TECHNICAL FIELD

The invention relates to a method of producing a curved composite reinforcement element and in particular a curved, elongate fibre reinforced polymer element. The invention also relates to a method of producing a flexible pipe with such

reinforcement element, and the flexible pipe.

BACKGROUND ART

Fibre reinforced composites are well known in the art. Fibre reinforced composites are produced from thermoplastic polymers as well as from thermosetting polymers, which are reinforced with fibres. Fibre reinforced composites have among other things been used as reinforcement elements in pipe structures. When used as a reinforcement element the fibre reinforced composites are often in the form of strips reinforced with longitudinally oriented fibres. Such fibre reinforced

composites are usually produced by a pultrution method e.g. as described in US 6,872,343. The method disclosed in US 6,872,343 comprises preparing a

continuous fiber- reinforced thermoplastic composite article by drawing a fibre bundle continuously through a melt of a thermoplastic resin, such that the bundle of fibres is fully impregnated. The impregnated fibre is drawn through a

consolidation die, where the element is shaped, where after it is cooled.

US 6,106,944 discloses a similar method of producing a structural member with an exterior fibre- reinforced structural layer formed of a thermoplastic profile, which may be thermo-shaped by pultrusion. EP 1 559 939 describes a composite tubular assembly formed by a core or tube which is reinforced by a multitape product which is wrapped in alternate non- bonded helical wraps on the core or tube. In order to obtain tapes with a desired strength, each tape is first formed by impregnating a fibrous strip with a

thermosetting resin and then such tapes are fed from spools to the core of the tube. Each tape is composed of a plurality of superimposed thin tape strips formed of predominantly, unidirectional fibers, which are impregnated with an epoxy or another suitable bonding resin. The multi-layer tapes are wrapped with a

polyethylene or similar plastic or thin metallic strip or covered by thermoplastic extrusion to confine them as a unit together, such that the bonding adhesive between the tape strips is prevented from escaping from the wrap. After the tape has been applied on the tubular core, the bonding resin may be cured. Generally reinforcement elements of thermoplastic material are in many situations not very suitable for use in reinforcing flexible unbonded pipes, such pipes usually comprise a number of reinforcement layers which are not bonded to each other, and accordingly the requirement to the strength of the individual elements of the reinforcement layers are relatively high, also in consideration of the fact that such unbonded pipe normally are required to operate at high and varying pressure and temperatures.

Flexible unbonded pipes of the present type for offshore transportation of fluids are well known in the art. Such pipes usually comprise an inner liner also often called an inner sealing sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed through the pipe, and one or more

armouring layers on the outer side of the inner liner (outer armouring layer(s)). An outer sealing sheath may be provided with the object of forming a barrier against the ingress of fluids from the pipe surroundings to the armour layers.

Typical unbonded flexible pipes are e.g. disclosed in WO0161232A1, US 6123114 and US 6085799.

The term "unbonded" means in this text that at least two of the layers including the armouring layers and polymer layers are not bonded to each other. In practice the known pipe normally comprises at least two armouring layers located outside the inner sealing sheath. These armouring layers are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.

WO 02/095281 discloses a method of manufacturing a reinforcement element for use in the manufacture of reinforcement layers for flexible pipes. The

reinforcement element comprises a plurality of relatively thin strength imparting cured layers fixed to each other by intermediate layers of thermoplastic material. Immediately after the strength imparting layers have been fused with the thermoplastic material, the reinforcement element is applied onto the flexible pipe. The thermoplastic material will be in a molten state, which makes it possible to bend and shape the reinforcement element to the desired curvature with substantially no mechanical stress.

DISCLOSURE OF INVENTION

The object of the invention is to provide a novel fibre reinforced element which has a high residual strength in particular when wound on a flexible pipe and is simultaneously relatively simple to produce and to apply in the production of an unbonded flexible pipe.

This object has been achieved by the invention as defined in the claims and as described hereinafter. The invention and embodiments thereof have several additional beneficial properties which are explained in the following description.

The inventor of the present invention has found that by producing a curved at least partly cured fibre reinforced element, i.e. at least partly cured prior to its use, the curved at least partly cured, elongate fibre reinforced polymer element can be applied in the production of the flexible pipe, without causing any substantial tension and stress in the reinforcement element due to winding around the pipe. In an attempt to use strips of a fibre reinforced element in the production of a flexible unbonded pipe comprising helical winding of the fibre reinforced element around the pipe, it was found that the fibre reinforced element was subjected to a curvature tension and torsion tension which put the fibre reinforced element in a state of stress which eventually reduced the strength of the fibre reinforced element. For thin strips of a fibre reinforced element it was observed that the resulting tension could be reduced at least to some degree.

It was found that when using cured, elongate fibre reinforced polymer where the elongate fibre reinforced polymer was shaped to have a curved shape prior to curing and where the curved and cured, elongate fibre reinforced polymer element was helically wound around the pipe, the resulting tension were substantially reduced and accordingly the stress was likewise reduced resulting in a high strength of the fibre reinforced element and of the whole reinforcement of the unbonded flexible pipe. Until the present invention, curved, cured, elongate fibre reinforced polymer elements have not been provided. Accordingly the invention comprises a method of producing a curved, cured, elongate fibre reinforced polymer element. The method of producing a curved, cured, elongate fibre reinforced polymer element comprises

(i) providing a mouldable, curable impregnation substance; providing a fibre bundle impregnating the fibre bundle with the mouldable, curable impregnation substance; shaping the impregnated fibre bundle to a curved elongate element;

(v) activating the impregnation substance of the curved elongate

element to at least partly cure the impregnation substance; and (vi) winding the at least partly cured curved, elongated, fibre reinforced polymer element onto a bobbin, such that the curvatures it comprises on the bobbin have diameters in the interval of from about 80 % less than to about 80 % larger that an un-tensioned diameter of the at least partly cured curved, elongated, fibre reinforced polymer element.

The term "curable impregnation substance" is used to designate any substances which upon curing form a thermoset polymer. The curable impregnation substance is preferably a composition of two or more components, but can also be a one component substance. In other words, the mouldable, curable impregnation substance can comprise one or more polymers and/or one or more monomers for a polymer. The term "thermoset polymer" means herein all polymers that comprise a cross-linked network comprising chemical bonds that cannot be reversibly heated to its original mouldable state. When heating a thermoset material, it will maintain its shape until the temperature reaches the maximum temperature for the thermoset material and the thermoset material will start to decompose in a nonreversible way.

The term "cure" or "curing" means "partly or fully cure" respectively "partly or fully curing". The term "mouldable, curable impregnation substance" means that the curable impregnation substance can be sufficiently mouldable for use for impregnating the fibre bundle.

The winding of the at least partly cured curved, elongated, fibre reinforced polymer element onto a bobbin, may preferably be such that the curvatures it comprises on the bobbin have diameters in the interval of from about 20 % less than to about 20 % larger that an un-tensioned diameter of the at least partly cured curved, elongated, fibre reinforced polymer element. A thermosetting resin precursor means herein a precursor for a thermoset polymer (resin), which precursor is not a thermoplastic polymer. The thermosetting resin precursor can be a one-component precursor or it may comprise two, three or more components. In one embodiment the mouldable, curable impregnation substance comprises a thermosetting resin precursor capable of curing to form a thermoset polymer. The thermosetting resin precursor(s) are preferably selected from resin precursor(s) for epoxy polymer(s), vinyl-epoxy-ester polymer(s), polyester polymer(s), polyimide polymer(s), bis-maleimide polymer(s), cyanate ester polymer(s), vinyl polymer(s), benzoxazine polymer(s), benzocyclobutene polymer(s), or mixtures of resin precursors for thermoset polymers comprising at least one of the foregoing thermoset polymers.

The resin precursors are also called epoxy resins, vinyl-epoxy-ester resins, polyester resins, polyimide resins, bis-maleimide resins, cyanate ester resins, vinyl resins, benzoxazine resins and benzocyclobutene resins.

Thermosetting resin precursors are usually liquids or low melting point solids in their initial form. Usually, thermosetting resin precursors can be cured by the use of a curing agent (also referred to as "hardener" or " catalyst") and activation

(provided for example by heat) or a combination of the two. Once cured, the solid thermoset polymers cannot be converted back to their original liquid form. Unlike thermoplastic polymers, cured thermosetting resin precursors will not melt and flow but they may soften slightly when heated. However, they cannot be reshaped.

In one embodiment, the mouldable, curable impregnation substance comprises or consists essentially of epoxy resin (resin precursor for epoxy polymer) and optionally hardener as described below. Epoxy resins are widely used in a wide range of composite parts and structures. Epoxy resins have a relatively low shrinkage and the cured products have good resistance to corrosive components and good mechanical properties as well as good performance at elevated temperatures.

Usually, epoxy polymers are produced from a 2-part system comprising an epoxy resin, such as one or more epoxide components and a hardener (curing agent). The epoxide component consists of monomers or short chain polymers with one or more epoxide groups, e.g. one at either of its ends. The hardener may for example be one or more polyamine monomers, such as Triethylenetetramine (TETA). When these compounds are mixed together, the amine groups react with the epoxide groups to form a covalent bond. Each NH group can react with an epoxide group, so that the resulting polymer is heavily cross linked and thus rigid and strong.

The curing can usually be controlled through temperature and choice of resin and hardener compounds. The curing may take minutes to hours. Some formulations benefit from heating during the cure period, whereas others simply require time, and ambient temperatures. In the latter case the impregnation substance can be held at a low temperature during the impregnation to avoid a too early curing of the curable impregnation substance.

The epoxy resin may for example be a Bisphenol A Epoxy Resin D.E.R.™ 336, A/F Bisphenol F Epoxy Resin Resin D.E.R.™ 356 or a modified Bisphenol A Epoxy Resin D.E.R.™ 329 all provided by Dow Epoxy. In one embodiment the mouldable, curable impregnation substance comprises or consists essentially of one or more bisphenol epoxy resins and a one or more curing agents. The active molecules of the curing agent(s) may contain, di, tri or tetra functional groups or a mixture hereof.

In one embodiment the mouldable, curable impregnation substance comprises or consists essentially of a precursor for a vinyl-epoxy-ester polymer (vinyl-epoxy ester resin). Vinyl-epoxy-ester polymers are usually produced by reacting epoxide with acrylic or methacrylic acid. The reaction may be activated using organic peroxides. Vinyl-epoxy-ester polymers have usually high mechanical toughness and excellent corrosion resistance.

In one embodiment, the mouldable, curable impregnation substance comprises a resin a curing agent and a thermoplastic polymer to enhance the toughness of the mouldable, curable impregnation substance. Upon curing the thermoplastic polymer may bond to the network of the thermoset polymer or it may be as a filler in the thermoset polymer.

In one embodiment, the mouldable, curable impregnation substance comprises a thermoplastic polymer. In this embodiment the thermoplastic polymer should preferably be capable of cross-linking to cure to a state where it is no longer thermoplastic, but instead has become a thermoset polymer. Usually the

thermoplastic polymer will cure by a curing agent (cross-linking agent) and/or activation e.g. by heat, irradiation, moisture or other.

In one embodiment the thermoplastic polymer is cross-linkable by one or more of peroxide, electromagnetic radiation, hydrolyse and/or grafted silane (or for grafting silane).

In one embodiment the thermoplastic polymer is cross-linkable by peroxide which is activated by heat.

In one embodiment the thermoplastic polymer is cross-linkable by peroxide which is activated by electromagnetic waves, such as Infrared radiation.

In one embodiment the thermoplastic polymer is cross-linkable by electromagnetic waves, such a UV light.

In one embodiment the thermoplastic polymer is cross-linkable by hydrolyse.

In one embodiment the thermoplastic polymer is cross-linkable by grafting silane containing components e.g. using peroxide activated by heat/radiation where after the grafted thermoplastic polymer is subjected to hydrolyse. In one embodiment the mouldable, curable impregnation substance comprises a curing agent. The terms "curing agent" and "cross-linking agent" are used interchangeably. The curing agent can be a hardener (the term usually used when the precursor is a resin). The curing agent acts as a catalyst for the cross-linking reaction and will in many situations not be used. This means that small amounts of curing agent can often cure much larger amounts of thermosetting resin precursor or thermoplastic polymer. By increasing the amount of curing agent, the reaction time can usually be accelerated. Some curing agents will be used during the cross- linking process e.g. as water will be used during a hydrolyse process. In this situation the amount of curing agent can have a large influence on the final degree of curing (cross-linking degree).

In one embodiment the curing agent is selected from sulphur, Phenolic curing agents, Aliphatic Hardeners, amine and polyamine curing agents, peroxides, silanes and mixtures comprising at least one of the foregoing. The mouldable, curable impregnation substance may further comprise additives such as fillers and extenders. The amount of additives is selected in consideration of among other things cost (in some situations a large amount of relatively cheap additives can reduce cost), strength (too much additive can reduce cohesiveness and thereby strength) and other properties relating to the specific additive. The main weight part of the additive will often be fillers and extenders with the primary function of reducing cost. Other types of additives are for example pigments, plasticizers, UV stabillisators and/or absorbers, heat stabilisers, process stabilisers, metal deactivators, antioxidants, marine antifouling agents, microbiocides , algicides, dehydrators, thixotropic agents, wetting agents and fire retardants. In one embodiment the mouldable, curable impregnation substance comprises up to about 30 % by weight of additives, such as up to about 25 %, by weight of additives, such as up to about 20 %, by weight of additives such as up to about 15 %, by weight of additives such as up to about 10 %, by weight of additives, the weight % is of the mouldable, curable impregnation substance prior to curing. The term "additive" includes any component except curing agents and components that will be part of or be bonded to the network of the cured impregnation substance.

Examples of additives are monomers and polymers that are not a part of the curable network, carbon black, glass particles, glass fibres, mineral fibres, talcum, carbon, carbonates, silicates, metal particles and/or metal containing components, such as copper and/or copper containing components, clay silicates such as clay silicate selected from kaolinite, such as dickite, halloysite, nacrite and serpentine; smectite, such as pyrophyllite, talc, vermiculite, sauconite, saponite, nontronite hectorites (magnesiosilicates) and montmorillonite (bentonite); Illite; chlorite; and synthetic clays, such as hydrotalcite.

The term "% by weight of the additive" is determined as % by weight of the total mouldable, curable impregnation substance prior to curing and exclusive the fibre bundle. Fibres that are not a part of the fibre bundle are considered to be an additive.

In one embodiment the mouldable, curable impregnation substance comprises at least about 25 % by weight, such as at least about 50 % by weight, such as at least about 60 % by weight, such as at least about 70 % by weight, such as at least about 80 % by weight, such as at least about 90 % by weight of network forming component(s) selected from monomer(s), polymer(s), resin(s) and/or mixture(s) thereof.

The network forming component(s) comprises components that will be part of or be bonded to the network of the cured impregnation substance.

In one embodiment the mouldable, curable impregnation substance comprises at least about 25 % by weight, such as at least about 50 % by weight, such as at least about 60 % by weight, such as at least about 70 % by weight, such as at least about 80 % by weight, such as at least about 90 % by weight of network forming component(s) selected from synthetic and/or natural rosin(s),

thermoplastic polymer(s) and/or mixture(s) thereof.

The fibre bundle means a bundle of fibres, which can be held together to form an endless structure, i.e. the fibre bundle has a length preferably substantially corresponding to the length of the curved, elongate fibre reinforced polymer element. The fibre bundle preferably comprises a plurality of fibres connected to or intermingled into each other. The fibre bundle is preferably of the type that is suitable for a pultrusion process.

In one embodiment the fibre bundle has a structure such that it can be pulled through an impregnation basin and/or a pultrusion die.

The fibre bundle may preferably comprise strings, strands, threads, cords and/or a mixture comprising at least one of the foregoing and/or a cluster comprising at least one of the foregoing and/or roving or ravings comprising at least one of the foregoing and/or combed fibre bundles comprising at least one of the foregoing. The different methods for providing the fibre bundle are well known within the art of pultrusion. The fibre bundle may for example be or comprise spun, knitted, woven, braided fibres and/or comprise or be provided in the form of a regular or irregular network and/or a fibre bundle cut from one or more of the foregoing.

In one embodiment the fibre bundle is a bundle of endless threads and/or cords optionally held together and/or held with short and/or selected distances to each other.

The term "endless" means in practice very long and preferably substantially as long as the length of the curved, elongate fibre reinforced polymer element which it will be a part of. The fibre bundle may comprise any types of fibres, such as organic or inorganic fibres in particular synthetic fibres and/or combinations of organic and inorganic fibres. In one embodiment the fibre bundle comprises, one or more fibres preferably selected from at least one of carbon fibres, glass fibres, aramid fibres, steel fibres, polyethylene fibres, basalt fibres, mineral fibres and mixtures comprising at least one of the foregoing.

The method comprises impregnating the fibre bundle with the mouldable, curable impregnation substance. The impregnation may in principle be performed by any method such that the method which are known within the art of pultrusion. The impregnation may for example be performed as the impregnating methods described in US 6,395,210, US 6,872,343, US 2008/0241446 or in US 7,597,771.

In one embodiment the fibre bundle is impregnated by drawing the fibre bundle through the mouldable, curable impregnation substance. The mouldable, curable impregnation substance may for example be held in a basin and the fibre bundle may be drawn over one or more pulleys such that it is drawn through the mouldable, curable impregnation substance.

The mouldable, curable impregnation substance may be cooled to avoid a too early cross-linking or it may be heated to be sufficiently mouldable and have a high tackiness for easy wetting of the surfaces of the fibres of the fibre bundle. Whether it will be preferred to heat, cool or maintain the temperature at about room temperature (about 20 °C) of the mouldable, curable impregnation substance, depends mainly on the composition of the mouldable, curable impregnation substance and in particular its consistence and cross-linking properties.

In one embodiment the method comprises applying the mouldable, curable impregnation substance in an applicator cavity and drawing the fibre bundle through the mouldable, curable impregnation substance in the applicator cavity. The applicator cavity may for example be an open basin or a partly closed basin comprising an inlet and exit. In one embodiment the exit is arranged such that at least some excess mouldable, curable impregnation substance is wiped-off.

In general it is preferred that the method comprises wiping-off at least some excess mouldable, curable impregnation substance. The wiping-off adds to the control of the process and simultaneously the amount of fibre bundle to cured thermoset in a cross-section of the final curved, elongate fibre reinforced polymer element can be controlled and if desired increased. By wiping- off excess mouldable, curable impregnation substance, the strength of the final curved, elongate fibre reinforced polymer element can accordingly be increased.

Wiping-off may e.g. be performed by one or more wiping-off plates e.g. as described in US 5,891,560. In one embodiment the wiping-off or additional wiping- off is accomplished by pulling the fibre bundle with impregnation substance through a pultrusion die or by a capstan of a suitable form, and/or when shaping the impregnated fibre bundle.

In one embodiment the fibre bundle is impregnated with the mouldable, curable impregnation substance by applying the mouldable, curable impregnation

substance to the fibre bundle. The mouldable, curable impregnation substance may for example be applied by spraying, by brushing or by flowing the mouldable, curable impregnation substance through an applicator slot comprising the fibre bundle.

In one embodiment the fibre bundle is drawn through an applicator slot in the same direction as the mouldable, curable impregnation substance flow.

In one embodiment the fibre bundle is drawn through an applicator slot in counter current to the mouldable, curable impregnation substance flow.

In order to ensure a full impregnation the fibre bundle may be drawn over one or more pulleys and or capstans and/or it may be pulled through a pultrusion die.

Other methods for fully impregnating the fibre bundle are well known in the art.

The fibre bundle may in one embodiment be held in a desired pattern e.g.

optionally slightly spread if possible to make the impregnation and/or the following shaping of the curved, elongate fibre reinforced polymer element simpler. The impregnated fibre bundle may be shaped to have any elongate shape which has a curvature. Preferably the impregnated fibre bundle is shaped to have a curvature in substantially its whole length.

In one embodiment the impregnated fibre bundle is shaped to a strip. In order to produce a strip with a high strength for use in reinforcing an unbonded flexible pipe it is desired that the strip preferably has a thickness of at least about 1 mm, and preferably between about 1 mm and about 15 mm. In general the preferred thickness of the final curved, elongate fibre reinforced polymer element is from about 2 mm to about 10 mm, such as at least about 3 mm, such as at least about 4 mm, such as at least about 5 mm, such as at least about 6 mm, such as at least about 7 mm, such as at least about 8 mm, such as at least about 9 mm.

The width of the final curved, elongate fibre reinforced polymer element and/or of the impregnated fibre bundle may preferably be from about 2 mm to about 10 cm, such as from about 5 mm to about 5 cm, such as from 8 mm to 2 cm. In one embodiment the width of the impregnated fibre bundle is about 2 cm or more such as about 10 cm or more, such as about 20 cm and more and the method further comprises cutting the impregnated fibre bundle before or after curing to strips with width(s) of about 10 cm or less.

The thickness and/or the width may vary along the length of the impregnated fibre bundle and/or of the curved, elongate fibre reinforced polymer element, however, generally it is desired that at least the width is substantially constant along the length of the impregnated fibre bundle and/or of the curved, elongate fibre reinforced polymer element.

In one embodiment the thickness of the impregnated fibre bundle and/or the curved, elongate fibre reinforced polymer element varies along the length thereof. This embodiment may be useful if the curved, elongate fibre reinforced polymer element is to be used for reinforcing an unbonded flexible pipe where a higher reinforcement is desired in one section of the unbonded flexible pipe than in another section thereof.

In one embodiment the thickness of the impregnated fibre bundle and/or the curved, elongate fibre reinforced polymer element is substantially constant along the length thereof.

The impregnated fibre bundle is shaped to have a curvature with a diameter which is preferably 5 m or less, and preferably selected such that the at least partly cured, curved, elongate fibre reinforced polymer element will have an un-tensioned diameter, the un-tensioned diameter is preferably up to about 5 m, such as up to about 2 m, such as up to about 1 m, such as up to about 0.1 m, such as up to about 0.2 cm.

In one embodiment the impregnated fibre bundle is shaped to have a curvature such that the at least partly cured, curved, elongate fibre reinforced polymer element has an un-tensioned diameter, where the un-tensioned diameter is at least about 5 cm, such as at least about 10 cm, such as at least about 15 cm, such as at least about 20 cm, such at least about 25 cm.

The un-tensioned diameter is preferably selected such that in use the curved, elongate fibre reinforced polymer element will be wound to have a diameter which is from about 20 % higher than the un-tensioned diameter D to about 20 % less than the un-tensioned diameter D.

It should be observed that in situations where the curved, elongate fibre reinforced polymer element will be wound helically with a relative low angle to the axis of a pipe onto which it is wound, such as an angle of about 55 degree or less, the curved, elongate fibre reinforced polymer element may have an un-tensioned diameter D which is substantially larger such as up to about 50 % larger, such as between 5 and 40 % larger than the inner diameter of the layer comprising the helically wound curved elongate fibre reinforced polymer element (normally substantially identical to the diameter of the layer of the pipe immediately underlying the curved elongate fibre reinforced polymer element). This is further described below.

In one embodiment the impregnated fibre bundle is shaped to have a substantially constant cross-sectional profile, the cross-sectional profile preferably being substantially rectangular, U shaped; I shaped, C shaped profile, T- shaped profile, K shaped profile, Z shaped, X shaped, ψ (psi) shaped and combinations thereof. Such cross-sectional profiles, combinations thereof and optional engagement thereof are well known and are e.g. described in and shown in drawings in one or more of GB 1 404 394, US 3,311,133, US 3,687,169, US 3,858,616, US 4,549,581, US 4,706,713, US 5,213,637, US 5,407,744, US 5,601,893, US 5,645,109, US 5,669,420, US 5,730,188, US 5,730,188, US 5,813,439, US 5,837,083, US 5,922,149, US 6,016,847, US 6,065,501, US 6,145,546, US 6,192,941, US 6,253,793, US 6,283,161, US 6,291,079, US 6,354,333, US 6,382,681, US 6,390,141, US 6,408,891, US 6,415,825, US 6,454,897, US 6,516,833, US 6,668,867, US 6,691,743, US 6,739,355 US 6,840,286, US 6,889,717, US

6,889,718, US 6,904,939, US 6,978,806, US 6,981,526, US 7,032,623, US 7,311,123, US 7,487,803, US 23102044, WO 28025893, WO 2009024156, WO 2008077410 and WO 2008077409.

The shaping of the impregnated fibre bundle is preferably performed in-line i.e. immediately after impregnation and without any intermediate winding of the impregnated fibre bundle. The shaping may be performed in one operation or in two or more operations, e.g. by drawing the impregnated fibre bundle through shaping element(s) such as one or more dies, one or more capstans and or one or more pressing units. The shaping element or elements are together called the shaping device. In one embodiment the shaping comprises three operations performed in-line and comprising first shaping the thickness, second shaping the width e.g. by cutting off and third providing the impregnated fibre bundle with a curvature. In one embodiment the impregnated fibre bundle is shaped at least partly in a pultrusion die, by drawing the fibre bundle, optionally with impregnation

(alternatively the impregnation may also be performed in the pultrusion die) through the pultrusion die and/or by passing the fibre bundle along movable elements of the pultrusion die.

The pultrusion die is in one embodiment a rotary pultrusion die or comprises at least one rotary section. The pultrusion die can in this embodiment be used in the process of providing the impregnated fibre bundle with the curved shape.

In one embodiment the pultrusion die comprises at least one curved section for shaping the impregnated fibre bundle.

In one embodiment the fibre bundle is both impregnated and shaped in the pultrusion die.

In one embodiment the impregnated fibre bundle is further provided with a coating prior to or after curing. The coating is preferably different from the specific mouldable, curable impregnation substance used, but may be as the mouldable, curable impregnation substance described above. In one embodiment the coating is of a thermoplastic material. In one embodiment the coating has a lower shore hardness than the cured mouldable, curable impregnation substance.

In one embodiment the fibre bundle is impregnated and/or coated in the pultrusion die. In one embodiment the curved, elongate fibre reinforced polymer element is coated after curing.

The coating may be applied on all surface areas of the impregnated fibre bundle or on all surface areas of the curved, elongate fibre reinforced polymer element.

In one embodiment the coating in applied on only a part of the surface area of the impregnated fibre bundle or of the curved, elongate fibre reinforced polymer element. For example if the curved, elongate fibre reinforced polymer element is shaped as a curved strip with a first and a second side, the coating may be applied on the first side of the strip only.

In one embodiment the fibre bundle is impregnated with the mouldable, curable impregnation substance in the pultrusion die, the mouldable, curable impregnation substance preferably being pumped through at least a length section of the pultrusion die counter current to the direction of the fibre bundle. Thereby a good wetting of the fibre bundle can be provided.

When the impregnated fibre bundle is coated with a polymer coating, the polymer coating may for example be injected through one or more slots and/or holes in the pultrusion die.

In one embodiment of the method of producing a curved, elongate fibre reinforced polymer element, the mouldable, curable impregnation substance is heated prior to and/or during the impregnation. This is in particular suitable in situations where the mouldable, curable impregnation substance is or comprises thermoplastic polymer in order to make it sufficiently fluid to impregnate the fibre bundle. The

temperature of the mouldable, curable impregnation substance is preferably substantially below its curing temperature in order to reduce and preferably avoid curing prior to the impregnation of the fibre bundle. A minor level of curing may be acceptable, provided that the mouldable, curable impregnation substance has a consistence of a sufficiently low viscosity to impregnate the fibre bundle.

In one embodiment the method comprises using a pultrusion die, the pultrusion die comprises an exit for the impregnated fibre bundle which at that stage may be uncured, partly cured or fully cured. Preferably the impregnation substance is at least solidified. Preferably the pultrusion die comprises an exit section, immediately adjacent and prior to the exit, wherein the pultrusion die in the exit section has a curved shape with a substantially constant curvature. The exit section may for example comprise heating elements, infrared radiation and/or other activating elements for initiating the curing of the impregnation substance. The curing may be initiated/activated any time after the shaping or simultaneously with the shaping of the impregnated fibre bundle.

After the impregnated fibre bundle has been shaped in the shaping device it is in one embodiment at least solidified to be non-fluidic. The solidification may be provided by cooling (in particular if the impregnation substance comprises thermoplastic polymer(s)), or by providing that thermosetting polymer reaches its gel point. In one embodiment the curing of the impregnation substance is at least initiated/activated before the impregnated fibre bundle leaves the shaping device. In one embodiment the impregnation substance is at least partly cured before the impregnated fibre bundle leaves the shaping device.

In one embodiment the curing of the impregnation substance is at least initiated/activated before the impregnated fibre bundle is wound to a supporting element. In one embodiment the impregnation substance is at least partly cured before the impregnated fibre bundle is applied to a supporting element. In one embodiment the method comprises using a pultrusion die, and the method comprises at least partly curing the impregnation substance in the pultrusion die.

In one embodiment the method comprises at least providing that the impregnation substance is solidified preferably to be non-fluidic at about 25 °C, prior to winding onto a supporting element. Preferably the impregnation substance is at least partly cured on the supporting element.

In one embodiment the method comprises providing that the impregnation substance is at least partly cured prior to winding onto a supporting element. The impregnation substance may be further cured on the supporting element.

In one embodiment the method comprises providing that the impregnation substance is at least partly cured prior to applying the curved, elongate fibre reinforced polymer element onto a pipe. Generally it is desired that the impregnation substance is sufficiently cured to solidify and preferably to a degree where the impregnation substance is

substantially non-mouldable. Thereby the desired shape can be sufficiently maintained during storing of the curved, elongate fibre reinforced polymer element prior to its final use e.g. for reinforcement element on an unbonded flexible pipe.

In one embodiment the impregnation substance is cured at least to a state where it is not fluid at 20 °C.

In one embodiment the impregnation substance is cured at least to a degree of cross-linking of about 50 %, such as at least about 75 %, such as at least about 80 %, such as at least about 85 %, such as at least about 90 %, such as at least about 95 %, such as substantially fully cured.

Curing degrees can be measured using several different methods.

In one embodiment the curing degree is measured using differential thermal analysis (DTA). In one embodiment the curing degree is measured using shore hardness. In one embodiment the curing degree is measured using spectroscopic analysis. In one embodiment the curing degree is measured using hot set test. In one embodiment the curing degree is measured using gel content test.

In one embodiment the impregnation substance is cured at least to a shore D hardness of about 50 % or more, such as about 60 % or more, such as about 70 % or more, such as about 75 % or more, such as about 80 % or more, such as about 85 % or more, such as about 90 % or more, such as about 95 % or more of the shore D hardness of the fully cured impregnation substance, the Shore D hardness is determined at 25 °C.

The curing may be initiated/activated by any method. Such methods are well known.

In one embodiment the curing or partly curing comprises activating the curing process thermally and/or by irradiation. In one embodiment the curing or partly curing comprises activating the curing process by applying conventionally heat.

The curing may be performed as a one-step curing or in a curing cycle, e.g. with intermediate cooling. The curing cycle method is particularly beneficial for thick curved, elongate fibre reinforced polymer elements and may provide an increased curing of the impregnation substance far from the surface, while simultaneously ensuring that the impregnation substance closer to the surface is not degraded by overheating. In this connection it should be observed that most curing processes are exothermic. In one embodiment the curing or partly curing comprises activating the curing process by applying infrared radiation or UV radiation.

In one embodiment the curing or partly curing occurs spontaneously, and will for example start after a certain time of mixing the impregnation substance, which in this case should be mixed at a selected time prior to or simultaneously with the impregnation of the fibre bundle to ensure that the curing will be initiated at a desired time after shaping of the impregnated fibre bundle.

The curing can be performed at any pressure. In one embodiment the curing or partly curing is performed at an elevated pressure, such as at a pressure of 2 bars or more, such as a pressure of 5 bars or more. After being shaped, the shaped, impregnated fibre bundle which is preferably at least solidified, and more preferably in the form of the curved, elongate fibre reinforced polymer element which is at least partly cured, exits from the shaping device and is preferably wound for storing. Preferably the at least partly cured, curved, elongate fibre reinforced polymer element is wound onto a supporting element, such as a bobbin.

In order to avoid introduction of severe tension and stress in the curved, elongate fibre reinforced polymer element, the supporting element is preferably selected to have a supporting curvature which is relatively close to the curvature of the curved, elongate fibre reinforced polymer element in an un-tensioned state, and preferably the supporting curvature of the supporting element has a slightly smaller (up to about 20 %, preferably up to about 10 % smaller) diameter than the curvature of the curved, elongate fibre reinforced polymer element in an un-tensioned state.

In one embodiment the at least partly cured curved, elongated, fibre reinforced polymer element is wound such that mechanical tension in the at least partly cured curved, elongated, fibre reinforced polymer element does not exceed the ultimate tensile strength of the at least partly cured curved, elongated, fibre reinforced polymer element determined at 25 °C. Preferably the mechanical tension in the at least partly cured curved, elongated, fibre reinforced polymer element does not exceed about 30 % of the ultimate tensile strength of the at least partly cured, curved, elongated, fibre reinforced polymer element determined a 25 °C .

The tension is determined in N/m ² . Ultimate tensile strength (UTS), often

shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand before necking, which is when the specimen's cross- section starts to significantly contract. The UTS is usually found by performing a tensile test and recording the stress versus strain; the highest point of the stress- strain curve is the UTS. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen and the temperature of the test

environment and material.

In one embodiment the at least partly cured curved, elongated, fibre reinforced polymer element is wound such that the curvatures it comprises in wound condition have a diameter which is in the interval of from about 20 % less than to about 20 % larger that an un-tensioned diameter of the at least partly cured curved, elongated, fibre reinforced polymer element. In one embodiment the at least partly cured curved, elongated, fibre reinforced polymer element is wound such that the curvatures it comprises in wound condition have a diameter which is in the interval of from about 10 % less than to about 10 % larger that an un-tensioned diameter of the at least partly cured curved, elongated, fibre reinforced polymer element.

In one embodiment the partly cured curved, elongate fibre reinforced polymer element is subjected to an after curing, e.g. during storing.

The invention also relates to an at least partly cured curved, elongated, fibre reinforced polymer element obtainable by the method as described above. In one embodiment the method comprises embedding a fiber sensor into the curved, elongate fibre reinforced polymer element.

Further the invention relates to a wound, curved, elongated, fibre reinforced polymer element comprising a fibre bundle integrated in a thermoset polymer. The curved, elongate fibre reinforced polymer element is wound onto a supporting element. The supporting element is preferably a bobbin, which can be used for transporting and/or storing the curved, elongate fibre reinforced polymer element. It should be understood that the supporting unit is not the final destination for the curved, elongate fibre reinforced polymer element but merely an intermediate supporting element prior to using the curved, elongate fibre reinforced polymer element for reinforcing a pipe.

In one embodiment the elongate element preferably has an un-tensioned diameter which is between about 5 cm and about 5 m.

The curved, elongated, fibre reinforced polymer element may be obtained or at least is obtainable by the method described above. In one embodiment the curved, elongated, fibre reinforced polymer element is obtainable by a pultrusion process, the fibre bundle comprises natural fibres and/or synthetic fibres, preferably selected from carbon fibres, glass fibres, aramid fibres, steel fibres, polyethylene fibres, basalt fibres, mineral fibres and/or mixtures comprising at least one of the foregoing, and the thermoset polymer is obtained from curing an impregnation substance comprising a thermosetting resin precursor, preferably selected from epoxy resins, vinylepoxyester resins polyester resins, polyimide resins, bis-maleimide resins, cyanate ester resins, vinyl resins,

benzoxazine resins, benzocyclobutene resins, or mixtures comprising at least one of the foregoing thermosetting resin precursors.

In one embodiment the thermoset polymer is selected from epoxy polymer(s), vinyl-epoxy-ester polymer(s), polyester polymer(s), polyimide polymer(s), bis- maleimide polymer(s), cyanate ester polymer(s), vinyl polymer(s), benzoxazine polymer(s), benzocyclobutene polymer(s), or mixtures of resin precursors for thermoset polymers comprising at least one of the foregoing thermoset polymers.

In one embodiment the thermoset polymer is or comprises a cross-linked polymer, which is provided by cross-linking a thermoplastic polymer. In one embodiment the thermoset polymer comprises additive(s), such as fillers and extenders, pigments, plasticizers, UV stabillisators and/or absorbers, heat stabilisers, process stabilisers, metal deactivators, antioxidants, marine antifouling agents, microbiocides, algicides, dehydrators, thixotropic agents, wetting agents and fire retardants. In one embodiment the thermoset polymer comprises additive(s), such as carbon black, glass particles, glass fibres, mineral fibres, talcum, carbon, carbonates, silicates, metal particles and/or metal containing components, such as copper and/or copper containing components, clay silicates such as clay silicate selected from kaolinite, such as dickite, halloysite, nacrite and serpentine; smectite, such as pyrophyllite, talc, vermiculite, sauconite, saponite, nontronite hectorites

(magnesiosilicates) and montmorillonite (bentonite); Illite; chlorite; and synthetic clays, such as hydrotalcite. In one embodiment the fibre bundle preferably comprises a plurality of fibres connected to or intermingled into each other.

The fibre bundle may preferably comprise strings, strands, threads, cords and/or a mixture comprising at least one of the foregoing and/or a cluster comprising at least one of the foregoing and/or roving or ravings comprising at least one of the foregoing and/or combed fibre bundles comprising at least one of the foregoing.

The fibre bundle may comprise any types of fibres, natural fibres as well as synthetic fibres and/or combination thereof. In one embodiment the fibre bundle comprises, preferably selected from carbon fibres, glass fibres, aramid fibres, steel fibres, polyethylene fibres, mineral fibres and mixtures comprising at least one of the foregoing.

In order to avoid introducing severe tension and stress in the curved, elongate fibre reinforced polymer element, the supporting element is preferably selected to have a supporting curvature which is relatively close to the curvature of the curved, elongate fibre reinforced polymer element in an un-tensioned state, and preferably the supporting curvature of the supporting element has a slightly smaller (up to about 20 %, preferably up to about 10 % smaller) diameter than the curvature of the curved, elongate fibre reinforced polymer element in an un-tensioned state.

In one embodiment the at least partly cured curved, elongated, fibre reinforced polymer element is wound such that mechanical tension in the at least partly cured curved, elongated, fibre reinforced polymer element does not exceed the ultimate tensile strength of the at least partly cured curved, elongated, fibre reinforced polymer element determined at 25 °C. Preferably the mechanical tension in the at least partly cured curved, elongated, fibre reinforced polymer element does not exceed about 30 % of the ultimate tensile strength of the at least partly cured curved, elongated, fibre reinforced polymer element determined at 25 °C .

The invention further relates to an unbonded, flexible pipe, the pipe has a length and comprises a tubular inner sealing sheath defining a bore with a center axis along the length of the pipe, at least one armor layer surrounding the inner sealing sheath and optionally a carcass arranged in said bore for supporting the inner sealing sheath, wherein the at least one armor layer comprises a wound, curved, elongated, fibre reinforced polymer element as described above. The unbonded flexible pipe of the invention is much simpler to produce than comparable unbonded flexible pipes with prior art elongated, fibre reinforced polymer elements. Furthermore the curved, elongate fibre reinforced polymer element can be produced with a higher fibre bundle to polymer concentration which provides the curved, elongate fibre reinforced polymer element with a very high strength and accordingly the strength of the unbonded flexible pipe is also very high, and simultaneously the risk of undesired tension and stress in the curved, elongate fibre reinforced polymer element can be reduced to a minimum.

Unbonded flexible pipes are well known in the art and the unbonded flexible pipe of the invention may have a structure as any prior art unbonded flexible pipe with the difference that at least one armor layer comprises a wound, curved, elongated, fibre reinforced polymer element as described above.

Examples of prior art pipes are which can be modified to be a pipe of the invention by replacing one or more armor layers with armor layer(s) comprising a wound, curved, elongated, fibre reinforced polymer element as described above are described in any one of the prior art documents GB 1 404 394, US 3,311,133, US 3,687,169, US 3,858,616, US 4,549,581, US 4,706,713, US 5,213,637, US

5,407,744, US 5,601,893, US 5,645,109, US 5,669,420, US 5,730,188, US

5,730,188, US 5,813,439, US 5,837,083, US 5,922,149, US 6,016,847, US

6,065,501, US 6,085,799, US 6,123,114, US 6,145,546, US 6,192,941, US

6,253,793, US 6,283,161, US 6,291,079, US 6,354,333, US 6,382,681, US

6,390,141, US 6,408,891, US 6,415,825, US 6,454,897, US 6,516,833, US

6,668,867, US 6,691,743, US 6,739,355 US 6,840,286, US 6,889,717, US

6,889,718, US 6,904,939, US 6,978,806, US 6,981,526, US 7,032,623, US 7,311,123, US 7,487,803, US 23102044, WO0161232Al,WO 28025893, WO 2009024156, WO 2008077410 and WO 2008077409.

As indicated above in situations where the curved, elongate fibre reinforced polymer element is wound helically the desired un-tensioned diameter D of the curved, elongate fibre reinforced polymer element depend of at least the diameter d of the layer of the pipe underlying the curved elongate fibre reinforced polymer element (the layer onto which it is wound, which in practice constitutes the inner diameter of the layer comprising the curved elongate fibre reinforced polymer element), and the winding angle to the axis of the pipe. This is because the length section of one winding of the helically wound curved, elongate fibre reinforced polymer element has a length L, which if wound with an angle of about 90 degree to the axis of the pipe would have a fictive diameter d2 which in the optimal situation preferably is from about 0.5 * D to about 2 * D.

The fictive diameter can be calculated to be d2= d/Sin a, where a is the angle of the helically wound curved, elongate fibre reinforced polymer element and d is the inner diameter of the layer comprising the curved elongate fibre reinforced polymer element.

In a preferred embodiment d2 is from about 0.5 * D to about 2 * D, more preferably d2 is from about 0.7 * D to about 1.5 * D, such as from about 0.8 * D to about 1.2 * D, such as from about 0.9 * D to about 1.1 * D.

In one embodiment the curved, elongate fibre reinforced polymer element is helically wound, such that one winding has a winding diameter d, the winding diameter d is preferably between from about 0.5 D to about 2 D, preferably from about 0.8 D to about 1.2 D, wherein D is the non-tensioned diameter of the curved, elongated, fibre reinforced polymer element.

In one embodiment the at least one armor layer comprises a plurality of wound, curved, elongated, fibre reinforced polymer element as described above. In one embodiment the pipe comprises at least two armor layers each comprising one or more helically wound, curved, elongated, fibre reinforced polymer

element(s), the helically wound, curved, elongated, fibre reinforced polymer element(s) of one armour layer is/are cross-wound with respect to the helically wound, curved, elongated, fibre reinforced polymer element(s) of the other armour layer, and the at least two armour layers are preferably wound with a winding degree to the axis of the pipe of from about 35 degrees to about 65 degrees.

EXAMPLES

Example 1 A curved, elongate fibre reinforced polymer element is produced as follows:

An impregnation substance is prepared by mixing the elements thereof.

The fibre bundle made by combining roving drawn from numerous bobbins.

The impregnating and shaping was performed in a pultrusion die or partly in a pultrusion die and partly by use of a capstan. The curing was initiated/activated prior to wounding on to the supporting surface of the supporting element.

The following curved, elongate fibre reinforced polymer elements A-.... Is produced: A

80 % Bisphenol A Epoxy Resin D.E.R. ^tm 336.

Impregnation substance 10 % hardener 10 % additive

Fibre bundle Threads of aramid

Impregnation and shaping In a pultrusion die Strip with a width of 1.5 cm and a thickness

Shape of 3 mm. Curvature is uniform with a

diameter of about 2 m.

Curing Activated by conventional heat.

Curing degree about 50 % at the stage of

Curing degree

winding onto the supporting element

Supporting element is a bobbin with a

Supporting element supporting surface with a curvature having a diameter of about lm.

The curved, elongate fibre reinforced polymer

After curing element is after cured on the bobbing to a curing degree of at least about 75 %.

B - thermoplast

Impregnation substance PE powder mixed with organic peroxide

Fibre bundle Basalt roving

PE powder is blown into the fibre bundle prior to impregnate fibres.

Impregnation and shaping

Upon entry in the heated die the PE powder melts and impregnates the fibres.

Strip with a width of 1.5 cm and a thickness

Shape of 3 mm. Curvature is uniform with a

diameter of about 2 m.

Curing Activated by heat.

Curing degree about 50 % at the stage of

Curing degree

winding onto the supporting element

Supporting element is a bobbin with a

Supporting element supporting surface with a curvature having a diameter of about 1 m.

The curved, elongate fibre reinforced polymer

After curing element is after cured on the bobbing to a curing degree of at least about 75 %.

C - photocuring

Example 2

The curved, elongate fibre reinforced polymer elements produced was used in productions of armour layers of flexible unbonded pipes. Pipe I

Inner diameter 12 " gas export flowline

Carcass No carcass

Inner liner 5 mm thick PA12

Pressure armour Wound and interlocked profile of duplex steel

Intermediate liner 2 mm thick PA12

Two cross wound layers wound with a degree to the axis of the pipe of about 55 degree.

Tensile armour

Each layer has 30 strips of curved, elongate fibre reinforced polymer element A

Outer cover A liquid permeable mechanical protection

Insulation No insulation

Pipe II

8" gas export flowline for severe gas

Inner diameter

compositions

Carcass No carcass

Inner liner 7 mm thick PVdF

Pressure armour Wound and interlocked profile of duplex steel

Intermediate liner 5mm HDPE

Two cross wound layers wound with a degree to the axis of the pipe of about 55 degree.

Tensile armour

Each layer has 30 strips of curved, elongate fibre reinforced polymer element B

Outer cover A liquid permeable mechanical protection

Insulation No insulation Pipe III

Inner diameter 8 " gas riser

Carcass Wound and interlocked profile of duplex steel

Inner liner 5 mm thick PA12

Pressure armour Aramid tape covered with HDPE

Intermediate liner N/A

Two cross wound layers wound with a degree to the axis of the pipe of about 25 degree.

Tensile armour

Each layer has 20 strips of curved, elongate fibre reinforced polymer element B

Outer cover A liquid permeable mechanical protection

Insulation No insulation