High-pressure hydrogen container

Abstract

Provided is a high-pressure hydrogen container that inhibits damage due to diffusion of hydrogen into a metal structure. The high-pressure hydrogen container according to the present invention includes a cylindrical body made of a metal for storing high-pressure hydrogen, and a cover member that plugs an end portion of the cylindrical body, the cylindrical body including a joining portion for fixing the cover member to the end portion in a central axis direction of the cylindrical body, a cylindrical portion that is an outer contour of a storage portion for storing high-pressure hydrogen, and a sealing surface that is disposed between the joining portion and the cylindrical portion in the central axis direction and is formed on an inner surface of the cylindrical body, and the cover member including a sealing portion that abuts against the sealing surface of the cylindrical body, and a fixing portion that is fixed to the joining portion of the cylindrical body, wherein, when a region of the sealing surface that abuts against the sealing portion is set as an abutting region, a wall thickness from the abutting region to an outer surface of the cylindrical body is set as a wall thickness H, a portion of the cylindrical body that includes the joining portion and that generates a stress of a predetermined stress σ or more from the joining portion to the abutting region is set as a stress generation portion, and a distance between the abutting region and the stress generation portion is set as a distance L, the relationship between the wall thickness H and the distance L satisfies at least H < L.

Description

Technical Field

[0001] This invention relates to a high-pressure hydrogen container for storing high-pressure hydrogen. Background Technology

[0002] For example, a high-pressure hydrogen container used in a hydrogen station for storing high-pressure hydrogen employs a structure in which a cap is threadedly fixed to the open end of a high-pressure cylinder. The hydrogen gas filling the high-pressure cylinder in such a container is sealed by a resin sealing component, such as an O-ring, located between the inner circumferential surface of the high-pressure cylinder and the outer circumferential surface of the cap (see, for example, Patent Document 1).

[0003] However, according to Patent Document 1, trace amounts of hydrogen can permeate through the resin sealing component. Therefore, the hydrogen reaches the internal thread at the opening of the high-pressure cylinder, causing hydrogen-induced damage starting from the stress-concentrated thread bottom. To solve this problem, the high-pressure hydrogen container disclosed in Patent Document 1 is constructed with a through-hole in the gap between the internal thread and the resin sealing component to discharge gas from the gap, and oxygen-containing gas is introduced into the gap.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-56457 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The high-pressure hydrogen container disclosed in Patent Document 1 allows hydrogen that has permeated into the resin-sealed component and remained in the gap to be discharged through the through hole. Therefore, although an internally threaded portion adjacent to the gap and generating high stress is provided, the high-pressure hydrogen container suppresses cracking caused by hydrogen permeating into the resin-sealed component and remaining in the gap. However, when high-pressure hydrogen is stored in a metal container, hydrogen molecules present at a predetermined concentration within the container penetrate into the metal structure constituting the metal container and diffuse into the metal structure. That is, in the high-pressure hydrogen container of Patent Document 1, hydrogen from the high-pressure cylinder penetrates into the interior of the metal structure constituting the high-pressure cylinder, diffuses within the metal structure, and reaches the internally threaded portion. The internally threaded portion experiences stress concentration due to the screwing with the cap fastened to the open end of the high-pressure cylinder, thus generating high stress compared to other parts of the container. Furthermore, the high-pressure cylinder in Patent Document 1 has a contact surface perpendicular to the central axis provided on its inner circumferential surface. When the cap contacts the contact surface, an axial force is generated on the cap, and the cap is fastened to the internally threaded portion. Therefore, stress concentration occurs not only in the internal threads of the high-pressure hydrogen container but also around the contact surface. Consequently, the stress-generating areas in the internal threads and around the contact surface become the starting point for cracking and other damage due to the influence of hydrogen diffusing within the metal structure.

[0009] The present invention addresses the aforementioned problems and aims to provide a high-pressure hydrogen container that suppresses damage caused by hydrogen diffusion into the metal structure.

[0010] Methods for solving problems

[0011] The high-pressure hydrogen container of the present invention comprises a metal cylindrical body for storing high-pressure hydrogen and a capping member for blocking the end of the cylindrical body. The cylindrical body comprises: a joint for fixing the capping member to the end in the direction of the central axis of the cylindrical body; a cylindrical portion forming the outline of the storage portion for storing high-pressure hydrogen; and a sealing surface disposed between the joint and the cylindrical portion in the direction of the central axis and formed on the inner surface of the cylindrical body. The capping member comprises: a sealing portion abutting against the sealing surface of the cylindrical body; and a fixing portion fixed to the joint of the cylindrical body. When the area of ​​the sealing surface that abuts against the sealing portion is defined as the abutting area, the wall thickness from the abutting area to the outer surface of the cylindrical body is defined as the wall thickness H, the portion of the cylindrical body including the joint and the portion from the joint to the abutting area that generates a stress of a predetermined stress σ or more is defined as the stress generating portion, and the distance between the abutting area and the stress generating portion is defined as the distance L, the relationship between the wall thickness H and the distance L at least satisfies H. <L。

[0012] The effects of the invention

[0013] In the high-pressure hydrogen container according to the present invention, since the distance L between the stress generation portion that generates a specified stress by fixing the lid member to the cylinder body and the contact region satisfies the relationship H < L, the metal material constituting the cylinder body is not affected by hydrogen diffusion. Therefore, it is possible to suppress the influence of hydrogen diffusion into the metal structure of the high-pressure hydrogen container on the strength, and it is possible to provide a high-pressure hydrogen container with high reliability even when a high load is applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a cross-sectional view showing a high-pressure hydrogen container 100 according to Embodiment 1.

[0015] Figure 2 is Figure 1 an enlarged view of the vicinity of the internal thread portion 15 and the sealing surface 16 of

[0016] Figure 3 FIG. is a view showing the hydrogen diffusion state in the metal structure near the sealing portion 23 of the high-pressure hydrogen container 100 according to Embodiment 1.

[0017] Figure 4 FIG. is a view showing the correlation between the pressure of hydrogen gas and the initial amount of hydrogen that has penetrated into the metal structure.

[0018] Figure 5 FIG. is a view showing the correlation between the hydrogen diffusion coefficient D and the diffusion flux J.

[0019] Figure 6 FIG. is a view showing an example of the stress generation state around the internal thread portion 15 of the high-pressure hydrogen container 100 according to Embodiment 1.

[0020] Figure 7 FIG. is a view showing the relationship between the stress applied to the metal material and the number of cycles of the applied stress. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Hereinafter, preferred embodiments of the high-pressure hydrogen container of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments described below are suitable specific examples of the present invention, and thus various technically preferred limitations are imposed. However, unless there is a description specifically limiting the present invention in the following description, the scope of the present invention is not limited to these embodiments.

[0022] Embodiment 1.

[0023] <High-pressure hydrogen container 100>

[0024] Figure 1 FIG. shows a cross-sectional view of the high-pressure hydrogen container 100 according to Embodiment 1. Figure 1The high-pressure hydrogen container 100 shown schematically illustrates its structure. The high-pressure hydrogen container 100 is installed, for example, in a hydrogen station supplying hydrogen to vehicles, and stores high-pressure hydrogen inside. Fuel cell vehicles, for example, have tanks that store hydrogen at a high pressure of approximately 75 MPa. To fill the tank of such a vehicle with hydrogen, a high-pressure hydrogen container 100 is needed that can maintain an internal pressure higher than that of the vehicle's tank. Although the internal pressure of the high-pressure hydrogen container 100 decreases each time hydrogen is supplied to a fuel cell vehicle, the internal pressure is maintained at a high level. That is, the high-pressure hydrogen container 100 is subjected to periodic pressure fluctuations in a high-pressure region. Moreover, considering the frequency of hydrogen supply to the vehicle, the high-pressure hydrogen container 100 needs to withstand high pressure and high-cycle pressure fluctuations, and maintain durability over a long period.

[0025] <Composition of High-Pressure Hydrogen Container 100>

[0026] like Figure 1 As shown, the high-pressure hydrogen container 100 according to Embodiment 1 includes a metal cylindrical body 10 and a cover 20 fastened to the open end of the cylindrical body 10. The metal cylindrical body 10 is cylindrical in shape and open at both ends. An internal thread 15 is formed at the open end. The internal thread 15 is a thread formed on the inner surface of the cylindrical body 10. In addition, along the central axis direction of the cylindrical body 10 (along...) Figure 1 A cylindrical portion 13 is disposed in the central part along the central axis C, and the cylindrical portion 13 forms the outline of the hydrogen storage portion 12. The cylindrical portion 13 is a cylindrical part. In Embodiment 1, the wall thickness of the portion of the cylindrical portion 13 in which the storage portion 12 is disposed is set to, for example, t = 50 mm. Sometimes the cover 20 and the component that fixes the cover 20 to the end of the cylindrical body 10 are referred to as the cover component.

[0027] A sealing surface 16 is formed between the cylindrical portion 13 and the internal thread portion 15 along the central axis direction of the cylindrical body 10. The sealing surface 16 is a surface formed on the inner surface of the cylindrical body 10, which abuts against the sealing portion 23 of the cover 20, and is the part that prevents hydrogen from leaking from the inside of the high-pressure hydrogen container 100. In order to maintain the airtightness, the part of the sealing surface 16 that abuts against the sealing portion 23 can be made of a smooth surface.

[0028] In Embodiment 1, the cover 20 includes a first component 21 and a second component 22. The first component 21 has a sealing portion 23, and the second component 22 has an external thread portion 25. The first component 21 is a component that blocks the end of the hydrogen storage portion 12 in the direction of the central axis. The first component 21 is formed in a generally cylindrical shape, and in Embodiment 1, its outer diameter is smaller than the sealing surface 16 of the cylinder 10. A groove 21a is formed on the outer peripheral surface of the first component 21 (see...). Figure 2 The sealing component 24 is embedded therein. The sealing component 24 is, for example, an O-ring, but other sealing components may also be used.

[0029] Figure 2 yes Figure 1 An enlarged view of the periphery of the internal thread portion 15 and the sealing surface 16. The internal thread portion 15 is formed from the opening end 19 of the cylinder 10 within a defined range. A clearance portion 17 is disposed next to the internal thread portion 15. The clearance portion 17 is a stepped shape formed on the inner surface of the cylinder 10 between the internal thread portion 15 and the sealing surface 16, that is, a portion with an inner diameter larger than the internal thread portion 15, serving as a tool retraction point when machining the internal thread portion 15. In Embodiment 1, the two ends of the clearance portion 17 are inclined surfaces, which are connected to the internal thread portion 15 and the sealing surface 16, respectively. By slowing down the change in the inner diameter of the cylinder 10, the stress generated by the pressure of the storage portion 12 and the tightening of the internal thread portion 15 is mitigated.

[0030] A sealing surface 16 is formed next to the retraction portion 17 in the central axis direction. In Embodiment 1, the inner diameter of the sealing surface 16 is smaller than that of the retraction portion 17, and is formed to be the same as the inner diameter of the cylinder portion 13, but the inner diameter can be appropriately set to match the sealing portion 23 of the cover 20. By abutting against the sealing member 24, the sealing is achieved in a way that prevents hydrogen leakage from the storage portion 12. It should be noted that the wall thickness of the portion of the cylinder 10 where the sealing surface 16 is disposed is set to wall thickness H. This wall thickness H and the wall thickness t of the cylinder 10 in the storage portion 12 can also be set to different values. That is, a step can also be formed between the sealing surface 16 of the cylinder 10 and the inner surface of the storage portion 12. In Embodiment 1, as an example, a configuration where H = t is shown.

[0031] (Cylinder 10)

[0032] The cylindrical body 10 is made of, for example, low-alloy steel. That is, the cylindrical body 10 is made of steel such as chromium-molybdenum steel, nickel-chromium-molybdenum steel, manganese-chromium steel, manganese steel, or boron-infiltrated steel. Furthermore, the cylindrical body 10 is a cylindrical shape open at both ends, and internal threads 15, tool retraction portions 17 for threading, and sealing surfaces 16 are formed on the inner circumferential surfaces of both ends. Additionally, the inner side of the central portion of the cylindrical body 10 forms a cylindrical portion 13 that serves as a storage portion 12. It should be noted that in Embodiment 1, the cylindrical body 10 is a cylindrical shape open at both ends, but it can also be a bottomed cylindrical shape open at one end. Furthermore, the cylindrical body 10 is not limited to a cylindrical shape and can be other shapes such as an elliptical cylinder.

[0033] The decarburized layer is removed from the inner circumferential surface of the cylinder 10 by machining. Furthermore, after removing the decarburized layer, residual compressive stress is imparted by irradiating the inner circumferential surface of the cylinder 10 with high-mass shot peening. Residual compressive stress can also be imparted to the cylinder portion 13, the sealing surface 16, the shear portion 17, and the internal thread portion 15.

[0034] Hydrogen gas leaking from the sealing part 23 may sometimes accumulate in the retraction part 17 and the internal thread part 15. The strength of the stress-generating part M in the retraction part 17 and the internal thread part 15 may sometimes decrease due to the leaked hydrogen gas. Therefore, in order to discharge the accumulated hydrogen gas, a discharge hole (not shown) that communicates with the outside and the space formed by the retraction part 17 may be provided. Alternatively, multiple holes communicating with the outside and the retraction part 17 may be provided to allow the gas in the retraction part 17 to circulate with the outside air.

[0035] (Cover 20)

[0036] The cover 20 is engaged with the end of the cylinder 10. The cover 20 is positioned along the central axis of the storage compartment 12, sealing the end of the cylinder 10. The cover 20 includes a first component 21 facing the storage compartment 12 and a second component 22 fixed to the internal thread 15 of the cylinder 10. The first component 21, called a plug, is the component that seals the storage compartment 12. The second component 22, called a gland nut, is the component that secures the plug axially.

[0037] (Part 1, 21)

[0038] The first component 21 comes into contact with high-pressure hydrogen gas when hydrogen gas is filled into the storage section 12, and is therefore made of a material with high strength against low-temperature hydrogen gas. That is, the first component 21 is made of a material that ensures strength even at low temperatures, such as austenitic stainless steel. The first component 21 is formed in a generally cylindrical shape, and is formed such that at least its outer diameter is smaller than the inner diameter of the sealing surface 16. The end face of the first component 21 forms the axial surface of the storage section 12.

[0039] The outer peripheral surface of the first component 21 has a sealing portion 23. In Embodiment 1, the sealing portion 23 has a groove 21a and a sealing member 24. An O-ring, for example, is disposed on the groove 21a as the sealing member 24. The outer peripheral surface of the sealing member 24 abuts against the sealing surface 16 of the cylinder 10. The area in the sealing surface 16 of the cylinder 10 that abuts against the sealing member 24 is called the abutment area 18. The outer diameter of the sealing member 24 is set to be larger than the inner diameter of the sealing surface 16. Thus, the first component 21 is inserted into the inside of the cylinder 10 by pressing the sealing member 24 into it. The O-ring, which is the sealing member 24, is pressed by the sealing surface 16 and fills the interior of the groove 21a, sealing the gap between the bottom surface of the groove 21a and the sealing surface 16. Through the structure formed by these sealing portions 23 and the sealing surface 16, high-pressure hydrogen gas is sealed in a way that prevents leakage from the storage section 12.

[0040] (Part 2, 22)

[0041] The second component 22 has an external thread 25 that engages with the internal thread 15 of the cylinder 10 and an end face 29 that abuts against the end face 28 of the first component 21. The second component 22 suppresses the axial force exerted on the first component 21 by the high-pressure hydrogen gas from the storage section 12 and fixes the cover 20 to the end of the cylinder 10. The external thread 25 of the second component 22 engages with the internal thread 15 of the cylinder 10, and the axial position of the cover 20 is fixed. In Embodiment 1, the cylinder 10 and the cover 20 do not have surfaces that abut against each other in the axial direction. Therefore, at the engagement of the internal thread 15 of the cylinder 10 and the external thread 25 of the second component 22, the frictional force between the sealing portion 23 of the first component 21 and the sealing surface 16 of the cylinder 10, and the force generated by the high-pressure hydrogen gas from the storage section 12, are applied as an axial force. The axial force generates a tightening force between the internal thread 15 and the external thread 25, thus fixing the cover 20 to the end of the cylinder 10. It should be noted that the first component 21 and the cylinder 10 can also be configured to abut in the axial direction. Additionally, the second component 22 and the cylinder 10 can also be configured to abut in the axial direction. In this case, the tightening force between the internal thread 15 and the external thread 25 is generated by the axial force produced by the abutment in the axial direction.

[0042] In Embodiment 1, the first component 21 is formed in a cylindrical or disc shape, but a pipe may also be joined at the center. The pipe supplies liquid hydrogen or hydrogen gas to the storage section 12 from the outside. Alternatively, the pipe discharges the hydrogen gas stored in the storage section 12 to the outside. The high-pressure hydrogen container 100 stores hydrogen gas at high pressure, for example, by filling hydrogen gas into a hydrogen tank mounted in a vehicle. Since the first component 21 of the cover 20 is provided with a pipe, it may be exposed to low temperatures when supplying liquid hydrogen or hydrogen gas; therefore, it is desirable to use a material such as austenitic stainless steel that ensures strength even at low temperatures. In addition, the second component 22 of the cover 20 does not come into contact with hydrogen gas and is not directly exposed to low temperatures. Therefore, the second component 22 can be made of the same low-alloy steel as the cylinder 10, as long as the strength of the external threaded portion 25, which serves as the fixing part, is ensured.

[0043] In Embodiment 1, the first component 21 and the second component 22 are separate, thus allowing them to be constructed from different materials, ensuring durability and reducing costs. In Embodiment 1, by using only austenitic stainless steel for the first component 21 and other materials for the second component 22, costs are reduced while ensuring the fixing strength and durability of the cover 20. It should be noted that the first component 21 and the second component 22 can also be integrated. By forming them as one unit, there is an advantage in reducing the number of components constituting the high-pressure hydrogen container 100.

[0044] (Positional relationship between the stress-generating part M around the joint and the sealing part 23)

[0045] In Embodiment 1, the second component 22 of the cylinder body 10 is screwed with the internal thread portion 15, and pressure is applied by high-pressure hydrogen from the storage portion 12, so that a predetermined stress σ is generated in each part. In the cylinder body 10, as the parts where stress concentration is likely to occur, there are the tool withdrawal portion 17 and the bottom 15a of the internal thread portion 15. Here, from Figure 1 and 2 The shorter one of the distances from the contact region 18 where the sealing portion 23 of the high-pressure hydrogen container 100 contacts the sealing surface 16 shown in to the bottom 15a of the tool withdrawal portion 17 or the internal thread portion 15 where stress concentration occurs is set as the distance L, and the distance from the contact region 18 to the outer surface of the cylinder body 10 is set as the wall thickness H. In the high-pressure hydrogen container 100 according to Embodiment 1, the relationship between the distance L and the wall thickness H satisfies H < L. By such a setting, the tool withdrawal portion 17 and the internal thread portion 15 where stress concentration is likely to occur can suppress the occurrence of breakage such as hydrogen embrittlement cracking due to the influence of the hydrogen in the storage portion 12.

[0046] (Example of hydrogen diffusion into the metal constituting the high-pressure hydrogen container 100)

[0047] Figure 3 is a diagram showing the hydrogen diffusion state in the metal structure near the sealing portion 23 of the high-pressure hydrogen container 100 according to Embodiment 1. Figure 3 is a diagram obtained by analyzing the diffusion of hydrogen gas in the storage portion 12 into the metal structure of the high-pressure hydrogen container under specified conditions. The cylinder body 10 of the high-pressure hydrogen container 100 according to Embodiment 1 is made of low alloy steel, so hydrogen invades the metal structure and diffuses from the surface contacted by the hydrogen gas filled in the storage portion 12. In the high-pressure hydrogen container 100 according to Embodiment 1, hydrogen diffuses from the contact region 18 where the sealing portion 23 contacts the sealing surface 16 to the region near the sealing surface 16. In addition, in the cylindrical portion 13, hydrogen diffuses from the inner surface to the outer surface of the cylindrical portion 13. However, compared with the radial direction of the cylinder body 10, hydrogen diffusion is not much in the axial direction. Therefore, the hydrogen diffused in the metal structure does not reach the tool withdrawal portion 17 and the internal thread portion 15 of the cylinder body 10. It should be noted that in the lid body 20, in the region near the central axis C of the first component 21, hydrogen diffuses in a manner of permeating in the wall thickness direction.

[0048] Figure 3 shows the hydrogen diffusion state into the metal structure of each part of the high-pressure hydrogen container 100, especially when using chromium molybdenum steel (SCM435) and filling 95 MPa of hydrogen gas in the storage portion 12. In addition, Figure 3This diagram shows the state when hydrogen diffuses into the metal structure of various parts of the high-pressure hydrogen container 100 and reaches a stable state. Over time, hydrogen in the storage section 12 of the high-pressure hydrogen container 100 penetrates into the metal structure and soon permeates the cylinder 10. Figure 3 In this process, the hydrogen permeation cylinder 10's cylindrical portion 13 becomes a state where hydrogen from the permeation cylinder 13 flows out to an environment at atmospheric pressure where a high-pressure hydrogen container 100 is installed. In this state, the amount of hydrogen diffusing within the metal structure of the cylinder 10 diffuses towards the wall thickness direction, but diffuses less axially. Furthermore, Figure 3 In the storage section 12, the initial hydrogen concentration was 0.181 ppm (by weight), and the hydrogen diffusion coefficient D was 2.3 × 10⁻⁶. -10 [m 2 / s].

[0049] Figure 3 The graph representing the hydrogen diffusion state in the high-pressure hydrogen container 100 is derived based on the hydrogen diffusion flow rate J within the metal structure shown below.

[0050] [Mathematical Expression 1]

[0051]

[0052] Here,

[0053] J: Diffusion flux [ppm·mm / s]

[0054] D: Diffusion coefficient [mm] 2 / s]

[0055] Normalized concentration

[0056] c: Hydrogen concentration [ppm]

[0057] s: solubility [ppm·mm / N] 1 / 2 ]

[0058] p: hydrostatic stress (σ) x +σ Y +σ Z ) / 3[MPa]

[0059] κ p : Concentration-dependent hydrostatic stress (coefficient) effective coefficient.

[0060] Figure 4 This is a graph showing the relationship between the pressure of hydrogen gas and the initial amount of hydrogen penetrating into the metal structure. Figure 4 This graph, derived from a high-pressure hydrogen permeation test, shows the relationship between the hydrogen pressure P and the amount of hydrogen C0 penetrating the chromium-molybdenum steel (SCM435). According to... Figure 4It can be seen that the amount of hydrogen C0 infiltrating chromium-molybdenum steel increases with increasing pressure P. For example... Figure 4 As shown, C0 = 0.523P (1 / 2) The relationship is exp(-1000 / T). Here, T is the temperature. Figure 3 The pressure inside the storage section 12 of the high-pressure hydrogen container 100 shown is set to 95 MPa, therefore, by Figure 3 It can be seen that the initial hydrogen content C0 was 0.181 ppm by weight.

[0061] Figure 5 This is a graph showing the correlation between the hydrogen diffusion coefficient D and the diffusion flux J. Figure 5 Through with Figure 4 The graph was obtained from the same high-pressure hydrogen permeation test. Hydrogen gas was introduced into a chromium-molybdenum steel (SCM435) container, and the hydrogen diffusion coefficient D was determined based on its behavior from the start of introduction until it permeated the container and reached a steady state. Furthermore, the hydrogen concentration was set to 0 [wt ppm] at the interface between the high-pressure hydrogen container 100 and the external gas. It should be noted that... Figure 5 In this context, t represents time [s], and x represents the distance [m] from the surface where the metal and hydrogen gas come into contact. Figure 3 Show Figure 5 The hydrogen diffusion coefficient D = 2.3 × 10⁻⁶ -10 [m 2 Hydrogen diffusion state of high-pressure hydrogen container 100 [ / s].

[0062] It should be noted that, in obtaining Figure 3 The solubility s shown in the figure, when hydrogen diffuses into the high-pressure hydrogen container 100, is 0.076033 [ppm·mm / N] using a material with similar strength and microstructure to chromium-molybdenum steel (SCM435). 1 / 2 (Reference: Fujii T., Hazama T., Nakajima H., and Horita R.: Current Solutions to Hydrogen Problems in Steels, (1982), 361, ASM International Materials, Park, Ohio.) Additionally, regarding the effective coefficient of hydrostatic stress κ... p The values ​​were obtained by linear interpolation of the coefficients for the following concentrations.

[0063] 0.00ppm: 0.00000[N] 1 / 2 / mm]

[0064] 1.00ppm: 0.10803[N] 1 / 2 / mm]

[0065] 3.00ppm: 0.54014[N] 1 / 2 / mm]

[0066] (Stress generated in high-pressure hydrogen container 100)

[0067] Figure 6 The figure shows an example of the stress generation state around the internal thread portion 15 of the high-pressure hydrogen container 100 according to Embodiment 1. Figure 6 The diagram shows the hydrostatic stress distribution around the junction of the cylinder 10 and the cover 20 when the storage section 12 of the high-pressure hydrogen container 100 is filled with hydrogen gas at 95 MPa. Figure 6 In the cylinder 10 and cover 20, a certain degree of stress is generated as a whole due to the pressure of high-pressure hydrogen in the storage section 12, but it is sufficiently low compared to the tensile strength of the materials constituting the cylinder 10 and cover 20. However, in the cylinder 10, high stress σ is generated at the bottom 17a of the retractable part 17 and the valley bottom 15a located on the side of the storage section 12 of the internal thread part 15. The stress σ is the average hydrostatic stress in the three directions XYZ, given by σ=(σ X +σ Y +σ Z ) / 3 to find out. The higher the hydrostatic stress, the more easily the metal structure is affected by hydrogen.

[0068] In Embodiment 1, the stress-generating part M of the high-pressure hydrogen container 100 is the area including the internal thread part 15, the vicinity of the sealing surface 16, and the retraction part 17; it refers to the location where a stress of σ or higher is generated. The specified stress σ is, for example, 1 / 3 of the tensile strength of a metallic material. In Embodiment 1, Figure 6 The valley bottom 15a of the bottom 17a of the retraction portion 17 and the portion on the side of the storage portion 12 of the internal thread portion 15 shown corresponds to the stress generating portion M. For example... Figure 6 As shown, in the high-pressure hydrogen container 100 according to Embodiment 1, the bottom 17a of the retraction section 17 closest to the contact area 18 is designated as the stress-generating section M, and the distance L from the contact area 18 to the stress-generating section M is set to be greater than the wall thickness H from the contact area 18 to the outer surface of the cylinder 10. Conventionally, without considering hydrogen diffusion within the metal structure, the relationship between distance L and wall thickness H was set to a level that could withstand the pressure within the storage section 12. That is, the distance L was set to be as small as possible so that the high-pressure hydrogen container could withstand the pressure. However, in Embodiment 1, as... Figure 3 As shown, before hydrogen diffuses within the metal structure and reaches the stress-generating part M, it forms a hydrogen permeation cylinder 10 and flows out to the outside of the cylinder 10, so the stress-generating part M is not affected by hydrogen.

[0069] As described above, the relationship between the distance L and the wall thickness H is H < L. Specifically, if the coefficient is set to K, then H = K·L, and the coefficient K takes a value smaller than 1. The coefficient K varies depending on the material of the cylinder 10, the stress distribution generated in the cylinder 10, and the concentration of hydrogen in the storage portion 12, but in the high-pressure hydrogen container 100 of Embodiment 1, K < 1. It should be noted that the pressure inside the storage portion 12 of the high-pressure hydrogen container 100 according to Embodiment 1 is set to a pressure of 100 MPa or less in the usage state, and a portion where the tensile strength of the chromium molybdenum steel constituting the cylinder 10 is 1 / 3 of 930 MPa, that is, 310 MPa or more, is defined as the stress generation portion M. Figure 6 In the high-pressure hydrogen container 100 shown in Figure 6 , a stress of about 350 MPa is generated in the stress generation portion M at the bottom 17a of the relief portion 17, and a stress of about 490 MPa is generated in the stress generation portion M at the bottom 15a of the internal thread portion 15.

[0070] Figure 7 This is a graph showing the relationship between the stress applied to the metal material and the number of cycles of the applied stress. When a repeated stress is applied to the metal material, it may cause damage, but if the stress decreases, even if a repeated stress of 10 6 ~10 7 cycles or more is applied, it will not be damaged. The stress at this time is called the fatigue limit stress. Under the influence of hydrogen, in the low-cycle region where the number of repeated stresses is small, the stress that causes the metal material to break becomes lower compared to the case without the influence of hydrogen. However, as long as the repeated stress is below the fatigue limit stress, the influence of hydrogen can be ignored. Therefore, by setting the reference of the stress generation portion M to a portion that generates a stress above the fatigue limit stress of the metal material, the distance L can be set smaller. By setting the distance L as small as possible, sufficient strength can be ensured even in an environment affected by hydrogen, and the size of the portion other than the storage portion 12 of the high-pressure hydrogen container 100 can be reduced.

[0071] Furthermore, the high-pressure hydrogen container 100 is filled with high-pressure hydrogen at 75 MPa to 100 MPa, for example, supplied to a vehicle's hydrogen tank, thus experiencing frequent pressure fluctuations. For example, since a vehicle's hydrogen tank stores hydrogen at 75 MPa, the storage section 12 of the high-pressure hydrogen container 100 needs to be maintained at a pressure at least higher than 75 MPa. Therefore, after supplying hydrogen to a hydrogen tank or the like and the pressure in the storage section 12 decreases, the high-pressure hydrogen container 100 supplies liquid hydrogen or hydrogen gas to the storage section 12, causing it to become high-pressure again. Consequently, the cylinder 10 of the high-pressure hydrogen container 100 is frequently subjected to pressure fluctuations, for example, within a high-pressure region of 75 MPa to 100 MPa. Due to these pressure fluctuations, the cylinder 10 is in a state of constant stress, particularly at the joint between the cylinder 10 and the cover 20, where stress concentration is prone to occur, resulting in high stress and repeated stress amplitude. The high-pressure hydrogen container 100 needs to have high strength that will not be damaged even when repeatedly subjected to such high stress amplitudes.

[0072] The high-pressure hydrogen container 100 according to Embodiment 1 requires the high strength described above, therefore using low-alloy steel with high tensile strength and high fatigue strength. However, while low-alloy steel has high tensile strength and excellent toughness, resulting in high fatigue strength, its toughness decreases and leads to breakage if hydrogen penetrates into the metal structure. Conventionally, only the effect of hydrogen on the surface in contact with hydrogen was considered, but the high-pressure hydrogen container 100 according to Embodiment 1 suppresses the strength reduction of components caused by the effect of hydrogen diffusing into the metal structure of the components in contact with hydrogen. By appropriately setting the distance L from the stress-generating part M to the contact area 18 between the sealing part 23 and the sealing surface 16, the high-pressure hydrogen container 100 can suppress strength reduction and maximize the protection of the storage part 12, thereby improving volumetric efficiency.

[0073] The internal threaded portion 15 of the cylinder 10 is sometimes referred to as the joint portion. Additionally, the external threaded portion 25 of the cover 20 is sometimes referred to as the fixing portion. It should be noted that the internal threaded portion 15 and the external threaded portion 25 in Embodiment 1 can also be other joint structures. The joint between the cylinder 10 and the cover 20 can also be achieved by other jointing means such as fitting, welding, or fixing with bolts. When the joint between the cylinder 10 and the cover 20 is changed, the position of the stress-generating portion M changes relative to the high-pressure hydrogen container 100 according to Embodiment 1. However, even in this case, by satisfying the condition that the distance L is greater than the wall thickness H, the strength of the high-pressure hydrogen container 100 can be ensured. That is, as... Figure 6 As shown, the internal pressure of the high-pressure hydrogen container 100 is set to a predetermined condition, and the stress generated in the cylinder 10 is controlled to determine the stress-generating part M. At this time, the distance L between the contact area 18 where the sealing part 23 abuts and the stress-generating part M becomes greater than the wall thickness H, so the high-pressure hydrogen container 100 can ensure its strength regardless of the stored hydrogen.

[0074] It should be noted that in Embodiment 1, the stress generation part M is set as the part that generates a stress of "more than 1 / 3 of the tensile stress of the metal material", but it can also be set as the part that generates the "fatigue limit stress of the metal material".

[0075] Figure 6 The high-pressure hydrogen container 100 shown in Figure 3 is the same as that in

[0076] The wall thickness H from the abutting area 18 to the outer circumference of the cylinder 10: 50 mm

[0077] The wall thickness H2 of the bottom 17a of the relief part 17: 36 mm

[0078] The axial length S of the internal thread part 15: 217 mm

[0079] The wall thickness E of the first component 21: 110 mm

[0080] The outer diameter of the cylinder 10:

[0081] The wall thickness of the second component 22: 42 mm

[0082] In addition, Figure 6 The stress distribution of the high-pressure hydrogen container 100 shown in Figure 6 represents the state of the pressure in the storage part 12 being 95 MPa, and the cylinder 10 and the cover 20 in the state of the internal thread part 15 and the external thread part. In the high-pressure hydrogen container 100 as described above, the distance L from the abutting area 18 to the stress generation part M is 65.5 mm. This distance L is the distance L from the abutting area 18 to the stress generation part M that generates a stress of 310 MPa or more, which corresponds to Figure 6 the distance L1 shown in Figure 6 310 MPa is the stress of "1 / 3 of the tensile stress of the metal material". It should be noted that when the stress generation part M is the part that generates a stress of 465 MPa or more, 465 MPa is the "fatigue limit stress of the metal material", and the distance L is Figure 6 Figure 6 the distance L2 shown in i.e., 86 mm. For the high-pressure hydrogen container 100 that satisfies

[0083] H < L shown in Figure 6 Figure 6 Figure 2In the case of the shape indicated by a dashed line in the figure, the shortest distance h from the contact region 18 to the step 13a is the wall thickness H.

[0084] As described above, the state of stress generation in the high-pressure hydrogen container 100 under the pressure applied to the storage part 12 is obtained, and the position of the stress generation part M is determined. The stress generation part M is the part where the stress σ is 1 / 3 or more of the tensile stress of the metal material, or the fatigue limit stress of the metal material as described above. Depending on the shape of the high-pressure hydrogen container 100, the stress generation part M may correspond to multiple parts, but in this case, it is the stress generation part M closest to the contact region 18 that abuts against the sealing member 24. At this time, the high-pressure hydrogen container 100 is configured such that the relationship between the distance L from the contact region 18 to the stress generation part M and the wall thickness H satisfies H < L. By designing the distance L to be as small as possible while being larger than the wall thickness H, the stress generation part M is not affected by hydrogen and the strength is not reduced. Note that, in the case where there are multiple stress generation parts M, the shortest distance between the contact region 18 and the stress generation part M is set as the distance L, and the high-pressure hydrogen container 100 is configured to satisfy the condition of H < L.

[0085] In addition, the high-pressure hydrogen container 100 according to the first embodiment has a structure in which the first member 21 or the second member 22 abuts against the cylindrical body 10 in the axial direction. Therefore, as Figure 6 shown, the stress generation part M is located at the bottom 15a of the relief part 17 or the internal thread part 15. With such a configuration, the high-pressure hydrogen container 100 satisfies H < L, so the stress generation part M is not affected by hydrogen, and the strength can be ensured in the state of storing high-pressure hydrogen. Note that, for example, in the case where the high-pressure hydrogen container is configured such that the first member 21 abuts against the cylindrical body 10 in the axial direction, the stress generation part M is located around the axial contact part thereof. Therefore, it can be configured that the distance between the contact region 18 and its axial contact part is L, and the high-pressure hydrogen container satisfies H < L.

[0086] (Example)

[0087] Regarding the wall thickness H from the contact region 18 to the outer periphery of the cylindrical body 10, hydrogen diffusion analysis is performed when the distance L from the contact region 18 to the stress generation part M is changed. Table 1 shows the results of the maximum hydrogen concentration [ppm] accumulated in the stress generation part M.

[0088] Table 1

[0089]

[0090] As shown in Table 1, in the case of the embodiment, the influence of hydrogen does not reach the stress generation part M, and the strength can be ensured in the state of storing high-pressure hydrogen. On the other hand, in the case where H < L is not satisfied as in the comparative example, hydrogen accumulates in the stress generation part M. Therefore, as a result, in the state where high-pressure hydrogen is stored in the storage part 12, the fatigue strength of the high-pressure hydrogen container 100 is reduced.

[0091] The configuration shown in the above embodiment represents an example, and within the scope not departing from the gist, a part of the configuration may also be omitted or changed.

[0092] Explanation of reference numerals

[0093] 10 Cylinder body, 12 Storage part, 13 Cylindrical part, 15 Internal thread part, 15a Valley bottom, 16 Sealing surface, 17 Relief part, 17a Bottom, 18 Contact area, 19 Open end, 20 Cover body, 21 First component, 21a Groove, 22 Second component, 23 Sealing part, 24 Sealing member, 25 External thread part, 26 Sealing part, 27 End face, 100 High-pressure hydrogen container, C Central axis, C0 Hydrogen amount, D Hydrogen diffusion coefficient, H Wall thickness, J Diffusion flow rate, K Coefficient, L Distance, M Stress generation part, P Pressure, s Solubility, t Wall thickness, κ p Hydrostatic stress effective coefficient, σ Stress, Normalized concentration.

Claims

1. A high-pressure hydrogen container, which includes: A metal cylinder used for storing high-pressure hydrogen; and The cap component that blocks the end of the cylinder. The cylindrical body comprises: A joint for securing the end of the cover component in the direction of the central axis of the cylinder; The cylindrical section, which forms the outer contour of the storage section for high-pressure hydrogen; and A sealing surface, which is disposed between the joint and the cylindrical portion in the direction of the central axis and formed on the inner surface of the cylindrical body. The cover component includes: A sealing part, which abuts against the sealing surface of the cylinder; and The fixing part is fixed to the joint of the cylinder. The area in the sealing surface that abuts against the sealing part is defined as the abutment area. The wall thickness from the contact area to the outer surface of the cylinder is defined as wall thickness H. The portion of the cylinder containing the joint and extending from the joint to the abutment area that generates a stress of σ or higher is designated as the stress-generating portion. When the distance between the contact area and the stress-generating part is set as distance L, The relationship between the wall thickness H and the distance L at least satisfies H <L。 2. The high-pressure hydrogen container as described in claim 1, wherein, The cover component includes: The first component, which includes the sealing portion and is located on the cylindrical side; and The second component includes the aforementioned fixing part. The outer diameter of the first component is smaller than the inner diameter of the sealing surface.

3. The high-pressure hydrogen container as described in claim 1 or 2, wherein, The cover component includes: The first component, which includes the sealing portion and is located on the cylindrical side; and The second component includes the aforementioned fixing part. The first component is made of austenitic stainless steel.

4. The high-pressure hydrogen container as described in claim 1 or 2, wherein, The joint is an internally threaded portion formed on the inner circumferential surface of the end of the cylinder. The fixing part is formed on the external threaded part of the cover component. The joining part and the fixing part are screwed together.

5. The high-pressure hydrogen container as described in claim 1 or 2, wherein, The sealing part is an O-ring installed on the cover component.

6. The high-pressure hydrogen container as described in claim 1 or 2, wherein, When the cylinder is filled with high-pressure hydrogen, the stress σ is 1 / 3 of the tensile strength of the metal material constituting the cylinder.

7. The high-pressure hydrogen container as described in claim 1 or 2, wherein, When the cylinder is filled with high-pressure hydrogen, the stress σ is the fatigue limit stress of the metallic material constituting the cylinder.

8. The high-pressure hydrogen container as described in claim 1 or 2, wherein, The stress σ is hydrostatic stress.

9. The high-pressure hydrogen container as described in claim 1 or 2, wherein, When a coefficient K is set as the factor that varies at least according to the hydrogen concentration in the storage section and the hydrostatic stress generated in the cylinder, the relationship between the wall thickness H and the distance L can be expressed by H=K·L, where the coefficient K takes the value of K<1.

0.

10. The high-pressure hydrogen container as claimed in claim 1 or 2, wherein, The cylinder is made of low alloy steel.

11. The high-pressure hydrogen container as claimed in claim 1 or 2, wherein, The stress generating part includes multiple stress generating parts. The distance L is the distance between the contact area and the stress-generating part that is closest to the contact area among the plurality of stress-generating parts.

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