Device and method for airtightness test of gas pressure regulating device of dual-fuel engine

Abstract

A device and method for air tightness test of a dual-fuel engine gas pressure regulating device, comprising a first flange, a second flange, a third flange, an outer tube air intake valve, an inner tube air intake valve, an inner tube front air release valve, an outer tube air release valve, an air release valve, an inner tube rear air release valve, an inner tube front pressure gauge, a pressure gauge, an inner tube rear pressure gauge, an outer tube pressure gauge, a muffler, a pressure regulating valve, a low-pressure nitrogen unit and an air release main pipe; in the order of the inner tube first and the outer tube later, the air tightness test of the dual-fuel engine gas pressure regulating device is completed in stages before the double-off and double-off and release function ball valve group, inside the double-off and double-off and release function ball valve group, and between the double-off and double-off and release function ball valve group and the pressure regulating valve. The present invention can accurately find the leak location, avoid large-scale leak detection work, effectively avoid the risk of fully disassembling the assembled gas pressure regulating device to find leaks due to early quality problems, shorten the assembly cycle of the whole machine, and reduce labor intensity.

Description

Technical Field

[0001] The invention relates to a dual-fuel low-speed diesel engine, in particular to a device and method for airtightness testing of a fuel gas pressure regulating device of a dual-fuel engine, belonging to the technical field of diesel engine manufacturing. Background Art

[0002] With the development of science and technology, and the increasingly stringent environmental protection policies of the international community, the emission requirements for ships have become increasingly stringent, and dual-fuel diesel engines have emerged. Dual-fuel diesel engines have the characteristics of low NOx emissions, less particulate matter emissions, and good economy, and are one of the main development trends of diesel engines in the future. At present, the main types of dual fuels are: liquefied petroleum gas + diesel, liquefied methanol + diesel, natural gas + diesel, and ethane + diesel. For large dual-fuel main engines using natural gas fuel, a gas pressure regulating device is indispensable.

[0003] See also Figure 1 The gas pressure regulating device (IGPR) includes a control box and a natural gas channel formed by a double-block and double-break and release function ball valve group 02, a filter, a flow meter and a pressure regulating valve 03 which are connected in series in sequence through a gas double-walled pipe 01. The double-block and double-break and release function ball valve group 02 includes an inlet valve 021, an outlet valve 022 and a release valve 023. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a device and method for airtightness test of a gas pressure regulating device of a dual-fuel engine, so as to realize airtightness test of the gas pressure regulating device of a dual-fuel engine.

[0005] The technical solution of the present invention for solving the technical problem is as follows:

[0006] A device for air tightness test of a gas pressure regulating device of a dual-fuel engine, the gas pressure regulating device comprising a natural gas channel formed by sequentially connecting a double-off and double-off and release function ball valve group, a filter, a flow meter and a pressure regulating valve in series through a double-walled gas pipe, the double-walled gas pipe is composed of an inner pipe and an outer pipe, the double-off and double-off and release function ball valve group comprises an inlet valve, an outlet valve and a release valve; characterized in that: the device for air tightness test comprises a first flange, a second flange, a third flange, an outer pipe inlet valve, an inner pipe inlet valve, an inner pipe front air release valve, an outer pipe air release valve, an air release valve, an inner pipe rear air release valve, an inner pipe front pressure gauge, a pressure gauge, an inner pipe rear pressure gauge, an outer pipe pressure gauge, a muffler, a pressure regulating valve, a low-pressure nitrogen unit and an air release main pipe;

[0007] The first flange is sealingly mounted on the end face of the double-walled gas pipe located at the front end of the natural gas channel, the outer tube air intake valve is mounted on the first flange and communicated with the outer tube of the double-walled gas pipe, the inner tube air intake valve and the inner tube front air release valve are mounted on the first flange and communicated with the inner tube of the double-walled gas pipe, the low-pressure nitrogen unit is respectively connected to the outer tube air intake valve and the inner tube air intake valve through the pressure regulating valve to provide test gas, and the inner tube front pressure gauge is mounted between the inner tube front air release valve and the first flange;

[0008] The second flange is sealingly mounted on the side of the double-walled gas pipe located at the front end of the natural gas channel, the outer pipe gas relief valve is mounted on the second flange and communicated with the outer pipe of the double-walled gas pipe, the gas relief valve is connected to the relief valve of the double-block and relief function ball valve group, and the pressure gauge is connected between the gas relief valve and the relief valve;

[0009] The third flange is sealingly mounted on the end face of the pressure regulating valve located at the rear end of the natural gas channel, the inner tube rear air release valve is mounted on the third flange and communicated with the inner tube of the double-walled gas pipe, the inner tube rear pressure gauge is connected between the inner tube rear air release valve and the third flange, and the outer tube pressure gauge is mounted on the third flange and communicated with the outer tube of the double-walled gas pipe;

[0010] The exhaust main pipe is respectively connected to the inner tube front exhaust valve, the outer tube exhaust valve, the exhaust valve and the inner tube rear exhaust valve. One end of the muffler is connected to the exhaust main pipe, and the other end is an open exhaust port of the exhaust main pipe.

[0011] Furthermore, the outer tube air intake valve, the inner tube air intake valve, the inner tube front air release valve, the outer tube air release valve, the air release valve and the inner tube rear air release valve are needle valves.

[0012] Another technical solution of the present invention is as follows:

[0013] An airtightness test method for a dual-fuel engine gas pressure regulating device implemented by the above device comprises the following specific steps:

[0014] 1) Install the airtight test device on the gas pressure regulating device, open the pressure regulating valve of the gas pressure regulating device, close the remaining valves, and close all valves on the gastight test device;

[0015] 2) Inner tube airtightness test——

[0016] 2-1) Slowly open and adjust the pressure regulating valve, open the inner tube air inlet valve on the first flange, and the gas in the low-pressure nitrogen unit enters the inner tube before the inlet valve until the pressure on the pressure gauge in front of the inner tube rises to 16 Bar. After stabilization, close the inner tube air inlet valve, cut off the gas source, maintain the pressure in the inner tube and start timing. If the pressure drop within 1000 seconds is less than 0.4 Bar, the air tightness is qualified, open the inner tube front air release valve and muffler, and the gas in the inner tube before the inlet valve is released through the air release port of the air release main pipe;

[0017] 2-2) Close the air bleed valve in front of the inner tube, open the inlet valve of the double-off and double-break and discharge function ball valve group, open the inner tube air inlet valve, and the gas in the low-pressure nitrogen unit enters the inner tube before the outlet valve until the pressure on the pressure gauge in front of the inner tube and the pressure gauge rises to 16Bar. After stabilization, close the inlet valve and the inner tube air inlet valve, cut off the gas source, open the air bleed valve in front of the inner tube, and release the gas in the inner tube before the inlet valve until the pressure on the pressure gauge in front of the inner tube is 0, maintain the pressure in the double-off and double-break and discharge function ball valve group and start timing. If the pressure drop on the pressure gauge is less than 0.4Bar within 1000 seconds, the air tightness is qualified, open the discharge valve and the air bleed valve, and the gas between the inlet valve and the outlet valve of the double-off and double-break and discharge function ball valve group is released from the air bleed port through the air bleed main pipe and the muffler;

[0018] 2-3) Close the air leakage valve, the release valve and the air leakage valve in front of the inner tube, open the inlet valve and the outlet valve of the double-off and double-off and release function ball valve group, open the inner tube air inlet valve, and the gas in the low-pressure nitrogen unit enters the pressure regulating valve and the inner tube before it, until the pressure on the pressure gauge in front of the inner tube and the pressure gauge behind the inner tube rises to 16Bar. After stabilization, close the outlet valve of the double-off and double-off and release function ball valve group and the inner tube air inlet valve, cut off the gas source, open the air leakage valve, the release valve and the air leakage valve in front of the inner tube, and release the gas in the inner tube before the outlet valve. The gas in the inner tube is discharged until the pressure on the pressure gauge in front of the inner tube and the pressure gauge is 0, the pressure between the outlet valve and the pressure regulating valve is maintained and the timing is started. If the pressure drop on the pressure gauge behind the inner tube is less than 0.4 Bar within 1000 seconds, the air tightness is qualified, the air relief valve behind the inner tube is opened, and the gas between the pressure regulating valve and the outlet valve is discharged from the air relief port through the air relief main pipe and the muffler, and the inner tube air intake valve, the inner tube front air relief valve, the air relief valve and the inner tube rear air relief valve connected to the inner tube are closed, and the inner tube air tightness test is completed;

[0019] 3) External tube airtightness test——

[0020] Open the outer tube air inlet valve on the first flange, and the gas in the low-pressure nitrogen unit enters the outer tube of the double-walled gas pipe until the pressure on the outer tube pressure gauge of the third flange rises to 7 bar. After stabilization, close the outer tube air inlet valve, cut off the gas source, maintain the pressure in the outer tube and start timing. If the pressure drop is less than 0.4 Bar within 30 minutes, the air tightness of the outer tube is qualified. Open the outer tube air discharge valve on the second flange, and the gas in the outer tube is discharged from the air discharge port through the air discharge main pipe and the muffler. At this point, the entire air tightness test is completed.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention completes the air tightness test of the gas pressure regulating device of the dual-fuel engine in stages, in the order of inner tube first and outer tube later, before the double-off and double-off and discharge function ball valve group, inside the double-off and double-off and discharge function ball valve group, and between the double-off and double-off and discharge function ball valve group and the pressure regulating valve. The leakage position can be accurately found, and large-scale leak detection work can be avoided. The risk of completely disassembling the assembled gas pressure regulating device for leak detection due to quality problems in the early stage is effectively avoided, the assembly cycle of the whole machine is shortened, and the labor intensity is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the present invention.

[0024] Figure 2 It is a schematic diagram of the device structure of the present invention.

[0025] Figure 3 yes Figure 2 Enlarged view of part A in the middle.

[0026] Figure 4 yes Figure 2 Enlarged view of part B in the middle.

[0027] Figure 5 yes Figure 2 Enlarged view of part C in the middle.

[0028] In the figure,

[0029] 01—double-walled gas pipe, 02—double-off and double-break and release function ball valve group, 021—inlet valve, 022—outlet valve, 023—release valve, 03—pressure regulating valve, 1—first flange, 21—outer pipe air inlet valve, 22—inner pipe air inlet valve, 23—inner pipe front air relief valve, 24—outer pipe air relief valve, 25—air relief valve, 26—inner pipe rear air relief valve, 31—inner pipe front pressure gauge, 32—pressure gauge, 33—inner pipe rear pressure gauge, 34—outer pipe pressure gauge, 4—tee joint, 5—muffler, 6—third flange, 7—second flange, 8—pressure regulating valve, 9—low-pressure nitrogen unit, 10—air relief main pipe, 11—air relief port. DETAILED DESCRIPTION

[0030] The present invention is used for the air tightness test of the gas pressure regulating device of the dual-fuel engine to check or eliminate the leakage problem during the assembly process and complete the inspection work after assembly. The dual-fuel engine includes a gas regulating device, a gas distribution pipe, a gas ventilation pipe, a gas intake valve, a gas intake valve sealing oil pipe, a gas intake valve return pipe, a piston lower gas monitoring, a pilot oil injector, a pilot oil oil pipe, an intake valve hydraulic oil pipe, etc. Please refer to Figure 1 The gas pressure regulating device (IGPR) includes a control box and a natural gas channel formed by a double-off and double-off and release function ball valve group 02, a filter, a flow meter and a pressure regulating valve 03 connected in series through a double-walled gas pipe 01. The double-walled gas pipe 01 is composed of an inner pipe and an outer pipe. The double-off and double-off and release function ball valve group 02 includes an inlet valve 021, an outlet valve 022 and a release valve 023. The airtightness test uses a special airtightness test tool, and special flanges, joints, pressure reducing valves, pressure gauges, etc. are installed on the gas pressure regulating device to perform airtightness tests in the factory and submitted to the classification society.

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention shall not be limited thereto.

[0032] Please refer to Figure 2 , Figure 3 , Figure 4 and Figure 5 The airtight test device includes a first flange 1, a second flange 7, a third flange 6, an outer tube air intake valve 21, an inner tube air intake valve 22, an inner tube front air release valve 23, an outer tube air release valve 24, an air release valve 25, an inner tube rear air release valve 26, an inner tube front pressure gauge 31, a pressure gauge 32, an inner tube rear pressure gauge 33, an outer tube pressure gauge 34, a muffler 5, a pressure regulating valve 8, a low-pressure nitrogen unit 9 and an air release main pipe 10. All parts are connected according to different specifications of different models, especially different models have different specifications of special flanges.

[0033] See also Figure 1 The first flange 1 is sealed and installed on the end surface of the double-walled gas pipe 01 located at the front end of the natural gas channel. Figure 3 The outer tube air intake valve 21 is installed on the first flange 1 and is connected to the outer tube of the double-walled gas pipe 01. The inner tube air intake valve 22 and the inner tube front air leakage valve 23 are installed on the first flange 1 and are connected to the inner tube of the double-walled gas pipe 01. The low-pressure nitrogen unit 9 is connected to the outer tube air intake valve 21 and the inner tube air intake valve 22 respectively through the pressure regulating valve 8 to provide nitrogen for the test. The inner tube front pressure gauge 31 is installed between the inner tube front air leakage valve 23 and the first flange 1 through a three-way joint 4.

[0034] See also Figure 4 The second flange 7 is sealingly installed on the side of the double-walled gas pipe 01 located at the front end of the natural gas channel, the outer pipe relief valve 24 is installed on the second flange 7 and is connected to the outer pipe of the double-walled gas pipe 01, the relief valve 25 is connected to the relief valve 023 of the double-off and double-off and relief function ball valve group 02, and the pressure gauge 32 is connected between the relief valve 25 and the relief valve 023 through a three-way joint 4.

[0035] The third flange 6 is sealingly installed on the end face of the pressure regulating valve 03 located at the rear end of the natural gas channel, the inner tube rear air release valve 26 is installed on the third flange 6 and is connected to the inner tube of the double-walled gas pipe 01, the inner tube rear pressure gauge 33 is connected between the inner tube rear air release valve 26 and the third flange 6 through a three-way joint 4, and the outer tube pressure gauge 34 is installed on the third flange 6 and is connected to the outer tube of the double-walled gas pipe 01.

[0036] The exhaust main pipe 10 is respectively connected to the inner tube front exhaust valve 23, the outer tube exhaust valve 24, the exhaust valve 25 and the inner tube rear exhaust valve 26. One end of the muffler 5 is connected to the exhaust main pipe 10, and the other end is an open exhaust port 11 of the exhaust main pipe 10.

[0037] The outer tube air intake valve 21, the inner tube air intake valve 22, the inner tube front air release valve 23, the outer tube air release valve 24, the air release valve 25 and the inner tube rear air release valve 26 are needle valves.

[0038] The airtightness test method for the dual-fuel engine gas pressure regulating device of the present invention comprises the following specific steps: Figure 1 :

[0039] 1) Install the airtight test device on the gas pressure regulating device, open the pressure regulating valve 03 of the gas pressure regulating device, close the remaining valves, and close all the valves on the airtight test device.

[0040] 2) Inner tube airtightness test——

[0041] 2-1) Slowly open and adjust the pressure regulating valve 8 to an output pressure of 20 bar, open the inner tube air inlet valve 22 on the first flange 1, and the gas in the low-pressure nitrogen unit 9 enters the inner tube before the inlet valve 021 until the pressure on the pressure gauge 31 in front of the inner tube rises to 16 Bar. After stabilization, close the inner tube air inlet valve 22 to cut off the gas source; maintain the pressure in the inner tube and start timing. If the pressure drop within 1000 seconds is less than 0.4 Bar, the air tightness is qualified; open the inner tube front air release valve 23 and the muffler 5, and the gas in the inner tube before the inlet valve 021 is released through the air release port 11 of the air release main pipe 10 until the pressure on the pressure gauge 31 in front of the inner tube returns to zero.

[0042] 2-2) Close the inner tube front air release valve 23, open the inlet valve 021 of the double-off and double-break and release function ball valve group 02, open the inner tube air inlet valve 22, and the gas in the low-pressure nitrogen unit 9 enters the inner tube before the outlet valve 022 until the pressure on the pressure gauge 31 and the pressure gauge 32 before the inner tube rises to 16 Bar. After stabilization, close the inlet valve 021 and the inner tube air inlet valve 22 to cut off the gas source; open the inner tube front air release valve 23 to release the gas in the inner tube before the inlet valve 021. Until the pressure on the pressure gauge 31 in front of the inner tube is 0; maintain the pressure in the double-block and double-break and discharge functional ball valve group 02 and start timing. If the pressure drop on the pressure gauge 32 is less than 0.4Bar within 1000 seconds, the air tightness is qualified; open the discharge valve 023 and the air release valve 25, and the gas between the inlet valve 021 and the outlet valve 022 of the double-block and double-break and discharge functional ball valve group 02 is discharged from the air release port 11 through the air release main pipe 10 and the muffler 5 until the pressure on the pressure gauge 32 returns to zero.

[0043] 2-3) Close the inner tube front air leakage valve 23, the discharge valve 023 and the air leakage valve 25, open the inlet valve 021 and the outlet valve 022 of the double-off and discharge function ball valve group 02, open the inner tube air intake valve 22, and the gas in the low-pressure nitrogen unit 9 enters the pressure regulating valve 03 and the inner tube before it, until the pressure on the inner tube front pressure gauge 31 and the inner tube rear pressure gauge 33 rises to 16Bar, and after stabilization, close the outlet valve 022 of the double-off and discharge function ball valve group 02 and the inner tube air intake valve 22 to cut off the gas source; open the inner tube front air leakage valve 23, the discharge valve 023 and the air leakage valve 25 to discharge the gas in the inner tube before the outlet valve 022, Until the pressure on the pressure gauge 31 in front of the inner tube and the pressure gauge 32 is 0; maintain the pressure between the outlet valve 022 and the pressure regulating valve 03 and start timing. If the pressure drop on the pressure gauge 33 behind the inner tube is less than 0.4Bar within 1000 seconds, the air tightness is qualified; open the inner tube rear air release valve 26, and the gas between the pressure regulating valve 03 and the outlet valve 022 is released from the air release port 11 through the air release main pipe 10 and the muffler 5 until the pressure on the inner tube rear pressure gauge 33 returns to zero; close the inner tube intake valve 22, the inner tube front air release valve 23, the air release valve 25 and the inner tube rear air release valve 26 connected to the inner tube, and the inner tube air tightness test is completed.

[0044] 3) External tube airtightness test——

[0045] Adjust the pressure regulating valve 8 to an output pressure of 10 bar, open the outer tube air inlet valve 21 on the first flange 1, and the gas in the low-pressure nitrogen unit 9 enters the outer tube of the gas double-walled pipe 01 until the pressure on the outer tube pressure gauge 34 of the third flange 6 rises to 7 bar. After stabilization, close the outer tube air inlet valve 21 to cut off the gas source; maintain the pressure in the outer tube and start timing. If the pressure drop is less than 0.1 Bar within 30 minutes, the air tightness of the outer tube is qualified; open the outer tube air leakage valve 24 on the second flange 7, and the gas in the outer tube is discharged from the air leakage port 11 through the air leakage main pipe 10 and the muffler 5 until the pressure on the outer tube pressure gauge 34 returns to zero; at this point, the outer tube air tightness test is completed, and the entire air tightness test is completed at the same time.

[0046] The protection scope claimed by the present invention is not limited to the above-mentioned embodiments, but should also include other obvious changes and alternatives to the present invention.

Claims

1. A device for air tightness test of a gas pressure regulating device of a dual-fuel engine, the gas pressure regulating device comprising a natural gas channel formed by sequentially connecting a double-off and double-off and release function ball valve group, a filter, a flow meter and a pressure regulating valve in series through a double-walled gas pipe, the double-walled gas pipe is composed of an inner pipe and an outer pipe, the double-off and double-off and release function ball valve group comprises an inlet valve, an outlet valve and a release valve; characterized in that: The airtight test device includes a first flange, a second flange, a third flange, an outer tube air inlet valve, an inner tube air inlet valve, an inner tube front air release valve, an outer tube air release valve, an air release valve, an inner tube rear air release valve, an inner tube front pressure gauge, a pressure gauge, an inner tube rear pressure gauge, an outer tube pressure gauge, a muffler, a pressure regulating valve, a low-pressure nitrogen unit and an air release main pipe; The first flange is sealingly mounted on the end face of the double-walled gas pipe located at the front end of the natural gas channel, the outer tube air intake valve is mounted on the first flange and communicated with the outer tube of the double-walled gas pipe, the inner tube air intake valve and the inner tube front air release valve are mounted on the first flange and communicated with the inner tube of the double-walled gas pipe, the low-pressure nitrogen unit is respectively connected to the outer tube air intake valve and the inner tube air intake valve through the pressure regulating valve to provide test gas, and the inner tube front pressure gauge is mounted between the inner tube front air release valve and the first flange; The second flange is sealingly mounted on the side of the double-walled gas pipe located at the front end of the natural gas channel, the outer pipe gas relief valve is mounted on the second flange and communicated with the outer pipe of the double-walled gas pipe, the gas relief valve is connected to the relief valve of the double-block and relief function ball valve group, and the pressure gauge is connected between the gas relief valve and the relief valve; The third flange is sealingly mounted on the end face of the pressure regulating valve located at the rear end of the natural gas channel, the inner tube rear air release valve is mounted on the third flange and communicated with the inner tube of the double-walled gas pipe, the inner tube rear pressure gauge is connected between the inner tube rear air release valve and the third flange, and the outer tube pressure gauge is mounted on the third flange and communicated with the outer tube of the double-walled gas pipe; The exhaust main pipe is respectively connected to the inner tube front exhaust valve, the outer tube exhaust valve, the exhaust valve and the inner tube rear exhaust valve. One end of the muffler is connected to the exhaust main pipe, and the other end is an open exhaust port of the exhaust main pipe.

2. The device for airtightness test of the gas pressure regulating device of a dual-fuel engine according to claim 1, characterized in that: The outer tube air intake valve, the inner tube air intake valve, the inner tube front air release valve, the outer tube air release valve, the air release valve and the inner tube rear air release valve are needle valves.

3. An airtightness test method for a dual-fuel engine gas pressure regulating device implemented by the device of claim 1, characterized in that: The airtightness test method comprises the following specific steps: 1) Install the airtight test device on the gas pressure regulating device, open the pressure regulating valve of the gas pressure regulating device, close the remaining valves, and close all valves on the gastight test device; 2) Inner tube airtightness test—— 2-1) Slowly open and adjust the pressure regulating valve, open the inner tube air inlet valve on the first flange, and the gas in the low-pressure nitrogen unit enters the inner tube before the inlet valve until the pressure on the pressure gauge in front of the inner tube rises to 16 Bar. After stabilization, close the inner tube air inlet valve, cut off the gas source, maintain the pressure in the inner tube and start timing. If the pressure drop within 1000 seconds is less than 0.4 Bar, the air tightness is qualified, open the inner tube front air release valve and muffler, and the gas in the inner tube before the inlet valve is released through the air release port of the air release main pipe; 2-2) Close the air bleed valve in front of the inner tube, open the inlet valve of the double-off and double-break and discharge function ball valve group, open the inner tube air inlet valve, and the gas in the low-pressure nitrogen unit enters the inner tube before the outlet valve until the pressure on the pressure gauge in front of the inner tube and the pressure gauge rises to 16Bar. After stabilization, close the inlet valve and the inner tube air inlet valve, cut off the gas source, open the air bleed valve in front of the inner tube, and release the gas in the inner tube before the inlet valve until the pressure on the pressure gauge in front of the inner tube is 0, maintain the pressure in the double-off and double-break and discharge function ball valve group and start timing. If the pressure drop on the pressure gauge is less than 0.4Bar within 1000 seconds, the air tightness is qualified, open the discharge valve and the air bleed valve, and the gas between the inlet valve and the outlet valve of the double-off and double-break and discharge function ball valve group is released from the air bleed port through the air bleed main pipe and the muffler; 2-3) Close the air leakage valve, the release valve and the air leakage valve in front of the inner tube, open the inlet valve and the outlet valve of the double-off and double-off and release function ball valve group, open the inner tube air inlet valve, and the gas in the low-pressure nitrogen unit enters the pressure regulating valve and the inner tube before it, until the pressure on the pressure gauge in front of the inner tube and the pressure gauge behind the inner tube rises to 16Bar. After stabilization, close the outlet valve of the double-off and double-off and release function ball valve group and the inner tube air inlet valve, cut off the gas source, open the air leakage valve, the release valve and the air leakage valve in front of the inner tube, and release the gas in the inner tube before the outlet valve. The gas in the inner tube is discharged until the pressure on the pressure gauge in front of the inner tube and the pressure gauge is 0, the pressure between the outlet valve and the pressure regulating valve is maintained and the timing is started. If the pressure drop on the pressure gauge behind the inner tube is less than 0.4 Bar within 1000 seconds, the air tightness is qualified, the air relief valve behind the inner tube is opened, and the gas between the pressure regulating valve and the outlet valve is discharged from the air relief port through the air relief main pipe and the muffler, and the inner tube air intake valve, the inner tube front air relief valve, the air relief valve and the inner tube rear air relief valve connected to the inner tube are closed, and the inner tube air tightness test is completed; 3) External tube airtightness test—— Open the outer tube air inlet valve on the first flange, and the gas in the low-pressure nitrogen unit enters the outer tube of the double-walled gas pipe until the pressure on the outer tube pressure gauge of the third flange rises to 7 bar. After stabilization, close the outer tube air inlet valve, cut off the gas source, maintain the pressure in the outer tube and start timing. If the pressure drop is less than 0.1 Bar within 30 minutes, the air tightness of the outer tube is qualified. Open the outer tube air discharge valve on the second flange, and the gas in the outer tube is discharged from the air discharge port through the air discharge main pipe and the muffler. At this point, the entire air tightness test is completed.

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