width portion. A very strong and stable coverage of an inwards facing helicoidal interstice may be provided. The average thickness of the cover metallic strip may thereby be relatively thin, which reduces the required amount of metal applied for the cover metallic strip and thereby results both in saved cost and simultaneously reduces the weight of the carcass, which again ensures a reduction of the tensile forces acting during deployment of a flexible pipe comprising the carcass and / or during use of such flexible pipe, e.g. as a riser pipe. The stiffening width portion may conveniently be provided by providing the stiffening width portion to have a thickness exceeding a thickness of at least one of a first width section and a transition width section of the cover metallic strip.

[0021] The terms "laterally" and "lateral movement" mean a movement lengthwise relative to the carcass axis.

[0022] The phrases "surface-to surface contact" and "interfacial contact" are used interchangeably.

[0023] The term "substantially" should herein be taken to mean that ordinary product variances and tolerances are comprised.

[0024] It should be emphasized that the term "comprises / comprising" when used herein is to be interpreted as an open term, i.e. it should be taken to specify the presence of specifically stated feature(s), such as element(s), unit(s), integer(s), step(s) component(s) and combination(s) thereof, but does not preclude the presence or addition of one or more other stated features.

[0025] Throughout the description or claims, the singular encompasses the plural unless otherwise specified or required by the context.

[0026] The "an embodiment" should be interpreted to include examples of the invention comprising the feature(s) of the mentioned embodiment.

[0027] The term "about" is generally used to include what is within measurement uncertainties. When used in ranges the term "about" should herein be taken to mean that what is within measurement uncertainties is included in the range. The term "substantially" should herein be taken to mean that ordinary product variances and tolerances are comprised. All features of the invention and embodiments of the invention as described herein, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless there are specific reasons not to combine such features.

[0028] Any chemical or physical property is to be determined at standard conditions of 23°C and 1 atm. unless otherwise specified.

[0029] The carcass may conveniently be suitable for forming a carcass of a flexible pipe for transporting oil and / or gas. The flexible pipe may preferably be of the unbonded type e.g. as described in "API Recommended Practice 17 B", fifth edition 2014 and / or "Specification for unbonded flexible pipe" API 17J, fourth edition 2014" published by the American Petroleum Institute.

[0030] Such an unbonded flexible pipe for transporting oil and gas may comprise from the inside to the outer side a carcass supporting a surrounding pressure sheath defining the bore of the pipe for transporting the fluid. The pressure sheath is covered with one or more armor layers typically comprising a pressure armor (sometimes called a pressure vault), which again are covered with one or more layers of tensile armor, and optionally the flexible pipe is covered with an outer sheath adapted for shielding against ingress of water, such as sea water.

[0031] The carcass has a carcass axis defined as axis of the carcass. The carcass has a profile structure comprising a plurality of consecutive helical windings of at least one first metallic strip. Where desired the carcass may comprise two or more first metallic strips. Often it is desired to use a single first metallic strip, which may simplify the production and also ensure a desired high winding angle relative to the carcass axis, such as at least 75°, preferably 80° or larger, such as 85° or larger. Where there are two or more first metallic strips, these strips may be stacked onto each other.

[0032] The at least one first metallic strip has a profile comprising a first fold facing towards the carcass axis and a second fold facing away from the carcass axis and wherein the first and the second fold of the first strip being interlocked and wherein the profile structure comprises an inwards facing helicoidal interstice between the first fold and the second fold of the first strip in the windings of the least one first metallic strip. The first fold may conveniently be a fold of a first width section along a first edge of the at least one first metallic strip, and the second fold may conveniently be a fold along a second width section along a second edge of the at least one first metallic strip. The helically wound and interlocked at least one first metallic strip may form a basic structure of the carcass adapted for providing a flexible pipe comprising the carcass with collapse resistance, e.g. due to a hydrostatic pressure during use of the flexible pipe. The profile structure of the carcass comprises a helically wound cover metallic strip. The cover metallic strip comprises a first width section, a transition width section and a cover width section. Preferably, the cover metallic strip comprises from a first cover metallic strip edge to a second cover metallic strip edge the first width section, the transition width section and the cover width section.

[0033] The first width section of the helically wound cover metallic strip in respective windings of the cover metallic strip extends into the helicoidal interstice, thereby ensuring an anchoring in the basic structure provided by the helically wound and interlocked at least one first metallic strip.

[0034] The cover width section of the cover metallic strip is in the respective windings of the first metallic strip located to at least partially cover the inwards facing helicoidal interstice in adjacent windings of the cover metallic strip. Thereby, the inwards facing helicoidal interstice is at least partially covered by the cover width section.

[0035] Moreover, the cover width section comprises at least one stiffening width portion, wherein the stiffening width portion has a thickness exceeding a thickness of at least one of the first width section and the transition width section.

[0036] The stiffening width portion, provides the cover width section with resistance against undesired plastic deformation, which without the stiffening width portion may be caused by fluids flowing in the bore of the flexible pipe, such as fluid flowing with more or less turbulence e.g. caused by a variance in velocity and / or by a presence of gas, such as gas pockets and / or gas bubbles.

[0037] The term "metallic strip" is herein used to mean a strip comprising or consisting of metal. Preferably the metallic strip, such as at least one of the first metallic strip and the cover metallic strip, comprises at least one metal layer, such as a steel layer e.g. stainless steel. The metal of the at least one of the first metallic strip and the cover metallic strip may advantageously be of equal grade.

[0038] The term "inwards facing" is herein used to mean facing the carcass axis.

[0039] The term "outwards facing" is herein used to mean facing away from the carcass axis.

[0040] The term "profile" is herein used to mean a cross-sectional profile perpendicular to a length of at least one of the first metallic strip and / or of the cover metallic strip.

[0041] To ensure a desired strength against undesired plastic deformations in use, the stiffening width portion preferably has an average thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section, such as an average thickness of from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

[0042] In an embodiment, the basic structure of the carcass formed by the helically wound and interlocked at least one first metallic strip has a flattened S-shaped crosssection, with a first U-shaped part formed by the first fold and a second U-shaped part formed by the second fold, wherein the first U-shaped part has a first U-shape flat surface facing away from the carcass axis and the second U-shaped part has a second U-shape flat surface facing towards the carcass axis.

[0043] The shape of the stiffening width portion is preferably identical along the length of the cover metallic strip, i.e. with same width and same shape and structure, such as thickness structure along the length of the cover metallic strip. The stiffening width portion may have a substantially equal thickness along the width of the stiffening width portion. In an embodiment, the stiffening width portion has a varying thickness along the width thereof, for example the stiffening width portion may have a beveled width sub-portion e.g. adjacent to and optionally beveled towards the second edge of the cover width section. Thereby, at least a part of the stiffening width portion along the second edge of the cover metallic strip edge may be in conforming contact with the second U-shaped flat surface facing towards the carcass axis or at least a part of the stiffening width portion along the second edge of the cover metallic strip edge may be in conforming contact with a part of the cover width section which itself is in conforming contact with the second U-shape flat surface facing towards the carcass axis in an adjacent winding. Thereby, the risk of undesired plastic deformations of the cover width section of the cover metallic strip may be further reduced.

[0044] Advantageously, the stiffening width portion has a minimum thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section. The stiffening width portion has a minimum thickness of, for example, 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

[0045] Thanks to the present invention, the cover metallic strip may have an average thickness which is less, even substantially less than an average thickness of the at least one first metallic strip, while simultaneously providing a safe and stable coverage of the helicoidal interstice. Preferably, the thickness of the cover metallic strip has an average thickness of up to 50%, such as up to 25% of the average thickness of the at least one first metallic strip. Preferably, the at least one first metallic strip has same thickness in its entire width when in un-folded condition.

[0046] In an embodiment, the stiffening width portion is in the form of a single layer portion. In this embodiment, the cover metallic strip may for example be subjected to a rolling procedure or a similar mechanical treatment prior to shaping of the cover metallic strip, wherein the mechanical procedure provides the cover width section with a width portion, which is thicker that the cover metallic strip at the remaining width of the cover metallic strip, wherein the formed width section forms the stiffening width portion of the shaped cover width section.

[0047] In an embodiment, the stiffening width portion comprises a multilayer portion, such as a multilayer portion, preferably comprising from 2 to 10 layers, such up to 6 layers, such as 3, 4 or 5 layers. Thereby, the cover width section is relatively simple to produce to have the stiffening width portion.

[0048] In an embodiment, the stiffening width portion comprises at least one fold.

[0049] In an embodiment, the stiffening width portion comprises a folded portion of the cover width section comprising at least one fold, wherein the stiffening width portion has two or more folded sub width sections of the cover width section folded against itself to be in interfacial contact. In an embodiment, it is desired that the two or more folded sub width sections of the cover width section are folded to lie in parallel and in full contact against each other, preferably to ensure that liquid flowing in the bore of the flexible pipe is not inducing pressure to separate such folded sub width sections of the cover width section from each other. This is in particular important where the two or more folded sub width sections of the cover width section comprises folds towards the carcass axis.

[0050] In an embodiment, the stiffening width portion comprises the second edge portion of the cover width section folded back on itself in one or more folds. The stiffening width portion may preferably comprise a free edge of the cover width section.

[0051] It has been found that where the stiffening width portion comprises a free edge of the cover width section (i.e. the second edge of the cover metallic strip), the width of the stiffening width portion may be relatively narrow and still ensure a desired stiffening to ensure a stable protection against formation of vortex and vibrations. Thus, in an embodiment, the width of the stiffening width portion comprising a free edge of the cover width section has a width down to 1 cm or even less, such as down to 3 mm or less, such as down to 3 mm or less.

[0052] In an embodiment, the stiffening width portion comprises an edge portion of the cover width section folded back on itself in one or more folds comprising at least one fold in inward direction (towards the carcass axis) and / or one fold in outward direction (away from the carcass axis). In practice, it is preferred that the stiffening width portion comprises an edge portion of the cover width section folded back on itself in one or more folds, wherein the one or more fold(s) is / are in outward direction (away from the carcass axis). Thereby, the risk of undesired plastic deformations caused by fluid flowing in the bore may be practically eliminated even where the average thickness of the cover metallic strip is relatively thin, i.e. substantially thinner than the at least one first metallic strip.

[0053] In an embodiment, the cover width section extends laterally from the transition width section to cover the inwards facing helicoidal interstice between windings of the first metallic strip. The cover width section may preferably extend laterally from the transition width section to entirely cover the inwards facing helicoidal interstice between windings of the first metallic strip and more preferably extend to be in surface contact with at least a part of the second U-shape flat surface facing towards the carcass axis or to be in surface contact with a part of the cover width section, which itself is in conforming contact with at least a part of the second U-shape flat surface facing towards the carcass axis.

[0054] In an embodiment, the stiffening width portion comprises at least one fold wherein the at least one fold has an inner folding radius of about zero or of up to 5 times the average thickness of the cover width section in unfolded condition.

[0055] The inner folding radius is herein defined as the minimum radius in the fold of the curve of the surface of the cover width section folded towards itself.

[0056] Thus, where the fold is a sharp fold with no space between the layers folded towards each other even immediately adjacent to a bend of the stiffening width portion, i.e. where the stiffening width portion comprises a bend of the cover width section, the inner folding radius is zero or about zero.

[0057] In an embodiment, the stiffening width portion comprises at least one fold with an inner folding radius of at least 0.1 times the average thickness of the cover width section in unfolded condition, such as at least 0.5 times the average thickness of the cover width section in unfolded condition, such as from 0.7 to 3 times the average thickness of the cover width section in unfolded condition, such as from 1 to 2 times the average thickness of the cover width section in unfolded condition.

[0058] To ensure a high strength of the cover width section it may be desired to provide the stiffening width portion to comprise one or more folds, each with an inner folding radius of at least 0.1 times the average thickness of the cover width section in unfolded condition, since providing a very sharp fold may weaken the cover width section in the location of the bend of the fold.

[0059] In an embodiment, the stiffening width portion extends laterally, preferably from parallel width to up to an angle of 25 degrees to the axis of the carcass, such as up to an angle of 15 degrees to the axis of the carcass, such as up to an angle of 10 degrees to the axis of the carcass, such as up to an angle of 5 degrees to the axis of the carcass, such as up to an angle of 2 degrees to the axis of the carcass.

[0060] As it will be explained in connection with the figures, the angle of the cover width section and / or of the stiffening width portion relative to the carcass axis may depend on the width of the cover width section and / or the location of the stiffening width portion.

[0061] The stiffening width portion may in principle be located at any width positioning of the cover width section. In an embodiment, the stiffening width portion is located adjacent to and optionally comprising a free edge of the cover width section or up to a distance of from 1% to 100% of the cover width section minus the width of the stiffening width portion, such as up to 90% of the width of the cover width section, such as up to a distance of from 25% to 75% of the width of the cover width section.

[0062] The location of the stiffening width portion relative to the free edge of the cover width section may be determined as the minimum distance from the free edge of the cover width section to the stiffening width portion.

[0063] Advantageously, the stiffening width portion is at least partially located at the inwards facing helicoidal interstice, preferably such that the stiffening width portion is at least partially extending into the inwards facing helicoidal interstice.

[0064] In an embodiment, the stiffening width portion comprises 3 layers formed by folds of the cover width section. Preferably, the 3 layers comprises at least a flat sub portion which is preferably parallel with at least a non-folded portion of the cover width section, such as parallel with and in same plane as at least a non-folded portion of the cover width section.

[0065] In an embodiment, the stiffening width portion comprises at least one fold and wherein the stiffening width portion protrudes into the inwards facing helicoidal interstice, wherein the at least one fold preferably comprises a loop fold with a loop apex and a loop plane through the loop apex, wherein the loop plane is perpendicular to the carcass axis or has an angle perpendicular to the carcass axis of up to 60 degrees, such as up to 45 degrees, such as up to 30 degrees.

[0066] It has been found that where the stiffening width portion protrudes into the inwards facing helicoidal interstice, a very desired stiffening of the cover width section may be obtained, which simultaneously ensures that an edge portion of the cover width section may be firmly held in conforming contact (optionally via the cover width section in an adjacent winding) with the second U-shape flat surface facing towards the carcass axis to thereby further reduce the risk of undesired plastic deformations of the cover width section of cover metallic strip.

[0067] In an embodiment, the cover width section has a first non-folded portion located between the transition width section and the stiffening width portion and a second non-folded portion located at an opposite side of the stiffening width portion, wherein the first non-folded portion of the cover width section is in interfacial contact with the at least one first metallic strip and the second non-folded portion of the cover width section is in interfacial contact with the first non-folded portion of the cover width section in an adjacent winding.

[0068] Preferably, the first non-folded portion of the cover width section is in interfacial contact with the second U-shape flat surface facing towards the carcass axis in a winding of the at least one first metallic strip and the second non-folded portion of the cover width section is in interfacial contact with the first non-folded portion of the cover width section in an adjacent winding.

[0069] In an embodiment, the cover width section has a first non-folded portion located between the transition width section and the stiffening width portion and a second non-folded portion located at an opposite side of the stiffening width portion, wherein the second non-folded portion of the cover width section is parallel offset relative to the first non-folded portion of the cover width section, wherein the second non-folded portion of the cover width section is located closer to the carcass axis than the first non-folded portion of the cover width section. Thereby, a very desired and firm interfacial contact between the second non-folded portion of the cover width section and the first non-folded portion of the cover width section in an adjacent winding may be obtained.

[0070] The stiffening width portion is advantageously located to fully cover the inwards facing helicoidal interstice between the first fold and the second fold of the first strip in the windings of the least one first metallic strip.

[0071] Preferably, the stiffening width portion has a width of at least 1% of the width of the at least one first metallic strip in unfolded condition, such as at least 5% of the width of the least one first metallic strip in unfolded condition, such as from 8% to 50% of the width of the least one first metallic strip in unfolded condition, such as from 15% to 30% of the width of the least one first metallic strip in unfolded condition. In an embodiment, the stiffening width portion has a width of at least 2% of the width of the cover width section in unfolded condition, such as at least 8% of the width of the cover width section in unfolded condition, such as from 10% to 100% of the width of the cover width section in unfolded condition, such as from 15% to 50% of the width of the cover width section in unfolded condition.

[0072] In an embodiment, the first fold of the at least one first metallic strip comprises a first inwards folded edge portion and the second fold of the at least one first metallic strip comprises a second outwards folded edge portion. The interlocking between the first fold and the second fold of the first strip may comprise that the first inwards folded edge portion in the plurality of consecutive windings is interlocked with the second outwards folded edge portion in respective adjacent windings. To ensure a desired flexibility and bendability of the carcass, the first inwards folded edge portion and the second outwards folded edge portion is preferably shaped to allow adjacent windings to move laterally relative to each other, preferably to allow adjacent windings to move laterally a limited distance d relative to each other thereby allowing the inwards facing helicoidal interstice between the first fold and the second fold to vary along the length of the carcass between a maximal and a minimal distance between the second U-shape flat surface facing towards the carcass axis in respective adjacent windings.

[0073] The maximal and the minimal distance between the second U-shape flat surface facing towards the carcass axis in respective adjacent windings may differ with up to the limited lateral distance d that the adjacent windings are allowed to move.

[0074] In an embodiment, the transition width section of the cover metallic strip is located between the first width section and the cover width section. Preferably, the transition width section extends from the first width section and to the second cover width section.

[0075] In an embodiment, the transition width section extends into and is at least partly located in the helicoidal interstice and preferably in surface contact with a surface of the first fold, such as in contact with the first inwards folded edge portion. Preferably, the transition width section is in full surface-to-surface contact with the surface of the first fold, such as in full surface-to-surface contact with the first inwards folded edge portion. Thereby, the transition width section of the cover metallic strip may at least partly, e.g. together with the first width section, provide an anchoring of the cover metallic strip to the basic structure of the carcass comprising the helically wound and interlocked at least one first metallic strip.

[0076] The transition width section may conveniently form a transition between a first winding diameter of the cover metallic strip and a second winding diameter of the cover metallic strip, wherein the second winding diameter is larger than the first winding diameter and wherein the cover metallic strip has the first winding diameter at the border between the transition width section and the cover width section. Thereby, an effective anchoring to the basic structure of the carcass may be ensured.

[0077] In an embodiment, the transition width section comprises at least one curved portion. Preferably, the transition width section comprises a first curved portion adjacent to the first width section, and a second curved portion adjacent to the cover width section, wherein the first curved portion is curving inwards from the first width section and wherein the second curved portion is curving outwards from the cover width section, thereby conforming to a transition portion of the at least one first metallic strip located between the first U-shaped part and the second U-shaped part of the at least one first metallic strip with a flattened S-shaped cross-section.

[0078] In an embodiment, the first width section of the cover metallic strip comprises a first straight portion located adjacent to the transition width section. Preferably, the first straight portion is located adjacent to the first curved portion of the transition width section.

[0079] Advantageously, at least a portion of the first straight portion is constrained between the first fold e.g. provided by the first inwards folded edge portion and the second fold e.g. provided by the second outwards folded edge portion. Preferably, at least the portion of the first straight portion is constrained in mutual interlocking between the first fold (e.g. the first inwards folded edge portion) and the second fold (e.g. the second outwards folded edge portion). This constraining of at least a portion of the first straight portion between the first fold and the second fold of the at least one first metallic strip ensures a strong and reliable anchoring of the cover metallic strip even where the carcass is subjected to relatively large bends, e.g. when the carcass forms part of a riser pipe. In an embodiment, the first width section of the cover metallic strip comprises a first straight portion, and the cover width section comprises a second straight portion, wherein the helically winding comprises winding the first straight portion with a diameter that is larger than the winding of the second straight portion and wherein the transition width section preferably extends between the first straight portion and the second straight portion.

[0080] In an embodiment, the first width section comprises a curved portion, preferably curving downwards from the first straight portion, preferably the first fold (e.g. the first inwards folded edge portion, comprises a U shaped curvature comprising an outer straight portion, an intermediate curved portion and an inner portion, wherein the curved portion of the first width section preferably is in at least partial interfacial contact with a surface of the intermediate curved portion of the first fold, such as of the first inwards folded edge portion. Preferably, the curved portion of the first width section is in full interfacial contact with a surface of the intermediate curved portion of the first fold, such as of the first inwards folded edge portion.

[0081] The inner portion of the first fold may in at least a first sub-portion thereof be in physical contact with the interlocked second fold. Conveniently, the inner portion of the first fold, in at least a second sub-portion thereof is shaped to form a waveshaped lip supporting and at least partially constraining a portion of the second fold, such as a portion of the second outwards folded edge portion, thereby further increasing the anchoring of the cover metallic strip to the basic structure of the carcass.

[0082] The first width section may preferably extend to cover at least a part of the waveshaped lip to provide that a portion of the first width section is located between the wave-shaped lip and the second fold.

[0083] The invention also comprises a flexible pipe for conveying a fluid. The flexible pipe is preferably of the unbonded type. The flexible pipe has a carcass axis and may preferably comprise from the inside and out: a carcass, an internal pressure sheath and at least one armor layer, wherein the carcass is as described above.

[0084] It should be understood that the flexible pipe may comprise additional layers e.g. one or more insulation layers, one or more restraining layers, one or more anti-wear layers and / or one or more intermediate sealing layers.

[0085] The invention also comprises a method of producing a carcass for a flexible pipe.

[0086] The carcass comprises a carcass axis and the method comprises the following: providing at least one first metallic strip and a cover metallic strip, wherein the cover metallic strip comprises a first width section, a transition width section and a cover width section, shaping the first strip to have a profile comprising a first fold facing towards the carcass axis and a second fold facing away from the carcass axis, helically winding the first metallic strip and the cover metallic strip to form a plurality of consecutive helical and interlocked windings of the first metallic strip, forming an inwards facing helicoidal interstice between the first fold and the second fold of the at least one first metallic strip and providing the first width section of the cover metallic strip in respective windings of the helically wound cover metallic strip extends into the helicoidal interstice and the cover width section in the respective helical windings thereof covers the inwards facing helicoidal interstice in adjacent windings, wherein the cover width section comprises at least one stiffening width portion, wherein the stiffening width portion has a thickness exceeding a thickness of at least one of the first width section and the transition width section.

[0087] The method conveniently comprises shaping the at least one first strip to have a profile with a first fold adapted to face towards the carcass axis and a second fold adapted to face away from the carcass axis. The cover metallic strip is preferably provided to have a length and a width. The method comprises inserting at least a portion of the first width section of the cover strip into the first fold, providing that the cover width section of the cover metallic strip extends beyond the second fold and helically winding the first metallic strip and the cover metallic strip, to provide that the first fold engages and interlocks with the second fold and that the cover width section covers the inwards facing helicoidal interstice in adjacent windings. The transition width section and / or the first width section may in an embodiment be subjected to a pre-treatment before insertion into the first fold e.g. as described in EP 4045830B1.

[0088] The method may advantageously be performed to produce a carcass as described above.

[0089] Advantageously, the stiffening width portion has an average thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section. The average thickness of the stiffening width portion may preferably be from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

[0090] In an embodiment, the stiffening width portion has a minimum thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section. The minimum thickness of the stiffening width portion may preferably be from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

[0091] In an embodiment, the stiffening width portion is in the form of a single-layer portion.

[0092] In an embodiment, the stiffening width portion comprises a multilayer portion, such as a multilayer portion, preferably comprising from two to 10 layers, such as up to 6 layers, such as 3, 4 or 5 layers.

[0093] Advantageously, the method comprises folding the cover width section to form the stiffening width portion to comprise a folded portion, such as the multilayer portion comprising at least one fold.

[0094] Preferably, the method comprises forming the stiffening width portion by folding the cover width section to have two or more folded sub-width sections folded against itself to be in interfacial contact. The stiffening width portion may conveniently comprise an edge portion of the first width section e.g. as described above and the method may comprise folding the edge portion back on itself in one or more folds.

[0095] In an embodiment, the stiffening width portion comprises an edge portion of the first width section folded back on itself in one or more folds comprising at least one fold in inward direction towards the carcass axis and / or one fold in outward direction away from the carcass axis.

[0096] The method may in an embodiment comprise providing the cover width section to extend laterally from the transition width section to cover the inwards facing helicoidal interstice between windings of the first metallic strip, preferably as described above.

[0097] The method may conveniently comprise providing the stiffening width portion to comprise at least one fold with an inner folding radius of about zero or of up to 5 times the average thickness of the cover width section in unfolded condition, preferably such as described above.

[0098] The method may conveniently comprise providing the stiffening width portion be as described above, such as to have the shape, location and or structure as described above.

[0099] BRIEF DESCRIPTIONS OF EMBODIMENTS AND EXAMPLES

[0100] In the following the invention will be further illustrated by the description of a number of illustrative and non-limiting embodiments and examples of the present invention, with reference to the appended drawings.

[0101] The figures are schematic and are not drawn to scale and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

[0102] Figure 1 shows a perspective view of an unbonded flexible pipe where the respective layers of the pipe are successively exposed.

[0103] Figure 2 shows an installation comprising a flexible pipe.

[0104] Figure 3 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises an inwards folded and relatively narrow stiffening width portion comprising a second edge of the cover metallic strip.

[0105] Figure 4 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises an inwards folded and relatively wide stiffening width portion comprising a second edge of the cover metallic strip.

[0106] Figure 5 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises an outward folded and relatively narrow stiffening width portion with a loop fold and comprising a second edge of the cover metallic strip.

[0107] Figure 6 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises an outwards folded and medium wide stiffening width portion comprising a second edge of the cover metallic strip.

[0108] Figure 7 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises an outwards folded and narrow stiffening width portion comprising a second edge of the cover metallic strip.

[0109] Figure 8 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises a stiffening width portion protruding into the helicoidal interstice and comprising a loop fold with a loop apex and a loop plane through the loop apex, wherein the loop plane is perpendicular to the carcass axis.

[0110] Figure 9 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises a stiffening width portion protruding into the helicoidal interstice and comprising a loop fold with an open loop apex and a loop plane through the open loop apex, wherein the loop plane is perpendicular to the carcass axis.

[0111] Figure 10 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises a stiffening width portion protruding into the helicoidal interstice and comprising a loop fold with a loop apex and a loop plane through the loop apex, wherein the loop plane angled relatively to the carcass axis with the loop apex leaning towards transition width section in the same winding.

[0112] Figure 11 shows a cross-sectional sideview of a length of a carcass of an embodiment of the invention where the carcass comprises a helically wound and interlocked first metallic strip forming a basic structure of the carcass and with a helically wound cover metallic strip and wherein the cover width section comprises a stiffening width portion protruding into the helicoidal interstice and comprising two folds providing three layers and where the cover width section has a first non-folded portion located between the transition width section and the stiffening width portion and a second non-folded portion located at an opposite side of the stiffening width portion and where wherein the second non-folded portion of the cover width section is parallel offset relative to the first non-folded portion of the cover width section, wherein the second non-folded portion of the cover width section is located closer to the carcass axis than the first non-folded portion of the cover width section.

[0113] Figure 1 shows an example of an unbonded flexible pipe 1 comprising a plurality of layers and having a longitudinal carcass axis X-X, which also forms an axis of the pipe. From the inside to the outer side the unbonded flexible pipe comprises a carcass 10 supporting a pressure sheath 11 and providing a resistance against collapse of the pressure sheath 11. The pressure sheath 11 surrounds and defines the bore of the pipe in which a fluid may be transported. A pressure armor layer 12 is provided to surround the pressure sheath to reinforce the pressure sheath 11 against expansion and burst when the pressure in the bore becomes relative high. To reinforce against tensile forces two tensile armor layers 13, 14 are applied to surround the pressure armor layer 12 and finally an outer sheath 15 is applied to protect the pipe against ingress of water and / or to protect the armor layers 12, 13, 14. The flexible pipe 1 may preferably be an unbonded flexible pipe according to an embodiment of the invention.

[0114] It should be noted that the flexible pipe may comprise additional layers, such as insulating layer(s), anti-wear layer(s) as well as additional armor layers and intermediate sealing layer(s).

[0115] The installation shown in figure 2 is an offshore installation and comprises a flexible pipe in the form of a riser pipe 21 comprising a first end fitting 23a and a second end fitting, wherein the first end fitting 23a is connected to a seabed installation 22 located at or partly in the seabed S. The seabed installation 22 provides an access to a not shown production well located below the seabed. The second end fitting 23b of the riser pipe 21 is connected to a sea surface installation here in the form of a vessel 24. The vessel 24 comprises a hang-off structure to which the second end fitting 23b of the riser pipe 21 is connected for supplying fluid, such as oil and / or gas from the production well to a not shown container located on board of the vessel 24. The riser pipe 21 may preferably be a flexible pipe according to an embodiment of the invention.

[0116] The carcass shown in figure 3, has a carcass axis X-X and comprises a first metallic strip 31 and a cover metallic strip 32 comprising a first width section 32a, a transition width section 32b and a cover width section 32c.

[0117] The first metallic strip 31 has a profile comprising a first fold 31a facing towards the carcass axis and a second fold 31b facing away from the carcass axis. The first metallic strip 31 is helically wound and interlocked and the profile structure comprises an inwards facing helicoidal interstice 33 between the first fold 31a and the second fold 31b in the windings of the first metallic strip 31. As explained above, the carcass may in variations of this embodiment comprise two or more first metallic strips.

[0118] The helically wound and interlocked first metallic strip 31 with the inwards facing helicoidal interstice 33 forms a basic structure of the carcass.

[0119] As can be seen in figure 3, the basic structure of the helically wound and interlocked first metallic strip 31 also comprises an outwards facing helicoidal interstice 34.

[0120] In a variation of the embodiment shown in figure 3, the carcass comprises a secondary cover metallic strip with a secondary cover width section arranged to cover the outwards facing helicoidal interstice 34 to reduce or even avoid creep of a not shown polymer pressure sheath extruded onto the carcass.

[0121] The cover metallic strip comprises a first edge 36a and a second edge 36b. The cover width section 32c of the cover metallic strip 32 comprises an inwards folded and relatively narrow stiffening width portion 35 with a width w and comprising the second edge 36b of the cover metallic strip 32. The second edge 36b of the cover metallic strip 32 is also referred to as a free edge of the cover width section 32c. The stiffening width portion 35 is here provided with a single fold having an inner folding radius of about zero. Thereby, a portion of the cover width section 32c in a winding and located between the transition width section 32b and the stiffening width portion 35 may be firmly held in direct and conforming contact with the second U- shape flat surface 3 lbl formed by the second fold 31b in the same winding and facing towards the carcass axis X-X, which ensures a reduction of the risk of undesired plastic deformations of the cover width section of the cover metallic strip. At the same time, the stiffening width portion 35 with the second edge 36b forming an edge portion of the cover width section 32c may be firmly held in conforming contact here via the cover width section 32c in an adjacent winding, with the second U-shape flat surface 3 lbl in an adjacent winding and formed by the second fold 31b facing towards the carcass axis X-X to thereby further reduce the risk of undesired plastic deformations of the cover width section of cover metallic strip.

[0122] Due to the stiffening width portion 35 of the cover width section 32c of the cover metallic strip 32, the cover metallic strip may have a relatively low thickness t, which reduces the cost and weight of the carcass while simultaneously ensures that the risk of formation of vibrations in use of a flexible pipe comprising the carcass may be reduced or even fully avoided.

[0123] The basic structure of the carcass formed by the helically wound and interlocked at least one first metallic strip 31 has a flattened S-shaped cross-section, with a first U- shaped part formed by the first fold 31a and a second U-shaped part formed by the second fold 31b, wherein the first U-shaped part has a first U-shape flat surface facing away from the carcass axis X-X and the second U-shaped part has a second U-shape flat surface facing towards the carcass axis X-X.

[0124] The carcass shown in figure 4 has a carcass axis X-X and comprises a helically wound and interlocked first metallic strip 31 forming a basic structure of the carcass having an inwards facing helicoidal interstice 33 between the first fold 31a and the second fold 31b in the windings of the first metallic strip 31. The basic structure of figure 4 is as the basic structure of figure 3.

[0125] The carcass comprises a cover metallic strip 42 comprising a first width section 42a, a transition width section 42b and a cover width section 42c. The cover width section 42c covers the inwards facing helicoidal interstice 33 and comprises an inwards folded and relatively wide stiffening width portion 45 comprising a second edge 46b of the cover metallic strip. The relatively wide stiffening width portion 45 ensures an even higher reduction of the risk of undesired plastic deformations of the cover width section 42c of the cover metallic strip relative to the relatively narrow stiffening width portion 35 of the embodiment of figure 3. However, at the same time the relatively wide stiffening width portion 45 requires use of more metal, which adds to the cost and to the weight of the carcass relative to the relatively narrow stiffening width portion 35 of the embodiment of figure 3. Based on these considerations, the skilled person may select a desired width of the stiffening width portion of the cover metallic strip for a given flexible pipe and its intended use.

[0126] As seen in figure 4, the cover width section 42c with the stiffening width portion 45 extends laterally with an angle relative to the carcass axis X-X, here about 3° to the carcass axis X-X. This is required because the stiffening width portion 45 comprises the inward fold (i.e. a fold towards the carcass axis X-X). In a variation thereof comprising two or more inward folds, the cover width section would extend laterally with a larger angle relative to the carcass axis X-X than the angle of the embodiment shown in figure 4. As seen in figure 4, the transition width section 42b of the cover metallic strip 42 is located between the first width section 42a and the cover width section 42c. The transition width section 42b extends into and is at least partly located in the helicoidal interstice 33 in full surface-to-surface contact with a surface of the first fold 31a. Thereby, the transition width 42b of the cover metallic strip 42 may at least partly provide an anchoring of the cover metallic strip 42 to the basic structure of the carcass.

[0127] The transition width section 42b comprises a first curved portion 42bl adjacent to the first width section 42c , and a second curved portion 42b2 adjacent to the cover width section 42c, wherein the first curved portion 42bl is curving inwards from the first width section 42a and wherein the second curved portion 42b2 is curving outwards from the cover width section 42c, thereby conforming to a transition portion 41c of the first metallic strip 31 located between the first U-shaped part and the second U-shaped part of the at least one first metallic strip with a flattened S- shaped cross-section.

[0128] The first width section 42a of the cover metallic strip 42 comprises a first straight portion 42a 1 located adjacent to the transition width section 42b.

[0129] A portion of the first straight portion 42al is constrained between the first fold 31a and the second fold 31b. This constraining of at least a portion of the first straight portion 42al between the first fold 31a and the second fold 31b of the at least one first metallic strip ensures a strong and reliable anchoring of the cover metallic strip 31.

[0130] The first width section of the cover metallic strip 42a comprises the first straight portion 42al and the cover width section 42c comprises a second straight portion 42cl, wherein the first straight portion 42al is wound with a diameter that is larger than the winding of the second straight portion 42cl.

[0131] The first width section 42a comprises a curved portion 42a2 curving downwards from the first straight portion 42al. The curved portion 42a2 of the first width section 42a is in interfacial contact with the surface of the intermediate curved portion 41al of the first fold 31a.

[0132] The inner portion 41a2 of the first fold 31a comprises a wave-shaped lip 41a2'. The first width section 42a extends to cover at least a part of the wave-shaped lip 41a2' to provide that a portion of the first width section 42ai s located between the waveshaped lip 41a2' and the second fold 31b, thereby further increasing the anchoring of the cover metallic strip 42 to the basic structure of the carcass.

[0133] The carcass shown in figure 5 differs from the carcass of figure 4 in that it comprises a cover width section 52c comprising an outwards folded and relatively narrow stiffening width portion 55 with a loop fold comprising a loop 55a and comprises the second edge of the cover metallic strip 56b. The loop fold of the stiffening width portion 55 has a relatively large folding radius, which may be desired where the cover width section 52c of the cover metallic strip 42 is of a metal with a relatively low ductility.

[0134] The carcass shown in figure 6 differs from the carcass of figure 4 in that it comprises a cover width section 62c comprising an outwards folded and medium wide stiffening width portion 65 comprising a second edge 66b. The medium wide stiffening width portion 65 is sufficient wide to cover the helicoidal interstice 33, but is no wider than up to 50% of the cover width section.

[0135] The carcass shown in figure 7 differs from the carcass of figure 4 in that it comprises a cover width section 72c comprising an outwards folded and narrow stiffening width portion 75 comprising a second edge 76b.

[0136] The carcass shown in figure 8 differs from the carcass of figure 4 in that it comprises a cover width section 82c comprising a stiffening width portion 85 protruding into the helicoidal interstice 33 and comprising a loop fold with a loop apex 85a and a loop plane L-L through the loop apex, wherein the loop plane is perpendicular to the carcass axis X-X.

[0137] The cover width section 82c has a first non-folded portion 82cl located between the transition width section 32b and the stiffening width portion 85 and a second nonfolded portion located 82c2 at an opposite side of the stiffening width portion 85, wherein the first non-folded portion 82c2 of the cover width section 82c is in interfacial contact with the first metallic strip 31 and the second non-folded portion 82c2 of the cover width section 82c is in interfacial contact with the first non-folded portion 82cl of the cover width section 82c in an adjacent winding.

[0138] The second non-folded portion 82c2 of the cover width section 82c is parallel offset relative to the first non-folded portion 82cl of the cover width section 82c, wherein the second non-folded portion 82c2 of the cover width section 82c is located closer to the carcass axis X-X than the first non-folded portion 82cl of the cover width section 82. Thereby, a very desired and firm interfacial contact between the second non-folded portion of the cover width section and the first non-folded portion of the cover width section in an adjacent winding may be obtained.

[0139] The carcass shown in figure 9 differs from the carcass of figure 8 in that the stiffening width portion 95 protruding into the helicoidal interstice 33 comprises an open loop fold with an open loop apex 95a. The open loop fold of the stiffening width portion 95 has a relatively large folding radius, and the layers of the open loop fold are not touching each other. The stiffening width portion 95 with an open loop folding radius is specifically beneficial where the cover strip is made of a material with a relative low ductility.

[0140] The carcass shown in figure 10 differs from the carcass of figure 8 in that the stiffening width portion 105 protruding into the helicoidal interstice 33 comprises a loop fold with a loop apex 105a and a loop plane L-L through the loop apex 105a, wherein the loop plane is angled with an angle o relatively to the carcass axis X-X and with the loop apex leaning towards the transition width section 32b of cover metallic strip 32 in the same winding.

[0141] The angle o between the loop apex 105 and the carcass axis X-X corresponds to a folding angle 105b of the stiffening width portion 105.

[0142] The carcass shown in figure 11 differs from the carcass of figure 10 in that the stiffening width portion 115 protruding into the helicoidal interstice 33 comprises two folds providing three layers.

[0143] The cover width section 112c has a first non-folded portion 112cl located between the transition width section and the stiffening width portion and a second non-folded portion 112c2 located at an opposite side of the stiffening width portion 115 and where wherein the second non-folded portion 112c2 of the cover width section 112c is parallel offset relative to the first non-folded portion 112cl of the cover width section 112c, wherein the second non-folded portion 112c2 of the cover width section 112c is located closer to the carcass axis than the first non-folded portion 112cl of the cover width section 112c.

Claims

1. CLAIMS1. A carcass suitably for a flexible pipe, the carcass has a carcass axis and comprises a profile structure comprising a plurality of consecutive helical windings of at least one first metallic strip, wherein the at least one first metallic strip has a profile comprising a first fold facing towards said carcass axis and a second fold facing away from said carcass axis and wherein said first and said second fold of said first metallic strip being interlocked and wherein the profile structure comprises inwards facing helicoidal interstice between said first fold and said second fold of said at least one first metallic strip in the windings of said least one first metallic strip wherein said profile structure comprises a helically wound cover metallic strip, the cover metallic strip comprises a first width section, a transition width section and a cover width section, wherein the first width section in respective windings of the helically wound cover metallic strip extends into the helicoidal interstice and the cover width section in said respective helical windings thereof at least partially cover the inwards facing helicoidal interstice in adjacent windings and wherein said cover width section comprises at least one stiffening width portion, wherein said stiffening width portion has a thickness of at least one of the first width section and the transition width section.

2. The carcass of claim 1, wherein the stiffening width portion has an average thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section, such as an average thickness of from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

3. The carcass of claim 1 or claim 2, wherein the stiffening width portion has a minimum thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section, such as a minimum thickness of from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

4. The carcass of any one of the preceding claims, wherein the cover metallic strip has an average thickness which is less than an average thickness of the at least one first metallic strip, preferably the thickness of the cover metallic strip has an average thickness of up to 50%, such as up to 25% of the average thickness of the at least one first metallic strip, preferably the at least one first metallic strip has same thickness in its entire width when in un-folded condition.

5. The carcass of any one of the preceding claims, wherein the stiffening width portion is in the form of a single layer portion.

6. The carcass of any one of the preceding claims, wherein the stiffening width portion comprises a multilayer portion, such as a multilayer portion, preferably comprising from 2 to 10 layers, such as up to 6 layers, such as 3, 4 or 5 layers.

7. The carcass of any one of the preceding claims, wherein the stiffening width portion comprises a folded portion of said cover width section comprising at least one fold, wherein the stiffening width portion has two or more folded sub width sections of said cover width section folded against itself to be in interfacial contact.

8. The method of any one of the preceding claims, wherein the stiffening width portion comprises an edge portion of the cover width section folded back on itself in one or more folds, preferably the stiffening width portion comprises a free edge of the cover width section.

9. The method of any one of the preceding claims, wherein the stiffening width portion comprises an edge portion of the cover width section folded back on itself in one or more folds comprising at least one fold in inward direction and / or one fold in outward direction.

10. The carcass of any one of the preceding claims, wherein the cover width section extends laterally from the transition width section to cover said inwards facing helicoidal interstice between windings of the at least one first metallic strip.

11. The method of any one of the preceding claims, wherein the stiffening width portion comprises at least one fold, preferably the at least one fold has an inner folding radius of about zero or of up to 5 times the average thickness of the cover width section in unfolded condition, such as an inner folding radius of at least0.1 the average thickness of the cover width section in unfolded condition, such as at least 0.5 times the average thickness of the cover width section in unfolded condition, such as from 0.7 to 3 times the average thickness of the cover width section in unfolded condition, such as from 1 to 2 times the average thickness of the cover width section in unfolded condition.

12. The carcass of any one of the preceding claims, wherein the stiffening width portion extends laterally, preferably from parallel with up to an angle of 25 degrees to the axis of the carcass, such as up to an angle of 15 degrees to the axis of the carcass, such as up to an angle of 10 degrees to the axis of the carcass, such as up to an angle of 5 degrees to the axis of the carcass, such as up to an angle of 2 degrees to the axis of the carcass.

13. The carcass of any one of the preceding claims, wherein the stiffening width portion is located adjacent to a free edge of said cover width section or up to a distance of from 1% to 100% minus the width of the stiffening width portion, such as up to 90% of the width of the cover width section, such as up to a distance of from 25% to 75% of the width of the cover width section.

14. The carcass of any one of the preceding claims, wherein the stiffening width portion is at least partially located at said inwards facing helicoidal interstice, preferably said stiffening width portion is at least partially extending into said inwards facing helicoidal interstice.

15. The carcass of claim 14, wherein the stiffening width portion comprises 3 layers formed by folds of said cover width section, preferably said 3 layers comprises at least a flat sub portion which is preferably parallel with at least a nonfolded portion of the cover width section, such as parallel with and in same plane as at least a non-folded portion of the cover width section.

16. The carcass of claim 14, wherein the stiffening width portion comprises at least one fold and wherein the stiffening width portion protrudes into the inwards facing helicoidal interstice, wherein the at least one fold preferably comprises a loop fold with a loop apex and a loop plane through said loop apex, wherein said loop plane is perpendicular to the carcass axis or has an angle perpendicular to said carcass axis of up to 60 degrees, such as up to 45 degrees, such as up to 30 degrees.

17. The carcass of any one of claims 14-16, wherein said cover width section has a first non-folded portion located between said transition width section and said stiffening width portion and a second non-folded portion located at an opposite side of the stiffening width portion, wherein the first non-folded portion of the cover width section is in interfacial contact with said at least one first metallic strip and said second non-folded portion of the cover width section is in interfacial contact with said first non-folded portion of the cover width section in an adjacent winding.

18. The carcass of any one of claims 13-17, wherein said cover width section has a first non-folded portion located between said transition width section and said stiffening width portion and a second non-folded portion located at an opposite side of the stiffening width portion, wherein the second non-folded portion of the cover width section is parallel offset relative to said first non-folded portion of the cover width section, wherein the second non-folded portion of the cover width section is located closer to the carcass axis than the first non-folded portion of the cover width section.

19. The carcass of any one of the preceding claims, wherein the stiffening width portion is located to fully cover said inwards facing helicoidal interstice between said first fold and said second fold of said first metallic strip in the windings of said least one first metallic strip.

20. The carcass of any one of the preceding claims, wherein the stiffening width portion has a width of at least 1% of the width of the at least one first metallic strip in unfolded condition, such as at least 5% of the width of the least one first metallic strip in unfolded condition, such as from 8% to 50% of the width of the at least one first metallic strip in unfolded condition, such as from 15% to 30% of the width of the least one first metallic strip in unfolded condition.

21. The carcass of any one of the preceding claims, wherein the stiffening width portion has a width of at least 2% of the width of the cover width section in unfolded condition, such as at least 8% of the width of the cover width section in unfolded condition, such as from 10% to 100% of the width of the cover width section in unfolded condition, such as from 15% to 50% of the width of the cover width section in unfolded condition.

22. The carcass of any one of the preceding claims, wherein the first fold of said at least one first metallic strip comprises a first inwards folded edge portion and the second fold of said at least one first metallic strip comprises a second outwards folded edge portion, wherein the interlocking between said first fold and said second fold of said first metallic strip comprises that said first inwards folded edge portion in said plurality of consecutive windings is interlocked with said second outwards folded edge portion in respective adjacent windings allowing adjacent windings to move laterally relative to each other and forming the inwards facing helicoidal interstice between the first inwards folded edge portion and the second outwards folded edge portion.

23. The carcass of any one of the preceding claims, wherein the transition width section of the cover metallic strip is located between said first width section and said cover width section, preferably said transition width section extends from said first width section and to said second cover width section.

24. The carcass of any one of the preceding claims, wherein the transition width section extends into the helicoidal interstice of the cover metallic strip in surface contact with a surface of the first fold, preferably the transition width section is in full surface-to-surface contact with the surface of the first fold.

25. The carcass of any one of the preceding claims, wherein the transition width section forms a transition between a first winding diameter of the cover metallic strip and a second diameter of the cover metallic strip, wherein the second diameter is larger than the first diameter and wherein the cover metallic strip has the first diameter at the border between said transition width section and said cover width section.

26. The carcass of any one of the preceding claims, wherein said transition width section comprises at least one curved portion, preferably the transition width section comprises a first curved portion adjacent to the first width section, and a second curved portion adjacent to the cover width section, wherein the first curved portion is curving inwards from the first width section and wherein the second curved portion is curving outwards from the cover width section.

27. The carcass of any one of the preceding claims, wherein the first width section of the cover width section comprises a first straight portion located adjacentto said transition width section, preferably said first straight portion is located adjacent to said first curved portion of said transition width section.

28. The carcass of any one of the preceding claims, wherein the first width section of the cover width section comprises a first straight portion, preferably at least a portion of said first straight portion is constrained between said first fold and said second fold, preferably at least said portion of said first straight portion is constrained in mutual interlocking between said first fold and said second fold.

29. The carcass of any one of the preceding claims, wherein the first width section of the cover metallic strip comprises a first straight portion and the cover width section comprises a second straight portion, wherein the helically winding comprises winding the first straight portion with a diameter that is larger than the winding of the second straight portion and wherein the transition width section preferably extends between said first straight portion and said second straight portion.

30. The carcass of any one of the preceding claims, wherein the first width section comprises a curved portion, preferably curving downwards from said first straight portion, preferably said first fold comprises a U shaped curvature comprising an outer straight portion, an intermediate curved portion and an inner portion, wherein the curved portion of the first width section preferably is in at least partial interfacial contact with a surface of said intermediate curved portion of said first fold, preferably said curved portion of the first width section is in full interfacial contact with a surface of said intermediate curved portion of said first fold.

31. The carcass of claim 30, wherein the inner portion of said first fold in at least a first sub-portion thereof is in physical contact with the interlocked second fold, preferably said inner portion of said first fold in at least a second sub-portion thereof is shaped to form a wave-shaped lip supporting and at least partially constraining a portion of said second fold.

32. The carcass of claim 31, wherein the first width section extends to cover at least a part of said wave-shaped lip, providing that a portion of said first width section is located between said wave-shaped lip and said second fold.

33. A flexible pipe for conveying a fluid, said pipe comprising a carcass axis along the length of the pipe and from the inside and out:a carcass, an internal pressure sheath and at least one armor layer, wherein said carcass is according to any one of the preceding claims.

34. A method of producing a carcass for a flexible pipe, wherein the carcass comprises a carcass axis and the method comprises providing at least one first metallic strip and a cover metallic strip, wherein the cover metallic strip comprises a first width section, a transition width section and a cover width section, shaping said at least one first metallic strip to have a profile comprising a first fold facing towards said carcass axis and a second fold facing away from said carcass axis, helically winding said at least one first metallic strip and said cover metallic strip to form a plurality of consecutive helical and interlocked windings of said at least one first metallic strip, forming an inwards facing helicoidal interstice between the first fold and the second fold of said at least one first metallic strip and providing the first width section of the cover metallic strip in respective windings of the helically wound cover metallic strip extends into the helicoidal interstice and the cover width section in said respective helical windings thereof covers the inwards facing helicoidal interstice in adjacent windings, wherein the cover width section comprises at least one stiffening width portion, wherein said stiffening width portion has a thickness exceeding a thickness of at least one of the first width section and the transition width section.

35. A method of producing a carcass for a flexible pipe the method comprising providing at least one first metallic strip and shaping said at least one first metallic strip to have a profile with a first fold adapted to face towards said carcass axis and a second fold adapted to face away from said carcass axis, providing a cover metallic strip with a length and a width and inserting at least a portion of the first width section of the cover strip into the first fold, providing that the cover width section of said cover strip extends beyond said second fold andhelically winding said at least one first metallic strip and said cover strip, to provide that said at least one first fold engages and interlocks with said second fold and that said cover width section covers the inwards facing helicoidal interstice in adjacent windings.

36. The method of claim 35, wherein the method comprises producing a carcass according to any one of claims 1-32.

37. The method of claim 35 or claim 36, wherein the stiffening width portion has an average thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section, such as an average thickness of from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

38. The method of any one of claims 35-37, wherein the stiffening width portion has a minimum thickness of at least 110% of the average thickness of at least one of the first width section and the transition width section, such as a minimum thickness of from 120% to 400% of the average thickness of at least one of the first width section and the transition width section, such as from 130% to 200% of the average thickness of at least one of the first width section and the transition width section.

39. The method of any one of claims 35-38, wherein the stiffening width portion is in the form of a single layer portion.

40. The method of any one of claims 35-38, wherein the stiffening width portion comprises a multilayer portion, such as a multilayer portion, preferably comprising from two to 10 layers, such as up to 6 layers, such as 3, 4 or 5 layers.

41. The method of any one of claims 35-40, wherein the method comprises folding said cover width section to form said stiffening width portion to comprise a folded portion comprising at least one fold, wherein the method preferably comprises forming said stiffening width portion by folding said cover width section to have two or more width sections folded against itself to be in interfacial contact.

42. The method of any one of claims 35-41, wherein the stiffening width portion comprises an edge portion of the first width section and the method comprises folding said edge portion back on itself in one or more folds, preferably the stiffening width portion comprises a free edge of the cover width section.

43. The method of any one of claims 35-42, wherein the stiffening width portion comprises an edge portion of the first width section folded back on itself in one or more folds comprising at least one fold in inward direction and / or one fold in outward direction.

44. The method of any one of claims 35-43, wherein the method comprises providing said cover width section to extend laterally from the transition width section to cover said inwards facing helicoidal interstice between windings of the first metallic strip.

45. The method of any one of claims 35-44, wherein the method comprises providing said stiffening width portion to comprise at least one fold with an inner folding radius of about zero or of up to 5 times the average thickness of the cover width section in unfolded condition, such as an inner folding radius of at least 0.1 the average thickness of the cover width section in unfolded condition, such as at least 0.5 times the average thickness of the cover width section in unfolded condition, such as from 0.7 to 3 times the average thickness of the cover width section in unfolded condition, such as from 1 to 2 times the average thickness of the cover width section in unfolded condition.

46. The method of any one of claims 35-45, wherein the method comprises providing said stiffening width portion to extend laterally, preferably from parallel width to up to an angle of 25 degrees to the axis of the carcass, such as up to an angle of 15 degrees to the axis of the carcass, such as up to an angle of 10 degrees to the axis of the carcass, such as up to an angle of 5 degrees to the axis of the carcass.

47. The method of any one of claims 35-46, wherein the method comprises providing the stiffening width portion to be adjacent to a free edge of said cover width section or up to a distance of from 1% to 100% minus the width of the stiffening width portion, such as up to 90% of the width of the cover width section,such as up to a distance of from 25% to 75% of the width of the cover width section.

48. The method of any one of claims 35-47, wherein the method comprises providing the stiffening width portion to be at least partially located at said inwards facing helicoidal interstice, preferably said stiffening width portion is at least partially extending into said inwards facing helicoidal interstice.

49. The method of claim 48, wherein the method comprises providing the stiffening width portion to comprise 3 layers formed by folds of said cover width section, preferably said 3 layers comprises at least a flat sub portion which is preferably parallel with at least a non-folded portion of the cover width section, such as parallel with and in same plane as at least a non-folded portion of the cover width section.

50. The method of claim 48, wherein the method comprises providing the stiffening width portion to comprise at least one fold and wherein the stiffening width portion protrudes into the inwards facing helicoidal interstice, wherein the at least one fold preferably comprises a loop fold with a loop apex and a loop plane through said loop apex, wherein said loop plane is perpendicular to the carcass axis or has an angle to said carcass axis of up to 60 degrees, such as up to 45 degrees, such as up to 30 degrees.

51. The method of any one of claims 48-50, wherein the method comprises providing said cover width section to have a first non-folded portion located between said transition width section and said stiffening width portion and a second nonfolded portion located at an opposite side of the stiffening width portion, wherein the first non-folded portion of the cover width section is in interfacial contact with said at least one first metallic strip and said second non-folded portion of the cover width section is in interfacial contact with said first non-folded portion of the cover width section in an adjacent winding.

52. The method of any one of claims 48-51, wherein the method comprises providing said cover width section to have a first non-folded portion located between said transition width section and said stiffening width portion and a second nonfolded portion located at an opposite side of the stiffening width portion, wherein the second non-folded portion of the cover width section is parallel offset relative to saidfirst non-folded portion of the cover width section, wherein the second non-folded portion of the cover width section is located closer to the carcass axis than the first non-folded portion of the cover width section.

53. The method of any one of claims 35-52, wherein the method comprises providing the stiffening width portion to be located to fully cover said inwards facing helicoidal interstice between said first fold and said second fold of said first metallic strip in the windings of said least one first metallic strip.

54. The method of any one of claims 35-53, wherein the method comprises providing the stiffening width portion to have a width of at least 1% of the width of the at least one first metallic strip in unfolded condition, such as at least 5% of the width of the least one first metallic strip in unfolded condition, such as from 8% to 50% of the width of the least one first metallic strip in unfolded condition, such as from 15% to 30% of the width of the least one first metallic strip in unfolded condition.

55. The method of any one of claims 35-54, wherein the method comprises providing the stiffening width portion to have a width of at least 3% of the width of the cover width section in unfolded condition, such as at least 8% of the width of the cover width section in unfolded condition, such as from 10% to 100% of the width of the cover width section in unfolded condition, such as from 15% to 50% of the width of the cover width section in unfolded condition.

56. The method of any one of claims 35-55, wherein the method comprises providing the first fold of said at least one first metallic strip to comprise a first fold and the second fold of said at least one first metallic strip comprises a second fold, wherein the interlocking between said first fold and said second fold of said at least one first metallic strip comprises that said first fold in said plurality of consecutive windings is interlocked with said second fold in respective adjacent windings allowing adjacent windings to move laterally relative to each other and forming an inwards facing helicoidal interstice between the first inwards folded edge portion and the second fold.

57. The method of any one of claims 35-56, wherein the method comprises providing the transition width section of the cover metallic strip to be located between said first width section and said cover width section, preferably saidtransition width section extends from said first width section and to said second cover width section.

58. The method of any one of claims 35-57, wherein the method comprises providing the transition width section to extend into the helicoidal interstice of the cover metallic strip in surface contact with a surface of the first inwards folded edge portion, preferably the transition width section is in full surface-to-surface contact with the surface of the first fold.

59. The method of any one of claims 35-58, wherein the method comprises providing the transition width section to form a transition between a first winding diameter of the cover metallic strip and a second diameter of the cover metallic strip, wherein the second diameter is larger than the first diameter and wherein the cover metallic strip has the first diameter at the border between said transition width section and said cover width section.

60. The method of any one of claims 35-59, wherein the method comprises providing said transition width section to comprise at least one curved portion, preferably the method comprises providing the transition width section to comprise a first curved portion adjacent to the first width section, and a second curved portion adjacent to the cover width section, wherein the first curved portion is curving inwards from the first width section and wherein the second curved portion is curving outwards from the cover width section.

61. The method of any one of claims 35-60, wherein the method comprises providing the first width section of the cover width section to comprise a first straight portion located adjacent to said transition width section, preferably the method comprises providing said first straight portion to be located adjacent to said first curved portion of said transition width section.

62. The method of any one of claims 35-61, wherein the method comprises providing the first width section of the cover width section to comprise a first straight portion, preferably the method comprises providing at least a sub-portion of said first straight portion to be constrained between said first fold and said second fold, preferably the method comprises providing at least said sub-portion of said first straight portion to be constrained in mutual interlocking between said first fold and said second fold.

63. The method of any one of claims 35-62, wherein the method comprises providing the first width section of the cover metallic strip to comprise a first straight portion and the cover width section to comprise a second straight portion, wherein the providing of the helically winding comprises winding the first straight portion with a diameter that is larger than the winding of the second straight portion and wherein the transition width section preferably extends between said first straight portion and said second straight portion.

64. The method of any one of claims 35-63, wherein the method comprises providing the first width section to comprise a curved portion, preferably curving downwards from said first straight portion, preferably the method comprises providing said first fold to comprise a U shaped curvature comprising an outer straight portion, an intermediate curved portion and an inner portion, wherein the curved portion of the first width section preferably is in at least partial interfacial contact with a surface of said intermediate curved portion of said first fold, preferably said curved portion of the first width section preferably is in full interfacial contact with a surface of said intermediate curved portion of said first fold.

65. The method of any one of claims 35-64, wherein the method comprises providing the inner portion of said first fold in at least a first sub-portion thereof to be in physical contact with the interlocked second fold, preferably the method comprises providing said inner portion of said first fold in at least a second subportion thereof to be shaped to form a wave-shaped lip supporting and at least partially constraining a portion of said second fold.

66. The method of any one of claims 35-65, wherein the method comprises providing first width section to extend to cover at least a part of said wave-shaped lip, to provide that a portion of said first width section is located between said waveshaped lip and said second fold.

67. The method of any one of claims 35-66, wherein the helically winding comprises inserting said first width section of said cover strip into said first fold, providing that said cover width section of said cover strip extends beyond said second fold and provide said first fold to engage and interlocks with said second fold in adjacent windings and providing said cover width section to cover said inwards facing helicoidal interstice between windings of the first metallic strip.

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