Electrofusion sleeve for connecting non-standard electrofusion pipe ends

Abstract

The application discloses a kind of electric fusion sleeve for connecting non-standard electric fusion pipe head, it is related to oil and gas pipeline lining pipe repair technical field, wherein the electric fusion sleeve for connecting non-standard electric fusion pipe head, including pipe head plastic section and electric heat fusion connection component, pipe head plastic section is annular structure;Pipe head plastic section is set in electric heat fusion connection component, electric heat fusion connection component is hollow circular truncated cone structure with both ends open, and the first plug-in structure and the second plug-in structure are formed respectively in the both ends of electric heat fusion connection component along its axial direction, the sharp corner part of first plug-in structure is inserted into non-standard electric fusion pipe head and is electric heat fusion connection with non-standard electric fusion pipe head, and the sharp corner part of second plug-in structure is inserted into standard electric fusion pipe head and is electric heat fusion connection with standard electric fusion pipe head.The application can simplify the construction complexity of oil and gas pipeline lining pipe repair, and ensure oil and gas fluid conveying efficiency.

Description

Technical Field

[0001] This invention relates to the field of oil and gas pipeline lining repair technology, and in particular to an electrofusion sleeve for connecting non-standard electrofusion pipe heads. Background Technology

[0002] In pipeline engineering repair practice, high-barrier polyethylene lining technology has become a key solution for media leakage caused by corrosion in oilfield gathering and transportation pipelines and long-distance oil and gas pipelines. These pipelines operate for extended periods in environments containing easily permeable media such as hydrogen, oil and gas, and sulfur-containing liquids, making them prone to gas permeation, hydrogen embrittlement, and corrosion, threatening transportation safety.

[0003] However, the inner wall of the old steel pipe exhibits significant unevenness due to long-term corrosion, requiring the outer diameter of the HBPE liner to dynamically adapt to the old pipe profile during the insertion process. This adaptation results in the inner diameter of the pipe head of each liner section being smaller than the standard size, forming a "non-standard electrofusion pipe head".

[0004] Existing connection methods are forced to adopt an interim process: first, a standard-sized HBPE thick-walled pipe is fixed to a non-standard pipe end through on-site hot-melt welding, converting it into a standard pipe end, and then a conventional standard electrofusion sleeve is used to complete the final connection. This method requires additional welding equipment and professional personnel, and the excavation of a large operating pit to accommodate the welding process. This interim connection method causes multiple technical defects: the welding process increases construction complexity, prolongs the construction period, and drives up costs; the interface between the thick-walled pipe and the inner liner creates a radial step, causing the stepped portion in the pipeline flow section to obstruct the fluid transport path and reduce transport efficiency; more seriously, commercially available standard electrofusion sleeves generally lack a high-barrier layer structure, causing the gas barrier chain of the pipeline system to be interrupted at the joint, resulting in a "short plank effect." When transporting highly permeable media such as hydrogen, gas permeation, hydrogen embrittlement, and corrosion are prone to occur in the joint area, significantly weakening the sealing performance and long-term reliability of the repair system, and severely restricting the repair effect. Summary of the Invention

[0005] The main objective of this invention is to provide an electrofusion sleeve for connecting non-standard electrofusion pipe heads, which aims to simplify the construction complexity of repairing oil and gas pipeline lining pipes and ensure the efficiency of oil and gas fluid transportation.

[0006] To achieve the above objectives, the present invention proposes an electrofusion sleeve for connecting non-standard electrofusion tube heads, wherein the inner diameter of the non-standard electrofusion tube head is smaller than the inner diameter of the standard electrofusion tube head, and the electrofusion sleeve for connecting the non-standard electrofusion tube head comprises: The tube head shaping section has a ring structure, and the non-standard electrofusion tube head and the standard electrofusion tube head are respectively disposed at both ends of the tube head shaping section; An electrofusion connection assembly is provided, wherein a tube head shaping section is sleeved on the outside of the electrofusion connection assembly. The electrofusion connection assembly is a hollow frustum-shaped structure with open ends. A first insertion structure and a second insertion structure are formed at both ends along its axial direction. The ends of the first insertion structure and the second insertion structure protrude to form sharp corners. The inner diameter of the first insertion structure is smaller than the inner diameter of the second insertion structure. The sharp corner of the first insertion structure extends into the non-standard electrofusion tube head and is electrofusion-fused to the non-standard electrofusion tube head. The sharp corner of the second insertion structure extends into the standard electrofusion tube head and is electrofusion-fused to the standard electrofusion tube head. The electrofusion connection assembly, the non-standard electrofusion tube head, the standard electrofusion tube head, and the tube head shaping section are coaxially arranged.

[0007] The technical solution of this invention employs an electrofusion sleeve structure comprising a pipe head shaping section and an electrofusion connection assembly. The hollow frustum-shaped structure of the electrofusion connection assembly achieves a gradient change in the inner diameter of the first and second insertion structures, precisely adapting to and directly electrofusion-connecting non-standard and standard electrofusion pipe heads. This eliminates the need for thick-walled pipe welding processes and the associated specialized equipment, personnel, and operating pits required in traditional transitional connection methods. By integrating a multi-layered composite structure identical to that of the HBPE liner pipe into the electrofusion connection assembly, the barrier layer extends from the non-standard electrofusion pipe head through the electrofusion connection assembly to the standard electrofusion pipe head, forming a continuous barrier path and eliminating the problem of gas barrier chain interruption at the joint. The smooth conical inner surface of the hollow frustum-shaped structure eliminates the steps on the inner wall of the pipe, ensuring laminar fluid transport. Through the first heating wire, the second... The differentiated heating arrangement of two heating wires and multiple third heating wires allows the sharp corners of the first and second plug-in structures to melt preferentially and penetrate the inner wall of the tube head. Simultaneously, the open channels formed by the multiple third heating wires extending axially and spaced circumferentially guide the molten material to spontaneously flow and fill the connection interface under gravity, reducing void formation. The electrofusion element installed on the inner wall of the tube head shaping section provides a limiting effect on the prefabricated transition structure when not energized, improving alignment accuracy. After energization, it melts and fills the gaps, compensating for radial displacement and reducing axial deviation, thus improving connection coaxiality. The addition of an electrofusion guide section extends the connection range to the tube body, increasing the connection area and dispersing stress. This achieves a comprehensive technical effect: simplifying the construction process, reducing costs, eliminating inner wall steps, ensuring continuous barrier performance, and improving connection strength and sealing performance. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0009] Figure 1 This is a schematic diagram of an embodiment of the electrofusion sleeve for connecting non-standard electrofusion tube heads provided by the present invention; Figure 2 This is a schematic diagram of another embodiment of the electrofusion sleeve for connecting non-standard electrofusion tube heads provided by the present invention; Figure 3 This is a schematic diagram of a structure of an embodiment of the tube head shaping section involved in the present invention; Figure 4 This is an exploded structural diagram of an embodiment of the electrofusion welding assembly involved in the present invention; Figure 5 This is a partial cross-sectional view of an embodiment of the pipe head shaping section and electrofusion connection assembly involved in the present invention; Figure 6 A schematic diagram of the cross-sectional structure formed by connecting non-standard and standard electrofusion tube heads in existing technology; Figure 7 This is a schematic diagram of the cross-sectional structure formed by connecting a non-standard electrofusion tube head and a standard electrofusion tube head using the present invention.

[0010] Explanation of icon numbers: 10. Non-standard electrofusion tube ends; 20. Standard electrofusion tube ends; 100. Tube head shaping section; 200. Electrofusion connection assembly; 300. Electrofusion component; 400. Electrofusion guide section; 101. Fusion space; 102. Installation space; 210. First plug-in structure; 220. Second plug-in structure; 230. Sharp corner; 240. Prefabricated transition structure; 250. Electrofusion structure; 251. First heating wire; 252. Second heating wire; 253. Third heating wire.

[0011] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0012] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0013] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0014] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0015] In pipeline repair practice, the inner wall of old steel pipes exhibits significant unevenness due to long-term corrosion, requiring the outer diameter of the HBPE liner to dynamically adapt to the old pipe profile during installation. This adaptation results in the inner diameter of each liner section's end being smaller than the standard size, forming a "non-standard electrofusion end." Existing connection solutions are forced to adopt a transitional process: first, a standard-sized HBPE thick-walled pipe is fixed to the non-standard end through on-site hot-melt welding, converting it into a standard end, and then a conventional standard electrofusion sleeve is used to complete the final connection. This method requires additional welding equipment and professional personnel, and the excavation of a large operating pit to accommodate the welding process. This transitional connection method leads to multiple technical drawbacks: the welding process increases construction complexity, prolongs the construction period, and drives up costs; a radial step is created at the interface between the thick-walled pipe and the liner, causing the stepped portion in the pipeline flow section to obstruct the fluid transport path (see [link to relevant documentation]). Figure 6 This reduces transport efficiency; more seriously, commercially available standard electrofusion sleeves generally lack a high-barrier layer structure, causing the gas barrier chain in the pipeline system to be interrupted at the joint, resulting in a "weakest link effect." When transporting highly permeable media such as hydrogen, gas permeation, hydrogen embrittlement, and corrosion are prone to occur in the joint area, significantly weakening the sealing performance and long-term reliability of the repair system and severely restricting the repair effect.

[0016] To address this technical problem, the present invention proposes an electrofusion sleeve for connecting non-standard electrofusion tube heads.

[0017] Please see Figure 1 , Figure 2 and Figure 3 In one embodiment of the present invention, the electrofusion sleeve for connecting non-standard electrofusion tube heads has an inner diameter of non-standard electrofusion tube head 10 smaller than that of standard electrofusion tube head 20. The electrofusion sleeve for connecting non-standard electrofusion tube heads includes a tube head shaping section 100 and an electrofusion connection assembly 200. The tube head shaping section 100 has an annular structure, and the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20 are respectively disposed at both ends of the tube head shaping section 100. The tube head shaping section 100 is sleeved outside the electrofusion connection assembly 200, which has a hollow frustum-shaped structure with open ends. The electrofusion connection assembly 200 forms a first [missing information] at both ends along its axial direction. A first plug-in structure 210 and a second plug-in structure 220 are provided. The ends of both the first plug-in structure 210 and the second plug-in structure 220 protrude to form sharp corners 230. The inner diameter of the first plug-in structure 210 is smaller than that of the second plug-in structure 220. The sharp corners 230 of the first plug-in structure 210 extend into the non-standard electrofusion tube head 10 and are electrofused together with the non-standard electrofusion tube head 10. The sharp corners 230 of the second plug-in structure 220 extend into the standard electrofusion tube head 20 and are electrofused together with the standard electrofusion tube head 20. The electrofusion connection assembly 200, the non-standard electrofusion tube head 10, the standard electrofusion tube head 20, and the tube head shaping section 100 are coaxially arranged.

[0018] For ease of understanding, the following explains some key terms in this embodiment: Non-standard electrofusion pipe head 10 refers to the pipe head of an HBPE liner pipe with an inner diameter smaller than the conventional standard size due to uneven inner wall or size limitations of the old steel pipe during pipeline repair.

[0019] The standard electrofusion pipe head 20 refers to a pipe head conforming to industry specifications or market-standard sizes for HBPE lined pipes. The electrofusion sleeve is a component used to connect pipes; it typically contains an electrothermal element that melts and solidifies the pipe materials to be connected by applying electricity, thus forming a connection. The pipe head shaping section 100 is a component of the electrofusion sleeve, its main function being to provide positional limits and support for the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20 to be connected, ensuring they remain coaxially aligned during the connection process. The electrofusion connection assembly 200 is the core functional component of the electrofusion sleeve, containing an electrothermal element that generates heat by applying electricity, melting the pipe head materials to be connected, thereby achieving an electrofusion connection between the pipe heads. This assembly is typically designed to accommodate the connection requirements of pipe heads of different sizes. The first insertion structure 210 and the second insertion structure 220 are structures formed at both ends of the electrofusion connection assembly 200 along its axial direction, used for insertion with the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20, respectively. Their design takes into account the compatibility with different pipe head sizes. The pointed end 230, the protruding portion at the end of the first insertion structure 210 and the second insertion structure 220, is designed to facilitate insertion into the pipe head to be connected and to assist in the melting and filling of materials during the electrofusion connection process. Electrofusion connection is a connection technology that melts polymer materials through electrical heating, forming intermolecular bonds after cooling. It is commonly used for connecting polyethylene pipes to achieve sealing and structural integrity. HBPE pipe refers to high-barrier polyethylene pipe, characterized by its gas barrier properties, and is commonly used in pipeline systems for transporting easily permeable media such as hydrogen and oil. The electrofusion connection object in this application is an HBPE pipe.

[0020] In one embodiment, the tube head shaping section 100 has an annular structure, and a non-standard electrofusion tube head 10 and a standard electrofusion tube head 20 are respectively disposed at both ends of the tube head shaping section 100. The electrofusion connection assembly 200 has a hollow frustum-shaped structure with open ends. The electrofusion connection assembly 200 forms a first insertion structure 210 and a second insertion structure 220 at its two ends along its axial direction, respectively. The ends of the first insertion structure 210 and the second insertion structure 220 both protrude to form sharp corner portions 230. The inner diameter of the first insertion structure 210 is smaller than the inner diameter of the second insertion structure 220. The sharp corner portion 230 of the first insertion structure 210 extends into the non-standard electrofusion tube head 10 and is electrofusion-fused with the non-standard electrofusion tube head 10. The sharp corner portion 230 of the second insertion structure 220 extends into the standard electrofusion tube head 20 and is electrofusion-fused with the standard electrofusion tube head 20. The tube head shaping section 100 is sleeved outside the electrofusion connection assembly 200. The electrofusion connection assembly 200, the non-standard electrofusion tube head 10, the standard electrofusion tube head 20 and the tube head shaping section 100 are coaxially arranged.

[0021] This application provides a technical solution for connecting non-standard electrofusion tube heads using an electrofusion sleeve. This solution addresses the problem of uneven corrosion on the inner wall of old steel pipes, which causes the inner diameter of the tube head after insertion of the HBPE liner to be smaller than the standard size. The tube head shaping section 100 acts as an external constraint structure, limiting the positions of the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20. This ensures that they remain coaxial during insertion, preventing stress concentration or sealing failure at the connection interface due to axial misalignment.

[0022] The electrofusion connection assembly 200 adopts a hollow frustum structure. This structure creates a gradient change in the inner diameter of the first insertion structure 210 and the second insertion structure 220. The inner diameter of the first insertion structure 210 matches the outer diameter of the non-standard electrofusion tube head 10, while the inner diameter of the second insertion structure 220 matches the outer diameter of the standard electrofusion tube head 20, thus achieving precise adaptation to tube heads of different specifications. During the connection process, after the electrofusion connection assembly 200 is energized, the built-in resistance wire converts electrical energy into heat energy. The heat is concentrated and conducted to the sharp corners 230 at the ends of the first and second insertion structures 210 and 220. Due to its geometric shape, the sharp corners 230 have a stress concentration effect, which can preferentially soften and penetrate the surface of the HBPE pipe under heating, forming a preliminary mechanical anchorage.

[0023] As the heating temperature rises to the melting temperature range of HBPE material, the non-standard electrofusion head 10 and the standard electrofusion head 20 are slowly pushed in along the axial direction of the head shaping section 100. The pointed corner 230 continuously embeds itself into the inner wall of the head during the electrofusion process. The head material undergoes molecular chain segment movement in its thermoplastic state, forming molecular chain entanglement with the surface of the pointed corner 230 of the electrofusion connection assembly 200. During this process, the tapered profile of the pointed corner 230 guides the molten material to fill the connection interface, eliminating microscopic gaps. Simultaneously, the annular constraint of the head shaping section 100 prevents radial deformation of the head during thermal expansion, ensuring the circumferential uniformity of the connection interface.

[0024] Once the non-standard electrofusion head 10 and the standard electrofusion head 20 are fully inserted into their predetermined positions, the electrofusion connection assembly 200 stops supplying power, and the connection area enters the cooling and solidification stage. During this stage, the molten HBPE material molecular chains recrystallize, forming strong molecular bonds with the sharp corner 230 of the electrofusion connection assembly 200, achieving a transition from mechanical anchoring to chemical bonding. Because the sharp corner 230 has penetrated deep into the inner wall of the head, the effective bonding area of ​​the connection interface is significantly increased, ensuring tensile strength and sealing performance.

[0025] The electrofusion sleeve used in this application for connecting non-standard electrofusion tube heads directly connects the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20 through the hollow frustum structure of the electrofusion connection assembly 200. This eliminates the need to use thick-walled pipes as transition parts for on-site hot-melt welding, thereby saving the need for welding equipment, professional welding personnel, and the excavation of large operation pits, reducing construction complexity, shortening the construction period, and reducing cost input.

[0026] Compared to traditional transition connection methods, the electrofusion connection assembly 200 of this application eliminates the radial steps generated at the interface between the thick-walled pipe and the inner liner pipe. In conventional solutions, the difference in wall thickness between the thick-walled pipe and the inner liner pipe causes protruding steps to form on the inner wall of the pipe. These steps partially obstruct fluid flow, causing local turbulence and pressure loss, thus reducing transport efficiency. The electrofusion connection assembly 200 of this application, with its hollow frustum structure and smoothly transitioning conical profile on its inner surface, eliminates radial steps on the inner wall of the pipe after connection. The fluid remains in a laminar flow state when passing through the connection area, avoiding energy loss and improving transport efficiency.

[0027] More importantly, the electrofusion connection assembly 200 of this application can adopt the same multi-layer composite structure as the HBPE liner pipe, including an internal barrier layer. This barrier layer is made of a crystalline polymer material with a chain molecular structure, consistent with the barrier layer material of the HBPE liner pipe. After connection, the barrier layer of the electrofusion connection assembly 200, together with the barrier layers of the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20, forms a continuous barrier path, ensuring that the gas barrier chain of the pipeline system is not interrupted at the joint. When transporting highly permeable media such as hydrogen, oil and gas, and sulfur-containing liquids, the barrier layer in the connection area effectively blocks the permeation path of the media molecules, preventing gas permeation, hydrogen embrittlement, and corrosion at the joint, ensuring the sealing and long-term reliability of the repair system.

[0028] Traditional standard electrofusion sleeves lack a barrier layer structure, making the joint area a weak link in the gas barrier chain, resulting in a "short plank effect." Media preferentially penetrate at this point, causing material degradation and significantly shortening the service life of the pipeline system. This application fundamentally solves the problem of insufficient barrier performance at the joint by integrating a barrier layer into the electrofusion connection assembly 200. This ensures that the repaired pipeline system as a whole has uniform gas barrier capability, meeting the technical requirements for oil and gas pipeline integrity management.

[0029] In one embodiment, the first insertion structure 210 and the second insertion structure 220 of the electrofusion connection assembly 200 have a tapered structure with a cone angle of 30° to 60°. This cone angle range can ensure that the cone angle 230 can be smoothly inserted into the HBPE pipe under heating conditions, and can also avoid excessive stress concentration caused by the cone angle being too small, which can lead to pipe cracking.

[0030] The tapered profile of the pointed corner 230 causes its cross-sectional diameter to change continuously along the axial direction. When the pointed corner 230 is inserted into the non-standard electrofusion tube head 10, its tapered shape and gradually increasing cross-sectional diameter from the front end to the rear end ensure that for non-standard electrofusion tube heads 10 with different inner diameters, the pointed corner 230 can find a cross-sectional diameter corresponding to the inner wall of the tube head on its profile, forming an annular contact zone at this point. Thus, a set of prefabricated transition structures 240 with fixed dimensions can connect any non-standard electrofusion tube head 10 with an inner diameter within the range between the front and rear diameters of the pointed corner 230, achieving adaptive connection of standard parts to non-standard tube heads.

[0031] In one embodiment, a positioning boss is provided on the inner surface of the pipe head shaping section 100. The positioning boss abuts against the end faces of the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20, limiting the axial insertion depth of the pipe head and ensuring the consistency of the embedment depth of the sharp corner 230 into the inner wall of the pipe head, thus avoiding differences in connection strength caused by uneven insertion depth. The height of the positioning boss is matched according to the length of the sharp corner 230 and the wall thickness of the HBPE pipe, ensuring that the sharp corner 230 will not penetrate the inner wall of the pipe after being fully embedded, preventing contamination or obstruction of the fluid inside the pipe.

[0032] In summary, the electrofusion sleeve used in this application for connecting non-standard electrofusion tube heads achieves direct electrofusion connection between non-standard electrofusion tube heads 10 and standard electrofusion tube heads 20 through the coaxial limiting effect of the tube head shaping section 100 and the gradient adaptation structure of the electrofusion connection assembly 200, eliminating the transition welding process, simplifying the construction process, and reducing costs; through the hollow frustum structure (see [link to application]), it achieves direct electrofusion connection between non-standard electrofusion tube heads 10 and standard electrofusion tube heads 20, eliminating the transition welding process, simplifying the construction process, and reducing costs. Figure 7 This invention eliminates steps on the inner wall of the pipeline, improving transport efficiency. By integrating a barrier layer, it ensures continuous gas barrier at the joint, preventing media penetration, hydrogen embrittlement, and corrosion, significantly improving the sealing and long-term reliability of the repair system. This effectively solves the technical challenge of connecting non-standard electrofusion pipe heads 10 in trenchless repair of old steel pipelines. Specifically, by directly connecting the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20, this application avoids the cumbersome transition pipe welding process in existing technologies, thereby simplifying the construction process, reducing construction costs, and shortening the construction period. The design of this electrofusion sleeve ensures that the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20 can be coaxially connected, effectively preventing the formation of a step structure inside the pipeline and ensuring smooth fluid transport. Furthermore, since the electrofusion connection is applied to HBPE pipes, this connection method can maintain the overall barrier performance of the pipeline system, solving the problem of barrier performance interruption in existing technologies and improving the overall effect and long-term reliability of pipeline repair.

[0033] Please continue reading. Figures 1 to 3 And see Figure 4 and Figure 5In an embodiment of the present invention, the electrofusion connection assembly 200 includes a prefabricated transition structure 240 and an electrofusion structure 250. The prefabricated transition structure 240 is a hollow frustum-shaped structure with open ends. A fusion space 101 is provided between the prefabricated transition structure 240 and the inner wall of the tube head shaping section 100. The electrofusion structure 250 is laid in the fusion space 101 and has a shape adapted to the prefabricated transition structure 240. The two ends of the prefabricated transition structure 240, which are spaced apart along its axial direction, respectively form a first insertion structure 210 and a second insertion structure 220.

[0034] In one embodiment, the electrofusion connection assembly 200 includes a prefabricated transition structure 240 and an electrofusion structure 250. The prefabricated transition structure 240 is a hollow frustum-shaped structure with openings at both ends. A fusion space 101 is provided between the prefabricated transition structure 240 and the inner wall of the tube head shaping section 100. The electrofusion structure 250 is laid within the fusion space 101 and has a shape adapted to the prefabricated transition structure 240. The two ends of the prefabricated transition structure 240, which are spaced apart along its axial direction, respectively form a first insertion structure 210 and a second insertion structure 220.

[0035] In the implementation of this application, the prefabricated transition structure 240 serves as the structural support of the electrofusion connection assembly 200. Its hollow frustum structure ensures a gradient transition in the inner diameter from the first insertion structure 210 to the second insertion structure 220. The wall thickness of the prefabricated transition structure 240 is uniformly distributed along the axial direction. When subjected to the radial pressure generated when the non-standard electrofusion head 10 and the standard electrofusion head 20 are pushed in, it can maintain structural stability and prevent deformation or cracking caused by local wall thinning. The material of the prefabricated transition structure 240 is the same multi-layer composite material system as the HBPE inner liner, which includes, from the inside out, a first polyethylene layer, a first adhesive layer, a barrier layer, a second adhesive layer, and a second polyethylene layer. This material system ensures that the prefabricated transition structure 240, the non-standard electrofusion head 10, and the standard electrofusion head 20 have the same melting temperature range and molecular chain motion characteristics in the thermoplastic state, creating conditions for achieving homogeneous molecular bonding.

[0036] The fusion space 101 between the prefabricated transition structure 240 and the inner wall of the tube head shaping section 100 provides a accommodating area for the laying of the electrothermal fusion structure 250. The radial thickness of the fusion space 101 is precisely controlled according to the wire diameter and laying density of the electrothermal fusion structure 250, and is typically set within the range of 2 to 5 mm. This thickness ensures that the heat generated by the electrothermal fusion structure 250 during electric heating can be fully conducted to the inner and outer surfaces of the prefabricated transition structure 240, while also preventing the fusion space 101 from being too large, which would cause heat dissipation in the air layer and reduce heating efficiency. The axial length of the fusion space 101 covers the entire frustum-shaped area of ​​the prefabricated transition structure 240, ensuring that the sharp corners 230 of the first insertion structure 210 and the second insertion structure 220 are both within the effective heating range.

[0037] The electrofusion structure 250 is laid in the fusion space 101, and its shape is adapted to the hollow frustum-shaped outer contour of the prefabricated transition structure 240.

[0038] During the connection process, the electrofusion structure 250 is powered by an external power source. When current flows through the resistance wire, heat is generated according to Joule's law. The heat is transferred from the surface of the resistance wire to the wall of the prefabricated transition structure 240 by thermal conduction. The second polyethylene layer of the prefabricated transition structure 240 first absorbs heat. After the temperature rises to the melting temperature, the activity of the molecular chain segments increases, and the heat continues to be conducted to the inner layers, softening the second adhesive layer, the barrier layer, the first adhesive layer, and the first polyethylene layer in sequence. When the first polyethylene layer reaches a molten state, a molten thin layer is formed on the surface of the sharp corners 230 of the first insertion structure 210 and the second insertion structure 220. This molten thin layer permeates with the molten material on the inner wall of the tube head as the sharp corners 230 penetrate into the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20.

[0039] Because the electrofusion structure 250 is shaped to fit the prefabricated transition structure 240, the spiral winding path of the resistance wire is distributed along the frustum-shaped contour, making the heating power density of the first insertion structure 210 and the second insertion structure 220 similar. The inner diameter of the first insertion structure 210 is smaller, and its circumference is shorter than that of the second insertion structure 220, but the number of turns of the resistance wire in this area is increased accordingly, compensating for the insufficient heating area caused by the difference in circumference length, ensuring that the sharp corners 230 of the two insertion structures reach the melting temperature simultaneously, and avoiding differences in connection strength caused by uneven heating.

[0040] As the non-standard electrofusion head 10 and the standard electrofusion head 20 are slowly pushed into the tube head shaping section 100 along its axial direction, the annular constraint of the shaping section 100 restricts the radial displacement of the tube head, allowing the pushing force to be transmitted axially to the pointed corner 230. The pointed corner 230, in its molten state, has a reduced yield strength, enabling it to embed into the inner wall of the tube head with a relatively small pushing force, thus preventing cracking of the tube head end face or deformation of the prefabricated transition structure 240 due to excessive pushing force. The tapered profile of the pointed corner 230 exerts a compressive force on the inner wall material of the tube head during embedding. Under the compressive force, the molten material fills the microscopic depressions at the connection interface, eliminating interface voids and improving the contact area and sealing performance.

[0041] Once the pointed end 230 is fully embedded in the inner wall of the pipe head, the electrofusion structure 250 stops supplying power, and the connection area enters the cooling and solidification stage. During the cooling process, the molten material of the prefabricated transition structure 240 and the pipe head cools down synchronously, the molecular chain segment movement speed slows down, and it gradually returns to a glassy or crystalline state. Since the prefabricated transition structure 240 and the pipe head use the same multilayer composite material system, the coefficients of thermal expansion and crystallization shrinkage rates of each layer are similar, and no significant thermal stress concentration will occur at the connection interface during the cooling process, avoiding interface cracking or delamination. After cooling, a continuous molecular bond layer is formed at the connection interface. The strength of this bond layer is close to the bulk strength of the HBPE material, and it can withstand the internal pressure and axial stress generated by the pipeline system when transporting the medium.

[0042] This application separates the structural load-bearing function from the heating function by decomposing the electrofusion connection assembly 200 into two components: a prefabricated transition structure 240 and an electrofusion structure 250. The prefabricated transition structure 240 focuses on providing a gradient-adaptive plug structure and the continuity of the barrier layer, while the electrofusion structure 250 focuses on providing uniform and controllable heating energy. The two work together to complete the connection between the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20.

[0043] This application achieves decoupling of heating function and structural function by setting a prefabricated transition structure 240 and an electrofusion structure 250 in the electrofusion connection assembly 200, and utilizing the fusion space 101 between the prefabricated transition structure 240 and the inner wall of the tube head shaping section 100 to accommodate the electrofusion structure 250. This improves heating efficiency, production flexibility and maintenance convenience, while ensuring the strength and sealing of the connection interface, providing technical guarantee for the reliable connection of non-standard electrofusion tube head 10 and standard electrofusion tube head 20.

[0044] Please continue reading. Figure 1 , Figure 3 and Figure 5In an embodiment of the present invention, the prefabricated transition structure 240 includes a first polyethylene layer, a first adhesive layer, a barrier layer, a second adhesive layer and a second polyethylene layer stacked sequentially from the inside to the outside. A fusion space 101 is provided between the second polyethylene layer and the inner wall of the pipe head shaping section 100. The electrothermal fusion structure 250 is laid on the second polyethylene layer.

[0045] Specifically, the first polyethylene layer is the innermost layer of the prefabricated transition structure 240, and its main function is to directly electrofusion connect with the non-standard electrofusion head 10 and the standard electrofusion head 20 to be connected. Polyethylene (PE) material has good compatibility with the head material (e.g., HBPE pipe), ensuring a strong and uniform fusion interface during electrofusion, thereby achieving reliable sealing and connection. A first adhesive layer is disposed between the first polyethylene layer and the barrier layer, providing effective adhesion between the two. In multi-layer structures, compatibility issues may exist between different materials; the adhesive layer overcomes these problems, ensuring a tight bond between layers and preventing delamination during manufacturing, installation, or use, thus maintaining the integrity and stability of the prefabricated transition structure 240. This adhesive layer can be made of hot melt adhesive, modified polyethylene, or co-extruded adhesive resin. The barrier layer is a key functional layer in the prefabricated transition structure 240, and its main function is to prevent or significantly reduce the penetration of media such as gases (e.g., hydrogen, natural gas) or liquids (e.g., oil). In pipeline connections transporting easily permeable media, the presence of a barrier layer is crucial for ensuring the sealing and safety of the pipeline system. The barrier layer can be made of ethylene-vinyl alcohol copolymer (EVOH), polyamide (PA), or special polyethylene materials with high barrier properties. A second adhesive layer is positioned between the barrier layer and the second polyethylene layer, serving a similar function to the first adhesive layer: ensuring a strong bond between the barrier layer and the second polyethylene layer, preventing delamination, and thus guaranteeing the multi-layer composite performance of the prefabricated transition structure 240. The second polyethylene layer is the outermost layer of the prefabricated transition structure 240. On one hand, it provides mechanical protection and support for the internal barrier layer; on the other hand, it is in direct contact with the electrofusion structure 250 and fuses with the inner wall of the pipe head shaping section 100 and the molten material within the fusion space 101 during the electrofusion process, further enhancing the overall strength and sealing of the connection. The fusion space 101 is located between the second polyethylene layer and the inner wall of the pipe head shaping section 100, providing a laying position for the electrofusion structure 250 and providing the necessary volume for the melting, flow, and filling of materials during the electrofusion process. The electrofusion structure 250 is laid on the second polyethylene layer. This laying method ensures that when the electrofusion structure 250 is electrically heated, it can directly and effectively transfer heat to the second polyethylene layer, causing it to melt rapidly. This, in turn, drives the entire prefabricated transition structure 240 to fuse with the pipe head shaping section 100 and the pipe head material, initiating and completing the electrofusion connection process.

[0046] Through the above technical solution, the prefabricated transition structure 240 is designed as a multi-layer composite structure consisting of a first polyethylene layer, a first adhesive layer, a barrier layer, a second adhesive layer, and a second polyethylene layer stacked sequentially from the inside out. The electrofusion structure 250 is laid on the second polyethylene layer, thereby significantly improving the connection performance and applicability of the electrofusion sleeve. Specifically, the good compatibility between the first polyethylene layer and the pipe head material ensures efficient and robust fusion bonding; the introduction of the barrier layer effectively solves the potential permeation problem at the connection point when transporting easily permeable media such as hydrogen and oil, greatly improving the sealing and safety of the connection; while the first and second adhesive layers ensure a tight bond between the multi-layer structures, avoiding delamination and maintaining the long-term stability and structural integrity of the prefabricated transition structure 240. Furthermore, the second polyethylene layer, as the heat conduction interface of the electrofusion structure 250, ensures efficient and uniform heat transfer, promoting the full filling of the fusion space 101 and the uniform melting of the material. This layered design enables the prefabricated transition structure 240 to simultaneously possess excellent fusion performance, barrier performance, and structural stability, thus providing a more reliable, durable, and functional solution when connecting non-standard electrofusion tube heads 10 and standard electrofusion tube heads 20, especially suitable for application scenarios with strict requirements for connection quality and media barrier performance.

[0047] Please see Figure 1 , Figure 3 , Figure 4 and Figure 5 In an embodiment of the present invention, the two ends of the barrier layer spaced apart along its axial direction are respectively formed into a first insertion structure 210 and a second insertion structure 220. The two ends of the electrothermal fusion structure 250 spaced apart along its axial direction are respectively flanged to form a first heating edge and a second heating edge. The first heating edge and the second heating edge are respectively abutted against the sharp corner portion 230 of the first insertion structure 210 and the sharp corner portion 230 of the second insertion structure 220.

[0048] In the implementation of this application, the barrier layer, as the core functional layer of the prefabricated transition structure 240, directly determines the barrier performance distribution of the first insertion structure 210 and the second insertion structure 220 by the position of its two axial ends. The barrier layer extends axially from the small-diameter end to the large-diameter end of the prefabricated transition structure 240, forming the first insertion structure 210 and the second insertion structure 220 at the two axially spaced ends, respectively. This configuration ensures that the barrier layer covers the entire frustum-shaped area of ​​the prefabricated transition structure 240, including the sharp corners 230 of the first insertion structure 210 and the second insertion structure 220, so that when the sharp corners 230 are electrofused with the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20, the barrier layer material is present at the connection interface.

[0049] During welding, the molten PE fills all voids at the joint interface under internal pressure, encapsulating and covering the exposed barrier layer end face at the pipe cross-section. After cooling and solidification, the barrier layer end face is completely encapsulated by a continuous layer of PE material, with a tight fit between the encapsulation layer and the barrier layer cross-section. Gas molecules must pass through the PE encapsulation layer to bypass the barrier layer fracture and then penetrate laterally at the PE-barrier layer interface, resulting in an extremely long penetration path. Thus, the barrier layer forms a functionally continuous barrier system at the joint, and its barrier function is not interrupted by a physical break.

[0050] In conventional solutions, if the axial length of the barrier layer is shorter than the prefabricated transition structure 240, the barrier layer is missing at the sharp corner 230. After connection, the sharp corner 230 region consists only of a polyethylene layer and an adhesive layer, making this region a preferred path for gas permeation. During pipeline transport, gas molecules diffuse along the concentration gradient from the high-pressure side to the low-pressure side. Permeation is hindered when encountering the barrier layer, but in the region where the barrier layer is missing at the sharp corner 230, gas molecules can directly penetrate the polyethylene layer and adhesive layer, bypassing the barrier layer to form a permeation short circuit. This results in the barrier performance of the entire pipeline system being determined by the weak point in the sharp corner 230 region, creating a bottleneck effect. This application eliminates the missing barrier layer region by extending the barrier layer to the sharp corner 230 of the first insertion structure 210 and the second insertion structure 220, ensuring that the barrier performance of the connection interface is consistent with that of the pipeline body.

[0051] The electrofusion structure 250 has two ends spaced apart along its axial direction, each flanged to form a first heating edge and a second heating edge. The flanged operation causes the resistance wire to turn radially from a circumferential direction at both ends of the prefabricated transition structure 240, forming an inwardly bent edge structure. The first heating edge is located at the pointed corner 230 of the first insertion structure 210, and the second heating edge is located at the pointed corner 230 of the second insertion structure 220. The two heating edges are respectively abutted against the outer surface of the corresponding pointed corner 230. This abutting arrangement uses mechanical pressure to ensure a tight fit between the resistance wire and the surface of the second polyethylene layer of the pointed corner 230, eliminating contact thermal resistance and improving heat conduction efficiency.

[0052] During the connection process, after the electrofusion structure 250 is energized, heat is generated by the spiral winding portion of the resistance wire along the circumference of the prefabricated transition structure 240. This heat is then conducted radially to each layer of the prefabricated transition structure 240. Simultaneously, the first and second heating edges, acting as end flanges of the resistance wire, form a locally heated reinforcement zone at the sharp corner 230. The sharp corner 230, as a critical part connecting the prefabricated transition structure 240 to the tube head, needs to reach the melting temperature first during the electrofusion process to ensure that the sharp corner 230 can smoothly penetrate the inner wall of the tube head and form a preliminary mechanical anchorage.

[0053] The abutting arrangement of the first and second heating edges at the corner 230 ensures the axial temperature uniformity of the corner 230. The tapered profile of the corner 230 causes its wall thickness to gradually decrease from the base to the tip in the radial direction. If heat conduction relies solely on the circumferentially wound portion, the tip of the corner 230, due to its thinner wall, dissipates heat faster, resulting in a lower temperature than the base and creating an axial temperature gradient. This temperature gradient leads to insufficient melting at the tip of the corner 230, resulting in weaker mechanical anchoring when it penetrates the inner wall of the tube head, thus reducing the connection strength. This application addresses this by providing heating edges at the corner 230, allowing the resistance wire to directly heat the tip region, compensating for the heat loss caused by the reduced wall thickness. This makes the axial temperature distribution of the corner 230 more uniform, ensuring that the tip and base reach melting temperature simultaneously, guaranteeing consistent melting throughout the entire corner 230, and improving the uniformity of the connection strength.

[0054] During the cooling and solidification stage, the first and second heating edges are de-energized, and the molten material in the corner 230 region begins to cool. Because the heating edges provide additional heat input to the corner 230, the temperature of the corner 230 at the end of heating is slightly higher than that of the middle of the wall. During the cooling process, the temperature drop rate of the corner 230 tends to be consistent with that of the middle of the wall, avoiding thermal stress concentration caused by the difference in cooling rate.

[0055] This application achieves dual optimization of barrier performance coverage and concentrated heating power by extending the barrier layer to the sharp corners 230 of the first and second plug-in structures 210 and pressing the heating edge of the electrothermal fusion structure 250 against the sharp corners 230. The presence of the barrier layer at the sharp corners 230 ensures the continuity of the barrier path at the connection interface, eliminating gas permeation short circuits; the pressing of the heating edge against the sharp corners 230 ensures preferential melting at the sharp corners 230 and maintains uniform axial temperature, improving connection strength and reliability.

[0056] Compared to designs where the barrier layer does not extend to the sharp corner 230 or the heating edge is not tightly abutted, the configuration of this application has the following advantages: First, after the barrier layer covers the sharp corner 230, the gas permeability coefficient of the connection interface at the sharp corner 230 position is consistent with that of the pipe body. When transporting highly permeable media such as hydrogen, the sharp corner 230 area will not become a weak point in permeability. The barrier performance of the entire pipeline system is determined by the intrinsic permeability coefficient of the barrier layer, avoiding the weak link effect. Second, the heating edge is tightly abutted at the sharp corner 230, which increases the heating power density of the sharp corner 230 during the electrofusion process, shortens the time for the sharp corner 230 to reach the melting temperature, reduces the waiting time before the non-standard electrofusion head 10 and the standard electrofusion head 20 are pushed in, and improves the connection efficiency. Furthermore, the direct heating of the tip of the pointed part 230 by the heating edge eliminates the axial temperature gradient, allowing the tip and base of the pointed part 230 to melt synchronously. This results in a uniform mechanical anchoring effect when it penetrates the inner wall of the tube head, and a consistent distribution of connection strength, thus avoiding connection failure due to insufficient local strength.

[0057] In one embodiment, the flange angle of the first heating edge and the second heating edge is controlled within the range of 45° to 90°. If the flange angle is too small, the contact area between the heating edge and the sharp corner 230 will be insufficient, resulting in a decrease in heat flux density; if the flange angle is too large, the heating edge will extend too far radially, occupying the fusion space 101 and affecting the overall arrangement of the electrothermal fusion structure 250. This flange angle range ensures sufficient contact between the heating edge and the sharp corner 230 while avoiding excessive occupation of the fusion space 101, thus achieving a balance between heating efficiency and space utilization.

[0058] This application achieves seamless connection of the barrier passage at the connection interface and concentrated enhancement of the heating power of the sharp corner 230 by extending the barrier layer along its axial direction to the sharp corner 230 of the first plug structure 210 and the second plug structure 220, and by pressing the heating edge of the electrofusion structure 250 against the sharp corner 230. This eliminates the technical defects of gas permeation short circuit and uneven connection strength, and provides a barrier performance guarantee and process optimization solution for the reliable connection of non-standard electrofusion tube head 10 and standard electrofusion tube head 20. It effectively solves the technical problems of missing barrier layer at the joint and insufficient melting of the sharp corner 230.

[0059] Please see Figure 1 , Figure 3 , Figure 4 and Figure 5 In an embodiment of the present invention, the electrothermal fusion structure 250 includes a first heating wire 251, a second heating wire 252 and a plurality of third heating wires 253. The first heating wire 251 and the second heating wire 252 respectively form a first heating edge and a second heating edge. The plurality of third heating wires 253 are laid on a second polyethylene layer and are spaced apart between the first heating wire 251 and the second heating wire 252.

[0060] Specifically, the first heating wire 251 and the second heating wire 252 are resistance wires used to generate heat, typically made of a metallic material with high resistivity, such as a nickel-chromium alloy or a copper-nickel alloy. They are designed to form the first heating edge and the second heating edge, respectively, and their main function is to provide concentrated and efficient heating to the sharp corners 230 of the first insertion structure 210 and the second insertion structure 220 during the electrofusion connection process. By tightly abutting these heating wires against the sharp corners 230, it can be ensured that the ends of the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20 can quickly reach a molten state during the axial insertion of the tube head shaping section 100, thereby achieving effective fusion with the prefabricated transition structure 240.

[0061] Multiple third heating wires 253 are also resistance heating elements, laid on the second polyethylene layer and spaced apart between the first heating wires 251 and the second heating wires 252. The main function of these third heating wires 253 is to provide uniform and continuous heating for the main body of the prefabricated transition structure 240. They can be arranged in various ways, such as extending along the axial direction of the prefabricated transition structure 240 and spaced apart circumferentially, or wound in a spiral or serpentine manner, to ensure that the polyethylene material in the entire fusion space 101 is heated uniformly. Through the distributed heating of multiple third heating wires 253, heating blind spots or excessive temperature gradients between the first heating wires 251 and the second heating wires 252 can be avoided, thereby ensuring that the non-standard electrofusion head 10, the standard electrofusion head 20, and the polyethylene layer of the prefabricated transition structure 240 achieve full and uniform fusion throughout the connection area.

[0062] Through the above technical solution, the electrofusion welding assembly 200 constructs a more complete and refined heating system by introducing a first heating wire 251, a second heating wire 252, and multiple third heating wires 253. The first and second heating wires 251 and 252 focus on efficiently heating the critical sharp corner area 230, ensuring the initial weld strength when the tube head is inserted. Simultaneously, the multiple third heating wires 253 are responsible for comprehensively and uniformly heating the main body of the prefabricated transition structure 240, effectively solving the problem of incomplete fusion or uneven heating that may result from relying solely on edge heating. This regional, collaborative heating design ensures that the polyethylene material within the entire fusion space 101 can fully melt and form a homogeneous melt, thereby significantly improving the overall strength, sealing performance, and reliability of the electrofusion weld. It effectively avoids potential defects caused by insufficient or uneven heating at the connection point, thus ensuring the long-term stable operation of the connector.

[0063] Please see Figure 1 , Figure 3 , Figure 4 and Figure 5 In an embodiment of the present invention, a plurality of third heating wires 253 extend along the axial direction of the prefabricated transition structure 240, and the plurality of third heating wires 253 are arranged at intervals along the circumferential direction of the prefabricated transition structure 240.

[0064] In the implementation of this application, multiple third heating wires 253 extend axially along the prefabricated transition structure 240. Specifically, each third heating wire 253 extends from a position near the first insertion structure 210 along the frustum-shaped outline of the prefabricated transition structure 240 towards a position near the second insertion structure 220. The extension direction of the heating wire is parallel to or slightly inclined to the axis of the prefabricated transition structure 240. This axial extension arrangement forms heating lines distributed axially on the wall of the prefabricated transition structure 240. Compared to a spiral winding arrangement along the circumference, the axial extension arrangement eliminates gaps in the circumferential direction of the heating wires, avoiding the formation of annular heat concentration and heat sparse areas during heating.

[0065] Multiple third heating wires 253 are arranged at circumferential intervals along the prefabricated transition structure 240, meaning that multiple third heating wires 253 are evenly distributed in the circumferential direction of the prefabricated transition structure 240, and a certain circumferential distance is maintained between adjacent third heating wires 253. In one embodiment, the number of third heating wires 253 is 4 to 12, and the circumferential distance between adjacent third heating wires 253 is 30° to 90°. This circumferential spacing ensures that any position of the prefabricated transition structure 240 in the circumferential direction is within the heating radiation range of a certain third heating wire 253, while forming an open channel without heating wires occupying the space between adjacent third heating wires 253. This open channel plays a crucial role in guiding the flow of molten material during the electrothermal fusion connection process.

[0066] During the connection process, after the electrofusion structure 250 is energized, the first heating wire 251, the second heating wire 252, and multiple third heating wires 253 heat up simultaneously, and the materials of each layer of the prefabricated transition structure 240 gradually heat up and reach a molten state. When the first polyethylene layer, the first adhesive layer, the barrier layer, the second adhesive layer, and the second polyethylene layer all reach their melting temperatures, the material changes from a solid state to a viscous flow state, and the mobility of the molecular chain segments increases. The tube head shaping section 100 is a ring-shaped rigid structure. When heated inside, the PE material of the prefabricated transition structure 240 and the tube head undergoes thermal expansion, increasing in volume. Due to the rigid constraint of the tube head shaping section 100, which restricts the outward radial expansion of the material, this volume increase is converted into internal pressure acting on all fillable interfaces in the confined space. This thermal expansion internal pressure uniformly presses the molten material into all gaps between the non-standard electrofusion tube head 10, the standard electrofusion tube head 20, and the prefabricated transition structure 240, and is the main driving force for melt filling.

[0067] After cooling and solidification, the molten material buildup in this area results in localized material enrichment, causing the wall thickness of the prefabricated transition structure 240 to fluctuate periodically in the axial direction. Areas with thicker walls correspond to molten material accumulation locations, while areas with thinner walls correspond to locations occupied by the heating wires. This periodic fluctuation in wall thickness leads to uneven stress distribution in the prefabricated transition structure 240 under internal pressure, with areas of thinner walls becoming stress concentration points, potentially leading to fatigue cracking during long-term use. Furthermore, the accumulation of molten material between adjacent coils prevents some molten material from flowing to the connection interface between the non-standard electrofusion head 10 and the standard electrofusion head 20, resulting in insufficient molten material filling at the connection interface, forming microscopic voids, and reducing connection strength and sealing performance.

[0068] Once the material of the prefabricated transition structure 240 reaches a molten state, the molten material is forced into the gaps between the connecting interfaces under the drive of thermal expansion internal pressure. At the same time, gravity plays an auxiliary role in this process, promoting the full filling of the lower half interface by the melt. The molten material flows through the open channel between adjacent third heating wires 253 and gradually accumulates in the gap between the inner wall of the tube head shaping section 100 and the electrothermal fusion connection assembly 200.

[0069] As the molten material continues to flow and accumulate, the gap between the inner wall of the tube head shaping section 100 and the electrofusion connection assembly 200 is gradually filled by the molten material. The molten material first fills the connection interface between the non-standard electrofusion tube head 10 and the first insertion structure 210, then flows axially upwards, filling the fusion space 101 between the middle of the prefabricated transition structure 240 wall and the inner wall of the tube head shaping section 100, and finally fills the connection interface between the standard electrofusion tube head 20 and the second insertion structure 220. This filling process occurs spontaneously under gravity, without the need for external pressure or injection, simplifying the connection operation and improving connection efficiency.

[0070] The spontaneous filling process of the molten material under gravity ensures uniform distribution and sufficient filling at the interface. Compared to the accumulation of molten material between adjacent heating wire coils, the open channel arrangement of this application allows the molten material to flow freely along the axial direction, avoiding local accumulation and missing parts, and eliminating microscopic voids at the interface. After cooling and solidification, a continuous and dense molecular bonded layer is formed at the interface. The thickness of this bonded layer is uniformly distributed in the axial direction, without thickness fluctuations caused by molten material accumulation, ensuring consistent connection strength and sealing performance.

[0071] In one embodiment, there are six third heating wires 253, evenly distributed circumferentially along the prefabricated transition structure 240, with a circumferential spacing of 60° between adjacent third heating wires 253. This arrangement creates six direct heating areas and six open channel areas in the circumferential direction of the prefabricated transition structure 240, with the heating areas and open channel areas alternating to form a symmetrical temperature distribution pattern. During the electrothermal fusion connection process, the molten material flows axially through the six open channels, with the flow path evenly distributed circumferentially, avoiding excessive or insufficient local melt due to concentrated flow paths and ensuring uniform melt distribution at the connection interface.

[0072] In another embodiment, there are eight third heating wires 253, evenly distributed circumferentially along the prefabricated transition structure 240, with a circumferential spacing of 45° between adjacent third heating wires 253. This arrangement creates eight direct heating areas and eight open channel areas in the circumferential direction of the prefabricated transition structure 240. Compared to an arrangement with six third heating wires 253, eight third heating wires 253 increase the number of open channels, reduce the width of each open channel, and make the flow path of the molten material more dispersed and the flow process more uniform, further improving the uniformity of the molten material distribution at the interface.

[0073] This application optimizes the arrangement of heating wires by extending multiple third heating wires 253 axially along the prefabricated transition structure 240 and circumferentially spaced, eliminating the problem of molten material accumulation caused by spiral winding. The axial extension arrangement creates an open channel between adjacent third heating wires 253, providing an unobstructed path for the axial flow of molten material. Under the action of gravity, the molten material flows along the open channel and accumulates in the gap between the inner wall of the tube head shaping section 100 and the electrofusion connection assembly 200 in the direction of the non-standard electrofusion tube head 10, until it fills the part where the standard electrofusion tube head 20 is located, reducing the voids generated after the molten material solidifies and improving the connection strength and sealing performance.

[0074] Compared to the spiral winding arrangement, the axially extended circumferentially spaced arrangement of this application has the following advantages: First, it eliminates the accumulation of molten material between adjacent heating wire coils, avoids the periodic fluctuation of the 240mm wall thickness of the prefabricated transition structure in the axial direction, reduces the risk of stress concentration, and improves the structural pressure resistance. Second, the open channel provides a free flow path for the molten material, allowing the molten material to spontaneously fill the connection interface under gravity, without the need for external pressurization or injection, simplifying the connection operation and improving the connection efficiency. Third, the free flow of the molten material in the open channel ensures that the molten material is evenly distributed and fully filled at the connection interface, eliminating micro-voids and improving the consistency of connection strength and sealing performance. Finally, the temperature gradient distribution in the open channel area promotes the uniform distribution of the molten material in the circumferential direction and forms a gradient cooling characteristic during the cooling process, reducing thermal stress concentration and preventing material cracking.

[0075] In an embodiment of the present invention, a plurality of third heating wires 253 are connected end to end and wound around the outer periphery of the prefabricated transition structure 240.

[0076] The phrase "multiple third heating wires 253 connected end to end" refers to connecting several independent third heating wires 253 into one or more continuous heating circuits through conductive connection methods (such as welding, crimping, or mechanical connection), or directly using a single continuous heating wire to wind itself, naturally forming an end-to-end structure during the winding process. This connection method ensures that the current can flow smoothly through the entire heating area, avoiding insufficient local heating due to breaks or poor contact.

[0077] "Wrapped around the outer periphery of the prefabricated transition structure 240" means that these end-to-end third heating wires 253 are evenly wound around the outer surface of the prefabricated transition structure 240 in a spiral or circular manner. This winding method allows the heating wires to fit tightly against the prefabricated transition structure 240, thereby achieving efficient heat transfer. The winding density and spacing can be precisely designed according to the specific dimensions of the prefabricated transition structure 240 and the required heating power to ensure uniform heat distribution throughout the fusion area. For example, materials with good resistivity and high-temperature resistance, such as nickel-chromium alloy wire or iron-chromium-aluminum alloy wire, can be wound around the outer surface of the prefabricated transition structure 240 with a preset pitch and tension using automated winding equipment, and then fixed using high-temperature resistant adhesives or through subsequent coating processes to prevent displacement during subsequent operations.

[0078] By connecting multiple third heating wires 253 end-to-end and winding them around the outer periphery of the prefabricated transition structure 240 using the above technical solution, a continuous and uniformly distributed heating area can be formed. When the electrofusion structure 250 is energized, current flows through these wound heating wires, generating heat and uniformly transferring it to the prefabricated transition structure 240, the non-standard electrofusion tube head 10, and the standard electrofusion tube head 20. This winding arrangement, compared to simply spaced straight heating wires, can more effectively cover the fusion area, reducing the risk of local overheating or underheating, thereby ensuring that the polyethylene layer melts more thoroughly and uniformly within the fusion space 101. In addition, this structure facilitates automated production and installation, improves manufacturing efficiency and product consistency, and ultimately forms a high-strength, well-sealed electrofusion connection, effectively avoiding potential defects caused by uneven heating at the connection point.

[0079] Please see Figure 1 , Figure 3 , Figure 4 and Figure 5 In an embodiment of the present invention, one end of each third heating wire 253 is electrically connected to the first heating wire 251, and the other end of each third heating wire 253 is electrically connected to the second heating wire 252. The first heating wire 251 is electrically connected to the positive terminal of an external power supply, and the second heating wire 252 is electrically connected to the negative terminal of an external power supply.

[0080] Specifically, one end of each third heating wire 253 is electrically connected to the first heating wire 251, and the other end of each third heating wire 253 is electrically connected to the second heating wire 252, aiming to construct a complete heating circuit. This electrical connection can be achieved in various ways, such as welding, crimping, conductive adhesive bonding, or mechanical fastening, ensuring a stable electrical path between the third heating wire 253 and the first and second heating wires 251 and 252. This connection method allows multiple third heating wires 253 to form a parallel or series (parallel in this case) circuit structure with the first and second heating wires 251 and 252, thereby effectively drawing current from the power source and generating heat. The first heating wire 251 is electrically connected to the positive terminal of the external power source, and the second heating wire 252 is electrically connected to the negative terminal of the external power source, clarifying the power supply method of the entire electrothermal fusion assembly 200. This can be achieved by connecting a power cord to the terminals of the first and second heating wires 251 and 252 or through an integrated plug. The external power supply can be either DC or AC, and its voltage and current parameters should match the rated power and resistance characteristics of the heating wire to ensure that the electrofusion connection assembly 200 can reach the expected heating temperature and heating rate after being energized. This connection method ensures that current can pass through the entire electrofusion network, thereby generating uniform and controllable heat in the corresponding area of ​​the electrofusion connection assembly 200.

[0081] The above technical solution clarifies the electrical connection relationship between the first heating wire 251, the second heating wire 252, and multiple third heating wires 253 in the electrofusion connection assembly 200. Each third heating wire 253 is connected in parallel between the first heating wire 251 and the second heating wire 252, and power is supplied to the first heating wire 251 and the second heating wire 252 respectively by the positive and negative terminals of an external power source, forming a complete and controlled heating circuit. This connection method ensures that the current flows evenly through all heating wires, thereby achieving uniform heating of the entire electrofusion connection assembly 200. This effectively avoids local overheating or underheating caused by uneven heating, significantly improving the reliability and connection quality of the electrofusion connection, and ensuring that the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20 can be firmly and sealed together.

[0082] Please continue reading. Figures 1 to 5 In an embodiment of the present invention, the inner wall of the pipe head shaping section 100 is recessed to form an installation space 102. An electrothermal fusion element 300 is disposed in the installation space 102. The electrothermal fusion element 300 has an annular structure and is sleeved on the electrothermal fusion connection assembly 200. The electrothermal fusion element 300 is disposed between the inner wall of the pipe head shaping section 100 and the electrothermal fusion connection assembly 200.

[0083] During the connection process, before the electrofusion connection assembly 200 is energized, the electrofusion element 300 is in a solid state and has not melted. At this time, the radial clamping force applied by the electrofusion element 300 to the prefabricated transition structure 240 and the frictional force between the electrofusion element 300 and the installation space 102 work together to restrict the radial and axial displacement of the prefabricated transition structure 240 within the pipe head shaping section 100. This limiting effect plays a positioning and stabilizing role during the insertion of the prefabricated transition structure 240 into the pipe head shaping section 100, preventing the prefabricated transition structure 240 from becoming eccentric or tilted due to uneven insertion force or deviation in the inner diameter of the pipe head shaping section 100, ensuring that the axis of the prefabricated transition structure 240 coincides with the axis of the pipe head shaping section 100, and providing an accurate initial position for subsequent electrofusion connection.

[0084] After the electrofusion welding assembly 200 is energized, the first heating wire 251, the second heating wire 252, and multiple third heating wires 253 begin to heat up. The heat is conducted to each layer of the prefabricated transition structure 240, with the second polyethylene layer, the second adhesive layer, the barrier layer, the first adhesive layer, and the first polyethylene layer sequentially heating up and reaching their melting temperatures. Simultaneously, heat is conducted outward through the second polyethylene layer of the prefabricated transition structure 240 to the electrofusion piece 300. The inner surface of the electrofusion piece 300 first receives heat, causing its temperature to rise. Subsequently, the heat is conducted radially outward from the electrofusion piece 300, gradually increasing the overall temperature of the electrofusion piece 300. Within 2 to 4 minutes after energization, the temperature of the electrofusion piece 300 reaches its melting temperature, typically 100 to 130 degrees Celsius. The electrofusion piece 300 transitions from a solid state to a viscous flow state, softening and becoming fluid.

[0085] After the electrofusion element 300 melts, its radial clamping force on the prefabricated transition structure 240 decreases, and the material's deformability in the radial direction increases. If the prefabricated transition structure 240 experiences radial displacement due to the difference in inner diameter between the standard electrofusion tube head 20 and the non-standard electrofusion tube head 10, i.e., the outer diameters of the prefabricated transition structure 240 are different in the first insertion structure 210 and the second insertion structure 220, causing the radial position of the prefabricated transition structure 240 within the tube head shaping section 100 to deviate from the center, the molten material of the electrofusion element 300 can flow in the radial direction, filling the gap between the prefabricated transition structure 240 and the inner wall of the tube head shaping section 100, compensating for the voids caused by the radial displacement.

[0086] In one embodiment, the inner diameter of the non-standard electrofusion head 10 is 50 mm, the inner diameter of the standard electrofusion head 20 is 75 mm, the outer diameter of the first insertion structure 210 of the prefabricated transition structure 240 is 49 mm, the outer diameter of the second insertion structure 220 is 74 mm, the radial gap between the first insertion structure 210 and the inner wall of the non-standard electrofusion head 10 is 0.5 mm, and the radial gap between the second insertion structure 220 and the inner wall of the standard electrofusion head 20 is 0.5 mm. Ideally, the axis of the prefabricated transition structure 240 coincides with the axis of the head shaping section 100, and the radial gap is evenly distributed in the circumferential direction. However, during actual installation, due to uneven insertion force or deviation of the inner diameter of the head shaping section 100, the prefabricated transition structure 240 may experience radial displacement, causing the axis of the first insertion structure 210 or the second insertion structure 220 to deviate from the axis of the head shaping section 100. This results in uneven distribution of the radial gap in the circumferential direction, with the gap increasing on one side and decreasing or even disappearing on the other side.

[0087] After the electrofusion element 300 melts, its material flows radially from the side with smaller gaps to the side with larger gaps, filling the voids on the side with larger gaps. This makes the radial support force on the prefabricated transition structure 240 more uniform, and the axis of the prefabricated transition structure 240 gradually returns to the axis position of the tube head shaping section 100, reducing the axial deviation. In one embodiment, the initial radial displacement of the prefabricated transition structure 240 is 1 to 3 mm. After the electrofusion element 300 melts, the molten material fills the gaps, and the radial displacement decreases to 0.2 to 0.5 mm. The axial deviation decreases from the initial 0.5 to 1.5 degrees to 0.1 to 0.3 degrees, which to a certain extent prevents the axis of the standard electrofusion tube head 20 and the non-standard electrofusion tube head 10 from deviating, improving the coaxiality of the connection.

[0088] The material of the electrothermal melt 300 is the same as that of the first or second adhesive layer, enabling the electrothermal melt 300 to form a chemical bond with the barrier layer or polyethylene layer of the prefabricated transition structure 240 after melting. In one embodiment, the electrothermal melt 300 is made of maleic anhydride-grafted polyethylene, the second adhesive layer of the prefabricated transition structure 240 is also made of maleic anhydride-grafted polyethylene, and the barrier layer is made of ethylene-vinyl alcohol copolymer. After the electrothermal melt 300 melts, the maleic anhydride groups in its molecular chain segments undergo esterification with the vinyl alcohol groups of the barrier layer to form covalent bonds. At the same time, the polyethylene backbone of the electrothermal melt 300 undergoes segment diffusion and entanglement with the polyethylene molecular chains of the second polyethylene layer to form molecular bonds. The chemical and molecular bonding enables a strong interfacial bond between the electrothermal melt 300 and the prefabricated transition structure 240, with a shear strength of 5 to 15 MPa and a peel strength of 50 to 150 N / cm, ensuring that the electrothermal melt 300 will not detach from the surface of the prefabricated transition structure 240 after cooling and solidification.

[0089] The outer surface of the electrothermal melt 300 contacts the polyethylene material on the inner wall of the tube head shaping section 100. After the electrothermal melt 300 melts, its polyethylene main chain undergoes segment diffusion and entanglement with the polyethylene molecular chains on the inner wall of the tube head shaping section 100, forming molecular bonds. This molecular bond creates a strong interfacial bond between the electrothermal melt 300 and the tube head shaping section 100. The shear strength and peel strength are comparable to the interfacial bond strength between the electrothermal melt 300 and the prefabricated transition structure 240, ensuring that the electrothermal melt 300 forms an intermediate layer connecting the prefabricated transition structure 240 and the tube head shaping section 100 after cooling and solidification, thus improving the connection strength and sealing performance.

[0090] During the cooling and solidification stage, the electrofusion connection assembly 200 is de-energized, and the molten materials of the prefabricated transition structure 240, the electrofusion piece 300, and the tube head shaping section 100 begin to cool. Because the electrofusion piece 300 is located between the prefabricated transition structure 240 and the tube head shaping section 100, its cooling rate is affected by the heat conduction of the materials on both sides, and its cooling rate falls between that of the prefabricated transition structure 240 and the tube head shaping section 100. After cooling and solidification, the electrofusion piece 300 changes from a viscous flow state to a solid state, and its mechanical strength is restored. The solidified electrofusion piece 300 retains its shape after filling the gap in the molten state, forming a ring structure with non-uniform thickness; the electrofusion piece 300 on the side with a larger gap is thicker, and the electrofusion piece 300 on the side with a smaller gap is thinner. The non-uniform thickness distribution ensures that the supporting force applied by the electrothermal fusion piece 300 to the prefabricated transition structure 240 in the radial direction is uniform, and the axial position of the prefabricated transition structure 240 is stable, ensuring that the connected pipeline system will not experience fatigue failure due to stress concentration caused by axial deviation during long-term use.

[0091] The electrofusion element 300, when the electrofusion connection assembly 200 is not energized, limits the prefabricated transition structure 240, playing a crucial auxiliary positioning role during installation. In one embodiment, after the prefabricated transition structure 240 is inserted into the tube head shaping section 100, the operator needs to adjust the axial position of the prefabricated transition structure 240 so that the pointed corner 230 of the first insertion structure 210 is aligned with the end face of the non-standard electrofusion tube head 10, and the pointed corner 230 of the second insertion structure 220 is aligned with the end face of the standard electrofusion tube head 20. During the adjustment process, without the limiting effect of the electrofusion element 300, the prefabricated transition structure 240 may slide or tilt within the tube head shaping section 100 due to its own weight or external vibration, resulting in reduced alignment accuracy between the pointed corner 230 and the tube head end face, affecting the subsequent electrofusion connection quality.

[0092] The electrothermal fusion piece 300 restricts the axial and radial displacement of the prefabricated transition structure 240 through its radial clamping force on the prefabricated transition structure 240 and the frictional force between it and the installation space 102, so that the prefabricated transition structure 240 remains stable during the adjustment process, and the alignment accuracy between the sharp corner 230 and the end face of the tube head is improved, providing stable initial conditions for electrothermal fusion connection.

[0093] This application achieves radial displacement compensation and axial deviation control of the prefabricated transition structure 240 by setting an installation space 102 on the inner wall of the pipe head shaping section 100 and setting an electrofusion element 300 within the installation space 102. When the electrofusion connection assembly 200 is not energized, the electrofusion element 300 applies a limiting effect to the prefabricated transition structure 240, ensuring the positional stability of the prefabricated transition structure 240 during installation and adjustment. After the electrofusion connection assembly 200 is energized, the electrofusion element 300 melts and flows to fill the gap, compensating for the radial displacement of the prefabricated transition structure 240 caused by the difference in inner diameter between the standard electrofusion pipe head 20 and the non-standard electrofusion pipe head 10, reducing axial deviation and improving connection coaxiality. The electrofusion element 300 is made of the same material as the first or second adhesive layer, enabling it to form a strong chemical and molecular bond with the prefabricated transition structure 240 and the pipe head shaping section 100 after melting, improving connection strength and sealing performance.

[0094] Please see Figure 1 , Figure 2 and Figure 3 In an embodiment of the present invention, the electrofusion sleeve for connecting non-standard electrofusion tube heads further includes two electrofusion guide sections 400, which are respectively disposed at both ends of the tube head shaping section 100. The non-standard electrofusion tube head 10, the standard electrofusion tube head 20, the tube head shaping section 100 and the two electrofusion guide sections 400 are coaxially arranged.

[0095] Specifically, the two electrofusion guide sections 400 are structures used to assist in connecting the non-standard electrofusion tube head 10 and the standard electrofusion tube head 20 to the electrofusion sleeve. They are respectively located at both ends of the tube head shaping section 100, forming a longer connection together with the tube head shaping section 100. Their main function is to provide additional connection length and support, allowing the electrofusion sleeve to not only connect to the tube head but also to the corresponding part of the tube body, thereby enhancing the integrity and stability of the connection. In practical applications, these two guide sections can use similar materials and manufacturing processes as the tube head shaping section 100 to ensure good compatibility with the tube head shaping section 100.

[0096] Two electrofusion guide sections 400 are used to respectively sleeve and electrofusion the corresponding portions of the pipe body of the non-standard electrofusion head 10 and the corresponding portions of the pipe body of the standard electrofusion head 20. This means that the electrofusion guide sections 400 are not just simple sleeve structures; they also integrate electrofusion functionality. By applying electricity and heating, the polyethylene layer of the guide section melts with the corresponding portions of the pipe body of the non-standard electrofusion head 10 and the standard electrofusion head 20, thereby forming a strong electrofusion connection. This connection method extends the connection area between the electrofusion sleeve and the pipe from the head to the body, significantly increasing the connection area and contact length, thereby dispersing connection stress and improving the mechanical strength and sealing reliability of the connection.

[0097] By adding two electrofusion guide sections 400 to the electrofusion sleeve and making them, together with the pipe head shaping section 100, have a multi-layer stacked structure, this application can extend the range of electrofusion connection from the pipe head to the pipe body. This design significantly increases the connection area and length between the electrofusion sleeve and the non-standard electrofusion pipe head 10 and the standard electrofusion pipe head 20, thereby effectively dispersing the stress in the connection area and greatly improving the mechanical strength and pull-out resistance of the connection. In particular, since both the pipe head shaping section 100 and the electrofusion guide section 400 contain a barrier layer, the entire connection area has excellent barrier performance, which can effectively prevent the leakage of easily permeable media such as hydrogen and oil, ensuring the long-term safety and reliability of the transportation system. In addition, by setting the electrofusion guide section 400 coaxially with the pipe head shaping section 100 and electrofusion welding it with the pipe body, the geometric accuracy and fluid transportation smoothness of the entire pipeline connection system are further guaranteed, avoiding additional resistance or stress concentration problems caused by connection misalignment, thereby improving the overall operating efficiency and service life of the pipeline system.

[0098] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. An electrofusion sleeve for connecting a non-standard electrofusion tube head, wherein the inner diameter of the non-standard electrofusion tube head is smaller than the inner diameter of a standard electrofusion tube head, characterized in that, The electrofusion sleeve for connecting non-standard electrofusion tube heads includes: The tube head shaping section has a ring structure, and the non-standard electrofusion tube head and the standard electrofusion tube head are respectively disposed at both ends of the tube head shaping section; An electrofusion connection assembly is provided, wherein a tube head shaping section is fitted over the electrofusion connection assembly. The electrofusion connection assembly is a hollow frustum-shaped structure with open ends. A first insertion structure and a second insertion structure are formed at both ends along its axial direction. Both the first and second insertion structures have protruding sharp corners at their ends. The inner diameter of the first insertion structure is smaller than that of the second insertion structure. The sharp corner of the first insertion structure extends into the non-standard electrofusion tube head and is electrofusion-fused to it. The sharp corner of the second insertion structure extends into the standard electrofusion tube head and is electrofusion-fused to it. The electrofusion connection assembly, the non-standard electrofusion tube head, the standard electrofusion tube head, and the tube head shaping section are coaxially arranged. The electrofusion connection assembly includes a prefabricated transition structure and an electrofusion structure. The prefabricated transition structure is a hollow frustum-shaped structure with open ends. A fusion space is provided between the prefabricated transition structure and the inner wall of the pipe head shaping section. The electrofusion structure is laid in the fusion space and has a shape adapted to the prefabricated transition structure. The two ends of the prefabricated transition structure, spaced apart along its axial direction, respectively form the first insertion structure and the second insertion structure. The prefabricated transition structure includes a first polyethylene layer, a first adhesive layer, a barrier layer, a second adhesive layer, and a second polyethylene layer stacked sequentially from the inside to the outside. The fusion space is provided between the second polyethylene layer and the inner wall of the pipe head shaping section, and the electrofusion structure is laid on the second polyethylene layer.

2. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in claim 1, characterized in that, The barrier layer is spaced apart along its axial direction at both ends to form the first insertion structure and the second insertion structure, respectively. The electrothermal fusion structure is spaced apart along its axial direction at both ends to form the first heating edge and the second heating edge, respectively. The first heating edge and the second heating edge are respectively abutted against the sharp corner of the first insertion structure and the sharp corner of the second insertion structure.

3. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in claim 2, characterized in that, The electrothermal fusion structure includes a first heating wire, a second heating wire, and a plurality of third heating wires. The first heating wire and the second heating wire respectively form the first heating edge and the second heating edge. The plurality of third heating wires are laid on the second polyethylene layer and are spaced apart between the first heating wire and the second heating wire.

4. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in claim 3, characterized in that, The plurality of third heating wires extend along the axial direction of the prefabricated transition structure, and the plurality of third heating wires are arranged at circumferential intervals along the prefabricated transition structure.

5. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in claim 3, characterized in that, Multiple third heating wires are connected end to end and wound around the outer periphery of the prefabricated transition structure.

6. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in claim 3, characterized in that, One end of each of the third heating wires is electrically connected to the first heating wire, and the other end of each of the third heating wires is electrically connected to the second heating wire. The first heating wire is electrically connected to the positive terminal of an external power supply, and the second heating wire is electrically connected to the negative terminal of an external power supply.

7. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in any one of claims 1 to 6, characterized in that, The inner wall of the pipe head shaping section is recessed to form an installation space. An electrothermal fusion element is provided in the installation space. The electrothermal fusion element has a ring structure and is sleeved on the electrothermal fusion connection assembly. The electrothermal fusion element is located between the inner wall of the pipe head shaping section and the electrothermal fusion connection assembly.

8. The electrofusion sleeve for connecting non-standard electrofusion tube heads as described in any one of claims 1 to 6, characterized in that, The electrofusion sleeve for connecting non-standard electrofusion tube heads also includes two electrofusion guide sections, which are respectively disposed at both ends of the tube head shaping section. The non-standard electrofusion tube head, the standard electrofusion tube head, the tube head shaping section, and the two electrofusion guide sections are coaxially arranged.

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