Airtightness inspection method for tank-penetrating part, and liquefied gas tank

Abstract

Provided is an airtightness inspection method for a tank-penetrating part of a liquefied gas tank, the tank-penetrating part having a penetration pipe provided so as to penetrate a tank wall of the liquefied gas tank, and the method comprising: attaching a plug to an inner opening and / or an outer opening of the penetration pipe to form a closed space communicating with at least one location to be inspected inside the penetration pipe; expelling air from the closed space, and then pressurizing the closed space to a prescribed inspection pressure by supplying an inspection gas thereto; covering, from the outside of the penetration pipe and with a barrier bag not having gas permeability, the location to be inspected; detecting the inspection gas leaked into the barrier bag from the closed space; and supplying a purge gas to the closed space and discharging the inspection gas from the closed space.

Description

Tank penetration airtightness inspection method and liquefied gas tank

[0001] The present disclosure relates to a technique for inspecting the airtightness of a tank penetration provided in a tank wall of a liquefied gas tank for passing cables or piping through.

[0002] Liquefied gas tanks that store liquefied gas are required to be airtight to prevent the vaporized liquefied gas from leaking to the outside. Therefore, after the installation work of a liquefied gas tank is completed, an airtightness test is performed on the liquefied gas tank to confirm its airtightness, i.e., to confirm that there is no gas leakage. In such an airtight test, a test gas is generally sealed inside the liquefied gas tank to be tested, and the test gas leaking to the outside is detected or pressure fluctuations inside the liquefied gas tank are measured to detect leakage of the test gas and evaluate the airtightness of the liquefied gas tank.

[0003] In the conventional airtightness inspection method described above, the amount of inspection gas used increases as the capacity of the liquefied gas tank to be inspected increases. Therefore, Patent Document 1 proposes an airtightness inspection method for liquefied gas tanks that can reduce the amount of inspection gas used by recirculating the inspection gas.

[0004] Japanese Patent Application Laid-Open No. 2023-546050

[0005] Liquefied gas tanks are provided with inserts such as cables and piping that extend from the inside to the outside of the tank. Liquefied gas tanks are provided with tank penetrations in order to pass the inserts through the tank wall while maintaining the airtightness of the liquefied gas tank. For example, a tank penetration on a conventional liquefied gas tank is composed of a penetration pipe that penetrates the tank wall and a lid that is placed inside or at the end of the penetration pipe. When the insert is a cable, for example, a flange equipped with an airtight terminal or a cable feedthrough is used as the lid. When the insert is a pipe, for example, a flange equipped with a fluid feedthrough is used as the lid. Sometimes, a pipe or cable is not passed through the tank penetration, but the pipe is connected to the penetration pipe.

[0006] Conventionally, even when inspecting the airtightness of tank penetrations in liquefied gas tanks, the entire tank is filled with a test gas and leakage of the test gas from the tank penetrations is detected. This method requires filling the tank with the test gas until the tank reaches a predetermined test pressure, which requires a large amount of test gas and takes a long time. For example, when the liquefied gas tank is a storage container for liquefied hydrogen, helium gas, which has a molecular weight close to that of hydrogen gas, is used as the main component of the test gas. Helium gas is a relatively expensive gas, so it is preferable to use as little test gas as possible.

[0007] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a technology that can reduce the amount of inspection gas used when inspecting the airtightness of tank penetrations in liquefied gas tanks.

[0008] In order to solve the above problems, a method for inspecting the airtightness of a tank penetration part according to one embodiment of the present disclosure is a method for inspecting the airtightness of a tank penetration part of a liquefied gas tank, wherein the tank penetration part has a penetration pipe that penetrates a tank wall of the liquefied gas tank, and includes: forming a closed space inside the penetration pipe that is connected to at least one location to be inspected by attaching a plug to at least one of an inner opening and an outer opening of the penetration pipe; expelling air from the closed space, and then supplying an inspection gas to the closed space to pressurize it up to a predetermined inspection pressure; covering the location to be inspected with a gas-impermeable barrier bag from the outside of the penetration pipe; detecting the inspection gas that has leaked from the closed space into the barrier bag; and supplying a purge gas to the closed space and discharging the inspection gas from the closed space.

[0009] According to the present disclosure, a technology can be provided that can reduce the amount of inspection gas used in airtight inspection of tank penetrations in liquefied gas tanks.

[0010]

[0013] Fig. 1 is a schematic configuration diagram of a liquefied gas carrier equipped with a liquefied gas tank to which an airtightness inspection method according to an embodiment of the present disclosure is applied. Fig. 2 is a schematic cross-sectional view of the liquefied gas tank. Fig. 3 is a schematic cross-sectional view of a tank penetration through which a cable of the liquefied gas tank is inserted. Fig. 4 is a schematic cross-sectional view of a tank penetration through which a piping of the liquefied gas tank is inserted. Fig. 5 is a schematic cross-sectional view of a tank penetration without an insert of the liquefied gas tank. Fig. 6 is a diagram showing a state during an airtightness inspection of the tank penetration of Fig. 5. Fig. 7 is a flow chart of an airtightness inspection method for a tank penetration. Fig. 8 is a cross-sectional view of a tank penetration during an airtightness inspection. Fig. 9 is a diagram illustrating how airtightness inspections are performed successively on a plurality of tank penetrations.

[0011] Next, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram of a liquefied gas carrier 10 equipped with a liquefied gas tank 1 to which an airtightness inspection method according to an embodiment of the present disclosure is applied. As shown in FIG. 1, the liquefied gas tank 1 to which the airtightness inspection method according to the present embodiment is applied is a cargo tank mounted on a hull 11 of the liquefied gas carrier 10 that transports liquefied gas. The liquefied gas tank 1 stores a liquefied gas such as liquefied hydrogen, LNG, or LPG. However, the airtightness inspection method according to the present disclosure is not limited to cargo tanks mounted on the liquefied gas carrier 10, but can be widely applied to liquefied gas tanks 1 that contain liquefied gas, such as fuel tanks mounted on liquefied gas-fueled ships and liquefied gas tanks installed on land.

[0012] <<Schematic Structure of Liquefied Gas Tank 1>> Figure 2 is a schematic cross-sectional view of the liquefied gas tank 1. As shown in Figure 2, the liquefied gas tank 1 according to this embodiment includes a tank body 31 and a tank dome 32 that protrudes upward from the top of the tank body 31. The top of the tank body 31 is covered by a tank cover 12. The liquefied gas tank 1 to which the airtightness inspection method according to the present disclosure is applied may be a single-shell tank or a multi-shell tank.

[0013] The interior of the tank body 31 is a storage space 51 in which liquefied gas is stored. In the liquefied gas tank 1 in which liquefied gas is stored, vaporized liquefied gas accumulates in the upper part of the storage space 51. The tank dome 32 protrudes upward from the top of the tank body 31, and a part of the tank dome 32 appears in the exposed space above the tank cover 12.

[0014] The liquefied gas tank 1 is provided with a tower (not shown) that extends from the top of the tank dome 32 into the tank body 31. A pump for pumping liquefied gas is installed at the bottom of the tower. Pipes and cables for delivering liquid are connected to the pump, and these extend through the tower, penetrate the tank wall of the tank dome 32, and into the exposed space above the tank cover 12. In addition, pipes for directing boil-off gas generated by evaporation of the liquefied gas in the liquefied gas tank 1 to equipment outside the liquefied gas tank 1 also extend through the tank wall of the tank dome 32 and into the exposed space above the tank cover 12. Examples of the external equipment include a propulsion engine, a power generation engine, a reliquefaction device, and an atmospheric release device. The tank wall of the liquefied gas tank 1 is provided with a tank penetration P through which inserts 22, such as pipes and cables, can pass while maintaining airtightness.

[0015] <<Structure of Tank Penetration Part P>> As described above, the liquefied gas tank 1 is provided with a tank penetration part P in the wall of the tank body 31 or the tank dome 32 (i.e., the tank wall W) for passing through inserts 22 such as piping or cables extending inside and outside the liquefied gas tank 1. The liquefied gas tank 1 illustrated in Fig. 2 has a tank penetration part P that penetrates the wall of the tank dome 32, but it may also have a tank penetration part P that penetrates the tank wall of the tank body 31, or, if the tank body 31 is made of multiple shells, a tank penetration part P that continuously penetrates the multiple shells. These tank penetration parts P have a common structure.

[0016] FIG. 3 is a schematic cross-sectional view of a tank penetration P of a liquefied gas tank 1 through which a cable is passed. As shown in FIG. 3 , a penetration pipe 25 is provided in the tank penetration P of the liquefied gas tank 1, penetrating the tank wall W. While the illustrated penetration pipe 25 extends horizontally, the penetration pipe 25 may also extend vertically or obliquely through the tank wall W. The penetration pipe 25 may be composed of a single pipe or multiple pipes connected in series. For example, if the penetration pipe 25 is composed of multiple pipes, a first pipe 25a and a second pipe 25b, the first pipe 25a and the second pipe 25b are joined by fastening the flange of the first pipe 25a to the flange of the second pipe 25b with bolts and nuts. The joint between the first pipe 25a and the second pipe 25b is the target location for an airtightness inspection. A purge pipe 26 is connected to the penetration pipe 25. The purge pipe 26 is provided with a purge valve 68 that opens and closes the purge pipe 26 .

[0017] A lid 37 that airtightly seals the through pipe 25 is disposed at the inside or outer end of the through pipe 25. In the example shown in Fig. 3 , the inserted object 22 is a cable, and the lid 37 is composed of, for example, a flange 38 disposed at the outer end of the through pipe 25 and a feedthrough 39 (airtight terminal) coupled to the flange 38. The feedthrough 39 passes through the flange 38, and a cable is connected to both ends of the feedthrough 39. The through pipe 25 and the lid 37 are coupled together by fastening a flange 251 provided at the outer opening of the through pipe 25 to the flange 38 of the lid 37 with bolts and nuts.

[0018] The lid 37 has different configurations depending on the type of insert 22 and whether or not the insert 22 is present. Fig. 4 is a schematic cross-sectional view of a tank penetration P through which a pipe of a liquefied gas tank 1 is inserted. As shown in Fig. 4, when the insert 22 passed through the tank penetration P is a pipe, the lid 37 is composed of, for example, a flange 44 arranged at the outer end of the penetration pipe 25 and a fluid feedthrough 45 (i.e., a penetration pipe) fixed to the flange 44. The fluid feedthrough 45 penetrates the flange 44, and pipes are connected to both ends of the fluid feedthrough 45. The penetration pipe 25 and the lid 37 are joined by fastening a flange 251 provided at the outer opening of the penetration pipe 25 to the flange 44 of the lid 37 with bolts and nuts.

[0019] The penetration pipe 25 does not necessarily need to be inserted with an insert 22 such as a pipe or a cable. FIG. 5 is a schematic cross-sectional view of a tank penetration P of a liquefied gas tank 1 without an insert 22. When the insert 22 is not inserted into the penetration pipe 25, as shown in FIG. 5, the cover 37 that airtightly seals the penetration pipe 25 is composed of, for example, a valve assembly 49. The valve assembly 49 is composed of a valve casing 48 coupled to a flange 251 of the penetration pipe 25 and a valve 47 that can be seated on a valve seat provided in the valve casing 48. An external pipe 55 is connected to the valve assembly 49. As shown in FIG. 6, during an airtightness inspection of the tank penetration P, a temporary pipe 56 is connected to the valve assembly 49, and the open end of the temporary pipe 56 is closed with a blind flange 57.

[0020] In the tank penetration portion P, the joint between the penetration pipe 25 and the lid 37, the joint between the constituent pipes of the penetration pipe 25, and the like are the target locations for the airtightness inspection.

[0021] <<Method for Inspecting Airtightness of Tank Penetration P>> Here, a method for inspecting airtightness of the tank penetration P of the liquefied gas tank 1 will be described. An example will be given of an airtight inspection of a tank penetration P into which a cable is inserted as the insert 22, but airtight inspection can also be performed in the same way on a tank penetration P into which a pipe is inserted or a tank penetration P without the insert 22.

[0022] FIG. 7 is a flow chart of the airtightness inspection method for the tank penetration P, and FIG. 8 is a cross-sectional view of the tank penetration P during the airtightness inspection. As shown in FIG. 7 , first, a plug 61 is attached to the penetration pipe 25, and both the inner and outer openings of the penetration pipe 25 are sealed, thereby forming a closed space 62 inside the penetration pipe 25 that is in communication with at least one inspection target location (step S01). Note that the insert 22 may be left in the tank penetration P or may be removed. As shown in FIG. 8 , when the outer opening of the penetration pipe 25 is closed with the lid 37, the plug 61 is attached only to the inner opening of the penetration pipe 25. When both the outer and inner openings of the penetration pipe 25 are open, the plug 61 is attached to both the outer and inner openings.

[0023] The plug 61 is fitted into the penetration pipe 25. The plug 61 has an insertion portion 20 through which the object 22 can be airtightly inserted, and an outer peripheral surface that can be in close contact with the inner peripheral surface of the penetration pipe 25. The specific configuration of the plug 61 is not particularly limited. However, a plug 61 used with the object 22 retained in the tank penetration P may use a split multi-cable transit as the insertion portion 20. For example, the plug 61 shown in FIG. 7 has a multi-cable transit 71 that holds the object 22 inserted in the penetration pipe 25 sandwiched between split surfaces of a circular frame-shaped elastic element 72. The elastic element 72 is made of an elastic material, and by applying pressure to the elastic element 72 in the axial direction with a frame 73, the elastic deformation of the elastic element 72 allows the outer peripheral surface of the plug 61 to be in close contact with the inner peripheral surface of the penetration pipe 25. In this way, the inner opening of the penetration pipe 25 can be closed with the plug 61 while the object 22 is retained in the penetration pipe 25.

[0024] By attaching the plug 61 to the penetration pipe 25, a closed space 62 is temporarily formed within the penetration pipe 25, which is connected to at least one location to be inspected for airtightness testing. A gas supply pipe 63 and a pressure sensor 64 probe are inserted into the plug 61, along with the insert 22. The pressure sensor 64 detects the pressure in the closed space 62. The gas supply pipe 63 is used to supply a test gas and a purge gas to the closed space 62. A supply valve 69 is provided on the gas supply pipe 63. The supply valve 69 can switch between supplying the test gas, supplying the purge gas, and closing the supply. The test gas is preferably an inert gas containing a gas with the same or similar molecular weight as the gas stored in the liquefied gas tank 1. For example, if the liquefied gas tank 1 is a storage container for liquefied hydrogen, helium gas, which has a molecular weight similar to that of hydrogen gas, which is the vaporized gas of liquefied hydrogen, is used as the main component of the test gas. In this case, the inspection gas may be, for example, approximately 100% helium gas by volume or a mixture of helium gas and nitrogen gas. The helium gas content of this mixture may be approximately 5% to 10% by volume. Using a mixture of helium gas and nitrogen gas can reduce costs compared to using 100% helium gas by volume. Furthermore, when the liquefied gas tank 1 is a storage container for liquefied hydrogen, the inspection gas may be a mixture of hydrogen gas and nitrogen gas. The hydrogen gas content of this mixture may be approximately 5% by volume.

[0025] Next, the purge valve 68 is opened to supply purge gas into the closed space 62 to expel air from the closed space 62, and then, with the purge valve 68 closed, the supply valve 69 is switched to supplying test gas, and the test gas is supplied to the closed space 62 through the gas supply pipe 63 to pressurize it to a predetermined test pressure (step S02).

[0026] Next, the inspection target portion of the tank penetration portion P is covered with a barrier bag 65 made of a gas-impermeable barrier film (step S03). The barrier bag 65 is closed to prevent gas from leaking from inside the barrier bag 65 to the outside. A test gas detector 66 is connected to the barrier bag 65 to detect leakage of the test gas into the barrier bag 65. The test gas detector 66 detects the main component of the test gas. For example, if the main component of the test gas is helium gas, a helium detector is used as the test gas detector 66. Note that the order of steps S03 and S02 may be reversed.

[0027] After the closed space 62 is pressurized to the inspection pressure, the closed space 62 is maintained at the predetermined inspection pressure for a predetermined inspection time. The inspection pressure is a pressure higher than atmospheric pressure and is determined in advance according to the design conditions of the liquefied gas tank 1.

[0028] During the above-described inspection time, the test gas detector 66 detects test gas leaked from the closed space 62 into the barrier bag 65 (step S04). If a test gas leak occurs at the inspection target location, the test gas in the closed space 62 leaks into the barrier bag 65, and the test gas is detected by the test gas detector 66. On the other hand, if a test gas leak does not occur at the inspection target location of the tank penetration P, the test gas does not leak into the barrier bag 65 throughout the inspection time, and the test gas is not detected by the test gas detector 66. The airtightness of the inspection target location is evaluated based on the amount of test gas leaked into the barrier bag 65. For example, if test gas leaks into the barrier bag 65, the location is evaluated as "poor airtightness," and if not, the location is evaluated as "good airtightness." Furthermore, for example, if the amount of test gas leaked into the barrier bag 65 is equal to or greater than a predetermined threshold, the location is evaluated as "poor airtightness," and if it is less than the threshold, the location is evaluated as "good airtightness."

[0029] After the above-mentioned inspection time has elapsed, the purge valve 68 is opened and the supply valve 69 is switched to supplying purge gas, supplying the purge gas to the closed space 62 through the gas supply pipe 63, and discharging the inspection gas in the closed space 62 to the outside through the purge pipe 26 (step S05). The barrier bag 65 may be removed before the purge gas is supplied. Air or an inert gas such as nitrogen can be used as the purge gas. Finally, the plug 61 is removed from the penetration pipe 25 to complete the inspection. The plug 61 may be left in the penetration pipe 25 as a heat insulating material.

[0030] According to the above airtightness inspection method, it is possible to inspect the airtightness of the tank penetration P by filling the inspection gas only into the closed space 62 inside the penetration pipe 25, rather than distributing the inspection gas throughout the liquefied gas tank 1. In this way, the amount of inspection gas used can be reduced, which results in a reduction in the cost related to the inspection gas and a reduction in the time required to fill the inspection gas.

[0031] <<Continuous Airtightness Inspection Method for Tank Penetrations P>> The above-described airtightness inspection method can be applied continuously to two or more tank penetrations P. Below, as shown in Fig. 9 , a case where airtightness inspection is performed continuously on a first tank penetration P1 and a second tank penetration P2 will be described.

[0032] First, the processes from step S01 to step S04 described above are performed for the first tank penetration P1. Before performing the process of step S05 described above for the first tank penetration P1, the processes from step S01 to step S02 described above are performed for the second tank penetration P2. Then, the process of step S05 described above for the first tank penetration P1 and the process of step S03 described above for the second tank penetration P2 are simultaneously performed. Specifically, the purge pipe 26 connected to the first tank penetration P1 and the gas supply pipe 63 of the second tank penetration P2 are connected by a temporary hose 70, and purge gas is supplied to the closed space 62 of the first tank penetration P1. As a result, the purge gas supplied to the closed space 62 of the first tank penetration P1 exhausts the inspection gas from the closed space 62 of the first tank penetration P1, and the exhausted inspection gas flows into the closed space 62 of the second tank penetration P2. In this way, the inspection gas used to inspect the first tank penetration P1 is reused to inspect the second tank penetration P2. However, if the amount of the inspection gas reused or the partial pressure of the main components is insufficient for inspecting the second tank penetration P2, additional inspection gas is supplied to the closed space 62 of the second tank penetration P2. The processes from step S04 to step S05 described above are performed for the second tank penetration P2.

[0033] As described above, airtightness inspections of the first tank penetration P1 and the second tank penetration P2 can be performed consecutively. By reusing the inspection gas used at the first tank penetration P1 as the inspection gas for the second tank penetration P2, the amount of inspection gas used can be reduced, thereby reducing the cost associated with the inspection gas. Note that the above-described airtightness inspection method can also be applied to perform airtightness inspections of three or more tank penetrations P consecutively.

[0034] [Summary] The method for inspecting airtightness of a tank penetration P according to the first item of the present disclosure is a method for inspecting airtightness of a tank penetration P of a liquefied gas tank 1, wherein the tank penetration P has a penetration pipe 25 that penetrates a tank wall W of the liquefied gas tank 1, and includes: i) attaching a plug 61 to at least one of an inner opening and an outer opening of the penetration pipe 25 to form a closed space 62 inside the penetration pipe 25 that is in communication with at least one location to be inspected; ii) after purging air from the closed space 62, supplying an inspection gas into the closed space 62 to pressurize it up to a predetermined inspection pressure; iii) covering the location to be inspected from the outside of the penetration pipe 25 with a gas-impermeable barrier bag 65; iv) detecting the inspection gas that has leaked from the closed space 62 into the barrier bag 65; and v) supplying a purge gas into the closed space 62 and discharging the inspection gas from the closed space 62.

[0035] According to the above airtightness inspection method, it is possible to inspect the airtightness of the tank penetration P by filling the inspection gas only into the closed space 62 inside the penetration pipe 25, rather than distributing the inspection gas throughout the liquefied gas tank 1. This allows for a reduction in the amount of inspection gas used compared to when the inspection gas is distributed throughout the liquefied gas tank 1. As a result, it is possible to reduce the cost of the inspection gas and the time required to fill the inspection gas.

[0036] The airtightness inspection method for a tank penetration section P relating to the second item of the present disclosure is the airtightness inspection method for a tank penetration section P relating to the first item, in which the stopper body 61 has an insertion section 20 through which an inserting object 22 passed through the penetration pipe 25 can be airtightly inserted, and the stopper body 61 is placed inside the penetration pipe 25 with the outer surface of the stopper body 61 and the inner surface of the penetration pipe 25 in close contact with each other.

[0037] Since the plug 61 is disposed inside the penetration pipe 25, there is no need for work such as welding or fastening a flange to attach the plug 61 to the penetration pipe 25. Furthermore, with the insert 22 inserted into the penetration pipe 25, it is possible to perform an airtightness inspection of the tank penetration part P.

[0038] The airtightness inspection method for a tank penetration P according to the third item of the present disclosure is the airtightness inspection method for a tank penetration P according to the first or second item, wherein the liquefied gas tank 1 has different tank penetrations P, a first tank penetration P1 and a second tank penetration P2, and airtightness inspection (i.e., steps i) to v) above is performed for each of the first tank penetration P1 and the second tank penetration P2 using the airtightness inspection method according to the first or second item, and the inspection gas discharged from the closed space 62 of the first tank penetration P1 is reused as the inspection gas to be introduced into the closed space 62 of the second tank penetration P2.

[0039] The inspection gas used in inspecting the first tank penetration P1 is reused in inspecting the second tank penetration P2, so the total amount of inspection gas used can be reduced when performing airtight inspections of multiple tank penetrations P.

[0040] The airtightness inspection method for a tank penetration part P relating to the fourth item of the present disclosure is an airtightness inspection method for a tank penetration part P relating to any of the first to third items, in which the liquefied gas tank 1 is a storage container for liquefied hydrogen, and the inspection gas is helium gas or a mixed gas of hydrogen gas and nitrogen gas.

[0041] Helium gas is relatively expensive, but the airtightness inspection method according to the present disclosure reduces the amount of inspection gas used, thereby reducing the costs associated with airtightness inspection.

[0042] The liquefied gas tank 1 according to the fifth item of the present disclosure is a liquefied gas tank 1 for storing liquefied gas, and comprises: a tank wall W; a penetration pipe 25 extending through the tank wall W; a lid 37 for closing the outer opening of the penetration pipe 25; and a stopper 61 having an insertion portion 20 through which an insert 22 passed through the penetration pipe 25 can be airtightly inserted, the stopper 61 being disposed within the penetration pipe 25 with its outer surface in close contact with the inner surface of the penetration pipe 25, and having a closed space 62 inside the penetration pipe 25 between the lid 37 and the stopper 61 that is connected to at least one location to be inspected for airtightness.

[0043] With the liquefied gas tank 1 configured as described above, it is possible to inspect the airtightness of the tank penetration P by filling the inspection gas only into the closed space 62 inside the penetration pipe 25, rather than distributing the inspection gas throughout the liquefied gas tank 1. This allows for a reduction in the amount of inspection gas used compared to when the inspection gas is distributed throughout the liquefied gas tank 1. As a result, it is possible to reduce the cost of the inspection gas and the time required to fill the inspection gas. Furthermore, the plug 61 placed in the penetration pipe 25 can guide and support the insertion object 22.

[0044] The foregoing disclosure has been presented for purposes of illustration and description and is not intended to limit the disclosure to the form disclosed herein. For example, in the foregoing Detailed Description, various features of the disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Furthermore, multiple features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. A method for inspecting the airtightness of a tank penetration of a liquefied gas tank, wherein the tank penetration has a penetration pipe that penetrates through the tank wall of the liquefied gas tank, and the method includes: attaching a plug to at least one of the inner opening and the outer opening of the penetration pipe to form a closed space inside the penetration pipe that is connected to at least one location to be inspected; expelling air from the closed space, and then supplying an inspection gas into the closed space to pressurize it up to a predetermined inspection pressure; covering the location to be inspected from the outside of the penetration pipe with a gas-impermeable barrier bag; detecting the inspection gas that has leaked from the closed space into the barrier bag; and supplying a purge gas into the closed space and discharging the inspection gas from the closed space.

2. An airtightness inspection method for a tank penetration as described in claim 1, wherein the plug has an insertion portion through which an object passed through the penetration pipe can be airtightly inserted, and the plug is placed inside the penetration pipe with its outer surface in close contact with the inner surface of the penetration pipe.

3. The liquefied gas tank has a first tank penetration and a second tank penetration that are different from each other, and an airtightness inspection method as set forth in claim 1 or 2 is performed on each of the first tank penetration and the second tank penetration, and the inspection gas discharged from the closed space of the first tank penetration is reused as the inspection gas to be introduced into the closed space of the second tank penetration.

4. The method for inspecting an airtightness of a tank penetration as set forth in claim 1 or 2, wherein the liquefied gas tank is a storage container for liquefied hydrogen, and the inspection gas is helium gas or a mixed gas of hydrogen gas and nitrogen gas.

5. A liquefied gas tank for storing liquefied gas, comprising: a tank wall; a penetration pipe that penetrates the tank wall; a lid that closes the outer opening of the penetration pipe; and a plug that has an insertion portion that allows an object passed through the penetration pipe to be airtightly inserted therethrough, and is placed inside the penetration pipe with its outer surface in close contact with the inner surface of the penetration pipe, and has a closed space inside the penetration pipe between the lid and the plug that is connected to at least one location to be inspected for airtightness.

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