Connecting method of large HDPE (High-Density Polyethylene) pipeline

Abstract

The invention relates to the technical field of pipeline connection, in particular to a large HDPE (high-density polyethylene) pipeline connection method which comprises the following steps: S1, acquiring the real length LZ of a closure section to be mounted; s2, a fixed section of the telescopic joint is welded to an end pipe joint of the closure section, and a butt flange is installed on a telescopic section of the telescopic joint; other pipe joints of the closure section are welded to the length away from the telescopic joint by two to three pipe joints; obtaining the length LH of the welded real pipe joints of the closure section, and calculating the cutting length l1 of the remaining pipe joints of the closure section; cutting the rest of the pipe joints, continuously welding to the length of one pipe joint away from the telescopic joint, and calculating the cutting length l2 of the last pipe joint; the pipeline connecting method comprises the steps of (S1) welding a closure section, (S2) welding the closure section, (S3) obtaining the real length LZ'of the closure section after welding is completed, (S4) putting the closure section into water, and butting a butt joint flange and the installed pipeline, and (S5) encapsulating an expansion joint through concrete. The pipeline connecting method can ensure that the length of the remaining pipe joint of the closure section is cut more accurately, and the situation that the HDPE pipeline is difficult to butt due to the influence of factors such as temperature, welding errors and measurement errors is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline connection, and in particular to a connection method for large HDPE pipelines. Background Art

[0002] The seawater cooling system is a cooling system that uses a water pumping station to pump seawater to onshore industrial facilities such as refineries that require a large amount of heat exchange for heat exchange, and then discharges it back into the ocean. When installing the seawater cooling system pipeline, the installation of offshore HDPE pipes is limited by the construction of the onshore water pumping station. The conventional construction method is to wait until the onshore water pumping station is completed before digging the foundation trench in front of the water pumping station, and then install the pipeline. However, this construction plan takes too long to complete, which will result in excessively high costs, and the construction period cannot meet actual construction needs.

[0003] Therefore, in order to improve construction efficiency, the installation can be carried out synchronously from the middle section of the offshore HDPE pipeline to both sides. This construction method can effectively improve construction efficiency. However, since the length of the HDPE pipeline in the entire cooling system is often long (≥1000m) and the diameter of the HDPE pipeline is large (≥3000mm), in this large HDPE pipeline system, it is almost impossible for the last section of the HDPE pipeline on the sea side to be smoothly connected with the land side pipeline according to the designed length. Especially in desert areas, which are greatly affected by temperature differences, HDPE pipelines are more sensitive to temperature changes. Due to the influence of thermal expansion and contraction, it is difficult to accurately determine the length of the HDPE pipeline in the joint section. At the same time, the welding between different HDPE pipelines in the joint section will also have a certain impact on the final pipeline connection, making pipeline connection very difficult. Any carelessness will cause leakage problems due to mismatched connection lengths. Summary of the invention

[0004] The purpose of the invention is to overcome the difficulties in connecting large HDPE pipes and the shortcomings of leakage problems that are prone to occur due to mismatched connection lengths, and to provide a connection method for large HDPE pipes.

[0005] In a first aspect, the present invention provides a method for connecting large HDPE pipes, comprising the following steps:

[0006] S1. Get the actual length L of the joint section to be installed Z ;

[0007] S2. Weld the fixed section of the expansion joint to the end pipe section of the closure section, and install the docking flange of the expansion section of the expansion joint;

[0008] Weld the remaining pipe sections of the joint section to the length of two to three pipe sections away from the expansion joint;

[0009] Get the actual length L of the pipe segment that has been welded H, calculate the cutting length l1 of the remaining pipe section of the joint section, l1=l-(L Z -L S -L F -L H ) / y;

[0010] Where l is the length of the pipe segment;

[0011] L S is the length of the expansion joint in the neutral position;

[0012] L F is the length of the butt flange;

[0013] y is the number of remaining pipe segments;

[0014] Cut the remaining pipe sections and continue welding until the distance from the expansion joint is one pipe section long. Calculate the cutting length l2 of the last pipe section, l2 = l-(L Z -L S -L F -L H );

[0015] S3. After the joint section is welded on land, the actual length L of the joint section after welding is obtained Z ', ensure that L Z 'Meet the needs of closure;

[0016] S4. Launch the closure section, adjust the length of the expansion joint, and connect the docking flange to the installed pipe;

[0017] S5.Concrete encapsulated expansion joint.

[0018] The connection method of the large HDPE pipeline provided by the present invention comprehensively considers the influence of the temperature difference change of offshore construction and the special environment of the desert area on the HDPE pipeline. On the one hand, the actual length of the joint section and the actual length of the pipe section that has been welded are actively obtained to calculate the cutting length of the remaining pipe section of the joint section, which can ensure that the remaining pipe section length of the joint section is cut more accurately, and avoid the HDPE pipeline being affected by factors such as temperature, welding error, and measurement error, resulting in final docking difficulties. On the other hand, the cutting length of the remaining pipe section of the joint section is evenly distributed to each remaining pipe to be welded, avoiding the cutting of a single pipe too long and the ballast spacing being too small, ensuring the stability of the HDPE pipeline under lateral load, and being able to more effectively resist the lateral impact of wind and waves, and improving the connection reliability. When welding to the last pipe section, the cutting length of the last pipe section is repeatedly calculated to ensure that the final joint section length meets the HDPE pipeline docking requirements. The introduction of the expansion joint allows the precise docking of the docking flange and the installed pipeline to be ensured by adjusting the length of the expansion joint after the joint section is launched, thereby achieving a tighter and more secure connection. The watertightness of the expansion joint after installation is based on the compression of the EPDM sealing ring. However, since the expansion joint cannot provide axial resistance, pouring underwater encapsulating concrete after the expansion joint is installed can effectively prevent the expansion joint from moving after installation and affecting the watertightness.

[0019] Preferably, S1 comprises the following steps:

[0020] According to the position of the installed pipeline before and after the joint section, the length L of the joint section is measured at different time periods. i , i = 1, 2...n, obtain the actual length L of the joint section Z , L Z =(L1+L2+…L n ) / n.

[0021] HDPE pipes are very sensitive to temperature changes. In desert areas and offshore construction environments, the large temperature difference between day and night may cause the length of the joint section to change significantly over time. By taking multiple measurements at different time periods and taking the average value, the impact of temperature differences on the length of the pipeline can be fully considered, making the measurement results closer to the actual installation status of the joint section; since a more reliable true length of the joint section is obtained, the length of the joint section can be more accurately controlled during the subsequent pipe cutting and welding process, reducing the possibility of docking difficulties. The precise length of the joint section ensures the sealing and firmness of the final connection, thereby reducing the risk of leakage and improving the success rate of docking and the reliability of the connection.

[0022] Preferably, the length L of the joint section is measured every 2h-4h. i .

[0023] The 2 to 4 hour interval ensures the continuity of measurement and the reliability of data, making the average length of the joint section closer to the actual length, reducing the risk of leakage due to mismatched butt lengths, and ensuring the tightness and sealing of the connection.

[0024] Preferably, the end pipe sections of the fixed section and the joint section in S2 are hot-melt welded.

[0025] Hot-melt welding is an efficient connection method that can melt and fuse the materials of two sections of HDPE pipe into one, forming a seamless and high-strength connection. Compared with mechanical connection or other methods, the fixed section and the end pipe joint after hot-melt welding become a whole, which greatly improves the strength and stability of the connection and helps to withstand the stress caused by construction and environmental loads.

[0026] Preferably, in S2, the actual length L of the pipe segment that has been welded is obtained. H , including the following steps:

[0027] The length of the welded pipe section of the joint section is measured every 2-4 hours, and the average length of the welded pipe section is calculated as the actual length L of the welded pipe section. H .

[0028] The temperature in ocean and desert areas varies greatly, which will cause the length of HDPE pipes to expand and contract. By measuring the length of welded pipe sections every 2 to 4 hours, the dynamic effect of ambient temperature on the length can be captured. Multiple measurements and averaging can eliminate the error caused by temperature fluctuations in a single measurement, ensuring that the actual pipe section length obtained is more accurate.

[0029] Preferably, S2 L S The telescopic section of the telescopic joint can be extended or retracted by ±500mm.

[0030] Preferably, S3 comprises the following steps:

[0031] After the welding of the joint section is completed on land, the length of the joint section after welding is measured every 2h-4h, and the average length of the joint section after welding is obtained as the actual length L of the joint section after welding. Z ', ensure that L Z 'Meet the needs of closure.

[0032] After the welding of the joint section is completed, the actual length of the joint section after welding is calculated again, which can effectively eliminate the deviation caused by temperature difference, make the actual length of the joint section after welding more stable and reliable, and ensure that the joint section meets the docking requirements.

[0033] Preferably, S4 comprises the following steps:

[0034] S41. Adjust the expansion joint to the minimum expansion position, and install and tighten all the sealing ring fastening bolts of the expansion joint;

[0035] S42. Fixed telescopic section;

[0036] S43. Put the joint section into water, adjust the joint section and the installed pipeline to the same elevation, loosen the sealing ring fastening bolts, adjust the length of the expansion section, connect the butt flange with the installed pipeline flange, and retighten the sealing ring fastening bolts.

[0037] Before launching, adjust the expansion joint to the minimum expansion position and tighten the sealing ring and fastening bolts to prevent water from entering the expansion joint during the floating operation of the HDPE pipe, which may cause water to enter the joint section of the HDPE pipe (the entire joint section is sealed by a blind plate during floating operation). Fixing the expansion section can prevent the expansion section from accidentally slipping out during transportation and avoid damage to the expansion joint during launching.

[0038] Preferably, in S43, the bolt torque when the docking flange is connected to the installed pipe flange is 225N·m-235N·m; the torque when the sealing ring fastening bolts are tightened is 450N·m-460N·m.

[0039] Different tightening torques are designed for different bolts. For example, a torque wrench can be used to test the torque of each screw to ensure that each bolt can reach the designed torque and improve the water tightness of the HDPE pipe connection.

[0040] Preferably, S5 comprises the following steps:

[0041] S51. Install a template at the sealing ring fastening bolt, the template comprising a first template, a second template and a top reinforcement rib, the first template and the second template are mirror images of each other, the first template and the second template are assembled to form a rectangular frame structure with a U-shaped notch, the top reinforcement ribs cross each other and connect the tops of the first template and the second template, the U-shaped notch faces downward so that the template cover is set on the telescopic joint;

[0042] S52. Pour concrete into the formwork to enclose the expansion joint.

[0043] The template provided by the present invention can be stably stuck above the expansion joint through the U-shaped notch to prevent the template from moving during the pouring of concrete. The template structure can well control the amount of concrete poured. The sealing ring of the expansion joint is encapsulated by concrete to tighten the bolt position to achieve permanent support and protection. Concrete encapsulation not only improves the structural strength of the expansion joint, but also provides higher compression and shear resistance, preventing the expansion joint from being displaced or losing water tightness due to water flow impact or thermal expansion and contraction during subsequent use. Through the solidification of concrete, a solid protective layer is formed, which greatly improves the stability and water tightness of the expansion joint.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The connection method of large HDPE pipes provided by the present invention comprehensively considers the temperature difference changes in offshore construction and the influence of the special environment of desert areas on HDPE pipes. On the one hand, it actively obtains the real length of the joint section and the real length of the pipe section that has been welded to calculate the cutting length of the remaining pipe section of the joint section, which can ensure that the remaining pipe section length of the joint section is cut more accurately, and avoid the HDPE pipe being affected by factors such as temperature, welding error, and measurement error, which leads to difficulties in the final docking. On the other hand, the cutting length of the remaining pipe section of the joint section is evenly distributed to each remaining pipe to be welded, avoiding the cutting of a single pipe too long and the ballast spacing being too small, ensuring the stability of the HDPE pipe under lateral load, and being able to more effectively resist the lateral impact of wind and waves, and improving the connection reliability;

[0046] 2. The connection method of large HDPE pipes provided by the present invention repeatedly calculates the cutting length of the last pipe section when welding to the last pipe section, ensuring that the length of the final joint section meets the HDPE pipe docking requirements. The introduction of the expansion joint allows the precise docking of the docking flange and the installed pipe by adjusting the length of the expansion joint after the joint section is launched, thereby achieving a tighter and more secure connection. The watertightness of the installed expansion joint is based on the compression of the EPDM sealing ring, but because the expansion joint cannot provide axial resistance, the underwater encapsulation concrete is poured after the expansion joint is installed, which can effectively prevent the expansion joint from moving after installation and affecting the watertightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is the position relationship diagram of the joint section (not installed) and the installed pipes before and after;

[0048] Figure 2 It is a schematic diagram when the telescopic joint is in the minimum telescopic position;

[0049] Figure 3 It is a schematic diagram when the expansion joint is in the neutral position;

[0050] Figure 4It is a schematic diagram when the telescopic joint is in the maximum telescopic position;

[0051] Figure 5 This is a schematic diagram of the welding of the fixed section of the telescopic joint when the telescopic section is not connected;

[0052] Figure 6 This is a schematic diagram of the telescopic section of the telescopic joint being connected;

[0053] Figure 7 This is a schematic diagram of the template installation location;

[0054] Figure 8 This is a schematic diagram of the template structure.

[0055] Markings in the figure:

[0056] 1-joint section, 11-pipe section, 2-expansion joint, 21-fixed section, 22-expansion section, 23-sealing ring fastening bolts, 3-jointing flange, 4-installed pipe, 5-template, 51-first template, 52-second template, 53-top reinforcement rib, 54-U-shaped notch. DETAILED DESCRIPTION

[0057] The present invention is further described in detail below in conjunction with specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0058] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or position relationship such as "up", "down", "left", "right", "center", "inside", "outside", etc. are all based on the expression of the orientation or position relationship shown in the drawings, or are the orientation or position relationship when the invented product / equipment / device is usually used. These terms of orientation or position relationship are only for the convenience of describing the scheme of the present invention or simplifying the description in the specific embodiments, so as to facilitate the technicians to quickly understand the scheme, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation on the present invention.

[0059] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simplified to mean that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the scheme of the present invention.

[0060] In addition, the expressions “first”, “second”, “third”, etc., which appear in the terms, are merely used to distinguish the description of the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0061] In addition, in the description of the embodiments of the present invention, "several", "plurality" and "a number" represent at least 2. It can be any number such as 2, 3, 4, 5, 6, 7, 8, 9, and even more than 9.

[0062] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "install", "connect", "connected", "provided with", "laid", and "arranged" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, and can be welding, riveting, bolting, threading, and other commonly used connection means in the field. This connection can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the internal connection of two elements.

[0063] HDPE pipe is a pipe made of high-density polyethylene (English name: "High Density Polyethylene", abbreviated as "HDPE").

[0064] GRP pipe is a glass fiber reinforced resin plastic pipe (English name is "Glass-reinforced plastics").

[0065] Example 1

[0066] When the scheme of synchronously installing pipelines from the middle section of the offshore HDPE pipeline to both sides is adopted, there is bound to be a problem of docking the sea-side HDPE pipeline with the land-side pipeline (such as HDPE pipeline or GRP pipeline). For example Figure 1 As shown, Figure 1 The installed pipeline 4 on the left side may be a landside pipeline. Figure 1 The installed pipeline 4 on the middle right side can be a sea-side HDPE pipeline, and the dotted line portion between the two sections of the pipeline is the joint section 1.

[0067] This embodiment provides a method for connecting a large HDPE pipe (the overall length of the HDPE pipe is ≥1000m, and the diameter of the HDPE pipe is ≥3000mm), comprising the following steps:

[0068] S1. Obtain the actual length L of the joint section 1 to be installed Z , unit: m;

[0069] Specifically, the actual length L of the joint section 1 Z The method for obtaining is to measure the length L of the joint section 1 at different time periods according to the position of the installed pipeline 4 before and after the joint section 1 i , i = 1, 2...n, unit m, obtain the actual length L of the joint section 1 Z , L Z =(L1+L2+…L n ) / n.

[0070] HDPE pipes are very sensitive to temperature changes. In desert areas and offshore construction environments, the large temperature difference between day and night may cause the length of the joint section 1 to change significantly over time. By taking multiple measurements at different time periods and taking the average value, the impact of temperature differences on the length of the pipeline can be fully considered, making the measurement results closer to the actual installation status of the joint section 1; since a more reliable true length of the joint section 1 is obtained, the length of the joint section 1 can be more accurately controlled during the subsequent pipeline cutting and welding process, reducing the possibility of docking difficulties. The precise length of the joint section 1 ensures the sealing and firmness of the final connection, thereby reducing the risk of leakage and improving the success rate of docking and the reliability of the connection.

[0071] Furthermore, the length L of the joint section 1 can be measured every 2-4 hours in 24 hours a day. i If necessary, the measurement time can be extended, for example, for 2-3 consecutive days. The 2 to 4 hour interval ensures the continuity of the measurement and the reliability of the data, making the average length of the joint section 1 closer to the actual length, reducing the risk of leakage caused by the mismatch of the butt joint length, and ensuring the tightness and sealing of the connection.

[0072] S2. The fixed section 21 of the expansion joint 2 is welded to the end pipe section 11 of the closure section 1, for example, the end of the fixed section 21 is hot-melt welded to the end pipe section 11 of the closure section 1; the end of the expansion joint 22 of the expansion joint 2 is installed at the docking flange 3;

[0073] like Figure 2 , Figure 3 , Figure 4 The telescopic joint 2 is shown in three different states. The telescopic joint 2 used in this embodiment is as follows Figure 2-Figure 3 As shown, the right side is the fixed section 21, which has a larger diameter, and the left side is the telescopic section 22, which has a smaller diameter than the fixed section 21. The telescopic section 22 is movably connected to the inside of the fixed section 21, and a sealing ring fastening bolt 23 is provided on the fixed section 21. By tightening the sealing ring fastening bolt 23, pressure can be applied to the sealing ring between the telescopic section 22 and the fixed section 21 to seal the telescopic section 22 and the fixed section 21. Loosening the sealing ring fastening bolt 23 can drag the telescopic section 22 to telescope. Specifically, for example, the telescopic section 2 of this embodiment can provide a longitudinal tolerance of +1000mm / -0mm. If Figure 2 When the telescopic section 2 is in the minimum telescopic position, no longitudinal tolerance is provided. Figure 3 When the telescopic section 2 is in the neutral position, it can provide a longitudinal tolerance of ±500 mm, that is, the telescopic section 22 can be telescoped by ±500 mm. Figure 4 The telescopic section 2 shown can provide a longitudinal tolerance of +1000 mm when it is in the maximum telescopic position.

[0074] The remaining pipe segments 11 of the joint section 1 are welded to a length of two to three pipe segments 11 away from the expansion joint 2; for example Figure 1 In the embodiment, the pipe segments 11 can be welded sequentially from right to left until the distance from the installed pipeline 4 and the welded expansion joint 2 on the left side is two to three pipe segments 11 lengths. Of course, the welding of the pipe segments 11 is performed on land at this time.

[0075] Get the actual length L of the pipe segment that has been welded in the joint section 1 H , unit: m.

[0076] The actual length of the pipe segment L after welding in the joint section 1 H The method of obtaining L is similar to that of obtaining L Z Specifically, the length of the welded pipe segment 11 of the closure section 1 is measured every 2h-4h, and the average length of the welded pipe segment 11 is calculated as the actual length L of the welded pipe segment 1. H .

[0077] The temperature in ocean and desert areas varies greatly, which will cause the length of HDPE pipes to expand and contract. By measuring the length of the welded pipe section 11 every 2 to 4 hours, the dynamic effect of ambient temperature on the length can be captured. Multiple measurements and averaging can eliminate the error caused by temperature fluctuations in a single measurement, ensuring that the actual length of the pipe section 11 obtained in the end is more accurate.

[0078] Calculate the cutting length l1 of the remaining pipe section 11 of the joint section 1, unit m, l1 = l-(L Z -L S -L F -L H ) / y;

[0079] Wherein, l is the length of the pipe section 11, in m;

[0080] L S is the length of the telescopic joint 2 in the neutral position, in m;

[0081] L F is the length of the docking flange 3, in m;

[0082] y is the number of remaining pipe segments 11;

[0083] Cut the remaining pipe section 11 and continue welding until the distance from the expansion joint 2 is one pipe section 11 long. Calculate the cutting length l2 of the last pipe section 11, in m, l2 = l-(L Z -L S -L F -L H );

[0084] S3. After the welding of the joint section 1 is completed on land, the actual length L of the joint section 1 after welding is completed is obtained. Z ', ensure that L Z 'Meet the needs of closure;

[0085] The actual length L of the joint section 1 after welding is completed Z ' is obtained in a similar way to obtain L Z or get the length of L H Specifically, the last pipe segment 11, which is one pipe segment 11 away from the expansion joint 2, is welded to the end pipe segment 11 of the joint segment 1 that has been welded to the fixed segment 21 before, and the welding of the joint segment 1 on land is completed. The length of the joint segment 1 after welding is measured every 2h-4h, and the average length of the joint segment 1 after welding is obtained as the actual length L of the joint segment 1 after welding. Z ', ensure that L Z 'Meet the needs of closure.

[0086] S4. The closure section 1 is launched, the length of the expansion joint 2 is adjusted, and the docking flange 3 is docked with the installed pipe 4;

[0087] Specifically, S4 includes the following steps:

[0088] S41. Adjust the expansion joint 2 to the minimum expansion position, install and tighten all the sealing ring fastening bolts 23 of the expansion joint 2;

[0089] S42. Fix the telescopic section 22; for example, some lugs may be welded on the fixed section 21 and the telescopic section 22, and then the fixed section 21 and the telescopic section 22 may be pulled by a hand chain hoist to prevent the telescopic section 22 from moving during transportation.

[0090] S43. Transport the closure section 1 into the water, such as Figure 5 As shown, adjust the joint section 1 and the installed pipeline 4 to the same elevation, loosen the sealing ring fastening bolts 23, as shown in FIG. Figure 6 As shown, adjust the length of the telescopic section 22, connect the butt flange 3 to the installed pipeline 4 flange, and re-tighten the sealing ring fastening bolts 23.

[0091] Before launching, adjust the expansion joint 2 to the minimum expansion position and tighten the sealing ring and fastening bolts 23 to prevent water from entering the expansion joint 2 and causing water to enter the closure section 1 during the floating transportation of the HDPE pipe (the entire closure section 1 is sealed by a blind plate during floating transportation). Fixing the expansion section 22 can prevent the expansion section 22 from accidentally slipping out during transportation, thereby avoiding damage to the expansion joint 2 when launching.

[0092] Furthermore, when the butt flange 3 is connected to the flange of the installed pipe 4, the bolt torque is 225N·m-235N·m; when the sealing ring fastening bolts 23 are tightened, the torque is 450N·m-460N·m.

[0093] S5.Concrete encapsulated expansion joint 2.

[0094] Specifically, S5 includes the following steps:

[0095] S51. Install the template 5 at the sealing ring fastening bolt 23, such as Figure 8 As shown, the template 5 includes a first template 51, a second template 52 and a top reinforcement rib 53. The first template 51 and the second template 52 are mirror images of each other. The first template 51 and the second template 52 are assembled to form a rectangular frame structure with a U-shaped notch 54. The top reinforcement ribs 53 cross each other and connect the tops of the first template 51 and the second template 52. Figure 7 As shown, the U-shaped notch 54 faces downward so that the template 5 covers the telescopic joint 2;

[0096] S52. Pour concrete into the formwork 5 to encapsulate the expansion joint 2.

[0097] The template 5 can be stably stuck above the expansion joint 2 through the U-shaped notch 54 to prevent the template 5 from moving during the pouring of concrete. The template 5 structure can well control the amount of concrete poured. The concrete encapsulates the sealing ring fastening bolt 23 of the expansion joint 2 to achieve permanent support and protection. The concrete encapsulation not only improves the structural strength of the expansion joint 2, but also provides higher compression and shear resistance, preventing the expansion joint 2 from being displaced or losing water tightness due to water flow impact or thermal expansion and contraction during subsequent use. Through the solidification of the concrete, a solid protective layer is formed, which greatly improves the stability and water tightness of the expansion joint 2.

[0098] The connection method of large HDPE pipes provided in this embodiment comprehensively considers the temperature difference changes in offshore construction and the influence of the special environment of desert areas on HDPE pipes. On the one hand, the actual length of the joint section 1 and the actual length of the welded pipe section 11 are actively obtained to calculate the cutting length of the remaining pipe section 11 of the joint section 1, which can ensure that the length of the remaining pipe section 11 of the joint section 1 is cut more accurately, and avoid the HDPE pipe being affected by factors such as temperature, welding error, and measurement error, resulting in difficulties in the final docking. On the other hand, the cutting length of the remaining pipe section 11 of the joint section 1 is evenly distributed to each remaining pipe to be welded, avoiding the cutting of a single pipe too long and the ballast spacing being too small, ensuring the stability of the HDPE pipe under lateral load, and being able to more effectively resist the lateral impact of wind and waves, and improving the connection reliability. When welding to the last pipe section 11, the cutting length of the last pipe section 11 is repeatedly calculated to ensure that the final length of the joint section 1 meets the HDPE pipe docking requirements. The introduction of the expansion joint 2 enables the precise docking of the docking flange 3 and the installed pipe 4 to be ensured by adjusting the length of the expansion joint 22 after the joint section 1 is launched, thereby achieving a tighter and more secure connection. The water tightness of the expansion joint 2 after installation is based on the compression of the EPDM sealing ring (ethylene propylene diene monomer rubber sealing ring), but since the expansion joint 2 cannot provide axial resistance, the underwater encapsulation concrete is poured after the expansion joint 2 is installed, which can effectively prevent the expansion joint 2 from moving after installation and affecting the water tightness.

[0099] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for connecting large HDPE pipes, characterized in that: The following steps are involved: S1. Obtain the actual length L of the joint section (1) to be installed Z ; S2. The fixed section (21) of the expansion joint (2) is welded to the end pipe section (1) of the closure section (11), and the expansion section (22) of the expansion joint (2) is installed with a docking flange (3); Weld the remaining pipe sections (11) of the joint section (1) to a length of two to three pipe sections (11) from the expansion joint (2); Get the actual length L of the welded pipe section (1) H , calculate the cutting length l1 of the remaining pipe section (11) of the joint section (1), l1 = l-(L Z -L S -L F -L H ) / y; Where, l is the length of the pipe segment (11); L S is the length of the telescopic joint (2) in the neutral position; L F is the length of the butt flange (3); y is the number of remaining pipe segments (11); Cut the remaining pipe sections (11), continue welding until the distance from the expansion joint (2) is the length of one pipe section (11), and calculate the cutting length l2 of the last pipe section (11), l2 = l-(L Z -L S -L F -L H ); S3. After the onshore welding of the joint section (1) is completed, the actual length L of the joint section (1) after welding is completed is obtained. Z ', ensure that L Z 'Meet the needs of joint closure; S4. The closure section (1) is launched, the length of the expansion joint (2) is adjusted, and the docking flange (3) is docked with the installed pipe (4); S5. Concrete encapsulated expansion joint (2).

2. A method for connecting large HDPE pipes according to claim 1, characterized in that: S1 includes the following steps: According to the position of the installed pipeline (4) before and after the joint section (1), the length L of the joint section (1) is measured at different time periods. i , i = 1, 2...n, obtain the actual length L of the joint section (1) Z , L Z =(L1+L2+…L n ) / n.

3. A method for connecting large HDPE pipes according to claim 2, characterized in that: The length L of the joint section (1) is measured every 2-4 hours. i .

4. A method for connecting large HDPE pipes according to claim 1, characterized in that: The fixed section (21) in S2 is hot-melt welded to the end pipe section (11) of the joint section (1).

5. A method for connecting large HDPE pipes according to claim 1, characterized in that: S2 obtains the actual length L of the pipe segment that has been welded in the joint section (1) H , including the following steps: The length of the welded pipe section (11) of the joint section (1) is measured every 2-4 hours, and the average length of the welded pipe section (11) is calculated as the actual length L of the welded pipe section (1). H .

6. A method for connecting large HDPE pipes according to claim 1, characterized in that: S2L S The telescopic section (22) of the telescopic joint (2) is capable of telescoping to a length of ±500 mm.

7. A method for connecting large HDPE pipes according to claim 1, characterized in that: S3 includes the following steps: After the welding of the joint section (1) is completed on land, the length of the joint section (1) after welding is measured every 2h-4h, and the average value of the length of the joint section (1) after welding is obtained as the actual length L of the joint section (1) after welding. Z ', ensure that L Z 'Meet the needs of closure.

8. A method for connecting large HDPE pipes according to claim 1, characterized in that: S4 includes the following steps: S41. Adjust the expansion joint (2) to the minimum expansion position, install and tighten all the sealing ring fastening bolts (23) of the expansion joint (2); S42. Fixed telescopic section (22); S43. The closure section (1) is put into water, and the closure section (1) and the installed pipe (4) are adjusted to the same elevation. The sealing ring fastening bolts (23) are loosened, and the length of the expansion section (22) is adjusted. The butt flange (3) is connected to the flange of the installed pipe (4), and the sealing ring fastening bolts (23) are re-tightened.

9. A method for connecting large HDPE pipes according to claim 8, characterized in that: In S43, the bolt torque when the butt flange (3) is connected to the flange of the installed pipeline (4) is 225N·m-235N·m; the torque when the sealing ring fastening bolt (23) is tightened is 450N·m-460N·m.

10. A method for connecting large HDPE pipes according to claim 1, characterized in that: S5 includes the following steps: S51. Install a template (5) at the sealing ring fastening bolt (23), wherein the template (5) comprises a first template (51), a second template (52) and a top reinforcing rib (53), wherein the first template (51) and the second template (52) are mirror images of each other, and the first template (51) and the second template (52) are assembled to form a rectangular frame structure having a U-shaped notch (54), wherein the top reinforcing rib (53) crosses each other and connects the tops of the first template (51) and the second template (52), and the U-shaped notch (54) faces downward so that the template (5) is covered on the telescopic joint (2); S52. Pour concrete into the formwork (5) to encapsulate the expansion joint (2).

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