A dual fluid loop thermal control system suitable for high orbit spacecraft

Abstract

The present invention discloses a dual fluid loop thermal control system suitable for high-orbit spacecraft, the system comprising two independent fluid loops; one end of the two independent fluid loops is pre-buried in an instrument panel of the spacecraft, and the other end is pre-buried on a radiator, when the working fluid in the fluid loop flows through the two fluid loops respectively, the heat of the load installed on the instrument panel is collected, the heat is transferred to the respective radiators, and the heat is dissipated into outer space; the present invention adopts dual fluid loops to solve the single point failure risk of the system, when one of the fluid loops fails and cannot work normally, the other fluid loop can still take away the heat of the load on the instrument panel through the pre-buried pipeline of the instrument panel, although the heat dissipation capacity of the whole spacecraft is slightly reduced, the layout design of the pre-buried pipeline of the instrument panel can achieve 75% of the original heat dissipation capacity, and the reliability of the thermal control system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of spacecraft, and in particular relates to a dual-fluid loop thermal control system suitable for high-orbit spacecraft. Background Art

[0002] With the improvement of payload performance, the demand for heat dissipation capacity of future high-orbit spacecraft such as communications and remote sensing will become increasingly higher. Traditional passive heat dissipation methods alone can no longer meet the needs of payloads and platforms. Active fluid loop thermal control technology is needed to supplement it or serve as the main heat dissipation method for the entire satellite.

[0003] At present, fluid circuit technology is generally used in low-orbit or deep-space exploration spacecraft, such as manned spacecraft, lunar exploration spacecraft, etc. The application of fluid circuit technology to high-orbit satellites has the following problems:

[0004] (1) The lifespan of high-orbit spacecraft is generally required to be more than 10 years. They cannot be repaired on orbit, so the reliability of the fluid circuit system needs to be improved;

[0005] (2) The high-orbit space environment is harsher than the low-orbit space environment. The raw materials and components in the fluid circuit system must meet the radiation environment during their service life, which puts higher requirements on system design and layout;

[0006] (3) Traditional fluid circuits mostly use cold plates to collect heat from the load. The cold plates are single points in the system. The more cold plates there are, the lower the system reliability. Summary of the invention

[0007] In view of this, the present invention provides a dual-fluid loop thermal control system suitable for high-orbit spacecraft, which can improve the reliability of the thermal control system and is suitable for high-orbit spacecraft.

[0008] The present invention is achieved through the following technical solutions:

[0009] A dual fluid loop thermal control system suitable for high-orbit spacecraft, the system comprising two independent fluid loops; one end of the two independent fluid loops is pre-buried in an instrument panel of the spacecraft, and the other end is pre-buried on a radiator. When the working fluid in the fluid loop flows through the two fluid loops respectively, the heat of the load installed on the instrument panel is collected, the heat is transferred to the respective radiators, and dissipated into outer space.

[0010] Furthermore, the working fluid in the fluid circuit is perfluorooctane.

[0011] Further, each fluid circuit includes: a pump valve assembly, an instrument panel pre-buried pipeline, a radiator and a connecting pipeline;

[0012] The instrument panel pre-buried pipeline is arranged in a rotating S shape and is pre-buried on the instrument panel;

[0013] The radiator is provided with a pre-buried radiator pipeline, which is arranged in a rotating S shape;

[0014] The connecting pipeline includes a connecting pipeline A and a connecting pipeline B; one end of the pre-buried pipeline of the instrument panel is connected to one end of the pre-buried pipeline of the radiator through the connecting pipeline A, and the other end of the pre-buried pipeline of the instrument panel is connected to the other end of the pre-buried pipeline of the radiator through the connecting pipeline B;

[0015] The pump-valve assembly is installed on the connecting pipeline, and is used to provide driving force for the flow of the working fluid and to add the working fluid.

[0016] Furthermore, the instrument panel pre-buried pipelines and the radiator pre-buried pipelines are both I-shaped pipelines.

[0017] Furthermore, a heat pipe is pre-buried on or externally attached to the instrument panel;

[0018] The pre-buried pipeline of the instrument panel is provided with a straight section part which is coupled with the heat pipe on the instrument panel; the straight section part is an I-shaped structure with fins.

[0019] Further, the instrument panel of the spacecraft includes: an upper horizontal panel and a lower horizontal panel that are arranged opposite to each other;

[0020] The instrument panel pre-buried pipeline includes: an upper pre-buried pipeline and a lower pre-buried pipeline; the upper pre-buried pipeline is pre-buried on the upper horizontal plate, and the lower pre-buried pipeline is pre-buried on the lower horizontal plate. The upper pre-buried pipeline and the lower pre-buried pipeline are both arranged in a rotating S shape, and the upper pre-buried pipeline and the lower pre-buried pipeline form a connected instrument panel pre-buried pipeline.

[0021] Furthermore, the instrument panel pre-buried pipeline and the radiator pre-buried pipeline are both formed by welding more than two sections of pipelines.

[0022] Furthermore, the instrument panel pre-buried pipelines, connecting pipeline A and connecting pipeline B are all arranged in the cabin of the spacecraft; the radiator pre-buried pipelines of the radiator are arranged outside the cabin of the spacecraft or on the cabin surface of the spacecraft; the connection between the pipelines located in the cabin adopts a double sealing method of non-metallic O-ring sealing + metal gasket sealing, and the connection between the pipelines located outside the cabin or on the cabin surface adopts welding; that is, the connection between the instrument panel pre-buried pipeline and the connecting pipeline A and the connection between the instrument panel pre-buried pipeline and the connecting pipeline B both adopt a double sealing method of non-metallic O-ring sealing + metal gasket sealing; the connection between the radiator pre-buried pipeline and the connecting pipeline A and the connection between the radiator pre-buried pipeline and the connecting pipeline B both adopt welding.

[0023] Furthermore, the radiator is a north or south cabin panel of a spacecraft or a deployable radiating panel;

[0024] When the radiator is a deployable radiant panel, the radiator comprises: a radiant panel body and an deployable driving assembly; the radiant panel body is provided with a pre-buried pipeline of the radiator, and the deployable driving assembly is installed on the radiant panel body and is used to drive the radiant panel body to deploy or retract; the deployable radiant panel is located outside the cabin of the spacecraft, and when the spacecraft is launched, the deployable radiant panel is in a retracted state, and after the spacecraft enters orbit, the deployable radiant panel is deployed to dissipate heat;

[0025] When the radiator is a north-south cabin panel of a spacecraft, the north-south cabin panels of the spacecraft are provided with pre-buried pipelines of the radiator; the north-south cabin panels of the spacecraft are located on the cabin surface of the spacecraft and are used for heat dissipation.

[0026] Further, the pump-valve assembly includes: a circulation pump, a filter, an accumulator, a pressure sensor, a differential pressure sensor, a charging and discharging valve and a manual stop valve;

[0027] Four circulating pumps are installed in parallel on the connecting pipeline, and the circulating pumps are used to provide driving force for the flow of the working medium. When working, only one circulating pump works, and the other circulating pumps are used for backup;

[0028] Two pressure sensors are located on the pipelines at both ends of the circulating pump to monitor the pipeline pressure before and after the circulating pump;

[0029] The two ends of the pressure difference sensor are respectively connected to the pipelines at the two ends of the circulation pump to monitor the pressure difference before and after the circulation pump;

[0030] The filter is located at the front end of the circulation pump and is used to filter impurities in the circuit;

[0031] The two filling and discharging valves are located on the pipelines at both ends of the circulating pump, and both filling and discharging valves are working fluid filling interfaces;

[0032] The manual stop valve is located at the rear end of the circulation pump and is used for filling working fluid on the ground. It is normally open on track.

[0033] The accumulator is located on a pipeline between a charging and discharging valve and a filter, and is used for working fluid compensation and circuit pressure control.

[0034] Beneficial effects:

[0035] (1) The present invention adopts dual fluid circuits to solve the single-point failure risk of the system. When one of the fluid circuits fails and cannot work normally, the other fluid circuit can still take away the heat of the load on the instrument board through the pre-buried pipelines on the instrument board. Although the heat dissipation capacity of the entire spacecraft is slightly reduced, the layout design of the pre-buried pipelines on the instrument board can maintain 75% of the original heat dissipation capacity, thereby improving the reliability of the thermal control system.

[0036] (2) The present invention adopts perfluorooctane as the fluid circuit working fluid, which can meet the high-orbit radiation environment and is suitable for high-orbit spacecraft, especially for spacecraft with long life and high heat consumption.

[0037] (3) The present invention uses pre-buried pipelines on the instrument panel to collect heat from the load, avoiding the use of multiple cold plates, which not only meets the heat collection requirements, but also facilitates load layout and improves the reliability of the fluid circuit system.

[0038] (4) The pre-buried pipeline of the instrument panel of the present invention is provided with a straight section that is coupled with the heat pipe on the instrument panel to perform heat exchange, and the heat pipe is used to couple the dual fluid circuits to avoid a single point in the system.

[0039] (5) The present invention adopts a modular design, which reduces the difficulty of assembly and simplifies the assembly process.

[0040] (6) The in-cabin pipeline of the present invention adopts double sealing of non-metallic O-ring sealing + metal gasket sealing, and the out-cabin pipeline is connected by welding, which not only meets the pressure resistance requirements but also ensures the sealing ability of the pipeline in the high-orbit irradiation environment.

[0041] (7) When the radiator of the present invention adopts a deployable radiation plate, it can expand the heat dissipation area and improve the heat dissipation capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the overall system flow of the present invention;

[0043] Figure 2 It is a schematic diagram of the instrument panel pre-buried pipeline in the instrument panel;

[0044] Figure 3 A three-dimensional schematic diagram of the pre-buried pipelines for the instrument panel;

[0045] Figure 4 It is a schematic diagram of the pump and valve assembly;

[0046] Figure 5 This is a schematic diagram of the deployable radiator;

[0047] Among them, 1- pump a, 2- pump b, 3- pump c, 4- pump d, 5- pressure sensor a, 6- pressure sensor b, 7- differential pressure sensor, 8- filter, 9- manual stop valve, 10- add and discharge valve a, 11- add and discharge valve b, 12- accumulator, 13- radiator, 14- instrument board, 15- pump and valve assembly, 16- instrument board pre-buried pipeline, 17- heat pipe, 18- radiator pre-buried pipeline, 19- radiation board body, 20- expansion drive assembly. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0049] This embodiment provides a dual fluid loop thermal control system suitable for high orbit spacecraft. Figure 1 , including two independent fluid circuits; one end of the two independent fluid circuits is pre-buried in the instrument panel 14 of the spacecraft, and the other end is pre-buried on the radiator 13. When the working fluid in the fluid circuit flows through the two fluid circuits respectively, the heat of the load installed on the instrument panel 14 is collected, and the heat is transferred to the respective radiators 13 and dissipated into outer space;

[0050] The instrument panel 14 of the spacecraft includes: an upper horizontal panel and a lower horizontal panel arranged opposite to each other; both the upper horizontal panel and the lower horizontal panel are aluminum honeycomb panels; a heat pipe 17 is pre-buried or externally attached to the aluminum honeycomb panel, and the heat pipe 17 is used to even out the temperature on the surface of the instrument panel;

[0051] Each fluid circuit includes: a pump valve assembly 15, an instrument panel pre-buried pipeline 16, a radiator 13 and connecting pipelines;

[0052] The instrument panel pre-buried pipeline 16 includes: an upper pre-buried pipeline and a lower pre-buried pipeline; the upper pre-buried pipeline and the lower pre-buried pipeline are both I-shaped pipelines; the upper pre-buried pipeline is pre-buried on the upper horizontal plate, and the lower pre-buried pipeline is pre-buried on the lower horizontal plate, see the attached Figure 2-3 The upper pre-buried pipeline and the lower pre-buried pipeline are arranged in a rotating S shape, and the upper pre-buried pipeline and the lower pre-buried pipeline form a connected instrument panel pre-buried pipeline 16; wherein, a straight section is provided on the upper pre-buried pipeline to couple with the heat pipe 17 on the upper horizontal plate for heat exchange, and a straight section is provided on the lower pre-buried pipeline to couple with the heat pipe 17 on the lower horizontal plate for heat exchange; the parts of the upper pre-buried pipeline and the lower pre-buried pipeline respectively coupled with the heat pipe 17 (i.e., the straight section) are finned I-shaped structure, such as the height of the I-shaped structure is 14.9 mm (related to the thickness of the instrument panel), and the fin width of the I-shaped structure is 30 mm (related to the specification of the coupled heat pipe 17); the uncoupled parts of the upper pre-buried pipeline and the lower pre-buried pipeline are respectively I-shaped structures without fins, and both ends of the upper pre-buried pipeline and the lower pre-buried pipeline are provided with round tubes A; the upper pre-buried pipeline and the lower pre-buried pipeline are welded by two or more sections of pipelines, and then pre-buried in the instrument panel;

[0053] The radiator 13 is provided with a radiator pre-buried pipeline 18, which is an I-shaped pipeline and arranged in a rotating S shape; the radiator pre-buried pipeline 18 is welded by two or more sections of pipelines; both ends of the radiator pre-buried pipeline 18 are provided with round pipes B;

[0054] The connecting pipeline includes a connecting pipeline A and a connecting pipeline B, and the connecting pipeline A and the connecting pipeline B are both round pipes C;

[0055] One end of the instrument panel pre-buried pipeline 16 is connected to one end of the radiator pre-buried pipeline 18 of the radiator 13 through the connecting pipeline A, and the other end of the instrument panel pre-buried pipeline 16 is connected to the other end of the radiator pre-buried pipeline 18 of the radiator 13 through the connecting pipeline B. The instrument panel pre-buried pipeline 16, the connecting pipeline A, the radiator pre-buried pipeline 18 of the radiator 13 and the connecting pipeline B form a loop; a working fluid is provided in the loop, and the working fluid is perfluorooctane, which can withstand 4.5×10 4 Gy irradiation environment;

[0056] Among them, the instrument panel pre-buried pipeline 16, connecting pipeline A and connecting pipeline B are all arranged in the cabin of the spacecraft, and the material is aluminum alloy 5A06; the radiator pre-buried pipeline 18 of the radiator 13 is arranged outside the cabin of the spacecraft or on the cabin surface of the spacecraft, and is used for heat dissipation; the connection between the pipelines located in the cabin adopts a double sealing method of non-metallic O-ring sealing + metal gasket sealing, and the connection between the pipelines located outside the cabin or on the cabin surface adopts welding; that is, the connection between the instrument panel pre-buried pipeline 16 and the connecting pipeline A and the connection between the instrument panel pre-buried pipeline 16 and the connecting pipeline B both adopt a double sealing method of non-metallic O-ring sealing + metal gasket sealing; the connection between the radiator pre-buried pipeline 18 and the connecting pipeline A and the connection between the radiator pre-buried pipeline 18 and the connecting pipeline B both adopt welding;

[0057] The radiator 13 is a spacecraft north and south cabin panels or a deployable radiating panel. When the radiator 13 is a deployable radiating panel, see the attached Figure 5 The radiator 13 includes: a radiation panel body 19 and an unfolding drive assembly 20; the radiator pre-buried pipeline 18 is arranged on the radiation panel body 19, and the unfolding drive assembly 20 is installed on the radiation panel body 19, and is used to drive the radiation panel body 19 to unfold or retract; the unfoldable radiation panel is located outside the cabin of the spacecraft, and when the spacecraft is launched, the unfoldable radiation panel is in a retracted state, and after the spacecraft enters orbit, the unfoldable radiation panel is unfolded to dissipate heat;

[0058] When the radiator 13 is a spacecraft north and south cabin panels, the radiator pre-buried pipeline 18 is arranged on the spacecraft north and south cabin panels; the spacecraft north and south cabin panels are located on the cabin surface of the spacecraft and are used for heat dissipation;

[0059] A pump valve assembly 15 is installed on the connecting pipeline A or the connecting pipeline B; see the attached Figure 4 The pump-valve assembly 15 includes: a circulation pump, a filter 8, an accumulator 12, a pressure sensor, a differential pressure sensor 7, a charging and discharging valve and a manual stop valve 9;

[0060] There are four circulating pumps, namely pump a1, pump b2, pump c3 and pump d4, which are arranged in parallel; the circulating pumps are used to provide driving force for the flow of working fluids, and only one circulating pump is working during operation. To meet the life requirements, three circulating pumps are arranged for backup;

[0061] There are two pressure sensors, namely pressure sensor a5 and pressure sensor b6. Pressure sensor a5 is located on the pipeline at the front end of the circulation pump and is used to monitor the pipeline pressure before the circulation pump; pressure sensor b6 is located on the pipeline at the rear end of the circulation pump and is used to monitor the pipeline pressure after the circulation pump.

[0062] There is one pressure difference sensor 7, and both ends of the pressure difference sensor 7 are respectively connected to the pipelines at both ends of the circulation pump to monitor the pressure difference before and after the circulation pump;

[0063] The filter 8 is one and is located at the front end of the circulation pump and is used to filter impurities in the circuit;

[0064] There are two adding and discharging valves, namely, adding and discharging valve a10 and adding and discharging valve b11. Adding and discharging valve a10 is located on the pipeline at the front end of the circulating pump, and adding and discharging valve b11 is located on the pipeline at the rear end of the circulating pump. Both adding and discharging valves are working medium filling interfaces;

[0065] The manual stop valve 9 is one and is located at the rear end of the circulating pump. It is used for filling working fluid on the ground and is normally open on the track.

[0066] The accumulator 12 is one and is located on the pipeline between the charging and discharging valve a10 and the filter 8, and is used to compensate for the thermal expansion of the pipeline;

[0067] Among them, the equipment shells of the circulation pump, the filter 8, and the accumulator 12 are made of aluminum alloy with a thickness of not less than 2 mm, or stainless steel with a thickness of not less than 1 mm.

[0068] Working principle: The working fluid in each fluid circuit is driven by a circulating pump to flow in the pipeline, collect the heat on the instrument panel, and transmit it to the radiator 13 for dissipation. The two fluid circuits are in the same state; when one fluid circuit is not working, the other fluid circuit can also realize the heat collection of the entire instrument panel;

[0069] According to the heat dissipation requirements and temperature indicators, the flow rate of the fluid circuit and the specifications of the pipeline are determined. If the heat dissipation requirement of a single fluid circuit is 1700W, the flow rate of the fluid circuit is set to 500L / h, and the inner diameters of round tubes A, B and C are 12mm and the wall thickness is 1mm.

[0070] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual fluid loop thermal control system suitable for high orbit spacecraft, characterized in that: The system comprises two independent fluid circuits; one end of each of the two independent fluid circuits is pre-buried in an instrument panel (14) of the spacecraft, and the other end is pre-buried in a radiator (13); when the working fluid in the fluid circuit flows through the two fluid circuits respectively, the heat of the load installed on the instrument panel (14) is collected, and the heat is transferred to the respective radiators (13) to be discharged into outer space; Each fluid circuit includes: a pump valve assembly (15), an instrument panel pre-buried pipeline (16), a radiator (13) and a connecting pipeline; The instrument panel pre-buried pipeline (16) is arranged in a rotating S-shape and is pre-buried on the instrument panel (14); The radiator (13) is provided with a radiator pre-buried pipeline (18), and the radiator pre-buried pipeline (18) is arranged in a rotating S shape; The connecting pipeline comprises a connecting pipeline A and a connecting pipeline B; one end of the instrument panel pre-buried pipeline (16) is connected to one end of the radiator pre-buried pipeline (18) of the radiator (13) via the connecting pipeline A, and the other end of the instrument panel pre-buried pipeline (16) is connected to the other end of the radiator pre-buried pipeline (18) of the radiator (13) via the connecting pipeline B; The pump valve assembly (15) is installed on the connecting pipeline and is used to provide a driving force for the flow of the working fluid and to add the working fluid; The radiator (13) is a north or south cabin panel of a spacecraft or a deployable radiating panel; When the radiator (13) is a deployable radiant panel, the radiator (13) comprises: a radiant panel body (19) and an deployment drive assembly (20); the radiator pre-buried pipeline (18) is arranged on the radiant panel body (19); the deployment drive assembly (20) is mounted on the radiant panel body (19) and is used to drive the radiant panel body (19) to be deployed or retracted; the deployable radiant panel is located outside the cabin of the spacecraft; when the spacecraft is launched, the deployable radiant panel is in a retracted state; after the spacecraft enters orbit, the deployable radiant panel is deployed to dissipate heat; When the radiator (13) is a north-south cabin panel of a spacecraft, the north-south cabin panels of the spacecraft are provided with the radiator pre-buried pipelines (18); the north-south cabin panels of the spacecraft are located on the cabin surface of the spacecraft and are used for heat dissipation; The pump-valve assembly (15) comprises: a circulation pump, a filter (8), an accumulator (12), a pressure sensor, a differential pressure sensor (7), a charging and discharging valve and a manual stop valve (9); Four circulation pumps are installed in parallel on the connecting pipeline, and the circulation pumps are used to provide driving force for the flow of the working medium. When working, only (1) circulation pump is working, and the other (3) circulation pumps are used for backup; Two pressure sensors are located on the pipelines at both ends of the circulating pump to monitor the pipeline pressure before and after the circulating pump; The two ends of the pressure difference sensor (7) are respectively connected to the pipelines at the two ends of the circulation pump, so as to monitor the pressure difference before and after the circulation pump; The filter (8) is located at the front end of the circulation pump and is used to filter impurities in the circuit; The two filling and discharging valves are located on the pipelines at both ends of the circulating pump, and both filling and discharging valves are working fluid filling interfaces; The manual stop valve (9) is located at the rear end of the circulation pump and is used for filling working fluid on the ground and is normally open on track; The accumulator (12) is located on a pipeline between a charging and discharging valve and a filter (8) and is used for working fluid compensation and circuit pressure control.

2. A dual fluid loop thermal control system suitable for high orbit spacecraft as claimed in claim 1, characterized in that: The working fluid in the fluid circuit is perfluorooctane.

3. A dual fluid loop thermal control system suitable for high orbit spacecraft as claimed in claim 1, characterized in that: The instrument panel pre-buried pipeline (16) and the radiator pre-buried pipeline (18) are both I-shaped pipelines.

4. A dual fluid loop thermal control system suitable for high orbit spacecraft as claimed in claim 3, characterized in that: A heat pipe (17) is pre-buried on or attached to the instrument panel (14); The instrument panel pre-buried pipeline (16) is provided with a straight section portion coupled with a heat pipe (17) on the instrument panel (14); the straight section portion is an I-shaped structure with fins.

5. A dual fluid loop thermal control system suitable for high orbit spacecraft according to any one of claims 1 to 4, characterized in that: The instrument panel (14) of the spacecraft comprises: an upper horizontal panel and a lower horizontal panel which are arranged opposite to each other; The instrument panel pre-buried pipeline (16) comprises: an upper pre-buried pipeline and a lower pre-buried pipeline; the upper pre-buried pipeline is pre-buried on the upper horizontal plate, and the lower pre-buried pipeline is pre-buried on the lower horizontal plate; the upper pre-buried pipeline and the lower pre-buried pipeline are both arranged in a rotating S shape, and the upper pre-buried pipeline and the lower pre-buried pipeline form a connected instrument panel pre-buried pipeline (16).

6. A dual fluid loop thermal control system suitable for high orbit spacecraft according to any one of claims 1 to 4, characterized in that: The instrument panel pre-buried pipeline (16) and the radiator pre-buried pipeline (18) are both formed by welding two or more pipeline sections.

7. A dual fluid loop thermal control system suitable for high orbit spacecraft according to any one of claims 1 to 4, characterized in that: The instrument panel pre-buried pipeline (16), connecting pipeline A and connecting pipeline B are all arranged in the cabin of the spacecraft; the radiator pre-buried pipeline (18) of the radiator (13) is arranged outside the cabin of the spacecraft or on the cabin surface of the spacecraft; the connection between the pipelines located in the cabin adopts a double sealing method of non-metallic O-ring sealing + metal gasket sealing, and the connection between the pipelines located outside the cabin or on the cabin surface adopts welding; that is, the connection between the instrument panel pre-buried pipeline (16) and the connecting pipeline A and the connection between the instrument panel pre-buried pipeline (16) and the connecting pipeline B both adopt a double sealing method of non-metallic O-ring sealing + metal gasket sealing; the connection between the radiator pre-buried pipeline (18) and the connecting pipeline A and the connection between the radiator pre-buried pipeline (18) and the connecting pipeline B both adopt welding.

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