Electrofusion fittings with non-metallic pipeline leakage monitoring function and their processing methods

Abstract

The present invention relates to the field of pipeline leakage monitoring, aiming to provide an electrofusion fitting with a non-metallic pipeline leakage monitoring function and its processing method. The electrofusion fitting includes a resistance wire and a terminal. The terminal is arranged in a tubular sheath, and two sheaths are respectively configured with seals. Both the sheath and the seal are made of insulating materials. In one of the seals, an internal wire for connecting the terminal and an external wire is provided, and an external wire access port is provided. A part of the resistance wire is exposed in the inner cavity of the electrofusion fitting and serves as an internal monitoring electrode. The novel electrofusion joint proposed based on the resistance monitoring principle in the present invention can be used for monitoring the leakage of fluid media generated in a non-metallic pipeline system, solving the problem of difficult leakage monitoring of non-metallic pipelines. It does not require complex detection equipment, the testing method is easy to implement, and the cost of non-metallic pipeline leakage monitoring is reduced. The monitoring electrode and the terminal are integrally formed by welding and melting, with better sealing performance and component strength.

Description

Technical Field

[0001] The present invention relates to the field of pipeline leakage monitoring, and particularly relates to an electrofusion fitting with a non-metallic pipeline leakage monitoring function and a processing method thereof. Background Art

[0002] Pipelines are the core facilities for energy and water transportation and are the lifelines related to the development of the national economy and human survival. With the adjustment of China's energy structure and the acceleration of the urbanization process, non-metallic pipelines are widely used in major national projects. For example, they are used as high-pressure crossover pipes in the beach and shallow sea oil industry, as gas transmission pipelines in urban gas pipe networks, as cooling water circulation pipelines in nuclear power plants, and are also ideal substitutes for oil well injection pipes and low-pressure marine hoses in shallow seas. China has become the country with the largest production and demand of non-metallic pipelines, and the application prospect is very broad.

[0003] Non-metallic pipelines are widely used in various applications, and their service environments are complex and harsh, and they are easily affected by external loads caused by terrain changes and natural disasters. In actual use, resource waste and safety accidents caused by the leakage of non-metallic pipelines occur continuously. According to statistics, the water loss of urban water supply pipe networks in China reaches 21.5%, and the water loss in some northern cities even reaches about 40%. Among them, the water loss caused by pipeline leakage accounts for about 50%, resulting in serious water resource waste. For non-metallic pipelines used for oil and gas transportation, they have high pressure and large diameters. The leakage of this type of pipeline not only causes power waste and environmental pollution, but also poses a threat to people's lives and property safety.

[0004] To solve the resource waste and safety accidents caused by pipeline leakage, it is necessary to build a pipeline leakage monitoring system to monitor the pipeline leakage status in real time, detect pipeline leakage hazards early and eliminate them, reduce the operation and maintenance costs of the pipeline, reduce resource waste, and improve the safety and service life of the pipeline. At present, the main methods for pipeline leakage monitoring are: acoustic detection technology and optical fiber detection technology. The acoustic detection technology is based on the propagation law of sound waves in a medium to perform leakage monitoring and positioning. For metal pressure pipelines, once a pipeline leaks, due to the pressure difference inside and outside the pipeline, the medium will flow out from the leakage point at a certain speed to form a jet, thereby generating sound waves at the leakage point. This method has been relatively successfully applied in metal pipelines. However, in non-metallic pipelines, due to the fast attenuation rate of sound waves in non-metallic (plastic) materials and the short propagation distance, the system construction cost is high. Moreover, this method is greatly interfered by external noise and generates more false alarms. Therefore, the acoustic detection technology cannot be applied to the leakage of non-metallic pipelines. In the optical fiber detection technology, it is difficult to decouple the optical fiber signals affected by temperature and strain factors, and the optical fiber material is easily broken and requires special maintenance, which limits its application.

[0005] The present invention modifies the structure of existing polyethylene electrofusion fittings to reduce the installation cost of the existing non-metal leakage monitoring system and improve the construction efficiency. On the basis of minimizing the changes or modifications to the existing polyethylene pipe fitting processing technology, processing equipment and molds as much as possible, an electrofusion fitting suitable for non-metal pipeline leakage detection and monitoring is developed, and its specific manufacturing method is proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an electrofusion fitting with a non-metal pipeline leakage monitoring function and its processing method in view of the deficiencies in the prior art.

[0007] To solve the above technical problem, the solution adopted by the present invention is:

[0008] Provide an electrofusion fitting with a non-metal pipeline leakage monitoring function, including a resistance wire for welding disposed inside the electrofusion fitting. Two terminal posts are provided on the outer side of the electrofusion fitting, and the bottom ends of the terminal posts are respectively connected to both ends of the resistance wire; the terminal posts are disposed in a tubular sheath, and two sheaths are respectively provided with sealing members, and both the sheath and the sealing member are made of insulating materials; in one of the sealing members, an internal wire for connecting the terminal post and an external wire is provided with an external wire access port; a part of the resistance wire is exposed in the inner cavity of the electrofusion fitting and serves as an internal monitoring electrode.

[0009] In the present invention, the resistance wire is wound around the circumference of the electrofusion fitting to form two connected heating regions; the resistance wire exposed in the inner cavity of the electrofusion fitting is the resistance wire for connecting the two heating regions.

[0010] In the present invention, a retaining ring or a retaining block is provided on the inner wall of the electrofusion fitting to retain a gap between the ends of the two pipes when nesting and welding the pipe fittings; the resistance wire exposed in the inner cavity of the electrofusion fitting is located on the surface of the retaining ring or the retaining block.

[0011] In the present invention, the retaining ring or the retaining block is in a circumferential ring shape.

[0012] In the present invention, a strip electrode, a block electrode or a ring electrode connected to the resistance wire is disposed in the inner cavity of the electrofusion fitting; the strip electrode, the block electrode or the ring electrode is used to replace the resistance wire and serves as an internal monitoring electrode.

[0013] In the present invention, the sheath has an internal thread or an external thread, the sealing member has a matching external thread or internal thread, and the sheath and the sealing member are tightly screwed together to achieve insulation and sealing.

[0014] The present invention further provides a processing method for the electrofusion fitting, including:

[0015] (1) The electrofusion joint is manufactured in the conventional production method of the bare wire of the electrofusion fitting: the resistance wire is wound around the mandrel by the original wire winding process to form the heating areas on both sides, and the middle section of the resistance wire connecting the heating areas forms the monitoring electrode by the parallel wire winding method, and then injection molding is carried out; during injection molding, a tubular sheath is formed around the external terminal of the electrofusion fitting, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting; or,

[0016] (2) The electrofusion joint is manufactured in the conventional production method of the plastic-coated wire of the electrofusion fitting: the plastic-coated resistance wire is wound around the mandrel by the original wire winding process to form the heating areas on both sides, and the middle section of the resistance wire connecting the heating areas forms the monitoring electrode by the parallel wire winding method after removing the outer insulating plastic, and then injection molding is carried out; during injection molding, a tubular sheath is formed around the external terminal of the electrofusion fitting, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting; or,

[0017] (3) The electrofusion joint is manufactured in the conventional production method of the post-wound wire of the electrofusion fitting: injection molding is carried out using the mandrel to form a tubular sheath around the external terminal of the electrofusion fitting; a retaining ring or a retaining block is formed by turning inside the electrofusion fitting, and the resistance wire is circumferentially arranged on the inner wall, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting.

[0018] In the present invention, it further includes: embedding a strip electrode, a block electrode or a ring electrode in the electrofusion fitting, and making one side of the strip electrode, the block electrode or the ring electrode connected to the resistance wire, and the other side exposed in the inner cavity of the electrofusion fitting; using the strip electrode, the block electrode or the ring electrode to replace the resistance wire as the internal monitoring electrode.

[0019] In the present invention, it further includes: configuring seals for the two tubular sheaths; the sheath has internal threads or external threads, and the seal has matching external threads or internal threads, and the two are tightly screwed together to achieve insulation and sealing; in one of the seals, an internal wire for connecting the terminal and the external wire is provided.

[0020] Description of the invention principle:

[0021] The present invention ingeniously utilizes the heating resistance wire and the terminal of the electrofusion welding as the electrodes for leakage monitoring. That is, the terminal is used to connect the power supply during welding and to connect the external wire and the internal monitoring electrode after welding; while the resistance wire is used to generate heat during the welding process and to connect the internal monitoring electrode in contact with the internal medium after welding. The present invention uses a part of the resistance wire (or a strip electrode, a block electrode or a ring electrode connected to the resistance wire) exposed to the internal cavity of the electrofusion fitting as the internal monitoring electrode. Since this part of the resistance wire is arranged in a way of combining wires, it does not directly participate in the welding between the electrofusion fitting and the pipe during the welding process. The presence of the retaining ring or the retaining block is used to retain the gap and position the middle position, and at the same time ensure that the resistance wire, the strip electrode, the block electrode or the ring electrode are exposed to the internal cavity of the electrofusion fitting and can be in direct contact with the internal medium.

[0022] During use, the axial monitoring electrode is fixed or laid directly below the pipeline; after installation, ensure good insulation between the internal monitoring electrode and the axial monitoring electrode. In this way, when leakage occurs at any circumferential position of the pipeline, the leaked part of the fluid will flow along the outer wall of the pipeline to the axial monitoring electrode below the pipeline. The leaked fluid of the pipeline and the fluid in the pipeline conduct the axial monitoring electrode and the internal monitoring electrode to form a loop, and the resistance value measured by the detection circuit will be significantly reduced, thereby monitoring the medium leakage generated by the pipeline.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) The existing acoustic wave and optical fiber detection technologies are difficult to be applied to the leakage monitoring of non-metallic pipelines. The novel electrofusion joint proposed by the present invention based on the resistance monitoring principle can be used for the leakage monitoring of fluid media generated in non-metallic pipeline systems, solving the problem of difficult leakage monitoring of non-metallic pipelines.

[0025] (2) In view of the large number of electrofusion joints used in the pipeline installation process, the novel electrofusion joints of the present invention can be selected and arranged according to the pipeline monitoring accuracy requirements. Considering that the increase in manufacturing cost is not much, even all electrofusion joints of the present invention can be used. While completing the pipeline installation, external wires are connected at appropriate positions according to the monitoring accuracy requirements to arrange multiple monitoring subsystems, and each subsystem is responsible for the leakage monitoring of the pipeline within its arranged range.

[0026] (3) Compared with other leakage monitoring technologies, using the electrofusion joint of the present invention does not require complex detection equipment, and the test method is easy to implement, reducing the cost of non-metallic pipeline leakage monitoring.

[0027] (4) The inventor separately applied for a Chinese invention patent application "A System and Method for Monitoring Non-Metallic Leakage" (201910804807.3). The implementation of its technical solution requires drilling holes in the pipeline and then fixing the circumferential monitoring electrodes on the pipeline wall. The internal monitoring electrodes and the external wires are sealed by threads or hot melt adhesives. Compared with this technology, the present invention utilizes the structural characteristics and working principle of the electrofusion fitting itself and does not require additional accessories and construction processes. During the welding process of the electrofusion fitting, the internal monitoring electrodes can be implanted into the internal structure of the pipeline; the internal monitoring electrodes and the external terminal posts are melted into one body through the welding of the electrofusion fitting, and the sealing performance and component strength are better.

[0028] (5) The structural improvement of the electrofusion fitting product of the present invention can be easily achieved through simple core design in the three major production processes of existing electrofusion fittings, without the need to transform the injection molding equipment, greatly reducing the manufacturing, construction and maintenance costs of the non-metallic pipeline leakage monitoring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of the structure and principle of the electrofusion fitting described in the present invention;

[0030] Figure 2 is a structural diagram of the fully sealed part (left) and the sealed part providing wiring seal (right) of the present invention;

[0031] Figure 3 is a working schematic diagram of the electrofusion fitting in the embodiment.

[0032] Reference numerals: 1 internal monitoring electrode; 2 terminal post; 3 sheath; 4 fully sealed part; 5 resistance wire; 6 retaining ring; 7 sealed part providing wiring seal; 8 external wire; 9 hot melt adhesive; 10 pipe material; 11 external wire; 12 resistance value detection module; 13 axial monitoring electrode; 14 thread; 15 copper bar. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0034] The electrofusion fitting with the function of monitoring non-metallic pipeline leakage in the present invention includes a resistance wire 5 for welding arranged inside the electrofusion fitting, and two metal terminal posts 2 are arranged on the outside of the electrofusion fitting. The bottom ends of the terminal posts 2 are respectively connected to both ends of the resistance wire 5; the terminal posts 2 are arranged in an insulating tubular sheath 3, and two sheaths 3 are respectively configured with sealed parts (fully sealed part 4 and sealed part 7 providing wiring seal);

[0035] The resistance wire 5 is wound circumferentially around the electrofusion fitting to form two connected heating zones; the part in the middle for connecting the two heating zones is exposed in the inner cavity of the electrofusion fitting and serves as the internal monitoring electrode 1. By providing a circumferential annular retaining ring 6 (or a retaining block) on the inner wall of the electrofusion fitting, a gap is reserved between the ends of the two pipes 10 when nesting and welding the pipes, ensuring that the internal monitoring electrode 1 is located on the surface of the retaining ring 6.

[0036] As another implementation, strip electrodes, block electrodes or ring electrodes connected to the resistance wire can be provided on the surface of the retaining ring 6, and the strip electrodes, block electrodes or ring electrodes are exposed in the inner cavity of the electrofusion fitting; the strip electrodes, block electrodes or ring electrodes are used to replace the monitoring electrodes in the way of combining the resistance wires and serve as the internal monitoring electrodes.

[0037] The sheath 3 has internal or external threads, and the seal has matching external or internal threads. The sheath 3 and the seal are tightly screwed together to achieve insulation and sealing. Figure 1 、 2 In the illustrated embodiment, the complete seal 4 is made of an insulating material; the outside of the seal 7 is made of an insulating material, and a copper bar 15 is embedded inside. The inner hole of the copper bar 15 is tightly fitted with the terminal 2. The top of the copper bar 15 is provided with an external wire access port to provide a sealed and fastened access for the external wire 11. The wire access port should ensure that the wiring part is insulated from the installation environment, and the external thread of the seal is tightly fitted with the internal thread of the sheath. Alternatively, an internal wire for connecting the terminal 2 and the external wire 11 can be provided in the seal, and the wire connection is realized outside the seal 7.

[0038] Examples of the product processing and manufacturing methods:

[0039] Regarding the three manufacturing methods for electrofusion fittings: the bare wire production method, the plastic-coated wire production method and the post-laying wire production method;

[0040] (1) The bare wire production method:

[0041] The modification method: As Figure 1 shown, the mold of the product is modified. A retaining groove is machined in the middle of the mold core for arranging the internal monitoring electrode 1 and the retaining ring 6, and a section of thread is machined on the mold sheath pin for forming the internal thread of the sheath 3. The seal is applicable to all electrofusion fittings within the same manufacturer. A separate set of seal molds is opened and developed and produced according to the Figure 2 structure shown.

[0042] Production process: When producing electrofusion fittings by normal process, wind the resistance wire around the mold core. When winding to the middle section of the resistance wire reaching the internal monitoring electrode arrangement area, start to wind tightly to ensure that each resistance wire within the internal monitoring electrode area is in a parallel wire state (or place strip electrodes, block electrodes or ring electrodes in the internal monitoring electrode arrangement area. When the resistance wire passes through the internal monitoring electrode arrangement area, the resistance wire passes through the strip electrodes, block electrodes or ring electrodes by normal wire winding process to ensure a good contact environment between the resistance wire and the strip electrodes, block electrodes or ring electrodes). After winding, put it into the mold for injection molding, rotate and remove the terminal post sheath pin to ensure the integrity of the internal thread of the sheath, and a main body of an electrofusion fitting with leakage detection function is formed; when producing the seal, put a copper column into the seal cavity providing seal wiring. After injection molding, ensure the integrity of the external thread of the seal and its tight fit with the external thread of the electrode sheath of the electrofusion fitting.

[0043] (2) Production method of plastic-coated wire:

[0044] Modification method: Modify the mold of the product, machine a section of retaining groove in the middle of the mold core for arranging the internal monitoring electrode 1 and the retaining ring 6, and machine a section of thread on the mold sheath pin for forming the internal thread of the sheath 3. The seal is applicable to all electrofusion fittings within the same manufacturer. Open a separate set of seal molds and develop and produce according to the Figure 2 structure shown in

[0045] Production process: When producing electrofusion fittings by normal process, first treat the insulating layer of the middle section of the plastic-coated wire to expose the resistance wire of the internal monitoring electrode to the air; then wind the resistance wire around the mold core in a conventional manner. When winding to the middle section of the resistance wire reaching the internal monitoring electrode arrangement area, start to wind tightly to ensure that each resistance wire within the internal monitoring electrode area is exposed to the air and in a parallel wire state (or place strip electrodes, block electrodes or ring electrodes in the internal monitoring electrode arrangement area. When the resistance wire passes through the internal monitoring electrode arrangement area, the resistance wire passes through the strip electrodes, block electrodes or ring electrodes by normal wire winding process to ensure a good contact environment between the resistance wire and the strip electrodes, block electrodes or ring electrodes). After winding, put it into the mold for injection molding, rotate and remove the terminal post sheath pin to ensure the integrity of the internal thread of the sheath, and a main body of an electrofusion fitting with leakage detection function is formed; when producing the seal, put a copper column into the seal cavity providing seal wiring. After injection molding, ensure the integrity of the external thread of the seal and its tight fit with the external thread of the electrode sheath of the electrofusion fitting.

[0046] (3) Post-wiring production process:

[0047] Modification method: Machine a section of thread on the mold sheath pin for forming the internal thread of the sheath 3. The seal is applicable to all electrofusion fittings within the same manufacturer. Open a separate set of seal molds and develop and produce according to theFigure 2 Develop and produce the structure shown.

[0048] Production process: When the blank is injection-molded, ensure the integrity of the internal thread of the sleeve; change the wire-laying process in the wire-laying production process. When turning the inner surface, turn a step of the retaining ring height at the position of the internal monitoring electrode. During the wire-laying process, when the wire-laying tool reaches the position of the internal monitoring electrode, start closely laying the wire to ensure that each resistance wire is exposed to the air and in a parallel-wire state. After the wire-laying is completed, an electrofusion fitting body with a leakage detection function is formed; when producing the seal, place a copper column in the seal cavity providing the sealed connection. After injection molding, ensure the integrity of the external thread of the seal and its tight fit with the external thread of the electrode sheath of the electrofusion fitting.

[0049] Example of usage instructions:

[0050] After completing the welding of the fitting in the conventional operation mode, seal the terminal post 2 on the outside of the electrofusion fitting through the matching assembly of the seal and the sheath 3. The gap between the electrofusion fitting and the pipe 10 is sealed in the form of hot-melt adhesive. The internal monitoring electrode 1, the terminal post 2, the external wire connection, and the pipe installation environment are kept insulated. Keeping the pipe installation environment insulated means that when the pipe is laid in the soil or other media, ensure that the external terminal post of the electrofusion fitting and the connection between the terminal post and the wire are insulated from the soil or other media.

[0051] When using the electrofusion fitting of the present invention for non-metallic pipe leakage monitoring, connect the external axial monitoring electrode 13, the internal monitoring electrode 1, and the resistance value detection module 12, and form a leakage monitoring subsystem with the communication module. Multiple such subsystems can be arranged in segments along the pipe. Each subsystem is responsible for monitoring the leakage of the pipe within its arranged range to meet the accuracy requirements of the pipe system leakage monitoring. The host computer can receive the monitoring data transmitted by multiple leakage monitoring subsystems simultaneously, and judge whether the pipe leaks according to the received resistance value, and which pipe section covered by which leakage monitoring subsystem the leakage point belongs to.

[0052] The surface material of the non-metallic pipe is an insulating material. When the pipe does not leak, the axial monitoring electrode 13 arranged along the pipe axis and the internal monitoring electrode 1 inside the electrofusion joint are in an insulating state. At this time, the resistance value measured by the resistance value detection module 12 is very large, usually above 1000 MΩ. When the pipe leaks, the leaked part of the fluid will flow along the outer wall of the pipe to the axial monitoring electrode 13 below the pipe. Since fluid media such as water are conductive, the fluid inside the pipe and the leaked fluid conduct the axial monitoring electrode 13 and the internal monitoring electrode 1 to form a loop, and the resistance value measured by the resistance value detection module 12 will decrease significantly. Thus, the medium leakage generated by the pipe is monitored. The resistance value signal measured by the resistance value detection module 12 is transmitted to the host computer through the communication module, and the host computer judges whether the pipe leaks according to the change of the received resistance value.

[0053] Since the resistance value measured by the resistance value detection module will decrease significantly when the pipe leaks, in order to judge whether the pipe leaks, a characteristic value R needs to be set. s , the resistance value R measured by the resistance value detection module m is compared with this characteristic value R s . When the resistance value R m is greater than this characteristic value R s , it is considered that the pipeline has no leakage; when the resistance value R m is less than this characteristic value R s , it is considered that the pipeline leaks. Generally, the characteristic value R s can be set as the insulation resistance of the non-metallic pipe to be monitored, or after the plastic pipe and the monitoring system are installed, a high resistance meter can be used to measure it, and 10% of the measured resistance can be taken as the characteristic value R s . For an SDR11 PE100 gas pipeline with a wall thickness of 10 mm, R s can be taken as 200 MΩ.

Claims

1. A processing method of an electrofusion fitting with a non-metal pipe leakage monitoring function, including a resistance wire for welding inside the electrofusion fitting, and two terminal posts are arranged outside the electrofusion fitting, and the bottom ends of the terminal posts are respectively connected to both ends of the resistance wire; It is characterized in that, The terminal posts are arranged in tubular sheaths, and two sheaths are respectively configured with seals, and both the sheaths and the seals are made of insulating materials; in one of the seals, an internal wire for connecting the terminal post and an external wire is provided or an external wire access port is provided; a part of the resistance wire is exposed in the inner cavity of the electrofusion fitting and is used as an internal monitoring electrode; wherein, the electrofusion fitting is processed in the following manner: (1) Manufacture the electrofusion joint in the conventional production mode of the electrofusion fitting with exposed wire: the resistance wire is wound around the mandrel by the original wire winding process to form heating areas on both sides, and the middle section of the resistance wire connecting the heating areas forms a monitoring electrode by parallel wire winding, and then injection molding is carried out; when injection molding, a tubular sheath is formed around the terminal post outside the electrofusion fitting, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting; or, (2) Manufacture the electrofusion joint in the conventional production mode of the electrofusion fitting with plastic-coated wire: the plastic-coated resistance wire is wound around the mandrel by the original wire winding process to form heating areas on both sides, and the middle section of the resistance wire connecting the heating areas forms a monitoring electrode by parallel wire winding after removing the outer insulating plastic, and then injection molding is carried out; when injection molding, a tubular sheath is formed around the terminal post outside the electrofusion fitting, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting; or, (3) Manufacture the electrofusion joint in the conventional production mode of the electrofusion fitting with post-wound wire: use the mandrel for injection molding to form a tubular sheath around the terminal post outside the electrofusion fitting; a retaining ring or a retaining block is turned inside the electrofusion fitting, and the resistance wire is circumferentially arranged around the inner wall, and a part of the resistance wire is ensured to be exposed in the inner cavity of the electrofusion fitting; When the electrofusion fitting is used for non-metal pipe leakage monitoring, an external axial monitoring electrode, an internal monitoring electrode, and a resistance value detection module are connected, and a leakage monitoring subsystem is formed with a communication module. A plurality of the leakage monitoring subsystems are arranged in segments along the pipeline, and each leakage monitoring subsystem is responsible for monitoring the leakage of the pipeline within its arranged range.

2. According to the method described in claim 1, It is characterized in that, The resistance wire is wound circumferentially around the electrofusion fitting to form two interconnected heating areas; the resistance wire exposed in the inner cavity of the electrofusion fitting is used to connect the two heating areas.

3. According to the method described in claim 1, It is characterized in that, A retaining ring or a retaining block is provided on the inner wall of the electrofusion fitting to reserve a gap between the ends of the two pipes when nesting and welding the fittings; the resistance wire exposed in the inner cavity of the electrofusion fitting is located on the surface of the retaining ring or the retaining block.

4. According to the method described in claim 3, It is characterized in that, The retaining ring or the retaining block is in a circumferential ring shape.

5. According to the method described in any one of claims 1 to 4, It is characterized in that, A strip electrode, a block electrode or a ring electrode connected to a resistance wire is arranged in the inner cavity of the electrofusion fitting; the strip electrode, the block electrode or the ring electrode is used to replace the resistance wire and serve as an internal monitoring electrode.

6. The method according to any one of claims 1 to 4, characterized in that the sheath has an internal thread or an external thread, the seal has a matching external thread or internal thread, and the sheath and the seal are insulated and sealed by being tightly screwed together.

Images