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

Abstract

A liquid hydrogen tank having a tank in contact with liquid hydrogen, made of steel whose absorbed energy sE, measured by impact tests at a measurement temperature of -196°C or below using a three-sided slit Charpy impact test specimen, satisfies the following formula 1 or formula 2. sE≧19+0.68×ΔT···Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE≧19...Equation 2 In Equation 2, the measurement temperature is -253°C or lower.

Description

Technical Field

[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.

Background Art

[0002] Conventionally, steel materials have been used for cryogenic storage tanks for storing liquid hydrogen. For example, in Japanese Patent No. 5494166, as a method for providing a cryogenic thick steel plate with excellent arrest characteristics at a low cost, 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% to less than 10.0%, Al: 0.002 to 0.05%, N: 0.005% or less, the balance being composed of Fe and impurities, the residual γ amount at the plate thickness (1 / 4)t position is 3.0% by volume or more, and the average value of the equivalent circle diameter of the tissue unit surrounded by large-angle grain boundaries of 15° or more observed by the EBSP method at a magnification of 2000 times is 5.5 μm or less at the plate thickness (1 / 4)t position, a cryogenic thick steel plate and a method for manufacturing the same are disclosed.

[0003] Further, in Japanese Patent No. 5673399, as a steel material for cryogenic use having excellent fracture toughness, 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% and less than 10.0%, Al: 0.002 to 0.08%, N: 0.0015 to 0.0040%, the balance being composed of Fe and impurities, the residual γ amount at the (1 / 4)t position of the plate thickness t is 3.0% by volume or more, and the value represented by the 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 residual γ amount when a 1% plastic strain is applied in an environment of -165°C is 25% or less, a steel material for cryogenic use is disclosed.

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

[0005] Furthermore, Japanese Patent Publication No. 6-179909 discloses a method for producing cryogenic steel, in which steel is hot-rolled, quenched at a temperature above the Ac3 transformation point, then reheated to 680-710°C and quenched again, and tempered at 570-600°C, with the remainder being Fe and unavoidable impurities, and the impurities containing P and S being 0.001% or less by weight.

[0006] Furthermore, the Transactions of the Japan Society of Naval Architects and Engineers, 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. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Steel used in cryogenic storage tanks for liquid hydrogen (temperature -253°C) requires excellent fracture toughness. Conventionally, the arrestability of steel used in cryogenic storage tanks, such as those for LNG (temperature -162°C), has been evaluated by methods such as the mixed ESSO test. However, the mixed ESSO test is a large-scale test method, making it inefficient in terms of construction time and cost. Furthermore, when determining the arrestability of steel used in tanks for liquid hydrogen (temperature -253°C), for example, when conducting tests at temperatures below -253°C, one could consider using liquid helium (temperature -269°C). However, liquid helium is expensive, making it impractical to use in the large-scale mixed ESSO test, which requires a large amount of refrigerant. Therefore, there is a need to establish a simple and low-cost alternative test method for determining the arrestability of steel used in liquid hydrogen tanks.

[0008] This disclosure was made in view 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 can be manufactured simply and at low cost, and a method for designing a liquid hydrogen tank that can be designed simply and at low cost. [Means for solving the problem]

[0009] This disclosure includes the following aspects. <1> A liquid hydrogen tank having a tank in contact with liquid hydrogen, made of steel material whose absorbed energy sE (unit: J), measured by impact tests at a measurement temperature of -196°C or below using a three-sided slit Charpy impact test specimen, satisfies either formula 1 or formula 2 below. sE≧19+0.68×ΔT ··· Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE≧19 ··· Equation 2 In Equation 2, the measurement temperature is -253°C or lower. <2> A tank in contact with liquid hydrogen is constructed of steel material whose absorbed energy sE value, measured by an impact test at -196°C using a three-sided slit Charpy impact test specimen, is 57.76 J or higher, and which has an impact tank in contact with liquid hydrogen. <1> The liquid hydrogen tank described above. <3> A tank in contact with liquid hydrogen is provided, which is made of steel whose absorbed energy sE value, measured by impact tests at a measurement temperature of -253°C or lower using a three-sided slit Charpy impact test specimen, is 19 J or more. <1> The liquid hydrogen tank described above. <4> The thickness of the aforementioned steel material is 50 mm or less. <1> from <3> A liquid hydrogen tank as described in any one of the items. <5> The aforementioned steel material has a Ni content of 6.0 to 16.0 mass%, and a ferrite content of 50% or more as measured by magnetic induction. <1> from <4> A liquid hydrogen tank as described in any one of the items. <6> The process involves preparing a steel material in which the value of the absorbed energy sE (unit: J) is measured by an impact test using a three-sided slit Charpy impact test specimen at a measurement temperature of -196℃ or lower, and the value of the absorbed energy sE satisfies the following formula 1 or formula 2, A step of forming a tank that comes into contact with liquid hydrogen in a liquid hydrogen tank using the aforementioned steel material, A method for manufacturing a liquid hydrogen tank having [the specified characteristics]. sE≧19+0.68×ΔT ··· Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE = ≥ 19 ··· Equation 2 In Equation 2, the measurement temperature is -253°C or lower. <7> The value of the absorbed energy sE was measured at -196°C, and the absorbed energy sE was 57.76 J or higher. <6> A method for manufacturing a liquid hydrogen tank as described above. <8> The measurement of the value of the absorbed energy sE is carried out at -253°C or lower, and the value of the absorbed energy sE is 19 J or more. The method for manufacturing a liquid hydrogen tank according to <6>. <9> The thickness of the steel material is 50 mm or less. The method for manufacturing a liquid hydrogen tank according to any one of <6> to <8>. <10> The steel material has a Ni content of 6.0 to 16.0% by mass and a ratio of the bcc phase measured by the magnetic induction method of 50% or more. The method for manufacturing a liquid hydrogen tank according to any one of <6> to <9>. <11> A method for designing a liquid hydrogen tank, comprising: a step of setting a temperature below the liquefaction temperature of hydrogen as a set temperature; and a step of determining, based on the set temperature, a steel material used for a tank in contact with liquid hydrogen in the liquid hydrogen tank as a steel material satisfying the following formula 1 or formula 2 as a result of measuring the value of the absorbed energy sE (unit: J) by an impact test using a three-sided slit Charpy impact test specimen at a measurement temperature of -196°C or lower. sE ≧ 19 + 0.68 × ΔT ··· Formula 1 In Formula 1, the measurement temperature is within a range exceeding -253°C and being -196°C or lower, 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 lower. <12> The measurement of the value of the absorbed energy sE is carried out at -196°C. The value of the absorbed energy sE is 57.76 J or more. The method for designing a liquid hydrogen tank according to <11>. <13> The measurement of the value of the absorbed energy sE is carried out at -253°C or lower. The value of the absorbed energy sE is 19 J or more. The method for designing a liquid hydrogen tank according to <11>. <14> The thickness of the steel material is 50 mm or less. The method for designing a liquid hydrogen tank according to any one of <11> to <13>. <15> The steel material has a Ni content of 6.0 to 16.0% by mass and a ratio of the bcc phase measured by the magnetic induction method of 50% or more. The method for designing a liquid hydrogen tank according to any one of <11> to <14>.

Advantages of the Invention

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

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a perspective view showing an example of a liquid hydrogen tank according to the present disclosure. [Figure 2] FIG. 2 is a front view showing a hybrid ESSO test piece. [Figure 3A] FIG. 3A is a front view showing a three-sided slit Charpy impact test piece. [Figure 3B] FIG. 3B is a cross-sectional view showing a location where a slit is formed in a three-sided slit Charpy impact test piece. [Figure 4A] FIG. 4A is a view showing a location where a three-sided slit Charpy impact test piece in the present disclosure is taken, and is a view showing a location to be taken when the plate thickness of the steel plate is 25 mm or more. [Figure 4B] FIG. 4B is a view showing a location where a three-sided slit Charpy impact test piece in the present disclosure is taken, and is a view showing a location to be taken when the plate thickness of the steel plate is 12 mm or more and less than 25 mm. [Figure 5]Figure 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. [Figure 6] Figure 6 is a flow chart illustrating the design method for a liquid hydrogen tank in this disclosure. [Figure 7] Figure 7 is a flow chart showing the method for manufacturing a liquid hydrogen tank according to this disclosure. [Figure 8] Figure 8 shows an example of taking a three-sided slit Charpy impact test specimen from a liquid hydrogen tank according to the present disclosure. [Modes for carrying out the invention]

[0012] The embodiments of this disclosure are described in detail below.

[0013] In numerical ranges described in stages, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Within a numerical range, the upper or lower limit stated within that range may be replaced with the value shown in the example. The term "process" includes not only independent processes, but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved.

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

[0015] As shown in Figure 1, the inner tank 102 is manufactured using steel plates 110 whose absorbed energy values ​​have been measured by tests described later. More specifically, as shown in Figure 1, the inner tank 102 is formed by joining together multiple steel plates 110 so that it functions as a tank capable of storing liquid hydrogen. The multiple steel plates 110 are formed into the shape of the inner tank 102 by welding, for example. The inner tank 102 is an example of a "tank in contact with liquid hydrogen" in this disclosure.

[0016] The outer tank 104 holds the inner tank 102 in such a way that the thermal conductivity between them is reduced. The specific method for holding the inner tank 102 in such a way that the thermal conductivity is reduced can be any method, for example, by creating a vacuum gap or by filling it with a porous material. The outer tank 104 may be made of any material.

[0017] Furthermore, although the liquid hydrogen tank 100 shown in Figure 1 consists of two tanks, an inner tank 102 and an outer tank 104, the number of tanks in the liquid hydrogen tank 100 using the technology of this disclosure may be even greater. For example, it may have a tank that further covers the outer tank 104.

[0018] (Required performance and challenges for steel plate 110) The steel used in the inner tank 102 for storing liquid hydrogen (hydrogen at atmospheric pressure at a temperature of -253°C or below; hereafter, unless otherwise specified, this refers to the boiling point at atmospheric pressure. The same applies to other types of gases.) in a cryogenic tank requires excellent fracture toughness. Specifically, in addition to being resistant to brittle fracture even in a cryogenic environment, the steel must also possess excellent arrest properties (so-called arrest properties) that stop the propagation of brittle cracks in the steel portion (i.e., the base material) to prevent the collapse of the entire tank, even if brittle cracks occur in the welds of the tank.

[0019] Conventionally, the arrestability of 9% Ni steel and 7% Ni steel used in low-temperature storage tanks, such as above-ground tanks for storing LNG (natural gas at temperatures below -162°C), has been evaluated by a hybrid ESSO test using the hybrid ESSO test specimen 10 shown in Figure 2. Under normal test conditions, the applied stress is 393 MPa, which is the same level as the allowable stress during earthquakes in the LNG above-ground storage tank guidelines, and the test temperature is -165°C, which is approximately the same as the temperature of LNG. If it can be confirmed that a brittle crack generated from the notch 18 in the approach plate 12 propagates through the approach plate 12 and the welded joint 14 and then stops at the test plate 16 under these test conditions, it is judged that the steel plate 110 for above-ground LNG has sufficient arrestability.

[0020] However, the mixed ESSO test is a large-scale testing method, making it inefficient in terms of construction time and cost. Furthermore, due to difficulties in properly propagating cracks, particularly in the welded joint 14, the test often fails (i.e., a determination cannot be made), requiring retesting. In addition, when determining the arrestability of steel materials used in tanks for storing liquid hydrogen (temperature -253°C), it is conceivable to conduct the test at temperatures below -253°C, in which case liquid helium (helium at temperatures below -269°C) can be used. However, liquid helium is very expensive, and using it in the large-scale mixed ESSO test, which requires a large amount of refrigerant, is not practical.

[0021] Thus, there is a need to establish a simple and low-cost alternative test method for determining the arrestability of steel materials used in liquid hydrogen tanks 100. Here, the disclosers have found that measuring the absorbed energy sE by impact testing using a three-sided slit Charpy impact test specimen 6 is an appropriate method for determining the arrestability of steel materials at measurement temperatures of -196°C or lower.

[0022] (Three-sided slit Charpy impact test specimen 6) Figures 3A and 3B show a test specimen 10 (hereinafter referred to as the "three-sided slit Charpy impact test specimen") used in the three-sided slit Charpy impact test according to this disclosure. As shown in Figures 3A and 3B, the three-sided slit Charpy impact test specimen 6 is shaped like a rectangular parallelepiped with one side extended, and has slits 8 on three central faces in the longitudinal direction. More specifically, the three-sided slit Charpy impact test specimen 6 is a test specimen in which slits 8 are formed on three central faces in the depth direction of a rectangular prism-shaped steel material measuring 10 mm in length, 10 mm in width, and 55 mm in depth. The slits 8 have a width of 0.15 mm and a depth of 2 mm.

[0023] Furthermore, Figures 4A and 4B show the locations from which the three-sided slit Charpy impact test specimen 6 is taken from the steel material. In Figures 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 direction of the thickness of the steel material.

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

[0025] Although not shown in Figure 4A, the three-sided slit Charpy impact test specimen 6 is taken from within 50 mm of the end in the width direction of the steel material.

[0026] Figure 4B shows the locations where the three-sided slit Charpy impact test specimen 6 is taken when the thickness of the steel material is 12 mm or more and less than 25 mm. As shown in Figure 4B, when the thickness of the steel material is 12 mm or more and less than 25 mm, the three-sided slit Charpy impact test specimen 6 is taken such that one side of the specimen 6 is 1 mm in the thickness direction of the plate. The longitudinal direction of the three-sided slit Charpy impact test specimen 6 is the rolling direction of the steel material. In addition, the side of the three-sided slit Charpy impact test specimen 6 that does not have a slit 8 (the right side in Figure 4B) is considered to be the width direction of the steel material.

[0027] The slits 8 of the three-sided slit Charpy impact test specimen 6 in this disclosure may be formed by any method. For example, the slits 8 may be formed by wire-cut electrical discharge machining.

[0028] (Comparison of the three-sided slit Charpy impact test and the hybrid ESSO test) Next, we will explain the results of comparing the three-sided slit Charpy impact test and the composite ESSO test. In the test example, composite ESSO tests and three-sided slit Charpy impact tests were performed at -196°C, -165°C, and -120°C using multiple 9% Ni steel (JIS G3127 SL9N590) and 7% Ni steel (JIS G3127 SL7N590) with different plate thicknesses.

[0029] The composite ESSO test was conducted in accordance with the Japan Welding Society standard WES2815 (2014). First, a composite ESSO test specimen 10, as shown in Figure 2, was prepared. The composite ESSO test specimen 10 is a test specimen in which a pre-running plate 12 and a test plate 16 are welded together and connected by a weld 14, with a V-shaped notch 18 formed in the pre-running plate 12. The composite ESSO test specimen 10 has a widthwise length (i.e., the length from one end of the pre-running plate 12 to the other end of the test plate 16, the longitudinal length in Figure 2) of 500 mm, a length from one end of the pre-running plate 12 to the boundary between the weld 14 and the test plate 16 of 150 mm, and a tensile length (i.e., the longitudinal length of the weld 14, the transverse length in Figure 2) of 500 mm. The composite ESSO test specimen 10 was formed so that the rolling direction was the tensile direction in the test specimen (transverse direction in Figure 2). The hybrid ESSO test specimen 10 has a total length of approximately 3000 mm because fixtures for applying load are welded to both ends in the tensile direction. In the hybrid ESSO test, the hybrid ESSO test specimen 10 was first mounted on a large tensile testing machine and cooled to the temperature shown in Table 1. Liquid nitrogen was used as the coolant. After applying a tensile load to the hybrid ESSO test specimen 10 to apply a stress of 393 MPa, a brittle crack was induced by striking the notch 18 in the run-up plate 12 through a wedge. If the brittle crack propagated through the run-up plate 12 and the welded joint 14 and stopped at the test plate 16, it was determined to be "arrested," and if it penetrated the test plate 16, it was determined to be "propagated."

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

[0031] The prepared three-sided slit Charpy impact test specimens (6) were cooled to the temperatures listed in Table 1 using liquid nitrogen as a refrigerant. Cooling of the specimens with a refrigerant may be done by immersing the specimens in the refrigerant or by spraying the refrigerant onto the surface of the specimens. Alternatively, the temperature can be adjusted to a level higher than -196°C by utilizing the layer of cold air formed above the liquid nitrogen surface and adjusting the distance from the liquid surface that holds the specimens.

[0032] After cooling, a Charpy impact test was applied using a Charpy impact testing machine to the center of the position corresponding to the slit 8 on the side where the slit 8 was not formed in the three-sided slit Charpy impact test specimen 6, 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 specimen. Three three-sided slit Charpy impact tests were performed at the same temperature as the hybrid ESSO test, and the average value of their absorbed energy (sE) was calculated.

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

[0034] [Table 1]

[0035] In a typical V-notch Charpy impact test, a ductile fracture surface is often formed near the bottom of the notch, with a brittle fracture surface forming ahead of it. On the other hand, in a three-slit Charpy impact test, a brittle fracture surface is formed near the bottom of the notch (slit), with a ductile fracture surface forming ahead of it. In a three-slit Charpy impact test, this type of fracture surface is formed when a brittle crack is arrested at the boundary between the brittle and ductile fracture surfaces. In other words, the three-slit Charpy impact test is a suitable test method 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 bottom of the notch and a brittle fracture surface forms ahead of it; in such cases, the test results should be invalidated.

[0036] As shown in Table 1, for 9% Ni steel plates with a thickness of 31 mm, those that showed an absorbed energy sE of 15 J or more in the three-sided slit Charpy impact test also showed an arrest result in the hybrid ESSO test. On the other hand, No. 1 showed an absorbed energy sE of 13 J, and the hybrid ESSO test resulted in propagation. In the fracture surface of the hybrid ESSO test, it was confirmed that a shear lip had developed near the front and back surfaces of steel plate 110, suggesting that the test conditions were near the boundary between arrest and propagation. Furthermore, No. 5 showed an absorbed energy sE of 7 J, and the hybrid ESSO test resulted in propagation. In the fracture surface of the hybrid ESSO test, it was confirmed that the shear lip was not as developed compared to No. 1.

[0037] Note that in Table 1, although No. 6 and No. 8 have the same steel thickness and test temperature, the absorbed energy sE values ​​and the results of the hybrid ESSO test differ. This is due to the different heat treatments used for steel No. 6 and steel No. 8. In other words, the structural microstructure of steel No. 6 and steel No. 8 is different.

[0038] Furthermore, as shown in Table 1, for the 9% Ni steel with a plate thickness of 50 mm and the 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 temperature range of -196°C to -165°C.

[0039] Furthermore, the steel material preferably has a Ni content of 6.0% to 16.0% by mass, and a bcc phase ratio of 50% or more, as measured by magnetic induction. By having the Ni content and bcc phase ratio of the steel material within the above range, it is possible to achieve both excellent cryogenic toughness and high strength. Such steel material is also advantageous in terms of cost reduction. The bcc phase ratio may be 90% or more.

[0040] The nickel (Ni) content of steel can be confirmed on the steel inspection certificate. Alternatively, a sample may be taken during the steel processing process and the Ni content may be measured by X-ray fluorescence analysis. If it is difficult to take 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 microstructure of steel can be determined by the following method. A sample is taken from the steel material, and the bcc content (volume %) is measured on the sample surface using a FERITSCOPE® FMP30 (manufactured by Fischer Instruments, Inc.), with a Fischer Instruments, Inc. probe (FGAB 1.3-Fe) attached to the probe of the measuring instrument, by magnetic induction. The arithmetic mean of the measured bcc content is then calculated. The average value of the obtained bcc content is taken as the ratio of the bcc phase.

[0042] Based on the results shown in Table 1, 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. More specifically, if the absorbed impact energy sE is 19 J or higher in the three-sided slit Charpy impact test, it can be predicted that an arrest result will also be obtained in the hybrid ESSO test.

[0043] (Relationship between the absorbed impact energy sE of steel and the measurement temperature) Figure 5 shows the results of three-sided slit Charpy impact tests conducted at various measurement temperatures, illustrating the relationship between the temperature of the three-sided slit Charpy impact test specimen and the absorbed energy sE. As shown in Figure 5, when three-sided slit Charpy impact tests were performed on the same 9% Ni steel at different measurement temperatures and the absorbed energy sE was measured, 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, for every 1 K decrease in the measurement temperature from -196°C, the absorbed impact energy sE decreases by 0.684 J.

[0044] Based on the results in Figure 5, it can be said that in order to have an absorption shock energy sE of 19 J or more even at the boiling point of liquid hydrogen (i.e., -253°C), it is sufficient to use steel that satisfies the following equation 1.

[0045] sE≧19+0.68×ΔT ··· Formula 1 In Equation 1, the measured temperature is within the range of greater than -253°C to -196°C, and ΔT is the temperature difference between the measured temperature and -253°C.

[0046] Furthermore, in order to ensure arrestability even below -253°C, the absorbed energy sE must be 19J or higher. Therefore, in order to achieve an absorbed impact energy sE of 19J or higher even below -253°C, it is sufficient to use steel that satisfies the following equation 2.

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

[0048] Furthermore, since the above three-sided slit Charpy impact test is used as an evaluation test for the arrestability of the steel material constituting the tank that comes into contact with liquid hydrogen in the liquid hydrogen tank 100, conducting the test at a temperature close to the liquid hydrogen temperature (-253°C) allows for a more accurate determination of the arrestability. From this viewpoint, the measurement temperature is more preferably -240°C to -269°C, and even more preferably -253°C to -269°C.

[0049] Liquid hydrogen has a temperature of -253°C, and it is conceivable to use liquid hydrogen as a refrigerant in a three-sided slit Charpy impact test to evaluate the arrestability of the steel used in the liquid hydrogen tank 100. However, since liquid hydrogen is flammable and therefore not easy to handle, it is also conceivable to use liquid helium (temperature -269°C), which has an even lower temperature, as a refrigerant. Cooling of the test specimen with a refrigerant can be done by immersing the specimen in the refrigerant or by spraying the refrigerant onto the surface of the specimen. Furthermore, in the method of spraying the refrigerant onto the surface of the specimen, the measurement temperature (i.e., the temperature of the specimen) can be adjusted by adjusting the amount of refrigerant sprayed, and the measurement temperature can be adjusted to a temperature higher than the temperature of the refrigerant itself (for example, the temperature of liquid helium -269°C).

[0050] From the above considerations, it was confirmed that the method of measuring the absorbed energy sE by impact testing using a three-sided slit Charpy impact test specimen 6 is suitable as a method for determining the arrestability of steel materials at measurement temperatures below -196°C.

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

[0052] (Supplementary information regarding plate thickness) Furthermore, the stress state of steel material approaches a plane stress state closer to the surface, meaning it is more prone to plastic deformation and less prone to brittle crack propagation. Therefore, it is presumed that the arrestability increases as the plate thickness decreases. On the other hand, as the plate thickness increases, the region that can be considered to be in a plane stress state becomes smaller relative to the plate thickness, making plastic deformation less likely to occur, and thus brittle cracks are more likely to propagate. Based on the results in Table 1, the thickness of test piece 10 is 50 mm, and arrest was confirmed at this thickness, so it is presumed that arrest will not be a problem with thinner materials.

[0053] Therefore, based on the results in Table 1, it is preferable that the thickness of the steel used in the liquid hydrogen tank 100 be 50 mm or less. There is no particular lower limit to the thickness of the steel, but it can be said that it has been verified down 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 even to thicknesses of 10 mm or less.

[0054] Next, the design method for the liquid hydrogen tank 100 in this disclosure will be explained with reference to Figure 6.

[0055] (Design method for liquid hydrogen tank 100) Figure 6 is a flowchart illustrating the design method for the liquid hydrogen tank 100 in this disclosure. The designer of the liquid hydrogen tank 100 designs the liquid hydrogen tank 100 based on the procedure shown in Figure 6.

[0056] First, in step S102, the designer sets the tank's set temperature to be below the hydrogen liquefaction temperature. More specifically, the designer sets the temperature value specified in the specifications for the liquid hydrogen tank 100 to be below the liquefaction temperature of the liquid hydrogen tank 100.

[0057] Next, in step S104, the designer determines that the steel material for the inner tank 102 of the tank will satisfy Equation 1 or Equation 2 as a result of the impact test. More specifically, the designer determines that the steel material used for the inner tank 102 of the liquid hydrogen tank 100 will be steel material that satisfies Equation 1 or Equation 2 as described above.

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

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

[0060] (Supplementary information regarding the frequency of testing) In the steel material selection method described herein, it is preferable to specify that the inspection frequency be set to be three times at the same temperature for each heat-treated steel plate. Here, "each heat-treated steel plate" refers to each individual steel plate 110 used for the manufacture of the inner tank 102, before it is cold-worked and welded for the manufacture of the inner tank 102.

[0061] Next, the method for manufacturing the liquid hydrogen tank 100 in this disclosure will be explained with reference to Figure 7.

[0062] (Method for manufacturing a liquid hydrogen tank 100) Figure 7 is a flow chart showing the manufacturing method of the liquid hydrogen tank 100 in this disclosure. The manufacturer of the liquid hydrogen tank 100 manufactures the liquid hydrogen tank 100 according to the procedure shown in Figure 7.

[0063] First, as step S202, the manufacturer prepares steel materials that satisfy either Equation 1 or Equation 2 in the results of an impact test. More specifically, the manufacturer prepares steel materials that satisfy either Equation 1 or Equation 2 as described above, to be used in the inner tank 102 of the liquid hydrogen tank 100 designed according to the design procedure described above.

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

[0065] Next, in step S206, the manufacturer forms the other parts 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. In the manufacture of the liquid hydrogen tank 100, the procedures related to steps S202 to S206 described above do not have to be performed step by step. More specifically, in the manufacturing process of the liquid hydrogen tank 100, the steps corresponding to steps S202, S204, and S206 may be performed in parallel. For example, this includes a configuration in which the bottom portion of the outer tank 104 is formed (the step corresponding to step S206), the inner tank 102 is formed (the step corresponding to step S204), and then the other parts of the outer tank 104 are formed (the step corresponding to step S206).

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

[0068] Next, a method for evaluating the liquid hydrogen tank 100 according to this embodiment, that is, for inspecting whether or not steel material satisfying formula 1 or formula 2 is used in the inner tank 102, will be explained with reference to Figure 8.

[0069] (Inspection method for liquid hydrogen tank 100) Figure 8 shows an example of taking a three-sided slit Charpy impact test specimen 6 from a liquid hydrogen tank 100. As shown in Figure 8, when taking a three-sided slit Charpy impact test specimen 6 from the inner tank 102, the specimen 6 is taken from a location unaffected by welding. More specifically, as shown in Figure 8, it is preferable that the three-sided slit Charpy impact test specimen 6 is taken from a location at least 50 mm away from the welded area 112. It is also preferable that the longitudinal direction of the three-sided slit Charpy impact test specimen 6 is the rolling direction of the steel plate 110 forming 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 design method for the liquid hydrogen tank 100 according to this disclosure will be explained.

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

[0072] Specifically, it was found that if the absorbed energy sE measured by impact testing using a three-sided slit Charpy impact test specimen 6 satisfies either equation 1 or equation 2, then excellent arrest properties can be obtained for the steel material used in the tank that comes into contact with liquid hydrogen in the liquid hydrogen tank 100.

[0073] Furthermore, if the absorbed energy sE measured by an impact test using a three-sided slit Charpy impact test specimen 6 satisfies formula 1 or formula 2, the manufacturer of the steel material can specify that the steel material will be used in the inner tank 102 of a liquid hydrogen tank.

[0074] Furthermore, 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 it is less likely to fail compared to the hybrid ESSO test, making it more efficient in terms of construction period and cost. In addition, even when liquid helium is used as the refrigerant for the test, the amount of refrigerant required is less than that of the hybrid ESSO test, so it can be made less expensive from this point of view as well.

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

[0076] While embodiments of this disclosure have been described above with reference to the attached drawings, it is clear that any person with ordinary skill in the art to which this disclosure belongs could conceive of various modifications or applications within the scope of the technical idea described in the claims, and these too are naturally understood to fall within the technical scope of this disclosure.

[0077] The disclosure of Japanese Patent Application No. 2024-121377, filed on 26 July 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as the individual documents, patent applications, and technical standards are incorporated by reference in the same manner as described herein.

Claims

1. A liquid hydrogen tank having a tank in contact with liquid hydrogen, made of steel material whose absorbed energy sE value (unit: J) measured by an impact test at a measurement temperature of -196°C or below using a three-sided slit Charpy impact test specimen satisfies the following formula 1 or formula 2. sE≧19+0.68×ΔT... Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE≧19... Formula 2 In Equation 2, the measurement temperature is -253°C or lower.

2. A tank in contact with liquid hydrogen is constructed of steel material whose absorbed energy sE, measured by an impact test at -196°C using a three-sided slit Charpy impact test specimen, is 57.76 J or higher. A liquid hydrogen tank according to claim 1.

3. A tank in contact with liquid hydrogen is provided, which is made of steel material whose absorbed energy sE value, measured by impact tests at a measurement temperature of -253°C or lower using a three-sided slit Charpy impact test specimen, is 19 J or more. A liquid hydrogen tank according to claim 1.

4. The thickness of the steel material is 50 mm or less. A liquid hydrogen tank according to claim 1.

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

6. The process involves preparing a steel material in which the absorbed energy sE (unit: J) is measured by an impact test using a three-sided slit Charpy impact test specimen at a measurement temperature of -196°C or lower, and the absorbed energy sE value satisfies the following formula 1 or formula 2, A step of forming a tank that comes into contact with liquid hydrogen in a liquid hydrogen tank using the aforementioned steel material, A method for manufacturing a liquid hydrogen tank having [the specified characteristics]. sE≧19+0.68×ΔT... Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE≧19... Formula 2 In Equation 2, the measurement temperature is -253°C or lower.

7. The measurement of the absorbed energy sE was performed at -196°C. The value of the absorbed energy sE is 57.76 J or more. A method for manufacturing a liquid hydrogen tank according to claim 6.

8. The measurement of the absorbed energy sE was performed at -253°C or below. The value of the absorbed energy sE is 19 J or more. A method for manufacturing a liquid hydrogen tank according to claim 6.

9. The thickness of the steel material is 50 mm or less. A method for manufacturing a liquid hydrogen tank according to claim 6.

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

11. A process of setting a temperature below the liquefaction temperature of hydrogen as the target temperature, Based on the aforementioned set temperature, the steel material to be used in the tank that comes into contact with liquid hydrogen in the liquid hydrogen tank is determined to be a steel material whose absorbed energy sE (unit: J) is measured by an impact test using a three-sided slit Charpy impact test piece at a measurement temperature of -196°C or lower, and whose absorbed energy sE satisfies the following formula 1 or formula 2. A method for designing a liquid hydrogen tank having the following features. sE≧19+0.68×ΔT... Formula 1 In Equation 1, the measured 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 measured temperature and -253°C. sE≧19... Formula 2 In Equation 2, the measurement temperature is -253°C or lower.

12. The measurement of the absorbed energy sE was performed at -196°C. The value of the absorbed energy sE is 57.76 J or more. A method for designing a liquid hydrogen tank according to claim 11.

13. The measurement of the absorbed energy sE was performed at -253°C or below. The value of the absorbed energy sE is 19 J or more. A method for designing a liquid hydrogen tank according to claim 11.

14. The thickness of the steel material is 50 mm or less. A method for designing a liquid hydrogen tank according to claim 11.

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

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