Multilayer resin pipe, water electrolysis system, and hydrogen transfer method

Abstract

Provided are a multilayer resin pipe suitable for use in a water electrolysis system operating at high voltage, a water electrolysis system provided with this multilayer resin pipe, and a hydrogen transfer method using this multilayer resin pipe. The multilayer resin pipe has: an electrically insulating main pipe; an electrically insulating pressure resistant layer covering an outer surface of the main pipe; an electrically insulating gas barrier layer covering an inner surface of the main pipe; and an electrically insulating elution suppressing layer covering an inner surface of the gas barrier layer.

Description

Multilayer resin piping, water electrolysis system, and hydrogen transport method

[0001] The present disclosure relates to a multilayer resin piping, a water electrolysis system, and a method for transporting hydrogen.

[0002] In recent years, hydrogen energy has attracted attention as a clean alternative energy source. One method for producing hydrogen is water electrolysis. Water electrolysis systems are used at low voltages of several hundred volts and large currents of several hundred to several thousand amperes. To reduce the cost of hydrogen production, efforts are underway to increase the scale and capacity of water electrolysis systems, and it is expected that water electrolysis systems with a capacity of approximately 500 GW will be in practical use by 2050. In such water electrolysis systems, pipes made of SUS (Steel Use Stainless Steel), which have excellent leak-proofing properties and robustness, are used to transport hydrogen.

[0003] Patent Document 1 describes a laminated resin pipe used for transporting gas, which includes a barrier layer as an intermediate layer.

[0004] Japanese Patent Application Laid-Open No. 2019-086024

[0005] The water electrolysis stacks used in water electrolysis systems need to be used with a rectifier to convert AC power from the power grid to DC. In addition, because water electrolysis stacks need to be operated at low voltage, they also need to be used with a transformer to step down the power from the power grid. Therefore, by electrically connecting multiple water electrolysis stacks in series, it may be possible to reduce the number of devices used, such as transformers and rectifiers, leading to the low-cost production of large-scale water electrolysis systems.

[0006] Each water electrolysis stack in a water electrolysis system needs to be electrically insulated from auxiliary equipment (e.g., pumps, tanks, pure water supply equipment, and gas-liquid separators). Otherwise, workers and others may receive electric shock when touching the auxiliary equipment. In conventional water electrolysis systems, insulation is ensured by insulating plates provided at the ends of the water electrolysis stack. However, in a water electrolysis system having multiple water electrolysis stacks connected in series, some of the water electrolysis stacks have a high potential exceeding 1 kV. It is difficult to sufficiently insulate water electrolysis stacks with such a high potential using the insulating plates described above.

[0007] Therefore, the present inventors have developed resin piping that can be used in a water electrolysis system, based on the idea that using insulating piping for part of the piping would ensure insulation of the water electrolysis stack from auxiliary machinery. The present disclosure provides a multilayer resin piping suitable for use in a water electrolysis system operating at a high voltage, a water electrolysis system including the multilayer resin piping, and a method for transporting hydrogen using the multilayer resin piping.

[0008] The present disclosure can be exemplified by the following aspects: [1] A multilayer resin pipe having an electrically insulating main pipe, an electrically insulating pressure-resistant layer covering the outer surface of the main pipe, an electrically insulating gas barrier layer covering the inner surface of the main pipe, and an electrically insulating elution-suppressing layer covering the inner surface of the gas barrier layer. [2] The gas barrier layer has a solubility of 0 to 3 × 10 －１０ [cm ３ cm / cm ２ [3] The multilayer resin pipe according to aspect 1, wherein the elution-preventing layer has a hydrogen permeability coefficient of 0 μg / m ２ / day or more 2000μg / m ２ / day, the component elution amount being the concentration of ions in the liquid after 8 to 30 days according to a short-pipe water seal test method. [4] The multilayer resin pipe according to any one of Aspects 1 to 3, wherein the pressure-resistant layer is made of a glass fiber reinforced resin. [5] The multilayer resin pipe according to any one of Aspects 1 to 4, wherein the gas barrier layer is made of at least one resin selected from the group consisting of an ethylene-vinyl alcohol copolymer and a nylon-based resin. [6] The multilayer resin pipe according to any one of Aspects 1 to 5, wherein the elution-suppressing layer is made of at least one resin selected from the group consisting of high-density polyethylene, cross-linked polyethylene, a fluororesin, a vinyl chloride resin, and polypropylene. [7] The multilayer resin pipe according to any one of Aspects 1 to 6, wherein the main pipe is made of at least one resin selected from the group consisting of high-density polyethylene, cross-linked polyethylene, a fluororesin, and a vinyl chloride resin. [8] The multilayer resin pipe according to any one of Aspects 1 to 7, wherein the main pipe and the elution-suppressing layer are made of the same material. [9] A water electrolysis system comprising: a water electrolysis stack; and the multilayer resin piping according to any one of Aspects 1 to 8, connected to the water electrolysis stack.

[10] A method for transferring hydrogen in a water electrolysis system, the method comprising transferring the hydrogen through the multilayer resin piping according to any one of Aspects 1 to 8.

[0009] This specification includes the disclosure of Japanese Patent Application No. 2023-171434, from which the present application claims priority.

[0010] The present disclosure provides a multilayer resin pipe suitable for use in a water electrolysis system operating at a high voltage, a water electrolysis system including the multilayer resin pipe, and a hydrogen transport method using the multilayer resin pipe.

[0011] FIG. 1 is a schematic diagram illustrating an example of the configuration of a water electrolysis system according to an embodiment. FIG. 2 is a schematic diagram of a cross section taken along a cut plane perpendicular to the axis of a multilayer resin pipe according to an embodiment. FIG. 3 is a schematic perspective view of a multilayer resin pipe according to an embodiment, with some layers omitted to illustrate the layer configuration of the multilayer resin pipe. FIG. 4A is an example of a schematic end view of a flange-connected multilayer resin pipe. FIG. 4B is a schematic cross section of an end of a multilayer resin pipe and its vicinity taken along line IVB-IVB in FIG. 4A. FIG. 5A is another example of a schematic end view of a flange-connected multilayer resin pipe. FIG. 5B is a schematic cross section of an end of a multilayer resin pipe and its vicinity taken along line VB-VB in FIG. 5A. FIG. 6 is a schematic cross section of an end of a threadedly connected multilayer resin pipe and its vicinity taken along a cut plane including the axis of the multilayer resin pipe. FIG. 7 is a schematic cross section of an unreinforced pipe and a mechanical joint attached thereto taken along a cut plane including the axis of the unreinforced pipe. FIG. 8 is a schematic cross-sectional view of a multilayer resin pipe with the main pipe exposed at and near the end and a mechanical joint attached thereto, taken along a cutting plane including the axis of the unreinforced pipe.

[0012] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the same components or components having similar functions are designated by the same reference numerals, and repeated explanations may be omitted. For convenience of explanation, the dimensional ratios and shapes of each part in the drawings may be exaggerated and may differ from the actual dimensional ratios and shapes.

[0013] In this application, unless otherwise specified, numerical ranges expressed using the symbol "to" include the numerical values ​​written before and after the symbol "to" as the lower and upper limits, respectively. The upper and lower limits described in this application can be used alone or in any combination.

[0014] In this application, unless otherwise specified, the term "comprising" means that additional components or elements may be included, and encompasses "consisting essentially of" and "consisting of." The term "consisting essentially of" means that additional components or elements may be included that do not have a substantial adverse effect. The term "consisting of" means that the material or element listed is included only, but does not exclude the further inclusion of unavoidable impurities.

[0015] (1) Water Electrolysis System Fig. 1 shows an example of the configuration of a water electrolysis system according to an embodiment. The water electrolysis system 100 includes a plurality of water electrolysis stacks 2, and a pure water pipe 111, an oxygen pipe 112, and a hydrogen pipe 113 connected to the water electrolysis stacks 2. Typically, the water electrolysis system 100 further includes a DC power supply 107, a power cable 106, and auxiliary equipment (not shown) such as a pure water supply system and a gas-liquid separator.

[0016] Pure water from a pure water supply facility (not shown) is supplied to the water electrolysis stack 2 through a pure water supply line 103. In FIG. 1 , the dashed arrows on the pure water supply line 103 indicate the flow direction of the pure water. The pure water is electrolyzed into oxygen and hydrogen in the water electrolysis stack 2. Oxygen is transferred from the water electrolysis stack 2 to a gas tank (not shown) through an oxygen line 104. Similarly, hydrogen is transferred from the water electrolysis stack 2 to a gas tank or a supply destination through a hydrogen line 105. In FIG. 1 , the dashed-dotted arrows on the oxygen line 104 and the dashed-dotted arrows on the hydrogen line 105 indicate the flow directions of oxygen and hydrogen, respectively. The hydrogen and oxygen from the water electrolysis stack 2 usually contain moisture. Therefore, a gas-liquid separator (not shown) and / or a dehumidifier (not shown) for separating moisture from the hydrogen or oxygen may be provided on the oxygen line 104 and the hydrogen line 105.

[0017] The water electrolysis stacks 2 are electrically connected to a DC power supply 107 via power cables 106. The DC power supply 107 supplies DC power to the water electrolysis stacks 2. The water electrolysis stacks 2 are electrically connected in series. Note that in FIG. 1 , all of the water electrolysis stacks 2 are connected in series. However, some of the water electrolysis stacks 2 may be connected in parallel. For example, multiple groups of multiple water electrolysis stacks 2 electrically connected in parallel may be electrically connected in series. In the water electrolysis system 100 according to the embodiment, the water electrolysis stacks 2 are electrically connected in series, and therefore, some of the water electrolysis stacks 2 are at a high potential during operation of the water electrolysis system 100. The potential of the highest water electrolysis stack 2 is calculated as (the operating voltage of one water electrolysis stack 2) × (the number of water electrolysis stacks 2 connected in series).

[0018] An insulating pure water pipe 111 is provided in at least a portion of the pure water supply line 103, an insulating oxygen pipe 112 is provided in at least a portion of the oxygen line 104, and an insulating hydrogen pipe 113 is provided in at least a portion of the hydrogen line 105. This provides electrical insulation between the water electrolysis stack 2 and the auxiliary machinery, thereby preventing workers or the like from receiving an electric shock from high-voltage electricity from the water electrolysis stack 2 when they touch the auxiliary machinery.

[0019] A multilayer resin pipe according to an embodiment described below can be used as the hydrogen pipe 113. It is desirable that the hydrogen pipe 113 satisfy the following requirements.

[0020] i. Having pressure resistance that can withstand the pressure of the gas flowing through the piping For example, when both ends of the hydrogen piping 113 are sealed and a hydrostatic pressure of 1.25 times the design pressure is applied for one minute, it is desirable that the hydrogen piping 113 does not leak water, deform, break, or suffer any other abnormalities.

[0021] ii. Electrically insulating The hydrogen pipe 113 has a resistance of 10 ８ It is desirable that the resistivity of the hydrogen pipe 113 at 80° C. is 10 ８ ~10 １８The resistivity may be measured in Ωcm. The resistivity can be measured, for example, using an insulation resistance meter or a method in accordance with JIS K 6911-2006.

[0022] iii. Components of the piping are less likely to dissolve into water As described above, hydrogen from the water electrolysis stack 2 is usually accompanied by moisture. The moisture is preferably separated from the hydrogen using a gas-liquid separator and / or a dehumidifier (not shown) and recycled to the pure water supply line. When water is recycled, it is desirable that the recycled water does not contain impurities or that the impurity content is sufficiently low. Therefore, it is desirable that the components of the hydrogen piping 113 are prevented from dissolving into water or that the dissolution is sufficiently reduced.

[0023] iv. The pipe wall has high gas barrier properties (i.e., low hydrogen permeability). To prevent hydrogen leakage, the hydrogen pipe 113 has a pressure of 0 cm under the condition of a hydrogen gas pressure of 3 MPa. ３ / m / h or more 100cm ３ / m / h or less, especially 0 cm ３ / m / h or more 10cm ３ It is desirable that the hydrogen permeation rate is 1 / m / h or less. The hydrogen permeation rate represents the volume of hydrogen leaking from a 1-m-long pipe to the outside of the pipe per hour. The hydrogen permeation rate can be measured, for example, by a differential pressure method in accordance with JIS K 7126-2:2006 under conditions of 80°C.

[0024] It is desirable that the pure water pipe 111 and the oxygen pipe 112 also satisfy the above requirements i to iii. However, the pure water pipe 111 and the oxygen pipe 112 do not need to have gas barrier properties as high as those of the hydrogen pipe 113. A multilayer resin pipe according to an embodiment described later can also be used as the pure water pipe 111 and / or the oxygen pipe 112.

[0025] Furthermore, it is desirable that the hydrogen pipe 113, the pure water pipe 111, and the oxygen pipe 112 optionally satisfy the following requirements.

[0026] v. Having heat resistance capable of withstanding the operating temperature of the water electrolysis stack 2 Since the maximum operating temperature of the water electrolysis stack 2 is 60°C to 80°C, the hydrogen pipe 113, the pure water pipe 111, and the oxygen pipe 112 preferably have a heat resistance temperature of 80°C or higher, and are required to have a heat resistance temperature of at least 60°C or higher.

[0027] (2) Multilayer Resin Pipe The multilayer resin pipe 1 according to the embodiment shown in FIGS. 2 and 3 can satisfy the above requirements and can therefore be suitably used in a water electrolysis system that operates at a high voltage.

[0028] The multilayer resin pipe 1 according to the embodiment includes an electrically insulating main pipe 10, an electrically insulating pressure-resistant layer 13 covering the outer surface of the main pipe 10, an electrically insulating gas barrier layer 11 covering the inner surface of the main pipe 10, and an electrically insulating elution-suppressing layer 12 covering the inner surface of the gas barrier layer 11. In other words, the multilayer resin pipe 1 includes the pressure-resistant layer 13 as the outermost layer, the elution-suppressing layer 12 as the innermost layer, the main pipe 10 provided between the pressure-resistant layer 13 and the elution-suppressing layer 12, and the gas barrier layer 11 provided between the main pipe 10 and the elution-suppressing layer 12. The main pipe 10, the pressure-resistant layer 13, the gas barrier layer 11, and the elution-suppressing layer 12 all have a tubular shape.

[0029] 2-1) Main pipe 10 The main pipe 10 is made of an electrically insulating thermoplastic resin or thermosetting resin. ８ The resistivity at 80°C may be 10 ８ ~10 １８ The main pipe 10 may have a continuous use temperature of 60°C or higher. The continuous use temperature may be 60 to 180°C or higher. The continuous use temperature can be measured, for example, in accordance with UL746B, a UL standard established by the Underwriters Laboratories of America.

[0030] For example, the main pipe 10 may contain at least one material selected from the group consisting of high-density polyethylene (HDPE), cross-linked polyethylene, fluorine-based resin, and polyvinyl chloride resin. The main pipe 10 may consist essentially of at least one material selected from these groups, or may consist of at least one material selected from these groups. The main pipe 10 may further contain an additive such as a viscosity modifier. Furthermore, from the viewpoint of stable production of the multilayer resin pipe 1, the main pipe 10 may be made of the same material as the elution-suppressing layer 12 described below.

[0031] 2-2) Pressure-resistant layer 13 The pressure-resistant layer 13 is made of a fiber-reinforced resin made of an electrically insulating thermoplastic resin or thermosetting resin and an electrically insulating fiber material. The pressure-resistant layer 13 may be made of a glass-fiber-reinforced resin. For example, the pressure-resistant layer 13 may be made of a glass-fiber-reinforced resin made of a thermosetting epoxy and glass fiber. The pressure-resistant layer 13 is made of a material that can withstand temperatures of 1000K to 800K. ８ The resistivity at 80°C may be 10 ８ ~10 １８ The pressure-resistant layer 13 may have a continuous use temperature of 80° C. or higher. The continuous use temperature may be 60 to 180° C. or higher.

[0032] The pressure-resistant layer 13 has high pressure resistance. For example, it is desirable that when both ends of the pressure-resistant layer 13 are sealed and a hydrostatic pressure 1.25 times the design pressure is applied for one minute, water leakage, deformation, breakage, or other abnormalities do not occur in the hydrogen pipe 113. This prevents or reduces breakage, deformation, etc. of the multilayer resin pipe 1 due to the high-pressure fluid transported through the multilayer resin pipe 1, allowing the water electrolysis system to operate safely.

[0033] 2-3) Gas Barrier Layer 11 The gas barrier layer 11 is made of an electrically insulating thermoplastic resin or thermosetting resin. ８ The resistivity at 80°C may be 10 ８ ~10 １８The gas barrier layer 11 may have a melting point of 80°C or higher. The melting point may be 80 to 180°C or higher. The melting point of the gas barrier layer 11 can be measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121:2012, for example.

[0034] The gas barrier layer 11 has a viscosity of 0 to 3×10 －１０ [cm ３ cm / cm ２ Therefore, for example, the multilayer resin pipe 1 having a JIS standard size of 25A (inner diameter 27.6 mm, outer diameter 34.0 mm, wall thickness 3.2 mm) may have a hydrogen permeability coefficient of 0 to 100 cm under a hydrogen gas pressure of 3 MPa. ３ / m / h, especially 0-10cm ３ The multilayer resin pipe 1 can have a hydrogen permeation rate of 1000 kJ / m / h or less, and the leakage of hydrogen transported inside the multilayer resin pipe 1 to the outside of the multilayer resin pipe 1 can be prevented or sufficiently reduced. For example, the multilayer resin pipe 1 has a JIS standard size of 25A, and the gas barrier layer 11 has a thickness of 1×10 －１０ [cm ３ cm / cm ２ 1. / s / cmHg], the gas barrier layer 11 has a thickness of 1.0 mm, and the elution prevention layer 12 has a thickness of 0.2 mm, the multilayer resin pipe 1 has a hydrogen permeability of 7.1 cm under a hydrogen gas pressure of 3 MPa. ３ The hydrogen permeability coefficient is calculated for a thickness of 1 cm and an area of ​​1 cm under a hydrogen gas pressure of 1 cmHg. ２ The hydrogen permeability coefficient represents the volume of hydrogen that permeates per second through the gas barrier layer 11. The hydrogen permeability coefficient can be measured, for example, in accordance with JIS K 7126-2:2006 under conditions of 80°C.

[0035] The gas barrier layer 11 may be made of at least one material selected from the group consisting of nylon-based resins such as nylon 6 and nylon 11, and ethylene-vinyl alcohol copolymer resins. These resins have high hydrogen gas barrier properties. Specifically, the hydrogen permeability coefficient of nylon 6 is approximately 1 / 6 of that of high-density polyethylene, and the hydrogen permeability coefficient of ethylene-vinyl alcohol copolymer resin is approximately 1 / 60 of that of high-density polyethylene. The thickness of the gas barrier layer 11 may be determined based on the hydrogen permeability coefficient of the resin constituting the gas barrier layer 11, the allowable hydrogen permeation amount, the gas pressure and temperature of hydrogen flowing through the multilayer resin pipe 1, the pipe diameter and pipe length of the multilayer resin pipe 1, etc.

[0036] 2-4) Elution-preventing layer 12 The elution-preventing layer 12 is made of an electrically insulating thermoplastic resin or thermosetting resin whose components are not easily eluted in water. ８ The resistivity at 80°C may be 10 ８ ~10 １８ The main pipe 10 may have a continuous use temperature of 80° C. or higher. The continuous use temperature may be 60 to 180° C. or higher.

[0037] The amount of component elution from the elution-preventing layer 12 is 0 μg / m ２ / day or more 2000μg / m ２ / day. This can prevent or sufficiently reduce the leaching of impurities into water passing through the multilayer resin pipe 1. The amount of component leaching from the leaching-suppressing layer 12 is the concentration of ions in liquid after 8 to 30 days using a short-pipe water seal test. The ion concentration can be measured, for example, by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy). The leaching-suppressing layer 12 can be made of at least one material selected from the group consisting of high-density polyethylene, cross-linked polyethylene, fluorine-based resin, polyvinyl chloride resin, and polypropylene. The thickness of the leaching-suppressing layer 12 is not particularly limited, as long as it can prevent or sufficiently reduce the leaching of impurities into water from the multilayer resin pipe 1 and the multilayer resin pipe 1 has a wall thickness specified by the standard.

[0038] (3) Manufacturing Method of Multilayer Resin Pipe An example of a manufacturing method of the multilayer resin pipe 1 according to the embodiment will be described.

[0039] First, an unreinforced pipe is formed by co-extrusion molding, which comprises a main pipe 10 as the outermost layer, an elution-preventing layer 12 as the innermost layer, and a gas barrier layer 11 provided between the main pipe 10 and the elution-preventing layer 12. Co-extrusion molding makes it possible to form a seamless unreinforced pipe. A seamless unreinforced pipe has excellent gas barrier properties because hydrogen does not leak through the seams.

[0040] The main pipe 10 and the elution-preventing layer 12 may be made of the same material. In this case, the adhesive strength between the main pipe 10 and the gas barrier layer 11 is equal to the adhesive strength between the gas barrier layer 11 and the elution-preventing layer 12, and the thermal expansion coefficients of the main pipe 10 and the elution-preventing layer 12 are equal. This makes it possible to stably form a high-quality unreinforced pipe by co-extrusion molding.

[0041] Next, a pressure-resistant layer 13 is formed on the outer surface of the unreinforced pipe to obtain the multilayer resin pipe 1. Specifically, a cloth made of fibers such as glass fiber is wrapped around the outer surface of the unreinforced pipe, the cloth is impregnated with a resin composition, and the resin composition is cured. The process of wrapping the cloth, impregnating with the resin composition, and curing the resin composition is repeated several times. This forms the pressure-resistant layer 13.

[0042] (4) Connection of the multilayer resin piping An example of a structure provided on the multilayer resin piping 1 according to the embodiment for connecting the multilayer resin piping 1 to equipment such as the water electrolysis stack 2 will be described. Note that the multilayer resin piping 1 and the water electrolysis stack 2 may be connected by a method other than the example described below.

[0043] 4-1) Flange Connection The multilayer resin pipe 1 can be connected to equipment by a flange connection. An example of the end of the flange-connected multilayer resin pipe 1 and the structure in the vicinity thereof is shown in Figures 4A and 4B. A flange portion 25 is provided at the end of the multilayer resin pipe 1. The flange portion 25 has bolt holes 21. The flange portion 25 may be formed from the same material as the pressure-resistant layer 13. The flange portion 25 may be formed integrally with the pressure-resistant layer 13.

[0044] 5A and 5B show another example of the structure of the end of a flanged multilayer resin pipe 1 and its vicinity. The pressure-resistant layer 13 is cut at the end of the multilayer resin pipe 1 and its vicinity (see FIG. 5B), and a loose flange 23 with bolt holes 21 and an adapter 22 are attached to the outer surface of the cut pressure-resistant layer 13. The adapter 22 and loose flange 23 can be attached to the end of the multilayer resin pipe 1 after the multilayer resin pipe 1 is cut to the desired length. In this respect, flange connections using loose flanges 23 are highly convenient.

[0045] 4-2) Threaded Connection The multilayer resin pipe 1 may be connected to equipment such as the water electrolysis stack 2 by a threaded connection. FIG. 6 shows an example of the structure of the end of the multilayer resin pipe 1 and its vicinity to be threadedly connected. As shown in FIG. 6, a mechanical joint 30 is attached to the end of the multilayer resin pipe 1. The mechanical joint 30 comprises a clamping ring 31, a joint body 32, and a cap nut 33. The clamping ring 31 and the cap nut 33 are attached to the outer surface of the main pipe 10. The joint body 32 is threaded onto the cap nut 33, which presses the clamping ring 31 and causes it to bite into the main pipe 10. The gas barrier layer 11, the elution-preventing layer 12, and the pressure-resistant layer 13 of the clamping ring 31 attached to the outer surface of the main pipe 10 cause no or almost no damage to the clamping ring 31. Therefore, the mechanical joint 30 can be attached to the multilayer resin pipe 1 without impairing at all or almost without impairing the gas barrier properties, ion elution suppression performance, and pressure resistance of the multilayer resin pipe 1 .

[0046] The pressure-resistant layer 13 may cover a portion of the cap nut 33. The pressure-resistant layer 13 forms a convex portion in the portion covering the cap nut 33. This convex portion may have a tapered shape. That is, a taper may be formed between the portion of the pressure-resistant layer 13 covering the cap nut 33 and the portion covering the main pipe 10. Furthermore, the end of the pressure-resistant layer 13 covering the cap nut 33 may be rounded. These shapes alleviate electric field concentration and distribute stress due to the internal pressure of the multilayer resin pipe 1.

[0047] An example of a method for attaching a mechanical joint 30 to a multilayer resin pipe 1 will be described. As shown in Figure 7, an unreinforced pipe 15 (i.e., no pressure-resistant layer 13) consisting of a main pipe 10 as the outermost layer, an elution-preventing layer 12 as the innermost layer, and a gas barrier layer 11 provided between the main pipe 10 and the elution-preventing layer 12 is inserted into a cap nut 33 and a tightening ring 31, and then a joint body 32 is screwed onto the cap nut 33 and tightened. Thereafter, the pressure-resistant layer 13 is formed so as to cover a portion of the main pipe 10 and the cap nut 33. This results in a multilayer resin pipe 1 having a mechanical joint 30 attached to its end, as shown in Figure 6.

[0048] In another example of a method for attaching a mechanical joint 30 to a multilayer resin pipe 1, as shown in Figure 8, the pressure-resistant layer 13 is peeled off at the end and its vicinity of the multilayer resin pipe 1 to expose the main pipe 10. A cap nut 33 and a tightening ring 31 are attached to the outer surface of the exposed main pipe 10, and then a joint body 32 is screwed onto the cap nut 33 and tightened. Thereafter, an additional pressure-resistant layer 16 is formed to cover the exposed main pipe 10, the end and its vicinity of the pressure-resistant layer 13, and part of the cap nut 33. This results in a multilayer resin pipe 1 with a mechanical joint 30 attached to its end. The additional pressure-resistant layer 16 may be made of the same material as the pressure-resistant layer 13.

[0049] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and various modifications are possible without departing from the spirit of the claims. For example, the present disclosure is not necessarily limited to those including all of the configurations of the above embodiments. Part of the configuration of an embodiment may be replaced with another configuration, part of the configuration of an embodiment may be added to another form, or part of the configuration of an embodiment may be omitted.

[0050] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety.

[0051] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0052] An unreinforced pipe (JIS size: 25A) was formed by coextrusion molding. The unreinforced pipe consisted of a main pipe made of high-density polyethylene (continuous use temperature 121°C) as the outermost layer, an elution-preventing layer made of high-density polyethylene (continuous use temperature 121°C) as the innermost layer, and a gas barrier layer (thickness 0.6 mm) made of ethylene-vinyl alcohol copolymer (melting point 160°C) provided between the main pipe and the elution-preventing layer. The hydrogen permeability coefficient of the unreinforced pipe was measured at 80°C in accordance with JIS K 7126-2:2006. The hydrogen permeability coefficient was 8.4 × 10 －１１ [cc cm / cm ２ The gas barrier properties were excellent, with a thermal conductivity of 1 / s / cmHg. A pressure-resistant layer made of glass fiber reinforced resin (continuous use temperature 150°C) consisting of thermosetting epoxy and glass fiber was formed on the outer surface of this unreinforced pipe, to obtain a multilayer resin pipe.

[0053] 1... multilayer resin piping, 2... water electrolysis stack, 10... main pipe, 11... gas barrier layer, 12... elution prevention layer, 13... pressure-resistant layer, 15... unreinforced pipe, 21... bolt hole, 22... adapter, 23... loose flange, 25... flange portion, 30... mechanical joint, 31... fastening ring, 32... joint body, 33... cap nut, 100... water electrolysis system, 103... pure water supply line, 104... oxygen line, 105... hydrogen line, 106... power cable, 107... DC power supply, 111... pure water piping, 112... oxygen piping, 113... hydrogen piping

Claims

1. A multi-layer resin pipe comprising: an electrically insulating main pipe; an electrically insulating pressure-resistant layer covering an outer surface of the main pipe; an electrically insulating gas barrier layer covering an inner surface of the main pipe; and an electrically insulating elution-suppressing layer covering the inner surface of the gas barrier layer.

2. The gas barrier layer has a viscosity of 0 to 3×10 －１０ [cm ３ cm / cm ２ 2. The multilayer resin pipe according to claim 1, having a hydrogen permeability coefficient of [1 / s / cmHg].

3. The elution-suppressing layer is 0 μg / m ２ / day or more 2000μg / m ２ 2. The multi-layer resin pipe according to claim 1, wherein the amount of component elution is less than 1000 g / day, and the amount of component elution is a concentration of ions in the liquid for 8 to 30 days according to a short pipe water sealing test method.

4. The multi-layer resin pipe according to claim 1, wherein the pressure-resistant layer is made of glass fiber reinforced resin.

5. The multi-layer resin pipe according to claim 1, wherein the gas barrier layer is made of at least one material selected from the group consisting of ethylene-vinyl alcohol copolymers and nylon-based resins.

6. The multi-layer resin pipe according to claim 1, wherein the elution-preventing layer is made of at least one material selected from the group consisting of high-density polyethylene, cross-linked polyethylene, fluorine-based resin, polyvinyl chloride resin and polypropylene.

7. The multi-layer resin piping according to claim 1, wherein the main pipe is made of at least one material selected from the group consisting of high density polyethylene, cross-linked polyethylene, fluorine-based resin, and polyvinyl chloride resin.

8. The multi-layer resin pipe according to claim 1, wherein the main pipe and the elution prevention layer are made of the same material.

9. A water electrolysis system comprising: a water electrolysis stack; and the multilayer resin piping according to any one of claims 1 to 8, connected to the water electrolysis stack.

10. A method for transporting hydrogen in a water electrolysis system, comprising transporting the hydrogen through the multilayer resin piping according to any one of claims 1 to 8.

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