Device and method for detecting low internal and external leakage rates at low temperatures

Abstract

An apparatus and method for detecting low-temperature internal and external leakage rates, particularly relating to the detection of low-temperature internal and external leakage rates of multi-chamber equipment, including a leak detection gas source, a cold liquid tank, an internal coil Dewar tank, a leak detection tank, a reheating coil, a temperature monitor, a vacuum pump, a helium mass spectrometer leak detector, and pipelines and valves connecting various devices. Among them, the vacuum pump is connected to the leak detection tank to provide a vacuum environment inside the leak detection tank; the cold liquid tank is connected to the inlet and outlet of the device under test, and the outlet of the device under test is connected to the vent port to form a pre-cooling system; the leak detection gas source is connected to the internal coil of the Dewar tank and then to the inlet of the device under test, and the outlet of the device under test is connected to the helium mass spectrometer leak detector and the vacuum pump to form a leak detection system. The leak rate data measured by the apparatus and method of this invention provides a basis for judging whether the device under test meets the design requirements, ensuring the reliability and safety of the low-temperature operation of the equipment.

Description

Technical Field

[0001] The present invention relates to a device and method for low-temperature detection of internal and external leakage rates, and particularly to the detection of internal and external leakage rates of multi-chamber equipment at low temperature, belonging to the field of cryogenic technology. Background Art

[0002] The leakage rate of equipment is an extremely important indicator in engineering applications, such as the equipment in a vacuum cold box. The vacuum cold box maintains the vacuum degree inside the cold box and minimizes the heat convection inside the cold box as much as possible to achieve the cold insulation of the internal equipment. For the normal operation of the vacuum cold box, the vacuum degree inside the cold box needs to be maintained below 1×10 -3 Pa. If the leakage rate of the equipment inside the cold box is too high, it will cause the vacuum degree inside the cold box to be unable to be maintained, and the heat convection of the gas will take away the cold quantity on the surface of the equipment, resulting in excessive cold loss of the cold box and unbalanced heat load. Therefore, before installing the equipment into the cold box, it is necessary to detect its leakage rate to ensure that its actual leakage rate meets the requirements of the cold box operation.

[0003] Most of the weld defects of the equipment can be found and repaired through non-destructive testing such as ray and ultrasonic testing. The remaining more subtle defects need to be found through leakage detection such as airtightness test and helium leak detection. Some of these small defects will not cause equipment leakage at normal temperature, but when the equipment operates at low temperature, the tiny defects at the weld will become larger after the weld shrinks due to cold, resulting in a sharp increase in the leakage rate of the equipment. For plate-fin heat exchangers, there is also a possibility that the brazed welds will be locally de-welded due to excessive thermal stress generated by the low-temperature medium in the channels, resulting in serious leakage.

[0004] In previous engineering projects, there have been a large number of cases where the equipment passed the helium leak detection at normal temperature, but the leakage rate of the equipment inside the cold box increased after starting up and operating at low temperature. Therefore, the equipment passing the helium leak detection at normal temperature does not guarantee that its leakage rate still meets the requirements after being installed and operated in the cold box. Conducting low-temperature leak detection on the equipment inside the cold box can avoid a series of safety accidents caused by the leakage of low-temperature media due to the excessive leakage rate of the equipment that passed the leak detection at normal temperature during the low-temperature operation process as the temperature decreases. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a device and method for low-temperature detection of internal and external leakage rates, so as to realize the detection of internal and external leakage rates of equipment, especially multi-chamber equipment, at low temperature.

[0006] To solve the above technical problems, the present invention provides a low-temperature detection device for internal and external leakage rates. The device includes a leak detection gas source, a cold liquid tank, an internal coil Dewar tank, a leak detection tank, a reheating coil, a temperature monitor, a vacuum pump, and a helium mass spectrometer leak detector. Among them, the temperature monitor is connected to the device under test through a cable, and the rest of the devices are connected to each other through pipes. The leak detection tank is connected to the vacuum pump, and a leak detection tank vacuum valve and a vacuum pump valve are provided on the connecting pipe. The cold liquid tank is connected to the inlet and outlet of the device under test, the inlet and outlet of the device under test are connected to the vent port, the leak detection gas source is connected to the internal coil of the internal coil Dewar tank and then to the inlet of the device under test in the leak detection tank, and the outlet of the device under test is connected to the helium mass spectrometer leak detector and the vacuum pump respectively; the nitrogen source in the leak detection gas source is directly connected to the inlet of the device under test through a bypass.

[0007] Preferably: A vacuum system is formed among the leak detection tank, the leak detection tank vacuum valve, the vacuum pump valve, and the vacuum pump. The vacuum pump is used to evacuate the leak detection tank, and the vacuum degree of the leak detection tank reaches below 5 Pa.

[0008] Preferably: A pre-cooling system is formed among the cold liquid tank, the device under test, the reheating coil, and the vent port. Among them, one or more channel inlet valves are provided at the inlet of the device under test according to the number of channels, one or more channel outlet valves are provided at the outlet of the device under test according to the number of channels, a cold liquid tank valve A and a cold liquid tank valve B are provided at the connection between the cold liquid tank and the inlet and outlet of the device under test, a pre-cooling system valve A and a pre-cooling system valve B are provided at the front end of the reheating coil, and a vent valve is provided at the vent port. The connection of the pre-cooling system is in turn the cold liquid tank, the cold liquid tank valve A, the channel inlet valve, the device under test, the channel outlet valve, the pre-cooling system valve A, the reheating coil, the vent valve, and the vent port. Among them, during the pre-cooling of the device under test, the pre-cooling time is greatly shortened by switching the cold liquid tank valve A and the cold liquid tank valve B and the pre-cooling system valve A and the pre-cooling system valve B. At this time, the connection of the pre-cooling system is in turn the cold liquid tank, the cold liquid tank valve B, the channel outlet valve, the device under test, the channel inlet valve, the pre-cooling system valve B, the reheating coil, the vent valve, and the vent port. The reheating coil can reheat the cold gas at the inlet of the coil to room temperature through air.

[0009] Preferably, a leak detection system is formed among the leak detection gas source, the built-in coil Dewar tank, the device under test, the reheating coil, the vacuum pump, and the leak detection tank. A branch is added between the reheating coil and the vacuum pump valve to connect to a helium mass spectrometer leak detector with a leak detector valve. A cold leak detection valve is provided at the outlet of the built-in coil Dewar tank. Single or multiple channel inlet valves are provided at the inlet of the device under test according to the number of channels, and single or multiple channel outlet valves are provided at the outlet of the device under test according to the number of channels. A leak detection system valve and a vacuum pump valve are provided at the front end of the vacuum pump. The device to be detected is placed in the leak detection tank. The leak detection gas source is a helium-nitrogen mixture or a pure helium gas system. The helium-nitrogen mixture consists of a helium gas system and a nitrogen gas system. The helium gas system includes a helium gas cylinder and a helium gas leak detection valve, and the nitrogen gas system includes a nitrogen gas cylinder and a nitrogen gas leak detection valve.

[0010] Preferably, the built-in coil Dewar tank contains cryogenic liquid, which can cool the leak detection gas flowing through the coil to the corresponding temperature. The cryogenic liquid includes one of liquid nitrogen, liquid argon, liquid oxygen, liquid neon, liquid hydrogen, liquid helium, and mixed refrigerant.

[0011] Preferably, the leak detection tank adopts a vertical or horizontal structure. One end of the leak detection tank is sealed, and the head can be opened for installing the device under test. When the leak detection tank adopts a horizontal structure, a trolley and a guide rail for installing the device under test are arranged inside the leak detection tank; when the leak detection tank adopts a vertical structure, a bracket for fixing the device under test is arranged inside the leak detection tank. The contact points between the guide rail, the bracket and the leak detection tank are insulated with heat-insulating materials. The device under test is placed in the leak detection tank, and the pipes at the channel inlet and the channel outlet pass through the shell of the leak detection tank. A vacuum tube or a vacuum flange can be used at the penetration point to achieve heat insulation. A thermometer joint is arranged on the outer wall of the device under test to monitor the temperature of the device under test. When the size of the device under test is large, multiple thermometer joints can be set to monitor different parts of it.

[0012] Preferably, a nitrogen gas reheating valve is provided on the other side of the nitrogen gas cylinder. The nitrogen gas cylinder, the nitrogen gas reheating valve, the channel inlet valve, the device under test, the channel outlet valve, the pre-cooling system valve A, the reheating coil, the vent valve, and the vent port form a reheating system.

[0013] A method for using a low-temperature detection device for internal and external leakage rates, the method comprising the following steps:

[0014] (1) Place the device to be tested into the leak detection tank and connect the inlets and outlets of each chamber to the external system;

[0015] (2) Evacuate all chambers of the device to be tested and maintain a vacuum state;

[0016] (3) Evacuate the leak detection tank to below 3 - 8 Pa and measure the background leak rate of the leak detection tank;

[0017] (4) Simultaneously fill low-temperature liquid in the cold liquid tank into each cavity of the device to be tested to pre-cool the device to the set leak rate test temperature.

[0018] (5) Sequentially fill the helium-nitrogen mixture or helium pre-cooled in the Dewar tank into each cavity to the set leak detection pressure. Connect the helium mass spectrometer leak detector to the leak detection tank to measure the external leak rate at low temperature in each cavity. When measuring the external leak rate, except for the cavity being leak detected, the other cavities are kept in a vacuum state.

[0019] (6) Fill the helium-nitrogen mixture or helium pre-cooled in the Dewar tank into the cavity to be tested of the device to be tested to the set leak detection pressure. Connect the helium mass spectrometer leak detector to the adjacent cavity of the cavity to be tested to measure the internal leak rate at low temperature between different cavities.

[0020] By using the internal and external leak rate low-temperature detection device and method provided by the present invention, the external leak rate of the device under the set low-temperature leak detection temperature and the set leak detection pressure can be detected; for a multi-cavity device, the internal leak rate between different cavities of the device under the set low-temperature leak detection temperature and the set leak detection pressure can also be detected. The leak rate data measured by the device and method of the present invention provides a basis for judging whether the device to be tested meets the design requirements, and ensures the reliability and safety of the device during low-temperature operation. Description of the Drawings

[0021] Figure 1 It is a schematic cross-sectional structure diagram of the present invention. Detailed Embodiment

[0022] The present invention will be described in more detail below in conjunction with specific embodiments and the drawings, so that the layout and leak detection steps of this low-temperature leak detection device are clearer and more complete. This embodiment is only used to illustrate the present invention and does not limit the scope of the present invention.

[0023] This embodiment is to use this low-temperature leak detection device to detect the internal and external leak rates of all channels of a three-channel plate-fin heat exchanger at a low temperature of 100K under the design pressure.

[0024] Figure 1As shown in the figure, a low-temperature detection device for internal and external leakage rates includes a leak detection gas source, a cold liquid tank 7, an internal coil Dewar tank 6, a leak detection tank 1, a reheating coil 9, a temperature monitor 13, a vacuum pump 2, and a helium mass spectrometer leak detector 3. Among them, the temperature monitor 13 is connected to the device under test through a cable, and the rest of the devices are connected to each other through pipes. The leak detection tank 1 and the vacuum pump 2 are connected, and a leak detection tank vacuum valve 110 and a vacuum pump valve 111 are provided on the connecting pipe. The cold liquid tank 7 is connected to the inlet and outlet of the device under test, and the inlet and outlet of the device under test are connected to the vent port 10. The leak detection gas source is connected to the internal coil of the internal coil Dewar tank 6 and then to the inlet of the device under test in the leak detection tank. The outlet of the device under test is respectively connected to the helium mass spectrometer leak detector 3 and the vacuum pump 2; the nitrogen cylinder in the leak detection gas source is directly connected to the inlet of the device under test through a bypass.

[0025] A vacuum system is formed among the leak detection tank, the leak detection tank vacuum valve, the vacuum pump valve, and the vacuum pump. This vacuum pump is used to evacuate the leak detection tank, and the vacuum degree of the leak detection tank reaches below 5 Pa.

[0026] A pre-cooling system is formed among the cold liquid tank, the device under test, the reheating coil, and the vent port. Among them, single or multiple channel inlet valves are provided at the inlet of the device under test according to the number of channels, single or multiple channel outlet valves are provided at the outlet of the device under test according to the number of channels, a cold liquid tank valve A and a cold liquid tank valve B are provided at the connection between the cold liquid tank and the inlet and outlet of the device under test, a pre-cooling system valve A and a cold system valve B are provided at the front end of the reheating coil 9, and a vent valve is provided at the vent port. The connection of the pre-cooling system is in turn the cold liquid tank, the cold liquid tank valve A, the channel inlet valve, the device under test, the channel outlet valve, the pre-cooling system valve A, the reheating coil, the vent valve, and the vent port. Among them, during the process of pre-cooling the device under test, the pre-cooling time is greatly shortened by switching the cold liquid tank valve A and the cold liquid tank valve B and the pre-cooling system valve A and the pre-cooling system valve B. At this time, the connection of the pre-cooling system is in turn the cold liquid tank, the cold liquid tank valve B, the channel outlet valve, the device under test, the channel inlet valve, the pre-cooling system valve B, the reheating coil, the vent valve, and the vent port. This reheating coil can reheat the cold gas at the inlet of the coil to room temperature through air.

[0027] A leak detection system is formed among the leak detection gas source, the internal coil Dewar tank, the device under test, the reheating coil, the vacuum pump, and the leak detection tank. A branch is added between the reheating coil and the vacuum pump valve to connect the helium mass spectrometer leak detector with a leak detector valve. Among them, a cold leak detection gas valve is provided at the outlet of the internal coil Dewar tank, single or multiple channel inlet valves are provided at the inlet of the device under test according to the number of channels, single or multiple channel outlet valves are provided at the outlet of the device under test according to the number of channels, a leak detection system valve and a vacuum pump valve are provided at the front end of the vacuum pump, the device to be detected is placed in the leak detection tank, and the leak detection gas source is a helium-nitrogen mixture or a pure helium gas system. Among them, the helium-nitrogen mixture consists of a helium gas system and a nitrogen gas system. The helium gas system includes a helium gas cylinder and a helium gas leak detection valve, and the nitrogen gas system includes a nitrogen gas cylinder and a nitrogen gas leak detection valve.

[0028] The built-in coil Dewar flask is filled with cryogenic liquid, which can cool the leak-detecting gas flowing through the coil to the corresponding temperature. The cryogenic liquid includes one of liquid nitrogen, liquid argon, liquid oxygen, liquid neon, liquid hydrogen, liquid helium, and mixed refrigerant.

[0029] The leak-detecting flask adopts a vertical or horizontal structure. One end of the leak-detecting flask is sealed, and the head can be opened for installing the device under test. When the leak-detecting flask adopts a horizontal structure, a trolley and a guide rail for installing the device under test are arranged inside the leak-detecting flask; when the leak-detecting flask adopts a vertical structure, a bracket for fixing the device under test is arranged inside the leak-detecting flask. The contact points between the guide rail, the bracket and the leak-detecting flask are insulated with heat-insulating materials. The device under test is placed in the leak-detecting flask. The pipelines at the channel inlet and the channel outlet pass through the shell of the leak-detecting flask, and a vacuum tube or a vacuum flange can be adopted at the wall-piercing part to achieve heat insulation. A thermometer joint is arranged on the outer wall of the device under test to monitor the temperature of the device under test. When the size of the device under test is large, multiple thermometer joints can be set to monitor the temperature of different parts of it.

[0030] A nitrogen reheating valve is arranged on the other side of the nitrogen cylinder. The nitrogen cylinder, the nitrogen reheating valve, the channel inlet valve, the device under test, the channel outlet valve, the pre-cooling system valve A, the reheating coil, the vent valve, and the vent port form a reheating system.

[0031] A method for using a low-temperature detection device according to the internal and external leakage rates in applications, the method comprising the following steps:

[0032] (1) Place the device to be tested into the leak-detecting flask and connect the inlets and outlets of each chamber to the external system;

[0033] (2) Evacuate all the chambers of the device to be tested and maintain a vacuum state;

[0034] (3) Evacuate the leak-detecting flask to below 3 - 8 Pa and measure the background leakage rate of the leak-detecting flask;

[0035] (4) Simultaneously fill each chamber of the device to be tested with the cryogenic liquid in the cold liquid tank to pre-cool the device to the set leak rate test temperature;

[0036] (5) Sequentially fill each chamber with the helium-nitrogen mixture or helium pre-cooled in the Dewar flask to the set leak detection pressure. Connect the helium mass spectrometer leak detector to the leak-detecting flask and measure the external leakage rate at low temperature of each chamber. When measuring the external leakage rate, except for the chamber being leak-detected, the remaining chambers maintain a vacuum state;

[0037] (6) Fill the chamber to be tested of the device to be tested with the helium-nitrogen mixture or helium pre-cooled in the Dewar flask to the set leak detection pressure. Connect the helium mass spectrometer leak detector to the adjacent chamber of the chamber to be tested and measure the internal leakage rate at low temperature between different chambers. Specific embodiments

[0038] As shown Figure 1 in the figure, a vacuum flange is provided on the shell of the leak detection tank 1 and sealed with a flange cover. A joint passing through the flange cover is provided at the flange cover. The joint is connected to an external pipeline on the outer side of the flange cover, and a metal hose is connected to the inlet and outlet of the device under test 8 on the inner side of the flange cover. Before leak detection, the device under test 8 needs to be installed in the leak detection tank 1 first. The specific operation is to open the head of the leak detection tank 1, place the device under test 8 on the trolley 11, then place the device under test 8 together with the trolley 11 on the guide rail 12 and push it into the leak detection tank 1 along the guide rail 12, connect the pipelines at the outlet and inlet of the device under test 8, and then install the head of the leak detection tank 1 back after completion.

[0039] The leak detection tank 1, the leak detection tank vacuum valve 110, the vacuum pump valve 111, and the vacuum pump 2 are connected in sequence to form a vacuum system. The vacuum pump pumps the vacuum degree of the leak detection tank to below 5 Pa.

[0040] The cold liquid tank 7, the cold liquid tank valve A 106A, the channel inlet valve 107, the device under test 8, the channel outlet valve 108, the pre-cooling system valve A 109, the reheating coil 9, the vent valve 112, and the vent port 10 are connected in sequence to form a pre-cooling system. During the pre-cooling process, swapping the inlet and outlet of liquid nitrogen can significantly shorten the pre-cooling time of the device under test 8. For this purpose, a cold liquid tank valve B 106B and a pre-cooling system valve B 105 are provided. At this time, the connection of the pre-cooling system is in sequence: cold liquid tank, cold liquid tank valve B, channel outlet valve, device under test, channel inlet valve, pre-cooling system valve B, reheating coil, vent valve, vent port. Swapping the cold liquid inlet and outlet can be achieved by switching the cold liquid tank valves A / B and the pre-cooling system valves A / B.

[0041] The three channels of the device under test 8 are channel A, channel B, and channel C respectively. The inlet and outlet of channel A are A1 and A2 respectively, the inlet and outlet of channel B are B1 and B2 respectively, and the inlet and outlet of channel C are C1 and C2 respectively. In the above pre-cooling system, the pipeline after the cold liquid tank valve A 106A is divided into three parallel branch pipes and connected to the inlets A1, B1, and C1 respectively. Channel inlet valves A 107A, channel inlet valves B 107B, and channel inlet valves C 107C are respectively provided on the branch pipes; the pipeline before the pre-cooling system valve A 109 is divided into three parallel branch pipes and connected to the outlets A2, B2, and C2 respectively. Channel outlet valves A 108A, channel outlet valves B 108B, and channel outlet valves C 108C are respectively provided on the branch pipes.

[0042] In this embodiment, the leak detection temperature is 100 K, and liquid nitrogen is contained in the cold liquid tank 7.

[0043] In this embodiment, during the pre-cooling process, the cooling rate of the device under test 8 needs to be controlled below 2 K / min, and the cold liquid tank valves A and B adopt needle valves.

[0044] In this embodiment, thermometers are respectively arranged on the outer walls of the front, middle, and rear measuring points of the device under test 8 to monitor the temperature.

[0045] In this case, a helium-nitrogen mixture is used as the leak detection gas source. A helium leak detection valve 101 is connected behind the helium gas cylinder 4, and a nitrogen leak detection valve 102 is connected behind the nitrogen gas cylinder 5. The two form a leak detection gas source (as shown within the dashed box in Figure 1 ). The leak detection gas source is connected to the internal coil of the cryogenic coil dewar 6, the cold leak detection valve 104, the channel inlet valve 107, the device under test 8, the channel outlet valve 108, the pre-cooling system valve A 109, the reheating coil 9, the leak detection system valve 114, the vacuum pump valve 111, the vacuum pump 2, and the leak detection tank 1. At the same time, a branch is added between the reheating coil 9 and the vacuum pump valve 111 to connect the leak detector valve 113 and the leak detector 3. The above devices form a leak detection system.

[0046] In the leak detection system, the pipeline and valve arrangement between the cold leak detection valve 104 and the inlet of the device under test 8 are the same as those between the cold liquid tank valve A 106A and the inlet of the device under test 8 in the pre-cooling system; the pipeline and valve arrangement between the pre-cooling system valve A 109 and the outlet of the device under test 8 in the leak detection system are the same as those between the pre-cooling system valve A 109 and the outlet of the device under test 8 in the pre-cooling system.

[0047] The nitrogen gas cylinder 5, the nitrogen reheating valve 103, the channel inlet valve 107, the device under test 8, the channel outlet valve 108, the pre-cooling system valve A 109, the reheating coil 9, the vent valve 112, and the vent port 10 are connected in sequence to form a reheating system.

[0048] According to Figure 1 After connecting the pipelines and devices as shown, the following steps are taken to detect the low-temperature internal and external leakage rates of the device under test:

[0049] 1. Open the channel outlet valve A 108A, the channel outlet valve B 108B, the channel outlet valve C 108C, the pre-cooling system valve A 109, the leak detection system valve 114, the leak detection tank vacuum valve 110, and the vacuum pump valve 111, and keep the other valves closed. Turn on the vacuum pump 2 to evacuate the channels A, B, and C of the device under test 8 and the leak detection tank 1 to 5 Pa. Close the pre-cooling system valve A 109 and the vacuum pump valve 111, and open the leak detector valve 113 to measure the background leakage rate of the leak detection tank 1.

[0050] 2. Open the cold liquid tank valve A 106A, channel inlet valve A 107A, channel inlet valve B 107B, channel inlet valve C 107C, channel outlet valve A 108A, channel outlet valve B 108B, channel outlet valve C 108C, pre-cooling system valve A 109, vent valve 112, leak detection tank vacuum valve 110, and vacuum pump valve 111. Keep the remaining valves closed. Liquid nitrogen flows from the cold liquid tank 7 into channels A, B, and C of the device under test 8 to pre-cool the device under test 8. By adjusting the opening degree of the cold liquid tank valve A 106A, control the cooling rate of the device under test 8 during the entire pre-cooling process to be below 2 K / min. At the same time, the vacuum pump 2 continuously evacuates the leak detection tank 1 to maintain the adiabatic performance of the leak detection tank 1 during the pre-cooling process. When the temperature measurement point in the middle of the device under test 8 shows that it has reached below 120 K, close the cold liquid tank valve A 106A and the pre-cooling system valve A 109, open the cold liquid tank valve B 106B and the pre-cooling system valve B 105, and swap the liquid nitrogen inlet and outlet, which can significantly shorten the pre-cooling time. End the pre-cooling when the three temperature measurement points of the device under test 8 all reach below 100 K.

[0051] 3. Equipment internal and external leakage rate test: First, evacuate all channels of the device under test 8 to 5 Pa according to the above method and close the inlet and outlet valves of the device under test. Open the helium leak detection valve 101, nitrogen leak detection valve 102, cold leak detection valve 104, and channel inlet valve A 107A. Keep the remaining valves closed. Pre-cool the helium-nitrogen mixed gas with a volume ratio of about 3:7 through the built-in coil Dewar tank 6 (the Dewar tank is filled with liquid nitrogen) and then charge it into channel A until the pressure in channel A reaches the design requirement. Open the leak detection tank vacuum valve 110, leak detection system valve 114, and leak detector valve 113. At this time, the helium mass spectrometer leak detector 3 is connected to the leak detection tank 1 to measure the external leakage rate of channel A. Close the leak detection system valve 114, open the channel outlet valve B 108B and the pre-cooling system valve A 109. At this time, the helium mass spectrometer leak detector 3 is connected to channel B to measure the internal leakage rate between channel A and channel B. Close the channel outlet valve B 108B, open the channel outlet valve C 108C, and measure the internal leakage rate between channel A and channel C. Close the channel inlet valve A 107A and the leak detector valve 113, open the channel outlet valve A 108A, leak detection system valve 114, and vacuum pump valve 111. Turn on the vacuum pump 2 to evacuate channel A. After completion, close the channel outlet valve A 108A, leak detection system valve 114, vacuum pump valve 111, and vacuum pump 2.

[0052] Test the external and internal leakage rates of the remaining channels B and C in sequence according to the above method.

[0053] 4. According to the background leakage rate of the leak detection tank 1, correspondingly convert the measured external leakage rates of channels A, B, and C to obtain the actual internal and external leakage rate values of the three channels at low temperature.

[0054] If the leak rate of a certain channel of the device under test 8 exceeds the allowable value, the leak point can be found for repair welding. Passing the detection again proves that the leak rate of the device at the detection temperature meets the usage requirements. By using this low-temperature leak detection device and method, leak points that may occur in the device under low-temperature conditions can be discovered in advance and remedied, avoiding a series of safety accidents caused by the leakage of low-temperature media due to the exceeding of the leak rate as the temperature decreases during the low-temperature operation of the device with a qualified leak rate at normal temperature.

Claims

1. A low-temperature detection device for internal and external leakage rates. The device includes a leak detection gas source, a cold liquid tank (7), an internal coil Dewar tank (6), a leak detection tank (1), a reheating coil (9), a temperature monitor (13), a vacuum pump (2), and a helium mass spectrometer leak detector (3). Among them, the temperature monitor (13) is connected to the device under test through a cable, and the remaining devices are connected to each other through pipes. It is characterized in that: The leak detection tank (1) is connected to the vacuum pump (2), and a leak detection tank vacuum valve (110) and a vacuum pump valve (111) are provided on the connecting pipeline. The cold liquid tank (7) is connected to the inlet and outlet of the device under test. The inlet and outlet of the device under test are connected to the vent port (10). The leak detection gas source is connected to the internal coil of the built-in coil Dewar tank (6) and then to the inlet of the device under test in the leak detection tank. The outlet of the device under test is respectively connected to the helium mass spectrometer leak detector (3) and the vacuum pump (2). The nitrogen gas cylinder in the leak detection gas source is directly connected to the inlet of the device under test through a bypass. A vacuum system is formed among the leak detection tank, the leak detection tank vacuum valve, the vacuum pump valve, and the vacuum pump. This vacuum pump is used to evacuate the leak detection tank, and the vacuum degree of the leak detection tank reaches below 5 Pa. A pre-cooling system is formed among the cold liquid tank, the device under test, the reheating coil, and the vent port. Among them, single or multiple channel inlet valves are provided at the inlet of the device under test according to the number of channels, single or multiple channel outlet valves are provided at the outlet of the device under test according to the number of channels, a cold liquid tank valve A and a cold liquid tank valve B are provided at the connection between the cold liquid tank and the inlet and outlet of the device under test, a pre-cooling system valve A and a pre-cooling system valve B are provided at the front end of the reheating coil (9), and a vent valve is provided at the vent port. The connection of the pre-cooling system is in sequence: cold liquid tank, cold liquid tank valve A, channel inlet valve, device under test, channel outlet valve, pre-cooling system valve A, reheating coil, vent valve, vent port. Among them, during the process of pre-cooling the device under test, the pre-cooling time is greatly shortened by switching the cold liquid tank valve A and the cold liquid tank valve B and the pre-cooling system valve A and the pre-cooling system valve B. At this time, the connection of the pre-cooling system is in sequence: cold liquid tank, cold liquid tank valve B, channel outlet valve, device under test, channel inlet valve, pre-cooling system valve B, reheating coil, vent valve, vent port. This reheating coil can reheat the cold gas at the coil inlet to room temperature through air.

2. The low-temperature detection device for internal and external leakage rates according to claim 1, wherein: A leak detection system is formed among the leak detection gas source, the built-in coil Dewar tank, the device under test, the reheating coil, the vacuum pump, and the leak detection tank. A branch is added to connect the helium mass spectrometer leak detector with a leak detector valve between the reheating coil and the vacuum pump valve. Among them, a cold leak detection gas valve is provided at the outlet of the built-in coil Dewar tank, single or multiple channel inlet valves are provided at the inlet of the device under test according to the number of channels, single or multiple channel outlet valves are provided at the outlet of the device under test according to the number of channels, a leak detection system valve and a vacuum pump valve are provided at the front end of the vacuum pump, the device to be detected is placed in the leak detection tank, and the leak detection gas source is a helium-nitrogen mixed gas or pure helium gas system. Among them, the helium-nitrogen mixed gas is composed of a helium gas system and a nitrogen gas system. The helium gas system includes a helium gas cylinder and a helium leak detection valve, and the nitrogen gas system includes a nitrogen gas cylinder and a nitrogen leak detection valve.

3. The low-temperature detection device for internal and external leakage rates according to claim 1 or 2, characterized in that: The built-in coil Dewar tank contains cryogenic liquid, which can cool the leak detection gas flowing through the coil to the corresponding temperature. The cryogenic liquid includes one of liquid nitrogen, liquid argon, liquid oxygen, liquid neon, liquid hydrogen, liquid helium, and mixed refrigerant.

4. The low-temperature detection device for internal and external leakage rates according to claim 1 or 2, characterized in that: The leak detection tank adopts a vertical or horizontal structure. One end of the leak detection tank is sealed, and the head can be opened for installing the device under test. When the leak detection tank adopts a horizontal structure, a trolley and a guide rail for installing the device under test are arranged inside the leak detection tank; when the leak detection tank adopts a vertical structure, a bracket for fixing the device under test is arranged inside the leak detection tank. The contact points of the guide rail and the bracket with the leak detection tank are insulated with heat insulation materials. The device under test is placed in the leak detection tank. The pipelines at the channel inlet and the channel outlet pass through the shell of the leak detection tank, and a vacuum tube or a vacuum flange can be used at the penetration point to achieve heat insulation. A thermometer joint is arranged on the outer wall of the device under test to monitor the temperature of the device under test.

5. The low-temperature detection device for internal and external leakage rates according to claim 1, wherein: A nitrogen rewarming valve is arranged on the other side of the nitrogen cylinder. The nitrogen cylinder, the nitrogen rewarming valve, the channel inlet valve, the device under test, the channel outlet valve, the pre-cooling system valve A, the reheating coil, the vent valve, and the vent port form a rewarming system.

6. A method for using the low-temperature detection device for internal and external leakage rates according to any one of claims 1-5, characterized in that: The method includes the following steps: (1) Place the device to be tested in the leak detection tank and connect the inlets and outlets of each chamber to the external system; (2) Evacuate all chambers of the device to be tested and maintain a vacuum state; (3) Evacuate the leak detection tank to below 5 Pa and measure the background leak rate of the leak detection tank; (4) Simultaneously fill each chamber of the device to be tested with the cryogenic liquid in the cryogenic liquid tank to pre-cool the device to the set leak rate test temperature; (5) Sequentially fill each chamber with the helium-nitrogen mixture or helium pre-cooled in the Dewar tank to the set leak detection pressure. The helium mass spectrometer leak detector is connected to the leak detection tank to measure the external leak rate at low temperature of each chamber. When measuring the external leak rate, except for the chamber being leak-detected, the other chambers maintain a vacuum state; (6) Fill the chamber to be tested of the device to be tested with the helium-nitrogen mixture or helium pre-cooled in the Dewar tank to the set leak detection pressure. The helium mass spectrometer leak detector is connected to the adjacent chamber of the chamber to be tested to measure the internal leak rate at low temperature between different chambers.

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