CN116670420A

CN116670420A - Composite pipe

Info

Publication number: CN116670420A
Application number: CN202180083888.8A
Authority: CN
Inventors: J·F·普拉特; D·R·汤普森
Original assignee: Cytec Industries Inc
Current assignee: Cytec Industries Inc
Priority date: 2020-12-15
Filing date: 2021-12-15
Publication date: 2023-08-29

Abstract

A windable pipe suitable for use in the petroleum industry, and more particularly a windable composite pipe having the ability to withstand high stresses and high crack resistance.

Description

Composite pipe

RELATED APPLICATIONS

The present application claims priority from U.S. provisional application US 63/125,423, filed on 12/15 in 2020, and from european patent application EP 21160555.5 filed on 3/3 2021, the entire contents of which are incorporated herein by reference for all purposes.

Technical Field

The present application relates to tubing suitable for use in the petroleum industry, and more particularly to a windable composite tubing having the ability to withstand high stresses.

Background

Reelable tubing (i.e., tubing that may be reeled on a reel) is commonly used in a variety of well operations. Typical well operations include running a wireline cable downhole with a well tool, working uphole by delivering various chemicals downhole, and working on the inner surface of a borehole. The tubing required to be used is spoolable so that it can be used in connection with one well and then transported on a reel to another well location. Steel coiled tubing is typically coilable because the steel used in the product exhibits high ductility (i.e., the ability to plastically deform). However, the weight of conventional steel pipes is very high, also when submerged. At large depths of water, the tension at the top is extremely high and therefore flexible steel pipes are used only in shallower water.

The oil and gas industry is looking for lighter weight pipes for the subsea transportation of crude oil from deep sea fields to surface vessels that are not limited by steel pipes and are highly chemical resistant.

In recent years, fiber reinforced polymer tubes (hereinafter referred to as "composite tubes") have been proposed as alternative solutions because they are not corroded and offer many benefits, such as higher strength to weight ratio when compared to metal tubes, and the potential for windability makes them easier to transport and install than metal tubes. The basic design of the composite pipe consists of an internal fluid barrier (typically a layer of thermoplastic material) around which the reinforcement is wound in a continuous process. The reinforcement laminate consists of a plurality of oppositely wound fibrous layers (typically glass or carbon) in a polymer matrix. The polymer matrix may comprise a thermoset or thermoplastic polymer.

It is an object of the present application to provide a windable composite tube wherein the polymer matrix of the reinforcement laminate is a thermoplastic material.

Another object of the present application includes providing a composite tube that can be repeatedly wound and bent without suffering fatigue sufficient to cause cracking and failure of the tube.

Other objects of the present application include providing a windable tube capable of transporting corrosive fluids without causing corrosion in the windable tube, providing a coiled tube having a lighter weight, and providing a coiled tube capable of withstanding higher internal pressure levels and higher external pressure levels without losing the integrity of the tube.

These and other objects will be apparent from the following description.

Disclosure of Invention

The present application relates to a composite tube comprising:

-an inner liner of thermoplastic material, and

a reinforcing laminate surrounding the inner liner,

wherein the reinforcement laminate comprises at least two layers:

-at least one layer (L1) free of reinforcing fibers and comprising a vinylidene fluoride polymer, and

-at least one layer (L2) comprising vinylidene fluoride polymer and continuous reinforcing fibers.

The liner is in contact with the fluid being conveyed. The reinforcement laminate is typically continuously bonded to the liner.

The composite tube may optionally include an outer protective layer surrounding the reinforcement laminate.

The composite tube of the present application is capable of maintaining an open cell configuration when wound on a spool.

Brief description of the drawings

Fig. 1 shows the 90 ° flexural stress-strain curves of the laminates of examples 1 to 3 and comparative example 1.

Detailed Description

A first object of the present application is a composite tube comprising:

-an inner liner of thermoplastic material, and

a reinforcing laminate surrounding the inner liner,

wherein the reinforcement laminate comprises at least two layers:

-at least one layer (L1) free of reinforcing fibres, comprising a vinylidene fluoride polymer, and

For the purposes of the present application, the term "thermoplastic" is intended to mean polymers and/or compositions which are solid at room or use temperature, which soften when heated and harden again when cooled, without appreciable change in chemical and physical properties. Such definitions can be found, for example, in the edition of MARK s.m. alger, under the name Polymer Science Dictionary [ polymer science dictionary ] LONDON: ELSEVIER APPLIED SCIENCE [ alsifer application science ], page 1989.476.

The indefinite article "a" in the expression "a vinylidene fluoride polymer" is intended to mean "one or more", or "at least one", unless indicated otherwise.

The use of parentheses "()" before and after the name, symbol or number of a compound, such as "layer (L1)", "layer (L2)", etc., has the purpose of distinguishing that name, symbol or number better from the remainder of the text only; therefore, the parentheses may also be omitted.

Throughout this text, when numerical ranges are indicated, the end points of the ranges are included.

The expression "vinylidene fluoride polymer" or "VDF polymer" is equivalent and is used within the framework of the present application to indicate a polymer consisting essentially of recurring units, more than 50% by mole of which are derived from vinylidene fluoride (VDF).

Vinylidene fluoride polymers suitable for use in the tube of the present application are polymers comprising:

(a) At least 60% by moles, preferably at least 75% by moles, more preferably 85% by moles of recurring units derived from vinylidene fluoride (VDF);

(b) Optionally from 0.1% to 15%, preferably from 0.1% to 12%, more preferably from 0.1% to 10% by mole of recurring units derived from fluorinated monomers other than VDF; and

(c) Optionally from 0.1% to 5% by mole, preferably from 0.1% to 3% by mole, more preferably from 0.1% to 1% by mole of recurring units derived from one or more hydrogenated comonomers, where "hydrogenated comonomer" refers to a non-halogenated comonomer,

all the above mol% refer to the total moles of repeating units of the VDF polymer.

The fluorinated monomer other than VDF is advantageously selected from the group consisting of: vinyl Fluoride (VF) ₁ ) The method comprises the steps of carrying out a first treatment on the surface of the Trifluoroethylene (VF) ₃ ) The method comprises the steps of carrying out a first treatment on the surface of the Chlorotrifluoroethylene (CTFE); 1, 2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl) vinyl ethers such as perfluoro (methyl) vinyl ether (PMVE), perfluoro (ethyl) vinyl ether (PEVE) and perfluoro (propyl) vinyl ether (PPVE); perfluoro (1, 3-dioxole); perfluoro (2, 2-dimethyl-1, 3-dioxole) (PDD). Preferably, the possible additional fluorinated monomers are selected from Chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF) ₃ ) Tetrafluoroethylene (TFE).

The choice of the one or more hydrogenated comonomers is not particularly limited; alpha-olefins, (meth) acrylic monomers, vinyl ether monomers, styrene monomers may be used.

Among the suitable VDF polymers, mention may be made of polymers comprising:

(a') at least 60% by mole, preferably at least 75% by mole, more preferably 85% by mole of vinylidene fluoride (VDF);

(b') optionally from 0.1% to 15%, preferably from 0.1% to 12%, more preferably from 0.1% to 10% by mole of a fluorinated comonomer selected from the group consisting of Vinyl Fluoride (VF) ₁ ) Chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), and mixtures thereof; and

(c ') from 0.1 to 5% by mole, preferably from 0.1 to 3% by mole, more preferably from 0.1 to 1% by mole of one or more fluorinated or hydrogenated comonomers, based on the total amount of monomers (a ') and (b ').

Non-limiting examples of VDF polymers useful in the tubes of the application are, for example, homopolymers of VDF, VDF/TFE copolymers, VDF/TFE/HFP copolymers, VDF/TFE/CTFE copolymers, VDF/TFE/TrFE copolymers, VDF/CTFE copolymers, VDF/HFP copolymers, VDF/TFE/HFP/CTFE copolymers, VDF/TFE/perfluorocrotonic acid copolymers, VDF/TFE/maleic acid copolymers, and the like.

The polymer (VDF) may be semi-crystalline or amorphous.

The term "semicrystalline" is intended herein to mean a polymer (VDF) having a heat of fusion of from 10 to 90J/g, preferably from 30 to 60J/g, more preferably from 35 to 55J/g, as measured according to ASTM D3418-08.

The term "amorphous" is intended herein to mean a polymer (VDF) having a heat of fusion of less than 5J/g, preferably less than 3J/g, more preferably less than 2J/g, as measured according to ASTM D-3418-08.

Preferably, the polymer (VDF) is semicrystalline.

Lining(s)

The liner acts as a barrier against the pressurized oil/gas flow. It protects the reinforced laminate from exposure to abrasion, wear, chemicals, heat, etc. The term "liner" as used herein refers to a tube.

The liner is made of a thermoplastic material. In some embodiments, the liner is made of a thermoplastic material capable of withstanding temperatures of about 100 ℃ to 200 ℃. Suitable thermoplastic materials for the liner may be selected from the group consisting of: polyamides (e.g., PA11, PA12, PA6, 12), high Density Polyethylene (HDPE), crosslinked Polyethylene (PEX), polypropylene, vinylidene fluoride polymer, ethylene tetrafluoroethylene copolymer, polyetheretherketone Polymer (PEEK), polyphenylene sulfide, polyethersulfone, and mixtures thereof.

In one embodiment, the liner comprises a vinylidene fluoride polymer.

In a preferred embodiment, the liner comprises a mixture of at least one VDF homopolymer and at least one VDF copolymerThe VDF copolymer is selected from the group consisting of: VDF copolymer comprising from 0.1 to 15mol.%, preferably from 0.1 to 12mol.%, more preferably from 0.1 to 10mol.% of a fluorinated comonomer selected from the group consisting of Vinyl Fluoride (VF) ₁ ) Chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), and mixtures thereof.

The liner thickness may be from 5.0 to 15.0mm, for example from 6.0 to 14.0mm or from 7.0 to 13.0mm (+ -0.5 mm).

The liner may be obtained by extrusion.

Reinforced laminate

The reinforced laminate comprises at least two layers: at least one layer comprising vinylidene fluoride polymer [ layer (L1) ] free of continuous reinforcing fibers and at least one layer comprising vinylidene fluoride polymer and continuous reinforcing fibers [ layer (L2) ].

Layer (L1) comprises a vinylidene fluoride polymer as defined above.

In addition to the vinylidene fluoride polymer, or advantageously the VDF homopolymer, the layer (L1) may optionally comprise additional components, such as one or more additives and/or one or more reinforcing agents. When layer (L1) comprises one or more reinforcing agents, however, such agents are not continuous reinforcing fibers as defined below.

The optional additives may be selected from the group consisting of: (i) colorants such as dyes, (ii) pigments such as titanium dioxide, zinc sulfide and zinc oxide, (iii) light stabilizers such as UV stabilizers, (iv) heat stabilizers, (v) antioxidants, (vi) acid scavengers, (vii) processing aids, (viii) nucleating agents, (ix) internal and/or external lubricants, (x) flame retardants, (xi) smoke suppressants, (x) antistatic agents, (xi) antiblocking agents, (xii) conductive additives such as carbon black and carbon nanofibers, (xiii) plasticizers, (xiv) flow modifiers, (xv) extenders, and (xvii) flow aids, and mixtures thereof.

When present, the weight% of optional additives and/or reinforcing agents advantageously ranges from 0.05wt.% to 5wt.%, e.g., from 0.1wt.% to 4wt.% or from 0.2wt.% to 3wt.%, based on the total weight of the total composition.

Advantageously, the layer (L1) comprises a VDF homopolymer. Layer (L1) may consist essentially of VDF homopolymer.

For the purposes of the present application, the expression "consisting essentially of" is understood to mean that any additional components other than those listed are present in an amount of at most 1wt.%, preferably at most 0.5wt.%, based on the total weight of the given composition, so as not to substantially alter the properties of the composition.

The layer (L1) may have a thickness ranging from 20 to 150 μm, preferably from 30 to 140 μm or from 40 to 130 μm.

The layer (L2) comprises a vinylidene fluoride polymer as defined above, and continuous reinforcing fibers.

As used herein, the term "fiber" has its ordinary meaning as known to those skilled in the art and may include one or more fibrous materials suitable for reinforcing composite structures, i.e., "reinforcing fibers". The term "fiber" as used herein refers to a fiber having a length of at least 0.5 mm. The expression "continuous fibers" indicates fibers having a length of greater than or equal to 3mm, more typically greater than or equal to 10mm, and an aspect ratio of greater than or equal to 500, more typically greater than or equal to 5,000.

The fibers may be organic fibers, inorganic fibers, or mixtures thereof. Suitable fibers for use as the reinforcing fiber component include, for example, carbon fibers, graphite fibers, glass fibers such as E-glass fibers, ceramic fibers such as silicon carbide fibers, synthetic polymer fibers such as aramid fibers, polyimide fibers, high-modulus Polyethylene (PE) fibers, polyester fibers, and polybenzoxazole fibers such as poly-p-phenylene-benzobisoxazole (PBO) fibers, aramid fibers, boron fibers, basalt fibers, quartz fibers, alumina fibers, zirconia fibers, and mixtures thereof.

In one embodiment, the fibers include carbon fibers, glass fibers, or both carbon and glass fibers.

In some embodiments, the fibers comprise at least one carbon fiber. As used herein, the term "carbon fiber" is intended to include graphitized, partially graphitized, and non-graphitized carbon reinforcing fibers, as well as mixtures thereof. Carbon fibers can be obtained by heat treatment and pyrolysis of different polymer precursors like for example rayon, polyacrylonitrile (PAN), aromatic polyamide or phenolic resin; carbon fibers may also be obtained from pitch materials. The term "graphite fibers" is intended to mean carbon fibers obtained by high temperature pyrolysis (above 2000 ℃) of carbon fibers, wherein the carbon atoms are arranged in a similar manner to the graphite structure. The carbon fibers are preferably selected from the group consisting of: PAN-based carbon fibers, pitch-based carbon fibers, graphite fibers, and mixtures thereof. The carbon fibers may be sized or unsized. In one embodiment, the carbon fibers are sized carbon fibers. Suitable sizing for the carbon fibers is one that is thermally compatible with the desired processing temperature and may be selected from, for example, polyamideimide, polyether imide, and polyimide polymers, each of which may optionally include additives, such as nucleating agents, to improve the interfacial properties of the fibers.

In some embodiments, the continuous reinforcing fibers comprise at least one glass fiber. The glass fibers may have a circular cross-section or a non-circular cross-section (e.g., an elliptical or rectangular cross-section). When glass fibers having a circular cross section are used, they preferably have an average glass fiber diameter of 3 to 30 μm, particularly preferably an average glass fiber diameter of 5 to 12 μm. Depending on the type of glass from which they are made, different types of glass fibers having a circular cross section are available on the market. Glass fibers made of E-or S-glass may be cited notably.

In some embodiments, the glass fiber is a standard E-glass material having a non-circular cross-section. In some embodiments, the polymer composition includes S-glass fibers having a circular cross-section.

The fibers may be included in the layer (L2) in a number of different forms or configurations. The continuous fibers may take any of unidirectional, multi-dimensional, nonwoven, woven, knitted, uncrimped, mesh, stitched, entangled, and braided configurations, as well as crimped, felt, and chopped mat structures. In some embodiments, continuous fibers suitable for use with the tube of the present application may be in the form of rovings or tows (including individual tows or rovings, tows/tows or expanded tows). Roving generally refers to a plurality of continuous untwisted fiber filaments, such as glass fibers, optionally reinforced with a chemical bonding material. Similarly, a tow generally refers to a plurality of continuous individual filaments, such as carbon filaments, optionally with an organic coating.

In some embodiments, fibers suitable for use with the tube of the present application may be in the form of unidirectional tapes. As used herein, "belt" means a strip of material having longitudinally extending fibers aligned along a single axis of the strip material. Tapes are advantageous because they can be used in manual or automated layup processes to produce composite materials having relatively complex shapes. In one embodiment, layer (L2) comprises unidirectional continuous fiber reinforced tape.

In general, the continuous reinforcing fibers may comprise at least 15% by volume of the total volume of the layer (L2). Typically, the continuous reinforcing fibers are at least 20%, at least 25%, even at least 30% of the total volume of the layer (L2). The continuous reinforcing fibers are not more than 80%, not more than 75%, or even not more than 70% by volume of the total volume of the layer (L2). The continuous reinforcing fibers may conveniently comprise from 20% to 75%, from 25% to 70%, from 25% to 65% and even from 30% to 60% of the total volume of the layer (L2). The vinylidene fluoride polymer may then occupy the remainder of the volume of the layer (L2).

The layer (L2) may preferably have a thickness ranging from 100 μm to 600 μm, preferably from 150 to 550 μm or from 200 to 500 μm.

Structure of reinforced laminate

The reinforced laminate comprises at least one layer (L1) and at least one layer (L2) as detailed above. The reinforced laminate of the present application may comprise more than one layer (L1) and more than one layer (L2).

The total number of layers (L1) + (L2) in the reinforcement laminate may be any integer ranging from 2 to 40, from 2 to 30, from 3 to 30. In an embodiment of the application, the reinforced laminate has a total number of layers (L1) + (L2) from 4 to 20.

The reinforcement laminate may or may not contain the same number of layers (L1) and (L2). In a preferred embodiment, the number of layers (L1) is equal to or smaller than the number of layers (L2).

When more than one layer (L1) and/or more than one layer (L2) is present in the reinforcement laminate, the layers may be arranged according to any configuration.

In one embodiment, the reinforcement laminate has a construction comprising alternating layers. As an example, in a reinforced laminate comprising a total of 8 layers, wherein 4 layers are layer (L1) and wherein 4 layers are layer (L2), the alternating configuration may be as follows:

-(L1)/(L2)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)。

other non-limiting alternate configurations containing an odd number of layers (L1) + (L2) are, for example:

-(L2)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)；

-(L2)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)。

in another embodiment, layers (L1) and (L2) are arranged in a non-alternating configuration.

In an aspect of the embodiment, the reinforcement laminate may comprise one or more connected layers (L2), at least 2 connected layers (L1) followed by at least 2 alternating layers (L2) and (L1).

Non-limiting examples of constructions according to this aspect of the application are, for example:

-(L2)/(L1)/(L1)/(L2)/(L1)；

-(L2)/(L2)/(L1)/(L1)/(L2)/(L1)；

-(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L1)/(L2)；

-(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)；

-(L2)/(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)/(L1)/(L2)。

it has been found that a construction comprising 1 to 5 connected layers (L2), 2 connected layers (L1) and 2 to 10 alternating layers (L2) and (L1) provides advantageous results in terms of the mechanical properties of the laminate with respect to a reinforced laminate structure comprising only layers (L2).

In another aspect, the reinforcement laminate may include one or more tie layers (L2), at least 2 tie layers (L1), one or more tie layers (L2), one or more tie layers (L1), and one or more tie layers (L2).

-(L2)/(L2)/(L1)/(L1)/(L2)/(L1)/(L2)；

-(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L2)/(L1)/(L2)；

-(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L2)/(L1)/(L1)/(L2)/(L2)；

-(L2)/(L2)/(L2)/(L2)/(L1)/(L1)/(L2)/(L2)/(L1)/(L1)/(L2)/(L2)。

it has been found that a construction comprising 1 to 5 connected layers (L2), 2 connected layers (L1), 2 connected layers (L2), 2 connected layers (L1), and 2 to 10 connected layers (L2) provides advantageous results in terms of the mechanical properties of the laminate relative to a reinforced laminate structure comprising only layers (L2).

Without wishing to be bound by theory, it is believed that in addition to improving certain mechanical properties, layer (L1) also acts as a crack stop, thus reducing crack propagation through the reinforced laminate.

Other layers in the composite pipe

The composite tube may optionally contain other layers in addition to the inner liner and the reinforcement laminate.

The composite tube may advantageously comprise an outer protective layer surrounding the reinforcement laminate. The outer layer protects the reinforced laminate from external exposure to abrasion, wear, chemicals, heat, etc. Each layer of the tube is designed to be just strong enough to withstand the stresses to which it is exposed at its own location within the tube.

The outer layer may be a thermoset or thermoplastic polymer, elastomer, and/or composite, wherein the composite includes a filled polymer composite, a polymer/metal composite, and/or a metal. In some embodiments, the outer layer may include one or more of High Density Polyethylene (HDPE), crosslinked Polyethylene (PEX), vinylidene fluoride polymer, polyamide, polyethylene terephthalate, polyphenylene sulfide, and/or polypropylene. Typical thicknesses of the outer layer may range from 4 to 15mm, from 4 to 10mm.

Manufacture of composite pipe

The composite tube of the present application may be manufactured according to techniques known to those skilled in the art.

The liner is typically prepared by extrusion.

The reinforced laminate may typically be prepared by laminating the layer (L1) and the layer (L2) together in a suitable configuration. The layers (L2) may be arranged in such a way that the continuous fibres in each layer (L2) are at an appropriate angle relative to the continuous fibres in the other layers (L2) to maximize the resistance of the composite tube to internal and external stresses and mechanical stresses generated in use.

Alternatively, the continuous fibers in layer (L2) are aligned in the same direction.

The composite tube according to the application may be manufactured, for example, by winding the reinforcement laminate as detailed above onto a thermoplastic tube (i.e. the inner liner in the finished tube).

In this manufacturing method, a seamless structure may be achieved by completely or partially melting the matrix polymer of the reinforcement laminate and/or thermoplastic inner layer with heat, and then by interconnecting the layers in the molten state.

The reinforcement laminate may be wound onto the liner by winding the reinforcement laminate at a winding angle of 0 ° -180 °, typically 60 ° -140 °, even 70 ° -110 °, 80 ° -100 °. The choice of the winding angle depends on the intended use of the tube and the stresses it will be subjected to. The angles are chosen such that the ability of the tube to withstand axial loads and radial compounding is optimal.

After winding or other manufacturing methods, the thermoplastic composite tube may be coated with an outer layer, such as a thermoplastic or thermosetting polymer layer and/or some other coating material layer, that will adhere to the outermost layer and whose purpose is to protect the thermoplastic composite tube from impact, radiation, thermal effects, combustion, cooling effects, corrosion, and/or other environmental effects.

The manufacture of the composite tube can advantageously be carried out by joining a reinforcing laminate in the form of a tape to the inner liner using the so-called prepreg method. The reinforcing laminate in the form of a strip of suitable width (selected according to the diameter of the core tube and the selected winding angle) is guided from the roll onto the circumference of the rotary liner. Seamless fusion of the reinforcement laminate and the thermoplastic innerliner is achieved by heating the reinforcement laminate to its softening or melting point and then directing the reinforcement laminate onto the surface of the innerliner. In addition, the surface of the liner may also be heated at the melting point such that the outermost surface of the liner will be at a temperature at which softening and/or melting may occur. Fusion can also be ensured by press forming the tube at the melting point by a press roll or the like.

In the tube of the present application, the reinforcement laminate may be integrally attached to the liner. An advantage of the bonded liner is that under certain operating conditions, the outer surface of the tube may be subjected to higher pressures than the interior of the tube. If the liner is not bonded to the reinforcement laminate, external pressure may force the liner to deform and separate from the reinforcement laminate such that the liner collapses.

The disclosure of any patent, patent application, and publication incorporated herein by reference should be given priority to the description of the application to the extent that it may result in the terminology being unclear.

Examples

The present disclosure will now be described in more detail with reference to the following examples, which are intended to be illustrative only and are not intended to limit the scope of the present disclosure.

Raw materials

Layer (L1):1010 (vinylidene homopolymer) 0.25 thick film

Layer (L2): evolite ^TM F1160, available from Solvay, comprises continuous carbon fibers and a unidirectional tape of semi-crystalline vinylidene polymer.

Examples 1 to 3 comparative example 1

The reinforcement laminate was prepared by laying up layers (L1) or (L2) into the following test laminate stack:

the laminate was vacuum bagged and then autoclaved using a straight ramp heating and cooling cycle while applying 635-735mm Hg vacuum. The ramp rate of the temperature rise from 23 ℃ to the highest process temperature is 2-5 ℃/min, while the cooling rate from the highest temperature back to room temperature environment (23 ℃) is 2-7 ℃/min. When the temperature reached the maximum temperature (210 ℃), a pressure of 0.34MPa was then applied, and held at the maximum temperature and pressure for 15 minutes, then cooled under the applied pressure. The pressure applied to the stack is maintained until the stack has cooled to below 93 ℃.

The 90 ° flexural strength of the samples was determined at 23 ℃ according to ASTM D790. The results are reported in figure 1.

The graph of fig. 1 shows that the laminates of examples 1 to 3 have better flex resistance than laminates consisting of layer (L2) alone. The improved resistance to bending corresponds to a better resistance of the laminates according to examples 1 to 3 to stress under the operating conditions of the composite tube.

Claims

1. A composite tube, comprising:

-an inner liner of thermoplastic material, and

a reinforcing laminate surrounding the inner liner,

wherein the reinforcement laminate comprises at least two layers:

-at least one layer (L1) free of reinforcing fibers, such layer comprising a vinylidene fluoride polymer, and

2. The composite tube of claim 1, further comprising an outer protective layer surrounding the reinforcement laminate.

3. The composite tube according to claim 1 or 2, wherein the continuous reinforcing fibers in layer (L2) are selected from the group consisting of: carbon fiber, glass fiber, and mixtures thereof.

4. A composite tube according to any one of claims 1 to 3, wherein the continuous reinforcing fibres constitute at least 15% by volume of the total volume of the layer (L2).

5. The composite tube of any one of claims 1 to 4, wherein the vinylidene fluoride polymer in layer (L1) and/or layer (L2) is a vinylidene fluoride homopolymer.

6. The composite tube of any one of claims 1-5, wherein the reinforced laminate has a total number of layers [ (L1) + (L2) ] comprised between 5 and 20.

7. The composite tube of any one of claims 1 to 6, wherein the reinforcement laminate has a construction comprising alternating layers (L1) and (L2).

8. The composite tube of any one of claims 1 to 6, wherein the reinforcement laminate comprises one or more connected layers (L2), at least 2 connected layers (L1) followed by at least 2 alternating layers (L2) and (L1).

9. The composite tube of claim 8, wherein the reinforcement laminate comprises 1 to 5 contiguous layers (L2), 2 contiguous layers (L1), and 2 to 10 alternating layers (L2) and (L1).

10. The composite tube of any one of claims 1 to 6, wherein the reinforcement laminate comprises one or more tie layers (L2), at least 2 tie layers (L1), one or more tie layers (L2), one or more tie layers (L1), and one or more tie layers (L2).

11. The composite tube of claim 10, wherein the reinforcement laminate comprises 1 to 5 tie layers (L2), 2 tie layers (L1), 2 tie layers (L2), 2 tie layers (L1), and 2 to 10 tie layers (L2).