Multilayered resin pipe, water electrolysis system, and method of transferring hydrogen

Abstract

To provide a multilayered resin pipe appropriate for use in a water electrolysis system operated at high voltage, a water electrolysis system equipped with the multilayered resin pipe, and a method of transferring hydrogen with the usage of the multilayered resin pipe.SOLUTION: A multilayered resin pipe includes an electrically insulated main pipe, an electrically insulated pressure-resistant layer covering an outer surface of the main pipe, an electrically insulated gas barrier layer covering an inner surface of the main pipe, and an electrically insulated elution inhibiting layer covering an inner surface of the gas barrier layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, hydrogen energy has been attracting attention as a clean alternative energy. 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. In order to reduce the cost of hydrogen production, efforts are being made 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, piping made of SUS (Steel Use Stainless), which has excellent leak prevention and robustness, is 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-086024 A Summary of the Invention [Problem to be solved by the invention]

[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 the 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 such as transformers and rectifiers used, leading to the low-cost manufacture 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 they touch 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 many water electrolysis stacks connected in series, some of the water electrolysis stacks have a high potential of more than 1 kV. It is difficult to sufficiently insulate such a high-potential water electrolysis stack with the above-mentioned insulating plates.

[0007] Therefore, the present inventors have developed a resin pipe that can be used as the piping of a water electrolysis system, in the belief that the water electrolysis stack can be reliably insulated from auxiliary machinery by using insulating piping for part of the piping. The present disclosure provides a multi-layer resin pipe suitable for use in a water electrolysis system operating at a high voltage, a water electrolysis system including the multi-layer resin pipe, and a method for transporting hydrogen using the multi-layer resin pipe. [Means for solving the problem]

[0008] Aspects of the present disclosure include the following. [1] 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 the inner surface of the main pipe; an electrically insulating elution-preventing layer covering an inner surface of the gas barrier layer; A multi-layer resin piping having [2] The gas barrier layer has a gas barrier strength 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 dissolution-suppressing layer is 0 μg / m 2 / day or more 2000μg / m2 3. The multi-layer resin pipe according to claim 1 or 2, wherein the amount of component elution is less than 1 / day, the amount of component elution being a concentration of ions in a liquid for 8 to 30 days according to a short pipe seal water test method. [4] 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] 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 material selected from the group consisting of an ethylene-vinyl alcohol copolymer and a nylon resin. [6] 6. The multilayer resin pipe according to any one of aspects 1 to 5, 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] 7. The multilayer resin pipe according to any one of Aspects 1 to 6, 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] A multilayer resin pipe according to any one of aspects 1 to 7, wherein the main pipe and the elution suppression layer are made of the same material. [9] A water electrolysis stack; a multilayer resin pipe according to any one of aspects 1 to 8, which is connected to the water electrolysis stack; A water electrolysis system comprising:

[10] A method for transporting hydrogen in a water electrolysis system, the method comprising transporting the hydrogen through the multilayer resin pipe according to any one of aspects 1 to 8. Effect of the Invention

[0009] The present disclosure can provide 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. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a water electrolysis system according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a cross section taken along a cut surface perpendicular to the axis of the multilayer resin pipe according to the embodiment. [Diagram 3] FIG. 3 is a schematic perspective view of a multilayer resin pipe according to an embodiment, in which some layers are omitted to show the layer structure of the multilayer resin pipe. [Figure 4A] FIG. 4A is a schematic end view of an example of a flange-connected multi-layer resin pipe. [Figure 4B] 4B is a schematic cross-sectional view of the end portion of the multilayer resin pipe and its vicinity taken along line IVB-IVB in FIG. 4A. [Figure 5A] FIG. 5A is a schematic end view of another example of a flange-connected multi-layer resin pipe. [Figure 5B] FIG. 5B is a schematic diagram of a cross section of the end portion of the multilayer resin pipe and its vicinity taken along line VB-VB in FIG. 5A. [Figure 6] FIG. 6 is a schematic cross-sectional view of an end portion of a multilayer resin pipe to be screw-connected and its vicinity, taken along a cutting plane including the axis of the multilayer resin pipe. [Figure 7] FIG. 7 is a schematic cross-sectional view of an unreinforced pipe and an attached mechanical joint, taken along a cutting plane including the axis of the unreinforced pipe. [Figure 8] FIG. 8 is a schematic diagram of a cross section of a multilayer resin pipe with a main pipe exposed at and near its end and a mechanical joint attached thereto, taken along a cut plane including the axis of an unreinforced pipe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the 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 given 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.

[0012] In this application, a numerical range expressed using the symbol "~" includes the numerical values ​​before and after the symbol "~" as the lower and upper limits, respectively, unless otherwise specified. The upper and lower limits described in this application can be used alone or in any combination.

[0013] In this application, the term "comprising" means that additional components or elements may be included, unless otherwise specified, and includes "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 is only the material or element listed, but does not exclude the further inclusion of unavoidable impurities.

[0014] (1) Water electrolysis system 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.

[0015] Pure water is supplied to the water electrolysis stack 2 from a pure water supply facility (not shown) through a pure water supply line 103. In FIG. 1, the dashed arrow of the pure water supply line 103 indicates the flow direction of the pure water. The pure water is electrolyzed into oxygen and hydrogen in the water electrolysis stack 2. The 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 arrow of the oxygen line 104 and the dashed arrow of the hydrogen line 105 indicate the flow directions of oxygen and hydrogen, respectively. 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 in the oxygen line 104 and the hydrogen line 105.

[0016] The water electrolysis stacks 2 are electrically connected to a DC power source 107 via a power cable 106. The DC power source 107 supplies DC power to the water electrolysis stacks 2. The water electrolysis stacks 2 are electrically connected in series. In FIG. 1, all the water electrolysis stacks 2 are connected in series. However, some of the water electrolysis stacks 2 may be connected in parallel. For example, a plurality of groups each consisting of a plurality of 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, during operation of the water electrolysis system 100, some of the water electrolysis stacks 2 are at a high potential. The potential of the highest water electrolysis stack 2 is (operating voltage of one water electrolysis stack 2)×(number of water electrolysis stacks 2 connected in series).

[0017] 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.

[0018] A multilayer resin pipe according to an embodiment described below can be used as the hydrogen pipe 113. It is desirable for the hydrogen pipe 113 to satisfy the following requirements.

[0019] i. It must have pressure resistance that can withstand the pressure of the gas flowing through the piping. For example, when both ends of the hydrogen pipe 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 pipe 113 does not leak water, deform, break, or experience other abnormalities.

[0020] ii. Electrically insulating The hydrogen pipe 113 is heated to 10 8 It is desirable that the resistivity of the hydrogen pipe 113 at 80° C. is 10 8 ~10 18 The resistivity may be measured in units of Ωcm. The resistivity can be measured, for example, by an insulation resistance meter or a method in accordance with JIS K 6911-2006.

[0021] iii. The components of the pipes are unlikely to dissolve in water As described above, hydrogen from the water electrolysis stack 2 usually accompanies moisture. The moisture is preferably separated from the hydrogen by a gas-liquid separator and / or a dehumidifier (not shown) and recirculated to the pure water supply line. When water is recirculated, it is preferable that the recirculated water does not contain impurities or that the impurity content is sufficiently small. For this reason, it is preferable that the components of the hydrogen pipe 113 are prevented from dissolving into the moisture or that the dissolution is sufficiently reduced.

[0022] iv. The tube wall has high gas barrier properties (i.e. low hydrogen permeability) In order to prevent hydrogen leakage, the hydrogen pipe 113 is connected to the piping 113 at 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 0cm 3 / m / h or more 10cm 3It is desirable for the hydrogen permeation rate to be less than 100 / m / h. The hydrogen permeation rate above indicates the volume of hydrogen that leaks from inside a 1m-long pipe to the outside of the pipe per hour. The hydrogen permeation rate can be measured, for example, at 80°C using a differential pressure method in accordance with JIS K 7126-2:2006.

[0023] It is desirable that the pure water pipe 111 and the oxygen pipe 112 also satisfy the above requirements i to iii. It is not necessary for the pure water pipe 111 and the oxygen pipe 112 to have such high gas barrier properties as 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.

[0024] Furthermore, it is desirable that the hydrogen pipe 113, the pure water pipe 111, and the oxygen pipe 112 optionally satisfy the following requirements.

[0025] 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, it is desirable for the hydrogen pipe 113, the pure water pipe 111, and the oxygen pipe 112 to have a heat resistance of 80°C or higher, and are required to have a heat resistance of at least 60°C or higher.

[0026] (2) Multilayer resin piping The multilayer resin pipe 1 according to the embodiment shown in FIGS. 2 and 3 can satisfy the above-mentioned requirements, and can therefore be suitably used in a water electrolysis system operating at a high voltage.

[0027] The multilayer resin pipe 1 according to the embodiment has 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 has 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.

[0028] 2-1) Master 10 The main pipe 10 is made of an electrically insulating thermoplastic resin or a 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 may be measured, for example, in accordance with UL746B of the UL standard by the Underwriters Laboratories.

[0029] For example, the main pipe 10 may contain at least one selected from the group consisting of high density polyethylene (HDPE), cross-linked polyethylene, fluororesin, and polyvinyl chloride resin, may consist essentially of at least one selected from these groups, or may consist of at least one selected from these groups. The main pipe 10 may further contain an additive such as a viscosity adjuster. 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 suppression layer 12 described below.

[0030] 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 ... 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.

[0031] The pressure-resistant layer 13 has high pressure resistance. For example, when both ends of the pressure-resistant layer 13 are sealed and a hydrostatic pressure of 1.25 times the design pressure is applied for one minute, it is desirable that 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 caused by the high-pressure fluid transported through the multilayer resin pipe 1, and allows the water electrolysis system to operate safely.

[0032] 2-3) Gas barrier layer 11 The gas barrier layer 11 is made of an electrically insulating thermoplastic resin or a thermosetting resin. 8 The resistivity at 80° C. may be 10 8 ~10 18 The 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.

[0033] The gas barrier layer 11 has a gas barrier capacity of 0 to 3×10 -10 [cm 3 cm / cm 2As a result, for example, the multi-layer 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) can have a hydrogen permeability of 0 to 100 cm under a hydrogen gas pressure of 3 MPa. 3 / m / h, especially 0-10cm 3 / m / h or less, and leakage of hydrogen transported inside the multilayer resin pipe 1 to the outside of the multilayer resin pipe 1 is 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 When the multilayer resin pipe 1 has a hydrogen permeability coefficient of 7.1 cmHg under a hydrogen gas pressure of 3 MPa, 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 coefficient of 7.1 cmHg 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 at a hydrogen gas pressure of 1 cmHg. 2 It represents the volume of hydrogen that permeates per second through the gas barrier layer 11. The hydrogen permeability coefficient can be measured, for example, under conditions of 80° C. in accordance with JIS K 7126-2:2006.

[0034] The gas barrier layer 11 may be made of at least one 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 about 1 / 6 of that of high-density polyethylene, and the hydrogen permeability coefficient of ethylene-vinyl alcohol copolymer resin is about 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, and the pipe diameter and pipe length of the multilayer resin pipe 1.

[0035] 2-4) Elution suppression layer 12 The elution prevention layer 12 is made of an electrically insulating thermoplastic resin or a 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.

[0036] The amount of component elution from the elution prevention layer 12 is 0 μg / m 2 / day or more 2000μg / m 2 / day. This can prevent or sufficiently reduce the elution of impurities into water passing through the inside of the multilayer resin pipe 1. The amount of component elution from the elution-preventing layer 12 is the concentration of ions in liquid for 8 to 30 days according to a short-pipe water-sealing test method. The ion concentration can be measured, for example, by ICP atomic emission spectrometry (inductively coupled plasma atomic emission spectrometry). The elution-preventing layer 12 may 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 elution-preventing layer 12 is not particularly limited as long as it can prevent or sufficiently reduce the elution of impurities from the multilayer resin pipe 1 into water and the multilayer resin pipe 1 has a wall thickness specified by a standard.

[0037] (3) Manufacturing method of multi-layer resin piping An example of a method for manufacturing the multilayer resin pipe 1 according to the embodiment will be described.

[0038] 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 seams.

[0039] 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 and the adhesive strength between the gas barrier layer 11 and the elution-preventing layer 12 are equal, 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.

[0040] 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.

[0041] (4) Connection of multi-layer resin piping A description will be given of an example of a structure provided on the multilayer resin piping 1 according to the embodiment in order to connect the multilayer resin piping 1 to equipment such as a water electrolysis stack 2. 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.

[0042] 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 are 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 is provided with a bolt hole 21. The flange portion 25 may be formed of the same material as the pressure-resistant layer 13. The flange portion 25 may be formed integrally with the pressure-resistant layer 13.

[0043] Another example of the structure of the end of the multilayer resin pipe 1 to be flanged and its vicinity is shown in Figures 5A and 5B. The pressure-resistant layer 13 is cut at the end of the multilayer resin pipe 1 and its vicinity (see Figure 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, a flange connection using a loose flange 23 is highly convenient.

[0044] 4-2) Screw-in connection The multilayer resin pipe 1 may be connected to equipment such as a water electrolysis stack 2 by a screw connection. An example of the structure of the end of the multilayer resin pipe 1 and its vicinity to be screwed is shown in FIG. 6. As shown in FIG. 6, a mechanical joint 30 is attached to the end of the multilayer resin pipe 1. The mechanical joint 30 is composed of a fastening ring 31, a joint body 32, and a cap nut 33. The fastening ring 31 and the cap nut 33 are attached to the outer surface of the main pipe 10. The joint body 32 is screwed into the cap nut 33, so that the cap nut 33 presses the fastening ring 31 to bite into the main pipe 10. The fastening ring 31 attached to the outer surface of the main pipe 10 is not damaged at all or almost not by the gas barrier layer 11, the elution suppression layer 12, and the pressure resistant layer 13. 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 property, the ion elution suppression performance, and the pressure resistance of the multilayer resin pipe 1.

[0045] The pressure-resistant layer 13 may cover a part 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 provided between the portion of the pressure-resistant layer 13 covering the cap nut 33 and the portion covering the main pipe 10. In addition, the end of the pressure-resistant layer 13 covering the cap nut 33 may be rounded. These shapes reduce electric field concentration and distribute stress due to the internal pressure of the multilayer resin pipe 1.

[0046] An example of a method for attaching a mechanical joint 30 to a multilayer resin pipe 1 will be described. As shown in Fig. 7, an unreinforced pipe 15 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 (i.e., no pressure-resistant layer 13 is provided) is inserted into a cap nut 33 and a fastening ring 31 in that order, and then a joint body 32 is screwed into the cap nut 33 and fastened. Thereafter, the pressure-resistant layer 13 is formed so as to cover a part of the main pipe 10 and the cap nut 33. As a result, a multilayer resin pipe 1 having a mechanical joint 30 attached to its end as shown in Fig. 6 is obtained.

[0047] In another example of a method for attaching a mechanical joint 30 to a multilayer resin pipe 1, as shown in FIG. 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 fastening 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 fastened. Thereafter, an additional pressure-resistant layer 16 is formed so as to cover the exposed main pipe 10, the end and its vicinity of the pressure-resistant layer 13, and a 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.

[0048] Although the embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and various modifications are possible within the scope of the claims. For example, the present disclosure is not necessarily limited to those having all the configurations of the above embodiment. It is possible to replace a part of the configuration of one embodiment with another configuration, add a part of the configuration of one embodiment to another form, or omit a part of the configuration of one embodiment. EXAMPLES

[0049] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0050] An unreinforced pipe (JIS standard size: 25A) was formed by co-extrusion molding, consisting of a main pipe made of high density polyethylene (continuous use temperature 121°C) as the outermost layer, an elution prevention 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 prevention layer. The hydrogen permeability of the unreinforced pipe was measured at 80°C in accordance with JIS K 7126-2:2006. The hydrogen permeability was 8.4 x 10 -11 [cc·cm / cm 2 / s / cmHg], which showed good gas barrier properties. 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 multi-layer resin pipe. [Explanation of symbols]

[0051] 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···Tightening 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 source, 111···Pure water piping, 112···Oxygen piping, 113···Hydrogen piping

Claims

1. 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 the inner surface of the main pipe; an electrically insulating elution-preventing layer covering an inner surface of the gas barrier layer; A multi-layer resin piping having

2. The gas barrier layer has a thickness 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 a glass fiber reinforced resin.

5. 2. 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. 2. 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. 2. The multi-layer resin pipe 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 stack; The multilayer resin pipe according to any one of claims 1 to 8, which is connected to the water electrolysis stack; A water electrolysis system comprising:

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

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