Pressure vessel for high-pressure hydrogen gas

Abstract

A pressure vessel for high-pressure hydrogen gas, comprising a steel container that is composed of two or more steel pipes or tubes connected by screw threads, wherein the steel pipes or tubes have a chemical composition containing, in mass%, C: 0.005 % to 0.60 %, Si: 0.001 % to 2.0 %, Mn: 0.01 % to 5.0 %, P: 0.0001 % to 0.060 %, S: 0.00001 % to 0.010 %, N: 0.00001 % to 0.010 %, Al: 0.0001 % to 1.00 %, O: 0.010 % or less, H: 0 % to 0.0010 %. A pressure vessel for high-pressure hydrogen gas capable of large-capacity hydrogen storage with a single pressure vessel while being easy to produce, transport, and install.

Description

High-pressure hydrogen gas storage tank

[0001] The present invention relates to a high-pressure hydrogen gas pressure accumulator, and more particularly to a high-pressure hydrogen gas pressure accumulator that is capable of storing a large amount of hydrogen.

[0002] As efforts to reduce CO2 emissions accelerate, the need for hydrogen utilization is increasing. To utilize hydrogen, there is a need to develop methods for safely storing large amounts of hydrogen.

[0003] One method being considered for storing large amounts of hydrogen is to store it in liquid form, but because liquid hydrogen needs to be stored at extremely low temperatures of -253°C or below, the cost of the storage equipment and the running costs of maintaining the low temperatures are high.

[0004] Another method for storing large amounts of hydrogen is to compress and store hydrogen in a gaseous state. Hydrogen gas has traditionally been stored in cylinders at a pressure of around 15 MPa. However, efforts are being made at hydrogen stations and elsewhere to store hydrogen gas at higher pressures of 40 MPa or more in order to further increase storage capacity.

[0005] Various materials and structures have been proposed for containers (pressure vessels) that store hydrogen gas at high pressures as described above, but they can be broadly divided into the following four types: (1) Type 1 containers made entirely of metal; (2) Type 2 containers in which the outer periphery (only the cylindrical part) of a metal liner is hoop-wrapped with FRP (fiber-reinforced plastic); (3) Type 3 containers in which the outer periphery (entire including the dome part) of a metal liner is fully wrapped with FRP; and (4) Type 4 containers in which the outer periphery (entire including the dome part) of a non-metallic liner is fully wrapped with FRP.

[0006] As a specific example of the Type 1 container, for example, Patent Document 1 discloses a container using a straight-shaped steel container. Also, as a specific example of the Type 2 container, for example, Patent Document 2 discloses a container in which the outer periphery of a Cr-Mo steel liner is coated with FRP. As a specific example of the Type 3 container, for example, Non-Patent Document 1 discloses a container in which the outer periphery of an aluminum liner is coated with FRP. As a specific example of the Type 4 container, for example, Patent Document 3 discloses a container in which the outer periphery of a resin liner is coated with FRP.

[0007] JP 2019-044969 A JP 2009-293799 A International Publication No. 2016 / 167034

[0008] ENEOS Technical Review, June 2013, Vol. 55, No. 2, pp. 69-72. Edited by the Japan Heat Treatment Association, "Introduction to the Structure and Properties of Metallic Materials - Heat Treatment and Structure Control to Make the Most of Materials," Taiga Publishing, 2004.

[0009] As mentioned above, various types of pressure accumulators have been proposed, but all of them are only a few meters long and several tens of centimeters in diameter, with a limited capacity of approximately 300 L per pressure accumulator. Therefore, in order to increase the amount of hydrogen gas stored at hydrogen stations and other facilities, it has been necessary to increase the number of pressure accumulators installed. When installing pressure accumulators, valves, supports, etc. are required for each pressure accumulator, so increasing the number of installations increases equipment costs and is therefore inefficient.

[0010] Therefore, instead of increasing the number of pressure accumulators to be installed, it is possible to increase the capacity per pressure accumulator by increasing the outer diameter or length. However, if the pressure accumulator is made larger than the currently standard size, its size and weight make it difficult to manufacture and also difficult to transport to the installation site. For example, in order to transport the pressure accumulators from the manufacturing site to the installation site, a large-scale measure would be required, such as using a special transport vehicle and transporting them at night while restricting the passage of other vehicles. In addition, if the installation site has space constraints, it would be necessary to manufacture pressure accumulators of various sizes to suit the installation site, which is inefficient.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a high-pressure hydrogen gas accumulator that is easy to manufacture, transport, and install, yet is capable of storing large amounts of hydrogen with just one unit.

[0012] The present invention has been made to solve the above problems, and has the following gist and configuration.

[0013] 1. A high-pressure hydrogen accumulator having a steel vessel, wherein the steel vessel is made of two or more steel pipes joined together by screws.

[0014] 2. The high-pressure hydrogen gas accumulator according to item 1 above, wherein the threaded connection is achieved by a coupling provided inside the steel pipe.

[0015] 3. The high-pressure hydrogen gas accumulator according to item 1 above, wherein the threaded connection is achieved by a coupling provided on the outside of the steel pipe.

[0016] 4. The high-pressure hydrogen gas accumulator according to any one of the above items 1 to 3, wherein a seal member is provided at the joint between the two or more steel pipes.

[0017] 5. The high-pressure hydrogen gas accumulator according to any one of claims 1 to 4 above, wherein the steel pipe has a composition containing, in mass%, C: 0.005 to 0.60%, Si: 0.001 to 2.0%, Mn: 0.01 to 5.0%, P: 0.0001 to 0.060%, S: 0.00001 to 0.010%, N: 0.00001 to 0.010%, Al: 0.0001 to 1.00%, O: 0.010% or less, and H: 0 to 0.0010%, with the balance being Fe and unavoidable impurities.

[0018] 6. The chemical composition is, in mass%, Mo: 0.0001 to 5.0%, Cr: 0.0001 to 5.0%, Ni: 0.0001 to 5.0%, Cu: 0.0001 to 5.0%, Co: 0.0001 to 5.0%, B: 0.0001 to 0.01%, V: 0.0001 to 1.0%, W: 0.0001 to 5.0%, Nb: 0.0001 to 0.1%, Ti: 0.0001 to 0.1%, Zr: 0.0001 to 0.2%, Hf: 0.0001 to 0.2%, Ta: 0.0001 to 0.2%, Sb: 0.0001 to 0.2%, 6. The high-pressure hydrogen gas accumulator according to claim 5, further containing at least one selected from the group consisting of Sn: 0.0001 to 0.2%, Ca: 0.0001 to 0.01%, Mg: 0.0001 to 0.01%, and REM: 0.0001 to 0.5%.

[0019] 7. The area fraction of retained austenite in the structure of the steel pipe is 0 to 3%, and the number density of inclusions with an aspect ratio of 2.0 or more and a major axis of 10 μm or more is 10 pieces / 100 mm 2 7. The high-pressure hydrogen gas accumulator according to claim 5 or 6, which is:

[0020] In the high-pressure hydrogen gas accumulator of the present invention, a steel container is constructed by connecting multiple steel pipes with screws. Therefore, it is possible to manufacture and transport the accumulator in units of steel pipes that are smaller than the overall size of the accumulator, and then connect them together at the installation site to complete the accumulator. Therefore, the high-pressure hydrogen gas accumulator of the present invention is excellent in productivity and transportability. Furthermore, since the capacity can be freely adjusted by changing the number of steel pipes connected, it is easy to achieve the optimal hydrogen storage amount depending on the installation location. Therefore, the high-pressure hydrogen gas accumulator of the present invention can be suitably used not only in hydrogen stations, but also in various locations where hydrogen storage is required, such as offshore wind power plants, mountainous areas, on ships, and at ports.

[0021] FIG. 1 is a cross-sectional view schematically illustrating the structure of a joint portion of a high-pressure hydrogen gas accumulator according to a first embodiment of the present invention. FIG. 1 is a cross-sectional view schematically illustrating the structure of a joint portion of a high-pressure hydrogen gas accumulator according to a second embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating an example of the structure when an O-ring is used in the second embodiment. FIG. 3 is a cross-sectional view schematically illustrating the structure of a joint portion of a high-pressure hydrogen gas accumulator according to a third embodiment of the present invention. FIG. 4 is a cross-sectional view schematically illustrating an example of the structure when an O-ring is used in the third embodiment. FIG. 5 is a cross-sectional view schematically illustrating the structure of a joint portion of a high-pressure hydrogen gas accumulator according to a fourth embodiment of the present invention. FIG. 6 is a cross-sectional view schematically illustrating an example of the structure when a leak port is provided in the fourth embodiment of the present invention. FIG. 7 is a cross-sectional view schematically illustrating the structure of a high-pressure hydrogen gas accumulator according to the first embodiment of the present invention.

[0022] Next, a method for carrying out the present invention will be specifically described. Note that the following description shows a preferred embodiment of the present invention, and the present invention is not limited to the following description in any way.

[0023] [High-Pressure Hydrogen Gas Pressure Accumulator] The pressure accumulator of the present invention is a high-pressure hydrogen gas pressure accumulator and includes a steel container. The high-pressure hydrogen gas pressure accumulator can be used, for example, as a pressure accumulator for a hydrogen station, but is not limited thereto and can be used for any purpose.

[0024] The high-pressure hydrogen gas accumulator of the present invention may be composed of only a steel container, or may have a carbon fiber reinforced plastic (CFRP) layer (described later) on at least a portion of the surface of the steel container.

[0025] [Steel container] In the present invention, it is important that the steel container is made of two or more steel pipes joined together by screws. Therefore, the steel container does not have a welded joint between the steel pipes. The main effects of this will be described below.

[0026] First, the high-pressure hydrogen gas accumulator of the present invention can be manufactured and transported in a state in which it is divided into a plurality of steel pipes, and then assembled to a predetermined size at the installation site. Therefore, even large-capacity accumulators can be easily manufactured and transported. Furthermore, accumulators of desired capacities can be obtained simply by changing the number of steel pipes to be connected.

[0027] Welding is a commonly used method for connecting multiple steel pipes. However, when steel pipes are joined by welding, the structure at the joint becomes the weld structure. The weld structure is a structure that is altered by the heat during welding, and has inferior toughness compared to the base material. Furthermore, when welding is performed at the installation site, it is difficult to precisely control the welding conditions, making it difficult to ensure weld quality. Therefore, when joining steel pipes by welding, there is a risk of fracture occurring at the joint between the steel pipes when filled with high-pressure hydrogen gas.

[0028] In contrast, in the present invention, steel pipes are joined together with screws, eliminating the need for on-site welding and allowing the accumulator to be easily assembled. Furthermore, the strength is superior to that achieved by welding. The method of joining steel pipes together with screws will be described later.

[0029] The material of the steel pipe is not particularly limited and any steel can be used, but from the viewpoint of cost reduction, it is preferable to use a steel pipe made of low alloy steel.

[0030] In one embodiment of the present invention, it is preferable to use a steel pipe having a chemical composition containing, in mass%, C: 0.005 to 0.60%, Si: 0.001 to 2.0%, Mn: 0.01 to 5.0%, P: 0.0001 to 0.060%, S: 0.00001 to 0.010%, N: 0.00001 to 0.010%, Al: 0.0001 to 1.00%, O: 0.010% or less, and H: 0 to 0.0010%, with the balance being Fe and unavoidable impurities.

[0031] Note that H is an element that may be contained in steel depending on the manufacturing conditions, etc. However, from the viewpoint of further improving fracture toughness, it is preferable that the H content is small, specifically, 0.0010% or less. The lower the H content, the better, so the lower limit of the H content may be 0%.

[0032] The composition of the elements is, in mass %, Mo: 0.0001 to 5.0%, Cr: 0.0001 to 5.0%, Ni: 0.0001 to 5.0%, Cu: 0.0001 to 5.0%, Co: 0.0001 to 5.0%, B: 0.0001 to 0.01%, V: 0.0001 to 1.0%, W: 0.0001 to 5.0%, Nb: 0.0001 to 0.1%, Ti: 0.0001 to 0.1%, Zr: 0.0001 to 0.2%, Hf: 0.0001 to 0.2%, Ta: 0.0001 to 0.2%, Sb: 0.0001 to 0.2%, It may further contain at least one selected from the group consisting of Sn: 0.0001 to 0.2%, Ca: 0.0001 to 0.01%, Mg: 0.0001 to 0.01%, and REM: 0.0001 to 0.5%.

[0033] The two or more steel pipes may have the same or different chemical compositions, but from the viewpoint of preventing corrosion caused by potential differences between the steel pipes, it is preferable that all of the steel pipes constituting the steel vessel have the same chemical composition.

[0034] The structure of the steel pipe is not particularly limited, and any structure can be used. From the viewpoint of reducing the rate of fatigue crack propagation and improving hydrogen gas resistance, it is preferable that the area fraction of retained austenite is 0 to 3%, and the number density of inclusions with an aspect ratio of 2.0 or more and a major axis of 10 μm or more is 10 pieces / 100 mm 2 It is preferable to use a steel pipe having a structure of 0 pieces / 100 mm or less. 2 It may be.

[0035] In the disclosure of this specification, the term "structure" refers to the structure at the longitudinal center of the steel pipe and at a quarter-way position on the inner wall. That is, the area fraction of each structure is the area fraction of the structure at the longitudinal center of the steel pipe and at a quarter-way position on the inner wall. Similarly, the number density of the above-mentioned inclusions is the number density at the longitudinal center of the steel pipe and at a quarter-way position on the inner wall.

[0036] The area fraction of retained austenite can be measured by X-ray diffraction. In this measurement, a test piece is taken from the center of the steel pipe in the longitudinal direction, at a position 1 / 4 of the inner wall thickness, and the cut surface of the test piece is chemically polished before measurement. In this measurement, a Co-Kα radiation source is used for the incident X-rays, and the area fraction of retained austenite is calculated from the intensity ratio of the (200), (211), and (220) planes of ferrite to the (200), (220), and (311) planes of austenite.

[0037] The number density of the inclusions can be determined by observation using an optical microscope. First, a test piece for measuring inclusions is taken from the center of the longitudinal direction of the steel pipe, at a position 1 / 4 of the inner wall thickness. The dimensions of the test piece are 20 mm in the length direction, 5 mm in the width direction, and 15 mm in the wall thickness direction. Next, the test piece is embedded in resin so that the plane consisting of the longitudinal direction and the wall thickness direction relative to the rolling direction of the steel pipe (L cross section) becomes the observation surface, and the surface is mirror-polished. The mirror-polished surface is observed with an optical microscope, and the number of inclusions with an aspect ratio of 2.0 or more and a length of 10 μm or more in a 10 mm × 10 mm area is counted. The number of inclusions obtained is divided into the area of ​​the area (100 mm 2 ) to calculate the number density.

[0038] Ten test pieces for measuring inclusions are taken from each steel pipe to be measured, and the arithmetic mean of the number densities of these 10 test pieces is used as the number density of inclusions in that steel pipe. The aspect ratio and major diameter of the inclusions are determined in accordance with JIS G0555:2020 (Microscopic Testing Method for Nonmetallic Inclusions in Steel).

[0039] From the same viewpoint, the total area fraction of martensite and bainite in the structure of the steel pipe is preferably 80% or more, and the area fraction of martensite is more preferably 80% or more. The upper limit of the total area fraction of martensite and bainite is not particularly limited, but may be 100%. The upper limit of the area fraction of martensite is not particularly limited, but may be 100%. The area fraction of ferrite is preferably 5% or less. The lower limit of the area fraction of ferrite is not particularly limited, but may be 0%. In this specification, martensite is defined to include tempered martensite.

[0040] The area fractions of martensite, bainite, and ferrite can be determined by taking a microstructural photograph under a microscope and analyzing the image of the microstructural photograph. The microstructural observation can be performed using either an optical microscope or a scanning electron microscope at an appropriate magnification between 100 and 5000 times. The test specimen used for the microstructural observation is taken at the longitudinal center of the steel pipe, at a position corresponding to 1 / 4 of the inner wall thickness. The cross section of the sampled test specimen is etched using a 3 vol% nital solution to reveal the microstructure, and then the microstructural observation is performed. The identification of each structure in the microstructural photograph can be performed, for example, by comparing the structure of each part of the microstructural photograph with the microstructural photographs included in Non-Patent Document 2.

[0041] The two or more steel pipes may have the same or different structures, but it is preferable that they have the same structure.

[0042] When storing hydrogen in a pressure vessel, it is necessary to consider hydrogen embrittlement of the material. From the viewpoint of preventing hydrogen embrittlement, the tensile strength (TS) of each of the two or more steel pipes is preferably 1100 MPa or less, and more preferably 950 MPa or less. On the other hand, although there is no limitation on the lower limit of the tensile strength, if the tensile strength is low, it is necessary to increase the wall thickness of the steel pipe to ensure the strength required for the pressure vessel, which will result in increased costs. Therefore, it is preferable that the tensile strength of each of the two or more steel pipes is 800 MPa or more.

[0043] The steel pipe is not particularly limited, and may be one manufactured by any method, such as an electric resistance welded pipe, a spiral steel pipe, a UOE steel pipe, a steel pipe formed by hollowing out the interior of a steel material by machining or the like, a steel pipe manufactured by forging, or a seamless steel pipe formed by rolling a heated steel billet into a steel pipe shape.

[0044] In the present invention, it is essential that the steel pipes are joined together by screws rather than by welding, but welding is permitted in the manufacture of the individual steel pipes themselves for the following reasons.

[0045] That is, as mentioned above, when joining steel pipes together on-site, it is difficult to precisely control the welding conditions, and therefore welding quality becomes an issue. However, welding when manufacturing steel pipes is generally performed under strictly controlled conditions in factories such as steel mills, resulting in high weld quality. In addition, post-weld heat treatment is also performed as necessary to improve the mechanical properties of the weld. Therefore, compared to welds formed when steel pipes are welded together on-site, the welds of ordinary steel pipes themselves are less likely to cause fracture. Therefore, it is also possible to use steel pipes manufactured using welding, such as electric resistance welded pipes, spiral steel pipes, and UOE steel pipes.

[0046] However, from the viewpoint of further reducing the risk of fracture and enabling use at higher pressures, it is preferable to use a seamless steel pipe as the steel pipe. Seamless steel pipes are particularly suitable because they have no welds, so the properties of the base material are uniform throughout the steel pipe, and they are less expensive than steel pipes manufactured by boring or forging, yet have superior properties such as toughness.

[0047] Furthermore, the length of each steel pipe is not particularly limited and can be any length. However, if the length of the steel pipe is excessively short, the number of joints per pressure vessel increases, which leads to increased costs. Therefore, the length of each of the two or more steel pipes is preferably 3 m or more, and more preferably 5 m or more. On the other hand, if the individual steel pipes are long, the number of joints can be reduced, which may reduce costs, but if they are too long, transportation may be difficult. The length of each of the two or more steel pipes is preferably 100 m or less, more preferably 12 m or less so that it can be transported by vehicle, and even more preferably 6 m or less.

[0048] As described above, the high-pressure hydrogen gas accumulator of the present invention can ensure any volume by connecting a number of steel pipes according to the space available at the installation location, without being subject to manufacturing and transportation constraints. Therefore, the number of steel pipes constituting one steel vessel is not particularly limited and can be any number equal to or greater than two. For example, when loading onto a tanker or the like, several tens to a hundred and several tens of steel pipes can be connected to form an accumulator with a length of several tens to several hundred meters. Furthermore, an ultra-large-capacity accumulator can also be constructed by connecting a large number of steel pipes, exceeding several hundred. Therefore, there is no upper limit on the number of steel pipes, and any number can be used according to the space available at the installation location. For example, in one embodiment of the present invention, the number of steel pipes may be 1,000 or less, 500 or less, 200 or less, or 100 or less.

[0049] [Structure of Joint Portion] In the present invention, the structure of the portion where steel pipes are joined together by a screw (hereinafter referred to as the "joint portion") is not particularly limited, and any structure can be used as long as it allows steel pipes to be connected by a screw. Furthermore, the shape of the screw is not particularly limited, and any shape can be used as long as it can support the required stress.

[0050] The steel pipes constituting the steel container are preferably arranged so that their central axes are coaxial. By arranging the central axes of the steel pipes coaxially, connection by a threaded structure can be more easily performed.

[0051] In the present invention, since steel pipes are joined together using threads, if the central axes of adjacent steel pipes are misaligned significantly, stress such as bending will be applied to the thread structure, causing breakage. Therefore, the misalignment of the central axes of the steel pipes constituting the steel container is preferably 5 mm or less, and more preferably 1 mm or less. Here, the misalignment of the central axes of the steel pipes constituting the steel container is defined as the maximum value of the misalignment between the central axis of each steel pipe included in the steel container and the central axis of the steel pipe adjacent to that steel pipe.

[0052] It is also preferable to place a sealing member at the joint. By providing a sealing member, it is possible to further prevent leakage of hydrogen gas. The sealing member can typically be placed between two adjacent steel pipes. Furthermore, when connecting using a coupling, which will be described later, it is preferable to place a sealing member between the steel pipe and the coupling adjacent to the steel pipe. The sealing member is not particularly limited, and any sealing member such as a gasket, packing, or O-ring can be used.

[0053] The material of the sealing member is not particularly limited, and any material can be used, such as metal, resin, etc. From the viewpoint of improving sealing performance, it is preferable to use resin, copper, etc., which can deform when the screw is tightened to improve sealing performance.

[0054] From the viewpoint of more reliably preventing leakage, it is more preferable to arrange the sealing members in a double configuration, where the double configuration means that two sealing members are arranged between the steel pipe and a member adjacent to the steel pipe (another steel pipe or a coupling).

[0055] Furthermore, in a structure in which steel pipes are joined together with screws, as in the present invention, stress is concentrated at the threaded portion. Therefore, it is preferable to position the sealing member closer to the interior of the steel container than the threaded portion. By positioning the sealing member closer to the interior of the steel container than the threaded portion, it is possible to prevent the threaded portion from coming into contact with hydrogen gas. As a result, hydrogen embrittlement of the threaded portion can be suppressed, thereby reducing the risk of fracture of the steel container.

[0056] The steel container can be provided with lids on both ends. Any lid can be used as the lid as long as it can seal the steel container. There are no particular restrictions on the material of the lid, but it is generally preferable to use a steel lid. The lid is preferably a screw-on lid.

[0057] Four preferred joint structures will be described below with reference to the drawings. In the following embodiments, the steel pipes have the same inner and outer diameters, but the inner and outer diameters of the individual steel pipes may be the same or different.

[0058] 1 is a cross-sectional schematic diagram showing the structure of a joint portion of a high-pressure hydrogen gas accumulator 1 according to a first embodiment of the present invention. The steel vessel of the high-pressure hydrogen gas accumulator in this embodiment is made up of a plurality of steel pipes 10, and adjacent steel pipes are joined together by screws having the structure shown in FIG.

[0059] That is, a female thread portion 11a is formed at one end of the first steel pipe 10a, and a male thread portion 12b that screws together with the female thread portion 11a of the first steel pipe 10a is provided at one end of the second steel pipe 10b. The first steel pipe 10a and the second steel pipe 10b are connected by screwing together the female thread portion 11a of the first steel pipe 10a and the male thread portion 12b of the second steel pipe 10b.

[0060] When a sealing portion is to be placed, it is preferable to place it at a position further to the left of the leftmost thread portion of the female thread portion 11a, i.e., at a position that can prevent hydrogen gas from reaching the thread portion (see Figure 3 of the second embodiment described below).

[0061] The steel container can be provided with lids on both ends. Any lid can be used as the lid as long as it can seal the steel container. For example, as shown in Figure 8, a screw-on lid 50 can be provided on the end of the steel container. Note that lids can be provided in a similar manner in other embodiments described later. Note that the steel container shown in Figure 8 is made up of two steel pipes connected by screws, but the number of steel pipes may be any number equal to or greater than two.

[0062] Second Embodiment Fig. 2 is a cross-sectional schematic diagram showing the structure of a joint portion of a high-pressure hydrogen gas accumulator 1 according to a second embodiment of the present invention. The steel vessel of the high-pressure hydrogen gas accumulator in this embodiment is made up of a plurality of steel pipes 10, and adjacent steel pipes are joined together using couplings 20 provided inside the steel pipes as shown in Fig. 2.

[0063] That is, a female thread portion 11a is formed at one end of the first steel pipe 10a, and a male thread portion 22 that screws onto the female thread portion 11a of the first steel pipe 10a is provided at one end of the coupling 20. A female thread portion 11b is formed at one end of the second steel pipe 10b, and a male thread portion 22 that screws onto the female thread portion 11b of the second steel pipe 10b is provided at the other end of the coupling 20. The first steel pipe 10a and the second steel pipe 10b are connected via the coupling 20 by screwing the female thread portion 11a of the first steel pipe 10a into the male thread portion 22 at one end of the coupling 20, and by screwing the female thread portion 11b of the second steel pipe 10b into the male thread portion 22 at the other end of the coupling 20.

[0064] Furthermore, as shown in Figure 3, it is preferable to provide an O-ring 30 as a sealing member between the steel pipe 10 and the coupling 20. In particular, by arranging two O-rings 30 as shown in Figure 3, leakage of hydrogen gas can be more reliably prevented.

[0065] 2 and 3 show a case where the inner diameter of the coupling 20 is the same as the inner diameter of the steel pipe 10, but the inner diameter of the coupling 20 may be different from the inner diameter of the steel pipe 10. Also, in the example shown in Figures 2 and 3, the first steel pipe 10a and the second steel pipe 10b are in contact with each other, but they may be separated from each other.

[0066] (Third embodiment) Figure 4 is a cross-sectional schematic diagram showing the structure of a joint portion of a high-pressure hydrogen gas accumulator 1 according to a third embodiment of the present invention. The steel vessel of the high-pressure hydrogen gas accumulator in this embodiment is made up of a plurality of steel pipes 10, and adjacent steel pipes are joined together using couplings 20 provided inside the steel pipes as shown in Figure 4.

[0067] That is, a male threaded portion 12a is formed at one end of the first steel pipe 10a, and a female threaded portion 21 that threadably engages with the male threaded portion 12a of the first steel pipe 10a is provided at one end of the coupling 20. A male threaded portion 12b is formed at one end of the second steel pipe 10b, and a female threaded portion 21 that threadably engages with the male threaded portion 12b of the second steel pipe 10b is provided at the other end of the coupling 20. The first steel pipe 10a and the second steel pipe 10b are connected via the coupling 20 by threading the male threaded portion 12a of the first steel pipe 10a into the female threaded portion 21 at one end of the coupling 20, and the male threaded portion 12b of the second steel pipe 10b into the female threaded portion 21 at the other end of the coupling 20.

[0068] Furthermore, as shown in Fig. 5, it is preferable to provide an O-ring 30 as a sealing member between the steel pipe 10 and the coupling 20. In particular, in the example shown in Fig. 5, an O-ring is provided not only between the first steel pipe 10a and the coupling 20 and between the second steel pipe 10b and the coupling 20, but also between the first steel pipe 10a and the second steel pipe 10b (at the abutting portion).

[0069] 4 and 5 show a case where the inner diameter of the coupling 20 and the inner diameter of the steel pipe 10 are the same, but the inner diameter of the coupling 20 and the inner diameter of the steel pipe 10 may be different. Also, in the example shown in Figures 4 and 5, the first steel pipe 10a and the second steel pipe 10b are in contact with each other, but they may be separated as will be explained in the following fourth embodiment.

[0070] (Fourth Embodiment) Figure 6 is a cross-sectional schematic diagram showing the structure of a joint portion of a high-pressure hydrogen gas accumulator 1 according to a fourth embodiment of the present invention. In the steel vessel of this embodiment, similar to the third embodiment, adjacent steel pipes are joined together using a coupling 20 provided inside the steel pipes. However, whereas the ends of the first steel pipe 10a and the second steel pipe 10b abut against each other in the third embodiment, the ends of the first steel pipe 10a and the second steel pipe 10b do not directly contact each other in this embodiment. Other aspects of the fourth embodiment are similar to those of the third embodiment. For example, as shown in Figure 7, it is preferable to provide an O-ring 30 as a sealing member between the steel pipe 10 and the coupling 20.

[0071] Furthermore, it is also preferable to install at least one leak port for detecting hydrogen leaks. By placing a hydrogen detector at the tip of the leak port, hydrogen gas leaks can be detected. The location of the leak port is not particularly limited, but it is preferable to install it between one or both of the end of the coupling and the thread closest to that end, and between the seal member and the thread closest to the seal member. Figure 7 shows an example of the arrangement when a leak port 40 is provided. A hydrogen detector (not shown) or the like can be connected to the leak port 40.

[0072] It is also possible to provide a leak port when steel pipes are directly connected to each other with screws as shown in Figure 1, or when a coupling is used that is provided on the inside of the steel pipe as shown in Figures 2 and 3. However, in such cases, it is necessary to provide a leak port in the steel pipe. On the other hand, when a coupling is used that is provided on the outside of the steel pipe as shown in Figure 7 above, it is only necessary to provide a leak port in the coupling, making manufacturing easier.

[0073] Regardless of the structure of the joint, it is also preferable to apply a pressure of 1.5 times or more the working pressure after screw tightening to impart compressive residual stress to the thread root. By imparting compressive residual stress, the number of times the thread can be used can be increased.

[0074] From the viewpoint of corrosion prevention, it is preferable to apply anticorrosion treatment such as painting to the surface. It is also preferable to install a support stand near the screw joint to reduce excessive stress on the joint.

[0075] Next, in order to confirm the effect of the present invention, a steel container was produced using a plurality of steel pipes, and its performance was evaluated.

[0076] Specifically, two steel pipes each having the material, type, and dimensions shown in Table 1 were first prepared, and the two steel pipes were joined together to form a steel container using the joining method shown in Table 1. The symbols for the steel pipe materials in Table 1 represent the following steel types: a: X52 b: SCM435 c: SNCN439 d: X65

[0077] The symbols A to F for the joining methods shown in Table 1 represent the following structures. The structures of A to E are as shown in Figures 1 to 5, respectively. A resin O-ring was used. A: Direct screw joining B: Inner coupling (without O-ring) C: Inner coupling (with O-ring) D: Outer coupling (without O-ring) E: Outer coupling (with O-ring) F: Welding

[0078] Both ends of the container were sealed with 110 mm thick lids having the same thread shape as the joints. In all examples, the lids were made of SNCM439 steel with a tensile strength (TS) of 900 MPa, and the SNCM439 steel was forged into the lid shape. Hydrogen gas was introduced by connecting a pipe to a hole drilled in the center of the lid. The lid may have a structure including two parts: a lid without a thread structure and a threaded member supporting the lid.

[0079] Of the materials used, SCM435 and SNCM439 steels were adjusted to TS800 to 900 MPa by quenching and tempering, while X52 and X65 were produced by hot rolling.

[0080] For comparison, No. 7 used an electric resistance welded steel pipe, and these electric resistance welded steel pipes were joined by welding. No. 8 used UOE steel pipes. Welding was performed under standard conditions for each steel type. The joints of Nos. 1 to 6, which were joined by threads, were not welded and therefore retained the base metal structure, while the joint structures of Nos. 7 to 9 were welded structures.

[0081] The area fractions of martensite (M), bainite (B), retained austenite (RA), and ferrite in each steel pipe were measured using the method described above. The number density of inclusions with an aspect ratio of 2.0 or more and a major axis of 10 μm or more was also measured using the method described above. Test specimens taken from the center of the steel pipe in the longitudinal direction and at a quarter-way position on the inner wall thickness were used to measure the area fractions and number density of inclusions. The measurement results are also shown in Table 1.

[0082] (Pressure Increase Test) A high-pressure hydrogen gas pressure vessel was fabricated using the obtained steel container, and pure hydrogen was actually filled inside to check for hydrogen leakage from threaded joints or welds. Specifically, hydrogen gas was pressurized to a predetermined pressure using a compressor and filled into the high-pressure hydrogen gas pressure vessel. This state was maintained for 10 minutes, and a test was conducted to determine whether or not hydrogen gas leakage occurred. The test was repeated while increasing the pressure in 5 MPa increments up to a maximum of 50 MPa, and the highest pressure at which leakage did not occur was determined. The evaluation results are also shown in Table 1.

[0083] (Toughness) Furthermore, the manufactured pressure vessels were used to evaluate the toughness of the joints in hydrogen gas in accordance with ASTM-E1820. Specifically, three test specimens were taken from each pressure vessel from the joints (for steel vessels joined by welding, from the weld metal and HAZ (heat affected zone)) so that the test specimens were oriented in the L-C direction, and the fracture toughness was measured. The test method may be either ASME E1681 or a method according to ASTM E399. The test environment was pure hydrogen at 21 MPa. The average fracture toughness value of the three test specimens was 52 MPa m 1 / 2 Higher is better, 52 MPa m 1 / 2 The following cases were judged to be defective. The evaluation results are shown in Table 1.

[0084] As can be seen from the results shown in Table 1, the high-pressure hydrogen gas accumulator satisfying the conditions of the present invention had a maximum pressure of 15 MPa or more at which leakage did not occur, and also had good toughness of the joints in hydrogen gas. In contrast, the accumulator joined by welding had a maximum pressure of 10 MPa at which leakage did not occur, and also had poor toughness of the joints in hydrogen gas.

[0085] As described above, according to the present invention, by connecting steel pipes that are easy to produce and transport, it is possible to easily create a large-capacity pressure accumulator that can stably store high-pressure hydrogen gas. In this example, the steel container was made using two steel pipes, but even if three or more pipes are used, the load on each connection will basically not change as long as the pressure is the same. For reference, Table 1 also shows the number of steel pipes required to make a pressure accumulator that can store 1,000 kg of hydrogen, which is 10 times the hydrogen storage capacity of a typical hydrogen station (approximately 100 kg), using steel pipes of the sizes of each example.

[0086]

[0087] REFERENCE SIGNS LIST 1 High-pressure hydrogen gas accumulator 10 Steel pipe (10a First steel pipe) (10b Second steel pipe) 11 Female thread portion 12 Male thread portion 20 Coupling 21 Female thread portion 22 Male thread portion 30 O-ring 40 Leak port 50 Lid

Claims

1. A pressure accumulator for high-pressure hydrogen, comprising a steel container, wherein the steel container is composed of two or more steel pipes connected by screws.

2. The pressure accumulator for high-pressure hydrogen gas according to claim 1, wherein the connection by the screws is performed by a coupling provided inside the steel pipe.

3. The pressure accumulator for high-pressure hydrogen gas according to claim 1, wherein the connection by the screws is performed by a coupling provided outside the steel pipe.

4. The pressure accumulator for high-pressure hydrogen gas according to any one of claims 1 to 3, having a sealing member at the connection portion of the two or more steel pipes.

5. The steel pipe has, in mass%, C: 0.005 to 0.60%, Si: 0.001 to 2.0%, Mn: 0.01 to 5.0%, P: 0.0001 to 0.060%, S: 0.00001 to 0.010%, N: 0.00001 to 0.010%, Al: 0.0001 to 1.00%, O: 0.010% or less, and H: 0 to 0.0010%, and has a component composition consisting of the balance Fe and unavoidable impurities. The pressure accumulator for high-pressure hydrogen gas according to any one of claims 1 to 4.

6. The component composition has, in mass%, Mo: 0.0001 to 5.0%, Cr: 0.0001 to 5.0%, Ni: 0.0001 to 5.0%, Cu: 0.0001 to 5.0%, Co: 0.0001 to 5.0%, B: 0.0001 to 0.01%, V: 0.0001 to 1.0%, W: 0.0001 to 5.0%, Nb: 0.0001 to 0.1%, Ti: 0.0001 to 0.1%, Zr: 0.0001 to 0.2%, Hf: 0.0001 to 0.2%, Ta: 0.0001 to 0.2%, Sb: 0.0001 to 0.2%, Sn: 0.0001 to 0.2%, Ca: 0.0001 to 0.01%, Mg: 0.0001 to 0.01%, and REM: 0.0001 to 0.5%. The pressure accumulator for high-pressure hydrogen gas according to claim 5, further containing at least one selected from the group consisting of.

7. The area fraction of retained austenite in the structure of the steel pipe is 0 to 3%, and the number density of inclusions having an aspect ratio of 2.0 or more and a major axis of 10 μm or more is 10 pieces / 100 mm 2 The accumulator for high-pressure hydrogen gas according to claim 5 or 6, wherein the number density is 10 pieces / 100 mm or less.

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