Strip for pipe reinforcement with degassing channels

Abstract

A reinforcement strip (200) for reinforcement of pipes. The reinforcement strip comprises strength members (210) held in parallel in a plastic material (212), such that one or more of the strength members comprises channels (422) in the longitudinal direction of the reinforcement strip. The said channel has volume of at least 70 millilitre per kilometre (ml / km) of the strength member. The channels can be used for venting the interior of the cords or as monitoring channels to detect the presence of harmful gasses such as hydrogensulphide or carbondixode. The invention also extends to a flexible pipe reinforced with at least one such reinforcement strip and a method to monitor such a flexible pipe.

Description

STRIP FOR PIPE REINFORCEMENT WITH DEGASSING CHANNELSDescriptionTechnical Field

[0001] The invention relates to a strip for the reinforcement of flexible pipes for the pressurized transport of fluids such as water, oil, or gas. The invention also relates to a flexible pipe reinforced with such strips. The invention further provides for a method to monitor fluid transmission through the wall of the flexible pipe.Background Art

[0002] Pipes are the predominant means for transporting fluids over short to very long distances. Traditionally, rigid steel pipes have been widely used; however, their production generates significant greenhouse gas emissions, as the manufacture of steel releases nearly twice its mass in carbon dioxide. Additionally, steel pipes are prone to corrosion, often necessitating the use of internal liners and / or continuous monitoring. Steel pipes also lack flexibility, which can limit their application in certain environments.

[0003] To overcome these drawbacks, the industry has increasingly adopted flexible, reinforced pipes for long-distance fluid transport. Such flexible pipes are generally constructed around an impervious polymeric inner liner, also referred to as an inner layer, inner sheath, or inner tube. This inner liner may be combined with multiple additional layers serving different functions. For instance, an inner carcass may be provided inside the inner tube to prevent collapse, reinforcement layers may be employed to enhance the wall strength of the pipe, and outer protective layers may be incorporated to safeguard the pipe during demanding use conditions.

[0004] Two principal designs of flexible pipes are prevalent in the art: bonded and non-bonded types. These designs are distinguished by the interaction of the reinforcement layers surrounding the inner liner.

[0005] In non-bonded flexible pipes, the reinforcement layers are able to move relative to the inner liner and / or relative to one another when the pipe isbent. Conventional non-bonded flexible pipes generally include layers of armor wires helically wound around the inner liner, with successive layers arranged in opposite lay directions. To mitigate wear and reduce friction between crossing armor wires, intermediate anti-wear or anti-friction layers are typically inserted between the inner liner and the inner armor wire layer, between successive armor wire layers, or between the outer armor layer and the outer protective layer. In addition, to prevent displacement of armor wires (commonly referred to as "birdcaging"), an anti-birdcaging layer is often wound between the outer armor layer and the protective layer.

[0006] Despite these measures, armor wires in non-bonded flexible pipes may eventually be exposed to aggressive environments containing water, hydrogen sulfide, and carbon dioxide. To resist hydrogen embrittlement under such conditions, the steel used for armor wires must have a very low carbon content, typically less than 0.12 wt%. However, such low-carbon steels exhibit tensile strengths typically below 800 N / mm2, significantly lower than the tensile strengths above 1500 N / mm2that are readily achievable with high-carbon steels. As a result, non-bonded flexible pipe designs are relatively complex, heavy, and limited in mechanical performance.

[0007] As background to the current application US 2015 / 0027580 A1 is introduced that describes a non-bonded flexible pipe reinforced with elongate reinforcement elements. The elongate reinforcement elements further comprise a plurality of elongate armor strips and an elongate support element comprising a channel, such that the plurality of elongate armor strips are arranged in the channel of the elongate support element. The reference mentions use of ‘Steel fibres’ as reinforcement of the strips, but the disclosure is silent on what is meant by that.

[0008] US 2013 / 0340877 A1 describes a non-bonded flexible pipe wherein a primary maintaining passage is formed in an annulus between the inner sealing sheath and a second healing sheath. The primary maintaining passage is a web formed by a plurality of passages between armouring wires and layers. A secondary maintaining passage is a single channel extending over the length of the pipe. The primary and secondary passagesare in fluidic connection at the end of the flexible pipe and serve as a pathway to circulate a maintaining fluid that is preferably a gas, for example a drying gas. As the maintaining fluid removes moisture in the primary passages i.e. between the metallic reinforcement elements, the lifetime of the flexible pipe can be greatly increased.

[0009] A flexible pipe wherein the reinforcement is unitary with the pipe wall — that is, the reinforcement cannot move relative to the inner liner or within the reinforcement layers — is referred to as a bonded flexible pipe. The wall of a bonded flexible pipe is usually made of thermosetting materials, most notably rubber, that are reinforced with closely and helically wound reinforcement wires such as steel wires or steel cords. These are subsequently vulcanized and bonded to the rubber. The sealing and adhesion achieved by brass- or zinc-coated steel cords allow for the use of higher tensile strength wires, such as high-carbon steel cords. However, the bonding of the reinforcement layers increases the bending stiffness of the pipe, as the reinforcing wires cannot move relative to one another, thereby resulting in a stiffer pipe.

[0010] As of the early 1990s, Reinforced Thermoplastic Pipes (RTPs) were introduced as an alternative. In RTPs, the inner liner is not reinforced with discrete, non-connected armor wires or with a solid wall of rubber reinforced by individually wound steel wires or steel cords, but rather with strips in which the reinforcement is embedded in a thermoplastic resin. The reinforcement may consist of carbon fibers, glass fibers, aramid fibers, or steel wires or cords of high tensile strength. For example, WO 2002 / 090812 describes an RTP pipe reinforced with strips containing steel wires. The strip of plastic material containing wires is then wound spirally around the plastic pipe body.

[0011] One of the problems associated with such reinforcement strips is that fluids such as hydrogen oxide, hydrogen sulfide, methane, and carbon dioxide can diffuse through the plastic material covering the steel wires. When these fluids accumulate near the steel wires, they may induce corrosion, thereby compromising the integrity of the reinforcement wall.Disclosure of Invention

[0012] It is an object of the invention to provide a reinforcement strip for the reinforcement of pipes wherein accumulation of fluids or gases is prevented or at the least abated. It is a further object of the invention to provide a reinforcement strip wherein the diffusion of accumulated fluids or gases can be monitored and analysed. It is a still further object of the invention to provide a flexible pipe wherein monitoring of the condition of the flexible pipe is possible in a convenient way. It is a furthermore object of the invention to provide a method to monitor such flexible pipe.

[0013] Prior art reinforcement strips and flexible pipes generally focus on mechanical strength, corrosion resistance of coatings, or adhesion of reinforcement layers. They do not address the accumulation of diffused fluids within the reinforcement. The present invention identifies for the first time that such accumulation can compromise the structural integrity of the reinforcement strip. The present invention relates to the reinforcement strips used for flexible pipes and to a flexible pipe comprising such reinforcement strips.

[0014] According to a first aspect of the invention, a reinforcement strip for the reinforcement of flexible pipes is provided. The strip comprises a plurality of strength members arranged substantially parallel and embedded within a plastic material. A distinguishing feature is that one or more of the strength members include longitudinal channels extending along the strip, wherein the channel has volume of at least 70 millilitre per kilometre (ml / km) of the strength member. The strength members in the strip may be adhere, be chemically anchored to or may be mechanically anchored with the polymer / plastic material of the reinforcement strip.

[0015] Within the context of the present invention, a ‘plastic material is any polymer material that is suitable for holding the strength members. More preferably is that the polymer material fully encapsulates the strength members, so that no strength member is exposed except at the ends of the strip. Particularly preferred plastic materials are thermoplastic materials although thermosetting materials can equally well be used although they may requireadditional, energy consuming hardening steps. Particularly interesting thermosetting materials are rubbers.

[0016] The preferred polymeric material is the thermoplastic materials. Particularly preferred are thermoplastic materials that are compatible or even identical with the thermoplastic material the inner liner is made of. The thermoplastic material is e.g. selected from polyolefines, such as polyethylene or polypropylene; polyamides, e.g. poly amide-imide, polyamide-11 (PA-11), polyamide-12 (PA-12) or polyamide-6 (PA-6)); polyurethanes; polyureas; polyesters; polyacetals; polyethers, e.g. polyether sulphone (PES); polyoxides; polysulfides, e.g. polyphenylene sulphide (PPS); polysulphones, e.g. polyarylsulphone (PAS); polyacrylates; polyethylene terephthalate (PET); polyether-ether-ketones (PEEK); polyvinyls; polyacrylonitrils; polyetherketoneketone (PEKK); copolymers of the preceding; fluorous polymers e.g. polyvinylidene difluoride (PVDF), or compounds comprising one or more of the above mentioned polymers.

[0017] The channels as described in the present invention function to collect fluids that diffuse through the polymer matrix. The collected fluids may be removed by vacuum pumping or purging with an inert gas, such as nitrogen. Alternatively, the channels may be used to accumulate fluid samples over extended lengths for analysis or can be filled with anticorrosive or scavenger media to further protect the strength members. To ensure that fluids diffusing through the polymer material can be reliably collected and transported away from the vicinity of the strength member, the channel volume should be at least about 70 ml / km of the strength member, more preferably at least about 100 ml / km of the strength member, to secure sufficient capacity for fluid transport. On the other hand, excessively large channel volumes, for example above 10,000 ml / km, may undesirably increase the stiffness of the strength member and compromise the flexibility of the pipe. A practical and effective range is therefore between about 70 and 2,000 ml / km of strength member, and more preferably between 100 and 200 ml / km of the strength member. If the channel volume is too low, insufficient fluid will be collected, and the purpose of the channels is defeated. If the channel volume is too high, the strength members becomeexcessively stiff, impairing flexibility of the pipe. The present invention therefore provides a workable balance between effective fluid collection and mechanical flexibility of the pipe.

[0018] Alternatively, or in addition, the channel volume may be expressed relative to the strip surface area i.e. volume over the length and the width of the strip into which the strength members are embedded. This will also relate to the number of strength members that are embedded over the width of the reinforcement strip. When defined on an areal basis, the longitudinal channels preferably should provide a volume of at least 30 ml per square meter (ml / m2) of strip, preferably at least 40 ml / m2’ more preferably at least 50 ml / m2or more than 100 ml / m2, to allow for adequate fluid collection across the reinforcement wall. To avoid excessive stiffening of the reinforcement strip, the channel volume should preferably not more than 1000 ml per square meter, and more preferably not more than 100 ml per square meter. The channel volume may be expressed relative to the strip surface area also corresponds to a void layer of an equivalent thickness over the area of the strip. E.g. a volume of at least 30 ml per square meter (ml / m2) of strip corresponds to equivalent void layer having thickness of 0.03 mm over the area of the strip. These ranges represent a balance between maintaining sufficient flexibility of the pipe and providing enough channel space for diffused fluids to be transported away from the strength members.

[0019] The strength members may be selected from carbon fibres, glass fibres, aramid fibres, steel fibres or combination thereof. In accordance with the present invention, steel cords are preferred. Fibres or fibre-based yarns such as carbon, glass, or aramid contain many very fine filaments, but the channels formed are too small and deformable to reliably transport fluids. On other hand, steel cords can be composed of with a limited number of relatively thick filaments, typically with filaments having diameters in the range of 0.20 and 0.70 mm, preferably 0.25-0.60 mm, more preferably 0.30-0.60 mm, including all between ranges. Being metallic, these filaments are not laterally compressible and, when twisted together, form distinct interstices or voids that function as channels. Thicker filaments (e.g., above0.25 mm, or more preferably above 0.30 mm or 0.35 mm) provide larger interstices, which are desirable for fluid transport.

[0020] Further, the cross-sectional area of the channel formed between the strength members is proportional to the diameter of the fibres or filaments of the strength member. For example, when twisting three filaments of diameter ‘d’ mm together, a three-pointed internal interstice or void forms in between the three filaments with a cross-sectional area of 0.04031 xd2. Hence a steel cord will form longitudinal channels, the cross-sectional area of which will scale with the diameters of the steel filaments. Multiplying this area with the length of the cord in the strip will give the volume in a single cord over that length. This can e.g. be expressed in millilitre per kilometre (ml / km) of steel cord. Multiplied by the number of steel cords in the strip this yields a total volume in the channels per unit of strip length. When dividing this total volume in the channels by the width of the strip gives a total channel volume per unit area of strip e.g. expressed in millilitre per square metre (ml / m2).

[0021] The steel filaments may be twisted in many configurations. Strands of 2 to 30 filaments, preferably 3 to 25 filaments or more preferably 7 to 15 filaments 7-15, can be twisted together to form a strand. Strands may also be combined into ropes, though ropes are less preferred due to added complexity and elongation under load. Within context of this invention, steel cords in the from of strands are preferred as they provide good balance between the bending stiffness and the strength of the steel cord.

[0022] In a first preferred embodiment, the steel cord is a single lay cord, in which all filaments are twisted in one operation with the same lay direction and lay length. The lay may be left-hand (S) or right-hand (Z). Diameters of the filaments may be equal or varied.

[0023] Suitable examples include:• “1 xd1 |6xd2”, where one central filament of diameter d1 is surrounded by six filaments having diameter d2 at a certain lay lengthin “Z” or “S” direction, producing six interstices. In preferred embodiment, the diameter d1 is larger than diameter d2.• 3xd1 |9xd2, with three central filaments having diameter d1 surrounded by nine outer filaments having diameter d2, yielding thirteen interstices.• 1 xd0|5xd1 |10xd2, is preferred arrangement, wherein the central filament is omitted thereby creating a void at centre, i.e. O|5xd1110xd2, “O” denotes the void.• Alternatively, O|4xd1 |8xd2 could be considered but is less preferred as the interstice at centre is very small.This arrangement can be easily extended to• 1 |6|12 and 1 |6|12|18 with 24 and 54 interstices respectively. However, O|6| 12 is less preferred as the configuration is not stable.3|9|15 and 3|9|15|21 with 37 and 73 interstices respectively. However, with these arrangements as the number of interstices rises, the cord diameter becomes too big (when using equal filament diameters), or the filaments become too small (when striving to keep the same overall cord diameter).

[0024] In a second preferred embodiment, the steel cord is a layered cord, comprising a core (single filament, doublet (2x1 strand), triplet (3x1 strand), or n-tuplet (nx1 strand)) surrounded by one or more layers of filaments having different lay lengths and / or directions.

[0025] The suitable examples include:• 2xd1+7xd2, wherein smaller inner filaments with diameter d1 are surrounded by larger outer filaments having diameter d2 to maintain open channels. Outer filaments have larger diameters to reduce gap formation in outer layer, thereby abating polymer ingress in the channel. This construction is preferred as it provides large channels with few filaments.• 3xd1+9xd2, where a triplet with diameter d1 , a first lay length and direction is surrounded by nine filaments with diameter d2, a second lay length and direction different from first lay length and direction.• Other arrangements such as1+6+12 and 1+6+12+18 with 19 and 37 filaments respectively and 3+9+15 and 3+9+15+21 with 27 and 48 filaments respectively can also be considered but are less preferred even though the number of interstices rises, the cord diameter becomes too big (when using equal filament diameters), or the filaments become too small (when striving to keep the same overall cord diameter).

[0026] Layered cords are generally preferred because they offer more channel volume for a given diameter and produce more open structures than single lay cords. Further, like single lay steel cords, the cord constructions with a void at centre can be considered. The void can be created by omitting the core filament / s.

[0027] It should be noted that within the reinforcement strip the number of strands in ‘S’ direction is preferably equal to the number of strands in ‘Z’ direction to avoid twisting tendency when pulling on the strip. For example, the signs alternate between adjacent steel cords.

[0028] The steel cords are made up of filaments. In accordance with present invention, the steel cords are preferably designed such that the outer layer of filaments is substantially closed, meaning that adjacent filaments in the outermost layer are in close contact with one another. A closed outer layer prevents the surrounding polymer matrix from penetrating into the interstices during manufacture, which would otherwise block or significantly reduce the effectiveness of the longitudinal channels. At the same time, the closed configuration ensures that the cord maintains sufficient structural integrity and resists lateral deformation during embedding into the polymer strip. However, complete sealing of the inter-filament gaps is not desired, as this would also hinder ingress of diffused fluids into the channels. Therefore, it is preferred that the inter-filament gaps in the outer layer are fine-tuned within a narrow range: sufficiently small to prevent polymer intrusion, yet sufficiently large to allow passage of diffusing fluids. Accordingly, the gaps between the filaments of the outer layer should be e.g., less than 20 pm, preferably less than 15 pm and more than e.g., at least 2, preferably, at least 5 pm or at least 10 pm. This balance ensuresreliable formation of fluid-accessible channels that remain open and effective throughout the service life of the reinforcement strip. The ability to deliberately engineer such micro-gaps by adjusting filament diameter, lay length, and / or surface undulation represents an important aspect of the invention, as it reconciles two conflicting requirements — polymer exclusion and fluid ingress — within a single cord design.

[0029] Gap size between the filaments in outer layer may also be controlled by imparting micro-undulation to one or more filaments. Micro-undulated filaments exhibit small bends of about 2-10 pm amplitude, produced by plastically deforming the wire (e.g., via gear-tooth contact or polygonal wheels under tension). Preferably, at least one outer filament is microundulated, although multiple or all filaments may be so treated.

[0030] In a further preferred embodiment of the reinforcement strip, one or more of the channels may comprise a sensor fibre. Preferably maximum one sensor fibre is present in one steel cord, or even maximum one sensor fibre is present in one reinforcement strip. For example, the sensor fibre can be present in a void left by leaving a core filament out of the construction.

[0031] The sensor fibre is incorporated to obtain condition information of the reinforcement strip. The sensor fibre can be- An optical fibre of which the transmission degrades in the presence of fluids- An optical bragg grating fibre which allows for the measurement of elongation of the fibre- A fibre that of which the transmission depends on temperature- A dielectric electro active polymer fibre that also can be used to measure extension.- A molecule sensitive fibre. The conductivity thereof changes based on the presence of one or more molecules e.g. H2O, CO2, CPU or H2S.

[0032] In a further preferred embodiment of the reinforcement strip, the strip comprises a porous material patch. The patch is in contact with a pluralityof the strength members and is embedded in the plastic material. The patch serves as a collector for fluids that may travel along the channels in the reinforcement members. Possibly the channels are locally opened to allow fluids to enter the porous material patch.

[0033] The porous material patch can be used to collect fluid samples. Alternatively, the porous material patch can be sensitive to one or more molecules such as e.g. H2O, CO2, CH4 or H2S. The electrical conductivity of patch may change depending on the presence of the molecules. The function of the porous patch is to monitor the condition of the reinforcement strip.

[0034] According a second aspect of the invention a flexible pipe is claimed. The flexible pipe has an inner liner defining a bore through which fluids are transported. The inner liner is reinforced with two or more layers of reinforcement strips helically wound around this inner liner. The reinforcement layers are further covered with a polymer layer for protection of the reinforcement and the pipe in general. Characteristic about the pipe is that the reinforcement strips have the combinations of features according the first aspect of the invention.

[0035] Reinforcement strips are wound under a helical angle and are provided in pairs to balance out possible imperfections in winding angles. The reinforcement layers maybe bonded or not bonded to one another. The flexible pipe may be further provided with an inner reinforcement, inside the inner liner and close to the wall thereof, to prevent collapse of the pipe. The outer polymer layer may also be reinforced with woven fabrics or short fibres to toughen the layer against abusive use of the flexible pipe. A typical example of the second embodiment is a Thermoplastic Reinforced Pipe (TRP), put the invention is not limited to such a pipe design. The invention can equally be used in a non-bonded or bonded flexible pipe.

[0036] In a further preferred embodiment of the flexible pipe at least one of the reinforcement strips is provided with a port. The port is for extracting gas out of the one or more tensile members of reinforcement strip or for feeding, injecting gas into the one or more channels of the one or more tensilemembers of the reinforcement strip. The port can be situated at one or both the ends of the reinforcement strip. Alternatively, the port can be situated midways of the reinforcement strip. Not all reinforcement strips must be provided with a port. It may for example be more convenient to provide only the reinforcement strips of the outer layer with a port as these are easily accessible.

[0037] The port may be advantageously provided with a gas receiving chamber, that is a hollow, wherein gas or fluids can collect. Preferably the chamber collects gases or fluids that come through the channels in the tension members of the reinforcement layer. The chamber is thus open to the tension members. By preference the port further comprises a gas sensor, a power supply, and a wireless communication unit. This all can be embedded or made of the same plastic material of the reinforcement strip.

[0038] The gas sensor can be a gas specific sensor for sensing H2O, CO2, CH4 or H2S. The power supply can take the form of a battery. Alternatively, or additionally the power supply of the port may be provided with an induction coil for collecting and transforming variable magnetic fields into electricity that may be directly consumed by the senor or wireless communication unit, stored in a battery or super capacitor.

[0039] With the port the presence of gas or fluid in the chamber can be established by means of a wireless device, that connects with the wireless communication unit of the port. Alternatively, the collected gas in the collection chamber can extracted e.g. by a syringe to confirm the nature of the gas.

[0040] In a third aspect of the invention, a method or monitoring a flexible pipe according the second aspect is described. The method comprises the steps of:- Connecting a gas extraction unit to the port of the strip,- Extracting gas out of the gas flow channel of the tensile memberAnalysing the type of gas and the amount thereof,Based in the type of gas and the amount of gas extracted, make an assessment on the condition of the flexible pipe.Brief Description of Figures in the Drawings

[0041] FIGURE 1 shows an inventive flexible pipe according the second aspect of the invention.

[0042] FIGURE 2 shows an embodiment of a reinforcement strip according the first aspect of the invention.

[0043] FIGURE 3 shows a detail of a first preferred embodiment of the reinforcement strip.

[0044] FIGURE 4 shows a detail of a second preferred embodiment of the reinforcement strip.

[0045] FIGURE 5 shows a detail of a third preferred embodiment of the reinforcement strip.Note that over different embodiments reference numbers having equal units and tens refer to similar features across drawings, the hundred number indicating the figure number.Mode(s) for Carrying Out the Invention

[0046] In the following the invention will be further explained by presenting examples of how the invention can be realised in practice. Although the specific examples may contain further inventive features, these examples are not limiting the invention in any way. The invention is limited only by the Claims and the Disclosure of Invention.

[0047] FIGURE 1 shows a flexible pipe 100 according the second aspect of the invention. The flexible pipe 100 has an inner liner 102 that is made of high- density polyethylene (HDPE). The inner diameter of the bore of the inner liner is 6 inch or about 152 mm. There are two reinforcement strips 104, 106 that are helically wound around the inner liner in ‘Z’ and ‘S’ direction respectively. An outer protective layer 108 of polyethylene is extruded around the outer reinforcement layer. The pipe has an outer diameter ofabout 200 mm. The pipe is designed for a working pressure of 10 MPa (about 1500 psi) with a minimum burst pressure of 20 MPa (about 3000 psi).

[0048] The reinforcement strip is shown in more detail in FIGURE 2. The reinforcement strip 200 has a length, a thickness and a width, the thickness being the smallest dimension of 2 mm, the width being 290 mm in this case and the length being several hundreds of meters. The reinforcement strip 200 is helically wound around the inner liner or first reinforcement layer at an angle of about 57° close to neutral angle. The plastic material 212 is polyethylene and holds strength members 210, 210’ etc. parallel to one another. The strength member 210, 210’ etc are steel cords and the lay lengths alternate from S to Z in one cord to the next. The cords have a diameter of 1.5 mm and a breaking load of 3700 N each. The cords are composed of steel filaments characterized by high tensile strength of about 3350 N / mm2. The reinforcement strip has a lateral strength of 1267 newton per millimetre in width direction.

[0049] FIGURES 3, 4 and 5 shows cross-sections of different embodiments of the reinforcement strip. The embodiments differ in the steel cord that has been used as a strength member. In FIGURE 3 the reinforcement strip 300 shows steel cords 310, 310’, 310” equally spaced over the width of the reinforcement strip and embedded in the plastic material 314. The steel cord is of the single lay type comprising 3|9 configuration wherein the three inner filaments 318 have a diameter of 0.385 mm and the 9 outer filaments have a diameter 0.36 mm. The lay length is 12.5 mm and - as mentioned - alternates S to Z from even to odd numbered steel cord. Within the steel cord voids or interstices 320 can be discerned. These interstices have a volume of 953 ml over one kilometre of steel cord. In total the volume of the channels taken over the area of the strip is 329 ml / m2.

[0050] The reference method of this application for measuring the volume of the channels is the Washburn method. In the Washburn method, a sample of reinforcement strip is cut in a length of 100 mm and hung in a Dynamic Contact Angle Measuring Device and Tensiometer (DCAT). One end of the strip sample is made to contact n-heptane held in a recipient. All measurements are performed at standard temperature and humidity. Then-heptane rises into the channels of the steel cord by capillary forces as the n-heptane wets the metal filaments very well. The rise in weight is measured by the DCAT. The n-heptane reaches the top of the strip where it evaporates. At that stage the channels are completely filled with n-heptane and the mass of the sample does no longer increase. From the increased mass of the complete sample and considering the known density of n- heptane, the total volume of the channels in the strips can be derived. By dividing by the number of steel cords in the strip and the length of the strip sample one obtains a volume expressible as millilitre per kilometre of steel cord.

[0051] FIGURE 4 shows another embodiment of the inventive reinforcement strip 400 wherein an attempt was made to increase the volume of the channels. A steel cord 410 with layered construction is depicted. The core is a 3x0.355 mm triplet of steel wires 418 twisted at 12.5 mm in S direction. In a second twisting operation, 9 filaments 416 of diameter 0.385 are twisted around the core at a lay of 20 mm in Z direction. The resulting cord 410 can designated as 3x0.355+9x0.385. The design is such that the gaps, the opening between the outer filaments 416 is minimal. They are on average, nine gaps, about 3 micro-metres. This prevents the entrance of the polymer 414 that could block the central channels 422, 422’, 422”. As the filaments 418 of the core and of the outer layer 416 do no longer intermesh (as they did in the 3|9 construction) the channel volume is much increased. The volume of the channels in one steel cord is 3200 ml / km. Expressed as a volume per unit area this becomes 1805 ml / m2.

[0052] FIGURE 5 describes another single lay construction of the type indicated above as O|5|10. This construction is derived from a 115| 10 but is produced without using a core wire. The diameters of the 5 intermediate layer filament 518 is 0.3 mm, the diameters of the 10 outer layer filaments 516 is 0.31 mm. A channel forms 521 at the centre. The channel 521 has a volume per unit length of 49 ml / km. In one steel cord 510 an optical bragg grating fibre 530 is incorporated. The optical bragg grating fibre allows to detect excessive extension of the reinforcement strip.

[0053] FIGURE 2 shows in another embodiment applicable to all reinforcement strips described a patch of porous material 230 that is buried under the polymer 212. The porous material 230 is a fibre felt that is inserted between the steel cords and the polymer 212 during manufacturing. The fibre felt is surface treated such that it changes it’s conductivity when H2S is detected.The change in conductivity can be detected over the leads 232, 232’. For example, the fibre felt can be treated with lead (II) acetate that is reactive to H2S.

Claims

Claims1. A reinforcement strip for reinforcement of pipes, said reinforcement strip comprising strength members held in parallel in a plastic material, characterised in that one or more of the strength members comprises channels in the longitudinal direction of the reinforcement strip, wherein the channel has volume of at least 70 millilitre per kilometre (ml / km) of the strength member.

2. The reinforcement strip according to claim 1 , wherein said plastic material is selected from a thermoplastic material or a thermosetting material.

3. The reinforcement strip according to claim 2, wherein said plastic material is thermoplastic material selected from polyolefines, polyamides, polyurethanes, polyureas, polyesters, polyacetals, polyethers, polyoxides, polysulfides, polysulphones, polyacrylates, polyethylene terephthalate (PET), polyether- ether-ketones (PEEK), polyvinyls, polyacrylonitrils, polyetherketoneketone (PEKK), copolymers of the preceding, fluorous polymers, or compounds comprising one or more of the above mentioned polymers.

4. The reinforcement strip according to claim 1 , wherein said strength member is selected from carbon fibres, glass fibres, aramid fibres, steel fibres or combination thereof.

5. The reinforcement strip according to claim 4, wherein said strength member is steel cord.

6. The reinforcement strip according to claim 5, wherein said strength member is a single lay steel cord.

7. The reinforcement strip according to claim 5, wherein said strength member is a layered steel cord.

8. The reinforcement strip according to any one of claims 5 to 7, wherein in the said steel cord, a core filament is omitted to create a void at centre.

9. The reinforcement strip according to any one of claims 1 to 8, wherein the volume of all said channels in the steel cords of the strip is at least 30 millilitre per square meter of the strip.

10. The reinforcement strip according to any one of claims 1 to 9, wherein one or more of the said channels comprises a sensor fibre, said sensor fibre being one out of the group comprising an optical fibre, an optical bragg grating fibre, a temperature sensing fibre, a dielectric electro active polymer fibre, and a molecule sensitive fibre.11 . The reinforcement strip according to any one of claims 1 to 10, wherein the strip comprises a porous material patch in contact with a plurality of said strength members, said porous material patch being embedded in said plastic material.

12. A flexible pipe comprising an inner liner defining a bore, two or more layers of reinforcement, a layer of reinforcement comprising reinforcement strips helically wound around said inner liner, an outer polymer layer covering said two or more layers of reinforcement characterised in that at least one of said reinforcement strips is according to any one of claims 1 to 11.

13. A flexible pipe according to claim 12, wherein said reinforcement strip is provided with a port, said port for extracting gas out of and / or for feeding gas into the one or more tensile members of said reinforcement strip.

14. The flexible pipe according to claim 13, wherein said port is provided with a gas receiving chamber, a gas sensor, a power supply, and a wireless communication unit.

15. A method for monitoring a flexible pipe comprising the steps of- Connecting a gas extraction unit to the port of the strip- Extracting gas out of the gas flow channel of the tensile member- Analysing the type of gas and the amount of gasBased on the type of gas and the amount of gas extracted, asses the condition of the flexible pipe.

Images