System for detecting defect in non-adhesive insulation structure for liquefied gas storage and method for detecting defect in non-adhesive insulation structure for liquefied gas storage

Abstract

The present invention relates to a system and method for detecting a defect in a non-adhesive insulation structure for a liquefied gas storage tank for storing liquefied gas, the system comprising: an injection unit for injecting gas into a leakage path formed in a separation space between an outer wall of a liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; a gas storage unit connected to the injection unit and storing gas to be injected into the leakage path; an outlet unit for discharging the gas injected into the leakage path; and a pressure gauge for measuring the pressure in the leakage path, wherein, after injecting the gas into the leakage path through the injection unit, it is determined if an insulating unit formed on the sheet layer is defective by checking whether the pressure in the leakage path is maintained above a reference pressure.

Description

System for verifying defects in non-adhesive insulation structures of liquefied gas storage tanks and method for verifying defects in non-adhesive insulation structures of liquefied gas storage tanks

[0001] The present invention relates to a defect verification system and method for a non-adhesive insulation structure of a liquefied gas storage tank for storing liquefied gas. Specifically, it relates to a defect verification system and method for a non-adhesive insulation structure of a liquefied gas storage tank that enables efficient drying and inert gas replacement operations after the storage tank is installed by identifying defect points on the insulation structure in advance and repairing them prior to the hull installation and sea trial of the liquefied gas storage tank with the insulation structure formed thereon.

[0002] Due to the recent tightening of environmental pollution regulations for ships, interest in eco-friendly, high-efficiency liquefied gas fuels, such as Liquefied Natural Gas (LNG) or Liquefied Petroleum Gas (LPG), is increasing.

[0003] Liquefied natural gas is obtained by cooling and liquefying methane produced by refining natural gas extracted from gas fields, while liquefied petroleum gas is a fuel made by compressing gases composed mainly of propane and butane, which are found along with petroleum in oil fields, into a liquid at room temperature.

[0004] In particular, liquefied natural gas (hereinafter referred to as 'LNG') is obtained by cooling natural gas to a cryogenic temperature (about -163°C), and since its volume is reduced to approximately 1 / 600 of that of natural gas in a gaseous state, it is very suitable for long-distance transportation by sea.

[0005] Liquefied gas is transported in a gaseous state through onshore or offshore gas pipelines, or transported to distant consumption sites while stored in a liquid state on transport vessels.

[0006] Liquefied gas carriers that transport liquefied gas, such as LNG, to sail the seas and unload the liquefied gas at onshore destinations, or LNG RVs (Regasification Vessels) that transport LNG to sail the seas, arrive at onshore destinations, and then regasify the stored LNG to unload it in the form of natural gas, are equipped with liquefied gas storage tanks (commonly referred to as 'cargo tanks') capable of withstanding the cryogenic temperatures of LNG.

[0007] In addition, liquefied gas storage tanks installed on LNG carriers or LNG RVs are also included in offshore structures such as LNG FPSO (Floating, Production, Storage and Offloading), which is used to liquefy and store produced natural gas directly at sea and transfer the stored LNG to an LNG carrier when necessary, and LNG FSRU (Floating Storage and Regasification Unit), which stores LNG unloaded from an LNG carrier at sea and then vaporizes the LNG as needed to supply it to onshore demand centers.

[0008] These liquefied gas storage tanks can be classified into membrane type and independent type depending on whether the load of the cargo acts directly on the insulation material.

[0009] Membrane-type storage tanks are divided into No. 96 and Mark III types, and independent storage tanks are divided into Type A, Type B, and Type C according to the regulations of the International Maritime Organization (IMO). Among these, Type B independent storage tanks include spherical MOSS tanks and prismatic SPB tanks.

[0010] The membrane-type storage tank is directly connected to the structure of the hull and is not separated from the hull, and has a structure in which a primary barrier and a secondary barrier are laminated on the inner wall of the hull. As the membrane-type tank is directly connected to the hull, the load of the liquefied gas stored inside is not supported by the storage tank but is transferred to the hull.

[0011] In contrast, standalone storage tanks are manufactured to be mounted on the hull separately from the hull structure and feature a structure in which insulation surrounds the outer walls. Since standalone storage tanks are separated from the hull and supported by support structures installed inside the hull, the load of the liquefied gas stored inside acts directly on the tank.

[0012] Unlike membrane storage tanks, independent storage tanks do not have a complex barrier structure and are relatively advantageous in terms of structural stability against sloshing compared to membrane storage tanks. In addition, since insulation is provided on the outer wall of the storage tank, maintenance by workers becomes easier.

[0013] The aforementioned technical configuration is provided as background technology to aid in understanding the present invention and does not constitute prior art widely known in the technical field to which the present invention belongs.

[0014] Generally, after the manufacturing of a standalone storage tank is completed, it is temporarily kept outdoors until it is loaded onto a hull. In the above-mentioned insulation structure formation process, if the insulation structure is formed on the entire outer surface of the standalone storage tank, interference may occur at connection points, etc., when the standalone storage tank is loaded onto the hull. Therefore, considering this, a pending area is created where the formation of the insulation structure is partially withheld. During this temporary waiting period, rainwater flows in through the pending area and continuously accumulates in the upper and lower parallel sections and corners of the tank via leakage paths. Consequently, there is a problem in that a significant amount of time is required for drying and inert gas replacement work to prevent condensation before injecting cryogenic liquefied gas after loading onto the hull.

[0015] Furthermore, when forming a multi-layered insulation structure for standalone storage tanks using spray foam, inspecting the foam for defects on each layer individually would result in an excessively long timeframe for the formation process. Consequently, inspections are currently conducted only on the final surface after the entire insulation structure is completed. In this process, it is difficult to identify and address micro-defects or potential defects that may arise during the curing of the spray foam in advance. As a result, there is a problem where rainwater may infiltrate through micro-defects and potential defects in the insulation structure.

[0016] The present invention aims to provide a defect verification system and method for a non-adhesive insulation structure of a liquefied gas storage tank, which enables the rapid and effective performance of drying and inert gas replacement operations after hull installation by identifying and repairing defect points in the work hold area and / or insulation structure in advance after the completion of the insulation structure formation process of the independent storage tank and before installation on the hull.

[0017] To solve the above-mentioned problem, the present invention provides a defect verification system for a non-adhesive insulation structure of a liquefied gas storage tank, comprising: an injection part for injecting gas into a leakage path formed in a spaced-apart space between the outer wall of the liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; a gas storage part connected to the injection part and storing gas to be injected into the leakage path; an outlet part for discharging gas injected into the leakage path; and a pressure gauge for measuring pressure within the leakage path; wherein, after injecting gas into the leakage path through the injection part, the system verifies whether the pressure within the leakage path is maintained above a reference pressure to verify whether there is a defect in the insulation part formed on the sheet layer.

[0018] In the above defect verification system, the liquefied gas storage tank may be an independent storage tank.

[0019] The above defect verification system may further include a flow meter provided on the injection part and for verifying the flow rate of the gas injected into the leakage path.

[0020] In the above defect verification system, the pressure gauge may be provided on the injection part, the outlet part, or the leakage path.

[0021] In the above defect verification system, the reference pressure may be atmospheric pressure.

[0022] In the above defect verification system, the gas injected into the leakage path through the injection part may be a dry gas.

[0023] In addition, the present invention provides a method for checking defects in a non-adhesive insulation structure of a liquefied gas storage tank, comprising: a step of injecting gas into a leakage path formed in a gap space between the outer wall of the liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; and a defect checking step of checking whether the pressure within the leakage path is maintained above a reference pressure.

[0024] In the above defect verification method, the liquefied gas storage tank may be an independent storage tank.

[0025] In the above defect verification method, the liquefied gas storage tank may be an independent storage tank not mounted on the hull.

[0026] In the above defect verification method, the defect verification step may further include: a step of verifying a defect point of the insulation formed on the sheet layer when the pressure within the leakage path is not maintained above a reference pressure; and a step of repairing the verified defect point of the insulation.

[0027] In the above defect verification method, the defect point of the insulation part may be identified by visual inspection or soapy water inspection.

[0028] In the above defect verification method, the reference pressure of the defect verification step may be atmospheric pressure.

[0029] In the above defect verification method, the gas injected into the leakage path may be a dry gas.

[0030] The present invention can secure excellent thermal insulation performance and structural stability of the insulation by injecting gas into a leakage path formed in the gap between the outer wall of a storage tank and the sheet layer surrounding the outer wall of the storage tank to pressurize it, and by checking whether the pressure within the leakage path is maintained above a reference pressure, thereby detecting in advance micro-defects that are difficult to identify by simple visual inspection and potential defects existing within the insulation.

[0031] In addition, the present invention can prevent rainwater from entering and accumulating through the work hold area or defective parts on the insulation section during the waiting period before mounting an independent storage tank with an insulation structure onto a hull by checking for defects in the insulation structure and repairing them in advance, thereby saving time required for drying and inert gas replacement work after mounting the storage tank onto the hull.

[0032] FIG. 1 is a cross-sectional view schematically illustrating the state in which a defect verification system for a non-adhesive insulation structure of a liquefied gas storage tank according to one embodiment of the present invention is installed in a liquefied gas storage tank.

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] First, it should be noted that when adding reference numerals to the components of each drawing, the same components are to have the same numeral whenever possible, even if they are shown on different drawings.

[0035] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0036] Preferred embodiments of the present invention will be described below, but the technical concept of the present invention is not limited thereto and can be modified and implemented in various ways by those skilled in the art.

[0037] In describing the present invention, liquefied gas may include all gaseous fuels generally stored in a liquefied state, such as LNG (Liquefied Natural Gas) at cryogenic temperatures (approximately -163°C), LPG (Liquefied Petroleum Gas), or liquefied ethylene gas, and the term liquefied gas may include not only liquefied gas in a liquid state but also vaporized liquefied gas.

[0038] < Defect Verification System for Non-Adhesive Insulation Structures of Liquefied Gas Storage Tanks >

[0039] FIG. 1 is a cross-sectional view schematically illustrating the state in which a defect verification system for a non-adhesive insulation structure of a liquefied gas storage tank according to one embodiment of the present invention is installed in a liquefied gas storage tank.

[0040] First, a liquefied gas storage tank (T) to which the defect verification system for the non-adhesive insulation structure of a liquefied gas storage tank according to the present invention is applied will be briefly described.

[0041] The above-mentioned liquefied gas storage tank (T) has a space formed inside for accommodating liquefied gas, and the outer wall (10) of the storage tank can be manufactured from an alloy that is resistant to low temperatures, such as aluminum alloy, SUS (Steel Use Stainless), or 9% nickel alloy (9% Nickel steel), and preferably, it can be made of high-manganese steel, which is inexpensive and has excellent brittleness resistance at low temperatures, so it can withstand ultra-low temperatures.

[0042] The above liquefied gas storage tank may be an independent liquefied gas storage tank provided separately from the structure of the hull and mounted on the hull, and preferably may be an independent liquefied gas storage tank of IMO Type B.

[0043] In the following, the defect verification system of the non-adhesive insulation structure of the liquefied gas storage tank (T) of the present invention has been described as being applied to an IMO TYPE B liquefied gas storage tank, but it is not necessarily limited thereto and can be applied to various types of liquefied gas storage tanks.

[0044] In one embodiment of the present invention, the liquefied gas storage tank (T) includes a sheet layer (40) installed at a certain distance from the outer wall (10) surrounding the outer wall (10) of the storage tank (T), and an insulation part (50) provided on the sheet layer. If necessary, it may further include a spacing member for spacing the outer wall (10) of the storage tank and the sheet layer (40) at a certain distance, a fixing part for fixing the sheet layer (40) and the insulation part (50) to the outer wall (10) of the storage tank, and a coating layer for protecting the outermost surface of the insulation part (50).

[0045] Additionally, the above-mentioned liquefied gas storage tank (T) may have an insulation section (50) formed but not yet mounted on the hull, and may have a pending area in which the formation of the insulation structure is partially withheld to exclude interference when mounted on the hull.

[0046] The outer wall (10) of the storage tank may be provided with studs that are connected to the fixing part to fix the sheet layer (40) and the insulation part (50).

[0047] The above sheet layer (40) may be formed by laminating a metal film capable of liquid tight or air tight, such as an aluminum film, and a reinforcing sheet of the glass fiber type.

[0048] The above-mentioned spacing member can be installed to be fitted into the stud and serves to space the outer wall (10) of the storage tank and the sheet layer (40) at a certain distance. The above-mentioned spacing member may be made of a plastic mesh material having excellent low-temperature toughness.

[0049] The insulation section (50) may be formed by applying a spray foam insulation material onto the sheet layer (40), and may have a thickness sufficient to ensure adequate insulation performance by considering the size of the outer wall (10) of the storage tank or the type or density of the insulation material applied onto the sheet layer (40). The insulation section (50) may be formed in multiple layers to maintain the liquefied gas stored inside the tank body in a cryogenic state. Additionally, the insulation section (50) may further include a reinforcing section installed within the insulation section (50). The reinforcing section acts as a reinforcing material that prevents the progression of cracks in the thickness direction.

[0050] The above fixing part may include an extension member, a washer member, and a fixing nut that is fastened to the other end of the extension member, wherein one end of the extension member is connected to a stud and the other end extends outwardly toward the outer wall of the storage tank. That is, the fixing part can be fixed by a structure in which a fixing nut fastened to the end of the extension member presses against a washer member located on the insulation part (50) or on a portion of the insulation layer among the plurality of insulation layers forming the insulation part.

[0051] Referring to FIG. 1, a defect verification system for a non-adhesive insulation structure of a liquefied gas storage tank (T) according to one embodiment of the present invention includes an injection section (100), a gas storage section (200), an outlet section (300), and a pressure gauge (500), and may further include a flow meter (400) as needed.

[0052] The injection section (100) is connected to the gas storage section (200) described later and provides a path for injecting gas into a leakage path formed in the gap space (S) between the outer wall (10) of the liquefied gas storage tank (T) and the sheet layer (40) surrounding the outer wall (10) of the liquefied gas storage tank.

[0053] An injection control valve (not shown) capable of controlling the supply amount of gas being injected may be provided on the injection part (100).

[0054] In one embodiment of the present invention, the defect verification system of the present invention may further include a flow meter (400) for verifying the flow rate of gas injected into the leakage path, and the flow meter (400) may be provided on the injection part (100).

[0055] The flow rate of the gas injected into the above leakage path is not particularly limited, but may be 3 to 15 L / min, and preferably 5 to 10 L / min, in order to shorten the time by checking for defects without damaging the insulation part.

[0056] The gas storage unit (200) is connected to the injection unit (100) and stores gas to be injected into a leakage path formed between the outer wall (10) of the storage tank and the sheet layer (40). At this time, the gas injected into the leakage path through the injection unit may be dry gas.

[0057] The above dry gas refers to a gas that does not contain water vapor. The above dry gas may be dry air or an inert gas, and the inert gas may be pure nitrogen, helium, argon, carbon dioxide, or a mixture thereof, but is not limited thereto, and preferably nitrogen may be used.

[0058] The outlet section (300) provides a path for discharging gas injected into the leakage path to the outside. In order to increase the efficiency of checking for defects on the insulation section (50), it is preferable that the outlet section (300) be installed far apart from the injection section (100).

[0059] An exhaust control valve (310) capable of controlling the discharge amount of the discharged gas may be provided on the above-mentioned outlet section (300).

[0060] The pressure gauge (500) measures the pressure in the leakage path pressurized by the gas injected through the injection part (100). The pressure gauge (500) may be provided on the injection part (100), the outlet part (300), or the leakage path, and it is preferable that the pressure gauge (500) be provided on the outlet part (300) in order to ensure accuracy in measuring the pressure in the leakage path and to minimize damage to the insulation part (50).

[0061] The injection section (100) and the outlet section (300) may be temporarily fixed by penetrating the sheet layer (40) and the insulation section (50) installed on the liquefied gas storage tank (T). Even if the injection section (100) and the outlet section (300) are not fixed to the liquefied gas storage tank (T), the injection section (100) and the outlet section (300) can be temporarily fixed through the insulation section (50) because they penetrate the insulation section (50).

[0062] Additionally, the injection section (100) and the outlet section (300) may be connected to separate pipes provided in a purging system for discharging liquefied gas leaked from a liquefied gas storage tank (T) in a leak path. When a purging system is provided in the liquefied gas storage tank (T), the injection section (100) may be connected to a purging gas injection pipe, and the outlet section (300) may be connected to a purging gas outlet pipe.

[0063] Meanwhile, although FIG. 1 illustrates an example in which one injection part (100) and one outlet part (300) are provided, it is obvious to a person skilled in the art that multiple injection parts (100) and outlet parts (300) may be provided, taking into account the size of the liquefied gas storage tank (T), the structure of the insulation part (50), etc.

[0064] The defect verification system of the present invention may verify whether there is a defect in the insulation part (50) formed on the sheet layer (40) by injecting gas into the leakage path through the injection part (100) and then checking whether the pressure within the leakage path is maintained above a reference pressure. When the pressure gauge (500) is provided on the outlet part (300), the pressure within the leakage path can be verified by measuring the pressure at the outlet part where the injected gas is discharged. The reference pressure is not particularly limited, but since a pressure within the leakage path that is too high can cause damage to the insulation part (50), it may be preferable to use atmospheric pressure as the reference pressure.

[0065] After injecting gas into the leakage path through the injection part (100), if the pressure within the leakage path is maintained above the reference pressure, it can be determined that there is no defect in the insulation part (50). Additionally, if the liquefied gas storage tank (T) has a pending area in which the formation of a partial insulation structure is withheld, it can be determined that the airtightness and watertightness of the pending area are maintained.

[0066] Meanwhile, if only micro-defects exist on the insulation section (50), the pressure within the leakage path may be maintained above the reference pressure, making it difficult to confirm the existence of micro-defects. Accordingly, a gas other than oxygen is injected into the leakage path, and the amount of oxygen within the leakage path is checked through the oxygen detector to determine whether micro-defects exist in the insulation section (50).

[0067] At this time, it is preferable that the diameter of the outlet section (300) be the minimum diameter into which an oxygen detector can be inserted. Since the outlet section (300) can be installed to be temporarily fixed by penetrating the insulation section (50), it is preferable that the smaller the diameter, the more the damage to the insulation section (50) can be minimized during temporary fixation.

[0068] After injecting gas into the leakage path through the injection part (100), if the pressure within the leakage path is not maintained above a reference pressure, it can be determined that there is a defect in the insulation part (50). Additionally, if the liquefied gas storage tank (T) has a pending area in which the formation of a partial insulation structure is withheld, it can be determined that the airtightness and watertightness of the pending area are not maintained.

[0069] If there is a defect in the insulation section (50) or the work hold area, the defect point can be identified using a visual inspection or a soap water inspection, and the identified defect point can be repaired in advance. In this way, by identifying and repairing defect points in the work hold area and / or insulation structure in advance before mounting the storage tank with the insulation structure onto the hull, the drying work and inert gas replacement work can be performed quickly and effectively after mounting onto the hull.

[0070] In the case of conventional technology, rainwater enters the leakage path through a defect point on the insulation section (50) or the work hold area, and thus a significant amount of time is required for drying and inert gas replacement work to prevent condensation in the leakage path before injecting cryogenic liquefied gas after hull installation. In contrast, if the defect point is repaired in advance by applying the defect verification system of the non-adhesive insulation structure of the liquefied gas storage tank of the present invention, the entry of rainwater into the leakage path can be blocked, thereby minimizing the time required for drying and inert gas replacement work.

[0071] < Method for Identifying Defects in Non-Adhesive Insulation Structures of Liquefied Gas Storage Tanks >

[0072] In addition, the present invention provides a method for verifying defects in the non-adhesive insulation structure of a liquefied gas storage tank.

[0073] A method for verifying defects in a non-adhesive insulation structure of a liquefied gas storage tank according to the present invention comprises: a step of injecting gas into a leakage path formed in a gap between the outer wall of the liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; and a defect verification step of verifying whether the pressure within the leakage path is maintained above a reference pressure.

[0074] The method for verifying defects in the non-adhesive insulation structure of a liquefied gas storage tank according to the present invention utilizes the defect verification system for the non-adhesive insulation structure of a liquefied gas storage tank described above. Detailed descriptions of components identical to the defect verification system for the non-adhesive insulation structure of a liquefied gas storage tank described above are omitted, and the contents regarding the < defect verification system for the non-adhesive insulation structure of a liquefied gas storage tank> described above may be applied without limitation.

[0075] In one embodiment of the present invention, the liquefied gas storage tank (T) may be an independent storage tank, and preferably may be an independent liquefied gas storage tank of IMO Type B.

[0076] Additionally, the above-mentioned liquefied gas storage tank (T) may have an insulation section (50) formed but not yet mounted on the hull, and may have a pending area in which the formation of the insulation structure is partially withheld to exclude interference when mounted on the hull.

[0077] In one embodiment of the present invention, the gas injected into the leakage path may be a dry gas. The dry gas refers to a gas that does not contain water vapor. The dry gas may be dry air or an inert gas, and the inert gas may be pure nitrogen, helium, argon, carbon dioxide, or a mixture thereof, but is not limited thereto, and preferably nitrogen may be used.

[0078] In one embodiment of the present invention, the defect verification step may further include: a step of verifying a defect point of the insulation portion (50) formed on the sheet layer (40) when the pressure in the leakage path is not maintained above a reference pressure; and a step of repairing the verified defect point of the insulation portion (50).

[0079] In one embodiment of the present invention, the pressure within the leakage path can be verified by measuring the pressure at the outlet (300) where the injected gas is discharged.

[0080] In one embodiment of the present invention, the reference pressure of the defect verification step may be atmospheric pressure. The reference pressure is not particularly limited, but since a pressure within the leakage path that is too high can cause damage to the insulation part (50), it may be preferable to use atmospheric pressure as the reference pressure.

[0081] In one embodiment of the present invention, the defect point of the insulation part (50) may be identified by visual inspection or by soapy water inspection. The soapy water inspection can identify the defect point by applying soapy water to the surface or work hold area of ​​the insulation part (50), injecting gas into the leakage path, and checking the point where gas bubbles are formed.

[0082] Meanwhile, in the above defect verification step, if the pressure within the leakage path is maintained above the reference pressure, it can be determined that there is no defect in the insulation part (50). In addition, if the liquefied gas storage tank (T) has a pending area in which the formation of a partial insulation structure is withheld, it can be determined that the airtightness and watertightness of the pending area are maintained.

[0083] Meanwhile, if only micro-defects exist on the insulation section (50), the pressure within the leakage path may be maintained above the reference pressure, making it difficult to confirm the existence of micro-defects. Accordingly, a gas other than oxygen is injected into the leakage path, and the amount of oxygen within the leakage path is checked through the oxygen detector to determine whether micro-defects exist in the insulation section (50).

[0084] The above description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications, changes, and substitutions within the scope of the essential characteristics of the present invention without departing from its nature.

[0085] The embodiments disclosed in this invention and the accompanying drawings are intended to explain, not limit, the technical concept of the invention, and the scope of the technical concept of the invention is not limited by these embodiments and accompanying drawings.

[0086] Furthermore, the scope of protection of the present invention shall be interpreted by the claims below, and all technical ideas within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

[0087] [Explanation of the symbol]

[0088] T: Liquefied gas storage tank

[0089] S: Separation space (leakage path)

[0090] 10: Storage tank outer wall

[0091] 40: Sheet layer

[0092] 50: Insulation section

[0093] 100: Injection part

[0094] 200: Gas storage unit

[0095] 300: Exit section

[0096] 310: Outlet control valve

[0097] 400: Flow meter

[0098] 500: Pressure gauge

Claims

1. As a defect verification system for the non-adhesive insulation structure of liquefied gas storage tanks, An injection part for injecting gas into a leakage path formed in the gap between the outer wall of a liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; A gas storage unit connected to the injection unit and storing gas for injecting into the leakage path; An outlet section for discharging gas injected into the above leakage path; and A pressure gauge for measuring pressure within the above leakage path; is included, A defect verification system that injects gas into the leakage path through the injection port and checks whether the pressure within the leakage path is maintained above a reference pressure to determine whether there is a defect in the insulation portion formed on the sheet layer.

2. In Claim 1, The above liquefied gas storage tank is a defect verification system that is an independent storage tank.

3. In Claim 1, A defect detection system further comprising: a flow meter provided on the injection part and for checking the flow rate of gas injected into the leakage path.

4. In Claim 1, The above pressure gauge is a defect detection system provided on the injection part, the outlet part, or the leakage path.

5. In Claim 1, A defect verification system in which the above reference pressure is atmospheric pressure.

6. In Claim 1, A defect verification system in which the gas injected into the leakage path through the above injection port is a dry gas.

7. As a method for verifying defects in the non-adhesive insulation structure of a liquefied gas storage tank, A step of injecting gas into a leakage path formed in a gap between the outer wall of a liquefied gas storage tank and a sheet layer surrounding the outer wall of the liquefied gas storage tank; and A defect verification method comprising a defect verification step for verifying whether the pressure within the above-mentioned leakage path is maintained above a reference pressure.

8. In Claim 7, A defect verification method in which the above-mentioned liquefied gas storage tank is an independent storage tank.

9. In Claim 8, A defect verification method in which the above-mentioned liquefied gas storage tank is an independent storage tank not mounted on the hull.

10. In Claim 7, In the above defect verification step, if the pressure within the leakage path is not maintained above the reference pressure, A step of identifying a defect point of the insulation portion formed on the above sheet layer; and A defect identification method comprising further a step of repairing the defect point of the insulation identified above.

11. In Claim 10, A defect identification method in which the defect point of the above-mentioned insulation part is identified by visual inspection or soapy water inspection.

12. In Claim 7, A defect verification method in which the reference pressure of the above defect verification step is atmospheric pressure.

13. In Claim 7, A defect verification method in which the gas injected into the above leakage path is a dry gas.

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