Method for detecting tightness of secondary shielding layer of LNG (Liquefied Natural Gas) film tank

Abstract

The invention discloses a tightness detection method for a secondary shielding layer of an LNG film tank, the LNG film tank comprises an outer tank body, a heat insulation module, the secondary shielding layer and a top bridge plate, and the heat insulation module, the secondary shielding layer and the top bridge plate are located in the outer tank body. The leakproofness detection method comprises the following steps: after a secondary shielding layer is adhered to a heat insulation module in a secondary shielding space and is cured, performing a first sound test on the secondary shielding space in a preset environment; and after the first sound test meets the standard. And after the top bridge plate is mounted at the adhesion position of the secondary shielding layer and cured, performing a second sound test on the secondary shielding space in the preset environment. According to the sound test, when the secondary shielding space is in a vacuum state, the position of a leakage point of the secondary shielding layer is judged according to howling of gas leakage in the secondary shielding space, the position of the leakage point of the secondary shielding layer can be effectively found out, leakproofness detection and leakage point repairing of the secondary shielding layer of the LNG film tank are achieved, the secondary shielding layer is made to be safe and reliable, and the service life of the LNG film tank is prolonged. And the leakproofness of the secondary shielding layer is ensured.

Description

Technical Field

[0001] This application belongs to the technical field of tightness detection of thin-film tanks, and specifically relates to a method for detecting the tightness of the secondary shielding layer of an LNG thin-film tank. Background Art

[0002] An LNG (Liquefied Natural Gas) thin-film tank includes a concrete outer tank, an insulation module, a secondary shielding layer, a primary shielding layer, and a tank top. A secondary shielding space is formed between the secondary shielding layer and the concrete outer tank, and the insulation module is located within the secondary shielding space. A primary shielding space is formed between the secondary shielding layer and the concrete outer tank and the primary shielding layer, and a tank interior space is formed between the primary shielding layer and the tank top.

[0003] The tank interior space is usually used to store liquefied natural gas. The tightness of the primary shielding layer and the secondary shielding layer directly affects the safety of liquefied natural gas storage. Comparative document CN115406595A discloses a system and method for measuring the overall leakage rate of the primary shielding layer of an onshore storage tank, which effectively measures the overall leakage rate of the primary shielding layer in a safe, economical, and reliable manner. However, since the tank body of the LNG thin-film tank has not been completed and the large and small door openings are not closed, it is impossible to pressurize the tank interior, so this method is not applicable to the tightness detection of the secondary shielding layer. Therefore, how to measure the tightness of the secondary shielding layer has become an urgent problem to be solved. Summary of the Invention

[0004] In order to solve the technical problem of how to measure the tightness of the secondary shielding layer in the related art, this application provides a method for detecting the tightness of the secondary shielding layer of an LNG thin-film tank, characterized in that the LNG thin-film tank includes an outer tank, an insulation module, a secondary shielding layer, and a top bridge plate. The insulation module, the secondary shielding layer, and the top bridge plate are located within the outer tank, and the detection method includes:

[0005] Assembling the secondary shielding layer to the outer tank to enclose and form a secondary shielding space with the outer tank, and the insulation module is located within the secondary shielding space;

[0006] After the secondary shielding layer is adhered and cured on the insulation module, a first sound test is performed on the secondary shielding space in a preset environment;

[0007] After the first sound test meets the standard, assembling the top bridge plate to the adhesion position of the secondary shielding layer located on the insulation module;

[0008] After the top bridge plate is installed and cured at the adhesion position of the secondary shielding layer, a second sound test is performed on the secondary shielding space in the preset environment;

[0009] Among them, the sound test is to determine the leakage point position of the secondary shielding layer according to the whistling sound of gas leakage in the secondary shielding space when the secondary shielding space is in a vacuum state.

[0010] In some embodiments, the first sound test method includes:

[0011] Vacuum the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value;

[0012] Keep the pressure in the secondary shielding space for a first set time period, and within the first set time period, determine the leakage point position of the secondary shielding layer according to the pressure difference in the secondary shielding space and the whistling sound of gas leakage;

[0013] When the leakage point is detected, repair the leakage point;

[0014] Repeat the above steps until the number of leakage points is zero.

[0015] In some embodiments, the step of vacuuming the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value includes:

[0016] Open the vacuum pumping assembly communicated with the secondary shielding space to vacuum the secondary shielding space;

[0017] Judge whether the negative pressure value in the secondary shielding space is below the set negative pressure value according to the pressure gauge communicated with the secondary shielding space;

[0018] When the negative pressure value in the secondary shielding space is below the set negative pressure value, close the vacuum pumping assembly.

[0019] In some embodiments, the vacuum pumping assembly includes a vacuum pump, a vacuum pumping pipeline and an air extraction control valve. The vacuum pump is located outside the outer tank body. One end of the vacuum pumping pipeline is communicated with the secondary shielding space, the other end is communicated with the vacuum pump, and the air extraction control valve is connected in series to the vacuum pumping pipeline.

[0020] In some embodiments, after repeating the above steps until the number of leakage points is zero, it further includes:

[0021] Restore the secondary shielding space to the atmospheric pressure state.

[0022] In some embodiments, the step of restoring the secondary shielding space to the atmospheric pressure state includes:

[0023] Open the pressure relief valve communicated with the secondary shielding space to make the secondary shielding space restore to the atmospheric pressure state.

[0024] In some embodiments, after evacuating the secondary shielding space until the negative pressure value inside the secondary shielding space is below a set negative pressure value, the following steps are included:

[0025] Record the negative pressure value inside the secondary shielding space as the first actual negative pressure value;

[0026] After maintaining the pressure in the secondary shielding space for a first set time period, the following steps are included:

[0027] Record the negative pressure value inside the secondary shielding space as the first pressure-maintaining negative pressure value;

[0028] The step of determining the leakage point position of the secondary shielding layer according to the pressure difference of the secondary shielding space and the whistling sound of gas leakage includes:

[0029] Determine the leakage point position of the secondary shielding layer according to the first actual negative pressure value, the first pressure-maintaining negative pressure value, and the whistling sound of gas leakage inside the secondary shielding space.

[0030] In some embodiments, the step of determining the leakage point position of the secondary shielding layer according to the first actual negative pressure value, the first pressure-maintaining negative pressure value, and the whistling sound of gas leakage inside the secondary shielding space includes:

[0031] Obtain the first actual negative pressure value and the first pressure-maintaining negative pressure value, and determine whether the pressure difference between the first actual negative pressure value and the first pressure-maintaining negative pressure value is within the standard pressure difference range;

[0032] If the pressure difference between the first actual negative pressure value and the first pressure-maintaining negative pressure value is within the standard pressure difference range, determine the leakage point position of the secondary shielding layer according to the whistling sound of gas leakage inside the secondary shielding space.

[0033] In some embodiments, the second sound test method includes:

[0034] Evacuate the secondary shielding space until the negative pressure value inside the secondary shielding space is below a set negative pressure value;

[0035] Maintain the pressure in the secondary shielding space for a second set time period. During the second set time period, determine the leakage point position of the secondary shielding layer according to the pressure difference of the secondary shielding space and the whistling sound of gas leakage;

[0036] When the leakage point is detected, repair the leakage point;

[0037] Repeat the above steps until the leakage point position is zero;

[0038] Restore the secondary shielding space to the atmospheric pressure state.

[0039] In some embodiments, after evacuating the secondary shielding space until the negative pressure value inside the secondary shielding space is below a set negative pressure value, the following steps are included:

[0040] Record the negative pressure value inside the secondary shielding space as the second actual negative pressure value;

[0041] After maintaining the pressure inside the secondary shielding space for a second set time period, the following steps are included:

[0042] Record the negative pressure value inside the secondary shielding space as the second pressure-maintaining negative pressure value;

[0043] Judge the leakage point position of the secondary shielding layer according to the second actual negative pressure value, the second pressure-maintaining negative pressure value, and the whistling sound of gas leakage inside the secondary shielding space.

[0044] According to the method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank provided by the present application, the LNG thin-film tank includes an outer tank body, an adiabatic module, a secondary shielding layer, and a top bridge plate. The adiabatic module, the secondary shielding layer, and the top bridge plate are located inside the outer tank body. The tightness detection method includes: assembling the secondary shielding layer to the outer tank body to form a secondary shielding space surrounded by the outer tank body, and the adiabatic module is located inside the secondary shielding space. After the secondary shielding layer is adhered and cured on the adiabatic module, a first sound test is carried out on the secondary shielding space in a preset environment. After the first sound test meets the standard, the top bridge plate is assembled to the adhesion position of the secondary shielding layer on the adiabatic module. After the top bridge plate is installed and cured at the adhesion position of the secondary shielding layer, a second sound test is carried out on the secondary shielding space in a preset environment. The sound test is to judge the leakage point position of the secondary shielding layer according to the whistling sound of gas leakage inside the secondary shielding space when the secondary shielding space is in a vacuum state, which can effectively find out the leakage point position of the secondary shielding layer, realize the tightness detection of the secondary shielding layer of the LNG thin-film tank, repair the leakage point, make the secondary shielding layer safe and reliable, and ensure the tightness of the secondary shielding layer. Description of the Drawings

[0045] Figure 1 It is a schematic structural diagram of an LNG thin-film tank in one or more embodiments of the present application;

[0046] Figure 2 It is a schematic flow chart of the method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank in one or more embodiments of the present application;

[0047] Figure 3 It is a schematic flow chart of the first sound test method in one or more embodiments of the present application;

[0048] Figure 4 It is a time curve graph of pumping and discharging vacuum inside the secondary shielding space of the sound test in one or more embodiments of the present application;

[0049] Figure 5 The pressure change curve within the secondary shielding space in one or more embodiments of the present application.

[0050] Explanation of reference numerals:

[0051] 10. Outer tank body; 20. Secondary shielding layer; 40. Secondary shielding space; 50. Vacuum pumping assembly; 51. Vacuum pump; 52. Air extraction control valve; 53. Vacuum pumping pipeline; 60. Pressure gauge; 70. Pressure relief valve; 80. Primary shielding layer; 90. Tank top. Detailed implementation manners

[0052] In order to enable those skilled in the art in the technical field to which the present application pertains to more clearly understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0053] Please refer to Figure 1 , the LNG thin-film tank includes an outer tank body 10, an insulation module (not shown in the figure), a primary shielding layer 80, a secondary shielding layer 20, a top bridge plate (not shown in the figure), and a tank top 90. It should be noted that the primary shielding layer 80 in the figure is not completed, and the tightness of the secondary shielding layer 20 needs to be detected. After repairing the leakage points of the secondary shielding layer 20, the construction of the primary shielding layer 80 is carried out. The outer tank body 10 and the tank top 90 are usually made of concrete. The primary shielding layer 80 is usually a 304L stainless steel corrugated plate with a thickness of 1.2 mm and having longitudinal and transverse grooves. The secondary shielding layer 20 is usually a three-layer composite sheet of two layers of fiberglass cloth and one layer of aluminum foil. Above 5 meters in the vertical direction inside the LNG thin-film tank, the primary shielding layer 80 is hermetically connected to the outer tank body 10 to form a primary shielding space (not shown in the figure). Below 5 meters in the vertical direction inside the LNG thin-film tank, the secondary shielding layer 20 is hermetically connected to the outer tank body 10 to form a secondary shielding space 40. The insulation module is located inside the secondary shielding space 40. The insulation module can be polyurethane foam or the like, which can be set according to actual needs and is not limited in the present application. The top bridge plate is assembled to the adhesion positions between different component sheets of the secondary shielding layer 20 located on the insulation module and the adhesion positions between the secondary shielding layer 20 and the stainless steel inside the outer tank body 10; a primary shielding space is formed between the secondary shielding layer 20 and the primary shielding layer 80; the primary shielding layer 80 is hermetically connected to the tank top 90 to form the internal space of the tank.

[0054] The space inside the tank is usually used to store liquefied natural gas. The tightness of the primary shielding layer 80 and the secondary shielding layer 20 directly affects the safety of liquefied natural gas storage. The comparative document CN115406595A discloses a system and method for measuring the overall leakage rate of the primary shielding layer of an onshore storage tank, which can effectively measure the overall leakage rate of the primary shielding layer 80 in a safe, economical and reliable manner. However, since the tank body of the LNG membrane tank has not been completed and the large and small door openings are not closed, it is impossible to pressurize the inside of the tank, so this method is not applicable to the tightness detection of the secondary shielding layer 20. Therefore, how to measure the tightness of the secondary shielding layer 20 has become an urgent problem to be solved.

[0055] To solve the technical problem of how to measure the tightness of the secondary shielding layer 20 in the related art, this application provides a method for detecting the tightness of the secondary shielding layer of an LNG membrane tank. The method for detecting the tightness of the secondary shielding layer of an LNG membrane tank is applied to a tightness detection system, and the tightness detection system is used to measure the tightness of the secondary shielding layer 20 of the LNG membrane tank. Please refer to Figure 1 , the tightness detection system includes a vacuum pumping assembly 50, a gas pressure monitoring assembly (not shown in the figure), and a pressure relief valve 70.

[0056] The vacuum pumping assembly 50 includes a vacuum pump 51, a vacuum pumping pipeline 53, and a pumping control valve 52. The vacuum pump 51 is located outside the outer tank body 10. One end of the vacuum pumping pipeline 53 communicates with the secondary shielding space 40, and the other end communicates with the vacuum pump 51. An embedded pipeline is placed in the concrete wall of the outer tank body 10, and the embedded pipeline communicates with the secondary shielding space 40. The side of the vacuum pumping pipeline 53 away from the vacuum pump 51 can communicate with the embedded pipeline to achieve communication with the secondary shielding space 40. The vacuum pump 51 communicates with the secondary shielding space 40 through the vacuum pumping pipeline 53 and the embedded pipeline, and the vacuum pump 51 can extract the gas in the secondary shielding space 40 to make the secondary shielding space 40 in a vacuum state. The pumping speed of the vacuum pump 51 can be such that at least a pumping speed of 1 m 2 per hour can be guaranteed for a tank surface of 20 m 3 under atmospheric pressure, so as to effectively control the pumping time of the secondary shielding space 40. The pumping speed can also be set according to actual needs, and this application does not make any limitations.

[0057] The pumping control valve 52 is connected in series to the vacuum pumping pipeline 53 and communicates with the vacuum pumping pipeline 53, and is used to control the opening and closing of the vacuum pump 51, and can accurately control the vacuum pumping time of the secondary shielding layer 20. In some embodiments, the pumping control valve 52 can be arranged between the end of the vacuum pumping pipeline 53 away from the vacuum pump 51 and the secondary shielding layer 20, and the vacuum pumping pipeline 53 communicates with the secondary shielding space 40 through the pumping control valve 52. The pumping control valve 52 can also be arranged between the end of the vacuum pumping pipeline 53 close to the vacuum pump 51 and the vacuum pump 51, and the vacuum pump 51 communicates with the vacuum pumping pipeline 53 through the pumping control valve 52.

[0058] The gas pressure monitoring component includes a pressure gauge 60, which is installed on the vacuum pumping pipeline 53 and located between the outer tank 10 and the air extraction control valve 52. When the vacuum pump 51 extracts the gas in the secondary shielding space 40, the pressure gauge 60 can monitor the pressure change in the secondary shielding space 40 in real time. In some embodiments, the pressure gauge 60 can also be installed on the outer tank 10 and communicated with the secondary shielding space 40, and the installation position of the pressure gauge 60 can be set according to actual needs, which is not limited in this application.

[0059] The pressure relief valve 70 is installed on the outer tank 10 and communicated with the secondary shielding space 40. When the pressure relief valve 70 is opened, the secondary shielding space 40 can be communicated with the outside world, and the pressure in the secondary shielding space 40 can be restored to the atmospheric pressure state. When the pressure relief valve 70 is closed, the vacuum pump 51 can be started to extract the vacuum of the secondary shielding space 40, so that the secondary shielding space 40 is in a vacuum state.

[0060] Please refer to Figure 2 , the method for detecting the tightness of the secondary shielding layer of the LNG thin film tank includes:

[0061] S102. Assemble the secondary shielding layer 20 to the outer tank 10 to form a secondary shielding space 40 surrounded by the outer tank 10, and the insulation module is located in the secondary shielding space 40.

[0062] In the preparatory stage of detecting the tightness of the secondary shielding layer 20, connect the vacuum pump 51, the vacuum pumping pipeline 53, the air extraction control valve 52, the pressure gauge 60 and the pressure relief valve 70 in place to build a detection system for the tightness of the secondary shielding layer.

[0063] Assemble the insulation module into the outer tank 10, and the secondary shielding layer 20 adheres to the side wall of the insulation module away from the outer tank 10 and adheres to the stainless steel inside the outer tank, so that the secondary shielding layer 20 and the outer tank 10 surround to form a secondary shielding space 40, so that the insulation module can be located in the secondary shielding space 40, which can improve the heat preservation performance of the LNG thin film tank.

[0064] It should be noted that the construction of the detection system for the tightness of the secondary shielding layer can be completed before the secondary shielding layer 20 adheres to the insulation module, or after the secondary shielding layer 20 adheres to the insulation module, which can be set according to actual needs and is not limited in this application.

[0065] S104. After the secondary shielding layer adheres to and cures on the insulation module, conduct the first sound test on the secondary shielding space in a preset environment.

[0066] Before the tightness test of the secondary shielding layer 20, after the secondary shielding layer 20 is adhered and cured on the adiabatic module, it needs to be left standing for a first set period of time to make the adhesion positions of the secondary shielding layer 20 (including the adhesion positions between different component sheets of the secondary shielding layer 20 and the adhesion positions between the secondary shielding layer and the stainless steel on the outer tank 10) firmly connected. The first set period of time can be 24 hours, or it can be set according to the actual situation, which is not limited in this application.

[0067] On the premise of ensuring the firmness of the adhesion positions of the secondary shielding layer 20, use a vacuum pump 51 to evacuate the secondary shielding space 40 in a preset environment to make the secondary shielding space 40 in a vacuum state, and judge the leakage point position of the secondary shielding layer 20 according to the whistling sound of gas leakage in the secondary shielding space 40.

[0068] The preset environment can be a quiet environment, which can prevent noise from affecting the listening of the whistling sound. The quiet environment can be an environment where other operations around the LNG thin-film tank stop at night and there is no influence of other operation noises. In some embodiments, the quiet environment can also be an artificially created low-decibel noise environment, and the noise decibel value of the environment can be based on the actual need to clearly hear the whistling sound of gas leakage, which is not limited in this application.

[0069] The sound test is to judge the leakage point position of the secondary shielding layer 20 according to the whistling sound of gas leakage in the secondary shielding space 40 when the secondary shielding space 40 is in a vacuum state. Since a strong pressure difference will be generated at the leakage point position on the secondary shielding layer 20, then when there is a leakage point on the secondary shielding layer 20, a large whistling sound will be generated. In this way, when a person listens in a quiet environment, the position point of the whistling sound can be quickly judged, so as to determine the leakage point on the secondary shielding layer 20. In order to ensure the accuracy of the leakage point position on the secondary shielding layer 20, the person can listen at multiple different position points inside the outer tank 10 to comprehensively confirm the leakage point position.

[0070] It should be noted that the leakage point position can appear at the adhesion position between the secondary shielding layer 20 and the outer tank 10, or at the adhesion position between different component sheets of the secondary shielding layer 20. When a leakage point is detected, repair the leakage point to ensure the tightness of the secondary shielding layer 20. Until the number of leakage point positions detected by the sound test in the secondary shielding space 40 is zero, it can be determined that the first sound test meets the tightness standard of the secondary shielding space 40.

[0071] S106. After the first sound test meets the standard, assemble the top bridge plate to the adhesion position of the secondary shielding layer on the adiabatic module.

[0072] After the first sound test meets the tightness standard of the secondary shielding space 40, in order to improve the connection stability between the secondary shielding layer 20 and the outer tank 10, the top bridge plate is assembled at the adhesion positions between different component sheets of the secondary shielding layer 20 and at the adhesion positions between the secondary shielding layer and the stainless steel on the outer tank 10, so as to improve the adhesion strength between different component sheets of the secondary shielding layer 20 and the adhesion strength between the secondary shielding layer 20 and the outer tank 10, and thus the tightness of the secondary shielding layer 20 can also be improved.

[0073] S108. After the top bridge plate is installed and cured at the adhesion position of the secondary shielding layer, a second sound test is carried out on the secondary shielding space in the preset environment.

[0074] After the top bridge plate is installed and cured, it is left standing for a second set time period to make the top bridge plate firmly connected to the secondary shielding layer 20 and the outer tank 10. The second set time period can be 24 hours, or it can be set according to the actual situation, and the present application does not make a limitation.

[0075] Use a vacuum pump 51 to evacuate the secondary shielding space 40 to make the secondary shielding space 40 in a vacuum state, and judge the leakage point position of the secondary shielding layer 20 according to the whistling sound of gas leakage in the secondary shielding space 40 in a quiet environment.

[0076] When a leakage point is detected, repair the leakage point to ensure the tightness of the secondary shielding layer 20. Until the position of the leakage point detected by the sound test in the secondary shielding space 40 is zero, it can be determined that the tightness of the secondary shielding space 40 meets the standard. When no leakage point is detected, it can be directly determined that the tightness of the secondary shielding space 40 meets the standard.

[0077] Through two sound tests, the leakage point position of the secondary shielding layer 20 can be accurately found, and the tightness detection of the secondary shielding layer 20 of the LNG thin-film tank can be realized. Repair the leakage point to make the secondary shielding layer 20 safe and reliable and ensure the tightness of the secondary shielding space 40.

[0078] The first sound test method includes:

[0079] S202. Evacuate the secondary shielding space 40 until the negative pressure value in the secondary shielding space 40 is below the set negative pressure value.

[0080] In the preparatory stage of the first sound test, connect the vacuum pump 51 to the embedded pipeline in the outer tank 10 through a vacuum pipeline, and connect the air extraction control valve 52 in series to the vacuum pipeline. The pressure gauge 60 and the pressure relief valve 70 are respectively connected to the secondary shielding space 40.

[0081] S202 specifically includes turning on the vacuum pump 51 connected to the secondary shielding space 40 to evacuate the secondary shielding space 40.

[0082] Judge whether the negative pressure value in the secondary shielding space 40 is below the set negative pressure value according to the pressure gauge 60 connected to the secondary shielding space 40. The set negative pressure value can usually be -500 mbarg, so that under the pressure difference environment formed between the secondary shielding space 40 and the external environment, the whistling sound of gas leakage can be clearly heard.

[0083] When the negative pressure value in the secondary shielding space 40 is below the set negative pressure value, turn off the vacuum pump 51.

[0084] S204. Record the negative pressure value in the secondary shielding space 40 as the first actual negative pressure value.

[0085] S206. Keep the pressure in the secondary shielding space 40 for the first set time period.

[0086] S208. Record the negative pressure value in the secondary shielding space 40 as the first pressure-holding negative pressure value.

[0087] S210. Within the first set time period, judge the position of the leakage point of the secondary shielding layer 20 according to the pressure difference in the secondary shielding space 40 and the whistling sound of gas leakage.

[0088] S210 specifically includes judging the position of the leakage point of the secondary shielding layer 20 according to the first actual negative pressure value, the first pressure-holding negative pressure value and the whistling sound of gas leakage in the secondary shielding space 40.

[0089] Specifically, obtain the first actual negative pressure value and the first pressure-holding negative pressure value, and judge whether the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is within the standard pressure difference range.

[0090] If the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is within the standard pressure difference range, judge the position of the leakage point of the secondary shielding layer 20 according to the whistling sound of gas leakage in the secondary shielding space 40.

[0091] It should be noted that when the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is not within the standard pressure difference range, it can be considered that there is a leakage point on the secondary shielding layer 20 or the pipeline connecting the secondary shielding space 40 leaks, or there may only be a leakage point on the secondary shielding layer 20, or there may only be a leakage in the pipeline connecting the secondary shielding space 40. Therefore, when the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is within the standard pressure difference range, the position of the leakage point of the secondary shielding layer 20 can be judged according to the whistling sound.

[0092] S212. When a leakage point is detected, repair the leakage point.

[0093] S214. Repeat S202 to S212 until the position of the leakage point of the secondary shielding layer 20 is zero, indicating that the tightness of the secondary shielding space 40 meets the standard.

[0094] S216. Restore the secondary shielding space 40 to atmospheric pressure.

[0095] Specifically, S216 includes: opening the pressure relief valve 70 communicating with the secondary shielding space 40 to restore the secondary shielding space 40 to atmospheric pressure.

[0096] In order to effectively detect the location of the leakage point on the secondary shielding layer 20, S202 to S214 in the first sound test method need to be repeated multiple times.

[0097] Please refer to Figures 3 to 5 , taking the first sound test method in this application repeated three times as an example for expansion:

[0098] Step 1: Use the vacuum pump 51 to evacuate the secondary shielding space 40 to a negative pressure value below -500 mbarg within 1 hour, stop evacuating, and record the first negative pressure value (which can be understood as the first actual negative pressure value) as -501.2 mbarg.

[0099] Step 2: Keep the pressure for within 30 minutes. After the pressure holding ends, record the second negative pressure value (which can be understood as the first pressure holding negative pressure value) as -490.9 mbarg. During the pressure holding time, listen for whistling sounds in the secondary shielding space 40 to determine the location of the leakage point on the secondary shielding layer 20. When a leakage point is detected, repair the leakage point and then repeat Step 1; when no leakage point is detected, perform Step 3.

[0100] Step 3: Evacuate again. Make the secondary shielding space 40 reach a negative pressure value below -500 mbarg again within 10 minutes, stop evacuating, and record the third negative pressure value as -501.5 mbarg. Then keep the pressure for within 30 minutes. After the pressure holding ends, record the fourth negative pressure value as -492.6 mbarg. During the pressure holding time, listen for whistling sounds in the secondary shielding space 40 to determine the location of the leakage point on the secondary shielding layer 20. When a leakage point is detected, repair the leakage point and then repeat Step 1; when no leakage point is detected, perform Step 4.

[0101] Step 4: Evacuate for the third time. Make the secondary shielding space 40 reach a negative pressure value below -500 mbarg again within 10 minutes, stop evacuating, and record the fifth negative pressure value as -500.3 mbarg. Then keep the pressure for within 1 hour. After the pressure holding ends, record the sixth negative pressure value as -482.6 mbarg. During the pressure holding time, listen for whistling sounds in the secondary shielding space 40 to determine the location of the leakage point on the secondary shielding layer 20. When a leakage point is detected, repair the leakage point and then repeat Step 1. When no leakage point is detected, perform Step 5.

[0102] Step 5: Open the pressure relief valve 70 to restore the secondary shielding space 40 to atmospheric pressure within 1 hour.

[0103] During the sound test, the secondary shielding space 40 is evacuated by a vacuum pump 51, and the negative pressure value inside the secondary shielding space is measured by a pressure gauge 60.

[0104] It should be noted that the first negative pressure value, the third negative pressure value, and the fifth negative pressure value can be understood as the first actual negative pressure value, and the second negative pressure value, the fourth negative pressure value, and the sixth negative pressure value can be understood as the first pressure-holding negative pressure value.

[0105] Due to the large volume of the LNG thin-film tank, the secondary shielding space 40 is also relatively large. After the first evacuation of the secondary shielding space 40, due to insufficient air flow, there is a deviation between the negative pressure value shown on the pressure gauge 60 and the actual negative pressure value. By evacuating and pressure-holding the secondary shielding space 40 for the second and third times, the negative pressure value is closer to the actual value, which is beneficial for comparing the pressure curve.

[0106] Figure 5 It is a pressure change curve graph of the secondary shielding space in one or more embodiments of the present application. The pressure difference in each vacuum-holding stage of the secondary shielding space 40 can be obtained from the graph. Due to the different materials of the secondary shielding layer 20, the pressure drop of the secondary shielding space 40 is also different. Therefore, it is impossible to determine the leakage of the secondary shielding layer 20 only through the pressure difference value. In this case, it is necessary to judge the leakage point position of the secondary shielding layer through the whistling sound of gas leakage in the secondary shielding space 40 during the sound test. It should be noted that when there is a large change in the pressure value during the pressure-holding stage, it is necessary to detect and eliminate the leakage of the connecting pipeline to the LNG thin-film tank before judging the leakage point position of the secondary shielding layer according to the whistling sound of gas leakage in the secondary shielding space 40.

[0107] After the first sound test, the number of leakage points of the secondary shielding layer 20 is zero, and the tightness of the secondary shielding space 40 is reliable. In order to improve the connection stability between the secondary shielding layer 20 and the outer tank body 10, the top bridge plate is assembled at the connection position between the secondary shielding layer 20 and the outer tank body 10 to improve the connection strength between the secondary shielding layer 20 and the outer tank body 10, so that the secondary shielding layer 20 and the outer tank body 10 are firmly connected, and further the tightness of the secondary shielding space 40 can be improved.

[0108] After assembling the top bridge plate at the connection position between the secondary shielding layer 20 and the outer tank body 10, a second sound test is carried out on the secondary shielding space 40. The second sound test includes:

[0109] S302: Evacuate the secondary shielding space 40 until the negative pressure value inside the secondary shielding space 40 is below the set negative pressure value.

[0110] S304: Record the negative pressure value inside the secondary shielding space 40 as the second actual negative pressure value.

[0111] S306: Hold the pressure in the secondary shielding space 40 for a second set time period.

[0112] S308. Record the negative pressure value in the secondary shielding space 40 as the second pressure-holding negative pressure value.

[0113] S310. Within the second set time period, determine the location of the leakage point of the secondary shielding layer 20 based on the pressure difference within the secondary shielding space 40 and the whistling sound of gas leakage.

[0114] Specifically, S310 includes determining the location of the leakage point of the secondary shielding layer 20 based on the second actual negative pressure value, the second pressure-holding negative pressure value, and the whistling sound of gas leakage within the secondary shielding space 40.

[0115] Specifically, obtain the second actual negative pressure value and the second pressure-holding negative pressure value, and determine whether the pressure difference between the second actual negative pressure value and the second pressure-holding negative pressure value is within the standard pressure difference range.

[0116] If the pressure difference between the second actual negative pressure value and the second pressure-holding negative pressure value is within the standard pressure difference range, determine the location of the leakage point of the secondary shielding layer 20 based on the whistling sound of gas leakage within the outer tank body 10.

[0117] S312. When a leakage point is detected, repair the leakage point.

[0118] S314. Repeat S302 to S312 until the number of leakage points of the secondary shielding layer 20 is zero, indicating that the tightness of the secondary shielding space 40 meets the standard.

[0119] S316. Restore the secondary shielding space 40 to the atmospheric pressure state.

[0120] Specifically, S316 includes: opening the pressure relief valve 70 communicating with the secondary shielding space 40 to restore the secondary shielding space 40 to the atmospheric pressure state.

[0121] In order to effectively detect the location of the leakage point on the secondary shielding layer 20, S302 to S314 in the second sound test method need to be repeated multiple times.

[0122] The process of the second sound test in this application is the same as that of the first sound test. Please refer to the above steps 1 to 5, and details are not described here.

[0123] Through the two sound tests, the location of the leakage point of the secondary shielding layer 20 can be accurately found, realizing the tightness detection of the secondary shielding layer 20 of the LNG thin-film tank. Repair the leakage point to improve the safety and reliability of the secondary shielding layer 20 and ensure the tightness of the secondary shielding space 40.

[0124] In this application, unless otherwise clearly defined or limited, the first feature being "on" or "under" the second feature may include direct contact between the first and second features, or may include the first and second features not being in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is less than that of the second feature.

[0125] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0126] In this application, unless otherwise clearly defined or limited, terms such as "connection" and "fixation" shall be understood in a broad sense. For example, "fixation" may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0127] In addition, in this application, descriptions such as "first" and "second" are only for descriptive purposes, and should not be construed as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of this application, the meaning of "a plurality of" is two or more, unless otherwise clearly and specifically defined.

[0128] Although the embodiments of this application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of this application, and the scope of this application is defined by the claims and their equivalents.

Claims

1. A method for detecting the tightness of the secondary shielding layer of an LNG membrane tank, characterized in that, The LNG thin-film tank includes an outer tank body, an adiabatic module, a secondary shielding layer and a top bridge plate. The adiabatic module, the secondary shielding layer and the top bridge plate are located inside the outer tank body. The detection method includes: Assembling the secondary shielding layer to the outer tank body to form a secondary shielding space surrounded by the outer tank body, and the adiabatic module is located in the secondary shielding space; After the secondary shielding layer is adhered and cured on the adiabatic module, a first sound test is performed on the secondary shielding space in a preset environment; After the first sound test meets the standard, the top bridge plate is assembled to the adhesion position of the secondary shielding layer on the adiabatic module; After the top bridge plate is installed and cured at the adhesion position of the secondary shielding layer, a second sound test is performed on the secondary shielding space in the preset environment; Wherein, in the sound test, when the secondary shielding space is in a vacuum state, the leakage point position of the secondary shielding layer is judged according to the whistling sound of gas leakage in the secondary shielding space.

2. The tightness detection method for the secondary shielding layer of the LNG thin-film tank according to claim 1, characterized in that, The first sound test method includes: Vacuumizing the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value; Maintaining the pressure in the secondary shielding space for a first set time period. During the first set time period, the leakage point position of the secondary shielding layer is judged according to the pressure difference in the secondary shielding space and the whistling sound of gas leakage; When the leakage point is detected, repair the leakage point; Repeat the above steps until the number of leakage points is zero.

3. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 2, wherein, The step of vacuumizing the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value includes: Opening the vacuumizing component communicated with the secondary shielding space to vacuumize the secondary shielding space; Judging whether the negative pressure value in the secondary shielding space is below the set negative pressure value according to the pressure gauge communicated with the secondary shielding space; When the negative pressure value in the secondary shielding space is below the set negative pressure value, closing the vacuumizing component.

4. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 3, characterized in that, The vacuumizing component includes a vacuum pump, a vacuumizing pipeline and an air extraction control valve. The vacuum pump is located outside the outer tank body. One end of the vacuumizing pipeline is communicated with the secondary shielding space, and the other end is communicated with the vacuum pump. The air extraction control valve is connected in series to the vacuumizing pipeline.

5. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 2, wherein, After repeating the above steps until the number of leakage points is zero, it further includes: Restoring the secondary shielding space to the atmospheric pressure state.

6. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 5, wherein The step of restoring the secondary shielding space to the atmospheric pressure state includes: Opening the pressure relief valve communicated with the secondary shielding space to restore the secondary shielding space to the atmospheric pressure state.

7. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 2, characterized in that, After vacuumizing the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value, it includes: Recording the negative pressure value in the secondary shielding space as the first actual negative pressure value; After maintaining the pressure in the secondary shielding space for the first set time period, it includes: Recording the negative pressure value in the secondary shielding space as the first pressure-maintaining negative pressure value; The step of judging the leakage point position of the secondary shielding layer according to the pressure difference in the secondary shielding space and the whistling sound of gas leakage includes: Judge the leakage point position of the secondary shielding layer according to the first actual negative pressure value, the first pressure-holding negative pressure value and the whistling sound of gas leakage in the secondary shielding space.

8. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 7, characterized in that, The judging of the leakage point position of the secondary shielding layer according to the first actual negative pressure value, the first pressure-holding negative pressure value and the whistling sound of gas leakage in the secondary shielding space includes: Obtain the first actual negative pressure value and the first pressure-holding negative pressure value, and judge whether the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is within the standard pressure difference range; If the pressure difference between the first actual negative pressure value and the first pressure-holding negative pressure value is within the standard pressure difference range, judge the leakage point position of the secondary shielding layer according to the whistling sound of gas leakage in the secondary shielding space.

9. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 1, wherein, The second sound test method includes: Vacuum the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value; Keep the pressure in the secondary shielding space for a second set time period, and judge the leakage point position of the secondary shielding layer according to the pressure difference and the whistling sound of gas leakage in the secondary shielding space during the second set time period; When the leakage point is detected, repair the leakage point; Repeat the above steps until the leakage point position is zero; Restore the secondary shielding space to the atmospheric pressure state.

10. The method for detecting the tightness of the secondary shielding layer of the LNG thin-film tank according to claim 2, characterized in that, After vacuuming the secondary shielding space until the negative pressure value in the secondary shielding space is below the set negative pressure value, it includes: Record the negative pressure value in the secondary shielding space as the second actual negative pressure value; After keeping the pressure in the secondary shielding space for the second set time period, it includes: Record the negative pressure value in the secondary shielding space as the second pressure-holding negative pressure value; Judge the leakage point position of the secondary shielding layer according to the second actual negative pressure value, the second pressure-holding negative pressure value and the whistling sound of gas leakage in the secondary shielding space.

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