Liquefied ammonia tank, manufacturing method of inner tank of liquefied ammonia tank, and design method of inner tank of liquefied ammonia tank

Abstract

To provide a liquefied ammonia tank, and a manufacturing method and a design method of an inner tank of the liquefied ammonia tank, capable of realizing excellent arrest characteristic.SOLUTION: A liquefied ammonia tank comprises an outer tank and an inner tank provided inside the outer tank. The inner tank includes a bottom part, a side wall part and a roof part. The side wall part of the inner tank is constituted by connecting a plurality of steel materials via a welding part, and a lateral direction of the steel material is aligned in a height direction of the inner tank. A length in the lateral direction of the steel material is 500 mm or more. A first welding part in the lateral direction extending in the lateral direction of one steel material is located at a different position in a longitudinal direction of the steel material from a second welding part in the lateral direction extending in the lateral direction of another steel material adjacent in the lateral direction. A distance in the longitudinal direction of the steel material between the first welding part in the lateral direction and the second welding part in the lateral direction is 300 mm or more. A Kca value at -35°C of the steel material is 6000 N / mm3 / 2 or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a liquefied ammonia tank, a manufacturing method for an inner tank of a liquefied ammonia tank, and a design method for the inner tank of a liquefied ammonia tank. [Background technology]

[0002] In recent years, ammonia has been attracting attention not only as a fuel that does not emit carbon dioxide, but also as a means of transporting hydrogen (hydrogen carrier), which is one of the next-generation energy options. Ammonia becomes liquid at low temperatures, and it is expected to be transported as liquefied ammonia and stored in designated storage tanks.

[0003] Incidentally, a tank for storing liquefied petroleum gas, which is made by welding steel material with a Ni content of 2.3 to 3.5% with a welding material with a Ni content of 6 to 12%, has been proposed (see, for example, Patent Document 1 below). Patent Document 1 considers crack propagation arrestability (arrestability) as a new approach to the safety of low-temperature tanks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 60-215195 Summary of the Invention [Problem to be solved by the invention]

[0005] Steel materials and welding materials containing Ni are often used in conventional liquefied gas tanks such as that disclosed in Patent Document 1. However, when storing liquefied ammonia, there is a concern about stress corrosion cracking (SCC) caused by ammonia, so steel materials and welding materials with a high Ni content cannot be used without special consideration.

[0006] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a liquefied ammonia tank, a manufacturing method for the inner tank of a liquefied ammonia tank, and a design method for the inner tank of a liquefied ammonia tank, which are capable of achieving excellent arrest characteristics. [Means for solving the problem]

[0007] As a result of intensive research into solving the above problems, the inventors have found that in order to realize a liquefied ammonia tank, it is necessary to focus on long crack arrest, which has not been considered in conventional liquefied gas tanks. Based on this finding, the inventors have further researched the invention, which will be described below. The gist of the present invention is as follows.

[0008] [1] A liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank, the inner tank having a bottom, a side wall, and a roof, the side wall of the inner tank being formed by connecting a plurality of steel materials via welds, the short side direction of the steel materials being arranged in accordance with the height direction of the inner tank, the length of the short side direction of the steel materials being 500 mm or more, a first short side weld extending in the short side direction of the steel materials and a second short side weld extending in the short side direction of another steel material adjacent in the short side direction being positioned differently in the longitudinal direction of the steel materials, the distance between the first short side weld and the second short side weld in the longitudinal direction of the steel materials being 300 mm or more, and the Kca value of the steel materials at -35°C being 6000 N / mm 3 / 2 That's it for the liquefied ammonia tank. [2] The liquefied ammonia tank described in [1], wherein the steel material and the welded portion satisfy the following formula (1). Here, in the following formula (1), σ d : Design stress of steel σ y : Yield stress of steel vE WM : Charpy absorbed energy of weld metal vE FL : Charpy absorbed energy of fusion line vE HAZ : Charpy absorbed energy of heat-affected zone of steel vE BM : Charpy absorbed energy of the base material of the steel and min(vE WM ,vE FL ,vE HAZ ) is written as vE WM , vE FL , vE HAZ This means that the smallest of the three values ​​is selected. [3] The liquefied ammonia tank described in [1], wherein the thickness of the steel material is 60 mm or less. [4] A liquefied ammonia tank as described in [1], wherein the longitudinal length of the steel material is 5,500 mm or less. [5] The liquefied ammonia tank described in [1], wherein the Ni content of the steel is 2.0 mass% or less, and the Ni content of the weld metal constituting the weld is less than 6.0 mass%. [6] A liquefied ammonia tank as described in [1], wherein the base material portion of the steel has a Vickers hardness of 240 or less, and the heat-affected portion of the steel has a Vickers hardness of 300 or less. [7] A method for manufacturing an inner tank of a liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank and having a bottom, a side wall, and a roof, the method comprising the steps of: 3 / 2 and a step of welding a plurality of the steel materials together to form the side wall portion of the inner tank, wherein the steel materials have a length in the short side direction of 500 mm or more, the short side direction of the steel materials is aligned with the height direction of the inner tank, and a weld extending in the short side direction of one of the steel materials and a weld extending in the short side direction of the other of the steel materials that are adjacent in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and the distance in the circumferential direction of the inner tank between the position of the weld extending in the short side direction of one of the steel materials and the position of the weld extending in the short side direction of the other steel material is 300 mm or more. [8] A method for designing an inner tank of a liquefied ammonia tank, the inner tank having an outer tank and an inner tank disposed inside the outer tank and having a bottom, a side wall, and a roof, the method comprising the steps of: welding a plurality of steel members together to form the side wall of the inner tank; and determining whether the Kca value of the steel members at -35°C is 6000 N / mm 3 / 2 a welded portion extending in the short side direction of one of the steel materials and a welded portion extending in the short side direction of the other of the steel materials that are adjacent in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and the distance in the circumferential direction of the inner tank between the position of the welded portion extending in the short side direction of one of the steel materials and the position of the welded portion extending in the short side direction of the other of the steel materials is set to 300 mm or more.

[0009]

number

[0010] According to one aspect of the present invention, it is possible to achieve better arrest characteristics in a liquefied ammonia tank. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating an example of the structure of a liquefied ammonia tank according to an embodiment of the present invention. [Diagram 2] 4 is a diagram illustrating an example of a side wall portion of the inner tank of the liquefied ammonia tank according to the embodiment. FIG. [Diagram 3] 4 is a diagram illustrating an example of a side wall portion of the inner tank of the liquefied ammonia tank according to the embodiment. FIG. [Figure 4] 4 is a view illustrating the vicinity of a welded portion of a side wall portion of an inner tank of the liquefied ammonia tank according to the embodiment. FIG. [Diagram 5] FIG. 1 is a diagram illustrating a test specimen for an ESSO test. [Figure 6]4A to 4C are diagrams illustrating a method for manufacturing the inner tank of the liquefied ammonia tank according to the embodiment. [Figure 7] FIG. 1 is a diagram illustrating a test specimen for an ultra-wide hybrid ESSO test. [Figure 8] FIG. 1 is a diagram illustrating a test specimen and a jig for an ultra-wide hybrid ESSO test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and duplicated explanations will be omitted.

[0013] (Regarding liquefied ammonia tanks) <Overall structure of the liquefied ammonia tank> The overall structure of a liquefied ammonia tank according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing a schematic diagram of an example of the overall structure of a liquefied ammonia tank according to the present embodiment.

[0014] The liquefied ammonia tank according to this embodiment is used for storing liquefied ammonia therein. As shown in Fig. 1, the liquefied ammonia tank 1 according to this embodiment has a double structure having a hollow outer tank 3 and an inner tank 5 disposed inside the outer tank 3. The inside of the inner tank 5 is hollow, and liquefied ammonia 7 is stored therein.

[0015] The specific shape of the liquefied ammonia tank 1 is not particularly limited, but it is preferable that the liquefied ammonia tank 1 has a flat-bottomed cylindrical vertical tank shape with a dome-shaped roof that has excellent earthquake resistance, as exemplified in FIG. 1.

[0016] The outer tank 3 is manufactured using, for example, various types of concrete or steel materials, and has a bottom 3a, a side wall 3b, and a roof 3c as shown in Fig. 1. The inside of the outer tank 3 is hollow, and an inner tank 5 capable of accommodating liquefied ammonia 7 is disposed therein. The specific structures of the bottom 3a, the side wall 3b, and the roof 3c are not particularly specified, and various known structures can be appropriately adopted in accordance with the structure of the outer tank in a conventional low-temperature liquefied gas tank.

[0017] The inner tank 5 is disposed inside the outer tank 3, and functions as a container for accommodating liquefied ammonia 7. The specific shape of the inner tank 5 is not particularly limited, but it is preferable that the inner tank 5 has a flat-bottomed cylindrical vertical tank shape having a dome-shaped roof with excellent earthquake resistance, as exemplified in FIG. 1. As shown in FIG. 1, the inner tank 5 has a bottom 5a, a side wall 5b, and a roof 5c. The inside of the inner tank 5 is hollow, and liquefied ammonia 7 is accommodated therein.

[0018] Here, the side wall 5b of the inner tank 5 is made of a specific steel material as described below and is configured to have a specific structure. The material used for the side wall 5b of the inner tank 5 and the structure of the side wall 5b of the inner tank 5 will be described in detail later.

[0019] In addition, the material of the bottom 5a and roof 5c of the inner tank 5 is not particularly limited, but since they are parts exposed to liquefied ammonia or may be exposed to liquefied ammonia, it is preferable to manufacture them using the same material as the side wall 5b as described below. In addition, the structure of the bottom 5a and roof 5c of the inner tank 5 is not particularly limited, and various known structures can be appropriately adopted in accordance with the structure of the bottom and roof of the inner tank in a conventional low-temperature liquefied gas tank. In conventional low-temperature liquefied gas tanks such as LPG, the use of a welding material with high toughness and high Ni content suppressed the propagation of brittle cracks and realized arrest characteristics. However, when it is necessary to select steel materials and welding materials in consideration of stress corrosion cracking due to ammonia, it is necessary to consider long crack arrest, in which a brittle crack generated in a welded part propagates to an adjacent steel material in the height direction of the inner tank and stops.

[0020] The maximum capacity of liquefied ammonia that can be accommodated in the inner tank 5 is not particularly specified, but is expected to be, for example, about 10,000 tons to 100,000 tons.

[0021] Furthermore, the liquefied ammonia tank 1 according to this embodiment may have various members other than the above-mentioned outer tank 3 and inner tank 5. For example, various types of cold insulators, heat insulating materials, liners, etc. (not shown) may be present between the outer tank 3 and inner tank 5 shown in FIG.

[0022] <Structure of the inner tank 5 of the liquefied ammonia tank 1> The structure of the inner tank 5 in the liquefied ammonia tank 1 according to this embodiment will be described with reference to FIGS.

[0023] FIG. 2 is a diagram for explaining an example of the side wall portion 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment. The side wall portion 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment is configured by connecting a plurality of steel materials via welded portions 13. As shown in FIG. 2, the steel materials are arranged so that the short side direction is the height direction of the inner tank 5. Focusing on a part of the height direction of the inner tank 5, a plurality of steel materials 11 in a curved state are arranged with their longitudinal ends butted against each other to form a cylindrical shape, and are connected to each other via welded portions 13. In the circumferential direction of the inner tank 5, the short side ends of the plurality of steel materials 11 are connected to each other via welded portions 13. In the following description, for convenience, the welded portions 13 may be referred to as short side welded portions 14 extending in the short side direction of the steel materials 11 and longitudinal welded portions 15 extending in the long side direction of the steel materials 11.

[0024] The degree of curvature of the multiple steel materials 11 is not particularly specified, and the curvature may be set appropriately depending on the maximum capacity of liquefied ammonia required for the liquefied ammonia tank 1. In addition, the number of steel materials 11 constituting the inner tank 5 is also not particularly specified, and may be set appropriately based on the maximum capacity of liquefied ammonia required for the liquefied ammonia tank 1 and the longitudinal and lateral lengths of the steel materials.

[0025] As shown in Fig. 2, adjacent steel materials 11 in the circumferential direction of the inner tank 5 are connected to each other by welds (transverse welds 14) extending in the transverse direction (height direction of the inner tank). The transverse welds 14 are formed by welding adjacent steel materials 11 together using a predetermined weld metal by a welding method such as butt welding. As shown in Fig. 2, the transverse welds 14 extend in a direction approximately parallel to the central axis of the cylindrical shape formed by the multiple steel materials 11 (the vertical direction in Fig. 2).

[0026] 2, the side wall portion 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment is configured by stacking a plurality of steel materials 11 so that the short side direction of the steel materials 11 coincides with the height direction of the liquefied ammonia tank 1 (more specifically, the height direction of the inner tank 5), and then connecting the steel materials 11 to each other via welds extending along the circumferential direction of the inner tank 5. The welds extending along the circumferential direction of the inner tank 5 and connecting the steel materials 11 adjacent in the height direction of the inner tank 5 can also be regarded as welds extending in the longitudinal direction of the steel materials 11 (longitudinal welds 15).

[0027] As shown in Fig. 2, the longitudinal positions of the short-side welds 14 extending in the short-side direction of the steel materials 11 adjacent to each other in the height direction of the inner tank are different. For example, when one steel material 11a and the other steel material 11b adjacent to each other in the height direction shown in Fig. 2 are taken into consideration, the circumferential positions of the first short-side welds 14a and the second short-side welds 14b extending in the height direction are different. This reduces the possibility that a brittle crack generated in the short-side welds 14a of one steel material 11a propagates in the height direction of the inner tank, reaches the short-side welds 14b of the other adjacent steel material 11b, and further propagates.

[0028] In the side wall 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment, the length (length a in FIG. 2) of the steel material 11 in the short side direction (height direction of the inner tank 5) is 500 mm or more. The reason why the length a of the steel material 11 in the short side direction is set to 500 mm or more will be explained with reference to FIG. 3. FIG. 3 is a diagram for explaining the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment, and shows a schematic planar development of a portion of the side wall 5b of the inner side 5.

[0029] As shown in FIG. 3, the steel materials 11a, 11b, and 11c are arranged along the height direction of the inner tank 5 of the liquefied ammonia tank 1, and are connected to each other by a longitudinal weld 15 extending in the circumferential direction of the inner tank 5. The brittle crack is generated at the position of point O in the short-side weld 14a of the steel material 11a, propagates along the short-side weld 14a, and reaches the position of point A shown in FIG. 3. As a result of verification by the present inventors, it was found that when the short-side length a of the steel material 11b is less than 500 mm, the brittle crack that reaches the position of point A does not stop midway through the steel material 11b, but propagates through the steel material 11b and reaches point A' shown in FIG. 3 (propagation route (1) shown by a broken line in FIG. 3). The brittle crack that reaches point A' may further propagate through the short-side weld 14c of the steel material 11c. In such a case, the brittle fracture that has occurred at the position of point O cannot be stopped, and the arrestability required for the liquefied ammonia tank 1 cannot be realized.

[0030] On the other hand, by making the length a in the short side direction of the steel material 11a 500 mm or more, when a brittle crack propagates along the propagation route (1) shown by the dashed line in Fig. 3, the propagation of the brittle crack stops halfway through the steel material 11b (long crack arrest), and the brittle crack that has reached point A in Fig. 3 can be prevented from propagating to point A'. As a result, the liquefied ammonia tank 1 according to this embodiment can achieve the arrest characteristics required for the liquefied ammonia tank 1.

[0031] 2 and 3, the longer the length a in the short-side direction of the steel material 11, the more it is possible to reduce the possibility that a brittle crack that has occurred will propagate to an adjacent steel material 11. The length in the short-side direction of the steel material 11 is preferably 1000 mm or more, and more preferably 1500 mm or more.

[0032] However, if the short-side length a of the steel material 11 exceeds 5500 mm, even if the crack propagating along the short-side welded portion 14a stops halfway through the steel material 11b, the opening formed by the brittle crack may be large. Therefore, the short-side length a of the steel material 11 is preferably 5500 mm or less. By making the short-side length a of the steel material 11 5500 mm or less, it is possible to reduce the opening formed by the propagation of the brittle crack. The short-side length a of the steel material 11 is preferably 4000 mm or less, and more preferably 3000 mm or less.

[0033] 2 and 3, the relationship between position A of a first short-side welded portion 14a extending in the short-side direction of one steel material 11a and position B of a second short-side welded portion 14b extending in the short-side direction of the other steel material 11b in the longitudinal direction (circumferential direction of the inner tank) of adjacent steel materials 11 in the height direction of the inner tank will be described. In the circumferential direction of adjacent steel materials 11 in the height direction of Fig. 2, the circumferential distance (length b in Fig. 2) between position B of the second short-side welded portion 14b, which is located closest to position A of the first short-side welded portion 14a, is 300 mm or more.

[0034] Usually, when a brittle crack generated in a welded portion propagates along the longitudinal welded portion 15, the brittle crack is considered to stop midway. However, when the length b between points AB in FIG. 3 is short, it is assumed that when a brittle crack generated at the position of point O reaches the position of point A of the steel material 11a, the brittle crack propagates along the longitudinal welded portion 15 extending in the circumferential direction of the inner tank 5 and reaches point B shown in FIG. 3. The brittle crack that reaches point B may further propagate through the short-side welded portion 14b of the steel material 11b (propagation route (2) shown by the broken line in FIG. 3). As a result of the study by the present inventors, it was found that when the length b between points AB is less than 300 mm, the brittle crack that propagates from the position of point A along the longitudinal welded portion 15 extending in the circumferential direction of the inner tank 5 may reach the position of point B.

[0035] On the other hand, by making the length b between points A and B 300 mm or more, when a brittle crack propagates along the propagation route (2) shown in Fig. 3, the crack can be stopped between points A and B of the longitudinal weld 15 and prevented from propagating to the transverse weld 14b. This makes it possible to realize the arrestability required for the liquefied ammonia tank 1 according to this embodiment.

[0036] 2 and 3, the longer the length b between points A and B, the more the possibility of a brittle crack propagating from the adjacent steel material 11a to the steel material 11b can be reduced. The length b between points A and B is preferably 1000 mm or more, and more preferably 2000 mm or more.

[0037] The longer the length b between points A and B, the better, and there is no particular upper limit. Since the size of the inner diameter and the circumferential length of the inner tank 5 are considered to be determined according to the maximum volume required for the liquefied ammonia tank 1, an appropriate length b between points A and B may be determined taking into consideration the number of steel materials 11 and the inner diameter and circumferential length. The upper limit of the length b between points A and B is essentially 1 / 2 the maximum length in the rolling direction of the steel materials 11 within the manufacturable range.

[0038] In the side wall portion 5b of the inner tank 5 as shown in FIG. 2, the number of layers of the steel materials 11 stacked in the height direction is not particularly specified, and may be appropriately determined taking into consideration the required maximum volume, the length a of the steel materials 11 in the short side direction, etc.

[0039] In the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment, the steel material 11 has a Kca value (brittle crack arrest toughness value) of 6000 N / mm 3 / 2 When long crack arrest is taken into consideration, the Kca value at -35°C is 6000N / mm 3 / 2 By using a steel material having the above mentioned properties, it becomes possible to stop a brittle crack propagating from a welded portion midway, and the arrestability required for a liquefied ammonia tank can be realized. The Kca value of the steel material 11 at -35°C is preferably 7000 N / mm 3 / 2More preferably, it is 8000N / mm 3 / 2 That's all.

[0040] On the other hand, the larger the Kca value at −35° C. of the steel material 11, the better, and the upper limit is not particularly specified. However, from the viewpoint of the manufacturing cost of the steel plate, the upper limit of the Kca value at −35° C. of the steel material 11 is set to 20000 N / mm 3 / 2 may be also possible.

[0041] The Kca value at -35°C can be measured by conducting a temperature gradient ESSO test in accordance with the WES 2815:2014 standard, and is 6000N / mm 3 / 2 The above steel materials can be selected.

[0042] Furthermore, the upper limit of the thickness of the steel material 11 (thickness t in FIG. 2) can be, for example, 60 mm, 50 mm, or 40 mm. On the other hand, the lower limit of the thickness of the steel material 11 is not particularly specified, and the thickness may be small as long as the liquefied ammonia tank can be manufactured. The lower limit of the thickness of the steel material 11 may be 10 mm.

[0043] Generally, when the Ni content of the steel material and the weld metal constituting the welded portion increases, there is a concern about the occurrence of ammonia SCC. The steel material 11 used in the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment is preferably a steel material having a Ni content of 2.0 mass% or less. The steel material 11 has a Kca value of 6000 N / mm at -35°C. 3 / 2 By selecting and using a steel material having the above properties and an Ni content of 2.0 mass% or less as a material, it is possible to realize the arrestability required for a liquefied ammonia tank and further improve the ammonia SCC resistance of the liquefied ammonia tank. The Ni content of the steel material 11 is more preferably 1.0 mass% or less, and further preferably 0.5 mass% or less.

[0044] The Ni content of the weld metal constituting the welded portion 13 (the transverse welded portion 14 and the longitudinal welded portion 15) is preferably less than 6.0 mass%, for example. The Ni content of the weld metal can be adjusted by selecting the welding material used for welding. When the Ni content of the weld metal is less than 6.0 mass%, it is possible to further improve the ammonia SCC resistance characteristics of the liquefied ammonia tank. The Ni content of the weld metal constituting the welded portion 13 is more preferably 5.0 mass% or less, further preferably 2.0 mass% or less, and even more preferably 1.0 mass% or less. The weld metal constituting the welded portion 13 may not contain Ni (i.e., the Ni content is 0 mass%). The Ni content of the weld metal constituting the welded portion 13 may be 7.0 mass% or less.

[0045] When the Ni content of the steel material 11 and the Ni content of the weld metal constituting the welded portion 13 in the inner tank 5 of the liquefied ammonia tank 1 are to be identified after the fact, measurements may be performed using a portable X-ray fluorescence analyzer, taking into consideration the difficulty of taking samples from the inner tank 5. More specifically, non-destructive elemental analysis measurements may be performed multiple times using a portable X-ray fluorescence analyzer at any positions in the steel material 11 and the welded portion 13 of the inner tank 5 of interest. Then, the average values ​​of the multiple measurement results obtained may be taken as the Ni content of the steel material 11 and the Ni content of the weld metal constituting the welded portion 13.

[0046] The side wall 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment is formed by welding together steel materials 11. Therefore, a heat-affected zone (HAZ) is formed in the steel material 11 at a portion located near the welded portion 13. The boundary between the weld metal and the heat-affected zone is a fusion line, and in this embodiment, the weld metal and the fusion line are referred to as the welded portion. In the following, more preferable conditions for the steel material 11 (base metal portion and heat-affected zone) and the welded portion 13 (welded metal and fusion line) will be described with reference to FIG. 4. FIG. 4 is a diagram for describing the vicinity of the welded portion of the inner tank of the liquefied ammonia tank according to this embodiment. FIG. 4 is an enlarged schematic view of the vicinity of a short-side welded portion 14 in the side wall 5b of the inner tank 5 as an example of the welded portion 13.

[0047] As shown in FIG. 4, in the steel material 11 located near the transverse welded portion 14, a heat-affected portion 11B in a state different from that of the base metal portion 11A of the steel material 11 is formed on the side closer to the transverse welded portion 14. The heat-affected portion 11B is a base metal heated by heat input of welding, and the Charpy absorbed energy of the heat-affected portion 11B is often lower than that of the base metal portion 11A of the steel material 11. The fusion line FL is a boundary between the weld metal and the heat-affected portion 11B. Here, it is preferable that the Charpy absorbed energy of the steel material 11 (base metal portion 11A and heat-affected portion 11B) and the transverse welded portion 14 (welded metal and fusion line FL) according to this embodiment, and the design stress and yield stress of the steel material 11 (base metal portion 11A) satisfy the relationship represented by the following formula (1).

[0048]

number

[0049] Here, in the above formula (1), σ d : Design stress of steel material 11 (base material portion 11A) σ y : Yield stress of steel material 11 (base material portion 11A) vE WM: Charpy absorbed energy of the weld metal constituting the weld 13 vE FL : Charpy absorbed energy of Fusion Line FL vE HAZ Charpy absorbed energy of heat-affected zone 11B of steel material 11 vE BM Charpy absorbed energy of base material 11A of steel material 11 and min(vE WM ,vE FL ,vE HAZ ) is written as vE WM , vE FL , vE HAZ This means that the smallest of the three values ​​is selected.

[0050] The inventors prepared a plurality of steel materials with different thicknesses t, mechanical properties (more specifically, yield stress (YS), tensile strength (TS) and elongation (EL)), and Charpy absorbed energy of the heat-affected zone at -35°C). These steel materials were welded using a plurality of welding materials with different Charpy absorbed energy at -35°C to prepare a plurality of test specimens for the ESSO test shown in FIG. 5, and an isothermal ESSO test was performed. Specifically, the inventors attached a pin chuck and a tab plate to each of the obtained test specimens by welding, and mounted them on a large tensile testing machine. Thereafter, the test specimens were cooled to -35°C, a tensile stress equivalent to the design stress of the steel material was applied, and a strike was applied to the notch portion via a wedge to generate and propagate a brittle crack, and the propagation path of the brittle crack was confirmed.

[0051] The inventors statistically analyzed the distribution of the obtained test results from various viewpoints while taking safety into consideration, and attempted to derive an equation that shows the boundary between a combination of conditions under which a brittle crack deviates to the base metal portion 11A and a combination of conditions under which a brittle crack propagates along the welded portion 13. The relationship expressed by the above equation (1) was formulated in this way.

[0052] The above formula (1) obtained in this manner suggests that when the toughness of the weld metal, heat-affected zone 11B, and fusion line FL constituting the weld 13 is significantly inferior to the toughness of the base metal portion 11A of the steel material 11, brittle cracks will be more likely to propagate along the weld 13.

[0053] When the design stress and yield stress of the steel material 11, and the Charpy absorbed energy of the base metal portion 11A, the heat-affected zone 11B, the weld metal constituting the welded portion 13, and the fusion line FL of the steel material 11 satisfy the relationship expressed by the above (1), a brittle crack is less likely to propagate along the welded portion 13. As a result, a brittle crack attempting to propagate through the welded portion 13 propagates in such a way as to deviate toward the base metal portion 11A of the steel material 11. As a result, when a brittle crack occurs in the welded portion 13, it becomes easier to prevent the brittle crack from propagating, and it becomes possible to further improve the safety of the inner tank 5 of the liquefied ammonia tank 1 against brittle fracture.

[0054] Here, the yield stress of the steel material 11 can be measured by a tensile test specified in JIS Z2241:2011. It is desirable to take a tensile test specimen from the steel material before welding, but after welding, a tensile test specimen may be taken while avoiding the welded portion 13. In addition, the Charpy absorbed energy of the base material portion 11A, the heat-affected portion 11B, the weld metal constituting the welded portion 13, and the fusion line FL of the steel material 11 can be measured by a Charpy impact test specified in JIS Z2242:2018.

[0055] More specifically, a tensile test for measuring the yield stress of the steel material 11 may be performed by taking a No. 4 tensile test piece as described in JIS Z 2241:2011 from the 1 / 4 position of the thickness in a direction perpendicular to the rolling direction.

[0056] Charpy absorbed energy vE of weld metal WMThe measurement can be performed by taking three V-notch test pieces as described in JIS Z2242:2018 at the 1 / 4 position of the thickness so that the center of the weld metal is located at the tip of the notch. The Charpy impact test is performed at -35°C, and the average value of the measured Charpy absorbed energy is vE WM Let us assume that.

[0057] Charpy absorbed energy vE of fusion line FL The measurement can be performed by taking three V-notch test pieces as described in JIS Z2242:2018 so that the fusion line is located at the tip of the notch at the 1 / 4 position of the thickness. The Charpy impact test is performed at -35°C, and the average value of the measured Charpy absorbed energy is called vE FL Let us assume that.

[0058] Charpy absorbed energy vE of heat affected zone HAZ The measurement can be performed by taking three V-notch test pieces as described in JIS Z2242:2018 so that the tip of the notch is located 1 mm away from the fusion line toward the base material at the 1 / 4 position of the thickness. The Charpy impact test is performed at -35°C, and the average value of the measured Charpy absorbed energy is called vE HAZ Let us assume that.

[0059] Charpy absorbed energy vE of base material BM The measurement can be performed by taking three V-notch test pieces as described in JIS Z2242:2018 so that the tip of the notch is located at a position 10 mm or more away from the fusion line toward the base material at the 1 / 4 position of the thickness. The Charpy impact test is performed at -35°C, and the average value of the measured Charpy absorbed energy is called vE BM Let us assume that.

[0060] In addition, generally, when the Vickers hardness of the base material 11A and the heat-affected zone 11B of the steel material 11 increases, there is concern about the occurrence of ammonia SCC. In the side wall portion 5b of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment, it is preferable that the Vickers hardness of the base material 11A of the steel material 11 is 240 or less, and the Vickers hardness of the heat-affected zone 11B of the steel material 11 is 300 or less. By making the Vickers hardness of the base material 11A and the heat-affected zone 11B of the steel material 11 as described above, the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment exhibits more excellent ammonia SCC resistance characteristics. The Vickers hardness of the base material 11A is more preferably 230 or less, and even more preferably 220 or less. Moreover, the Vickers hardness of the heat-affected zone 11B is more preferably 280 or less, and even more preferably 260 or less.

[0061] The lower limit of the Vickers hardness of the base metal portion 11A of the steel material 11 as described above is not particularly specified, but the lower limit is substantially about 120. The lower limit of the Vickers hardness of the heat-affected zone 11B of the steel material 11 as described above is also not particularly specified, but the lower limit is substantially about 150.

[0062] Here, the Vickers hardness of the base material 11A and the heat-affected zone 11B can be measured by carrying out a Vickers hardness test specified in JIS Z2244-1:2020. More specifically, for the base material 11A, 10 points are measured at a pitch of 0.5 mm at a position 2 mm below the surface under a load of 5 kg, and the maximum value of the obtained measured values ​​is used. For the heat-affected zone 11B, a cross section perpendicular to the weld line of the welded zone 13 is cut out, polished, and then corroded with a nital solution to reveal the heat-affected zone 11B. The range of the heat-affected zone is measured at a position 2 mm below the surface starting from the fusion line portion and at a pitch of 0.2 mm in the direction toward the base material under a load of 1 kg for the number of points according to the size of the heat-affected zone, and the maximum value of the obtained measured values ​​is used. The unit of the Vickers hardness of the base material is HV5, and the unit of the Vickers hardness of the heat-affected zone is HV1.

[0063] The liquefied ammonia tank 1 according to this embodiment has been described above with reference to FIGS.

[0064] (About the manufacturing method of liquefied ammonia tanks) <Overall flow> The liquefied ammonia tank 1 according to this embodiment is a double-structure storage tank having an outer tank 3 and an inner tank 5 disposed inside the outer tank 3. First, the overall flow of a manufacturing method for a liquefied ammonia tank having the above-mentioned double structure will be briefly described below.

[0065] The overall flow of the manufacturing method for the liquefied ammonia tank according to this embodiment is not particularly limited, and may be appropriately carried out in accordance with the overall flow of manufacturing methods for various known low-temperature liquefied gas tanks.

[0066] For example, first, the bottom of the outer tank is manufactured at the planned construction site of the liquefied ammonia tank. Then, at the site where the bottom of the outer tank was manufactured, the inner tank is manufactured using the bottom of the outer tank as a foundation. After that, the side walls and roof of the outer tank are manufactured in order on the bottom of the outer tank on which the inner tank is installed. For example, a liquefied ammonia tank can be manufactured by such a process.

[0067] In the above process, the method for manufacturing the bottom of the outer tank, the method for manufacturing the side wall of the outer tank, and the method for manufacturing the roof of the outer tank are not particularly specified, and may be appropriately performed in accordance with the methods for manufacturing the outer tank of various known cryogenic liquefied gas tanks. Therefore, detailed description of the method for manufacturing the outer tank will be omitted below.

[0068] <Manufacturing method for the inner vessel of the liquefied ammonia tank> The manufacturing method of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment includes, for example, a step of manufacturing a bottom portion 5a of the inner tank 5, a step of manufacturing a side wall portion 5b of the inner tank 5, and a step of manufacturing a roof portion 5c of the inner tank 5 at a predetermined location.

[0069] Here, the process for manufacturing the bottom 5a of the inner tank 5 is not particularly limited, and may be appropriately carried out in accordance with the manufacturing method of the bottom of the inner tank in various known low-temperature liquefied gas tanks.

[0070] The liquefied ammonia tank 1 according to this embodiment is mainly characterized in the structure of the side wall portion 5b of the inner tank 5. Therefore, hereinafter, a method for manufacturing the inner tank of the liquefied ammonia tank, which can realize the structure of the side wall portion 5b of the inner tank 5, will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining the method for manufacturing the inner tank of the liquefied ammonia tank according to this embodiment.

[0071] The manufacturing method of the inner tank 5 of the liquefied ammonia tank 1 according to this embodiment includes a step of selecting a steel material and a step of welding a plurality of steel materials together to form the side wall portion 5b of the inner tank 5. The step of manufacturing the side wall portion 5b of the inner tank 5 includes a step of welding a plurality of steel materials 11 in a curved state together to form the side wall portion of the inner tank.

[0072] The above steel material 11 has a Kca value of 6000N / mm 3 / 2 The Kca value at -35°C can be measured by carrying out a temperature gradient ESSO test in accordance with the WES 2815:2014 standard. All of the steel materials 11 have a Kca value of 6000 N / mm 3 / 2 Steel materials with a Kca value of 6000N / mm2 or more at -35°C may be used, but the areas where brittle cracks are likely to propagate must be identified and such areas must be partially reinforced with steel materials with a Kca value of 6000N / mm2 or more at -35°C. 3 / 2 The length (length a shown in FIG. 2) of the short side of the steel material 11 corresponding to the height direction of the inner tank 5 (i.e., the height direction of the inner tank 5) is 500 mm or more.

[0073] 6, welding is performed by arranging the steel materials 11 adjacent in the height direction of the inner tank 5 so that the positions of the welds extending in the short direction (i.e., short-side welds 14) are different. More specifically, as shown in FIG. 2, the welds 14a extending in the short direction of one steel material and the welds 14b extending in the short direction of the other steel material adjacent in the height direction 5 of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different.

[0074] At this time, the distance between the position of a weld extending in the short-side direction of one steel material and the position of a weld extending in the short-side direction of the other steel material in the circumferential direction of the inner tank 5 is set to 300 mm or more. More specifically, as shown in Fig. 2, in steel materials 11 adjacent in the height direction of the inner tank 5, the circumferential length between position A of a first short-side weld 14a extending in the height direction of the inner tank 5 in one steel material 11a and position B of a second short-side weld 14b extending in the height direction of the inner tank 5 and located closest to position A in the other steel material 11b is set to 300 mm or more.

[0075] By manufacturing the side wall portion 5b of the inner tank 5 in the above manner, it becomes possible to realize better arrest characteristics in the inner tank 5 of the liquefied ammonia tank 1.

[0076] After the side wall portion 5b of the inner tank 5 is formed, the roof portion 5c of the inner tank 5 is manufactured. Here, the process for manufacturing the roof portion 5c of the inner tank 5 is not particularly limited, and may be appropriately performed according to a manufacturing method for the roof portion of the inner tank in various known cryogenic liquefied gas tanks.

[0077] The manufacturing method for the inner tank of the liquefied ammonia tank according to this embodiment has been described above with reference to FIG.

[0078] (Design method of liquefied ammonia tank) Next, a method for designing the liquefied ammonia tank according to this embodiment will be described. First, in the liquefied ammonia tank 1 according to this embodiment, the design method of the outer tank 3 is not particularly specified, and various parameters including the design pressure may be appropriately set based on known design standards, etc.

[0079] Next, a method for designing the inner tank 5 in the liquefied ammonia tank 1 according to this embodiment will be described. First, various parameters that must be set based on certain guidelines, such as the design pressure when designing the inner tank 5, are set appropriately based on known design standards, etc. In addition, there is no particular provision for the design method of the bottom 5a and roof 5c of the inner tank 5, and various parameters including the design pressure may be set appropriately based on known design standards, etc.

[0080] In this embodiment, the design method of the inner tank 5 when forming the side wall portion of the inner tank 5 by welding a plurality of curved steel materials 11 to each other is determined as follows.

[0081] First, steel material 11 has a Kca value of 6000N / mm 3 / 2 Here, the short side direction of the steel material 11 corresponds to the height direction of the inner tank 5, and the length (length a shown in FIG. 2) of the steel material 11 in the short side direction (i.e., the height direction of the inner tank 5) is set to 500 mm or more.

[0082] In addition, when stacking the steel materials 11 in the height direction of the inner tank 5, the positions (circumferential positions of the inner tank) of the welds extending in the short direction (i.e., short-side welds 14) of the steel materials 11 adjacent in the height direction are set to be different, for example as shown in Figure 6, and the side wall portion 5b of the inner tank 5 is designed.

[0083] In this case, in adjacent steel materials 11 in the height direction of the inner tank 5, the circumferential length between position A of a first short-side welded portion 14a extending in the height direction of the inner tank 5 in one steel material 11 and position B of a second short-side welded portion 14b extending in the height direction of the inner tank 5 and located closest to position A in the other steel material 11 (for example, length b in Figure 2) is set to 300 mm or more.

[0084] By designing the structure of the side wall portion 5b of the inner tank 5 as described above, it is possible to realize better arrest characteristics in the inner tank 5 of the liquefied ammonia tank 1.

[0085] The method for designing the inner tank of the liquefied ammonia tank according to this embodiment has been described above. EXAMPLES

[0086] Next, the liquefied ammonia tank according to the present embodiment will be specifically described while showing examples and comparative examples. Note that the examples shown below are merely examples of the liquefied ammonia tank according to the present embodiment, and the liquefied ammonia tank according to the present embodiment is not limited to the following examples.

[0087] (Test Example) In the test example shown below, a liquefied ammonia tank has a double structure consisting of an outer tank and an inner tank. In order to evaluate the arrest characteristics of the inner tank of the liquefied ammonia tank, a test specimen simulating the structure of the side wall of the inner tank was fabricated using various steel materials, and an ultra-wide hybrid ESSO test was performed.

[0088] More specifically, in order to manufacture test specimens for the ultra-wide duplex ESSO test, steel materials having the properties shown in Table 1 below were prepared.

[0089] [Table 1]

[0090] Using these steel materials, butt welded joints were produced under the welding conditions shown in Table 2. The welding method used was either Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), or Submerged Arc Welding (SAW). The welding materials used were the commercially available welding rods shown in Table 2 below. The heat input during welding at each level was as shown in Table 2. Multiple butt welded joints were produced for each level.

[0091] Charpy impact test pieces were taken from each part of the welded joint, and the vE WM , vE FL , vE HAZ , vE BM The values ​​are also shown in Table 2. Samples for measuring Vickers hardness were taken from each part of the welded joint, and the Vickers hardness was measured. Samples were also taken from the weld metal of the welded joint, and the Ni content of the weld metal was measured using an X-ray fluorescence analyzer. The results are also shown in Table 2.

[0092] [Table 2]

[0093] The ultra-wide hybrid ESSO specimens shown in Figure 7 were manufactured using the same steel material and welding conditions as those for each welded joint. Note that multiple specimens were manufactured for each of the levels shown in Table 3 below. Table 3 below also shows the values ​​of the right and left sides of the above formula (1) calculated based on the Charpy test results shown in Table 2.

[0094] Each manufactured test specimen was welded to a pin chuck (jig) shown in Figure 8 and then mounted on a large tensile testing machine. Each test specimen was then cooled to -35°C and loaded with a specified stress. Next, the notch at the position shown in Figure 7 was struck with a wedge to intentionally generate a brittle crack.

[0095] The arrestability was evaluated for each test specimen in which a brittle crack had been initiated. The arrestability was evaluated by observing the propagation of the brittle crack in each test specimen and determining whether the brittle crack was arrested without breaking the specimen (arrested) or whether the brittle crack propagated and broke the specimen (propagated). In addition, when the brittle crack was arrested, the length of the crack arrest was also measured. The results are shown in Table 3 below.

[0096] [Table 3]

[0097] As is clear from Table 3, at the level corresponding to the inventive examples of the present invention, the brittle crack was arrested without fracture in the test specimens, and excellent arrestability was demonstrated. In particular, in the test specimens No. 3 and No. 5, which satisfied the above formula (1), the brittle crack deviated from the weld line immediately after initiation and arrested in the base material, so the crack arrest length was short.

[0098] On the other hand, in the level corresponding to the comparative example of the present invention, the brittle crack propagated without being stopped, and the test specimen was broken. Specifically, in Test Nos. 7 to 9, the brittle crack propagated through the base material due to the low Kca value of the steel material used for the test specimen, and as a result, the test specimen was broken. In Test No. 10, the brittle crack propagated through the base material due to the short length a, and as a result, the test specimen was broken. In Test No. 11, the brittle crack propagated through the weld due to the short length b, and as a result, the test specimen was broken.

[0099] In this test example, as is clear from the shape of the test specimen shown in Figure 7, the longitudinal length of the steel material used was up to 1600 mm, and the arrestability properties were evaluated mainly for cases where length a = 500 mm and length b = 300 mm. However, it is presumed that the evaluation results of the arrestability properties obtained from test specimens such as those shown in Figures 7 and 8 will show similar trends to those of this test example even if test specimens are prepared using steel material with a longitudinal length of more than 1600 mm and less than 5500 mm, and with lengths a and b of more than 500 mm and more than 300 mm, respectively.

[0100] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention.

[0101] The embodiments disclosed herein are illustrative and not restrictive in all respects. The above embodiments may be omitted, substituted, or modified in various forms without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above embodiments can be arbitrarily combined within a range that does not impair the effects of the components. Furthermore, the arbitrary combination naturally provides the actions and effects of each of the components in the combination, and also provides other actions and effects that are obvious to a person skilled in the art from the description of this specification.

[0102] In addition, the effects described in this specification are merely explanatory or exemplary, and are not limiting. In other words, the technology according to the present invention may achieve other effects that are apparent to a person skilled in the art from the description of this specification, in addition to or in place of the above effects.

[0103] The following configurations also fall within the technical scope of the present invention. [1] A liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank, The inner tank has a bottom, a side wall, and a roof, The side wall portion of the inner tank is formed by connecting a plurality of steel materials via welds, The short side direction of the steel material is aligned with the height direction of the inner tank, The length of the steel material in the short direction is 500 mm or more, A first short-side welded portion extending in a short-side direction of the steel material and a second short-side welded portion extending in a short-side direction of another steel material adjacent to the first short-side welded portion in the short-side direction are located at different positions in the longitudinal direction of the steel material, The distance between the first short-side welded portion and the second short-side welded portion in the longitudinal direction of the steel material is 300 mm or more; The Kca value of the steel at -35°C is 6000N / mm 3 / 2 That's it for the liquefied ammonia tank. [2] The liquefied ammonia tank according to [1], wherein the steel material and the welded portion satisfy the following formula (1). Here, in the following formula (1), σ d : Design stress of steel σ y : Yield stress of steel vE WM : Charpy absorbed energy of weld metal vE FL : Charpy absorbed energy of fusion line vE HAZ : Charpy absorbed energy of heat-affected zone of steel vE BM : Charpy absorbed energy of the base material of the steel and min(vE WM ,vE FL ,vE HAZ ) is written as vE WM , vE FL , vE HAZ This means that the smallest of the three values ​​is selected. [3] The liquefied ammonia tank described in [1] or [2], wherein the thickness of the steel material is 60 mm or less. [4] The liquefied ammonia tank according to any one of [1] to [3], wherein the length of the steel material in the longitudinal direction is 5,500 mm or less. [5] The Ni content of the steel material is 2.0 mass% or less, The liquefied ammonia tank according to any one of [1] to [4], wherein the Ni content of the weld metal constituting the welded portion is less than 6.0 mass %. [6] The liquefied ammonia tank according to any one of [1] to [5], wherein a Vickers hardness of a base metal portion of the steel material is 240 or less, and a Vickers hardness of a heat-affected portion of the steel material is 300 or less. [7] A method for manufacturing an inner tank of a liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank and having a bottom, a side wall, and a roof, comprising the steps of: Kca value at -35℃ is 6000N / mm 3 / 2 A step of selecting the above steel material; and welding a plurality of the steel materials together to form the side wall portion of the inner tank, The length of the steel material in the short direction is 500 mm or more, The short side direction of the steel materials is aligned with the height direction of the inner tank, and a weld extending in the short side direction of one of the steel materials and a weld extending in the short side direction of the other of the steel materials that are adjacent to each other in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and a welded portion extending in the short side direction of one of the steel materials and a welded portion extending in the short side direction of the other of the steel materials, the distance in the circumferential direction of the inner tank being 300 mm or more. [8] A method for designing an inner tank of a liquefied ammonia tank, the inner tank being disposed inside the outer tank and having a bottom, a side wall, and a roof, the method comprising the steps of: a step of welding a plurality of steel members together to form the side wall portion of the inner tank; The Kca value of the steel at -35℃ is 6000N / mm 3 / 2 or more, and the length of the short side of the steel material is set to 500 mm or more, The short side direction of the steel materials is aligned with the height direction of the inner tank, and a weld extending in the short side direction of one of the steel materials and a weld extending in the short side direction of the other of the steel materials that are adjacent to each other in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and a design method for the inner tank of a liquefied ammonia tank, wherein a distance in a circumferential direction of the inner tank between a position of a weld extending in a short side direction of one of the steel materials and a position of a weld extending in the short side direction of the other of the steel materials is set to 300 mm or more.

[0104]

number

[0105] 1. Liquefied ammonia tank 3 Outer tank 5 Inner tank 3a, 5a bottom 3b, 5b side wall part 3c, 5c Roof section 7. Liquefied Ammonia 10 Side wall member 11 Steel materials 11A Base metal part 11B Heat affected zone 13 Welding 14 Short side weld 15 Longitudinal weld

Claims

1. A liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank, The inner tank has a bottom, a side wall, and a roof, The side wall portion of the inner tank is formed by connecting a plurality of steel materials via welds, The short side direction of the steel material is aligned with the height direction of the inner tank, The length of the steel material in the short direction is 500 mm or more, A first short-side welded portion extending in a short-side direction of the steel material and a second short-side welded portion extending in a short-side direction of another steel material adjacent to the first short-side welded portion in the short-side direction are located at different positions in the longitudinal direction of the steel material, The distance between the first short-side welded portion and the second short-side welded portion in the longitudinal direction of the steel material is 300 mm or more; The Kca value of the steel at -35°C is 6000N / mm ３／２ That's it for the liquefied ammonia tank.

2. 2. The liquefied ammonia tank according to claim 1, wherein the steel material and the welded portion satisfy the following formula (1): [0010] Here, in the above formula (1), σ ｄ : Design stress of steel σ ｙ : Yield stress of steel vE ＷＭ : Charpy absorbed energy of weld metal vE ＦＬ : Charpy absorbed energy of fusion line vE ＨＡＺ : Charpy absorbed energy of heat-affected zone of steel vE ＢＭ : Charpy absorbed energy of steel base material and min(vE ＷＭ , vE ＦＬ , vE ＨＡＺ ) is written as vE ＷＭ , vE ＦＬ , vE ＨＡＺ This means that the smallest value of the three values ​​is selected.

3. 2. The liquefied ammonia tank according to claim 1, wherein the thickness of the steel material is 60 mm or less.

4. 2. The liquefied ammonia tank according to claim 1, wherein the longitudinal length of the steel material is 5,500 mm or less.

5. The Ni content of the steel material is 2.0 mass% or less, 2. The liquefied ammonia tank according to claim 1, wherein the Ni content of the weld metal constituting the welded portion is less than 6.0 mass %.

6. 2. The liquefied ammonia tank according to claim 1, wherein the base metal portion of the steel material has a Vickers hardness of 240 or less, and the heat-affected portion of the steel material has a Vickers hardness of 300 or less.

7. A method for manufacturing an inner tank of a liquefied ammonia tank having an outer tank and an inner tank disposed inside the outer tank and having a bottom, a side wall, and a roof, comprising the steps of: Kca value at -35°C is 6000N / mm ３／２ A step of selecting the above steel material; and welding a plurality of the steel materials together to form the side wall portion of the inner tank, The length of the steel material in the short direction is 500 mm or more, The short side direction of the steel materials is aligned with the height direction of the inner tank, and a weld extending in the short side direction of one of the steel materials and a weld extending in the short side direction of the other of the steel materials that are adjacent to each other in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and a welded portion extending in the short side direction of one of the steel materials and a welded portion extending in the short side direction of the other of the steel materials, the distance in the circumferential direction of the inner tank being 300 mm or more.

8. A method for designing an inner tank of a liquefied ammonia tank, the inner tank being disposed inside the outer tank and having a bottom, a side wall, and a roof, the method comprising the steps of: a step of welding a plurality of steel members together to form the side wall portion of the inner tank; The Kca value of the steel material at -35°C is 6000N / mm ３／２ or more, and the length of the steel material in the short direction is set to 500 mm or more, The short side direction of the steel materials is aligned with the height direction of the inner tank, and a weld extending in the short side direction of one of the steel materials and a weld extending in the short side direction of the other of the steel materials that are adjacent to each other in the height direction of the inner tank are arranged so that their positions in the circumferential direction of the inner tank are different, and a design method for the inner tank of a liquefied ammonia tank, wherein a distance in a circumferential direction of the inner tank between a position of a weld extending in a short side direction of one of the steel materials and a position of a weld extending in the short side direction of the other of the steel materials is set to 300 mm or more.

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