A system and method for detecting leaks in a vacuum insulated pipe line of a test station

Abstract

The present application relates to a kind of detection systems for detecting the leak of the inner tube of vacuum insulated pipeline of test station, including the vacuum insulated pipeline for transmitting the low-temperature liquid generated by cryogenic refrigerator to distribution valve box, the vacuum insulated pipeline is connected with at least one helium mass spectrometer leak detector;Wherein, the vacuum insulated pipeline is welded by several prefabricated sections through corresponding transition section, each prefabricated section includes internal pipeline, external pipeline and vacuum interlayer between internal pipeline and external pipeline, vacuum safety plug is arranged on the external pipeline of each prefabricated section, and at least one prefabricated section is connected with an auxiliary evacuation system.The present application also relates to a kind of detection method for detecting the leak of the inner tube of vacuum insulated pipeline of test station.The present application realizes the detection of the inner tube of vacuum insulated pipeline section by section, can accurately and quickly determine the inner tube with leak, and quickly and accurately locate the leak range, improve detection efficiency and detection accuracy.

Description

Technical Field

[0001] This invention relates to low-temperature insulated vacuum pipeline inspection technology, and more specifically to a detection system and method for leaks in the inner tube of a test station's vacuum insulated pipeline, used for rapid location of leaks in the inner tube weld. Background Technology

[0002] A cryogenic distribution and transmission system is installed between the superconducting testing platform and the cryogenic system. This system includes a cryogenic valve box and transmission pipelines. Its main function is to distribute the cryogenic liquid generated by the cryogenic refrigerator to various terminal devices through vacuum-insulated pipelines, meeting the control requirements of each terminal device for different parameters such as flow rate, pressure, temperature, and liquid level of the cryogenic liquid. To ensure smooth delivery and use of the cryogenic fluid and to provide a stable 2K experimental environment for the superconducting high-frequency testing platform, the total leakage rate of the vacuum-insulated pipelines at room temperature must be less than 1.0E. -9 Pa·m 3 / s.

[0003] Vacuum insulated pipelines are assembled on-site from several prefabricated sections. The inner tube contains hundreds of butt welds. When the installation is completed, the leakage rate may be qualified. However, after a period of cryogenic superfluid helium transport, the inner tube will undergo several alternating hot and cold changes, which will cause material fatigue and cracking of the welds, resulting in leakage in the inner tube. This will prevent the cryogenic device from recycling the cooling medium.

[0004] Traditional vacuum helium mass spectrometry leak detection requires re-evacuating the system and maintaining pressure if a leak is found. This method is time-consuming and cannot pinpoint the exact location of the leak in the inner tube. While positive pressure helium mass spectrometry leak detection is suitable for detecting leaks in the outer tubes of vacuum-insulated pipelines, it often requires the removal of all transition sections of the inner tube before leak detection can be performed, resulting in a large workload and long operation time. Because leaks cannot be resolved, pipelines worth tens of millions of dollars are often rendered unusable. Therefore, it is necessary to develop a rapid and effective leak detection solution to locate leaks in the inner tubes, enabling timely remedial action during equipment downtime, ensuring the vacuum-insulated pipeline returns to normal operating conditions, and preventing significant damage to the cryogenic system. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a detection system and method for leaks in the inner pipes of vacuum insulated pipelines at testing stations, which can quickly and accurately locate leaks in the inner pipes of vacuum insulated pipelines.

[0006] This invention provides a system for detecting leaks in the inner pipe of a vacuum-insulated pipeline at a test station. The system includes a vacuum-insulated pipeline for transmitting cryogenic liquid generated by a cryogenic refrigerator to a distribution valve box. The vacuum-insulated pipeline is connected to at least one helium mass spectrometer leak detector. The vacuum-insulated pipeline is constructed by welding several prefabricated sections through corresponding transition sections. Each prefabricated section includes an inner pipe, an outer pipe, and a vacuum interlayer between the inner and outer pipes. A vacuum safety plug is provided on the outer pipe of each prefabricated section, and at least one prefabricated section is connected to an auxiliary evacuation system.

[0007] Furthermore, the vacuum safety plug has a matching safety plug fixture, and the helium mass spectrometer leak detector is sealed to the safety plug fixture via a bellows.

[0008] Furthermore, the diameter of the bellows is the same as the diameter of the exhaust port of the helium mass spectrometer leak detector.

[0009] Furthermore, the corrugated pipe adopts a stainless steel corrugated pipe KF interface.

[0010] Furthermore, the auxiliary evacuation system includes a first vacuum unit acting on the vacuum interlayer and a second vacuum unit acting on the internal pipe.

[0011] Furthermore, the first vacuum unit includes a vacuum valve and a first vacuum pump group connected in sequence to the vacuum interlayer via a first extraction branch. A vacuum gauge is connected to a section of the first extraction branch between the vacuum interlayer and the vacuum valve, and a nitrogen storage tank is connected to a section of the first extraction branch between the vacuum valve and the first vacuum pump group.

[0012] Furthermore, the vacuum gauge is connected to the first extraction branch via an angle valve, the first nitrogen storage tank is connected to the first extraction branch via a nitrogen supply branch, and the nitrogen supply branch is equipped with a pressure gauge and an isolation valve.

[0013] Furthermore, the second vacuum unit includes several inner pipe branches that are respectively connected to each internal pipe. The inner pipe branches are connected to the second vacuum pump group through the second air extraction branch, connected to the recovery gas bag through the helium recovery branch, and connected to the helium storage tank through the helium supply branch.

[0014] Furthermore, a pump switching valve is provided on the second extraction branch, a gas bag on / off valve is provided on the helium recovery branch, a storage tank on / off valve is provided on the helium supply branch, and an inner pipe process valve is provided on the inner pipe branch.

[0015] This invention also provides a method for detecting leaks in the inner pipe of a vacuum-insulated pipeline at a testing station, comprising:

[0016] Step S1: Provide the above-mentioned detection system for leaks in the inner pipe of the vacuum insulation pipeline of the test station;

[0017] Step S2: Start the second vacuum pump unit of the second vacuum unit to evacuate the internal pipes of the vacuum insulation pipeline to below 5 Pa.

[0018] Step S3: Turn off the second vacuum pump group, turn on the first vacuum pump group and nitrogen storage tank of the first vacuum unit, and perform nitrogen replacement on the vacuum interlayer of the vacuum insulation pipeline several times. Each time, the vacuum is evacuated to below 5 Pa, and the residual helium impurities in the vacuum interlayer are washed away.

[0019] Step S4: Turn off the first vacuum pump group and the nitrogen storage tank, connect the vacuum insulation pipeline and the helium mass spectrometer leak detector, and perform vacuum negative pressure leak detection on the internal pipes of the vacuum insulation pipeline to determine the internal pipes with leaks.

[0020] Step S5: Perform vacuum negative pressure leak detection on each transition section of the internal pipe with a leak to identify the internal pipe transition section with a leak.

[0021] Step S6: Open the nitrogen storage tank, fill the vacuum jacket of the vacuum insulation pipeline with nitrogen, and remove the outer shell of the transition section where the leak is located.

[0022] Step S7: Open the helium storage tank, fill the internal pipe of the vacuum insulation pipeline with the leak with helium, and surround all or part of the transition section of the internal pipe where the leak is located with a helium hood. Use the suction gun mode of the helium mass spectrometer leak detector to determine the actual leak point.

[0023] The detection system and method for leaks in the inner tubes of vacuum insulated pipelines provided by this invention enables the detection of each inner tube and section of the vacuum insulated pipeline. It can accurately and quickly identify the inner tubes with leaks and quickly and accurately locate the range of leaks, thereby improving detection efficiency and accuracy. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the detection system for leaks in the inner pipe of a vacuum insulated pipeline at a test station according to the present invention.

[0025] Figure 2 yes Figure 1 A schematic diagram of the internal piping structure of a medium vacuum insulation pipeline.

[0026] Figure 3 This is an example diagram illustrating the leak detection method for the inner pipe of a vacuum insulated pipeline in a test station according to the present invention. Detailed Implementation

[0027] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0028] like Figure 1 As shown, the present invention provides a detection system for leaks in the inner pipe of a vacuum-insulated pipeline in a test station. The system includes a vacuum-insulated pipeline 3 for transferring cryogenic liquid generated by a cryogenic refrigerator 1 to a distribution valve box 2. The vacuum-insulated pipeline 3 is connected to at least one helium mass spectrometer leak detector 4. The vacuum-insulated pipeline 3 is constructed by welding several prefabricated sections 31 together with corresponding transition sections 32 (i.e., a long-distance vacuum-insulated pipeline 3 is formed by welding multiple short-distance prefabricated sections 31 on-site, with each transition section 32 serving as a connection section during on-site welding of the prefabricated sections 31). Each prefabricated section 31 includes multiple internal pipes, an external pipe, and a vacuum interlayer between the internal and external pipes. Each prefabricated section 31 has a vacuum safety plug 5 of the same specification on its external pipe, and at least one prefabricated section 31 is connected to an auxiliary evacuation system. It should be understood that the internal and external pipes of adjacent prefabricated sections 31 are interconnected to form a complete vacuum-insulated pipeline 3.

[0029] Each prefabricated section 31 has a matching safety plug 5 for controlling the connection and disconnection between the vacuum insulation pipeline 3 and external equipment and / or systems. The helium mass spectrometer leak detector 4 is sealed to the safety plug fixture via a bellows. The diameter of the bellows is the same as the diameter of the exhaust port of the helium mass spectrometer leak detector 4, and in this embodiment, the bellows uses a stainless steel bellows KF interface. It should be noted that if a leak is detected in a prefabricated section, only one helium mass spectrometer leak detector needs to be connected to the vacuum insulation pipeline 3; if a leak is detected in a transition section, two helium mass spectrometer leak detectors need to be connected to the vacuum insulation pipeline 3; when two helium mass spectrometer leak detectors are connected, the bellows used are of the same specification.

[0030] The auxiliary evacuation system has functions such as pre-vacuuming, gas diversion, reducing the reaction time and purging time of leak-indicating gas, and accelerating the leak detection process. It includes a first vacuum unit 61 acting on the vacuum interlayer and a second vacuum unit 62 acting on the internal pipes (see...). Figure 2 ).

[0031] The first vacuum unit 61 includes a vacuum valve 612 and a first vacuum pump group 613 connected sequentially to the vacuum interlayer via a first extraction branch 611. A vacuum gauge 614 is connected to a section of the first extraction branch 611 between the vacuum interlayer and the vacuum valve 612 to monitor the vacuum pressure within the vacuum interlayer. A nitrogen storage tank 615 is connected to a section of the first extraction branch 611 between the vacuum valve 612 and the first vacuum pump group 613 to fill the vacuum interlayer with nitrogen. The vacuum gauge 614 is connected to the first extraction branch 611 via an angle valve 616, and the nitrogen storage tank 615 is connected to the first extraction branch 611 via a nitrogen supply branch 617. The first nitrogen supply branch 617 is equipped with a pressure gauge 618 for monitoring the real-time supply pressure and an isolation valve 619 for controlling the on / off state of the pipeline.

[0032] like Figure 2 As shown (A-E in the diagram represent five internal pipes in the vacuum insulation pipeline), the second vacuum unit 62 includes several internal pipe branches 33 connected to each internal pipe. These internal pipe branches 33 are connected to the second vacuum pump group 622 via a second extraction branch 621, to a recovery gas bag 624 via a helium recovery branch 623, and to a helium storage tank 626 via a helium supply branch 625. The recovery gas bag 624 recovers helium from the internal pipes via the helium recovery branch 623, and the helium storage tank 626 fills the internal pipes with helium via the helium supply branch 625. Furthermore, the second extraction branch 621 is equipped with a pump switching valve 627 to control the connection between the second vacuum pump group 622 and all internal pipes. The helium recovery branch 623 is equipped with a gas bag on / off valve 628 to control the connection between the recovery gas bag 624 and all internal pipes. A storage tank on / off valve 629 is installed on the helium supply branch 625 to control the connection and disconnection between the helium storage tank 626 and all internal pipelines. In addition, each internal pipeline branch 33 is equipped with an internal pipeline process valve 34 to control the individual connection and disconnection of each internal pipeline branch 33.

[0033] It should be noted that the leak rate of all pipelines and connections in the aforementioned helium mass spectrometer leak detector 4 and the auxiliary evacuation system is less than 1.0E. -9 Pa·m 3 / s.

[0034] Based on the above-described detection system, the present invention also provides a method for detecting leaks in the inner pipes of a vacuum-insulated pipeline at a test station, the method comprising the following steps:

[0035] Step S1: Provide the above-mentioned detection system for leaks in the inner pipe of the vacuum insulation pipeline of the test station.

[0036] Step S2: Start the second vacuum pump group 622 of the second vacuum unit 62 to evacuate the internal pipes of the vacuum insulation pipeline 3 to below 5 Pa.

[0037] Step S3: Turn off the second vacuum pump group 622, turn on the first vacuum pump group 613 and nitrogen storage tank 615 of the first vacuum unit 61, and perform nitrogen replacement on the vacuum interlayer of the vacuum insulation pipeline 3 several times, evacuating to below 5 Pa each time, and cleaning the residual helium impurities in the vacuum interlayer.

[0038] Step S4: Turn off the first vacuum pump group 613 and nitrogen storage tank 615, connect the vacuum insulation pipeline 3 and helium mass spectrometer leak detector 4, and perform vacuum negative pressure leak detection on the internal pipes of the vacuum insulation pipeline 3 to determine the internal pipes with leaks.

[0039] Step S4 specifically includes:

[0040] Step S41: Connect a helium mass spectrometer leak detector 4 to a vacuum safety plug on an external pipe, run the helium mass spectrometer leak detector 4, and wait for the background leak rate of the helium mass spectrometer leak detector 4 to stabilize.

[0041] Step S42: Use helium storage tank 626 to sequentially fill each internal pipe with helium, and observe the leak rate value of helium mass spectrometer leak detector 4 after filling with helium. If the leak rate value exceeds 1.0E... -9 Pa·m 3 If the value is / s, it indicates a leak in the corresponding internal pipe. It should be noted that when filling with helium, the pressure in the internal pipe must be kept below one gauge pressure, and the helium concentration inside the internal pipe should be 10%–30%.

[0042] Step S5: Perform vacuum negative pressure leak detection on each transition section corresponding to the internal pipe with the leak to determine the transition section with the leak. Specifically, connect another helium mass spectrometer leak detector 4 of the same specification to other vacuum safety plugs on the external pipe in sequence. After each connection, wait for the background leak rate of the helium mass spectrometer leak detector 4 to stabilize, and use the helium storage tank 626 to fill the internal pipe with the leak with helium. Determine the transition section where the leak is located based on the leak rate values ​​of the two helium mass spectrometer leak detectors 4.

[0043] It should be noted that the helium mass spectrometer leak detector must be calibrated before performing vacuum negative pressure leak detection on internal pipes and transition sections.

[0044] Step S6: Open the nitrogen storage tank 615, fill the vacuum jacket of the vacuum insulation pipeline 3 with nitrogen, and remove the outer shell of the transition section where the leak is located.

[0045] Step S7: Surround all or part of the internal pipe transition section where the leak is located with a helium gas hood, and use the suction gun mode of the helium mass spectrometer leak detector 4 to determine the actual leak point. Specifically, insert the suction gun into the helium gas hood and fill the internal pipe with helium. After waiting for a certain period of time, observe the stable leak rate value of the helium mass spectrometer leak detector 4 to preliminarily determine the overall leak rate range of the transition section. Remove the helium gas hood and use the suction gun to check for leaks at the suspected locations of the transition section one by one. When the leak rate at a certain location is approximately the same as the overall leak rate range of the transition section, that location is the actual leak point. It should be noted that when using the suction gun for leak detection, the principle of moving from top to bottom, from far to near, and at a slow speed is usually adopted. When the suction gun moves to the actual leak point, the signal of the helium mass spectrometer leak detector 4 will be significantly enhanced. To shorten the leak detection time, a shorter suction gun hose, such as a metal hose or a plastic tube, should be selected.

[0046] After locating the actual leak point, the leak can be repaired. After repair, high-concentration, high-pressure helium gas (helium concentration ≥ 50%, pressure ≥ 2 bar) is injected into the internal pipeline for leak detection. First, a suction gun leak detection method is used. If the suction gun leak detection method fails to detect a suspected leak, the aforementioned vacuum negative pressure leak detection method is used to detect leaks in that transition section separately. After leak detection is completed, all helium gas injected into the internal pipeline is recovered into the recovery gas bag 624, and the vacuum jacket of the vacuum insulation pipeline 3 is evacuated.

[0047] Through the above steps, the method for detecting leaks in the inner pipe of a vacuum-insulated pipeline provided by this invention first connects the necessary equipment, then uses an auxiliary evacuation system to evacuate the pipeline to achieve the required vacuum environment. After connecting a helium mass spectrometer leak detector, helium is sequentially introduced into the inner pipe of the multi-layered insulated pipeline. The output of the helium mass spectrometer leak detector is used to determine the location of the leak in the inner pipe. This invention is clear, convenient, and practical, requires simple equipment, and has high leak detection efficiency.

[0048] The following combination Figure 2 and Figure 3 The method for detecting leaks in the inner pipe of a vacuum-insulated pipeline in a test station according to the present invention is further explained through a specific example. Figure 3 In the diagram, a to h represent the numbers of the vacuum safety plugs, and A' to I' represent the numbers of each transition section.

[0049] Step S1: In the aforementioned test station's vacuum insulated pipeline leak detection system, after long-term use, the five internal pipes A, B, C, D, and E of the vacuum insulated pipeline were filled with helium at room temperature. A helium mass spectrometer leak detector was then connected for negative pressure leak detection. The detected leak rate was 7.9E. -6 Pa·m 3 / s, vacuum value is 1.01Pa.

[0050] Step S2: Start the second vacuum pump group 622 of the second vacuum unit 62 to evacuate the internal pipes A, B, C, D, and E of the vacuum insulation pipeline 3 to 1.01 Pa.

[0051] Step S3: Turn off the second vacuum pump group 622, turn on the first vacuum pump group 613 and nitrogen storage tank 615 of the first vacuum unit 61, and perform nitrogen replacement on the vacuum interlayer of the vacuum insulation pipeline 3 3 to 4 times, evacuating to below 5 Pa each time, and cleaning the residual helium impurities in the interlayer. Before the last replacement, evacuate the vacuum interlayer to 1.01 Pa.

[0052] Step S4: Turn off the first vacuum pump group 613 and nitrogen storage tank 615. Connect and run the helium mass spectrometer leak detector 4 at the vacuum safety plug a of the vacuum insulation pipeline 3. Wait until the background leak rate of the helium mass spectrometer leak detector 4 stabilizes and displays a local leak rate of ≤1.0E. -13 Pa·m 3 At a rate of / s, mixed helium gas is sequentially introduced into internal pipes A, B, C, D, and F using helium storage tank 626. During introduction, the helium concentration in the internal pipes is 10%–30%, and the pressure is 1000 Pa. Using a fully open vacuum safety plug fixture, based on the output response of the helium mass spectrometer leak detector 4, it was found that when mixed helium gas was introduced into pipe B, the leak rate changed rapidly, and the maximum leak rate increased to 2.9E. -5 Pa·m 3 / s@1.01Pa, thus determining that the leak is in pipe B.

[0053] Step S5: After confirming a leak in tube B, connect the remaining safety plugs sequentially to the same specifications of helium mass spectrometer leak detector 4 via 500mm long DN25 corrugated tubing. When the background leak rate of helium mass spectrometer leak detector 4 stabilizes, pressurize tube B using helium storage tank 626, ensuring the pressure is below one gauge pressure. Determine which transition section has a leak based on the output response of helium mass spectrometer leak detector 4. The specific leak detection sequence is as follows:

[0054] 1) A helium mass spectrometer leak detector was set up at point a and point h of the vacuum plug. It was found that a helium leak was detected at point h before that at point a.

[0055] 2) The helium mass spectrometer leak detector was moved from point a to point b, and it was found that a helium leak was detected at point h before that at point b;

[0056] 3) The helium mass spectrometer leak detector was moved from point b to point c, and it was found that a helium leak was detected at point h before point c;

[0057] 4) The helium mass spectrometer leak detector was moved from point c to point d, and it was found that a helium leak was detected at point h before that at point d;

[0058] 5) The helium mass spectrometer leak detector was moved from point d to point g. It was found that helium leaks were detected at points g and d almost simultaneously, and the leak rate h ≈ g > d > c > b > a. Therefore, the leak was determined to be in the transition section I'.

[0059] Step S6: Open nitrogen storage tank 615, fill the vacuum jacket of vacuum insulation pipeline 3 with nitrogen, and remove the outer shell of transition section I'.

[0060] Step S7: Set the helium mass spectrometer leak detector to suction gun mode. Use a helium hood to completely enclose the suspected area or component of the transition section of the inner tube. Insert the suction gun connected to the helium mass spectrometer leak detector into the helium hood. Inject 2 bar of helium into tube B, wait for a certain reaction time, and observe the stable leak rate reading from the helium mass spectrometer leak detector. Then remove the helium hood and use the suction gun to sequentially check for leaks at the suspected areas of transition section I. When the signal from the helium mass spectrometer leak detector significantly increases, the maximum leak rate detected by the suction gun is 5.0 × 10⁻⁶. -6 Pa·m 3 / s, accurately locates the actual leak point with a length of 1-2mm.

[0061] After locating the actual leak point, repair or replace the leak. After repair, fill pipe B with high-concentration, high-pressure helium (helium concentration ≥ 50%, pressure ≥ 2 bar) for leak detection. First, use a suction gun leak detection method. If the suction gun method fails to detect a suspected leak, combine it with a vacuum negative pressure leak detection method to detect the transition section separately. After leak detection, recover all helium filled into the internal pipes into the recovery gas bag 624, and evacuate the vacuum jacket of the vacuum insulation pipeline 3.

[0062] This invention enables the inspection of each and every section of the inner tubes of a vacuum-insulated pipeline, accurately and quickly identifying leaks and pinpointing their location, thus improving detection efficiency and accuracy. Negative-pressure helium mass spectrometry leak detection can roughly determine the location of the leak in the transition section, offering advantages such as high sensitivity and low cost. Combined with positive-pressure suction gun leak detection, it can accurately detect the specific location of the leak, and the operation is simple, convenient, and fast. During the leak detection process, the leak detector and its auxiliary nitrogen and helium sources are simultaneously controlled, allowing for timely observation of leak rate changes, data analysis, and feedback. Multiple operators collaborate on these tasks. Through practical application on a vacuum-insulated pipeline at a test station, this invention can accurately and effectively determine the location, range, and leak rate of leaks.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for detecting leaks in the inner pipe of a vacuum-insulated pipeline at a testing station, characterized in that, include: Step S1 provides a detection system for leaks in the inner pipe of a vacuum-insulated pipeline at a test station. The system includes a vacuum-insulated pipeline for transmitting cryogenic liquid generated by a cryogenic refrigerator to a distribution valve box. The vacuum-insulated pipeline is connected to at least one helium mass spectrometer leak detector. The vacuum-insulated pipeline is constructed by welding several prefabricated sections through corresponding transition sections. Each prefabricated section includes multiple internal pipes, external pipes, and a vacuum interlayer between the internal and external pipes. Each prefabricated section has a vacuum safety plug on its external pipe, and at least one prefabricated section is connected to an auxiliary evacuation system. The vacuum safety plug has a matching safety plug fixture, and the helium mass spectrometer leak detector is sealed to the safety plug fixture via a corrugated pipe. The auxiliary evacuation system includes a first vacuum unit acting on the vacuum interlayer and a second vacuum unit acting on the internal pipes; the second vacuum unit includes several inner pipe branches connected to each internal pipe respectively, the inner pipe branches are connected to the second vacuum pump group through the second evacuation branch, connected to the recovery gas bag through the helium recovery branch, and connected to the helium storage tank through the helium supply branch. The second extraction branch is equipped with a pump switching valve, the helium recovery branch is equipped with a gas bag on / off valve, and the helium supply branch is equipped with a storage tank on / off valve to control the connection and disconnection between the helium storage tank and all internal pipes. The internal pipe branch is equipped with an internal pipe process valve to control the individual connection and disconnection of each internal pipe branch. Step S2: Start the second vacuum pump unit of the second vacuum unit to evacuate the internal pipes of the vacuum insulation pipeline to below 5 Pa. Step S3: Turn off the second vacuum pump group, turn on the first vacuum pump group and nitrogen storage tank of the first vacuum unit, and perform nitrogen replacement on the vacuum interlayer of the vacuum insulation pipeline several times. Each time, the vacuum is evacuated to below 5 Pa, and the residual helium impurities in the vacuum interlayer are washed away. Step S4: Turn off the first vacuum pump group and the nitrogen storage tank, connect the vacuum insulation pipeline and the helium mass spectrometer leak detector, and perform vacuum negative pressure leak detection on the internal pipes of the vacuum insulation pipeline to identify internal pipes with leaks; Step S4 specifically includes: Step S41: Connect a helium mass spectrometer leak detector to a vacuum safety plug on an external pipeline, run the helium mass spectrometer leak detector, and wait for the background leak rate of the helium mass spectrometer leak detector to stabilize. Step S42: Use a helium storage tank to sequentially fill each internal pipe with helium gas, and observe the leak rate value of the helium mass spectrometer leak detector after filling with helium gas. If the leak rate value exceeds 1.0E... -9 Pa·m 3 If / s, it indicates that there is a leak in the corresponding internal pipe; Step S5 involves performing vacuum negative pressure leak detection on each transition section corresponding to the internal pipe with a leak to determine the internal pipe transition section with the leak. Step S5 specifically includes: connecting another helium mass spectrometer leak detector of the same specification to other vacuum safety plugs on the external pipe in sequence. After each connection, once the background leak rate of the helium mass spectrometer leak detector is stable, helium gas is injected into the internal pipe with the leak using a helium storage tank. The output response of the helium mass spectrometer leak detector is used to determine which transition section has a leak. If two vacuum safety plugs detect helium leaks at approximately the same time, and the leak rate values ​​of the two helium mass spectrometer leak detectors are used to determine the transition section where the leak is located. The leak detection sequence of a mass spectrometer leak detector includes: The first and second vacuum safety plugs are located at opposite ends of the external pipe; If a helium mass spectrometer leak detector is placed at the first and second points of the vacuum safety plug, and a helium leak is detected at the second point before the first point, then the helium mass spectrometer leak detector is moved from the first point to the closer third point. Then, the third point of the vacuum safety plug is used as the new first point of the vacuum safety plug, and the above steps of setting up the helium mass spectrometer leak detector and detecting helium leaks are repeated until helium leaks are detected at the first point of the vacuum safety plug and the second point of the vacuum safety plug at approximately the same time. At this point, the transition section where the leak is located is determined. Step S6: Open the nitrogen storage tank, fill the vacuum jacket of the vacuum insulation pipeline with nitrogen, and remove the outer shell of the transition section where the leak is located. Step S7: Open the helium storage tank, fill the internal pipe of the vacuum insulation pipeline with the leak with helium, and surround all or part of the transition section of the internal pipe where the leak is located with a helium hood. Use the suction gun mode of the helium mass spectrometer leak detector to determine the actual leak point.

2. The method for detecting leaks in the inner pipe of a vacuum insulated pipeline at a test station according to claim 1, characterized in that, The diameter of the bellows is the same as the diameter of the exhaust port of the helium mass spectrometer leak detector.

3. The method for detecting leaks in the inner pipe of a vacuum insulated pipeline at a test station according to claim 1, characterized in that, The corrugated pipe adopts a stainless steel corrugated pipe KF interface.

4. The method for detecting leaks in the inner pipe of a vacuum insulated pipeline at a test station according to claim 1, characterized in that, The first vacuum unit includes a vacuum valve and a first vacuum pump group connected in sequence to the vacuum interlayer via a first extraction branch. A vacuum gauge is connected to a section of the first extraction branch between the vacuum interlayer and the vacuum valve, and a nitrogen storage tank is connected to a section of the first extraction branch between the vacuum valve and the first vacuum pump group.

5. The method for detecting leaks in the inner pipe of a vacuum insulated pipeline at a test station according to claim 4, characterized in that, The vacuum gauge is connected to the first extraction branch via an angle valve, and the nitrogen storage tank is connected to the first extraction branch via a nitrogen supply branch. The nitrogen supply branch is equipped with a pressure gauge and an isolation valve.

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