Overall test measurement method suitable for main shielding structure of low-temperature liquefied natural gas thin-film tank

Abstract

The invention discloses an integral test measurement method suitable for a main shielding structure of a low-temperature liquefied natural gas thin film tank. The method comprises the following steps of (1) checking before test, (2) standard integral test, (3) airtightness test during completion of a storage tank, (4) integral test after a temporary construction hole is closed, and (5) analysis and checking. According to the measurement method, data related to the overall sealing performance of the main shielding structure of the storage tank are obtained in the mode that the negative pressure difference is established between the heat insulation layer space and the storage tank and the pressure difference change is recorded, and the defects that traditional thin film tank main shielding sealing performance detection is low in work efficiency and insufficient in accuracy are overcome. Meanwhile, the invention provides a systematic detection sequence and steps of inspection before test, standard overall negative pressure test calibration, airtightness test during completion of the storage tank, overall test after closing of a temporary construction hole, analysis and inspection, and provides a technical means for improving the integrity and safety of the shielding structure of the low-temperature liquefied natural gas film tank. The defects of low working efficiency and insufficient accuracy in the prior art are overcome.

Description

Technical Field

[0001] The invention relates to the technical field of liquefied natural gas storage, and in particular to an overall test and measurement method suitable for a main shielding structure of a cryogenic liquefied natural gas membrane tank. Background Art

[0002] With the increasing demand for natural gas in my country, the construction of liquefied natural gas (LNG) receiving stations and their gas storage facilities has entered a period of rapid development. Conventional storage tanks are mainly full-capacity storage tanks, which adopt a prestressed reinforced concrete outer tank structure and a 9% Ni steel inner tank structure, with cold insulation materials filled in the middle. Almost all large-scale LNG storage tanks that have been built and are under construction in China are full-capacity storage tanks. The advantages of this type of storage tank are high safety, small footprint, high integrity, and high technical reliability. However, with the continuous development of large-scale storage tanks, the storage capacity of LNG full-capacity storage tanks has approached its limit due to factors such as the performance of LNG storage tank materials themselves, structural stress performance, and geological conditions. As an important type of LNG storage tank, membrane tanks have the advantages of large space utilization, modular construction, and high construction efficiency compared to full-capacity storage tanks. Due to the advantages of the structural system, theoretically, the maximum tank capacity can exceed the full-capacity tank, which is another important direction for LNG storage tanks to break through the tank capacity limit. At present, only a small number of receiving stations in China have carried out demonstration applications of LNG membrane tanks by referring to foreign proprietary technologies. However, due to the limitations of foreign patented technologies, China has not yet independently mastered the proprietary core technology of membrane storage tanks, and related construction methods have not yet been established.

[0003] The main shielding structure is the main container for LNG loading in membrane tanks. During the construction process, each main shielding structure needs to be connected by butt welding, lap welding, fillet welding, etc., so that it has the air tightness and liquid tightness of LNG, ensuring the safe operation of LNG storage devices at low temperature and normal pressure. However, with the development of large-scale storage tanks, the size of membrane tanks continues to increase, and the welding length during the construction of the main shielding structure is further increased. Whether the welding quality meets the standard is an important factor in ensuring the safety of membrane tanks. At the same time, the thickness of the main shielding of the membrane tank is less than 3mm. If protective measures are not taken during the construction process, it is easy to cause damage to the main shielding structure. The traditional sealing detection of the main shielding of membrane tanks mainly relies on the means of weld detection, which mainly relies on manual judgment, has a certain subjectivity and low detection efficiency.

[0004] Based on this, after the design and construction of the membrane tank was completed and before it was officially put into production, we further explored and proposed an overall test measurement method suitable for the main shielding structure of the cryogenic liquefied natural gas membrane tank to ensure that the membrane tank is safe, stable and reliable during actual operation. Summary of the invention

[0005] The present invention relates to an overall negative pressure test measurement method suitable for the main shielding structure of a cryogenic liquefied natural gas membrane tank. The test method uses a negative pressure differential between the insulation layer space and the storage tank and records the pressure differential change to obtain data on the overall sealing performance of the main shielding structure of the storage tank, solving the shortcomings of low efficiency and insufficient accuracy in the traditional main shielding sealing detection of membrane tanks. At the same time, the present invention proposes a systematic detection sequence and steps of pre-test inspection, standard overall negative pressure test calibration, airtightness test at the completion of the storage tank, overall test after the temporary construction opening is closed, analysis and inspection, providing a technical means for improving the integrity and safety of the shielding structure of the cryogenic liquefied natural gas membrane tank, and the main purpose is to solve the shortcomings of low efficiency and insufficient accuracy in the prior art.

[0006] To achieve the above-mentioned object, the present invention provides a method for measuring the overall negative pressure of the main shielding structure of a cryogenic liquefied natural gas membrane tank, comprising the following steps: (1) pre-test inspection, (2) standard overall test, (3) airtightness test at the completion of the tank, (4) overall test after the temporary construction opening is closed, and (5) analysis and inspection.

[0007] Furthermore, (1) pre-test inspections should be conducted to check the cleanliness of the main shielding structure; the perimeter of temporary construction openings should be sealed; all holes and openings connecting the insulation space to the atmosphere should be sealed; the air tightness of all pipelines should be checked, with emphasis on the air tightness of the pump line and all accessories;

[0008] Furthermore, (1) before the test, the insulation space is filled with ammonia and the dew point should be less than -20°C.

[0009] Furthermore, (1) the pre-test inspection should be carried out to ensure that the primary insulation space and the secondary insulation space are equipped with safety devices. When planning the overall installation plan, it should be ensured that these spaces will not experience accidental overpressure.

[0010] Furthermore, (1) before the test, check that the pressure in the primary insulation space and the secondary insulation space should not exceed 25 mbar. The pump circuit should also be equipped with a set of safety devices to limit the relative pressure to less than 25 mbar in the event of pump damage or operating error.

[0011] Furthermore, (2) the standard overall test should be conducted after the ammonia gas tightness test is completed, and after the scaffolding installation equipment (e.g., scaffolding) is removed, the main shielding structure of the cryogenic liquefied natural gas membrane tank should be tested again under overall negative pressure as a reference for observing the membrane tightness of the main shielding structure.

[0012] Furthermore, (2) the standard overall test shall be performed by evacuating the primary insulation layer space and the secondary insulation layer space, and the vacuum degree range shall be 800mbar+5%.

[0013] Furthermore, (2) the standard overall test should monitor the vacuum operation, and the vacuum change should be as close as possible to the fixed vacuum decay curve, with the time from atmospheric pressure to -800 mbar being 4 hours; when the vacuum degree in the insulation space reaches the above value, the vacuum pump and related pipeline valves are closed and should be stable for 1 hour.

[0014] Furthermore, (2) the standard integral test shall monitor and record the pressure of the primary insulation space and the secondary insulation space, the atmospheric pressure, the atmospheric temperature at at least three different heights in the tank and the external temperature within 24 hours after stabilization. The pressure and temperature shall be recorded continuously. The pressure detection interval shall not exceed 10 minutes within the first hour, the subsequent pressure detection interval shall not be less than 30 minutes, and the temperature recording interval shall not be less than 1 hour.

[0015] Furthermore, (3) the airtightness test at the completion of the tank should be carried out after (2) the standard overall test, scaffolding removal and final tank installation operations. During operations with a high risk of membrane damage, such as the installation and removal of scaffolding and hanging baskets, and hoisting operations, the sealing of the main shielding structure membrane should be monitored through continuous overall airtightness tests.

[0016] Furthermore, (3) the airtightness test of the tank upon completion shall be conducted for no less than two consecutive overall airtightness tests, and the process of the consecutive tests shall be the same as that of the (2) standard overall test.

[0017] Furthermore, (3) for the air tightness test of the tank upon completion, the pressure should be measured and recorded in each successive overall air tightness test, and the pressure value should not be greater than the previous one. The pressure value in the same period of the test, and the pressure value rising speed should not be greater than the rising speed in the same period of the previous test.

[0018] Furthermore, (4) overall test after the temporary construction openings are closed. After all temporary construction openings are closed (concrete wall construction is completed, insulation layer and membrane installation is completed and connected to the installed components, and local sealing test of membrane is completed), the final overall test should be carried out according to standard overall test conditions.

[0019] Further, (5) Analysis and Inspection. During the process of scaffolding removal and tank sealing, the readings recorded during (2) standard test should be plotted as a curve as a reference for the overall test. The readings recorded during (3) test should be compared with the readings of (2) to find out the cause of any abnormal pressure increase and make adjustments or repairs.

[0020] Furthermore, during (5) the analysis and inspection process, the pressure decay rate of the continuous overall test should not be significantly different from the result obtained during (2) the standard test, and it is determined that the main layer membrane has not been damaged and has not caused leakage. This situation continues until the temporary construction hole is closed, and the tank test is successful and the inspection is completed.

[0021] Furthermore, during (5) the analysis and inspection process, if a certain pressure value in the insulation space rises sharply compared to the reading during the standard test (2), it is possible that a leak occurred due to damage to the main shielding structure (during the removal of the scaffolding or the tank closure operation). If this happens, the main insulation layer space and the secondary insulation layer space should be filled with air to restore to atmospheric pressure. During operation, rapid inflation is used for the first 5 hours, and the inflation rate is slowed down in the last 1 hour until atmospheric pressure is reached. At the same time, a visual inspection of the tank wall is carried out starting from the bottom of the tank, and any damage found is repaired, and maintenance is carried out when the insulation layer pressure is at normal pressure. After the maintenance is completed, the penetration and sealing tests should be carried out again.

[0022] Furthermore, the test equipment and tools include vacuum pumps, exhaust pipelines, pressure sensors, stop valves, safety valves or hydraulic protection devices. The vacuum pump should have sufficient output capacity to produce 20m3 of air per 20m3 of air at normal pressure. 2 The measured surface area, the pump displacement should not be less than 1m 3 / h, the vacuum pump should be equipped with a vacuum display. The safety value of the safety valve or hydraulic protection device is 25mbar. The equipment and tools used in the experiment should be inspected by the supervisor before use.

[0023] Beneficial Effects

[0024] (1) The present invention adopts an overall measurement method for the main shielding structure of a cryogenic liquefied natural gas membrane tank. By establishing a negative pressure difference between the insulation layer space and the storage tank and recording the pressure difference change, data on the overall sealing performance of the main shielding structure of the storage tank is obtained, which solves the disadvantage of low construction efficiency when the traditional main shielding sealing test of the membrane tank is carried out for the quality inspection of each weld. The method can significantly reduce the construction and inspection period, and efficiently and reliably provide feedback on the sealing performance of the entire main shielding structure of the membrane tank from the global perspective, with good economic benefits.

[0025] (2) The present invention adopts an overall measurement method suitable for the main shielding structure of a cryogenic liquefied natural gas membrane tank. By evacuating the main insulation layer space and the secondary insulation layer space and using a pressure sensor, the process of the membrane tank air pressure change is quantified with visualized instrument data, thereby avoiding the problem of large errors in manual judgment and improving the credibility and objectivity of the detection results.

[0026] (3) The present invention adopts an overall measurement method for the main shielding structure of a cryogenic liquefied natural gas membrane tank, which proposes a systematic testing procedure including pre-test inspection, standard overall test, airtightness test at the completion of the storage tank, overall test after the temporary construction opening is closed, and analysis and inspection. That is, the sealing of the main shielding structure of the membrane tank is comprehensively tested throughout the construction cycle, providing a better technical means for improving the integrity and safety of the shielding structure of the cryogenic liquefied natural gas membrane tank.

[0027] The present invention adopts an overall measurement method suitable for the main shielding structure of a cryogenic liquefied natural gas membrane tank. It proposes to use a continuous overall airtightness test to detect the main shielding structure membrane during operations such as scaffolding and hanging basket installation and dismantling, and hoisting operations where the main shielding structure has a high risk of damage. That is, it focuses on major risk links that affect the construction of the main shielding structure, thereby ensuring the integrity and safety of the main shielding structure with a thickness of less than 3 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 It is a schematic diagram of a standard overall test in the overall test measurement method according to the present invention.

[0030] Figure 2 It is a schematic diagram of the air tightness test of the storage tank upon completion according to the present invention.

[0031] Figure 3 It is a schematic diagram of the final test after the temporary construction opening is closed according to the present invention.

[0032] Figure 4 This is a structural exploded diagram of the tank wall and bottom of a liquefied natural gas membrane storage tank.

[0033] Figure 5 This is a schematic diagram of the structure of a liquefied natural gas membrane storage tank. DETAILED DESCRIPTION

[0034] Hereinafter, the present invention will be described in detail. Before describing, it should be understood that the terms used in this specification and the appended claims should not be interpreted as being limited to the general meaning and dictionary meaning, but should be interpreted according to the meaning and concept corresponding to the technical aspects of the present invention on the basis of the principle that the inventor is allowed to appropriately define the terms for the best interpretation. Therefore, the descriptions presented here are only preferred examples for illustrative purposes and are not intended to limit the scope of the present invention, so that it should be understood that other equivalents or improvements can be obtained therefrom without departing from the spirit and scope of the present invention.

[0035] Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terms used in the specification and the appended claims should not be interpreted as limited to the general and dictionary meanings, but should be interpreted based on the principle of allowing the inventor to appropriately define the terms for the best interpretation, based on the meaning and concept corresponding to the technical level of the present invention. Therefore, the description herein is only a preferred example for illustrative purposes, and is not intended to limit the scope of the present invention, so it should be understood that other equivalent implementations and modifications can be made without departing from the spirit and scope of the present invention.

[0036] In this document, the terms "include", "including", "have", "contain" or any other similar terms are open conjunctions, which are intended to cover non-exclusive inclusions. For example, a composition or product containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or product. In addition, unless otherwise explicitly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or". For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and A and B are both true (or exist). In addition, in this document, the interpretation of the terms "include", "including", "have", and "contain" should be considered to have been specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as "consisting of" and "consisting essentially of".

[0037] In this article, all features or conditions defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible secondary ranges and individual values ​​within the range, especially integer values. For example, the range description of "1 to 8" should be deemed to have specifically disclosed all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., especially secondary ranges defined by all integer values, and should be deemed to have specifically disclosed individual values ​​such as 1, 2, 3, 4, 5, 6, 7, 8, etc. within the range. Unless otherwise specified, the above interpretation method applies to all contents of the entire present invention, regardless of whether the range is broad or not.

[0038] If the quantity or other numerical value or parameter is expressed as a range, a preferred range or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and the lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0039] like Figure 1 As shown, this patent should carry out a standard overall test after the completion of the ammonia gas tightness test, and will be used as a reference for observing the sealing of the main shielding structure film during the removal of the scaffolding. The standard overall test should be carried out to evacuate the main insulation layer space and the secondary insulation layer space. The vacuum range should be 800mbar+5%, and the vacuum time should be 4 hours. When the vacuum in the insulation layer space reaches the above value, the vacuum pump and related pipeline valves should be closed, and it should be stable for 1 hour. Then record the pressure of the main insulation layer space and the secondary insulation layer space, the atmospheric pressure, the atmospheric temperature at at least three different heights in the tank, and the external temperature within 24 hours after stabilization as required. If the results of the analysis and inspection are unqualified, it may be due to the damage of the main shielding structure that caused the leakage. The main insulation layer space and the secondary insulation layer space should be filled with gas to restore to atmospheric pressure to ensure that the insulation layer pressure is maintained at normal pressure. After the maintenance is completed, the penetration and sealing tests should be carried out again.

[0040] like Figure 2As shown, this patent should monitor the sealing of the main shielding structure membrane at the completion of the tank through continuous overall airtightness tests after the standard overall test and the installation and removal of the scaffolding hanging basket. For the airtightness test at the completion of the tank, the continuous overall airtightness test should not be less than two times, and the process of the continuous test should be the same as the standard overall test in Figure 1. For the airtightness test at the completion of the tank, the pressure should be measured and recorded in each continuous overall airtightness test, and the pressure value should not be greater than the previous one. The pressure value in the same period of the test, the pressure value rising rate should not be greater than the rising rate in the same period of the previous test. If the results of the analysis and inspection are unqualified, it is possible that the leakage is caused by damage to the main shielding structure. The main insulation layer space and the secondary insulation layer space should be injected with gas to restore to atmospheric pressure to ensure that the insulation layer pressure is maintained at normal pressure. After the maintenance is completed, the penetration and sealing tests should be carried out again.

[0041] like Figure 3 As shown, this patent should conduct the final test after the temporary construction openings are closed (concrete wall construction is completed, insulation layer and film installation are completed and connected to the installed parts, and the local sealing test of the film is completed). Test procedure and Figure 1 If the results of the analysis and inspection are unqualified, it is possible that the leakage is caused by damage to the main shielding structure. The main insulation layer space and the secondary insulation layer space should be filled with gas to restore to atmospheric pressure to ensure that the insulation layer pressure is normal. After the maintenance is completed, the penetration and sealing test should be repeated.

[0042] The following examples are only listed as examples of embodiments of the present invention and do not constitute any limitation to the present invention. It can be understood by those skilled in the art that modifications within the scope of the essence and concept of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products.

[0043] Example 1

[0044] The method for measuring the overall negative pressure of the main shielding structure of a cryogenic liquefied natural gas membrane tank comprises the following steps:

[0045] (1) Inspection before the test: Before the test, the insulation space is filled with ammonia and the dew point should be less than -20°C; the main insulation space and the secondary insulation space are equipped with safety devices. When planning the overall installation plan, it should be ensured that these spaces will not experience accidental overpressure. The pressure in the main insulation space and the secondary insulation space should not exceed 25mbar.

[0046] (2) Standard overall test: The standard overall test shall be carried out after the completion of the ammonia gas tightness test. After the scaffolding installation equipment is removed, the main shielding structure of the cryogenic liquefied natural gas membrane tank shall be tested for overall negative pressure again. As a reference for observing the sealing performance of the main shielding structure membrane, the main insulation layer space and the secondary insulation layer space shall be evacuated. The vacuum degree range shall be 800mbar+5%. The vacuum change shall be as close as possible to the fixed vacuum decay curve. The time from atmospheric pressure to -800mbar shall be 4 hours. When the vacuum degree in the insulation layer space reaches the above value, the vacuum pump and related pipeline valves shall be turned off and stabilized for 1 hour. The standard overall test shall monitor and record the pressure of the main insulation layer space and the secondary insulation layer space, the atmospheric pressure, the atmospheric temperature at at least three different heights in the tank and the external temperature within 24 hours after stabilization. The pressure and temperature shall be continuously recorded. The pressure detection time interval shall not be greater than 10 minutes within the first hour, and the subsequent pressure detection time interval shall not be less than 30 minutes. The temperature recording time interval shall not be less than 1 hour.

[0047] (3) Air tightness test upon completion of the tank: After step (2), the scaffolding is removed and the final tank installation is carried out. During the installation and removal of the scaffolding and hanging basket, hoisting operations and other operations with a high risk of membrane damage, the sealing of the main shielding structure membrane should be monitored through continuous overall air tightness tests. The continuous overall air tightness test should not be less than two times. The process of the continuous test should be the same as the standard overall test in step (2). The pressure should be measured and recorded in each continuous overall air tightness test. The pressure value should not be greater than the previous pressure value. The pressure value increase rate during the same period of the test should not be greater than the pressure increase rate during the same period of the previous test.

[0048] (4) Overall test after temporary construction openings are closed: After all temporary construction openings are closed (concrete wall construction is completed, insulation layer and film installation is completed and connected to installed components, and local sealing test of film is completed), the final overall test should be carried out according to standard overall test conditions.

[0049] (5) Analysis and inspection: The pressure decay rate of the continuous overall test should not be significantly different from the result obtained during the standard test in step (2). It is determined that the main layer membrane has not been damaged and has not caused leakage. This situation continues until the temporary construction hole is closed. The tank test is successful and the inspection is completed. At the same time, compared with the reading during the standard test in (2), a certain pressure value in the insulation space rises sharply. It is possible that the leakage is caused by damage to the main shielding structure (during the removal of the scaffolding or the tank closure operation). If this happens, the main insulation layer space and the secondary insulation layer space should be filled with gas to restore to atmospheric pressure. During the operation, fast inflation is used for the first 5 hours, and the inflation rate is slowed down in the last hour until atmospheric pressure is reached. At the same time, the tank wall is visually inspected from the bottom of the tank, and the damaged parts found are repaired. The insulation layer pressure is repaired at normal pressure. After the repair is completed, the penetration and sealing tests should be carried out again.

[0050] Example 2

[0051] A 200,000-cubic-meter membrane storage tank was built at an LNG receiving station. After the tank was built, a tightness test was required. Before the test began, the inspectors first used a dust-free cloth to thoroughly clean the surface of the main shielding structure to remove surface oil, dust and other pollutants. For the 2m×3m temporary construction hole on the tank, the integrity and installation firmness of the surrounding sealing strips were carefully checked.

[0052] To ensure the tightness of the testing environment, the testers used different methods to seal the pipe interfaces on the storage tanks: flange blind plates were used to seal pipe openings of DN200 and above, and rubber plugs were used to seal pipe openings below DN200. All sealing points were additionally sealed with vacuum sealant. The soapy water leak detection method was then used to check the air tightness of all pipelines, focusing on welds, flange connections, pump line joints, valve sealing surfaces and other parts prone to leakage, and leaks were repaired in a timely manner.

[0053] After the inspection, industrial-grade ammonia with a purity of not less than 99.9% was filled into the insulation space. The ammonia dew point was strictly controlled to reach -25°C and the inflation pressure was maintained at 20mbar. To ensure safety, two sets of safety valves with a rated pressure of 25mbar were installed in the main insulation space, two sets of 25mbar hydraulic protection devices were installed in the secondary insulation space, and one set of 25mbar safety valves was added to the pump circuit as backup protection.

[0054] The exhaust volume used for testing is 50m 3 / h, and the ultimate vacuum degree is 0.1Pa. It is equipped with a pressure sensor with a range of 0-1000mbar and an accuracy of 0.1% and a PT100 temperature sensor with an accuracy of ±0.1℃. The data acquisition system with a sampling frequency of 1Hz records various parameters in real time. The standard overall test starts with vacuuming from atmospheric pressure (1013mbar), reduces the pressure to -800mbar within 4 hours, and then maintains a stabilization period of 1 hour. During this period, the system continuously records the pressure of the primary insulation layer, the secondary insulation layer, the atmospheric pressure, and the temperature at three different heights of the bottom, middle and top of the tank and the external ambient temperature.

[0055] During the tank completion air tightness test phase, two consecutive tests were conducted using the same method, with a 24-hour interval between the two tests. The test process and parameter recording requirements are consistent with the standard test, and the pressure rise rate of the second test must not be greater than that of the first test. After the concrete wall construction of the temporary construction opening is completed, the insulation layer and film are installed and welded to the original structure, and the local sealing inspection is qualified, the final airtightness test is carried out.

[0056] Then the pressure rise within 24 hours does not exceed 50mbar, and the pressure change curve is stable without mutation points as the qualification criterion. If abnormality is found, the test is stopped immediately and nitrogen is filled into the insulation layer to restore it to normal pressure. Then the helium mass spectrometer leak detector is used to accurately locate the leak point, and the test is repeated after welding repair.

[0057] Through this complete testing process, the sealing performance of membrane storage tanks can be comprehensively evaluated, providing reliable guarantee for the safe operation of the tanks. After adjusting the relevant parameters, this method can also be applied to the sealing performance testing of membrane storage tanks of different sizes.

[0058] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for measuring the overall negative pressure of the main shielding structure of a cryogenic liquefied natural gas membrane tank, comprising the following steps: (1) Inspection before the test, (2) Standard overall test, (3) Air tightness test when the tank is completed, (4) Overall test after the temporary construction opening is closed, and (5) Analysis and inspection.

2. The method according to claim 1, characterized in that: (1) Before the test, the cleanliness of the main shielding structure should be checked; the periphery of the temporary construction opening should be sealed; all holes and openings connecting the insulation layer space to the atmosphere should be sealed; the air tightness of all pipelines should be checked, with emphasis on the air tightness of the pump line and all accessories; Preferably, (1) before the test, the insulation space is filled with ammonia gas, and the dew point should be less than -20°C; Preferably, (1) the pre-test inspection should be carried out to equip the primary insulation space and the secondary insulation space with safety devices; Preferably, (1) before the test, check that the pressure in the primary insulation space and the secondary insulation space should not exceed 25 mbar, and a set of safety devices is also provided in the pump circuit to limit the relative pressure to within 25 mbar in the event of pump damage or operating error.

3. The method according to claim 1, characterized in that (2) The standard overall test should be carried out after the ammonia gas tightness test is completed. After the scaffolding is removed and the equipment is installed, the main shielding structure of the cryogenic liquefied natural gas membrane tank should be tested for overall negative pressure again as a reference for observing the sealing performance of the membrane of the main shielding structure; Preferably, (2) the standard overall test shall be performed by evacuating the primary insulation layer space and the secondary insulation layer space, and the vacuum range shall be 800mbar+5%; Preferably, (2) the standard overall test should monitor the vacuum operation, and the vacuum change should be as close as possible to the fixed vacuum decay curve, and the time from atmospheric pressure to -800mbar is 4 hours; when the vacuum degree in the insulation space reaches the above value, the vacuum pump and related pipeline valves are turned off, and it should be stable for 1 hour; Preferably, (2) the standard overall test should monitor and record the pressure of the primary insulation space and the secondary insulation space, the atmospheric pressure, the atmospheric temperature at at least three different heights in the tank and the external temperature within 24 hours after stabilization. The pressure and temperature should be recorded continuously. The pressure detection time interval within the first hour should not be greater than 10 minutes, the subsequent pressure detection time interval should not be less than 30 minutes, and the temperature recording time interval should not be less than 1 hour.

4. The method according to claim 1, characterized in that: (3) The airtightness test at the completion of the tank should be carried out after (2) the standard overall test, and the scaffolding removal and final tank installation operations should be carried out; during the installation and removal of the scaffolding and hanging basket, lifting operations and other operations with a high risk of membrane damage, the sealing of the main shielding structure membrane should be monitored through continuous overall airtightness tests; Preferably, (3) the air tightness test of the tank upon completion, the continuous overall air tightness test should not be less than two times, and the process of the continuous test should be the same as (2) the standard overall test; Preferably, (3) during the air tightness test of the tank upon completion, the pressure should be measured and recorded in each successive overall air tightness test. The pressure value should not be greater than the pressure value of the previous test at the same time period, and the pressure value rising speed should not be greater than the pressure rising speed of the previous test at the same time period.

5. The method according to claim 1, characterized in that (4) Overall test after the temporary construction openings are closed: After all temporary construction openings are closed (concrete wall construction is completed, insulation layer and film installation is completed and connected to the installed parts, and local sealing test of the film is completed), the final overall test should be carried out according to standard overall test conditions.

6. The method according to claim 1, characterized in that (5) Analysis and inspection: During the process of scaffolding removal and tank sealing, the readings recorded during the standard test (2) should be plotted as a curve for the overall test. The readings recorded during the test (3) should be compared with the readings in (2) to identify the cause of any abnormal pressure increase and make adjustments or repairs; Preferably, during (5) the analysis and inspection process, the pressure decay rate of the continuous overall test should not be significantly different from the result obtained during (2) the standard test, and it is determined that the main layer membrane has not been damaged and has not caused leakage. This situation continues until the temporary construction hole is closed, and the tank test is successful and the inspection is completed; Preferably, during (5) the analysis and inspection process, if a certain pressure value in the insulation space rises sharply compared with the reading during the standard test (2), it is possible that a leakage has occurred due to damage to the main shielding structure (during the removal of the scaffolding or the tank closure operation). If this happens, the main insulation layer space and the secondary insulation layer space should be injected with air to restore to atmospheric pressure. During the operation, rapid inflation should be used for the first 5 hours and the inflation rate should be slowed down for the last hour until atmospheric pressure is reached. At the same time, a visual inspection of the tank wall should be carried out starting from the bottom of the tank, any damage found should be repaired, and maintenance should be carried out when the insulation layer pressure is at normal pressure. After the maintenance is completed, the penetration and sealing tests should be carried out again.

7. The method according to claim 1, characterized in that The test equipment and tools include vacuum pump, exhaust pipeline, pressure sensor, stop valve, safety valve or hydraulic protection device; the vacuum pump should have sufficient output capacity, every 20m under normal pressure 2 The measured surface area, the pump displacement should not be less than 1m 3 / h, the vacuum pump should be equipped with a vacuum display; The safety value of the safety valve or hydraulic protection device is 25mbar.

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