Vessel and tank design method

Abstract

This vessel comprises a hull, and a tank that is provided to the hull and is capable of selectively accommodating a liquefied gas and a corrosive liquid. The tank is provided with a spherical tank body having pressure resistance, and a corrosion-resistant layer composed of a corrosion-resistant paint laminated on the inner surface of the spherical tank body.

Description

Ship and tank design methods

[0001] This application claims priority to Japanese Patent Application No. 2024-052301, filed on March 27, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a spherical tank for LNG (liquefied natural gas) made of an aluminum alloy. This patent document 1 discloses a technology for further adding zinc to the tank, since the addition of magnesium to increase the strength and reduce the weight of the tank when enlarging the tank reduces general corrosion resistance, including SCC (stress corrosion cracking) resistance.

[0003] JP 2010-144186 A

[0004] By the way, when a carrier ship carrying liquefied gas arrives at its destination and unloads its cargo, its tanks become empty. If the ship were to return to the port where it loaded the cargo or head to another port in this state, it would simply be moving the carrier, which is not economical. Therefore, in order to improve the economic efficiency of the ship, a different type of cargo than the cargo unloaded at the destination is stored in the tanks before returning to the port of departure or heading to another port.

[0005] The different types of cargo mentioned above include various liquids, but also so-called corrosive cargoes that corrode the metals that make up tanks, such as carbon steel. When transporting such corrosive cargoes, measures are taken, such as using highly corrosion-resistant metals, such as stainless steel, for tanks, which do not corrode, or covering the inside of the tanks with corrosion-resistant paint. However, using highly corrosion-resistant metals for tanks significantly increases costs, so the inside of the tanks is generally painted.

[0006] On the other hand, liquefied gases include high-pressure cargoes that cannot maintain their liquid state unless transported at low temperatures and under pressure. Pressure tanks are used to transport such high-pressure cargoes, but the interiors of typical cylindrical tanks used as pressure tanks are complex, with reinforcing members such as saddle rings and barriers to prevent sloshing, and there is a possibility that the corrosion resistance provided by painting may not be guaranteed.

[0007] The present disclosure has been made in consideration of the above circumstances, and provides a ship and tank design method that enables the transportation of high-pressure cargo and corrosive cargo interchangeably while suppressing cost increases.

[0008] In order to solve the above problems, the following configuration is adopted: According to a first aspect of the present disclosure, a ship includes a hull and a cargo tank provided on the hull and capable of selectively storing a liquefied gas or a corrosive liquid, the cargo tank including a pressure-resistant spherical tank body and a corrosion-resistant layer made of corrosion-resistant paint laminated on the inner surface of the spherical tank body.

[0009] According to a second aspect of the present disclosure, the tank design method is a tank design method for the above-mentioned ship, and includes the steps of: determining the strain on the expansion side of the spherical tank body based on the internal pressure of the spherical tank body when the liquefied gas is stored in the spherical tank body; determining the strain on the contraction side of the spherical tank body based on the temperature inside the spherical tank body when the liquefied gas is stored in the spherical tank body; and determining the strength required for the corrosion-resistant layer based on the difference between the strain on the expansion side and the strain on the contraction side.

[0010] According to the ship and tank design method disclosed herein, it is possible to transport high-pressure cargo and corrosive cargo interchangeably while suppressing cost increases.

[0011] It is a plan view showing a schematic configuration of a ship according to an embodiment of the present disclosure. It is a half cross-sectional view of a liquefied gas tank provided in the ship as seen from the bow and stern direction. It is a flowchart of a tank design method according to an embodiment of the present disclosure.

[0012] Next, a ship and a tank design method according to an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of a ship according to an embodiment of the present disclosure. FIG. 2 is a half-sectional view of a liquefied gas tank provided on the ship, viewed from the bow-stern direction. <Ships> A ship 1 according to an embodiment of the present disclosure transports liquefied gas such as liquefied natural gas, liquefied petroleum gas, liquefied carbon dioxide, or liquefied ammonia. As shown in FIGS. 1 and 2, the ship 1 includes at least a hull 2 ​​and a cargo tank 20. In FIGS. 1 and 2, the bow-stern direction of the ship 1 is designated "Da," the width direction is designated "Dw," and the up-down direction is designated "Dv."

[0013] <Hull> The hull 2 ​​has a pair of side walls 3A, 3B that form its outer shell, a bottom 4, and an upper deck 5. The side walls 3A, 3B each have a pair of side shell plating that form the port and starboard sides. The bottom 4 has a bottom shell plating that connects the side walls 3A, 3B. The upper deck 5 is, for example, a full-length deck that is exposed to the outside. The hull 2 ​​of this embodiment has a superstructure 7 with accommodation areas on the upper deck 5 on the stern 2b side, and a cargo carrying compartment (hold) 8 is formed closer to the bow 2a than this superstructure 7.

[0014] <Cargo Tank> The cargo tank 20 is provided in the cargo loading compartment 8. In this embodiment, a case is illustrated in which a plurality of cargo tanks 20 are installed in the cargo loading compartment 8 lined up in the bow-stern direction Da. The upper portions 20a of the plurality of cargo tanks 20 illustrated in this embodiment each protrude above the upper deck 5 of the hull 2, and the upper portions 20a of the cargo tanks 20 are covered by tank covers 25 provided on the upper deck 5. An external heat insulating material (not shown) that suppresses heat input from the outside is provided between the inner surfaces 25i of the tank covers 25 and the outer surfaces 20o of the cargo tanks 20.

[0015] The cargo tank 20 is configured to be capable of selectively storing a low-temperature, high-pressure liquefied gas and a corrosive liquid. The cargo tank 20 of this embodiment is a Type C tank of the independent tank type defined in the IGC Code (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk) of the IMO (International Maritime Organization).

[0016] <Skirt> The cargo tank 20 is supported by the skirt 30. The skirt 30 has a cylindrical shape extending in the vertical direction Dv, and its lower end is connected to the top of a foundation deck section 9 or the like provided at the bottom of the cargo loading section 8. The connection structure between the cargo tank 20 and the skirt 30 may be any connection structure as long as the skirt 30 can support the cargo tank 20 from below, and various connection structures can be adopted.

[0017] <Low-temperature, high-pressure liquefied gas> Examples of the temperature and pressure of low-temperature, high-pressure liquefied gas stored in the storage space S of the cargo tank 20 include a temperature of −163° C. and a pressure of 4 bar for liquefied natural gas, a temperature of −50° C. and a pressure of 18 bar for liquefied petroleum gas, a temperature of −35° C. and a pressure of 19 bar for liquid carbon dioxide, and a temperature of −50° C. and a pressure of 5 bar for liquid ammonia.

[0018] <Corrosive Liquid> A corrosive liquid is a liquid that contains a component that corrodes the spherical tank body 21 when it comes into contact with the spherical tank body 21. The corrosive liquid is a liquid that can be stored in the storage space S at a temperature and pressure lower than that of the low-temperature, high-pressure liquefied gas stored in the storage space S. For example, if the corrosive liquid is methanol, it can be stored at room temperature (e.g., about 15°C to 25°C) and atmospheric pressure.

[0019] The cargo tank 20 includes a spherical tank body 21 and a corrosion-resistant layer 22. <Spherical Tank Body> The spherical tank body 21 is a pressure vessel made of low-temperature steel with a predetermined thickness and capable of storing low-temperature, high-pressure liquefied gas. The spherical tank body 21 has a pressure-resistant structure and an internal storage space S. The upper end of the skirt 30 is connected to the circumferential direction of the vertically intermediate portion of the spherical tank body 21 in this embodiment. While the spherical tank body 21 has a spherical shape, it is not limited to a true spherical shape with a constant radius of curvature. The "spherical shape" of the spherical tank body 21 also includes spherical shapes other than a true spherical shape, such as a flattened spherical shape whose vertical and radial dimensions differ. In this embodiment, a true spherical shape centered on point O is illustrated.

[0020] <Inner surface of spherical tank body> The spherical tank body 21 has a substantially flush spherical inner surface 21i with no protrusions protruding radially inward, except for piping related to cargo handling (not shown), towers for accommodating the piping, instruments, etc. In other words, the spherical tank body 21 does not have any protrusions such as reinforcing materials like saddle rings on cylindrical tanks or bulkheads to prevent sloshing.

[0021] <Corrosion-resistant layer> The corrosion-resistant layer 22 is made of corrosion-resistant paint laminated on the inner surface 21i of the spherical tank body 21. The corrosion-resistant layer 22 is intended to enable the storage of corrosive liquid within the spherical tank body 21, and prevents contact between the spherical tank body 21 and the fluid contained in the storage space S. The corrosion-resistant layer 22 also has enough strength to prevent cracks from occurring due to strains occurring in the spherical tank body 21. This corrosion-resistant layer 22 can be formed by applying corrosion-resistant paint so as to cover the entire inner surface 21i of the spherical tank body 21.

[0022] For example, if the spherical tank body 21 is made of carbon steel, a corrosive liquid that corrodes carbon steel may be a fluid containing methanol. If a fluid containing methanol is stored in the storage space as the corrosive liquid, inorganic zinc may be used as the corrosion-resistant layer 22.

[0023] Furthermore, for example, a liquefied gas containing hydrogen sulfide can be used as the corrosive liquid. The corrosive liquid is not limited to methanol or a corrosive liquid containing hydrogen sulfide, as long as it corrodes the spherical tank body 21.

[0024] <Tank Design Method> Next, a tank design method for the cargo tank 20 described above will be described with reference to the drawings. Fig. 3 is a flowchart of the tank design method according to an embodiment of the present disclosure. In the description of the tank design method according to this embodiment, a method for determining the strength of the corrosion-resistant layer 22 will be described as part of the design method for the cargo tank 20. In addition, in this embodiment, a case where the spherical tank body has a true spherical shape will be described as an example.

[0025] As shown in Figure 3, first, the strain on the expansion side of the spherical tank body 21 is calculated based on the internal pressure of the spherical tank body 21 when liquefied gas is stored in the spherical tank body 21 (step S01). Here, if "P" is the internal pressure, "R" is the radius of the spherical tank body, and "t" is the plate thickness of the spherical tank body, the stress "σ" acting on the spherical tank body 21 is given by σ = PR / 2t. Furthermore, if ν is Poisson's ratio and E is Young's modulus, the strain ε on the expansion side of the spherical tank body 21 is given by ＋ is ε ＋ = (1 - v) σ / E.

[0026] Next, the strain on the contraction side of the spherical tank body 21 is calculated based on the temperature inside the spherical tank body 21 when the liquefied gas is stored in the spherical tank body 21 (step S02). Here, if α is the linear expansion coefficient, i.e., the linear expansion coefficient of the material forming the spherical tank body 21, and ΔT is the temperature change, i.e., the temperature change before and after storing the liquefied gas in the spherical tank body 21, the strain ε on the contraction side of the spherical tank body 21 is calculated as follows: － is ε － = αΔT.

[0027] And the strain on the expansion side ε ＋ and the strain on the contraction side ε －The strength required for the corrosion-resistant layer 22 is determined based on the difference between the expansion-side strain ε+ and the contraction-side strain ε- (step S03). More specifically, the absolute value of the difference between the expansion-side strain ε+ and the contraction-side strain ε- is calculated, and the strength of the corrosion-resistant layer 22 is determined so that damage such as cracking will not occur when a strain of the absolute value of this difference occurs. The strength of the corrosion-resistant layer 22 varies depending on parameters such as the thickness of the corrosion-resistant layer 22 and the material of the corrosion-resistant layer 22. For example, if it is necessary to increase the strength of the corrosion-resistant layer 22, the material may be changed to one with a higher strength.

[0028] For example, the strain on the expansion side ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas, in which the strain ε on the expansion side when the internal pressure of the spherical tank body 21 is the highest is used to determine the strength required for the corrosion-resistant layer 22. ＋ and the strain ε on the contraction side when the temperature inside the spherical tank body 21 is the highest. － The strength of the corrosion-resistant layer 22 may be determined based on the difference between the strain ε on the expansion side when the internal pressure of the spherical tank body 21 is the highest. ＋ and the strain ε on the contraction side when the temperature inside the spherical tank body 21 is the highest. － The values ​​of and need not be values ​​at the same time as long as the liquefied gas is contained.

[0029] For example, the strain on the expansion side ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas, when the internal pressure of the spherical tank body 21 is the lowest, the strain ε on the expansion side is used to determine the strength required for the corrosion-resistant layer 22. ＋ and the strain ε on the contraction side when the temperature inside the spherical tank body 21 is the lowest. － The strength of the corrosion-resistant layer 22 may be determined based on the difference between the strain ε on the expansion side when the internal pressure of the spherical tank body 21 is the lowest. ＋ and the strain ε on the contraction side when the temperature inside the spherical tank body 21 is the lowest. － The values ​​of and need not be values ​​at the same time as long as the liquefied gas is contained.

[0030] Strain ε on the expansion side of the spherical tank body 21 ＋and the strain on the contraction side ε － The difference between the expansion strain ε and the expansion strain ε can be reduced by changing the parameters in the above equations. Therefore, the expansion strain ε can be reduced by changing the thickness and radius of the spherical tank body 21 or by changing the material (Poisson's ratio, Young's modulus, linear expansion coefficient) within the range allowed by the rules of the IGC code, etc. ＋ and the strain on the contraction side ε － It is desirable to reduce the difference between

[0031] (Operation and Effect) The ship 1 of the above embodiment includes a hull 2 ​​and a cargo tank 20 provided on the hull 2 ​​and capable of selectively storing liquefied gas and corrosive liquid. The cargo tank 20 includes a pressure-resistant spherical tank body 21 and a corrosion-resistant layer 22 made of corrosion-resistant paint laminated on the inner surface 21i of the spherical tank body 21. With this configuration, the spherical tank body 21 is pressure-resistant, allowing high-pressure liquefied gas to be stored in the cargo tank. Meanwhile, since the corrosion-resistant paint is laminated on the inner surface 21i of the spherical tank body 21, corrosive liquid can be stored and transported in the cargo tank without the need to form the spherical tank body 21 using expensive corrosion-resistant materials. Furthermore, since the spherical tank body 21 is spherical rather than cylindrical, there is no need to provide saddle rings, barriers to prevent sloshing, or the like. This prevents a partial decrease in the corrosion resistance of the corrosion-resistant layer 22 due to construction defects such as an insufficient thickness of the corrosion-resistant layer 22 on the inner surface 21i of the spherical tank body 21. This makes it possible to selectively transport high-pressure liquefied gas and corrosive liquid while suppressing cost increases.

[0032] The ship 1 of the above embodiment is provided with a cylindrical skirt 30 whose upper end is connected circumferentially to the vertically middle portion of the spherical tank body 21 and whose lower end is connected to the hull 2. This configuration eliminates the need to provide reinforcing materials or the like in the lower half of the spherical tank body 21, thereby preventing the structure of the spherical tank body 21 from becoming complicated. Therefore, deterioration of the corrosion resistance performance due to the corrosion-resistant layer 22 can be further prevented.

[0033] The ship 1 of the above embodiment employs an IMO tank type C in the IGC Code as the spherical tank body 21. By configuring the spherical tank body 21 in this manner, it is possible to ensure sufficient pressure resistance for storing high-pressure liquefied gas while providing a simple structure that does not require a secondary barrier or the like.

[0034] In the ship 1 of the above embodiment, when the corrosive liquid is methanol, the corrosion-resistant paint is inorganic zinc. This configuration can prevent corrosion of the inner surface 21i of the spherical tank body 21 when methanol is stored in the cargo tank 20, even if the spherical tank body 21 is made of a material that corrodes upon contact with methanol, such as carbon steel. Therefore, the cargo tank 20 can selectively transport high-pressure liquefied gas and methanol.

[0035] The tank design method of the above embodiment includes a step S01 of determining the strain on the expansion side of the spherical tank body 21 based on the internal pressure of the spherical tank body 21 when liquefied gas is stored in the spherical tank body 21, a step S02 of determining the strain on the contraction side of the spherical tank body 21 based on the temperature inside the spherical tank body 21 when liquefied gas is stored in the spherical tank body 21, and a step S03 of determining the strength required for the corrosion-resistant layer 22 based on the difference between the strain on the expansion side and the strain on the contraction side. As a result, the strain ε on the expansion side when liquefied gas is stored in the spherical tank body 21 is calculated. ＋ In comparison with the case where the corrosion-resistant layer 22 is formed to have a strength that does not cause defects such as cracks, taking only the corrosion resistance into consideration, it is possible to select the corrosion-resistant layer 22 having a lower strength. Therefore, it is possible to improve the degree of freedom in selecting the type of corrosion-resistant paint that forms the corrosion-resistant layer 22.

[0036] In the step S03 of determining the strength required for the corrosion-resistant layer 22 of the above embodiment, the expansion-side strain ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas, the strain ε when the internal pressure of the spherical tank body 21 is the highest is smaller than the strain ε when the internal pressure of the spherical tank body 21 is the highest. ＋ and the strain ε when the temperature inside the spherical tank body 21 is the highest. －The strength required for the corrosion-resistant layer 22 is determined based on the difference between the strain and the expansion strain. This makes it possible to determine the strength required for the corrosion-resistant layer 22 against the maximum strain on the expansion side that is expected when the spherical tank body 21 is navigating with liquefied gas stored in it. Therefore, it is possible to prevent defects such as cracks from occurring in the corrosion-resistant layer 22 regardless of changes in the pressure and temperature of the liquefied gas during navigation.

[0037] In the step S03 of determining the strength required for the corrosion-resistant layer 22 of the above embodiment, the expansion-side strain ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas, the strain ε when the internal pressure of the spherical tank body 21 is the lowest is ＋ and the strain ε when the temperature inside the spherical tank body 21 is the lowest. － The strength required for the corrosion-resistant layer 22 is determined based on the difference between the strain and the contraction strain. This makes it possible to determine the strength required for the corrosion-resistant layer 22 against the maximum strain on the contraction side that is expected when the spherical tank body 21 is navigating with liquefied gas stored in it. Therefore, it is possible to prevent defects such as cracks from occurring in the corrosion-resistant layer 22 regardless of changes in the pressure and temperature of the liquefied gas during navigation.

[0038] (Other Embodiments) The present disclosure is not limited to the configurations of the above-described embodiments, and design modifications are possible within the scope of the present disclosure. For example, in the above embodiment, the spherical tank body 21 is supported by a cylindrical skirt 30, but the present disclosure is not limited to a configuration in which the spherical tank body 21 is supported by a cylindrical skirt 30. For example, the spherical tank body 21 may be supported by a support structure that is not cylindrical.

[0039] Furthermore, in the above embodiment, the spherical tank body 21 is described as being tank type C in the IGC code, but the spherical tank body 21 may be any spherical tank of an independent tank type and is not limited to tank type C.

[0040] In the above embodiment, the case where only one layer of the corrosion-resistant layer 22 is provided has been described, but the corrosion-resistant layer 22 may be formed by stacking multiple layers. Furthermore, in the above embodiment, the case where the plate thickness of the spherical tank body 21 and the thickness of the corrosion-resistant layer 22 are constant has been described as an example, but the plate thickness of the spherical tank body 21 and the thickness of the corrosion-resistant layer 22 may be made different in some parts.

[0041] <Additional Notes> The ship and tank design method described in the embodiment can be understood, for example, as follows.

[0042] (1) According to a first aspect, a ship includes a hull 2 ​​and a cargo tank 20 provided in the hull 2 ​​and capable of selectively storing a liquefied gas and a corrosive liquid. The cargo tank 20 includes a pressure-resistant spherical tank body 21 and a corrosion-resistant layer 22 made of corrosion-resistant paint laminated on the inner surface 21i of the spherical tank body 21. Examples of liquefied gases include liquefied carbon dioxide, liquefied natural gas, liquefied petroleum gas, and liquefied ammonia. Examples of corrosive liquids include methanol. Examples of corrosion-resistant paint include inorganic zinc.

[0043] This allows corrosive liquid to be stored in the cargo tank 20 without using expensive corrosion-resistant materials to form the spherical tank body 21. Furthermore, since the spherical tank body 21 is spherical rather than cylindrical, there is no need to provide saddle rings or barriers to prevent sloshing. This prevents partial reduction in the corrosion resistance of the corrosion-resistant layer 22 due to construction defects such as an insufficient thickness of the corrosion-resistant layer 22 on the inner surface 21i of the spherical tank body 21. Therefore, it is possible to selectively transport high-pressure liquefied gas and corrosive liquid while suppressing cost increases.

[0044] (2) According to the second aspect, the vessel is the vessel of (1), and is provided with a cylindrical skirt 30 whose upper end is connected circumferentially to the middle part of the spherical tank body 21 in the vertical direction and whose lower end is connected to the hull 2.

[0045] This prevents the structure of the spherical tank body 21 from becoming complicated, and therefore further prevents the corrosion resistance performance of the corrosion-resistant layer 22 from decreasing.

[0046] (3) According to a third aspect, the ship is the ship of (2), and employs an IMO Tank Type C in the IGC Code as the spherical tank body 21.

[0047] This allows the spherical tank body 21 to have a simple structure that does not require secondary barriers, etc., while still ensuring sufficient pressure resistance to accommodate high-pressure liquefied gas.

[0048] (4) According to a fourth aspect, the ship is any one of the ships (1) to (3), wherein the corrosive liquid is methanol and the corrosion-resistant paint is inorganic zinc.

[0049] As a result, even if the spherical tank body 21 is made of a material that corrodes when it comes into contact with methanol, the methanol does not come into contact with the inner surface 21i of the spherical tank body 21, thereby preventing corrosion of the spherical tank body 21. Therefore, the cargo tank 20 can selectively transport high-pressure liquefied gas and methanol.

[0050] (5) According to a fifth aspect, the tank design method is a tank design method for a ship according to any one of (1) to (4), and includes a step S01 of determining a strain on the expansion side of the spherical tank body 21 based on the internal pressure of the spherical tank body 21 when liquefied gas is stored in the spherical tank body 21, a step S02 of determining a strain on the contraction side of the spherical tank body 21 based on the temperature inside the spherical tank body 21 when liquefied gas is stored in the spherical tank body 21, and a step S03 of determining a strain on the expansion side ε ＋ and the strain on the contraction side ε － and step S03 of determining the strength required for the corrosion-resistant layer 22 based on the difference between the strength and the corrosion-resistant layer 22.

[0051] As a result, the strain ε on the expansion side when the liquefied gas is stored in the spherical tank body 21 is ＋ In comparison with the case where the corrosion-resistant layer 22 is formed to have a strength that does not cause defects such as cracks, taking only the corrosion resistance into consideration, it is possible to select the corrosion-resistant layer 22 having a lower strength. Therefore, it is possible to improve the degree of freedom in selecting the type of corrosion-resistant paint that forms the corrosion-resistant layer 22.

[0052] (6) According to a sixth aspect, the tank design method is the tank design method of (5), and in the step S03 of determining the strength required for the corrosion-resistant layer 22, the strength required for the corrosion-resistant layer 22 is determined based on the difference between the strain when the internal pressure of the spherical tank body 21 is at its highest and the strain when the temperature inside the spherical tank body 21 is at its highest.

[0053] This results in the expansion strain ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas in which the strain on the expansion side is smaller, it is possible to determine the strength of the corrosion-resistant layer 22 required for the maximum strain on the expansion side that is expected when the spherical tank body 21 is navigating with the liquefied gas stored in it. Therefore, it is possible to prevent defects such as cracks from occurring in the corrosion-resistant layer 22 regardless of changes in the pressure and temperature of the liquefied gas during navigation, etc.

[0054] (7) According to a seventh aspect, the tank design method is the tank design method of (5), and in the step S03 of determining the strength required for the corrosion-resistant layer 22, the strength required for the corrosion-resistant layer 22 is determined based on the difference between the strain when the internal pressure of the spherical tank body 21 is at its lowest and the strain when the temperature inside the spherical tank body 21 is at its lowest.

[0055] This results in the expansion strain ε ＋ In contrast, the strain on the contraction side is ε － In the case of liquefied gas in which the strain on the contraction side is larger than the strain on the contraction side, it is possible to determine the strength of the corrosion-resistant layer 22 required for the maximum strain on the contraction side that is expected when the spherical tank body 21 is navigating with the liquefied gas stored in it. Therefore, it is possible to prevent defects such as cracks from occurring in the corrosion-resistant layer 22 regardless of changes in the pressure and temperature of the liquefied gas during navigation, etc.

[0056] According to the ship and tank design method disclosed herein, it is possible to transport high-pressure cargo and corrosive cargo interchangeably while suppressing cost increases.

[0057] DESCRIPTION OF SYMBOLS 1 Ship 2 Hull 2a Bow 2b Stern 4 Bottom 5 Upper deck 7 Superstructure 8 Cargo carrying area (hold) 9 Foundation deck 20 Cargo tank 20o Outer surface 20a Upper part 21 Spherical tank body 21i Inner surface 22 Corrosion-resistant layer 25 Tank cover 25i Inner surface 30 Skirt S Storage space

Claims

1. A ship comprising: a hull; and a cargo tank provided on the hull and capable of selectively storing liquefied gas and corrosive liquid, wherein the cargo tank comprises: a pressure-resistant spherical tank body; and a corrosion-resistant layer made of corrosion-resistant paint laminated on the inner surface of the spherical tank body.

2. The vessel according to claim 1, further comprising a cylindrical skirt whose upper end is connected circumferentially to the vertically middle portion of the spherical tank body and whose lower end is connected to the hull.

3. The ship according to claim 2, wherein the spherical tank body is an IMO tank type C in the IGC Code.

4. The vessel according to claim 1, wherein the corrosive liquid is methanol, and the corrosion-resistant paint is inorganic zinc.

5. A method for designing a ship as described in claim 1, comprising the steps of: determining the strain on the expansion side of the spherical tank body based on the internal pressure of the spherical tank body when the liquefied gas is stored in the spherical tank body; determining the strain on the contraction side of the spherical tank body based on the temperature inside the spherical tank body when the liquefied gas is stored in the spherical tank body; and determining the strength required for the corrosion-resistant layer based on the difference between the strain on the expansion side and the strain on the contraction side.

6. A tank design method as set forth in claim 5, wherein in the step of determining the strength required for the corrosion-resistant layer, the strength required for the corrosion-resistant layer is determined based on the difference between the strain when the internal pressure of the spherical tank body is at its highest and the strain when the temperature inside the spherical tank body is at its highest.

7. A tank design method as set forth in claim 5, wherein in the step of determining the strength required for the corrosion-resistant layer, the strength required for the corrosion-resistant layer is determined based on the difference between the strain when the internal pressure of the spherical tank body is at its lowest and the strain when the temperature inside the spherical tank body is at its lowest.

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