A threaded connection method and threaded connection piece for thin-walled geothermal buried pipe

Abstract

The present invention discloses a threaded connection method and a threaded connector for a thin-walled geothermal buried pipe, and relates to the technical field of geothermal injection and production well development, including a left buried pipe and a right buried pipe, wherein the outer parts of the butt ends of the left buried pipe and the right buried pipe are both threadedly connected with threaded connectors, and under the action of oil pressure, the annular plug will continue to move outward and be inserted and pressed against the inside of the annular groove, and at the same time, under the continuous action of oil pressure, the extrusion force of the annular plug on the annular groove will gradually increase, thereby further improving the stability of the connection between the annular sealing area of ​​the left buried pipe (right buried pipe) and the threaded connector, and when formation geothermal heat occurs, the hydraulic oil inside the connector system will adaptively expand under the action of geothermal heat, and after expansion, it will produce the adaptive squeezing protection effect on the annular sealing area as mentioned above, and finally, when geothermal heat occurs, the relatively weak annular sealing area of ​​the left buried pipe (right buried pipe) can also be tightened by adaptively changing with the formation pressure.

Description

Technical Field

[0001] The invention relates to the technical field of geothermal injection and production well development, and in particular to a threaded connection method and a threaded connection piece for a thin-walled geothermal buried pipe. Background Art

[0002] my country's geothermal resources are widely distributed and rich in reserves. At the same time, geothermal energy is green, low-carbon, sustainable and stable. Rational development of geothermal energy and efficient use of renewable energy are of great significance to my country's energy conservation and emission reduction, improvement of the atmospheric environment, and resolution of energy security issues. In particular, for medium-deep geothermal energy with a depth of 1-3 kilometers and a rock temperature of 50-100°C, its heat mainly comes from the decay of radioactive elements in the earth's core and the heat energy converted from potential energy when the earth was formed. Compared with shallow geothermal energy, it has greater depth, higher temperature, greater heat storage, and more sustainable and stable characteristics. Geothermal buried pipes are thermal energy channels used to develop geothermal energy. Low yield strength and thin-walled buried pipes have the advantages of good economy, high cost performance, and high formation heat exchange efficiency, so they are widely used.

[0003] At present, the existing buried pipe threaded connection has the following main problems:

[0004] 1. When geothermal buried pipes are connected, BC trapezoidal threads with API-5B standard threads for oil and gas development are generally used. They have the advantages of high connection strength and good anti-galling properties. However, during the production stage of geothermal injection and production wells, the relatively weak threaded ring seal area of ​​the buried pipe will be under abnormally high-pressure formation pressure system (due to the differential pressure between the formations, the pressure of the upper and lower formations will produce internal extrusion pressure on the threaded connector through the buried pipe, causing the weak inner ring seal area to deform inward during extrusion, resulting in disengagement, causing thread failure and ring seal failure). Thread failure including disengagement will occur, thereby causing external pressure leakage, causing formation water to enter the production casing to pollute the geothermal heating water, resulting in damage to the geothermal well and inability to produce.

[0005] 2. In addition to the damage to the buried pipe connection threads caused by the abnormally high underground pressure, geothermal phenomena can also cause problems with the buried pipe connection threads. The closer to the decay position of the radioactive elements in the earth's core, the higher the formation temperature. The temperature of the deep geothermal rock formation at a depth of 1-3 kilometers can reach 100°C. Geothermal pipes are generally made of metal. Under long-term underground high pressure and high temperature environment, the thermal expansion of the metal gradually accumulates, and thread failure will occur in the relatively weak thread ring sealing area, which will trigger a series of chain reactions and lead to production interruption.

[0006] In view of the above problems, it is urgently necessary to carry out innovative design based on the original thin-wall geothermal buried pipe threaded connectors. Summary of the invention

[0007] The technical solution of the present invention aims at the technical problem that the existing technical solutions are too single, and provides a solution that is significantly different from the existing technologies. Specifically, the purpose of the present invention is to provide a threaded connection method and a threaded connector for a thin-walled geothermal buried pipe, so as to solve the problem that the BC trapezoidal thread of the API-5B standard thread connection for oil and natural gas development is generally used when the geothermal buried pipe is connected. The BC trapezoidal thread has the advantages of high connection strength and good anti-sticking. However, during the production stage of geothermal injection and production wells, the relatively weak threaded ring sealing area of ​​the buried pipe will experience thread failure including disengagement under the abnormally high-pressure formation pressure system, thereby causing external pressure leakage, causing formation water to enter the production casing and pollute the geothermal heating water, resulting in damage to the geothermal well and inability to produce.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a threaded connector for a thin-walled geothermal buried pipe, comprising a left buried pipe and a right buried pipe, the outsides of the butt ends of the left buried pipe and the right buried pipe are threadedly connected with threaded connectors, and the interiors of the opposite ends of the two threaded connectors are provided with first annular grooves, and the left buried pipe and the right buried pipe are installed with annular butt fittings, and two groups of adaptive tightening components are installed in sequence from the inside to the outside in the annular sealing area where the left buried pipe and the right buried pipe are connected to the threaded connector, and adaptive tightening components are installed between the inner ports of the left buried pipe and the right buried pipe and the threaded connector.

[0009] Preferably, through holes penetrating both ends are opened at equal angles at the center of the annular docking piece, and both ends of the annular docking piece are slidably disposed inside the two first annular grooves respectively, and the first annular grooves are filled with hydraulic oil.

[0010] Preferably, the two groups of adaptive tightening components are spatially staggered and the combination of the two groups of adaptive tightening components achieves the closure of the lateral space of the annular sealing area.

[0011] Preferably, the adaptive tightening assembly includes an arc groove, an arc stopper, a cavity groove, a clamping block, an arc groove and a clamping groove, and an arc groove is provided inside the threaded connection, an arc stopper is slidably engaged inside the arc groove, and an arc groove is provided inside the left buried pipe and the right buried pipe, and the ends of the arc stopper pass through the threaded connection and are inserted into the arc groove, a cavity groove is provided inside the arc stopper, and a clamping block is symmetrically slidably arranged inside the cavity groove, and clamping grooves that are plug-in matching with the two clamping blocks are symmetrically provided inside the arc groove, and the arc groove is through-connected with the first annular groove.

[0012] Preferably, the arc-shaped groove is connected to the cavity between the two clamping blocks, and the upper surfaces of the clamping groove and the clamping block are both designed as inclined surfaces.

[0013] Preferably, the adaptive tightening assembly includes an annular groove, a second annular groove and an annular plug, and the docking ports of the left buried pipe and the right buried pipe with the threaded connector are both provided with an annular groove, the inside of the threaded connector and the docking ends of the left buried pipe and the right buried pipe are both provided with a second annular groove, and an annular plug is slidably arranged inside the second annular groove, the end of the annular plug matches and corresponds to the annular groove, and the second annular groove is through-connected with the first annular groove.

[0014] A threaded connection method for a thin-wall geothermal buried pipe comprises the following steps:

[0015] S1: placing the left underground pipe and the right underground pipe on the sides of the two threaded connectors respectively, and then gradually sleeve the threaded connector on the outer wall of the left underground pipe by rotating the threaded connector, and as the rotation proceeds, the end of the left underground pipe gradually exerts an inward squeezing and pushing action on the arc-shaped stopper, so that the arc-shaped stopper pushes the hydraulic oil inside the arc-shaped groove into the first annular groove;

[0016] S2: Since the first annular groove is filled with hydraulic oil, the hydraulic oil filled into the first annular groove will enter the second annular groove in the form of oil pressure and push the annular plug that is not yet limited, so that the annular plug gradually extends out from the inside of the threaded connector;

[0017] S3: Next, the threaded connector is gradually rotated and sleeved on the left buried pipe. When the left buried pipe is fully in place, the annular groove just fits on the outer end of the annular plug. At the same time, the arc-shaped stopper just corresponds to the arc-shaped groove. The connection between the left buried pipe and the threaded connector is completed. Then, the threaded connector on the right side is rotated and the right buried pipe is gradually pushed into the inside. At the same time, the connection between the right buried pipe and the threaded connector is completed according to the above principle. The connection process between the left buried pipe and the right buried pipe and the threaded connector has the advantages of saving time and effort in installation. When the traditional left and right pipes are connected by a connector, since the connector is a fixed part, the left and right pipes need to be lifted at the same time, and the left and right pipes need to be rotated at the same time to connect with the connector, which requires a lot of manpower, material resources and mechanical equipment.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Installation: The present invention uses two mutually rotatably connected threaded connectors as a connector body. When connecting, the left and right buried pipes can be connected in sequence. At the same time, when connecting, there is no need to rotate the pipes, only the connectors need to be rotated to achieve docking of the buried pipes on both sides. Compared with traditional connectors for docking pipes, it saves time and effort;

[0020] 2. The annular seal area is damaged by abnormally high formation pressure and geothermal phenomena (annular seal area protection): When the pipeline is installed and put into use, due to the differential pressure between the formations, the pressure of the two formations will generate internal squeezing pressure on the threaded connectors through the buried pipe. In simple terms, the differential formation pressure will generate a central force on the two threaded connectors through the left buried pipe and the right buried pipe. When subjected to the central force, the two threaded connectors will gradually approach and squeeze the hydraulic oil inside the first annular groove through the annular docking piece. When the hydraulic oil inside the first annular groove is under pressure, it will simultaneously inject oil into multiple arc grooves and one second annular groove. After receiving the oil, the pressure inside the arc groove gradually increases and pushes the arc stopper outward, causing the arc stopper to gradually enter the arc groove and engage with it. At the same time, as the With the continuous injection of oil pressure, the arc-shaped block cannot move further, so the oil will generate an outward thrust on the two blocks, so that the two blocks gradually enter the corresponding slots. After the blocks enter the slots, their inclined surfaces will gradually contact and press against the inclined surfaces of the slots, and as the oil gradually pressurizes the blocks, the extrusion pressure generated by the inclined surfaces of the blocks on the inclined surfaces of the slots becomes greater and greater, so that the relatively weak annular sealing area of ​​the left buried pipe (right buried pipe) is subjected to a tightening effect that adapts to changes in formation pressure. At the same time, as shown in Figures 1 and 2, the arc-shaped blocks are distributed at equal angles and in a closed space, that is, a ring-shaped cross-section is surrounded by a combination of multiple groups of arc-shaped blocks as a whole. In general, the relatively weak annular sealing area of ​​the left buried pipe (right buried pipe) can be subjected to a tightening effect that adapts to changes in formation pressure.

[0021] At the same time, when the oil is injected into the interior of the second annular groove, the annular plug will continue to move outward under the action of the oil pressure and be inserted tightly into the interior of the annular groove. At the same time, the extrusion force of the annular plug on the annular groove will gradually increase under the continuous action of the oil pressure, thereby further improving the stability of the connection between the annular sealing area of ​​the left buried pipe (right buried pipe) and the threaded connector. Moreover, when geothermal energy occurs in the formation, the hydraulic oil inside the connector system will adaptively expand under the action of geothermal energy. After expansion, it will produce the adaptive squeezing protection effect on the annular sealing area as mentioned above. Finally, when geothermal energy occurs, the relatively weak annular sealing area of ​​the left buried pipe (right buried pipe) can also be tightened by adaptively changing with the formation pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 It is a schematic diagram of the front cross-sectional structure of the present invention;

[0024] Figure 3 It is a structural schematic diagram of the annular docking piece of the present invention;

[0025] Figure 4It is a schematic diagram of the spatial distribution structure of the arc-shaped stopper of the present invention;

[0026] Figure 5 It is a structural schematic diagram of the annular plug block of the present invention;

[0027] Figure 6 It is a schematic diagram of the intercepted structure of the arc-shaped stopper of the present invention;

[0028] Figure 7 For the present invention Figure 2 The enlarged structural diagram at A in the middle;

[0029] Figure 8 This is a schematic diagram of the structure of the arc-shaped stopper of the present invention after being subjected to pressure changes;

[0030] Fig. 9 For the present invention Figure 2 The enlarged structural diagram at B in the middle;

[0031] Fig.10 For the present invention Figure 4 Enlarged structural diagram at point C in the middle.

[0032] In the figure: 1, left buried pipe; 2, right buried pipe; 3, threaded connector; 31, first annular groove; 32, annular docking piece; 4, arc groove; 41, arc stopper; 42, cavity groove; 43, clamping block; 44, arc groove; 45, clamping groove; 5, annular groove; 51, second annular groove; 52, annular plug. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] See also Figure 1-10 The present invention provides a technical solution: a threaded connector for a thin-walled geothermal buried pipe, comprising a left buried pipe 1 and a right buried pipe 2, the outer parts of the butt ends of the left buried pipe 1 and the right buried pipe 2 are both threadedly connected with threaded connectors 3, and the interiors of the opposite ends of the two threaded connectors 3 are both provided with first annular grooves 31, and the left buried pipe 1 and the right buried pipe 2 are installed with annular butt fittings 32, and two groups of adaptive tightening components are sequentially installed from the inside to the outside in the annular sealing area where the left buried pipe 1 and the right buried pipe 2 are connected to the threaded connector 3, and adaptive tightening components are installed between the inner ports of the left buried pipe 1 and the right buried pipe 2 and the threaded connector 3.

[0035] A through hole penetrating both ends is opened at the center of the annular docking member 32 at equal angles, and both ends of the annular docking member 32 are slidably disposed inside the two first annular grooves 31 , respectively, and the first annular grooves 31 are filled with hydraulic oil.

[0036] The two sets of adaptive tightening components are spatially staggered and the combination of the two sets of adaptive tightening components realizes the closure of the lateral space of the ring sealing area.

[0037] The adaptive tightening assembly includes an arc groove 4, an arc stopper 41, a cavity groove 42, a clamping block 43, an arc groove 44 and a clamping groove 45, and an arc groove 4 is opened inside the threaded connector 3, an arc stopper 41 is slidably engaged inside the arc groove 4, and an arc groove 44 is opened inside the left buried pipe 1 and the right buried pipe 2, and the end of the arc stopper 41 passes through the threaded connector 3 and is inserted into the arc groove 44, a cavity groove 42 is opened inside the arc stopper 41, and a clamping block 43 is symmetrically slidably arranged inside the cavity groove 42, and a clamping groove 45 that is symmetrically inserted and matched with the two clamping blocks 43 is opened inside the arc groove 44, and the arc groove 4 is connected to the first annular groove 31.

[0038] The arc groove 4 is connected to the cavity groove 42 between the two clamping blocks 43, and the upper surfaces of the clamping groove 45 and the clamping blocks 43 are both inclined.

[0039] The adaptive tightening component includes an annular groove 5, a second annular groove 51 and an annular plug block 52, and the docking ports of the left buried pipe 1 and the right buried pipe 2 with the threaded connector 3 are both provided with an annular groove 5, and the inside of the threaded connector 3 and the docking ends of the left buried pipe 1 and the right buried pipe 2 are both provided with a second annular groove 51, and an annular plug block 52 is slidably arranged inside the second annular groove 51, the end of the annular plug block 52 matches and corresponds to the annular groove 5, and the second annular groove 51 is through-connected with the first annular groove 31.

[0040] A threaded connection method for a thin-wall geothermal buried pipe comprises the following steps:

[0041] S1: The left buried pipe 1 and the right buried pipe 2 are respectively placed on the sides of the two threaded connectors 3, and then the threaded connector 3 is gradually sleeved on the outer wall of the left buried pipe 1 by rotating the threaded connector 3. As the rotation proceeds, the end of the left buried pipe 1 gradually exerts an inward squeezing and pushing action on the arc-shaped stopper 41, so that the arc-shaped stopper 41 pushes the hydraulic oil inside the arc-shaped groove 4 into the first annular groove 31;

[0042] S2: Since the first annular groove 31 is filled with hydraulic oil, the hydraulic oil filled into the first annular groove 31 will enter the second annular groove 51 in the form of oil pressure and push the annular plug 52 which is not yet limited, so that the annular plug 52 gradually extends out from the inside of the threaded connector 3;

[0043] S3: Next, the threaded connector 3 is gradually rotated and sleeved on the left buried pipe 1. When the left buried pipe 1 is fully in place, the annular groove 5 is just sleeved on the outer end of the annular plug 52. At the same time, the arc-shaped stopper 41 corresponds to the arc-shaped groove 44. The connection between the left buried pipe 1 and the threaded connector 3 is completed. Then, the threaded connector 3 on the right side is rotated and the right buried pipe 2 is gradually pushed into the inside thereof. At the same time, the connection between the right buried pipe 2 and the threaded connector 3 is completed according to the above principle. The connection process between the left buried pipe 1 and the right buried pipe 2 and the threaded connector 3 has the advantages of saving time and effort in installation. When the traditional left and right pipes are connected through a connector, since the connector is a fixed part, the left and right pipes need to be lifted at the same time, and the left and right pipes need to be rotated at the same time to connect with the connector, which requires a lot of manpower, material resources and mechanical equipment.

[0044] Working principle: When using the threaded connector of the thin-wall geothermal buried pipe, first, Figure 1 and Figure 2 As shown, the left buried pipe 1 and the right buried pipe 2 are respectively placed on the sides of the two threaded connectors 3, and then the threaded connector 3 is gradually sleeved on the outer wall of the left buried pipe 1 by rotating the threaded connector 3. As the rotation proceeds, the end of the left buried pipe 1 will gradually exert an inward squeezing and pushing effect on the arc block 41, so that the arc block 41 pushes the hydraulic oil inside the arc groove 4 into the first annular groove 31. However, since the first annular groove 31 is filled with hydraulic oil, the hydraulic oil filled into the first annular groove 31 will enter the second annular groove 51 in the form of oil pressure and push the annular plug 52 that is not yet limited, so that the annular plug 52 gradually extends from the inside of the threaded connector 3.

[0045] Next, the threaded connector 3 is gradually rotated and sleeved on the left buried pipe 1. When the left buried pipe 1 is fully in place, the annular groove 5 is just sleeved on the outer end of the annular plug 52. At the same time, the arc-shaped stopper 41 just corresponds to the arc-shaped groove 44. The connection between the left buried pipe 1 and the threaded connector 3 is completed. Then, the threaded connector 3 on the right side is rotated and the right buried pipe 2 is gradually pushed into the inside thereof. At the same time, the connection between the right buried pipe 2 and the threaded connector 3 is completed according to the above principle.

[0046] The above is the connection process of the left buried pipe 1 and the right buried pipe 2 with the threaded connector 3, which has the advantages of saving time and effort in installation. When the traditional left and right pipes are connected through a connector, since the connector is a fixed part, the left and right pipes need to be lifted at the same time, and the left and right pipes need to be rotated at the same time to connect with the connector, which requires a lot of manpower, material resources and mechanical equipment.

[0047] When the pipeline is installed and put into use, due to the differential pressure between the strata, the pressure of the two strata will generate internal squeezing force on the threaded connectors through the buried pipes. In simple terms, the differential pressure of the strata will generate a force in the middle on the two threaded connectors 3 through the left buried pipe 1 and the right buried pipe 2. When the force is in the middle, Figure 2 As shown, the two threaded connectors 3 will gradually approach and squeeze the hydraulic oil in the first annular groove 31 through the annular docking piece 32. When the hydraulic oil in the first annular groove 31 is pressurized, it will simultaneously inject oil into the multiple arc grooves 4 and the second annular groove 51. After receiving the oil, the pressure in the arc groove 4 gradually increases and pushes the arc stopper 41 outward, so that the arc stopper 41 gradually enters the arc groove 44 and engages with it. At the same time, as the oil pressure continues to be injected, the arc stopper 41 cannot continue to move. Therefore, the oil will generate an outward thrust on the two clamping blocks 43, so that the two clamping blocks 43 gradually enter the corresponding clamping grooves 45. Figure 8 As shown in FIG. 1 , after the block 43 enters the slot 45, its inclined surface gradually contacts and presses against the inclined surface of the slot 45. As the oil gradually pressurizes the block 43, the squeezing force exerted by the block 43 on the inclined surface of the slot 45 by the inclined surface becomes larger and larger, so that the relatively weak annular sealing area of ​​the left buried pipe 1 (right buried pipe 2) is tightened according to the formation pressure. Figure 3 and Figure 4 As shown, the arc-shaped blocks 41 are distributed at equal angles and in a closed space, that is, a circular cross-section is surrounded as a whole by a combination of multiple groups of arc-shaped blocks 41. In general, the relatively weak annular sealing area of ​​the left buried pipe 1 (right buried pipe 2) can be tightened adaptively according to the formation pressure.

[0048] At the same time, when the oil is injected into the interior of the second annular groove 51, the annular plug 52 will continue to move outward under the action of the oil pressure and be inserted tightly into the interior of the annular groove 5. At the same time, under the continuous action of the oil pressure, the squeezing force of the annular plug 52 on the annular groove 5 gradually increases, thereby further improving the stability of the connection between the annular sealing area of ​​the left buried pipe 1 (right buried pipe 2) and the threaded connector 3.

[0049] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. 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 threaded connector for a thin-walled geothermal buried pipe, comprising a left buried pipe (1) and a right buried pipe (2), characterized in that: The outsides of the butt ends of the left buried pipe (1) and the right buried pipe (2) are both threadedly connected with a threaded connector (3), and the insides of the opposite ends of the two threaded connectors (3) are both provided with a first annular groove (31), and the left buried pipe (1) and the right buried pipe (2) are installed with an annular butt joint (32), and the annular sealing area where the left buried pipe (1) and the right buried pipe (2) are connected to the threaded connector (3) is installed with two sets of adaptive tightening components in sequence from the inside to the outside, and an adaptive tightening component is installed between the inner ports of the left buried pipe (1) and the right buried pipe (2) and the threaded connector (3), and the adaptive tightening component includes an arc The threaded connector (3) comprises a curved groove (4), an arc-shaped stopper (41), a cavity groove (42), a clamping block (43), an arc-shaped groove (44) and a clamping groove (45), and the interior of the threaded connector (3) is provided with a curved groove (4), the interior of the curved groove (4) is slidably engaged with a curved stopper (41), and the exteriors of the left buried pipe (1) and the right buried pipe (2) are both provided with curved grooves (44), and the end of the curved stopper (41) passes through the threaded connector (3) and is inserted into the interior of the curved groove (44), the interior of the curved stopper (41) is provided with a cavity groove (42), and the interior of the cavity groove (42) is symmetrically slidably provided with a clamping block (43). ), and the arc-shaped groove (44) is symmetrically provided with a card slot (45) for plugging and matching with the two card blocks (43), the arc-shaped groove (4) is connected to the first annular groove (31), the arc-shaped groove (4) is connected to the cavity groove (42) between the two card blocks (43), and the upper surfaces of the card slot (45) and the card block (43) are both inclined, and the center of the annular docking member (32) is provided with a through hole that passes through both ends at equal angles, and the two ends of the annular docking member (32) are respectively slidably arranged inside the two first annular grooves (31), and the inside of the first annular groove (31) is filled with liquid. The adaptive tightening assembly comprises an annular groove (5), a second annular groove (51) and an annular plug (52), and the butt joint ports of the left buried pipe (1) and the right buried pipe (2) and the threaded connector (3) are both provided with an annular groove (5), the butt joint ends of the threaded connector (3) and the left buried pipe (1) and the right buried pipe (2) are both provided with a second annular groove (51), and an annular plug (52) is slidably arranged inside the second annular groove (51), the end of the annular plug (52) matches and corresponds to the annular groove (5), and the second annular groove (51) is connected to the first annular groove (31).

2. The threaded connector for a thin-walled geothermal buried pipe according to claim 1, characterized in that: The two groups of adaptive tightening components are spatially staggered and the combination of the two groups of adaptive tightening components realizes the closure of the lateral space of the ring sealing area.

3. A threaded connection method for a threaded connection piece of a thin-walled geothermal buried pipe according to any one of claims 1-2, characterized in that: The following steps are involved: S1: placing the left underground pipe (1) and the right underground pipe (2) on the sides of two threaded connectors (3), respectively, and then rotating the threaded connector (3) so that the threaded connector (3) is gradually sleeved onto the outer wall of the left underground pipe (1), and as the rotation proceeds, the end of the left underground pipe (1) gradually exerts an inward squeezing and pushing action on the arc-shaped stopper (41), so that the arc-shaped stopper (41) pushes the hydraulic oil inside the arc-shaped groove (4) into the first annular groove (31); S2: Since the first annular groove (31) is filled with hydraulic oil, the hydraulic oil that has filled into the first annular groove (31) will enter the second annular groove (51) in the form of oil pressure and push the annular plug (52) that is not yet limited, so that the annular plug (52) gradually extends out from the inside of the threaded connector (3); S3: Next, the threaded connector (3) is gradually rotated and sleeved on the left buried pipe (1). When the left buried pipe (1) is fully in place, the annular groove (5) is just sleeved on the outer end of the annular plug (52). At the same time, the arc-shaped stopper (41) is just corresponding to the arc-shaped groove (44). The connection between the left buried pipe (1) and the threaded connector (3) is completed. Then, the threaded connector (3) on the right side is rotated and the right buried pipe (2) is gradually pushed into the inside thereof. At the same time, the connection between the right buried pipe (2) and the threaded connector (3) is completed according to the above principle.

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