Reinforced thermoplastic cryostat for high temperature superconductors.

Abstract

The present invention provides a reinforced thermoplastic cryostat for superconductors, the reinforced thermoplastic cryostat including a thermoplastic conduit and a plurality of reinforced thermoplastic tapes helically wrapped around an outer surface of the thermoplastic conduit to provide a reinforced and flexible cryostat that meets desired performance and manufacturing requirements.

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic cryostat for high temperature superconductors (HTS), particularly for use in superconducting cable systems, that is hardened in a manner that provides the desired properties, including mechanical properties and necessary thermo-hydraulic performance, while facilitating a continuous manufacturing process to allow for overall cost reduction. [Background technology]

[0002] The current state of the art in high temperature superconductor (HTS) power cable design involves the use of metal alloy cryostats, typically corrugated tubes, adapted from adjacent industrial applications such as LNG transfer solutions, to house the HTS power cable and transmit pressurized cryogenic fluid to cool the HTS material.

[0003] Metal alloys are neither thermally efficient nor electrical insulators, which poses challenges to the design and reliability of cryostat systems and HTS power cables. A conventional cross-section of an HTS power cable system includes an inner corrugated tube concentrically positioned within an outer corrugated tube. The metal alloy cryostat is designed to mechanically withstand external mechanical loads and support the HTS power cable and cryogenic fluid within the inner corrugated tube. The corrugated tube addresses performance shortcomings of metal alloys, including their coefficient of thermal expansion (CTE), which causes dimensional contraction in both the longitudinal and radial directions. This corrugated structure of the inner corrugated tube creates significant pressure losses for the cryogenic fluid flow, resulting in a shorter longitudinal length of the HTS power cable system before the cryogenic fluid needs to be repressurized.

[0004] Due to the properties of the metal alloy, HTS power cables must include a separate dielectric insulation, typically polypropylene laminated paper with LN2 (PPLP) or equivalent, with the layer thickness proportional to the dielectric strength of the PPLP and LN2 and the voltage of the HTS power cable. Alternatively, the dielectric may be added to the outside of the corrugated cryostat using a conventional insulator such as XLPE. The need for a separate dielectric insulation layer in HTS power cables presumably necessitates a larger outer diameter for the HTS power cables, and therefore, in many embodiments, the inner corrugated tube must have a larger diameter to accommodate the HTS power cable and sufficient cryogenic fluid to achieve the target mass flow rate for cooling the HTS material.

[0005] There are currently no long-distance HTS power cables in operation. The longest is a 12 km project currently under development, which will use a conventional HTS power cable configuration using corrugated steel cryostats.

[0006] Short HTS power cable runs can be constructed using extruded aluminum pipe, stainless steel IC smooth pipe, or lined corrugated cryostats. Smooth-bore stainless steel cryostats are the most common technology for ground-based particle accelerators or LNG transfer pipes. These are typically installed with rolling or expansion devices to accommodate thermal contraction. Common metal alloys, such as stainless steel and aluminum, have large coefficients of thermal expansion / contraction, requiring multiple bellows-type expansion joints to compensate for the longitudinal contraction of the metal pipe when filled with cryogenic fluid. These joints introduce failure points and thermal leak paths into the system, reducing reliability.

[0007] Furthermore, metal alloys and carbon fiber composites are electrical and thermal conductors, requiring insulating layers that increase the overall size of the cryostat, thereby compromising its thermal-hydraulic performance and manufacturing and / or operating costs.

[0008] Smooth-bore metal cryostats cannot be produced in series, require welding in straight sections around 12 m long, and cannot be coiled for transport, increasing the costs of manufacturing, transporting, and deploying such systems. Similarly, carbon fiber thermoset cryostats cannot be coiled due to their high stiffness.

[0009] Corrugated metal cryostats create additional turbulence and friction with the liquid cryogenic fluid, resulting in additional heat generation and higher pressure losses accumulated over shorter distances, requiring additional pressure points in HTS power cable systems. Therefore, long-distance SCS with corrugated IC is not technically feasible.

[0010] Carbon fiber thermoset composites are known in the literature to develop cracks within the material when exposed to cryogenic environments, which could result in permeable leaks of cryogenic liquid into the vacuum chamber, potentially disrupting the operation of the SCS.

[0011] GB2350474A discloses a superconducting power cable that utilizes a polymer liner or cooling tube to provide flexibility. The cooling tube may be wrapped with polymer tape to increase the tube's strength and pressure resistance. To address the issue of temperature-induced distortion when operating at cryogenic temperatures, crimped or convoluted walls may be employed to provide a "bellows" shape.

[0012] All alternative solutions are currently economically and technically impractical for long-range SCS deployments (i.e., 100 km long).

[0013] Therefore, the main design problems and inefficiencies of state-of-the-art HTS power cable systems are as follows: Limited or single functional layer within a cable system, e.g., isolated dielectric insulators on conductors, and metallic cryostats enclosing vacuum and cryogenic fluids. Heat penetration through corrugated metal cryostats, more turbulence in the liquid cryogenic fluid, which generates more heat, higher pressure losses accumulated over shorter distances, which requires more pressurized points in the HTS power cable system, and higher friction coefficients in the cryogenic fluid, which generates more heat. · Larger diameter cryostats are required to accommodate multilayer HTS conductors, resulting in greater radiative heat penetration. -High thermal contraction and expansion rates with temperature changes. · Manufacturing complexity and associated costs. Non-corrugated steel cryostats present reliability challenges and additional transportation and installation complexities. · Lack of optimization of long distance superconducting power cables.

[0014] SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome the above-mentioned problems of the prior art. Summary of the Invention

[0015] According to a first aspect of the present invention, there is provided a reinforced thermoplastic cryostat for high temperature superconductors comprising a thermoplastic conduit and a plurality of reinforced thermoplastic tapes wrapped around an outer surface of the thermoplastic conduit in a helical orientation relative to an axial direction and bonded to the outer surface of the thermoplastic conduit, wherein the combination of the thermoplastic tapes and the cryostat has an axial coefficient of thermal expansion of between ±15e-6 / °C.

[0016] Preferably, the thermoplastic tape extends at a helix angle of between 20° and 50° relative to the axial direction, more preferably less than 45°, most preferably between 25° and 40°.

[0017] Preferably, the two or more thermoplastic tapes extend at different helix angles.

[0018] Preferably, two or more thermoplastic tapes extend in opposite directions around the outer surface of the thermoplastic conduit.

[0019] Preferably, the thermoplastic tapes are arranged in layers.

[0020] Preferably, the thermoplastic tapes of adjacent layers extend in opposite directions around the outer surface of the thermoplastic conduit.

[0021] Preferably, the thermoplastic tape comprises a fiber reinforcement.

[0022] Preferably, the thermoplastic tape comprises a substrate having reinforcing fibers supported thereon.

[0023] Preferably, the fibers have a negative coefficient of thermal expansion.

[0024] Preferably, the thermoplastic conduit comprises a polymer selected from PEEK, PA, PEI, TPI, HDPE, PP, PVDF, PPS, and / or ABS.

[0025] Preferably, the thermoplastic tape comprises a polymer selected from PEEK, PA, PEI, TPI, HDPE, PP, PVDF, PPS, and / or ABS.

[0026] Preferably, the thermoplastic conduit and the thermoplastic tape are constructed from the same material.

[0027] Preferably, the reinforcing fibers of the thermoplastic tape include carbon, glass, aramid, and / or basalt.

[0028] Preferably, the thermoplastic tape comprises a unidirectional fiber reinforced prepreg.

[0029] Preferably, the total radial thickness of the reinforcing tapes is equal to or greater than the radial thickness of the thermoplastic conduit.

[0030] Preferably, the reinforced thermoplastic tape contains 4 to 30 layers, more preferably 6 to 20 layers.

[0031] Preferably, the thermoplastic conduit comprises a smooth bore.

[0032] Preferably, the cryostat comprises at least one impermeable barrier layer.

[0033] Preferably, at least one barrier layer surrounds the thermoplastic tape.

[0034] Preferably, the barrier layer comprises aluminum, steel, EVOH, PET, LCP, PVDC, and / or PVOH.

[0035] Preferably, the cryostat includes a minimum bending radius of at least 0.5 m.

[0036] According to a second aspect of the present invention, there is provided a superconductor cable system comprising a reinforced thermoplastic cryostat according to the first aspect of the present invention, a superconductor extending longitudinally of the cryostat, and a supply of cryogen contained within the cryostat in thermal communication with the superconductor.

[0037] According to a third aspect of the present invention, there is provided a method for manufacturing a reinforced thermoplastic cryostat, comprising the steps of extruding a thermoplastic conduit; wrapping a plurality of reinforced thermoplastic tapes around an outer surface of the thermoplastic conduit in a helical direction at a helical angle relative to an axial direction; and adhering the thermoplastic tapes to the thermoplastic conduit to provide a cryostat having an axial coefficient of thermal expansion between ±15e-6 / °C.

[0038] Preferably, the method comprises wrapping the thermoplastic tape at a helix angle of between 20° and 50° relative to the axial direction, more preferably less than 45°, most preferably between 25° and 40°.

[0039] Preferably, the method includes continuously manufacturing a reinforced thermoplastic cryostat.

[0040] Preferably, the method includes wrapping two or more thermoplastic tapes at different helix angles.

[0041] Preferably, the method includes wrapping the thermoplastic tape around the conduit in a continuous process.

[0042] Preferably, the method includes adhering a thermoplastic tape to the outer surface of the thermoplastic conduit.

[0043] Preferably, the method includes applying heat and / or pressure to the thermoplastic tape to adhere it to the outer surface of the conduit.

[0044] Preferably, the method includes applying a fluid impermeable barrier layer to the cryostat.

[0045] Preferably, the method includes applying and sealing a barrier layer onto the thermoplastic tape.

[0046] Preferably, the method involves wrapping 4 to 30 layers of reinforced thermoplastic tape around the exterior surface of the thermoplastic conduit, more preferably 6 to 20 layers.

[0047] The present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0048] [Figure 1] 1 illustrates a reinforced thermoplastic cryostat according to one embodiment of the present invention. [Figure 2] 2 is a perspective view of one embodiment of a superconducting cable system according to an aspect of the present invention, including the reinforced thermoplastic cryostat shown in FIG. 1; [Figure 3] FIG. 2 is a perspective view of a second embodiment of a superconducting cable system according to an aspect of the present invention. [Figure 4] FIG. 10 is a perspective view showing a third embodiment of a superconducting cable system. [Figure 5] FIG. 10 is a perspective view showing a fourth embodiment of a superconducting cable system according to the present invention. [Figure 6] FIG. 10 is a perspective view showing a fifth embodiment of a superconducting cable system according to the present invention. [Figure 7] FIG. 10 is a perspective view showing a sixth embodiment of a superconducting cable system according to the present invention. [Figure 8] FIG. 10 is a perspective view showing a seventh embodiment of a superconducting cable system according to the present invention. [Figure 9] 1 is a graph showing the tradeoff between coefficient of thermal expansion (CTE), minimum bend radius (MBR), and burst pressure for a cryostat according to the present invention including a PEEK liner wrapped with carbon fiber reinforced PEEK tape wrapped at different angles. [Figure 10] 1 is a graph showing the tradeoff between CTE, MBR, and burst pressure of a cryostat according to the present invention containing a PEI liner wrapped with carbon fiber reinforced PEI tape wrapped at different angles. [Figure 11] 1 is a graph showing the tradeoff between CTE, MBR, and burst pressure of a cryostat according to the present invention containing a PEI liner wrapped with glass fiber reinforced PEI tape wrapped at different angles. [Figure 12] 1 is a graph showing the tradeoff between CTE, MBR, and burst pressure for a cryostat according to the present invention comprising a PA12 liner wrapped with carbon fiber reinforced PA12 tape wrapped at different angles. [Figure 13] 1 is a graph showing the trade-off between CTE, MBR, and burst pressure of a cryostat according to the present invention comprising a PP liner wrapped with carbon fiber reinforced PP tape wrapped at different angles. DETAILED DESCRIPTION OF THE INVENTION

[0049] Referring now to Figure 1 of the accompanying drawings, there is shown a perspective view of a reinforced thermoplastic tubular cryostat, designated generally herein as 10, which is particularly used in various embodiments of superconducting cable systems such as those shown in Figures 2-8, wherein the various embodiments of superconducting cable systems such as those shown in Figures 2-8 each utilize reinforced thermoplastic cryostat 10 to achieve improved performance and / or improved cost efficiency.

[0050] The primary function of cryostat 10 when used in a superconducting cable application is to contain the cryogen and facilitate thermal communication between the superconductor and the cryogen. Cryostat 10 must also provide structural integrity to the pressurized cryogen, be a dielectric insulator, act as a thermal insulator to minimize external heat intrusion, and act as a permeable barrier. Furthermore, to facilitate design and transportation while minimizing the cost of the superconducting cable system, cryostat 10 must have a low axial coefficient of thermal expansion (CTE), preferably near zero, to avoid or reduce the use of conventional bellows-type expansion joints, be capable of being wound on a reel, and be capable of being manufactured in long lengths, e.g., 100 meters or more, preferably 1 km or more, or more preferably 10 km or more.

[0051] Thus, the cryostat 10 includes an inner tubular conduit or liner 12 formed from a thermoplastic material, such as, but not limited to, PEEK, PA, PEI, TPI, HDPE, PP, PVDF, PPS, and ABS. However, it should be understood that other thermoplastic materials or blends thereof may be used. The use of a thermoplastic material allows for relatively low-cost manufacturing, for example, by continuous extrusion of the conduit or liner 12, while providing sufficient flexibility to allow for winding. The thermoplastic material of the liner 12 may be reinforced with additives or fillers to provide desired performance and / or mechanical properties to meet the above or other performance requirements.

[0052] Wrapped around the outer surface of the liner 12 are a plurality of reinforcement bands or tapes 14, which extend in a helical orientation around the liner 12. This helical orientation provides a reinforcement function while maintaining desired overall flexibility and permeability, as will be explained in more detail below. The angle at which the tapes 14 extend relative to the longitudinal axis of the liner 12 (hereinafter referred to as the "helical angle") can be varied to provide different levels or effects of reinforcement. In a preferred arrangement, at least two tapes 14a and 14b extend in opposite directions around the liner 12, i.e., at positive and negative helical angles relative to each other. The helical angle at which the tapes 14 extend has a significant effect on reinforcement performance, as will be explained in more detail below. The tape 14 may also be arranged in a particular layup, for example, having a first layer of one or more tapes 14a extending in a first helical direction to partially or completely encase the liner 12, followed by a second layer of one or more tapes 14b extending in a second helical direction to partially or completely encase the first layer. When multiple layers of tape 14 are provided, the helix angles of adjacent layers preferably alternate between positive and negative angles with each subsequent layer, e.g., +40° for one layer, -40° for the next layer, and then +40° again. A permeable barrier layer 16 is preferably provided around the outermost layer of tape 14 to cover the liner 12 and tape 14 stack and may comprise, for example, aluminum, although it will be understood that any suitable material or combination thereof may be employed. Another example of a metallic material is steel, while suitable polymers include ethylene vinyl alcohol (EVOH), polyethylene terephthalate (PET), liquid crystal polymer (LCP), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVOH), etc. An outer jacket 18 may be provided around the barrier layer 16. Barrier layers 16 may also be provided between layers of tape 14 or around the interior wall of liner 12, or multiple barrier layers 16 may be provided on both the inside and outside of liner 12.

[0053] The tape 14 is preferably formed from a substrate having reinforcing fibers integrated therein or otherwise entrapped or retained therein. The substrate is preferably formed from a thermoplastic material, most preferably the same thermoplastic material as the liner 12, e.g., polyetheretherketone (PEEK), polyamide (PA), polyethyleneimine (PEI), thermoplastic polyimide (TPI), high-density polyethylene (HDPE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyphenylene sulfide (PPS), and acrylonitrile butadiene styrene (ABS), and is used to facilitate in-situ bonding of the tape 14 to the liner 12 during fabrication of the cryostat 10. This may be achieved by any suitable means, such as, for example, the application of heat and / or pressure to bond the tape 14 to the liner 12. The reinforcing fibers may include, for example, carbon, glass, aramid, and / or basalt. As will be described in more detail below, tape 14 may be wrapped continuously around liner 12 and then heat and / or pressure may be applied to bond tape 14 to liner 12.

[0054] Using the tape 14 layup arrangement and specific helix angles, a fully integrated cryostat 10 can be fabricated with an axial CTE near or equal to zero, significantly lower than that of the thermoplastic liner 12 alone. A near-zero CTE is defined herein as within ±15e-6 / °C, more preferably ±5e-6 / °C, and most preferably 0 / °C, at cryogenic operating temperatures, e.g., between −196.3°C and −206.3°C, although it will be understood that other cryogenic temperatures may be required to suit particular applications. The provision of the reinforcing tape 14 does not impair the spoolability of the cryostat 10, and the cryostat 10 is strong enough to sustain typical operating and deployment loads required in superconducting cable applications. As detailed above, the tape 14 layup arrangement is such that the helix angle can be changed from positive to negative after each layer, forming a balanced, symmetrical, biaxial angle stack surrounding the liner 12. For the typical thermoplastic materials listed above, the optimal biaxial angle has been found, both theoretically and experimentally, to be between approximately 20° and 50°, preferably less than 45°, and more preferably between 25° and 40°, depending on the material used. This allows for the production of cryostat 10 with an axial CTE near zero, without a substantial increase in flexural modulus, allowing for winding. Winding at such helix angles is dominated by the strain at break of the thermoplastic substrate of tape 14 rather than the reinforcing fibers. At helix angles greater than 50°, such as 55°, typically used for maximally optimized pressure containment pipe, the thermoplastic begins to dominate the laminate, preventing the axial CTE from approaching zero. At smaller angles, such as 0°, the CTE can approach zero, but the resulting cryostat 10 becomes very stiff, and windability is dominated by the strain at break of the fibers, significantly reducing or preventing windability of the cryostat 10.The optimized angle for minimum axial CTE, reelable stiffness, and strain at break, as well as strength against operational and deployment loads, has been found to be between approximately 20° and 50°, preferably less than 45°, and more preferably between 25° and 40° (positive or negative angles) for the particular balanced layup arrangement described. This arrangement is ideal for long-distance HTS systems. This configuration allows the cryostat 10 to achieve a minimum bend radius of at least 0.5 m when reeled.

[0055] When the total radial thickness of the tape 14 layers is comparable to or greater than the thickness of the thermoplastic liner 12, this axial CTE minimization effect has been found to occur for multiple types of thermoplastic materials and reinforcing tapes 14, with the minimum axial CTE of the cryostat 10 found between 20° and 50°, more preferably between 25° and 40°. When the thickness of the liner 12 is significantly greater than the total thickness of the reinforcing tapes 14, the liner 12 dominates, and achieving an axial CTE of the cryostat 10 close to zero is not feasible. The use of negative CTE fibers, such as carbon fiber or aramid fiber, in the reinforcing tapes 14 further enhances this effect, allowing a negative axial CTE to be achieved. A zero CTE can also be achieved by optimizing the helix angle to a non-minimum angle. A negative CTE can be useful because thermal loads (compressive loads) induced by expansion during cryogenic exposure can counteract the effects of deployment loads (typically pre-tensioned to avoid buckling during deployment and subsea installation). It has also been shown that positive CTE fibers in the tape 14, such as fiberglass or basalt, can create a zero CTE cryostat 10 even though none of the components have a negative or near-zero CTE.

[0056] This phenomenon can be explained by the differential thermal expansion and stiffness of the reinforcing fibers of tape 14 and the thermoplastic substrate, as well as the layup arrangement of the alternating helix angle plies. As the temperature changes, the thermoplastic material cannot expand / contract in the longitudinal fiber direction of each layer of tape 14 due to the high stiffness and relatively low CTE of the reinforcing fibers constraining it compared to the thermoplastic substrate, and therefore the thermoplastic material is forced to move laterally, resulting in a scissoring effect between the oppositely oriented or angled plies of tape 14, which offsets the axial movement of the tape 14 and liner 12 laminate, forming a laminate whose CTE may even be lower than that of the fiber reinforcement.

[0057] The total number of reinforcing layers of tape 14 is determined by the thickness of the liner 12 or by the operating and deployment loads to provide a minimum amount for zero CTE effects. Beyond the liner 12 thickness, the flexural modulus and axial CTE of the cryostat 10 become dominated by the scissoring effect described above and remain relatively constant. As a result, additional reinforcing layers of tape 14 can be added at specific angles to accommodate higher operating and deployment loads as needed without compromising spoolability or CTE. Adding additional layers of tape 14 typically increases the burst strength of the cryostat 10, allowing it to accommodate higher cryogenic fluid pressures, which also typically increases the cryostat 10's tensile capacity for deployment and installation loads, such as those encountered in offshore cable laying operations. Additional layers of tape 14 with different helix angles can be added to the liner 12 and tape 14 stack, as long as the biaxially oriented configuration described above continues to dominate in the radial direction. It may also be beneficial to add additional tapes 14 in different orientations if increased load rating or capacity is desired, but continued biaxial lamination is preferred to avoid microcracking and to create a symmetrical, balanced laminate.

[0058] The addition of the reinforcing tape 14 also improves the permeation performance of the liner 12, as the reinforcing fibers are considered impermeable compared to the thermoplastic substrate of the tape 14. However, care must be taken to avoid microcracking of the laminate when exposed to cryogenic temperatures, as microcracking can occur in the laminate and create leak paths. The biaxial layup described above has been shown to minimize microcracking at cryogenic temperatures compared to other layups, such as cross-ply. Even if microcracking does occur in the laminate, the microcracks do not propagate beyond the reinforcing tape 14, so the liner 12 continues to function as a permeation barrier, preventing leak paths and compromising the vacuum. To improve the permeation performance of a fully reinforced cryostat 10, an additional aluminum film layer can be added beyond the barrier 16. The aluminum film layer can be wrapped and then adhesively secured to the cryostat 10. This creates a vacuum-tight, low-permeability barrier that improves the performance of the cryostat 10.

[0059] Without the use of reinforcing tape 14, thermoplastic cryostats typically have low-to-moderate strength, low stiffness, very high CTE, and moderate-to-high permeability, but are rated as unsuitable for use at cryogenic temperatures and pressures. Thermoplastic materials contract or expand significantly more than metals when subjected to temperature changes, and this phenomenon becomes apparent in cryostats when cryogenic fluids begin to flow. Using a dilatometer conforming to ASTM E228-17, the relative length changes of thermoplastic materials exposed to a temperature change from room temperature to 77 K were measured as follows: PEEK -0.8%, HDPE -2.13%, ABS -1.5% and -1.23%, PA12 -1.64%, and PEI -0.85%. In contrast, the relative length change in an HTS system using a corrugated stainless steel cryostat was approximately -0.29%. If thermoplastic materials were used alone, such high shrinkage would require the use of active thermal expansion management systems, such as bellows or roller-based systems, which would make the systems economically impractical and technically extremely challenging for long HTS cable systems.

[0060] Thermoplastic pipe materials can be filled with polymer blends or fiber reinforcements to lower their CTE. Fillers such as zirconium tungstate, carbon fiber, glass fiber, aramid fiber, and basalt fiber can reduce the CTE of thermoplastic compounds. However, changing the compound's CTE also affects manufacturability and other performance properties, such as stiffness and strength. Thermoplastic materials typically require high volume fractions of fillers to achieve a CTE close to that of stainless steel or aluminum, yet achieving a CTE close to zero is difficult. Adding such amounts of filler typically increases the stiffness of the pipe / cryostat and reduces the strain at break to a level that makes it impossible to coil. For example, adding carbon fiber reinforcement to PEEK at a volume fraction of 20–30% reduces the CTE to a level close to that of stainless steel, but also increases the stiffness to an unusable level and reduces the strain at break of the pipe / cryostat, making coiling impossible. Furthermore, adding a large amount of reinforcement to a thermoplastic material can lead to microcracking upon contact with cryogenic fluids, potentially compromising its structural performance at cryogenic temperatures. Therefore, achieving a zero axial CTE in a thermoplastic cryostat using filler / blend reinforcement alone is technically impractical for long-cable HTS systems because it would be impossible to spool and therefore impossible to transport over long lengths. This would also compromise the integrity of the cryostat's cryogenic retention. The laminated structure of the cryostat 10 of the present invention, including the thermoplastic liner 12 and the surrounding helical reinforcing tape 14, overcomes these problems and enables the use of thermoplastic materials in applications such as superconducting cable assemblies, as detailed in the following examples.

[0061] As detailed above, there are many thermoplastic materials or composites thereof that can be used for the liner 12 and the thermoplastic tape 14. Furthermore, there are many different fibers that can be used to reinforce the tape 14, each with a different fiber content. The tape 14 can be arranged or wrapped around the liner 12 in many different configurations, angles, number of layers, etc., and the dimensions of the liner 12 and tape 14 can also vary. Furthermore, there are variations in the material properties of the components of the cryostat 10, such as Young's modulus, yield strength and strain, ultimate strength, and CTE, all of which vary between room temperature and cryogenic operating temperatures (e.g., −196°C). All of these properties and variables affect the total axial CTE of the cryostat 10. In particular, it has been found that the layup or angle of the tape 14 has a significant effect on the overall axial CTE of the cryostat 10 and can be selected, with precise design, to achieve a desired axial CTE between ±15e-6 / °C, more preferably ±5e-6 / °C, and most preferably zero, regardless of the combination of materials and properties described above.

[0062] 9-13, there are shown a number of graphs illustrating the tradeoffs between the coefficient of thermal expansion (CTE), minimum bend radius (MBR), and burst pressure of a cryostat 10 according to the present invention for a given combination of liner 12, tape 14, and reinforcing fiber materials. Each graph shows several variations of the cryostat 10 in which the tape 14 is wrapped at different angles to illustrate the effect of the tape 14 layup on various desired operating characteristics. It can be seen that to achieve the minimum axial CTE, the tape 14 wrap angle should generally be less than the wrap angle that results in the highest burst strength, which has traditionally been the primary design characteristic. For example, in FIG. 9, a tape wrap angle of 60° results in the highest burst pressure, while an optimal CTE is achieved with a wrap angle of 30°. Wrap angles between 40° and 50° provide an acceptable balance of CTE and MBR. Similar characteristics can be seen for the different material selections graphed in FIGS. 10-13.

[0063] The cryostat 10, whose performance characteristics are graphically represented in Figure 9, includes a PEEK liner 12 with a tape 14 comprising carbon fiber reinforced PEEK, wrapped at an angle between 0° and 90° relative to the longitudinal axis. The polymer liner 12 is PEEK. The liner 12 has a Young's modulus of 4 GPa at room temperature (RT) and a Young's modulus of 5.5 GPa at -196°C. At room temperature, the strength and strain at yield are 51.13 MPa at 1.61% and a maximum stress of 82.5 MPa at 4.14%. At -196°C, the strength and strain at yield are 96.1 MPa at 1.92% and a maximum stress of 168 MPa at 3.5%. The CTE from 25°C to -196°C is 35 ppm / °C. The liner 12 has an inner diameter of 47.4 mm and a wall thickness of 1.7 mm.

[0064] The reinforcing fiber material is a high-strength, high-strain carbon fiber. For example, Hexcel AS4A carbon fiber has a Young's modulus of 231 GPa, a strength of 4431 MPa, and a strain at break of 1.7% at room temperature. Its CTE at 25°C to -196°C is -1 ppm / °C. The reinforcing tape 14 has a fiber volume fraction of 55 to 59% and a thickness of 2 mm. A total of six layers of tape 14 are wound.

[0065] The cryostat 10, whose performance characteristics are plotted in Figure 10, includes a PEI liner 12 and a tape 14 containing carbon fiber-reinforced PEI, wrapped at an angle between 0° and 90° relative to the longitudinal axis. The polymer liner 12 is PEI. The liner 12 has a Young's modulus of 3.1 GPa at room temperature (RT) and a Young's modulus of 4.8 GPa at -196°C. At RT, the strength and strain at yield are 52.7 MPa at 1.9% and a maximum stress of 98 MPa at 5.98%. At -196°C, the strength and strain at yield are 85 MPa at 2.1% and a maximum stress of 155 MPa at 4%. The CTE from 25°C to -196°C is 38 ppm / °C. The liner 12 has an inner diameter of 44.5 mm and a wall thickness of 0.65 mm.

[0066] The reinforcing fiber material is a high-strength, high-strain carbon fiber. For example, Hexcel AS4A carbon fiber has a Young's modulus of 231 GPa, a strength of 4431 MPa, and a strain at break of 1.7% at room temperature. Its CTE at 25°C to -196°C is -1 ppm / °C. The fiber volume fraction of the reinforcing tape 14 is 55 to 59%, and its thickness is 0.13 mm. A total of 12 layers of tape 14 are wound.

[0067] The cryostat 10, whose performance characteristics are graphically represented in Figure 11, includes a PEI liner 12 and a tape 14 containing glass fiber-reinforced PEI, wrapped at an angle between 0° and 90° relative to the longitudinal axis. The polymer liner 12 is PEI. The liner 12 has a Young's modulus of 3.1 GPa at room temperature (RT) and a Young's modulus of 4.8 GPa at -196°C. At RT, the strength and strain at yield are 52.7 MPa at 1.9% and a maximum stress of 98 MPa at 5.98%. At -196°C, the strength and strain at yield are 85 MPa at 2.1% and a maximum stress of 155 MPa at 4%. The CTE from 25°C to -196°C is 38 ppm / °C. The liner 12 has an inner diameter of 44.5 mm and a wall thickness of 0.65 mm.

[0068] The reinforcing fiber material is glass fiber. For example, AGY S-2 glass fiber has a Young's modulus of 86 GPa, a strength of 4600 MPa, and a strain at break of 5.4% at room temperature. The CTE at 25°C to -196°C is +1.6 ppm / °C. The fiber volume fraction of the reinforcing tape 14 is 55 to 59%, and the thickness is 0.25 mm. A total of 10 layers of tape 14 are wound.

[0069] The cryostat 10, whose performance characteristics are graphically represented in Figure 12, includes a PA12 liner 12 and a tape 14 comprising carbon fiber-reinforced PA12, wrapped at an angle between 0° and 90° relative to the longitudinal axis. The polymer liner 12 is PA12. The liner 12 has a Young's modulus of 1.3 GPa at room temperature (RT) and a Young's modulus of 5.2 GPa at -196°C. At room temperature, the strength and strain at yield are 17 MPa at 1.54% and a maximum stress of 40 MPa at 160%. At -196°C, the strength and strain at yield are 78 MPa at 1.69% and a maximum stress of 191 MPa at 11%. The CTE from 25°C to -196°C is 70 ppm / °C. The liner 12 has an inner diameter of 46 mm and a wall thickness of 2 mm.

[0070] The reinforcing fiber material is a high-strength, high-strain carbon fiber. For example, Hexcel AS4A carbon fiber has a Young's modulus of 231 GPa, a strength of 4431 MPa, and a strain at break of 1.7% at room temperature. Its CTE at 25°C to -196°C is -1 ppm / °C. The fiber volume fraction of the reinforcing tape 14 is 55 to 59%, and its thickness is 0.265 mm. A total of 12 layers of tape 14 are wound.

[0071] The cryostat 10, whose performance characteristics are graphically represented in Figure 13, includes a PP liner 12 and a tape 14 comprising carbon fiber reinforced PP, wrapped at an angle between 0° and 90° relative to the longitudinal axis. The polymer liner 12 is PA12. The liner 12 has a Young's modulus of 1.4 GPa at room temperature (RT) and a Young's modulus of 6.3 GPa at -196°C. At room temperature, the strength and strain at yield are 13 MPa at 1.02% and a maximum stress of 25 MPa at 7.57%. At -196°C, the strength and strain at yield are 15 MPa at 0.95% and a maximum stress of 72 MPa at 1.25%. The CTE from 25°C to -196°C is 56.5 ppm / °C. The liner 12 has an inner diameter of 45 mm and a wall thickness of 2 mm.

[0072] The reinforcing fiber material is a high-strength, high-strain carbon fiber. For example, Hexcel AS4A carbon fiber has a Young's modulus of 231 GPa, a strength of 4431 MPa, and a strain at break of 1.7% at room temperature. Its CTE at 25°C to -196°C is -1 ppm / °C. The fiber volume fraction of the reinforcing tape 14 is 55 to 59%, and its thickness is 0.16 mm. A total of 18 layers of tape 14 are wound.

[0073] Thus, from the above examples, it can be seen that there are many factors that affect the overall axial CTE of cryostat 10, which will vary depending on the material combination, properties, and / or dimensions utilized. By selectively designing cryostat 10, the axial CTE can be made very low, or approach zero, avoiding the need for bellows or other expansion joints over long distances. This is particularly beneficial in bulk cryogenic transport and superconducting cable applications, embodiments of which are described in more detail below.

[0074] 2 illustrates a first embodiment of a superconducting cable system according to one aspect of the present invention, generally referred to herein as superconducting cable system 20, which includes a superconductor 22 of a suitable material, which may include a single component or multiple components, such as an array or arrangement of superconducting ribbons. Cable system 20 further includes the aforementioned reinforced thermoplastic cryostat 10, through whose central lumen superconductor 22 extends longitudinally and which, in use, is at least partially filled with a cryogen 24, such as liquid hydrogen, liquid nitrogen, or liquid helium, although other liquid, gas, multiphase cryogens, or combinations of such cryogens are also contemplated. In this manner, superconductor 22 is in thermal communication with cryogen 24 to maintain the cryogenic temperatures necessary for superconductivity.

[0075] In the illustrated embodiment, the superconductor 22 is in direct contact with the cryogen 24 to establish thermal communication; however, as shown in later embodiments, indirect contact between the superconductor and the cryogen may still provide the necessary thermal communication. The operating temperature of the cryogen 24 may vary depending on the operational requirements and / or operating conditions of the cable system 20, or additional or alternative parameters; for example, if liquid nitrogen is used as the cryogen 24, the operating temperature may range from 67 K to 77 K under an operating pressure of 0 bar to 25 bar. However, it should be understood that these are exemplary parameters, and that lower or higher temperatures and / or pressures may be employed. It should also be understood that the superconductor 22 may be eccentrically positioned, helically extending, or in other similar configurations, as long as it extends longitudinally relative to the overall length of the cable system 20.

[0076] The cable system 20 further includes an insulating layer 26 surrounding the cryostat 10 and an outer cryostat 28 surrounding and housing the aforementioned components. To provide additional thermal insulation, an annular vacuum cavity 30 is defined between the inner cryostat 10 and the outer cryostat 28. The vacuum drawn within the annular vacuum cavity 30 reduces thermal convection within the cable system 20 and, in the illustrated embodiment, may be in the range of 1 to 1000 Pa, although other vacuum levels, such as hard or soft vacuums, may also be employed. A central support element 32 may optionally be provided within the annular vacuum cavity 30 to physically maintain the correct position of the inner cryostat 10 concentrically or otherwise with the outer cryostat 28 and to ensure a preferably uniform annular vacuum cavity 30. The outer cryostat 28 provides environmental protection for the cable system 20, reducing heat loss, preventing the penetration of contaminants such as particulate matter, and providing structural protection against surrounding environments, such as bodies of water, that may exert significant pressure on the outer cryostat 28. The outer cryostat 28 is preferably a multi-layer structure including a smooth-bore steel pipe or a corrugated steel pipe jacket for environmental protection. Alternatively, the outer cryostat 28 may include a polymer pipe with one or more optional electrical insulation layers (not shown) and / or a permeation barrier layer, which may be metal, for example. The central support element 32 may be of any suitable shape, configuration, and material and, in the illustrated embodiment, is helical so as to extend around the circumference of the annular cavity 30. Finally, the cable system 20 may include an external ballast 34 to ensure that the cable system 20 is submerged when deployed underwater, such as in a subsea application.

[0077] The use of a novel reinforced thermoplastic cryostat 10 provides the necessary performance characteristics, particularly a zero or near-zero axial CTE, to avoid or minimize thermal expansion / contraction issues during use. This avoids or significantly reduces the need for thermal expansion management systems, such as bellows-based expansion joints. Therefore, IC reliability and performance are improved while maintaining a smooth bore pipe geometry. This minimizes pressure loss compared to corrugated cryostats, thereby enabling longer superconducting cable systems. The liner 12 can be manufactured by extrusion, a continuous and inexpensive manufacturing process for thermoplastic materials. Furthermore, layers of reinforcing tape 14 can be subsequently added to the liner 12 by continuous additive manufacturing methods (automated tape winding, automated fiber placement, or similar), and then bonded in situ by applying heat and force to the liner 12 and tape 14 to form a fully bonded cryostat 10. The reinforcing tape 14 can be wrapped at the desired helix angle(s) during this continuous process. The technical performance of the fully bonded cryostat 10 can be varied as needed depending on many factors, such as the material of the liner 12, the material of the tapes 14 (both substrate and fiber), their respective dimensions, and the wrap angle of each reinforcing tape 14 and their arrangement (lay-up).

[0078] 3, a second embodiment of a superconducting cable system in accordance with the present invention is illustrated and is generally designated herein as superconducting cable system 120. In this second embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0079] The cable system 120 comprises a superconductor 122 configured with an inner superconducting element 122a, a first coaxial superconducting element 122b surrounding the inner element 122a and separated therefrom by an insulating layer 126, and a second coaxial superconducting element 122c surrounding the first coaxial superconducting element 122b and separated therefrom by an insulating layer 126. This arrangement is selected to conduct three-phase AC current. Of course, it will be understood that unipolar or biaxial bipolar DC conductors (not shown) can be used as alternatives. The superconductor 122 is coaxially disposed within the bore of the aforementioned reinforced thermoplastic cryostat 10, which contains a cryogen 124 within which the superconductor 122 is enclosed, establishing thermal communication therebetween. The thermal insulation layer 126 surrounds the inner cryostat 10 and may be in any suitable form including, for example, one or more of aerogel, nanoporous insulation, layered composite insulation, multi-layer insulation, or a thermal blanket.

[0080] An outer cryostat 128 surrounds the insulated inner cryostat 10, and a vacuum annular cavity 130 is defined between the inner cryostat 10 and the outer cryostat 128 to provide further insulation. An optional central support element 132 may be provided in the vacuum annular cavity 130 to physically maintain the correct position of the inner cryostat 10 concentrically or otherwise with the outer cryostat 128 to ensure a uniform vacuum annular region.

[0081] 4 is a diagram illustrating a third embodiment of a superconducting cable system in accordance with the present invention, generally designated herein as superconducting cable system 220. In this third embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0082] The cable system 220 comprises a superconductor 222 in a three-core, triaxial configuration including a first superconducting element 222a, a second superconducting element 222b, and a third coaxial superconducting element 222c arranged in a circular array to facilitate three-phase alternating current. The superconductor 222 is longitudinally disposed within the lumen of the reinforced thermoplastic cryostat 10, which includes a cryogen 224 surrounding the superconductor 222 and establishing thermal communication therebetween. A thermal insulation layer 226 surrounds the cryostat 10 and may be of any suitable form as previously described herein. An outer cryostat 228 surrounds the insulated inner cryostat 10, defining a vacuum annular cavity 230, which may include an optional central support element 232.

[0083] 5 is a diagram illustrating a fourth embodiment of a superconducting cable system in accordance with the present invention, generally designated herein as superconducting cable system 320. In this fourth embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0084] The cable system 320 includes a tubular superconductor 322 that is longitudinally positioned against and in thermal communication with the exterior surface of the first example reinforced thermoplastic cryostat 10. The cryostat 10 includes a cryogen 324, and the superconductor 322 is in thermal communication through the cryostat 10, which provides structural integrity to contain the pressurized cryogen 324 and acts as a permeation barrier.

[0085] The cable system 320 further includes a second instance of a cryostat 10' that surrounds the first or inner cryostat 10 and also includes a stack of liner and reinforcing tapes. However, the second cryostat 10' may have a thinner radial thickness or tape reinforcement, for example, if the second cryostat 10 is not subject to internal pressurization that may occur in a purely cryostat 10. The second cryostat 10' may therefore have a design and dimensions suited to lower structural and mechanical requirements and may not alone provide sufficient dielectric strength, merely providing minor mechanical protection for the superconductor 322. Accordingly, additional electrical and / or mechanical layers may be provided between the superconductor 322 and the second cryostat 10'.

[0086] An insulating layer 326 externally surrounds the second cryostat 10' and may be in any suitable form as previously described herein. An outer cryostat 328 surrounds the two cryostats 10, 10' and defines an evacuated annular cavity 330 therebetween, in which an optional central support element 332 may be provided. An optional ballast 334 may preferably be provided around the exterior of the outer cryostat 328.

[0087] 6 is a diagram illustrating a fifth embodiment of a superconducting cable system in accordance with the present invention, generally designated herein as superconducting cable system 420. In this fifth embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0088] 6, but includes a tubular three-phase coaxial superconductor 422 longitudinally disposed relative to and in thermal communication with the exterior surface of the reinforced thermoplastic cryostat 10. The superconductor 422 includes an inner tubular superconducting element 422a, a first tubular coaxial superconducting element 422b surrounding the inner element 422a and separated therefrom by an insulating layer 426, and a second tubular coaxial superconducting element 422c surrounding the first coaxial superconducting element 422b and separated therefrom by a further insulating layer 426. This arrangement is selected for conducting three-phase alternating current.

[0089] The cryostat 10 contains a cryogen 424 with which a superconductor 422 is in thermal communication through the cryostat 10. The cable system 420 further includes a second cryostat 10' surrounding the first cryostat 10. A thermal insulation layer 426 surrounds the second cryostat 10 and may be of any suitable form. An outer cryostat 428 surrounds the insulated cryostats 10, 10', defining an evacuated annular cavity 430 therebetween, which may include an optional central support element 432.

[0090] 7 is a diagram illustrating a sixth embodiment of a superconducting cable system in accordance with the present invention, generally designated herein as superconducting cable system 520. In this sixth embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0091] The cable system 520 includes a single-phase superconductor 522 and is longitudinally disposed against and in thermal communication with the exterior surface of the reinforced thermoplastic cryostat 10. The cryostat 10 contains a cryogen 524 with which the superconductor 522 is in thermal communication through the cryostat 10.

[0092] The cable system 520 further includes a second cryostat 10' surrounding the first cryostat 10. The second cryostat 10' defines a second lumen containing a second supply of cryogen 524 to provide improved thermal performance. This second supply may contain a different cryogen 524 than that contained within the cryostat 10. An electrical and / or mechanical layer 526 may be provided between the superconductor 522 and the second cryostat 10'.

[0093] An insulating layer 526 surrounds the second cryostat 10', and an outer cryostat 528 surrounds the insulated inner cryostats 10 and 10', defining a vacuum annular cavity 530 therebetween, and an optional central support element 532 may be provided.

[0094] 8 is a diagram illustrating a seventh embodiment of a superconducting cable system in accordance with the present invention, generally designated herein as superconducting cable system 620. In this seventh embodiment, like components are designated with like reference numerals and perform like functions unless otherwise specified.

[0095] The cable system 620 comprises a single-phase superconductor 622 of suitable form, extending longitudinally, preferably coaxially, within the lumen of the reinforced thermoplastic cryostat 10, which is filled with a cryogen 624. In this manner, the superconductor 622 is in direct thermal communication with the cryogen 624 to maintain the cryogenic temperatures necessary for superconductivity. The single-phase superconductor 622 may, of course, be replaced by a multi-phase superconductor, as previously described herein.

[0096] The cable system 620 further includes a second cryostat 10' surrounding the first cryostat 10. The second cryostat 10' defines a second lumen containing a second supply of cryogen 624, which may be the same as or different from the cryogen 624 contained within the first cryostat 10 and may be maintained at a different temperature, to provide improved thermal performance. An insulating layer 626 surrounds the second cryostat 10', and an outer cryostat 628 surrounds the insulated inner cryostats 10 and 10', defining a vacuum annular cavity 630 therebetween, and an optional central support element 632 may be provided.

[0097] The present invention is not limited to the embodiments described herein, which can be modified or varied without departing from the scope of the invention.

Claims

1. 1. A reinforced thermoplastic cryostat for high temperature superconductors, comprising: a thermoplastic conduit; and a plurality of reinforced thermoplastic tapes wound axially helically around an outer surface of the thermoplastic conduit and bonded to the outer surface of the thermoplastic conduit, wherein the combination of the thermoplastic tapes and the cryostat has an axial coefficient of thermal expansion between ±15e-6 / °C.

2. 2. The reinforced thermoplastic cryostat of claim 1, wherein the thermoplastic tape extends at a helix angle relative to the axial direction of between 20° and 50°, more preferably less than 45°, and most preferably between 25° and 40°.

3. 3. The reinforced thermoplastic cryostat of claim 1 or 2, wherein two or more of the thermoplastic tapes extend at different helical angles.

4. A reinforced thermoplastic cryostat according to any preceding claim, wherein two or more of the thermoplastic tapes extend in opposite directions around the outer surface of the thermoplastic conduit.

5. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic tapes are arranged in layers.

6. 6. The reinforced thermoplastic cryostat of claim 5, wherein the thermoplastic tapes of adjacent layers extend in opposite directions around the outer surface of the thermoplastic conduit.

7. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic tape comprises reinforcing fibres.

8. 6. The reinforced thermoplastic cryostat of claim 5, wherein the reinforcing fibers have a negative coefficient of thermal expansion.

9. 7. A reinforced thermoplastic cryostat according to claim 5 or 6, wherein the thermoplastic tape comprises a substrate on which the reinforcing fibers are held.

10. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic conduit comprises a polymer selected from PEEK, PA, PEI, TPI, HDPE, PP, PVDF, PPS and / or ABS.

11. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic tape comprises a polymer selected from PEEK, PA, PEI, TPI, HDPE, PP, PVDF, PPS and / or ABS.

12. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic conduit and the thermoplastic tape comprise the same material.

13. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the reinforcing fibres of the thermoplastic tape comprise carbon, glass, aramid and / or basalt.

14. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic tape comprises unidirectional fiber reinforced prepreg.

15. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic tape comprises unidirectional fiber reinforced prepreg.

16. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the sum of the radial thicknesses of the reinforcing tapes is equal to or greater than the radial thickness of the thermoplastic conduit.

17. A reinforced thermoplastic cryostat according to any of the preceding claims, wherein the number of layers of the reinforced thermoplastic tape is between 4 and 30, more preferably between 6 and 20.

18. 10. A reinforced thermoplastic cryostat according to any preceding claim, wherein the thermoplastic conduit comprises a smooth bore.

19. 10. A reinforced thermoplastic cryostat according to any preceding claim, comprising at least one impermeable barrier layer.

20. 20. The reinforced thermoplastic cryostat of claim 19, wherein the at least one barrier layer surrounds the thermoplastic tape.

21. 21. The reinforced thermoplastic cryostat of claim 19 or 20, wherein the barrier layer comprises aluminum, steel, EVOH, PET, LCP, PVDC, and / or PVOH.

22. 10. A reinforced thermoplastic cryostat according to any preceding claim, having a minimum bending radius of at least 0.5 m.

23. 10. A superconducting cable system comprising a reinforced thermoplastic cryostat according to any preceding claim, a superconductor extending longitudinally of said cryostat, and a cryogen supply contained within said cryostat in thermal communication with said superconductor.

24. 1. A method of manufacturing a reinforced thermoplastic cryostat for a superconducting cable system, the method comprising the steps of extruding a thermoplastic conduit, wrapping a plurality of reinforced thermoplastic tapes axially and helically around an outer surface of the thermoplastic conduit, and adhering the thermoplastic tapes to the thermoplastic conduit such that the cryostat has an axial coefficient of thermal expansion between ±15e-6 / °C.

25. 25. The method of claim 24, comprising winding the thermoplastic tape at a helix angle relative to the axial direction of between 20° and 50°, more preferably less than 45°, and most preferably between 25° and 40°.

26. 26. The method of claim 24 or 25, comprising continuously manufacturing the reinforced thermoplastic cryostat.

27. The method of any of claims 24 to 26, comprising winding two or more of the thermoplastic tapes at different helix angles.

28. The method of any of claims 24 to 27, comprising wrapping the thermoplastic tape around the conduit in a continuous process.

29. A method according to any one of claims 24 to 28, comprising applying heat and / or pressure to the thermoplastic tape to adhere it to the outer surface of the conduit.

30. A method according to any one of claims 24 to 29, comprising applying a fluid-impermeable barrier layer to the cryostat.

31. The method of any of claims 24 to 30, comprising applying and sealing the barrier layer over the thermoplastic tape.

32. 32. The method of any one of claims 24 to 31, comprising wrapping the reinforced thermoplastic tape around the outer surface of the thermoplastic conduit in 4 to 30 layers, more preferably 6 to 20 layers.

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