Liquid hydrogen tank, method for manufacturing liquid hydrogen tank, and method for designing liquid hydrogen tank

Abstract

Provided is a liquid hydrogen tank that comprises a tank that comes into contact with liquid hydrogen and is formed from a steel material that has absorption energy sE measured by an impact test at a measurement temperature of -196°C or lower using a three-surface slit Charpy impact test specimen, the absorption energy sE satisfying expression 1 or expression 2:　expression 1: sE≥19+0.68×ΔT, in expression 1, the measurement temperature is within a range from more than −253°C to no more than -196°C, and ΔT is a temperature difference between the measurement temperature and −253°C;　expression 2: sE≥19, in expression 2, the measurement temperature is −253°C or less.

Description

Liquid hydrogen tank, liquid hydrogen tank manufacturing method, and liquid hydrogen tank design method

[0001] The present disclosure relates to a liquid hydrogen tank, a method for manufacturing a liquid hydrogen tank, and a method for designing a liquid hydrogen tank.

[0002] Steel materials have traditionally been used for cryogenic storage tanks for storing liquid hydrogen. For example, Japanese Patent No. 5494166 discloses a method for providing a steel plate for cryogenic use having excellent crack arrestability at low cost, which contains, by mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.3%, Mn: 0.4 to 2.0%, P: 0.05% or less, S: 0.008% or less, Ni: more than 5.0% but less than 10.0%, Al: 0.002 to 0.05%, N: 0.005% or less, with the balance being Fe and impurities, the amount of retained γ at a position (¼)t in the plate thickness direction being 3.0% by volume or more, and the average circle-equivalent grain size of structural units surrounded by high-angle grain boundaries of 15° or more as observed by EBSP at a magnification of 2000 times is 5.5 μm or less at the position (¼)t in the plate thickness direction.

[0003] Furthermore, Japanese Patent No. 5673399 describes a steel material for cryogenic use having excellent fracture toughness, which contains, in mass%, C: 0.01 to 0.12%, Si: 0.01 to 0.3%, Mn: 0.4 to 2.0%, P: 0.05% or less, S: 0.008% or less, Ni: more than 5.0% but less than 10.0%, Al: 0.002 to 0.08%, N: 0.0015 to 0.0040%, with the balance being Fe and impurities, and 4) A steel material for cryogenic use is disclosed, in which the amount of retained γ at position t is 3.0% by volume or more, and the value shown by formula (1): σy,-165°C / σy,RT (where σy,-165°C represents the yield strength [MPa] at -165°C, and σy,RT represents the yield strength [MPa] at room temperature) is 1.3 or more, and further the reduction rate of the amount of retained γ when subjected to 1% plastic strain in an environment of -165°C is 25% or less.

[0004] Furthermore, Japanese Patent No. 6369003 describes a low-Ni cryogenic steel material that has high strength and excellent low-temperature toughness even in cryogenic environments, and has a chemical composition, in mass %, of C: 0.01 to 0.1%, Si: 0.005 to 0.6%, Mn: 0.3 to 2.0%, Ni: 5 to 8%, Cr: 0.6 to 1.0%, Mo: 0.01 to 0.5%, sol. Al: 0.002 to 0.08%, N: 0.0005 to 0.005%, Cu: 0 to 2.0%, V: 0 to 0.08%, Nb: 0 to 0.08%, Ti: 0 to 0.03%, B: 0 to 0.0030%, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, and REM: 0 to 0.0020%, with the balance being Fe and impurities, and (1) formula: sol. Al×N≦25×10 －５ The present invention discloses a steel material that satisfies the above requirements.

[0005] Furthermore, Japanese Patent Laid-Open Publication No. 6-179909 discloses a method for producing a steel material for cryogenic use, which comprises, by weight, 0.10% or less of C, 8.0 to 10.0% of Ni, and 1.0% or less of Mn, with the balance being Fe and unavoidable impurities, in which the impurities contain 0.001% or less of P and 0.001% or less of S, hot rolling the steel and then quenching it from a temperature equal to or higher than the Ac3 transformation point, reheating it to 680 to 710°C, re-quenching it, and tempering it at 570 to 600°C.

[0006] Furthermore, Proceedings of the Society of Naval Architects of Japan, No. 167, pp. 271-277, 1990, discloses a correlation equation between fracture transition temperature and brittle crack propagation arrest characteristics in a three-slit Charpy impact test.

[0007] Steel materials used in cryogenic storage tanks for storing liquid hydrogen (temperature -253°C) are required to have excellent fracture toughness. Conventionally, the arrestability of steel materials used in low-temperature storage tanks, such as tanks for storing LNG (temperature -162°C), has been evaluated, for example, by a hybrid ESSO test. However, the hybrid ESSO test is a large-scale test method, and is therefore inefficient in terms of construction time and cost. Furthermore, when determining the arrestability of steel materials used in tanks for storing liquid hydrogen (temperature -253°C), for example, when testing at temperatures below -253°C, a method using liquid helium (temperature -269°C) is considered. However, liquid helium is expensive, and its use in a hybrid ESSO test, which is large-scale and requires a large amount of refrigerant, is not practical. Therefore, there is a need for a simple, low-cost alternative test method for determining the arrestability of steel materials used in liquid hydrogen tanks.

[0008] The present disclosure has been made in light of the above circumstances, and aims to provide a liquid hydrogen tank with excellent arrestability that can be obtained simply and at low cost, a method for manufacturing a liquid hydrogen tank that allows for the simple and low-cost production of a liquid hydrogen tank with excellent arrestability, and a method for designing a liquid hydrogen tank that allows for the simple and low-cost design of a liquid hydrogen tank with excellent arrestability.

[0009] The present disclosure includes the following aspects. <1> A liquid hydrogen tank having a tank in contact with liquid hydrogen, the tank being made of a steel material whose absorbed energy sE (unit: J) value, measured in an impact test at a measurement temperature of -196°C or less using a three-sided slit Charpy impact test specimen, satisfies the following formula 1 or 2: sE≧19+0.68×ΔT (Formula 1) In formula 1, the measurement temperature is in the range of greater than -253°C and less than or equal to -196°C, and ΔT is the temperature difference between the measurement temperature and -253°C. sE≧19 (Formula 2) In formula 2, the measurement temperature is -253°C or less. <2> The liquid hydrogen tank according to <1>, having a tank in contact with liquid hydrogen, the tank being made of a steel material whose absorbed energy sE value, measured in an impact test at -196°C using a three-sided slit Charpy impact test specimen, is 57.76 J or more. <3> The liquid hydrogen tank according to <1>, having a tank in contact with liquid hydrogen, made of a steel material having an absorbed energy sE value of 19 J or more measured in an impact test at a measurement temperature of -253°C or less using a three-sided slit Charpy impact test specimen. <4> The liquid hydrogen tank according to any one of <1> to <3>, wherein the steel material has a thickness of 50 mm or less. <5> The liquid hydrogen tank according to any one of <1> to <4>, wherein the steel material has a Ni content of 6.0 to 16.0 mass% and a ferrite content measured by a magnetic induction method of 50% or more. <6> A method for manufacturing a liquid hydrogen tank, comprising the steps of: preparing a steel material whose absorbed energy sE value (unit: J) satisfies Formula 1 or Formula 2 below, as measured in an impact test at a measurement temperature of -196°C or less using a three-sided slit Charpy impact test specimen; and forming a tank in contact with liquid hydrogen in the liquid hydrogen tank using the steel material. sE≧19+0.68×ΔT Equation 1 In Equation 1, the measured temperature is in the range of more than −253°C and not more than −196°C, and ΔT is the temperature difference between the measured temperature and −253°C. sE=≧19 Equation 2 In Equation 2, the measured temperature is not more than −253°C. <7> The method for manufacturing a liquid hydrogen tank according to <6>, wherein the measurement of the value of absorbed energy sE is carried out at −196°C, and the absorbed energy sE is 57.76 J or more.<8> A method for manufacturing a liquid hydrogen tank according to <6>, wherein the measurement of the value of absorbed energy sE is carried out at -253°C or lower, and the value of absorbed energy sE is 19 J or greater. <9> A method for manufacturing a liquid hydrogen tank according to any one of <6> to <8>, wherein the thickness of the steel material is 50 mm or less. <10> A method for manufacturing a liquid hydrogen tank according to any one of <6> to <9>, wherein the steel material has a Ni content of 6.0 to 16.0 mass% and a bcc phase ratio measured by a magnetic induction method of 50% or greater. <11> A method for designing a liquid hydrogen tank, comprising the steps of: setting a temperature equal to or lower than the liquefaction temperature of hydrogen as a set temperature; and determining, based on the set temperature, a steel material to be used in a vessel in contact with liquid hydrogen in a liquid hydrogen tank as a steel material whose value of absorbed energy sE (unit: J) satisfies the following formula 1 or 2 as a result of measuring the value of absorbed energy sE in an impact test using a three-sided slit Charpy impact test piece at a measurement temperature of -196°C or lower: sE≧19+0.68×ΔT ...Equation 1 In Equation 1, the measured temperature is in the range of more than -253°C and less than or equal to -196°C, and ΔT is the temperature difference between the measured temperature and -253°C. sE≧19 ...Equation 2 In Equation 2, the measured temperature is less than or equal to -253°C. <12> The method for designing a liquid hydrogen tank according to <11>, wherein the measurement of the value of absorbed energy sE is carried out at -196°C, and the value of absorbed energy sE is 57.76 J or more. <13> The method for designing a liquid hydrogen tank according to <11>, wherein the measurement of the value of absorbed energy sE is carried out at less than or equal to -253°C, and the value of absorbed energy sE is 19 J or more. <14> The method for designing a liquid hydrogen tank according to any one of <11> to <13>, wherein the thickness of the steel material is 50 mm or less. <15> The method for designing a liquid hydrogen tank according to any one of <11> to <14>, wherein the steel material has a Ni content of 6.0 to 16.0 mass % and a bcc phase ratio measured by a magnetic induction method of 50% or more.

[0010] According to the present disclosure, it is possible to provide a liquid hydrogen tank with excellent arrestability that can be obtained simply and at low cost, a method for manufacturing a liquid hydrogen tank that allows for the simple and low-cost production of a liquid hydrogen tank with excellent arrestability, and a method for designing a liquid hydrogen tank that allows for the simple and low-cost design of a liquid hydrogen tank with excellent arrestability.

[0011] FIG. 1 is a perspective view showing an example of a liquid hydrogen tank according to the present disclosure. FIG. 2 is a front view showing a hybrid ESSO test specimen. FIG. 3A is a front view showing a three-sided slit Charpy impact test specimen. FIG. 3B is a cross-sectional view showing the locations where slits are formed in the three-sided slit Charpy impact test specimen. FIG. 4A is a diagram showing the locations from which a three-sided slit Charpy impact test specimen according to the present disclosure is taken, and is a diagram showing the locations from which the specimen is taken when the steel plate has a thickness of 25 mm or more. FIG. 4B is a diagram showing the locations from which a three-sided slit Charpy impact test specimen according to the present disclosure is taken, and is a diagram showing the locations from which the specimen is taken when the steel plate has a thickness of 12 mm or more and less than 25 mm. FIG. 5 is a graph showing the temperature dependence of the absorbed energy sE of 9% Ni steel obtained by a three-sided slit Charpy impact test. FIG. 6 is a flow chart showing a method for designing a liquid hydrogen tank according to the present disclosure. FIG. 7 is a flow chart showing a method for manufacturing a liquid hydrogen tank according to the present disclosure. FIG. 8 is a diagram showing an example of taking a three-sided slit Charpy impact test specimen from a liquid hydrogen tank according to the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail.

[0013] In numerical ranges described in stages, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In numerical ranges, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. The term "step" includes not only independent steps, but also steps that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0014] (Liquid Hydrogen Tank 100) Fig. 1 shows an example of a liquid hydrogen tank 100 according to the present disclosure. As shown in Fig. 1, the liquid hydrogen tank 100 has an inner tank 102 that comes into direct contact with liquid hydrogen and stores the liquid hydrogen, and an outer tank 104 that holds the inner tank 102.

[0015] As shown in Fig. 1, the inner tank 102 is manufactured using steel plates 110 whose absorbed energy values ​​have been measured by a test described below. More specifically, as shown in Fig. 1, the inner tank 102 is formed by joining together a plurality of steel plates 110 so as to function as a tank capable of storing liquid hydrogen. The plurality of steel plates 110 are formed into the shape of the inner tank 102 by, for example, welding. The inner tank 102 is an example of a "tank in contact with liquid hydrogen" in the present disclosure.

[0016] The outer vessel 104 holds the inner vessel 102 so as to reduce the thermal conductivity between the outer vessel 104 and the inner vessel 102. Any specific method may be used to hold the inner vessel 102 so as to reduce the thermal conductivity, and examples include providing a vacuum gap or filling the vessel with a porous material. The outer vessel 104 may be made of any material.

[0017] 1 is a tank consisting of two tanks, an inner tank 102 and an outer tank 104, but the number of tanks in the liquid hydrogen tank 100 to which the technology of the present disclosure is applied may be greater. For example, the liquid hydrogen tank 100 may have an additional tank that covers the outer tank 104.

[0018] (Performance and challenges required of steel plate 110) Excellent fracture toughness is required for the steel used in the inner tank 102, i.e., the tank for cryogenic temperatures, which stores liquid hydrogen (hydrogen at a temperature of -253°C or lower at atmospheric pressure. Hereinafter, unless otherwise specified, this refers to the boiling point at atmospheric pressure as well. The same applies to other types of gases). Specifically, in addition to being less susceptible to brittle fracture even in a cryogenic environment, the steel is required to have excellent properties (so-called arrestability) that stop the propagation of cracks in the steel part (i.e., the base material part) even if a brittle crack does occur in the welds of the tank, in order to prevent the collapse of the entire tank.

[0019] Conventionally, the arrestability of 9% Ni steel and 7% Ni steel used in low-temperature storage tanks, for example, aboveground tanks for storing LNG (natural gas at temperatures of −162° C. or lower), has been evaluated by a hybrid ESSO test using a hybrid ESSO test piece 10 shown in Fig. 2. Typical test conditions are a load stress of 393 MPa, which is the same level as the allowable stress during an earthquake in the LNG aboveground storage tank guidelines, and a test temperature of −165° C., which is approximately the same as the temperature of LNG. If it can be confirmed under these test conditions that a brittle crack initiated from a notch 18 in the run-up plate 12 propagates through the run-up plate 12 and the weld 14 and then stops at the test plate 16, the steel plate 110 is judged to have sufficient arrestability as an aboveground LNG steel plate.

[0020] However, because the hybrid ESSO test is a large-scale test method, it is inefficient in terms of construction time and cost. Furthermore, due to reasons such as the difficulty of successfully propagating a crack, particularly in the welded joint 14, the test often fails (i.e., a judgment cannot be made), requiring a retest. Furthermore, when judging the arrestability of steel materials used in tanks for storing liquid hydrogen (temperature -253°C), for example, it is conceivable to conduct the test at a temperature of -253°C or lower. In this case, a method using liquid helium (helium at a temperature of -269°C or lower) can be used. However, liquid helium is very expensive, and it is not practical to use liquid helium in a hybrid ESSO test, which is large-scale and requires a large amount of refrigerant.

[0021] Thus, there is a need for a simple, low-cost alternative test method for determining the arrestability of steel materials used in liquid hydrogen tanks 100. Here, the present inventors have discovered that a method of measuring absorbed energy sE through an impact test using a three-sided slit Charpy impact test piece 6 is an appropriate method for determining the arrestability of steel materials at measurement temperatures of −196°C or lower.

[0022] (Three-Slit Charpy Impact Test Specimen 6) Figures 3A and 3B show a test specimen 10 (hereinafter referred to as a "three-slit Charpy impact test specimen") used in the three-slit Charpy impact test according to the present disclosure. As shown in Figures 3A and 3B, the three-slit Charpy impact test specimen 6 has a rectangular parallelepiped shape with one side elongated, and has slits 8 on the three central longitudinal faces. More specifically, the three-slit Charpy impact test specimen 6 is a test specimen in which slits 8 are formed on the three central faces in the depth direction of a rectangular prism-shaped steel material measuring 10 mm long x 10 mm wide x 55 mm deep. The slits 8 are 0.15 mm wide and 2 mm deep.

[0023] 4A and 4B show the locations where the three-sided slit Charpy impact test specimens 6 are taken from the steel material. In Fig. 4A and 4B, arrow L indicates the rolling direction of the steel material, arrow t indicates the thickness of the steel material, and arrow C indicates the width direction of the plate material, which is perpendicular to the thickness direction of the steel material.

[0024] FIG. 4A shows the location from which a three-sided slit Charpy impact test specimen 6 is taken when the steel material has a thickness of 25 mm or more. As shown in FIG. 4A, when the steel material has a thickness of 25 mm or more, the three-sided slit Charpy impact test specimen 6 is taken so that its center is at a location corresponding to one-quarter of the plate thickness in the thickness direction. The longitudinal direction of the three-sided slit Charpy impact test specimen 6 is the rolling direction of the steel material. The side of the three-sided slit Charpy impact test specimen 6 that does not have a slit 8 (the right side of the drawing in FIG. 4A) is the width direction of the steel material.

[0025] Although not shown in FIG. 4A, the three-side slit Charpy impact test piece 6 is taken from a position inside 50 mm from the end of the steel material in the width direction.

[0026] Figure 4B shows the location from which a three-slit Charpy impact test specimen 6 is taken when the thickness of the steel material is 12 mm or more but less than 25 mm. As shown in Figure 4B, when the thickness of the steel material is 12 mm or more but less than 25 mm, the three-slit Charpy impact test specimen 6 is taken so that a location 1 mm from the thickness direction of the plate becomes one side of the three-slit Charpy impact test specimen 6. The longitudinal direction of the three-slit Charpy impact test specimen 6 is the rolling direction of the steel material. The side of the three-slit Charpy impact test specimen 6 that does not have a slit 8 (the right side of Figure 4B) is the width direction of the steel material.

[0027] The slits 8 of the three-sided Charpy impact test piece 6 according to the present disclosure may be formed by any method. For example, the slits 8 are formed by wire-cut electric discharge machining.

[0028] (Comparison between Three-Slit Charpy Impact Test and Hybrid ESSO Test) Next, the results of a comparison between the three-slit Charpy impact test and the hybrid ESSO test will be described. In the test example, a hybrid ESSO test and a three-slit Charpy impact test were performed at −196°C, −165°C, and −120°C using a plurality of 9% Ni steels (JIS G3127 SL9N590) and 7% Ni steels (JIS G3127 SL7N590) having different plate thicknesses.

[0029] The hybrid ESSO test was conducted in accordance with the Japan Welding Engineering Society standard WES2815 (2014). First, a hybrid ESSO test specimen 10 shown in FIG. 2 was prepared. The hybrid ESSO test specimen 10 was a test specimen in which a run-up plate 12 and a test plate 16 were welded together and connected by a weld 14, and a V-shaped notch 18 was formed in the run-up plate 12. The hybrid ESSO test specimen 10 had a width direction length (i.e., the length from one end of the run-up plate 12 to the other end of the test plate 16, the vertical length in FIG. 2 ) of 500 mm, a length from one end of the run-up plate 12 to the boundary between the weld 14 and the test plate 16 of 150 mm, and a tensile direction length (i.e., the longitudinal length of the weld 14, the horizontal length in FIG. 2 ) of 500 mm. The hybrid ESSO test specimen 10 was formed so that the rolling direction was the tensile direction of the test specimen (the horizontal direction in FIG. 2 ). The hybrid ESSO test piece 10 had a total length of approximately 3,000 mm because jigs for applying loads were attached by welding to both ends in the tensile direction. In the hybrid ESSO test, the hybrid ESSO test piece 10 was first attached to a large-scale tensile testing machine and cooled to the temperature shown in Table 1. Liquid nitrogen was used as the coolant. A tensile load was applied to the hybrid ESSO test piece 10 to apply a stress of 393 MPa, and then a brittle crack was generated by striking the notch 18 in the running plate 12 with a wedge. If the brittle crack propagated through the running plate 12 and the weld 14 and then stopped at the test plate 16, it was judged as "arrested," and if it penetrated the test plate 16, it was judged as "propagated."

[0030] For the impact test using a three-side slit Charpy impact test specimen, first, a three-side slit Charpy impact test specimen 6 shown in Figs. 3A and 3B was prepared.

[0031] The prepared three-sided slit Charpy impact test specimen 6 was cooled to the temperature shown in Table 1 using liquid nitrogen as a coolant. The test specimen can be cooled by immersing the specimen in the coolant or by spraying the coolant onto the surface of the test specimen. Alternatively, the layer of cold air formed above the liquid nitrogen surface can be utilized to adjust the distance from the liquid surface at which the test specimen is held, thereby adjusting the temperature to above -196°C.

[0032] After cooling, a Charpy impact tester was used to apply an impact to the center of the three-side slit Charpy impact test piece 6, at a position corresponding to the slit 8 on the side where the slit 8 was not formed, and the absorbed energy sE [J] was measured. The Charpy impact test was conducted in accordance with JIS Z 2242 (2018) except for the shape of the test piece. Three three-side slit Charpy impact tests were conducted at the same temperature as the hybrid ESSO test, and the average value of the absorbed energies (sE) was calculated.

[0033] The test results are shown in Table 1.

[0034]

[0035] In a typical V-notch Charpy impact test, a ductile fracture surface is formed near the notch root, and a brittle fracture surface is often formed ahead of it. On the other hand, in a three-slit Charpy impact test, a brittle fracture surface is formed near the notch (slit) root, and a ductile fracture surface is formed ahead of it. In a three-slit Charpy impact test, this type of fracture surface is formed when a brittle crack arrests at the boundary between the brittle and ductile fracture surfaces. In other words, the three-slit Charpy impact test is a test method suitable for evaluating arrestability. However, even in a three-slit Charpy impact test, there are rare cases where a ductile fracture surface is formed near the notch root and a brittle fracture surface is formed ahead of it, and in such cases the test results are invalid.

[0036] The results shown in Table 1 indicate that for 9% Ni steel with a plate thickness of 31 mm, specimens that exhibited an absorbed energy sE of 15 J or more in the three-sided slit Charpy impact test also exhibited arrest results in the hybrid ESSO test. On the other hand, specimen No. 1 exhibited an absorbed energy sE of 13 J, resulting in propagation in the hybrid ESSO test. The fracture surface of the hybrid ESSO test confirmed the formation of a developed shear lip on the fracture surface near the front and back surfaces of the steel plate 110, suggesting that the test conditions were near the boundary between arrest and propagation. Furthermore, specimen No. 5 exhibited an absorbed energy sE of 7 J, resulting in propagation in the hybrid ESSO test, confirming that the shear lip was less developed on the fracture surface of the hybrid ESSO test than specimen No. 1.

[0037] In Table 1, although steel No. 6 and No. 8 have the same thickness and test temperature, the absorbed energy sE value and the results of the hybrid ESSO test are different. This is because the heat treatment of steel No. 6 and steel No. 8 are different. In other words, steel No. 6 and steel No. 8 have different internal structures.

[0038] Furthermore, from the results shown in Table 1, for 9% Ni steel with a plate thickness of 50 mm and 7% Ni steel with a plate thickness of 47 mm to 50 mm, those that obtained an absorbed energy sE of 19 J in the three-sided slit Charpy impact test also obtained arrest results in the hybrid ESSO test at the same temperatures in the range of -196°C to -165°C.

[0039] The steel preferably has a Ni content of 6.0% by mass to 16.0% by mass and a bcc phase ratio of 50% or more as measured by a magnetic induction method. Having the Ni content and bcc phase ratio of the steel within the above ranges allows for both excellent cryogenic toughness and high strength. Such a steel is also advantageous in terms of cost reduction. The bcc phase ratio may be 90% or more.

[0040] The Ni content of steel can be confirmed in the steel inspection certificate. Alternatively, a sample may be collected when the steel is processed and subjected to X-ray fluorescence analysis to measure the Ni content. If it is difficult to collect a sample for analysis, such as after the manufacture of a tank, the Ni content may be measured using a portable X-ray fluorescence analyzer.

[0041] The ratio of the bcc phase in the structure of a steel material can be determined by the following method: A sample is taken from the steel material, and the bcc content (volume %) is measured on the surface of the sample using a FERITSCOPE (registered trademark) FMP30 (manufactured by Fischer Instruments Inc.) with a Fischer Instruments Inc. probe (FGAB 1.3-Fe) as the probe of the measuring instrument by a magnetic induction method, and the arithmetic mean value of the measured bcc contents is determined. The average value of the obtained bcc contents is taken as the ratio of the bcc phase.

[0042] From the above, it can be said that it is possible to predict the results of the hybrid ESSO test based on the three-sided slit Charpy impact test, based on the results shown in Table 1. More specifically, it can be predicted that when the absorbed impact energy sE in the three-sided slit Charpy impact test is 19 J or more, it is possible to predict that arrest results will also be obtained in the hybrid ESSO test.

[0043] (Relationship between absorbed impact energy sE of steel and measurement temperature) Here, FIG. 5 is a diagram showing the results of three-sided slit Charpy impact tests conducted at various measurement temperatures, and is a diagram showing the relationship between the temperature and absorbed energy sE of a three-sided slit Charpy impact test specimen. As shown in FIG. 5, when the same 9% Ni steel was subjected to three-sided slit Charpy impact tests at different measurement temperatures to measure the absorbed energy sE, the absorbed energy sE at −196°C (i.e., the boiling point of liquid nitrogen) was 68 J, and the absorbed energy sE at −253°C (i.e., the boiling point of liquid hydrogen) was 29 J. In other words, the difference between the absorbed energy sE of the three-sided slit Charpy impact test specimen 6 at −196°C and the absorbed energy sE at −253°C was 39 J. In other words, it can be said that the absorbed impact energy sE decreases by 0.684 J for every 1 K decrease in measurement temperature from −196°C.

[0044] Based on the results of FIG. 5, it can be said that in order to make the absorbed impact energy sE 19 J or more even at the boiling point of liquid hydrogen (i.e., −253° C.), it is sufficient to use a steel material that satisfies the following formula 1.

[0045] sE≧19+0.68×ΔT Equation 1 In Equation 1, the measured temperature is in the range of more than −253° C. to −196° C., and ΔT is the temperature difference between the measured temperature and −253° C.

[0046] In order to ensure arrestability even at temperatures below -253°C, the absorbed energy sE is required to be 19 J or more. Therefore, in order to ensure that the absorbed impact energy sE is 19 J or more even at temperatures below -253°C, it can be said that a steel material that satisfies the following formula 2 should be used.

[0047] sE≧19 Equation 2 In Equation 2, the measurement temperature is −253° C. or lower.

[0048] The three-sided slit Charpy impact test is used to evaluate the arrestability of the steel material that constitutes the tank that comes into contact with liquid hydrogen in the liquid hydrogen tank 100, and therefore arrestability can be determined more accurately by conducting the test at a temperature close to the liquid hydrogen temperature (-253°C). From this perspective, the measurement temperature is more preferably -240°C to -269°C, and even more preferably -253°C to -269°C.

[0049] The temperature of liquid hydrogen is −253°C, and it is conceivable to use liquid hydrogen as a coolant in a three-sided slit Charpy impact test to evaluate the arrestability of steel used in the liquid hydrogen tank 100. However, because liquid hydrogen is flammable and difficult to handle, it is also conceivable to use an even lower temperature liquid helium (temperature −269°C) as a coolant. The test specimen may be cooled by immersing the test specimen in the coolant, or by spraying the coolant onto the surface of the test specimen. Furthermore, in the method of spraying the coolant onto the surface of the test specimen, the measurement temperature (i.e., the temperature of the test specimen) can be adjusted by adjusting the amount of coolant sprayed, and the measurement temperature can be adjusted to a temperature higher than the temperature of the coolant itself (for example, the temperature of liquid helium −269°C).

[0050] From the above investigations, it has been confirmed that the method of measuring absorbed energy sE by impact testing using a three-sided slit Charpy impact test piece 6 is suitable as a method of determining the arrestability of steel materials at measurement temperatures of −196° C. or lower.

[0051] For example, it is preferable that the inner tank 102 of the liquid hydrogen tank 100 be made of a steel material having an absorbed energy sE of 57.76 J or more as measured in an impact test using a three-sided slit Charpy impact test piece 6 at a measurement temperature of -196°C. The absorbed energy sE as measured in an impact test using a three-sided slit Charpy impact test piece 6 at a measurement temperature of -196°C may be 58 J or more, or even 59 J or more. With this configuration, a liquid hydrogen tank 100 with excellent arrestability can be obtained easily and at low cost.

[0052] (Additional Information Regarding Plate Thickness) The stress state of a steel material is closer to a plane stress state near the surface, i.e., plastic deformation is more likely to occur and brittle cracks are less likely to propagate. Therefore, it is presumed that the arrestability increases as the plate thickness decreases. On the other hand, as the plate thickness increases, the area that can be considered to be in a plane stress state becomes smaller relative to the plate thickness, making it more difficult for plastic deformation to occur, and therefore brittle cracks are more likely to propagate. Based on the results in Table 1, the thickness of the test piece 10 was 50 mm, and arrest was confirmed at this thickness, so it is presumed that arrest would occur without any problems with thinner materials.

[0053] Therefore, based on the results in Table 1, it is preferable that the thickness of the steel material used for the liquid hydrogen tank 100 be 50 mm or less. There is no particular lower limit on the thickness of the steel material, but it can be said that it has been verified up to 10 mm, which is the size of the three-sided slit Charpy impact test specimen 6. Furthermore, as mentioned above, it is presumed that the arrestability increases as the plate thickness decreases, so it can be said that the same idea can be applied to thicknesses of 10 mm or less.

[0054] Next, a design method for the liquid hydrogen tank 100 according to the present disclosure will be described with reference to FIG.

[0055] (Method for Designing Liquid Hydrogen Tank 100) Fig. 6 is a flow diagram showing a method for designing the liquid hydrogen tank 100 in this disclosure. A designer of the liquid hydrogen tank 100 designs the liquid hydrogen tank 100 based on the procedure shown in Fig. 6.

[0056] First, in step S102, the designer sets the tank's set temperature to a temperature equal to or lower than the hydrogen liquefaction temperature. More specifically, the designer sets the temperature value set as the specifications for the liquid hydrogen tank 100 to a value equal to or lower than the liquid hydrogen tank 100's liquefaction temperature.

[0057] Next, in step S104, the designer determines that the steel material whose impact test results satisfy formula 1 or formula 2 will be the material for the tank's inner vessel 102. More specifically, the designer determines that the steel material to be used for the inner vessel 102 of the liquid hydrogen tank 100 should satisfy formula 1 or formula 2 as described above.

[0058] Next, in step S106, the designer determines other specifications of the liquid hydrogen tank 100. More specifically, the designer determines various specifications such as the size, installation position, and shape of the inner tank 102, the material of the outer tank 104, etc.

[0059] Based on the above procedure, the designer of the liquid hydrogen tank 100 designs the liquid hydrogen tank 100.

[0060] (Additional Information Regarding Inspection Frequency) In the steel selection method of the present disclosure, it is preferable to specify a specific inspection frequency of three inspections at the same temperature for each heat-treated steel plate. Here, "each heat-treated steel plate" refers to each steel plate 110 used to manufacture the inner tank 102 before it is cold-worked and welded for manufacturing the inner tank 102.

[0061] Next, a method for manufacturing the liquid hydrogen tank 100 according to the present disclosure will be described with reference to FIG.

[0062] (Method of Manufacturing Liquid Hydrogen Tank 100) Figure 7 is a flow diagram showing a method of manufacturing the liquid hydrogen tank 100 in this disclosure. The manufacturer of the liquid hydrogen tank 100 manufactures the liquid hydrogen tank 100 based on the procedure shown in Figure 7.

[0063] First, in step S202, the manufacturer prepares steel material whose impact test results satisfy Formula 1 or Formula 2. More specifically, the manufacturer prepares steel material that satisfies Formula 1 or Formula 2 as described above, as the steel material to be used for the inner tank 102 of the liquid hydrogen tank 100 designed based on the above-mentioned design procedure.

[0064] Next, in step S204, the manufacturer forms the inner tank 102 using steel material whose impact test results satisfy formula 1 or formula 2. More specifically, the manufacturer uses the steel material prepared in step S202 and cold works it to fit the shape of the inner tank 102 as shown in FIG.

[0065] Next, in step S206, the manufacturer forms the remaining portions of the liquid hydrogen tank 100. More specifically, the manufacturer forms the various structures of the liquid hydrogen tank 100, including the outer layer 104.

[0066] Based on the above procedure, the manufacturer of the liquid hydrogen tank 100 manufactures the liquid hydrogen tank 100. Note that in manufacturing the liquid hydrogen tank 100, the procedures relating to the above-mentioned steps S202 to S206 do not have to be performed step by step. More specifically, in the manufacturing process of the liquid hydrogen tank 100, the step corresponding to step S202, the step corresponding to step S204, and the step corresponding to step S206 may be performed in parallel. For example, an embodiment is also possible in which the bottom portion of the outer tank 104 is formed (step corresponding to step S206), and then the inner tank 102 is formed (step corresponding to step S204), and then the other portions of the outer tank 104 are formed (step corresponding to step S206).

[0067] Based on the above procedure, the liquid hydrogen tank 100 according to the present disclosure is manufactured.

[0068] Next, a method for evaluating the liquid hydrogen tank 100 according to this embodiment, that is, a method for inspecting whether or not the inner tank 102 is made of steel that satisfies formula 1 or formula 2, will be described with reference to FIG. 8.

[0069] (Method of inspecting a liquid hydrogen tank 100) Figure 8 is a diagram showing an example of how a three-slit Charpy impact test specimen 6 is taken from a liquid hydrogen tank 100. As shown in Figure 8, when taking a three-slit Charpy impact test specimen 6 from the inner tank 102, the three-slit Charpy impact test specimen 6 is taken from a location that is not affected by welding. More specifically, as shown in Figure 8, the three-slit Charpy impact test specimen 6 is preferably taken from a location that is 50 mm or more away from the welded portion 112. Furthermore, it is preferable that the longitudinal direction of the three-slit Charpy impact test specimen 6 is the rolling direction of the steel plate 110 that forms the inner tank 102.

[0070] Next, the effects of the liquid hydrogen tank 100, the method for manufacturing the liquid hydrogen tank 100, and the method for designing the liquid hydrogen tank 100 according to the present disclosure will be described.

[0071] (Effects of the liquid hydrogen tank 100, manufacturing method of the liquid hydrogen tank 100, and design method of the liquid hydrogen tank 100 according to the present disclosure) According to the embodiments of the present disclosure, it is possible to provide a liquid hydrogen tank 100 with excellent arrestability that can be obtained simply and at low cost, a manufacturing method of the liquid hydrogen tank 100 that allows for the easy and low-cost manufacture of a liquid hydrogen tank 100 with excellent arrestability, a design method of the liquid hydrogen tank 100 that allows for the easy and low-cost design of a liquid hydrogen tank 100 with excellent arrestability, and a manufacturing method of the liquid hydrogen tank 100.

[0072] Specifically, it has been found that when the absorbed energy sE measured by an impact test using a three-sided slit Charpy impact test piece 6 satisfies the above-mentioned formula 1 or formula 2, excellent arrestability can be obtained as a steel material used for the tank that comes into contact with liquid hydrogen in the liquid hydrogen tank 100.

[0073] Furthermore, when the absorbed energy sE measured by an impact test using a three-sided slit Charpy impact test piece 6 satisfies the above formula 1 or 2, the manufacturer of the steel material can clearly indicate the intended use of the steel material if the steel material is used for the inner tank 102 of a liquid hydrogen tank.

[0074] In addition, the impact test using the three-sided slit Charpy impact test specimen 6 is not a large-scale test method like the hybrid ESSO test, and the test is less likely to fail than the hybrid ESSO test, so it is more efficient in terms of construction period and cost. Furthermore, even when liquid helium is used as the refrigerant for the test, the amount of refrigerant required is smaller than that for the hybrid ESSO test, so that the cost can be reduced from this perspective as well.

[0075] As described above, according to the embodiment of the present disclosure, a liquid hydrogen tank 100 with excellent arrestability can be obtained easily and at low cost.

[0076] The above describes an embodiment of the present disclosure with reference to the accompanying drawings. However, it is clear that a person with ordinary knowledge in the field of technology to which the present disclosure pertains can conceive of various modifications or applications within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0077] The disclosure of Japanese Patent Application No. 2024-121377, filed on July 26, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and herein indicated to be incorporated by reference.

Claims

1. A liquid hydrogen tank having a vessel in contact with liquid hydrogen, constructed of steel material in which the value of absorbed energy sE (unit: J) measured in an impact test at a measurement temperature of -196°C or less using a three-sided slit Charpy impact test specimen satisfies the following formula 1 or 2: sE ≥ 19 + 0.68 x ΔT ... formula 1 In formula 1, the measurement temperature is in the range of more than -253°C or less and -196°C or less, and ΔT is the temperature difference between the measurement temperature and -253°C. sE ≥ 19 ... formula 2 In formula 2, the measurement temperature is -253°C or less.

2. The liquid hydrogen tank according to claim 1, which has a vessel in contact with liquid hydrogen, made of steel having an absorbed energy sE value of 57.76 J or more measured in an impact test at -196°C using a three-sided slit Charpy impact test piece.

3. The liquid hydrogen tank according to claim 1, which has a vessel in contact with liquid hydrogen, made of steel having an absorbed energy sE value of 19 J or more measured in an impact test at a measurement temperature of -253°C or less using a three-sided slit Charpy impact test specimen.

4. A liquid hydrogen tank according to any one of claims 1 to 3, wherein the thickness of the steel material is 50 mm or less.

5. A liquid hydrogen tank according to any one of claims 1 to 4, wherein the steel material has a Ni content of 6.0 to 16.0 mass % and a bcc phase ratio measured by a magnetic induction method of 50% or more.

6. A method for manufacturing a liquid hydrogen tank, comprising the steps of: preparing a steel material such that the value of absorbed energy sE (unit: J) measured in an impact test using a three-sided slit Charpy impact test piece at a measurement temperature of -196°C or less satisfies the following formula 1 or 2; and forming a vessel in a liquid hydrogen tank that comes into contact with liquid hydrogen using the steel material. sE ≧ 19 + 0.68 × ΔT ... formula 1 In formula 1, the measurement temperature is in the range of more than -253°C or less and -196°C or less, and ΔT is the temperature difference between the measurement temperature and -253°C. sE ≧ 19 ... formula 2 In formula 2, the measurement temperature is -253°C or less.

7. The method for manufacturing a liquid hydrogen tank according to claim 6, wherein the measurement of the value of absorbed energy sE is carried out at -196°C, and the value of absorbed energy sE is 57.76 J or more.

8. The method for manufacturing a liquid hydrogen tank according to claim 6, wherein the measurement of the value of absorbed energy sE is carried out at -253°C or lower, and the value of absorbed energy sE is 19 J or higher.

9. A method for manufacturing a liquid hydrogen tank according to any one of claims 6 to 8, wherein the thickness of the steel material is 50 mm or less.

10. A method for manufacturing a liquid hydrogen tank as set forth in any one of claims 6 to 9, wherein the steel material has a Ni content of 6.0 to 16.0 mass % and a bcc phase ratio measured by a magnetic induction method of 50% or more.

11. A method for designing a liquid hydrogen tank, comprising the steps of: setting a temperature equal to or lower than the liquefaction temperature of hydrogen as a set temperature; and determining, based on said set temperature, that the steel material to be used in a vessel in contact with liquid hydrogen in a liquid hydrogen tank is a steel material whose absorbed energy sE value (unit: J) is measured in an impact test using a three-sided slit Charpy impact test piece at a measurement temperature of -196°C or lower, and the value satisfies the following formula 1 or 2: sE ≧ 19 + 0.68 × ΔT ... formula 1 In formula 1, the measured temperature is in the range of greater than -253°C and equal to or lower than -196°C, and ΔT is the temperature difference between the measured temperature and -253°C. sE ≧ 19 ... formula 2 In formula 2, the measured temperature is equal to or lower than -253°C.

12. The method for designing a liquid hydrogen tank according to claim 11, wherein the measurement of the value of absorbed energy sE is carried out at -196°C, and the value of absorbed energy sE is 57.76 J or more.

13. The method for designing a liquid hydrogen tank according to claim 11, wherein the measurement of the value of absorbed energy sE is carried out at -253°C or lower, and the value of absorbed energy sE is 19 J or higher.

14. A method for designing a liquid hydrogen tank according to any one of claims 11 to 13, wherein the thickness of the steel material is 50 mm or less.

15. A method for designing a liquid hydrogen tank according to any one of claims 11 to 14, wherein the steel material has a Ni content of 6.0 to 16.0 mass % and a bcc phase ratio measured by a magnetic induction method of 50% or more.

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