Method for testing the tightness of a tank lead-through and liquefied gas

Abstract

To reduce a use amount of inspection gas in an airtightness inspection of a tank penetration part of a liquefied gas tank.SOLUTION: The method includes forming a closed space communicating with at least one inspection target location inside the penetration pipe by attaching a plug to at least one of an inner opening and an outer opening of the penetration pipe, supplying an inspection gas to the closed space to pressurize the closed space to a predetermined inspection pressure after expelling air from the closed space, covering the inspection target location with a barrier bag having no gas permeability from the outside of the penetration pipe, detecting the inspection gas leaking 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.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[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. [Background technology]

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-546050 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[0008] In order to solve the above problem, a method for inspecting an airtightness of a tank penetration according to one aspect of the present disclosure includes: A method for inspecting airtightness of a tank penetration of a liquefied gas tank, comprising: the tank penetration portion has a penetration pipe that penetrates through a tank wall of the liquefied gas tank, By attaching a plug to at least one of the inner opening and the outer opening of the penetration pipe, a closed space communicating with at least one inspection target location is formed inside the penetration pipe; After purging the air from the closed space, supply a test gas to the closed space and pressurize it to a predetermined test pressure; covering the inspection target location from the outside of the penetration pipe with a gas-impermeable barrier bag; Detecting the test gas leaking from the enclosed space into the barrier bag; and supplying a purge gas to the enclosed space and exhausting the test gas from the enclosed space. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a liquefied gas carrier equipped with a gas tank to which an airtightness inspection method according to an embodiment of the present disclosure is applied. [Figure 2] FIG. 2 is a schematic cross-sectional view of a liquefied gas tank. [Figure 3] FIG. 3 is a schematic cross-sectional view of a tank penetration part through which a cable of a liquefied gas tank is inserted. [Figure 4] FIG. 4 is a schematic cross-sectional view of a tank penetration portion through which the piping of a liquefied gas tank is inserted. [Figure 5] FIG. 5 is a schematic cross-sectional view of a tank penetration of a liquefied gas tank without an insert. [Figure 6] FIG. 6 is a diagram showing a state during an airtightness inspection of the tank penetration portion of FIG. [Figure 7] FIG. 7 is a flow chart of a method for inspecting the airtightness of a tank penetration. [Figure 8] FIG. 8 is a cross-sectional view of a tank penetration during an airtightness inspection. [Figure 9]FIG. 9 is a diagram illustrating how airtightness tests are carried out successively on a plurality of tank penetrations. DETAILED DESCRIPTION OF THE INVENTION

[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 this 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 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 store 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>> Fig. 2 is a schematic cross-sectional view of a liquefied gas tank 1. As shown in Fig. 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 that stores liquefied gas. In the liquefied gas tank 1 that stores liquefied gas, 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 conducting 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. A tank penetration P is provided in the tank wall of the liquefied gas tank 1, allowing insertion members 22, such as pipes and cables, to pass through while maintaining airtightness.

[0015] <<Structure of tank penetration part P>> As described above, the liquefied gas tank 1 is provided with tank penetration parts 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 pipes and 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 penetrates the multiple shells continuously. 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 diagonally 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, namely, 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 insert 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 appearance of the lid 37 varies 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 part P through which a piping of a liquefied gas tank 1 is inserted. As shown in Fig. 4, when the insert 22 passed through the tank penetration part P is a piping, the lid 37 is composed of, for example, a flange 44 arranged on 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 piping is 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 passed through by 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 passed through 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 by a blind flange 57.

[0020] In the tank penetration part P, the joint between the penetration pipe 25 and the lid body 37, the joint between the constituent pipes of the penetration pipe 25, and the like are the parts to be inspected for airtightness inspection.

[0021] <Airtightness inspection method for tank penetration P> Here, we will explain a method for inspecting the airtightness of the tank penetration P of the liquefied gas tank 1. We will take as an example a case where an airtightness inspection is performed on a tank penetration P into which a cable is inserted as the insert 22, but airtightness inspection can also be performed 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 opening and the inner opening of the penetration pipe 25 are open, the plug 61 is attached to each of the outer opening and the inner opening.

[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 segmented 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 the segmented surfaces of a circular frame-shaped elastic element 72. The elastic element 72 is made of an elastic material. By applying pressure to the elastic element 72 in the axial direction with a frame 73, the elastic deformation of the elastic element 72 can bring the outer peripheral surface of the plug 61 into 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 by the plug 61 with the object 22 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 test gas and 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 test gas, supplying 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 is, 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 supply 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 part P is covered with a barrier bag 65 made of a gas-impermeable barrier film (step S03). The barrier bag 65 is closed so that gas does not leak from inside the barrier bag 65 to the outside. A test gas detector 66 that detects leakage of the test gas into the barrier bag 65 is connected to 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 a 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-mentioned inspection time, the test gas detector 66 detects the test gas leaked from the closed space 62 into the barrier bag 65 (step S04). If a leak of the test gas 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 leak of the test gas 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 there is test gas leaked into the barrier bag 65, it is evaluated as "poor airtightness," and if there is no test gas leaked, it 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, it is evaluated as "poor airtightness," and if it is less than the threshold, it 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 may 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 spreading 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 consecutively to two or more tank penetrations P. Below, as shown in Fig. 9, a case where airtightness inspection is performed consecutively 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 for 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 cutting 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 through a tank wall W of the liquefied gas tank 1, i) By attaching a plug 61 to at least one of the inner opening and the outer opening of the penetration pipe 25, a closed space 62 communicating with at least one inspection target location is formed inside the penetration pipe 25; ii) After purging the air from the closed space 62, supplying a test gas into the closed space 62 and pressurizing it to a predetermined test pressure; iii) covering the inspection target area from the outside of the penetration pipe 25 with a gas-impermeable barrier bag 65; iv) detecting the test gas leaking from the enclosed space 62 into the barrier bag 65; and v) supplying a purge gas to the enclosed space 62 and exhausting the test gas from the enclosed 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 spreading the inspection gas throughout the liquefied gas tank 1. This makes it possible to reduce the amount of inspection gas used compared to when the inspection gas is spread throughout the liquefied gas tank 1. As a result, it is possible to reduce the cost related to 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 in close contact with the inner surface of the penetration pipe 25.

[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 part P according to a third item of the present disclosure is the airtightness inspection method for a tank penetration part P according to the first or second item, The liquefied gas tank 1 has a first tank penetration portion P1 and a second tank penetration portion P2, which are different from each other. An airtightness inspection (i.e., steps i) to v) is performed on 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 described above, The inspection gas discharged from the closed space 62 of the first tank penetration part P1 is reused as the inspection gas to be introduced into the closed space 62 of the second tank penetration part P2.

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

[0040] The fourth item of the present disclosure relates to an airtightness inspection method for a tank penetration P, which is an airtightness inspection method for a tank penetration P according to any one 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] A liquefied gas tank 1 according to a fifth aspect of the present disclosure is a liquefied gas tank 1 that stores liquefied gas, Tank wall W and A penetration pipe 25 penetrates through the tank wall W; a cover 37 that closes the outer opening of the through pipe 25; a plug (61) having an insertion portion (20) through which an object (22) passed through the through pipe (25) can be airtightly inserted, and the plug (61) is disposed in the through pipe (25) with its outer circumferential surface in close contact with the inner circumferential surface of the through pipe (25); The penetration pipe 25 has a closed space 62 between the lid 37 and the plug 61 inside, which is in communication with at least one location to be inspected for airtightness.

[0043] According to 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, the features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of symbols]

[0045] 1: Liquefied gas tank 20: Insertion part 22: Insert 25: Penetration pipe 61: Plug body 62: Closed space 65: Barrier bag P: Tank penetration P1: First tank penetration P2: Second tank penetration

Claims

1. A method for inspecting airtightness of a tank penetration of a liquefied gas tank, comprising: the tank penetration portion has a penetration pipe that penetrates through a tank wall of the liquefied gas tank, a plug is attached to at least one of the inner opening and the outer opening of the penetration pipe, thereby forming a closed space inside the penetration pipe that is in communication with at least one location to be inspected; After purging the air from the closed space, supply a test gas to the closed space and pressurize it to a predetermined test pressure; covering the inspection target location from the outside of the penetration pipe with a gas-impermeable barrier bag; Detecting the test gas leaking from the enclosed space into the barrier bag; and supplying a purge gas to the enclosed space and exhausting the test gas from the enclosed space; Method for inspecting tank penetrations for airtightness.

2. The plug has an insertion portion through which an insert passed through the through-pipe can be airtightly inserted, and the plug is placed in the through-pipe with the outer peripheral surface of the plug and the inner peripheral surface of the through-pipe in close contact with each other. The method for inspecting an airtightness of a tank penetration according to claim 1.

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

3. The method for inspecting an airtightness of a tank penetration according to claim 1 or 2.

4. the liquefied gas tank is a storage container for liquefied hydrogen, The test gas is helium gas or a mixture of hydrogen gas and nitrogen gas.

3. The method for inspecting an airtightness of a tank penetration according to claim 1 or 2.

5. A liquefied gas tank for storing liquefied gas, The tank wall and a penetration pipe installed through the tank wall; a cover that closes the outer opening of the through pipe; a plug having an insertion portion through which an inserting object passed through the through pipe can be airtightly inserted, and the plug is disposed in the through pipe with its outer peripheral surface in close contact with the inner peripheral surface of the through pipe, A closed space is provided between the lid and the plug inside the penetration pipe, the closed space being in communication with at least one location to be airtightly inspected. Liquefied gas tank.

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