Butt welding connection structure of steel-plastic composite pipe and connection method of butt welding connection structure

Abstract

The invention discloses a butt welding connection structure of a steel-plastic composite pipe and a connection method of the butt welding connection structure, relates to the technical field of composite pipe butt joint structures, and is mainly used for solving the problem that leakage risks exist in common steel-plastic composite pipe connection modes. According to the main structure, adjacent outer-layer steel pipes are connected in a butt welding mode through radial flaring sections which are arranged at the ends of the outer-layer steel pipes and are of an integrated structure with the outer-layer steel pipes; the end parts of the adjacent inner-layer plastic pipes are connected, a filler cavity is formed between the end parts of the adjacent inner-layer plastic pipes and the radial flaring sections which are in butt welding connection, and threaded holes communicated with the filler cavity are formed in the radial flaring sections. The invention provides a butt welding connection structure of a steel-plastic composite pipe and a connection method of the butt welding connection structure, which can ensure the loading capacity and the connection reliability of a connection part while completely preventing a medium in an inner-layer plastic pipe from being in contact with an outer-layer steel pipe, and increase the applicable working condition range of the product while avoiding the leakage of the medium.

Description

Technical Field

[0001] The invention relates to the technical field of composite pipe butt-jointing structures, and in particular to a butt-welding connection structure of a steel-plastic composite pipe and a connection method thereof. Background Art

[0002] Steel-plastic composite pipe is a composite pipe formed by bonding the outer steel pipe and the inner plastic pipe together with a hot melt adhesive layer. The outer steel pipe ensures pressure bearing and the inner plastic pipe is corrosion resistant. The two materials complement each other, reflecting the excellent performance characteristics of the product. It should be noted that the rationality and reliability of the connection method of the steel-plastic composite pipe are the key to determining its use effect. The common connection methods of today's steel-plastic composite pipes include threaded connection, groove connection, stainless steel joint butt welding connection, flange connection, etc.

[0003] However, these common steel-plastic composite pipe connection methods all have certain defects, specifically:

[0004] (1) Threaded connection, groove connection and stainless steel joint butt welding connection only realize the mechanical connection between the outer steel pipes, but not the connection between the inner lining plastic pipes. Therefore, it is difficult to avoid the contact between the conveying medium and the end of the outer steel pipe. When the conveying medium of the steel-plastic composite pipe is corrosive, it may cause rapid corrosion to the end of the outer steel pipe, causing leakage, and then leading to failure of the pipeline system.

[0005] (2) On the one hand, flange-connected steel-plastic composite pipes are not suitable for burial in the design specifications, which limits their operating conditions. On the other hand, during use, the plastic layer covering the flange sealing surface is prone to sealing failure due to uneven force, stress disappearance, deformation, aging and other factors, which can also cause leakage and lead to failure of the pipeline system.

[0006] Therefore, there is an urgent need for a new butt-welding connection structure and a connection method for a steel-plastic composite pipe that can solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a butt-welding connection structure of a steel-plastic composite pipe, which can completely prevent the medium in the inner plastic pipe from contacting the outer steel pipe while ensuring the pressure bearing capacity and connection reliability of the connection part, avoiding medium leakage while also increasing the applicable working range of the product.

[0008] Another object of the present invention is to provide a butt welding connection method for the above butt welding connection structure.

[0009] The technical solution of the present invention to solve the previous technical problem is: a butt-welding connection structure of a steel-plastic composite pipe and a connection method thereof, comprising at least two coaxially arranged steel-plastic composite pipes, the steel-plastic composite pipe comprising an outer steel pipe, a hot-melt adhesive layer and an inner plastic pipe arranged in sequence along its radial direction, the adjacent outer steel pipes are butt-welded through radial expansion sections arranged at their ends, and the radial expansion section and the outer steel pipe are an integrated structure; the ends of the adjacent inner plastic pipes are connected and a filling cavity is formed between the radial expansion sections connected by butt welding, and the radial expansion sections are all provided with threaded holes connected to the filling cavity.

[0010] As a further improvement of the present invention, filling material is injected into the filling cavity through the threaded hole.

[0011] As a further improvement of the present invention, a blocking bolt that matches the thread of the threaded hole is installed on the threaded hole.

[0012] As a further improvement of the present invention, the ends of adjacent inner plastic tubes are connected by hot-melt connection.

[0013] As a further improvement of the present invention, a socket-and-spigot connecting pipe is provided between the ends of the adjacent inner plastic pipes, and the two ends of the connecting pipe are respectively sleeved on the outer sides of the ends of the two inner plastic pipes.

[0014] As a further improvement of the present invention, a hot melt adhesive layer is also provided between the inner wall of the socket-and-spigot connection pipe and the outer wall of the inner plastic pipe.

[0015] The technical solution of the present invention to solve the second technical problem is: a butt welding connection method of a steel-plastic composite pipe, comprising the following steps:

[0016] S1. Perform pretreatment such as flattening and cleaning on the inner lining layers at both ends of the steel-plastic composite pipe;

[0017] S2. Preheating the end surface of the inner lining layer to be hot-melt-jointed;

[0018] S3, the end faces of the inner lining layers at the two ends to be connected are butt-welded by hot-melt, and the end faces of the radially expanded sections of the outer steel pipes are butt-welded to the required position for butt welding;

[0019] S4. Perform a bottom thin weld on the butt weld of the outer steel pipe, and respectively install a coolant inlet pipe and a coolant outlet pipe on the threaded holes on both sides to seal the packing cavity, and then connect a water pump to pass the circulating coolant to circulate the coolant;

[0020] S5. Butt welding is performed on the butt weld of the outer steel pipe, and the heat generated by welding is taken away by the circulating coolant during the welding process;

[0021] S6. After the butt welding is completed, clean and grind the weld, then inject the filler into the filler cavity through the threaded hole. After the filler solidifies, use the sealing bolts to seal the threaded holes on both sides to complete the installation construction.

[0022] As a further improvement of the present invention, in step S5, a portable temperature measuring instrument is used during the welding process to monitor the temperature of the welding area and adjacent areas.

[0023] As a further improvement of the present invention, when the inner lining layers at both ends to be connected are connected by a socket connection pipe, steps S2 and S3 are specifically as follows:

[0024] S2, coating the socket section of the inner lining layer with a cold-setting adhesive or performing a hot-melt preheating treatment;

[0025] S3, insert the inner lining layers at both ends to be connected into the socket connection pipe 8, and make the end faces of the radial expansion section 5 of the outer steel pipe 2 butt to the required position for butt welding;

[0026] The melting depth of the hot-melt socket connection of the inner lining layer is 60% of the wall thickness of the inner plastic pipe, and the length of the socket section of the inner lining layer is ≥ 1 / 2 of the socket depth of the socket connection pipe.

[0027] As a further improvement of the present invention, the manufacturing process of the steel-plastic composite pipe comprises the following steps:

[0028] S1', expanding the ends of the carbon steel base pipe to form a radial expansion section, processing the butt welding groove on the end face of the radial expansion section, processing the threaded hole on the side wall of the radial expansion section, and completing the production of the outer steel pipe;

[0029] S2', the inner lining layer composed of the inner plastic tube and the hot melt adhesive layer is formed by double-layer co-extrusion to form a double-layer structure of the inner plastic tube with the outer layer being the hot melt adhesive layer and the inner layer being the polymer material;

[0030] S3', insert the inner lining layer into the outer steel pipe after the expansion process through the pipe-threading equipment, then clamp the inflatable clamps at both ends of the semi-finished steel-plastic composite pipe, and pressurize the pipe to expand the inner lining layer outward. At the same time, the hot melt adhesive layer reaches the bonding temperature through electromagnetic induction heating, so that the inner lining layer and the outer steel pipe are bonded and fused into one;

[0031] S4', through the processing of the flat port equipment, the extended sections of the inner lining of the two ports are made flat and reach the required length for installation;

[0032] Wherein, in step S1', the volume of the filler cavity: the volume of the weld in the welding area is ≥10:1, the flaring height is 2.5-3 times the wall thickness of the steel pipe, and the flaring depth is 4-5 times the wall thickness of the steel pipe.

[0033] Beneficial Effects

[0034] Compared with the prior art, the butt welding connection structure of a steel-plastic composite pipe and the connection method thereof of the present invention have the following advantages:

[0035] 1. When two pipes with the connection structure are connected, the inner plastic pipes are connected as one body, so that the transported medium can only contact the inner plastic pipe, and the medium is completely prevented from contacting the outer steel pipe, thereby solving the problem of corrosion of the outer steel pipe and avoiding the problem of leakage of the medium due to pipeline corrosion; at the same time, since the adjacent outer steel pipes are connected by butt welding through the radial expansion section arranged at the end thereof, and the radial expansion section and the outer steel pipe are an integrated structure, the pressure bearing capacity and connection reliability of the connection part can be better guaranteed compared with the flange connection, and the applicable working condition range of the product can be increased; in addition, in the process of welding the adjacent outer steel pipes, the coolant input pipe / output pipe can be connected to the radial expansion section by threaded connection, so that the coolant is injected into the packing cavity during the welding process, thereby effectively avoiding the damage of the inner plastic pipe by the high temperature generated when the outer steel pipe is butt welded.

[0036] The present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, which are used to illustrate embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 is a cross-sectional view of embodiment 1 of the present invention;

[0039] Figure 2 is a cross-sectional view of embodiment 2 of the present invention;

[0040] Figure 3 It is a partial structural diagram of the radial expansion section of the present invention.

[0041] Among them: 1- steel-plastic composite pipe; 2- outer steel pipe; 3- hot melt adhesive layer; 4- inner plastic pipe; 5- radial expansion section; 6- stuffing cavity; 7- threaded hole; 8- socket connection pipe. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; of course, it can also be a mechanical connection or an electrical connection; in addition, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] Embodiments of the present invention will now be described with reference to the accompanying drawings.

[0045] Example 1

[0046] The specific embodiments of the present invention are as follows Figure 1 As shown, a butt-welding connection structure of a steel-plastic composite pipe and a connection method thereof include at least two coaxially arranged and sequentially connected steel-plastic composite pipes 1. The steel-plastic composite pipe 1 includes an outer steel pipe 2, a hot melt adhesive layer 3 and an inner plastic pipe 4 which are sequentially arranged along its radial direction from the outside to the inside. Among them, the adjacent outer steel pipes 2 are butt-welded through a radial expansion section 5 arranged at the end of the outer steel pipe 2, and the radial expansion section 5 and the outer steel pipe 2 are an integral structure. At the same time, the ends of the adjacent inner plastic pipes 4 are connected and a stuffing cavity 6 is formed between the radial expansion sections 5 connected by butt welding. In addition, the radial expansion sections 5 are all provided with threaded holes 7 connected to the stuffing cavity 6. In this embodiment, the radial expansion section 5 of the outer steel pipe 2 is trumpet-shaped, and the inner wall of the radial expansion section 5 does not contact the inner plastic pipe 4.

[0047] When assembling a long conveying pipeline through the steel-plastic composite pipe 1, first connect the ends of the coaxially adjacent inner plastic pipes 4 together; then, connect the coolant inlet pipe and the coolant outlet pipe to the two radial expansion sections 5 to be butt-welded through the threaded holes 7 respectively; then, butt-weld the radial expansion sections 5 of the adjacent outer steel pipes 2 through welding equipment, and, during the butt-welding process, the coolant inlet pipe and the coolant outlet pipe are opened at the same time, forming a coolant circulation between the stuffing cavity 6, the coolant inlet pipe and the coolant outlet pipe; finally, when the radial expansion sections 5 are butt-welded, it is only necessary to drain the coolant in the stuffing cavity 6 to complete the connection of the adjacent steel-plastic composite pipes 1.

[0048] When two steel-plastic composite pipes 1 are connected by this connection structure, because the inner plastic pipes 4 are connected as one body, the transported medium can only contact with the inner plastic pipe 4, completely preventing the medium from contacting with the outer steel pipe 2, thereby solving the problem of corrosion of the outer steel pipe 2 and avoiding the problem of leakage of the medium due to pipeline corrosion. At the same time, since the adjacent outer steel pipes 2 are connected by butt welding through the radial expansion section 5 set at their ends, and the radial expansion section 5 and the outer steel pipe 2 are an integrated structure, compared with the flange connection, this connection structure not only reduces the number of parts, but also can better ensure the pressure bearing capacity and connection reliability of the connection part, and can also increase the applicable working condition range of the product. In addition, in the process of welding the adjacent outer steel pipes 2, the coolant input pipe / output pipe can be connected to the radial expansion section 5 by threaded connection, so that the coolant is injected into the filler cavity 6 during the welding process, thereby effectively avoiding the damage of the inner plastic pipe 4 by the high temperature generated when the outer steel pipe 2 is butt welded.

[0049] In this connection structure, a filling material is injected into the filling cavity 6 through the threaded hole 7. The filling material is a solidified wrapped heat insulating material. The filling material can transmit the pressure of the conveying medium on the inner plastic tube 4 to the outer steel tube 2, that is, it can ensure the tensile strength of the connection of the steel-plastic composite pipe 1 along the medium conveying direction, and can ensure the high-pressure strength of the connection of the steel-plastic composite pipe 1 along the radial direction, thereby ensuring the strength of the connection of the steel-plastic composite pipe 1 when the conveying pipeline conveys high-pressure media. In this embodiment, in order to avoid leakage of the filling material 7 during the filling process and subsequent use. A plugging bolt that matches its thread is installed on the threaded hole 7.

[0050] In this embodiment, in order to achieve the connection between adjacent inner plastic tubes 4, the ends of adjacent inner plastic tubes 4 are connected by hot melting.

[0051] In this embodiment, the manufacturing process of the steel-plastic composite pipe 1 includes the following steps:

[0052] S1', expand the two end ports of the carbon steel base pipe to form a radial expansion section 5, or weld the expanded expansion section short pipe and the end of the carbon steel base pipe together, and process the welding groove on the end face of the radial expansion section 5, and process the threaded hole 7 on the side wall of the radial expansion section 5 to complete the production of the outer steel pipe 2;

[0053] S2', the inner lining layer composed of the inner plastic tube 4 and the hot melt adhesive layer 3 is formed by double-layer co-extrusion to form a double-layer structure in which the outer layer is the hot melt adhesive layer 3 and the inner layer is the inner plastic tube 4 of a polymer material such as polyethylene or polypropylene;

[0054] S3', insert the inner lining layer into the outer steel pipe 2 after the expansion process through the pipe penetration equipment; then clamp the inflatable clamps at both ends of the semi-finished steel-plastic composite pipe 1, and pressurize the pipe to make the inner lining layer expand outward; at the same time, the hot melt adhesive layer 3 reaches the bonding temperature through electromagnetic induction heating, so that the inner lining layer and the outer steel pipe 2 are bonded and fused into one;

[0055] S4', through the processing of the flat port equipment, the extended sections of the inner lining of the two ports are made flat and reach the required length for installation.

[0056] In step S1 of the above manufacturing process, the volume of the filling cavity 6: the volume of the weld in the welding area is ≥ 10:1, which ensures that the size of the expanded part meets the requirements of the butt welding connection, and also ensures that the outer dimensions and internal volume of the filling cavity 6 meet the circulation cooling efficiency. In addition, the expansion height is 2.5-3 times the wall thickness of the steel pipe, and the expansion depth is 4-5 times the wall thickness of the steel pipe, which can also ensure the structural strength of this part after filling, thereby ensuring the safety and reliability of the system.

[0057] In this embodiment, the connection process between the steel-plastic composite pipes 1 includes the following steps:

[0058] S1, pre-treating the inner lining layers of the two end ports of the steel-plastic composite pipe 1 by flattening and cleaning;

[0059] S2. Preheating the end surface of the inner lining layer to be hot-melt-jointed;

[0060] S3, the end faces of the inner lining layers at the two ends to be connected are butt-welded by hot-melting, and the end faces of the radial expansion section 5 of the outer steel pipe 2 are butt-welded to the required position;

[0061] S4, perform a bottom thin weld on the butt weld of the outer steel pipe 2, and respectively install a coolant inlet pipe and a coolant outlet pipe on the threaded holes 7 on both sides to seal the packing cavity 6, and then connect a water pump to pass the circulating coolant to circulate the coolant;

[0062] S5, butt welding is performed on the butt weld of the outer steel pipe 2, and the heat generated by welding is taken away by the circulating coolant during the welding process;

[0063] S6. After the butt welding is completed, clean and grind the weld, and then inject filler into the filler cavity 6 through the threaded hole 7. After the filler solidifies, use the sealing bolts to seal the threaded holes 7 on both sides to complete the installation construction.

[0064] In step S5 of the above connection process, a portable temperature measuring instrument is used during the welding process to monitor the temperature of the welding and adjacent parts to ensure that the inner plastic pipe 4 is not damaged by high temperature.

[0065] Example 2

[0066] The difference between this embodiment and embodiment 1 is as follows Figure 2 As shown, in order to realize the connection between adjacent inner plastic pipes 4, a socket connection pipe 8 is further provided between the ends of adjacent inner plastic pipes 4. The two ends of the connection pipe 8 are respectively sleeved on the outer sides of the ends of the two inner plastic pipes 4.

[0067] In this embodiment, a hot melt adhesive layer 3 is also provided between the inner wall of the socket-and-spigot connection pipe 8 and the outer wall of the inner plastic pipe 4. The socket-and-spigot connection pipe 8 is a plastic pipe.

[0068] In this embodiment, the manufacturing process of the steel-plastic composite pipe 1 includes the following steps:

[0069] S1', expand the two end ports of the carbon steel base pipe to form a radial expansion section 5, or weld the expanded expansion section short pipe and the end of the carbon steel base pipe together, and process the welding groove on the end face of the radial expansion section 5, and process the threaded hole 7 on the side wall of the radial expansion section 5 to complete the production of the outer steel pipe 2;

[0070] S2', the inner lining layer composed of the inner plastic tube 4 and the hot melt adhesive layer 3 is formed by double-layer co-extrusion to form a double-layer structure in which the outer layer is the hot melt adhesive layer 3 and the inner layer is the inner plastic tube 4 of a polymer material such as polyethylene or polypropylene;

[0071] S3', insert the inner lining layer into the outer steel pipe 2 after the expansion process through the pipe penetration equipment; then clamp the inflatable clamps at both ends of the semi-finished steel-plastic composite pipe 1, and pressurize the pipe to make the inner lining layer expand outward; at the same time, the hot melt adhesive layer 3 reaches the bonding temperature through electromagnetic induction heating, so that the inner lining layer and the outer steel pipe 2 are bonded and fused into one;

[0072] S4', through the processing of the flat port equipment, the extended sections of the inner lining of the two ports are made flat and reach the required length for installation.

[0073] In step S1 of the above manufacturing process, the volume of the filling cavity 6: the volume of the weld in the welding area is ≥ 10:1, which ensures that the size of the expanded part meets the requirements of the butt welding connection, and also ensures that the outer dimensions and internal volume of the filling cavity 6 meet the circulation cooling efficiency. In addition, the expansion height is 2.5-3 times the wall thickness of the steel pipe, and the expansion depth is 4-5 times the wall thickness of the steel pipe, which can also ensure the structural strength of this part after filling, thereby ensuring the safety and reliability of the system.

[0074] In this embodiment, the connection process between the steel-plastic composite pipes 1 includes the following steps:

[0075] S1, pre-treating the inner lining layers of the two end ports of the steel-plastic composite pipe 1 by flattening and cleaning;

[0076] S2, coating the socket section of the inner lining layer with a cold-setting adhesive or performing a hot-melt preheating treatment;

[0077] S3, insert the inner lining layers at both ends to be connected into the socket connection pipe 8, and make the end faces of the radial expansion section 5 of the outer steel pipe 2 butt to the required position for butt welding;

[0078] S4, perform a bottom thin weld on the butt weld of the outer steel pipe 2, and respectively install a coolant inlet pipe and a coolant outlet pipe on the threaded holes 7 on both sides to seal the packing cavity 6, and then connect a water pump to pass the circulating coolant to circulate the coolant;

[0079] S5, butt welding is performed on the butt weld of the outer steel pipe 2, and the heat generated by welding is taken away by the circulating coolant during the welding process;

[0080] S6. After the butt welding is completed, clean and grind the weld, and then inject filler into the filler cavity 6 through the threaded hole 7. After the filler solidifies, use the sealing bolts to seal the threaded holes 7 on both sides to complete the installation construction.

[0081] The melting depth of the hot-melt socket connection of the inner lining layer is about 60% of the wall thickness of the inner plastic pipe 4, and the length of the socket section of the inner lining layer is ≥ 1 / 2 of the socket depth of the socket connection pipe 8. At the same time, in step S5 of the above connection process, a portable temperature measuring instrument is used during the welding process to monitor the temperature of the welding and adjacent parts to ensure that the inner plastic pipe 4 will not be damaged by high temperature.

[0082] The present invention has been described above in conjunction with the best embodiments, but the present invention is not limited to the embodiments disclosed above, but should cover various modifications and equivalent combinations based on the essence of the present invention.

Claims

1. A butt-welding connection structure of a steel-plastic composite pipe, comprising at least two coaxially arranged steel-plastic composite pipes (1), wherein the steel-plastic composite pipe (1) comprises an outer steel pipe (2), a hot melt adhesive layer (3) and an inner plastic pipe (4) sequentially arranged along the radial direction thereof, characterized in that: The adjacent outer steel pipes (2) are connected by butt welding via radial expansion sections (5) arranged at their ends, and the radial expansion sections (5) and the outer steel pipes (2) are an integrated structure; the ends of the adjacent inner plastic pipes (4) are connected and a stuffing cavity (6) is formed between the butt-welded radial expansion sections (5), and the radial expansion sections (5) are all provided with threaded holes (7) connected to the stuffing cavity (6).

2. The butt welding connection structure of the steel-plastic composite pipe according to claim 1 is characterized in that: Filling material is injected into the filling cavity (6) through the threaded hole (7).

3. The butt welding connection structure of the steel-plastic composite pipe according to claim 1 or 2, characterized in that: A blocking bolt that matches the threaded hole (7) is installed on the threaded hole (7).

4. The butt welding connection structure of the steel-plastic composite pipe according to claim 1 is characterized in that: The ends of adjacent inner plastic tubes (4) are connected by hot melting.

5. The butt welding connection structure of the steel-plastic composite pipe according to claim 1 is characterized in that: A socket-and-spigot connection pipe (8) is also provided between the ends of the adjacent inner plastic pipes (4), and the two ends of the connection pipe (8) are respectively sleeved onto the outer sides of the ends of the two inner plastic pipes (4).

6. The butt welding connection structure of the steel-plastic composite pipe according to claim 5 is characterized in that: A hot melt adhesive layer (3) is also provided between the inner wall of the socket-and-spigot connection pipe (8) and the outer wall of the inner plastic pipe (4).

7. A butt welding connection method for steel-plastic composite pipes, characterized in that: The following steps are involved: S1. Performing pretreatment such as flattening and cleaning the inner lining layers at both end ports of the steel-plastic composite pipe (1); S2. Preheating the end surface of the inner lining layer to be hot-melt-jointed; S3, the end faces of the inner lining layers at the two ends to be connected are butt-melted together, and the end faces of the radial expansion section (5) of the outer steel pipe (2) are butt-welded to the required position for butt welding; S4, performing a bottom thin welding on the butt weld of the outer steel pipe (2), and respectively assembling a coolant inlet pipe and a coolant outlet pipe on the threaded holes (7) on both sides to seal the packing cavity (6), and then connecting a water pump to introduce circulating coolant to circulate the coolant; S5, butt welding the butt weld of the outer steel pipe (2), during which the heat generated by welding is removed by circulating coolant; S6. After the butt welding is completed, the weld is cleaned and polished, and then the filler is injected into the filler cavity (6) through the threaded hole (7). After the filler solidifies, the threaded holes (7) on both sides are sealed with sealing bolts to complete the installation construction.

8. The method for butt welding of steel-plastic composite pipes according to claim 7, characterized in that: In step S5, a portable temperature measuring instrument is used during the welding process to monitor the temperature of the welding area and adjacent areas.

9. The method for butt welding of steel-plastic composite pipes according to claim 8, characterized in that: When the inner lining layers at both ends to be connected are connected via the socket connection pipe (8), steps S2 and S3 are specifically as follows: S2, coating the socket section of the inner lining layer with a cold-setting adhesive or performing a hot-melt preheating treatment; S3, inserting the inner lining layers at both ends to be connected into the socket joint pipe (8), and making the end faces of the radial expansion section (5) of the outer steel pipe (2) butt to the required position for butt welding; The melting depth of the hot-melt socket connection of the inner lining layer is 60% of the wall thickness of the inner plastic pipe (4), and the length of the socket section of the inner lining layer is ≥ 1 / 2 of the socket depth of the socket connection pipe (8).

10. The method for butt welding a steel-plastic composite pipe according to any one of claims 7 to 9, characterized in that: The manufacturing process of the steel-plastic composite pipe (1) comprises the following steps: S1', expanding the ends of the carbon steel base pipe to form a radial expansion section (5), processing a butt welding groove on the end face of the radial expansion section (5), processing a threaded hole (7) on the side wall of the radial expansion section (5), and completing the production of the outer steel pipe (2); S2', the inner lining layer composed of the inner plastic tube (4) and the hot melt adhesive layer (3) is formed by double-layer co-extrusion to form a double-layer structure in which the outer layer is the hot melt adhesive layer (3) and the inner layer is the inner plastic tube (4) of a polymer material; S3', inserting the inner lining layer into the outer steel pipe (2) after the expansion process through the pipe insertion equipment, and then clamping the inflatable clamps at both ends of the semi-finished steel-plastic composite pipe (1), and pressurizing the pipe to make the inner lining layer expand outward, and at the same time, heating the hot melt adhesive layer (3) to the bonding temperature through electromagnetic induction heating, so that the inner lining layer and the outer steel pipe (2) are bonded and fused into one; S4', through the processing of the flat port equipment, the extended sections of the inner lining of the two ports are made flat and reach the required length for installation; Wherein, in step S1', the volume of the filling cavity (6): the volume of the weld in the welding area is ≥10:1, the flaring height is 2.5-3 times the wall thickness of the steel pipe, and the flaring depth is 4-5 times the wall thickness of the steel pipe.

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