"Multilayer pipe and use of a multilayer pipe"

Abstract

The present invention relates to a multilayer pipe (1) for conveying a hydrogen-containing fluid. The multilayer pipe (1) comprises at least an inner layer (2) forming a receiving chamber (7) for the fluid, a barrier layer (3) surrounding the inner layer (2), a middle layer (4) surrounding the barrier layer (3), a pressure-bearing layer (5) surrounding the middle layer (4), and an outer layer (6) surrounding the pressure-bearing layer (5). According to the invention, the middle layer (4) is made of a mixture of a thermoplastic elastomer (TPE) and an adhesion promoter or of a mixture of a thermoplastic vulcanizate (TPV) and an adhesion promoter. The invention further relates to the use of the multilayer pipe (1) in a medium-pressure system.

Description

[0001] The invention relates to a multilayer pipe for conveying a hydrogen-containing fluid, and to a use of this multilayer pipe.

[0002] Hydrogen is becoming increasingly important for energy production. It is typically stored under high pressure in a tank. For example, pressures in hydrogen tanks for vehicles can reach several hundred bar, particularly up to 700 bar. To transport the hydrogen or a hydrogen-containing fluid from the tank to its point of use, such as a fuel cell, the pressure of the fluid (pure hydrogen or a hydrogen-containing fluid) is reduced in a pressure regulator, usually to a pressure of 30 bar or less. The fluid is then distributed to its point of use via a medium-pressure system. Traditionally, this system consists of metallic pipes supplemented by braided elastomer hoses to compensate for installation and manufacturing tolerances. This multi-part pipe construction results in a high installation effort.Furthermore, both the metallic cables and the braided elastomer hoses are very heavy.

[0003] Multilayer pipes for fuel lines, i.e., lines for gasoline, diesel, kerosene, and the like, are generally known from the prior art. For example, a multilayer fuel line is known from DE 10 2011 089 616 A1. This fuel line has an inner layer of polyethylene, an outer layer of polyamide, and a barrier layer arranged between the inner and outer layers, which can be made of ethylene-vinyl alcohol copolymer (EVOH). An adhesion promoter layer can be arranged adjacent to the barrier layer. While the inner polyethylene layer prevents the oligomers from being washed out, it has only low stability, pressure resistance, and temperature resistance. To increase stiffness and thus pressure resistance, the outer layer is made of polyamide, which also leads to increased production costs.

[0004] An alternative design of a multilayer hose for automotive lines is described in EP 1 362 890 A1. The outer layer of this hose has a greater hardness than all the inner layers. The outer layer is made of polyamide. The inner layers are made of a thermoplastic elastomer. With this multilayer hose as well, stability, pressure resistance, and temperature resistance depend significantly on the thickness of the individual layers. Furthermore, hydrogen penetrates the wall of the multilayer hose and can escape from it.

[0005] The invention is based on the objective of providing a multilayer pipe for conveying a hydrogen-containing fluid, which reduces hydrogen permeation, exhibits improved flexibility and pressure resistance, has the lowest possible weight, and reduces assembly effort. Furthermore, the invention is based on the objective of providing a use for this multilayer pipe.

[0006] The object of the invention is achieved by a multilayer tube according to claim 1. The multilayer tube has at least one inner layer, which forms a receiving space for the fluid, a barrier layer surrounding the inner layer, a middle layer surrounding the barrier layer, a pressure-bearing layer surrounding the middle layer, and an outer layer surrounding the pressure-bearing layer. Furthermore, it is provided that the middle layer is made of a mixture of a thermoplastic elastomer (TPE) and an adhesion promoter or of a mixture of a thermoplastic vulcanizate (TPV) and an adhesion promoter. Because the multilayer tube according to the invention has several layers, the different layers can perform different functions. For example, the inner layer forms the receiving space for the fluid. The barrier layer serves as a barrier to prevent hydrogen from escaping, i.e., to reduce hydrogen permeation.The pressure-bearing layer provides stability to the multilayer pipe against the operating pressure of the fluid. This increases the pressure resistance and prevents the multilayer pipe from bursting. The outer layer protects the pressure-bearing layer from external influences. If the middle layer were made of only a thermoplastic material, the pressure-bearing layer and the barrier layer, in particular, would shift relative to each other.In contrast, the middle layer, which is a mixture, or compound, of a thermoplastic material, namely TPE or TPV, and an adhesion promoter, surprisingly causes the middle layer to bond with the layers immediately adjacent to it, such as the barrier layer and / or the bearing layer. This creates an adhesive bond between the middle layer and the layers adjacent to it, without requiring any additional manufacturing effort. At the same time, this structure allows the use of lightweight materials like TPE and TPV, thus reducing the weight of the multilayer tube and also improving its flexibility.This flexible multilayer pipe can compensate for installation and manufacturing tolerances during assembly in a medium-pressure system without requiring additional pipe sections made of a different material, thus reducing the assembly effort.

[0007] In particular, it is provided that the inner layer at least partially, and preferably completely, encloses the receiving space. Furthermore, it can be provided that the barrier layer partially or completely surrounds the inner layer, and / or that the middle layer partially or completely surrounds the barrier layer, and / or that the pressure-bearing layer partially or completely surrounds or envelops the middle layer, and / or that the outer layer partially or completely surrounds or envelops the pressure-bearing layer. Preferably, each layer is completely surrounded or enveloped by the layer surrounding it. It should be noted that preferably the respective thickness of each layer—i.e., the inner layer, the barrier layer, the middle layer, the pressure-bearing layer, and the outer layer—is essentially constant around the circumference of the multilayer tube.

[0008] A “hydrogen-containing fluid” within the meaning of the present invention is understood to be a fluid in which H2 molecules are present. This can be, for example, pure hydrogen in a gaseous and / or liquid state. However, a mixture of hydrogen and one or more other fluids is also a hydrogen-containing fluid within the meaning of the present invention.

[0009] The fluid can flow through the receiving chamber particularly efficiently if the receiving chamber has a round, and especially circular, cross-section. It is also advantageous if the inner layer has a round, and especially circular, cross-section. Furthermore, it is advantageous if the barrier layer and / or the middle layer and / or the pressure-bearing layer and / or the outer layer have a round, and especially circular, cross-section. It is preferably provided that the inner layer, the barrier layer, the middle layer, the pressure-bearing layer, and the outer layer are arranged concentrically around a common center point, preferably around the center point of the receiving chamber or around a centroid of the cross-section of the receiving chamber.

[0010] In particular, it is intended that the barrier layer will allow a hydrogen permeation of no more than 20 Ncm. 3The hydrogen permeation is determined according to test 6.7 of ISO 12619-14. (Ncm) 3 “ describes a standard cubic centimeter, i.e., the amount of fluid that occupies a volume of 1 cm³ at 1.01325 bar and 273.15 K (0 °C) 3 is included.

[0011] It is specifically stipulated that the pressure-retaining layer must have a burst pressure of at least 63 bar at 90 °C. The burst pressure at 90 °C is determined according to test 6.2 of ISO 12619-14. If the pressure-retaining layer has a burst pressure of at least 63 bar at 90 °C, permanent resistance to an operating pressure of up to 30 bar can be ensured. Additionally or alternatively, it is specifically stipulated that the pressure-retaining layer must have a burst pressure of at least 84 bar at room temperature. The burst pressure at room temperature is determined analogously to test 6.2 of ISO 12619-14.

[0012] To increase sustainability, it may be considered to use a TPE or TPV that contains thermoplastic recyclates, for example recycled polypropylene.

[0013] The thermoplastic vulcanizate can have a matrix made of a thermoplastic polymer, for example, polypropylene (PP). Preferably, rubber, preferably ethylene propylene diene monomer (EPDM) rubber, is incorporated into the matrix, particularly compounded into it. Such TPVs are known, for example, under the trade name Santoprene (a trademark of Celanese International Corporation).

[0014] In particular, it is provided that the outer layer has an adhesion promoter, preferably the same adhesion promoter as the middle layer. Alternatively or additionally, it is particularly provided that the outer layer forms an adhesive bond with the layer directly adjacent to the outer layer, preferably with the substrate layer. The adhesive bond can be created via a chemical reaction, for example by fusion. Preferably, an adhesive bond between the outer layer and the substrate layer can have a resistance, for example against relative movement between the outer layer and the substrate layer, that is greater than the resistance of an adhesive bond between the middle layer and the layer adjacent to the middle layer, for example the substrate layer.

[0015] In an advantageous embodiment of the invention, the barrier layer is arranged directly on the inner layer, and / or the middle layer directly on the barrier layer, and / or the pressure-bearing layer directly on the middle layer, and / or the outer layer directly on the pressure-bearing layer. In particular, when the barrier layer is arranged directly on the inner layer, the middle layer directly on the barrier layer, the pressure-bearing layer directly on the middle layer, and the outer layer directly on the pressure-bearing layer, the weight of the multilayer pipe can be reduced while maintaining high compressive strength. The wall thickness of the multilayer pipe then results at least from the sum of the thicknesses of the inner layer, the barrier layer, the middle layer, the pressure-bearing layer, and the outer layer.

[0016] Preferably, the outer layer is not surrounded by any further layer.

[0017] In particular, it is intended that the adhesion promoter of the middle layer be a polyolefin-based adhesion promoter. A polyolefin-based adhesion promoter allows for simultaneous adhesion to the barrier layer and to the substrate layer, especially to polyamide or polypropylene fibers of the substrate layer. It is further advantageous if the adhesion promoter is a thermoplastic polymer doped with maleic anhydride (MAH).

[0018] The manufacturing effort for the multilayer pipe can be further reduced if the maleic anhydride (MAH)-doped thermoplastic is polyethylene (PE) or polypropylene (PP). The flexibility-stiffness ratio of the multilayer pipe can be improved if the thermoplastic is low-density polyethylene (LDPE), preferably linear low-density polyethylene (LLDPE). A known adhesion promoter is offered under the trade name Orevac 18341. Orevac is a trademark of SK FUNCTIONAL POLYMER, a simplified joint-stock company.

[0019] Surprisingly, it has been found that particularly good adhesion can be achieved when the adhesion promoter in the middle layer comprises at least 35% by weight of the middle layer, in particular at least 40% by weight, preferably at least 50% by weight, and / or at most 60% by weight of the middle layer. A mixture for the middle layer consisting of 50% by weight adhesion promoter and 50% by weight of thermoplastic vulcanizate has proven to be particularly effective.

[0020] To further reduce manufacturing costs, the outer layer can be made of the same material as the middle layer. Furthermore, it is advantageous to use TPV for the outer layer, as TPV has low moisture absorption compared to many other thermoplastic materials. In particular, when the outer layer is made of TPV, very good resistance to external media, such as zinc chloride, is achieved.

[0021] The pressure-bearing layer serves to prevent deformation of the multilayer tube due to excessive fluid operating pressure. To further improve resistance to fluid operating pressure, the pressure-bearing layer may be provided with fibers, specifically polyamide (PA) and / or polypropylene (PP) fibers. In particular, the pressure-bearing layer is provided with polyamide fibers (PA) or polypropylene fibers (PP). A mixture of PA and PP fibers is also possible. Polyaramid fibers may also be provided additionally or alternatively. Furthermore, it is preferably provided that the fibers have a core and a sheath, with the core and sheath preferably being made of different materials. For example, it is provided that some, preferably all, of the fibers have a polyester (PES) core and the sheath is made of polypropylene.The use of polypropylene makes it possible to provide an adhesion promoter-free outer layer, for example, an outer layer consisting solely of TPV. Specifically, the substrate layer is designed to have coated polyamide fibers, and these fibers are electrically discharged before being coated with the outer layer, for example, by corona discharge activation. For bonding with the outer layer, an outer layer consisting of a mixture of TPV and an adhesion promoter is provided for the electrically discharged substrate layer. Alternatively or additionally, the substrate layer is designed to have PA fibers with a silane sizing.

[0022] The application of the print carrier layer can be facilitated if, alternatively or additionally, the print carrier layer is provided to be a braid. In particular, the braid consists of interwoven fibers. Preferably, the braid is a biaxial braid, more preferably a biaxial 2D circular braid. For example, the individual fibers of the braid can comprise polyamide fibers and / or polypropylene fibers. For example, it is provided that the braid is made of polypropylene fibers and polyamide fibers, in particular parallel polypropylene and polyamide fibers. Braids made of polyamide fibers are commercially available. Polypropylene fibers can be bonded to a middle layer containing polypropylene, for example, after or during an extrusion process.To increase the stability of the multilayer tube, it is particularly provided that the braid has a coverage of at least 50%, preferably at least 80%, more preferably at least 100%, and most preferably 100%. The higher the coverage, the less material from the adjacent layer, for example, the middle layer, can penetrate the bearing layer. With a coverage of 100%, the braid is essentially, preferably completely, free of gaps. Alternatively or additionally, it is particularly provided that the braid has a braiding angle of less than 90°, preferably between 15° and 75°, more preferably between 30° and 60°, more preferably between 45° and 60°, and most preferably 54°. The braiding angle extends between a longitudinal axis, in particular a central longitudinal axis of the multilayer tube, and a fiber of the braid.

[0023] To achieve sufficient stiffness, the pressure carrier layer may have a thickness of at least 0.2 millimeters (0.2 mm). The wall thickness of the multilayer tube can be reduced if the pressure carrier layer has a thickness of no more than 0.4 millimeters. Preferably, the pressure carrier layer has a thickness between 0.2 millimeters and 0.4 millimeters, preferably 0.4 millimeters. If the pressure carrier layer is a braid, its thickness may be at least one layer thickness of the braid, for example, exactly one layer thickness or exactly two layer thicknesses. In the case of two layer thicknesses, the braid is wrapped twice around the middle layer. One layer thickness of the pressure carrier layer is defined as one layer of the braid surrounding the middle layer.

[0024] To reduce hydrogen permeation, the barrier layer can be made using ethylene-vinyl alcohol copolymer (EVOH). EVOH provides a good barrier against hydrogen and can also be thermoplastically processed. The thermoplastic processability of at least the middle layer and the pressure support layer simplifies the production of the multilayer tube. To increase flexibility, the barrier layer can be made from a mixture of ethylene-vinyl alcohol copolymer (EVOH) and an elastic thermoplastic, preferably a thermoplastic elastomer (TPE).The manufacturing effort for the barrier layer can be reduced while simultaneously providing a sufficient barrier against hydrogen permeation if the ethylene-vinyl alcohol copolymer (EVOH) has an ethylene content of at most 30 mol%, preferably at most 27 mol%. To improve the adhesion between the barrier layer and the middle layer, it is preferably the case that the barrier layer is produced using EVOH and the middle layer contains MAH as an adhesion promoter.

[0025] To avoid negatively impacting the barrier layer's barrier properties, it can be designed to have a thickness of at least 0.1 millimeters. The weight of the multilayer pipe can be reduced and its flexibility improved, particularly if the barrier layer has a thickness of no more than 0.3 millimeters, preferably no more than 0.2 millimeters. Preferably, the barrier layer has a thickness between 0.1 millimeters and 0.2 millimeters, more preferably 0.1 millimeters.

[0026] In particular, the inner layer is designed to form a protective layer for the barrier layer. Especially if the barrier layer is manufactured using EVOH, it is essential to prevent it from being exposed to moist hydrogen. If EVOH is exposed to moist hydrogen, its moisture content increases, and its barrier capacity, and consequently that of the barrier layer, decreases. Therefore, the inner layer can extend the service life of the barrier layer and thus of the multilayer pipe.

[0027] Manufacturing costs can be further reduced if the inner layer is made of the same material as the middle layer. Furthermore, if the outer layer is made of the same material as both the middle and inner layers, manufacturing costs can be reduced even further.

[0028] Alternatively, the inner layer can be made of an electrically conductive material. An inner layer of electrically conductive material acts as a protective layer for the pressure-bearing layer and allows electrostatic charges to dissipate. This increases the safety of the multilayer pipe and any medium-pressure system in which it is used. Specifically, it is provided that, when installed, for example, in the medium-pressure system, the multilayer pipe is electrically connected to a ground point. This can be achieved by connecting each of the two ends of the multilayer pipe to a conductive connector, and connecting these connectors to the ground, for example, a vehicle ground point.

[0029] The adhesion between the inner layer and the barrier layer can be improved if the inner layer is made of an electrically conductive doped and adhesion-modified material. Specifically, the inner layer is made of an electrically conductive doped and adhesion-modified thermoplastic vulcanizate (TPV). For this purpose, a material known under the trade name Nylabond (registered European trademark of Miller Waste Mills, Inc. d / b / a RTP Company) can be used, for example. Additionally or alternatively, it is preferably provided that the inner layer comprises carbon fibers, preferably carbon nanofibers, and / or carbon black, for example conductive carbon black.Preferably, the inner layer is made of an adhesion-modified TPV containing carbon black, for example conductive carbon black, preferably compounded with carbon black, for example conductive carbon black. For example, the carbon nanofibers can be formed as carbon nanotubes.

[0030] In particular, the electrically conductive inner layer is designed to have a maximum resistance of less than 1 MΩ per meter of cable length. Test 6.6 according to ISO 12619-14 is used to determine the maximum resistance. This test measures the multilayer tube including the connector.

[0031] The material required for the multilayer pipe can be reduced if the inner layer is designed to have a thickness of at least 0.2 millimeters, and in particular a thickness of no more than 0.4 millimeters. Specifically, it is designed that the inner layer has a thickness between 0.2 millimeters and 0.4 millimeters. Surprisingly, it has been found that a low material requirement, with sufficient protection for the barrier layer and, where applicable, sufficient electrical conductivity, can be achieved if the inner layer is designed to have a thickness of 0.3 millimeters.

[0032] In a further development of the invention, it is proposed that the multilayer pipe has an outer diameter between 19.7 mm and 21 mm, particularly 20.3 mm. It is advantageous if the multilayer pipe has a circular outer circumference in cross-section. Alternatively or additionally, it is provided that the multilayer pipe has an inner diameter between 12.7 mm and 13 mm. This simplifies its interaction with commercially available push-fit connections for hydraulic lines with a nominal diameter of DN 12 mm. In particular, it is provided that the multilayer pipe has a circular inner circumference in cross-section. It is preferably provided that one inner circumference of the multilayer pipe is congruent with one inner circumference of the inner layer.In particular, for a multilayer tube with a circular cross-section, the outer diameter is calculated as twice the thickness of all layers and the inner diameter of the receiving space (inner diameter of the multilayer tube). If only an inner layer, a barrier layer, a middle layer, a pressure-bearing layer, and an outer layer are provided, the outer diameter is calculated as the sum of the inner diameter of the multilayer tube and twice the sum of the thicknesses of the inner layer, the barrier layer, one layer of the middle layer, the pressure-bearing layer, and one layer of the outer layer. It should also be noted that, advantageously, the thickness of one layer, and in particular the thickness of each layer, is essentially constant along the entire length of that layer."Essentially" in the context of the present invention is to be understood as including deviations caused by the chosen manufacturing process.

[0033] A multilayer pipe that meets the aforementioned requirements for compressive strength and is also flexible enough to compensate for tolerances during assembly can surprisingly be achieved, particularly when the multilayer pipe has a total layer thickness of at least 3.5 millimeters, more specifically a total layer thickness of no more than 4 millimeters, preferably a total layer thickness between 3.5 millimeters and 4 millimeters, and more preferably 3.8 millimeters. The total layer thickness is the sum of the maximum layer thicknesses of each layer of the multilayer pipe. In particular, for a multilayer pipe with constant layer thicknesses, the total layer thickness is the sum of all layer thicknesses.In the case that only an inner layer, a barrier layer, a middle layer, a pressure carrier layer and an outer layer are provided, the total layer thickness results from the sum of the layer thickness of the inner layer, the layer thickness of the barrier layer, a layer thickness of the middle layer, the layer thickness of the pressure carrier layer and a layer thickness of the outer layer.

[0034] For example, it is provided that the middle layer has a thickness of at least 1 millimeter. In particular, it is provided that the middle layer has a thickness of at most 3 millimeters. Preferably, it is provided that the middle layer has a thickness between 1 millimeter and 3 millimeters, preferably 2 millimeters. For example, the middle layer can have a thickness of 2.7 millimeters.

[0035] The outer layer also influences the flexibility and stability of the multilayer tube. Therefore, it can be additionally or alternatively provided that the outer layer has a thickness of at least 0.5 millimeters, in particular a thickness of no more than 1 millimeter, preferably a thickness between 0.5 millimeters and 1 millimeter, and preferably 1 millimeter. For example, the outer layer can have a thickness of 0.7 millimeters.

[0036] The problem is further solved by using the multilayer pipe according to the invention in a medium-pressure system according to claim 16. The preceding descriptions relating to the multilayer pipe according to the invention, in particular to its embodiments and advantages, apply equally to the use of the multilayer pipe in a medium-pressure system and vice versa. The medium-pressure system is in particular a medium-pressure system for a fuel cell, preferably a medium-pressure system of a hydrogen vehicle. Overall, the use of the multilayer pipe in a medium-pressure system makes it possible to provide a medium-pressure system with reduced hydrogen permeation, improved flexibility, and improved pressure resistance. At the same time, the medium-pressure system has a reduced weight and lower assembly costs.

[0037] Furthermore, a method for manufacturing a multilayer pipe for conveying a hydrogen-containing fluid is provided. The method comprises the following steps: - creating an inner layer that forms a receiving space for the fluid, - encasing the inner layer with a barrier layer, - encasing the barrier layer with a middle layer, - encasing the middle layer with a printing carrier layer, and - encasing the printing substrate layer with an outer layer.

[0038] Furthermore, it is provided that the middle layer is produced from a mixture of a thermoplastic elastomer (TPE) and an adhesion promoter or from a mixture of a thermoplastic vulcanizate (TPV) and an adhesion promoter. Due to the identical structure of the multilayer pipe according to the invention and the multilayer pipe produced by the method according to the invention, all embodiments and advantages described above with regard to the multilayer pipe apply equally to the method and vice versa. In particular, the method according to the invention is a method for producing a multilayer pipe according to the invention.

[0039] In particular, it is intended that at least the inner layer and / or the barrier layer and / or the middle layer will be produced using an extrusion process, for example by means of coextrusion.

[0040] Such methods are known from practice. Furthermore, it is specifically intended that the printing carrier layer is wrapped around the middle layer.

[0041] To increase sustainability, it is specifically intended that the thermoplastic elastomer and / or the thermoplastic vulcanizate contain a recycled content. Specifically, it is intended that the polyamide used in the manufacture of the multilayer pipe is at least partially recycled polyamide, and / or that the polypropylene used in the manufacture of the multilayer pipe is at least partially recycled polypropylene.

[0042] According to a particularly preferred embodiment, a multilayer tube with a total layer thickness of 3.8 millimeters (mm) is provided. In this multilayer tube, the individual layers were selected as shown in Table 1: Table 1 layer Layer thickness material inner layer 0.3 mm Electrically conductive and adhesion-modified TPV (Nylabond with conductive carbon black) Barrier layer 0.1 mm EVOH middle class 2 mm 50% by weight Orevac 1841 and 50% by weight Santoprene Pressure carrier layer 0.4 mm Braid made of PA fibers with 100% overlap and a braiding angle of 54° outer layer 1 mm Like middle class

[0043] Furthermore, the multilayer tube has a receiving chamber with a circular cross-section. The receiving chamber has an inner diameter of 12.7 millimeters, allowing the multilayer tube to interact with a conventional hydrogen connection, which has an inner diameter of 13 mm. Overall, according to this embodiment, the multilayer tube has a circular outer diameter of 20.3 millimeters (12.7 mm + 2 x 3.8 mm).

[0044] A multilayer pipe with this structure is flexible, allowing for different pipe routings and compensating for installation or manufacturing tolerances. Furthermore, this specific multilayer pipe design requires minimal material while achieving a burst pressure of more than 84 bar at 90 °C and more than 120 bar at room temperature. This ensures long-term resistance to a maximum operating pressure of 30 bar. Further experimentally determined properties of the multilayer pipe, as listed in Table 1, are shown in Table 2 below. Table 2 Characteristic Test procedure Target value Result Burst pressure at room temperature ISO 12619-14, Test 6.2 ≥ 84 bar > 120 bar Burst pressure at 90 °C analogous to ISO12619-14, Test 6.2 ≥ 63 bar > 85 bar Maximum resistance per meter of cable length ISO 12619-14, Test 6.6 < 1 MOhm / m 0.1 MOhm / m Maximum H2 permeation through the pipe wall at 90 °C and 21 bar overpressure per linear meter ISO 12619-14, Test 6.7 ≤ 20 Ncm 3 / h < 12 Ncm 3 / h

[0045] Surprisingly, it was found that the multilayer pipe not only meets but exceeds the target values ​​of all measured parameters. This embodiment provides a multilayer pipe that operates with less than 12 Ncm. 3The target maximum hydrogen permeation of at most 20 Ncm per linear meter per hour is achieved. 3 The per-hour value is significantly lower than the specified value, indicating reduced hydrogen permeation. The measured burst pressures at room temperature and 90 °C also significantly exceed the requirements, resulting in improved pressure resistance for the multilayer pipe. Furthermore, the electrical resistance per meter of pipe length, measured at 0.1 MΩ / m in this embodiment including the connectors, is ten times lower than the target value of less than 1 MΩ / m. These measurements were achieved while simultaneously reducing material usage, giving the multilayer pipe in this embodiment not only low weight but also surprisingly high flexibility and stability.

[0046] Further advantageous embodiments of the invention will become apparent from the following description of the figures and the dependent subclaims.

[0047] They show: Fig. 1 a cross-section through a multilayer tube according to the invention, and Fig. 2 a detailed view of a mesh for a pressure carrier layer of the multilayer tube.

[0048] The following description claims that the invention is not limited to the exemplary embodiments and not to all or several features of the described combinations of features; rather, each individual partial feature of each exemplary embodiment is also significant for the subject matter of the invention, independent of all other partial features described in connection therewith, both on its own and in combination with any features of another exemplary embodiment.

[0049] Fig.Figure 1 shows a cross-section through a multilayer pipe according to the invention for conveying a hydrogen-containing fluid. The multilayer pipe is generally designated by 1. The multilayer pipe 1 is intended for use in a medium-pressure system.

[0050] The multilayer tube 1 comprises an inner layer 2, a barrier layer 3, a middle layer 4, a pressure-bearing layer 5, and an outer layer 6. These layers are arranged from the inside out such that the inner layer 2 forms a receiving chamber 7 for the fluid. Furthermore, the barrier layer 3 surrounds the inner layer 2, the middle layer 4 surrounds the barrier layer 3, the pressure-bearing layer 5 surrounds the middle layer 4, and the outer layer 6 surrounds the pressure-bearing layer 5. In the present embodiment, the middle layer 4 is made of a mixture of a thermoplastic vulcanizate (TPV) and an adhesion promoter. Alternatively, a middle layer 4 made of a mixture of a thermoplastic elastomer (TPE) and an adhesion promoter would also be possible. In the present embodiment, the receiving chamber 7 has a circular cross-section.

[0051] Furthermore, barrier layer 3 exhibits a hydrogen permeation of at most 20 Ncm. 3 The pressure-bearing layer 5 exhibits permanent resistance to at least an operating pressure of 30 bar and a burst pressure of at least 84 bar at room temperature and at least a burst pressure of 63 bar at 90 °C.

[0052] As in Fig. As shown in Figure 1, the barrier layer 3 is arranged directly on the inner layer 2. Furthermore, the middle layer 4 is arranged directly on the barrier layer 3. The pressure carrier layer 5 is arranged directly on the middle layer 4. The outer layer 6 is arranged directly on the pressure carrier layer 5. The outer layer 6 is not surrounded by any other layer, so that the outer layer 6 is directly exposed to environmental influences.

[0053] The adhesion promoter of the middle layer 4 is a polyolefin-based adhesion promoter containing maleic anhydride (MAH). In the present embodiment, the adhesion promoter of the middle layer 4 is a thermoplastic polymer doped with maleic anhydride (MAH), for example polyethylene (PE).

[0054] The middle class 4 liability intermediary has a share of at least 35 percent and at most 60 percent of the total weight of middle class 4.

[0055] The middle layer 4 and the outer layer 6 are made of the same material.

[0056] The print carrier layer 5 has fibers 8 made of thermoplastic material. As in Fig.As shown in Figure 2, the fibers 8 are braided into a mesh 5a. The fibers 8 of the mesh 5a are arranged such that they form a 100% overlap. A surface located below the mesh 5a, in the case of the multilayer tube 1 an outer circumference 4a of the middle layer 4, is completely (100%) covered by the mesh 5a. The mesh 5a has a braiding angle α. The braiding angle α extends between a longitudinal axis 1a of the multilayer tube 1, preferably a central longitudinal axis of the multilayer tube 1, and a fiber 8.

[0057] As from Fig. As can be seen in Figure 1, the braid 5a is placed around the middle layer 4, thus forming the pressure carrier layer 5. The thickness d5 of the pressure carrier layer 5 is between 0.2 millimeters and 0.4 millimeters. The pressure carrier layer 5 is formed by at least one layer of the braid 5a.

[0058] While the print carrier layer 5 is arranged on the outer circumference 4a of the middle layer 4, the barrier layer 3 is arranged on the inner circumference 4b of the middle layer 4. Both the print carrier layer 5 and the barrier layer 3 are bonded to the middle layer 4. The barrier layer 3 is made using ethylene-vinyl alcohol copolymer (EVOH). Furthermore, the barrier layer 3 has a thickness d3 of between 0.1 millimeters and 0.3 millimeters.

[0059] It should be noted that the inner layer 2 can be made of the same material as the middle layer 4. Alternatively, the inner layer 2 can be made of an electrically conductive material. In particular, the inner layer 2 has an electrical resistance of less than 1 MOhm per meter of conductor length.

[0060] The inner layer 2 has a layer thickness d2, where the layer thickness d2 is between 0.2 millimeters and 0.4 millimeters.

[0061] Not only does the receiving chamber 7 for the fluid have a circular cross-section, but so does the multilayer tube 1. The multilayer tube 1 has an outer diameter 9 between 19.7 millimeters and 21 millimeters. An inner diameter 10 of the multilayer tube 1, which corresponds to an inner diameter 2a of the inner layer 2, is between 12.7 millimeters and 13 millimeters.

[0062] According to the present embodiment, the sum of the layer thickness d2 of the inner layer 2, the layer thickness d3 of the barrier layer 3, a layer thickness d4 of the middle layer 4, the layer thickness d5 of the printing carrier layer 5, and a layer thickness d6 of the outer layer 6 results in a total layer thickness d1. The total layer thickness d1 is at least 3.5 millimeters. The layer thickness d4 of the middle layer 4 is between 1 millimeter and 3 millimeters. The outer layer 6 has a layer thickness d6 of at least 0.5 millimeters and at most 1 millimeter.

[0063] The invention is not limited to the embodiments illustrated and described, but also encompasses all embodiments that have the same effect within the meaning of the invention. It is expressly emphasized that the embodiments are not limited to all features in combination; rather, each individual feature can also have inventive significance independently of all other features. Furthermore, the invention is not yet limited to the combination of features defined in claim 1, but can also be defined by any other combination of specific features from all disclosed individual features. This means that, in principle, virtually any individual feature of claim 1 can be omitted or replaced by at least one individual feature disclosed elsewhere in the application. Reference symbol list 1 multilayer pipe 1a Longitudinal axis 2 inner layer 2a Inner diameter 3 Barrier layer 4 Middle class 4a External circumference 4b Inner circumference 5. Pressure carrier layer 5a mesh 6 Outer layer 7 Recording room 8 fibers 8a first fiber 8b second fiber 9 Outer diameter 10 inner diameter α braiding angle d1 Total layer thickness d2 layer thickness inner layer d3 Layer thickness barrier layer d4 layer thickness middle layer d5 layer thickness pressure carrier layer d6 layer thickness outer layer QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2011 089 616 A1

[0003] EP 1 362 890 A1

[0004] Cited non-patent literature

[0000] ISO 12619

[0010] ISO12619-14

[0044]

Claims

Multilayer pipe (1) for conveying a hydrogen-containing fluid, comprising at least: - an inner layer (2) forming a receiving space (7) for the fluid, - a barrier layer (3) surrounding the inner layer (2), - a middle layer (4) surrounding the barrier layer (3), - a pressure carrier layer (5) surrounding the middle layer (4), and - an outer layer (6) surrounding the pressure carrier layer (5), wherein the middle layer (4) is made of a mixture of a thermoplastic elastomer (TPE) and an adhesion promoter or of a mixture of a thermoplastic vulcanizate (TPV) and an adhesion promoter. Multilayer tube (1) according to claim 1, characterized in that the barrier layer (3) is arranged directly on the inner layer (2) and / or the middle layer (4) is arranged directly on the barrier layer (3) and / or the pressure carrier layer (5) is arranged directly on the middle layer (4) and / or the outer layer (6) is arranged directly on the pressure carrier layer (5). Multilayer tube (1) according to claim 1 or 2, characterized in that the outer layer (6) is not surrounded by any further layer. Multilayer tube (1) according to one of claims 1 to 3, characterized in that the adhesion promoter of the middle layer (4) is a polyolefin-based adhesion promoter, in particular that the adhesion promoter comprises maleic anhydride (MAH), preferably that the adhesion promoter is a thermoplastic polymer doped with maleic anhydride (MAH). Multilayer tube (1) according to claim 4, characterized in that the thermoplastic polymer doped with maleic anhydride (MAH) is polyethylene (PE) or polypropylene (PP), in particular that the thermoplastic polymer is low-density polyethylene (LDPE), preferably that the thermoplastic polymer is linear low-density polyethylene (LLDPE). Multilayer tube (1) according to one of claims 1 to 5, characterized in that the adhesion promoter of the middle layer (4) has a proportion of the weight of the middle layer (4) of at least 35 percent by weight, in particular of at least 40 percent by weight, preferably of at least 50 percent by weight, and / or has a proportion of the weight of the middle layer (4) of at most 60 percent by weight. Multilayer tube (1) according to one of claims 1 to 6, characterized in that the outer layer (6) is made of the same material as the middle layer (4). Multilayer tube (1) according to one of claims 1 to 7, characterized in that the pressure carrier layer (5) comprises fibers, and that the fibers comprise polyamide (PA) and / or polypropylene (PP), and / or that the pressure carrier layer (5) is a braid (5a), preferably that the braid (5a) has a coverage of at least 50%, preferably at least 80%, further preferably at least 100%, most preferably 100%, and / or preferably that the braid (5a) has a braid angle (α) of less than 90°, preferably between 15° and 75°, further preferably between 30° and 60°, more preferably between 45° and 60°, most preferably 54°. Multilayer tube (1) according to one of claims 1 to 8, characterized in that the pressure carrier layer (5) has a layer thickness (d5) of at least 0.2 millimeters, in particular a layer thickness (d5) of at most 0.4 millimeters, preferably a layer thickness (d5) between 0.2 millimeters and 0.4 millimeters, preferably of 0.4 millimeters. Multilayer tube (1) according to one of claims 1 to 9, characterized in that the barrier layer (3) is produced using ethylene-vinyl alcohol copolymer (EVOH), in particular from a mixture of ethylene-vinyl alcohol copolymer (EVOH) and an elastic thermoplastic, preferably a thermoplastic elastomer (TPE), preferably wherein the ethylene-vinyl alcohol copolymer (EVOH) has an ethylene content of at most 30 mol%, preferably at most 27 mol%. Multilayer pipe (1) according to one of claims 1 to 10, characterized in that the barrier layer (3) has a layer thickness (d3) of at least 0.1 millimeters, in particular a layer thickness (d3) of at most 0.3 millimeters, preferably a layer thickness (d3) of at most 0.2 millimeters, preferably a layer thickness (d3) between 0.1 millimeters and 0.2 millimeters, preferably of 0.1 millimeters. Multilayer tube (1) according to one of claims 1 to 11, characterized in that the inner layer (2) is made of the same material as the middle layer (4). Multilayer tube (1) according to one of claims 1 to 11, characterized in that the inner layer (2) is made of an electrically conductive material, in particular that the inner layer (2) is made of an electrically conductive doped and adhesion-modified material, preferably that the inner layer (2) is made of an electrically conductive doped and adhesion-modified thermoplastic vulcanizate (TPV), and / or preferably that the inner layer (2) comprises carbon fibers, preferably carbon nanofibers, and / or carbon black. Multilayer tube (1) according to one of claims 1 to 13, characterized in that the inner layer (2) has a layer thickness (d2) of at least 0.2 millimeters, in particular a layer thickness (d2) of at most 0.4 millimeters, preferably a layer thickness (d2) between 0.2 millimeters and 0.4 millimeters, preferably 0.3 millimeters. Multilayer pipe (1) according to any one of claims 1 to 14, characterized in that the multilayer pipe (1) has an outer diameter (9) between 19.7 millimeters and 21 millimeters, in particular 20.3 millimeters, and / or that the multilayer pipe (1) has an inner diameter (10) between 12.7 millimeters and 13 millimeters, and / or that the multilayer pipe (1) has a total layer thickness (d1) of at least 3.5 millimeters, in particular a total layer thickness (d1) of at most 4 millimeters, preferably a total layer thickness (d1) between 3.5 millimeters and 4 millimeters, more preferably 3.8 millimeters, and / or that the middle layer (4) has a layer thickness (d4) of at least 1 millimeter, in particular a layer thickness (d4) of at most 3 millimeters, more preferably a layer thickness (d4) between 1 millimeter and 3 millimeters, more preferably 2 millimeters. and / or that the outer layer (6) has a layer thickness (d6) of at least 0,5 millimeters, in particular a layer thickness (d6) of at most 1 millimeter, preferably a layer thickness (d6) between 0.5 millimeters and 1 millimeter, preferably of 1 millimeter. Use of a multilayer tube (1) according to one of claims 1 to 15 in a medium pressure system, in particular in a medium pressure system for a fuel cell, preferably in a medium pressure system of a hydrogen vehicle.

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