A gas cylinder air tightness testing device and method for low temperature environment

Abstract

The present invention relates to a gas cylinder air tightness test device and method for use in a low-temperature environment, the test device comprising: a helium gas cylinder and a cryogenic medium tank; a filter, a first stop valve, a booster pump, a first safety valve, a first pressure gauge, a second stop valve, a first gas precooler, a second gas precooler, a cooling coil and a gas cylinder to be tested, and a gas outlet and a gas inlet forming a circulation loop in the second gas precooler, which are sequentially connected to the helium gas cylinder through a metal hose; a third stop valve, a cryogenic pump and a cryogenic medium input port, a cryogenic tank connected to the cryogenic medium input port, a cold screen fixedly connected to the cryogenic tank, a temperature gauge connected to the cryogenic tank, a second pressure gauge and a second safety valve. The test device of the present invention is simple and easy to design, does not need to be equipped with a large cooling device, has good process feasibility, low implementation cost, high heat exchange efficiency, and high accuracy of test results.

Description

Technical Field

[0001] The invention belongs to the technical field of air tightness testing, and in particular relates to an air tightness testing device and method for a gas cylinder applied in a low-temperature environment. Background Art

[0002] Helium is a special gas with a boiling point of -268.9℃. It can be used as a heat transfer medium, a cooling and inert protective gas, and a leak detection medium. It is widely used in low-temperature superconductivity, medical equipment, nuclear power equipment, and aerospace engineering. For example, in the aerospace field, helium is usually stored in high-pressure gas cylinders, which are placed in fuel tanks and used as pressurized gas or replacement gas. The working pressure of the gas cylinder is about 20-35MPa, and the working pressure of the fuel tank is about 0.1-0.8MPa.

[0003] With the rapid development of aerospace technology, aerospace systems have higher and higher requirements for cylinder pressure and container characteristic parameters. Compared with all-metal cylinders, composite gas cylinders have the advantages of light weight, high structural efficiency, good fatigue resistance and high safety and reliability. They have obvious advantages in structural optimization and weight reduction. Application in aerospace systems is one of the future development trends. Before the actual application of composite gas cylinders, they must first pass the air tightness test under simulated working conditions. For room temperature and normal pressure environment, the air tightness test of gas cylinders can usually be achieved by liquid coating method or water pressure test. However, for the above working conditions, especially the air tightness test of gas cylinders at liquid oxygen temperature, visual inspection or water filling cannot meet the test requirements. In the prior art, the air tightness test of low-temperature environment gas cylinders usually uses high-pressure nitrogen cylinders or high-pressure liquid nitrogen cryogenic cylinders as the gas source, which are connected to the medium input port of the gas cylinder to be tested through a pipeline. After directly pressurizing the gas cylinder to the working pressure, the pressure is maintained for about 3 minutes to see if the pressure gauge drops. The existing technology does not consider that when the gas cylinder is pressurized, the temperature of the gas inside the cylinder will rise due to the increase in internal pressure. When the cylinder is in a low temperature or ultra-low temperature environment (such as liquid oxygen temperature -183°C), the large temperature difference inside the cylinder is prone to produce large thermal stress, affecting the structural stability of the cylinder; the method of checking the pressure gauge is dangerous. In addition, if the cylinder is immersed in a low temperature medium, the high-pressure and high-temperature helium directly injected will also accelerate the volatilization of the surrounding low temperature medium, thereby increasing the environmental pressure and seriously affecting the test results.

[0004] Helium itself has a low boiling point and is a commonly used leak detection medium, which is suitable for testing the air tightness of gas cylinders in low-temperature environments. Considering the cost and safety of use, liquid nitrogen is usually used as a medium in low-temperature environments. However, the existing technology does not fully utilize the coldness of liquid nitrogen to cool the gas, and the heat exchange efficiency is low. Therefore, it is necessary to design a device that uses the coldness of liquid nitrogen to pre-cool the injected helium and then test the air tightness of the gas cylinder. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a gas cylinder air tightness testing device and method for use in a low temperature environment.

[0006] To achieve the above object, the first aspect of the present invention is to provide a gas cylinder air tightness testing device for use in a low temperature environment, comprising:

[0007] Helium cylinders and cryogenic medium tanks;

[0008] A filter, a first stop valve, a booster pump, a first safety valve, a first pressure gauge, a second stop valve, a first gas precooler, a second gas precooler, a cooling coil and a gas cylinder to be tested, which are sequentially connected to the helium gas cylinder through a metal hose, and a gas outlet and a gas inlet forming a circulation loop in the second gas precooler;

[0009] A third stop valve connected to the cryogenic medium tank in sequence through a metal hose, a cryogenic pump and a cryogenic medium input port, a cryogenic tank connected to the cryogenic medium input port, a cold shield fixedly connected to the cryogenic tank, a temperature gauge connected to the cryogenic tank, a second pressure gauge and a second safety valve, and a helium leak detector extending into the interior of the cryogenic tank;

[0010] The first gas precooler is embedded in the cold shield, the cooling coil and the gas cylinder to be tested are arranged in the low-temperature tank, and the gas outlet and the gas inlet are communicated with the interior of the low-temperature tank.

[0011] Optimally, the cold shield is made of a metal material with a large specific heat capacity.

[0012] Optimally, the first gas precooler is a disc-shaped copper tube.

[0013] Optimally, the helium delivery pipeline inside the second gas precooler is spiral and is provided with vertically staggered partitions inside, so as to increase the travel distance of the volatilized cryogenic medium gas and the contact time with the helium.

[0014] Optimally, the cooling coil is a thin-walled metal tube.

[0015] Optimally, fans are provided at both the gas outlet and the gas inlet, and the fans are used to increase the circulation of the low-temperature medium gas in the second gas precooler and the low-temperature tank.

[0016] A second aspect of the present invention is to provide a method for testing the air tightness of a gas cylinder in a low temperature environment, comprising:

[0017] (1) Open the helium cylinder, the first stop valve, and the second stop valve, and completely remove the air inside the cylinder to be tested by replacing the gas;

[0018] (2) Close the helium cylinder, the first stop valve and the second stop valve, record the initial value of the helium leak detector, open the second safety valve and the third stop valve, use the cryogenic pump to add the medium in the cryogenic medium tank into the cryogenic tank until the cylinder to be tested and the cooling coil are completely immersed, adjust the third stop valve, and observe the temperature gauge and the second pressure gauge to stabilize the temperature at the set value (both the temperature and the pressure can be adjusted according to the test requirements), for example, the temperature is -196°C and the ambient pressure is stabilized at 0.8MPa;

[0019] (3) Open the helium cylinder, the first stop valve and the first safety valve. After the transported gas is filtered and purified by the filter, the helium is pressurized by a booster pump to obtain high-temperature and high-pressure helium. Observe the first pressure gauge. When the reading reaches the predetermined pressure of 40 MPa, open the second stop valve.

[0020] (4) The pressurized helium undergoes heat exchange with the cold screen in the first gas precooler to achieve primary cooling; it undergoes closed heat exchange with the evaporated low-temperature medium gas in the second gas precooler to achieve secondary cooling; it undergoes heat exchange with the low-temperature medium in the low-temperature tank in the cooling coil to achieve tertiary cooling. After cooling, the helium enters the gas cylinder to be tested through the medium inlet;

[0021] (5) When the internal pressure of the gas cylinder to be tested reaches the preset pressure, for example, 35 MPa, maintain the pressure for 3 minutes, read the reading of the helium leak detector, and test the air tightness of the 35 MPa pressurized gas cylinder in a low temperature environment.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: the gas cylinder air tightness test device applied to the low temperature environment of the present invention performs the first pre-cooling of the superheated helium through the cold screen; the low temperature gas volatilized by liquid nitrogen is used to pre-cool the superheated helium gas for the second time through the second gas pre-cooler; finally, the superheated helium is pre-cooled for the third time using the cooling coil placed in the low temperature tank, and the volatilized nitrogen is recycled to ensure the stability of the pressure of the gas cylinder test environment, thereby improving the accuracy of the gas cylinder air tightness test. The gas cylinder air tightness test device applied to the low temperature environment of the present invention is simple and easy to design, does not need to be equipped with a large cooling device, has good process feasibility, low implementation cost, high heat exchange efficiency, and high accuracy of test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a gas cylinder air tightness testing device applied to a low temperature environment of the present invention;

[0024] Description of reference numerals:

[0025] 1. Helium cylinder; 2. Filter; 3. First stop valve; 4. Booster pump; 5. First safety valve; 6. First pressure gauge; 7. Second stop valve; 8. Cold screen; 9. First gas precooler; 10. Cryogenic tank; 11. Second gas precooler; 12. Gas outlet; 13. Gas inlet; 14. Cooling coil; 15. Gas cylinder to be tested; 16. Thermometer; 17. Second pressure gauge; 18. Helium leak detector; 19. Second safety valve; 20. Cryogenic medium inlet; 21. Cryogenic pump; 22. Third stop valve; 23. Cryogenic medium tank. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings.

[0027] like Figure 1 As shown, the gas cylinder air tightness testing device for low temperature environment of the present invention is generally used to detect the air tightness of the gas cylinder in low temperature environment or under the state of pressurization of 0.1-0.8MPa, and it mainly includes a helium gas cylinder 1, a filter 2, a first stop valve 3, a booster pump 4, a first safety valve 5, a first pressure gauge 6, a second stop valve 7, a cold screen 8, a first gas precooler 9, a low temperature tank 10, a second gas precooler 11, a gas outlet 12, a gas inlet 13, a cooling coil 14, a gas cylinder to be tested 15, a thermometer 16, a second pressure gauge 17, a helium leak detector 18, a second safety valve 19, a low temperature medium input port 20, a low temperature pump 21, a third stop valve 22 and a low temperature medium tank 23, etc.

[0028] The helium cylinder 1 is sequentially connected with a filter 2, a first stop valve 3, a booster pump 4, a first safety valve 5, a first pressure gauge 6, a second stop valve 7, a first gas precooler 9, a second gas precooler 11, a cooling coil 14 and a gas cylinder to be tested 15 through a metal hose, and a gas outlet 12 and a gas inlet 13 form a circulation loop in the second gas precooler 11.

[0029] The cryogenic medium tank 23 is connected to the third stop valve 22, the cryogenic pump 21 and the cryogenic medium input port 20 in sequence through a metal hose, the cryogenic tank 10 is connected to the cryogenic medium input port 20, and the cold shield 8 is fixedly connected to the cryogenic tank 10 (in this embodiment, the cold shield 8 is made of a metal material with a large specific heat capacity, such as aluminum). The thermometer 16, the second pressure gauge 17 and the second safety valve 19 are connected to the cryogenic tank 10 (the thermometer 16 and the second pressure gauge 17 are used to monitor the temperature and pressure in the cryogenic tank 10). The test probe of the helium leak detector 18 is placed inside the cryogenic tank 10 to monitor the leakage of the gas cylinder 15 to be tested during the test process.

[0030] Furthermore, the first gas precooler 9 is embedded in the cold shield 8 (the first gas precooler 9 is a disc-shaped copper tube). The cooling coil 14 and the gas cylinder 15 to be tested are arranged in the low temperature tank 10, and the gas outlet 12 and the gas inlet 13 are connected to the inside of the low temperature tank 10.

[0031] Furthermore, the helium delivery pipeline inside the second gas precooler 11 is spiral and is provided with vertically staggered partitions inside, so as to increase the travel distance of the volatilized cryogenic medium gas and the contact time with the helium.

[0032] Furthermore, the cooling coil 14 is a thin-walled metal tube.

[0033] Furthermore, fans are provided at the gas outlet 12 and the gas inlet 13, and the fans are used to increase the circulation of the low-temperature medium gas in the second gas precooler 11 and the low-temperature tank 10 (the fan can be a common axial flow fan).

[0034] Furthermore, the working pressure of the gas cylinder is: 20-35MPa.

[0035] Furthermore, the working temperature of the gas cylinder is: -196 and -183℃.

[0036] Furthermore, the ambient pressure of the gas cylinder is: 0.1-0.8MPa.

[0037] Furthermore, the power supply is 220V, 25kW.

[0038] Furthermore, the gas cylinder air tightness testing device used in low-temperature environments has an overall dimension of length*width*height: 1300*1500*1500 (mm).

[0039] Furthermore, the working time of the gas cylinder air tightness testing device used in low-temperature environments is 12 hours. It is worth noting that the working time is adjustable.

[0040] Furthermore, the superheated helium is cooled three times, and the temperature difference can be reduced by 30-65°C.

[0041] In this embodiment, the principle of the gas cylinder air tightness test device applied to low temperature environment is: when testing the air tightness of the gas cylinder 15 to be tested in a low temperature or ultra-low temperature environment, firstly, the air inside the gas cylinder 15 to be tested is completely replaced with helium, and then a low temperature medium is added, and the input helium is precooled by the low temperature medium. When the low temperature medium is added to the low temperature tank 10 to immerse the gas cylinder 15 to be tested, the cold shield 8 and the cooling coil 14 also obtain sufficient cooling capacity at the same time, and the low temperature medium evaporates to form a low temperature gas, which enters the second gas precooler 11 through the gas outlet 12 and is cooled. After the helium cylinder 1 is opened, the gas is purified by the filter 2, and the booster pump 4 is used to convert the gas into high-temperature and high-pressure gas. After the second stop valve 7 is opened, the helium will first exchange heat with the cold screen 8 in the first gas precooler 9 to perform a first-stage cooling; then the helium will undergo a second-stage cooling with the evaporated low-temperature medium in the second gas precooler 11; finally, the helium in the cooling coil 14 immersed in the low-temperature medium directly exchanges heat with the low-temperature medium to perform a third-stage cooling, and finally the cooled helium enters the inside of the gas cylinder to be tested 15 through the medium input port.

[0042] The method for testing the air tightness of a gas cylinder in a low temperature environment using the above device comprises the following steps:

[0043] (1) Open the helium cylinder 1, the first stop valve 3 and the second stop valve 7, and completely remove the air inside the gas cylinder 15 to be tested by replacing the gas;

[0044] (2) Close the helium cylinder 1, the first stop valve 3 and the second stop valve 7, record the initial value of the helium leak detector 18, open the second safety valve 19 and the third stop valve 22, use the cryogenic pump 21 to add the medium in the cryogenic medium tank 23 into the cryogenic tank 10 until the gas cylinder 15 to be tested and the cooling coil 14 are completely immersed, and adjust the third stop valve 22 while observing the thermometer 16 and the second pressure gauge 17 to stabilize the temperature at the set value (both the temperature and the pressure can be adjusted according to the test requirements), for example, the temperature is -196°C and the ambient pressure is stabilized at 0.8MPa;

[0045] (3) Open the helium cylinder 1, the first stop valve 3 and the first safety valve 5. After the transported gas is filtered and purified by the filter 2, the helium is pressurized by the booster pump 4 to obtain high-temperature and high-pressure helium. Observe the first pressure gauge 6. When the reading reaches the predetermined pressure of 40 MPa, open the second stop valve 7.

[0046] (4) The pressurized helium gas exchanges heat with the cold screen 8 in the first gas precooler 9 to perform the first-stage cooling; it exchanges closed heat with the evaporated low-temperature medium gas in the second gas precooler 11 to perform the second-stage cooling; it exchanges heat with the low-temperature medium in the low-temperature tank 10 in the cooling coil 14 to perform the third-stage cooling. After cooling, the helium gas enters the test gas cylinder 15 through the medium input port;

[0047] (5) When the internal pressure of the gas cylinder 15 to be tested reaches 35 MPa, maintain the pressure for 3 minutes, read the indication of the helium leak detector 18, and test the air tightness of the 35 MPa pressurized gas cylinder in a low temperature environment.

[0048] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A gas cylinder air tightness test device used in low temperature environment, characterized in that it include: Helium gas cylinder (1) and cryogenic medium tank (23); A filter (2), a first stop valve (3), a booster pump (4), a first safety valve (5), a first pressure gauge (6), a second stop valve (7), a first gas precooler (9), a second gas precooler (11), a cooling coil (14) and a gas cylinder to be tested (15) connected in sequence to the helium gas cylinder (1) via a metal hose, and a gas outlet (12) and a gas inlet (13) forming a circulation loop in the second gas precooler (11); A third stop valve (22) connected in sequence to the cryogenic medium tank (23) via a metal hose, a cryogenic pump (21) and a cryogenic medium input port (20), a cryogenic tank (10) connected to the cryogenic medium input port (20), a cold shield (8) fixedly connected to the cryogenic tank (10), a temperature gauge (16) connected to the cryogenic tank (10), a second pressure gauge (17) and a second safety valve (19), and a helium leak detector (18) extending into the interior of the cryogenic tank (10); The first gas precooler (9) is embedded in the cold shield (8), the cooling coil (14) and the gas cylinder to be tested (15) are arranged in the low-temperature tank (10), and the gas outlet (12) and the gas inlet (13) are in communication with the interior of the low-temperature tank (10); The cold shield (8) is made of a metal material with a large specific heat capacity, and fans are provided at both the gas outlet (12) and the gas inlet (13).

2. The gas cylinder air tightness testing device used in a low temperature environment according to claim 1 is characterized in that: The first gas precooler (9) is a disc-shaped copper tube.

3. The gas cylinder air tightness testing device for use in a low temperature environment according to claim 1, characterized in that: The helium delivery pipeline inside the second gas precooler (11) is spiral-shaped and is provided with vertically staggered partitions.

4. The gas cylinder air tightness testing device for use in a low temperature environment according to claim 1, characterized in that: The cooling coil (14) is a thin-walled metal tube.

5. A method for testing the air tightness of a gas cylinder in a low temperature environment, using the gas cylinder air tightness testing device described in any one of claims 1 to 4, characterized in that: It includes the following steps: (1) Open the helium cylinder (1), the first stop valve (3) and the second stop valve (7), and completely remove the air inside the gas cylinder (15) to be tested by replacing the gas; (2) Close the helium gas cylinder (1), the first stop valve (3) and the second stop valve (7), record the initial value of the helium leak detector (18), open the second safety valve (19) and the third stop valve (22), use the cryogenic pump (21) to add the medium in the cryogenic medium tank (23) into the cryogenic tank (10) until the gas cylinder (15) to be tested and the cooling coil (14) are completely immersed, and by adjusting the third stop valve (22) and observing the temperature gauge (16) and the second pressure gauge (17), the temperature and the ambient pressure are stabilized at a certain value, the temperature is -196 ° C, and the ambient pressure is 0.8 MPa; (3) Open the helium cylinder (1), the first stop valve (3) and the first safety valve (5), filter and purify the transported gas through the filter (2), use the booster pump (4) to boost the helium to obtain high-temperature and high-pressure helium, observe the first pressure gauge (6), and when the reading reaches the predetermined pressure of 40 MPa, open the second stop valve (7); (4) The pressurized helium gas exchanges heat with the cold screen (8) in the first gas precooler (9) to perform a first-stage cooling; the pressurized helium gas exchanges closed heat with the evaporated low-temperature medium gas in the second gas precooler (11) to perform a second-stage cooling; the pressurized helium gas exchanges heat with the low-temperature medium in the low-temperature tank (10) in the cooling coil (14) to perform a third-stage cooling. After cooling, the helium gas enters the interior of the gas cylinder to be tested (15) through the medium input port; (5) When the internal pressure of the gas cylinder (15) to be tested reaches the set working pressure, the working pressure is 35 MPa, and the pressure is maintained for 3 minutes. The reading of the helium leak detector (18) is read to test the air tightness of the 35 MPa pressurized gas cylinder in a low temperature environment.

Images