Interface enhanced rubber ring electrically fused steel skeleton polyethylene composite pipe and its preparation method and application

Abstract

The application discloses an interface enhanced rubber ring electrically fused steel skeleton polyethylene composite pipe and a preparation method and application thereof, and belongs to the technical field of pipes. The application introduces polar functional groups on the surface of the inner high-density polyethylene layer through plasma activation, and forms chemical bonding with the interface enhanced adhesive layer. A steel skeleton reinforced layer is formed by winding copper-plated steel wires coated with nano-silicon dioxide modified epoxy resin, and physical interlocking and chemical reaction with the interface enhanced adhesive layer are realized through online induction heating, so that a multi-stage interface enhanced system is constructed. A grid-shaped conductive layer is embedded in an integrated electrically fused welded pipe fitting, and an interface matching layer is coated, and a graded electrically fused welding process is combined to realize equal strength connection of a joint and a pipe body. The application solves the problems of "steel-plastic" interface debonding, low welding joint strength and poor sealing adaptability, and is suitable for high-sulfur oil and gas field gathering and deep-sea oil and gas exploitation.

Description

Technical Field

[0001] This invention relates to the field of pipeline technology, and in particular to an interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe, its preparation method, and its application. Background Technology

[0002] In the fields of oil and gas extraction and transportation, especially in extreme conditions such as deep-sea oil and gas field development, hydrogen sulfide-containing gas field gathering and transportation, and energy transportation in high-altitude and cold regions, pipeline systems face multiple severe challenges, including high pressure, strong corrosion, drastic temperature changes, and geological subsidence. While traditional metal pipelines (such as seamless steel pipes) have high strength, their corrosion resistance is poor, especially when transporting high-sulfur media, leading to frequent pitting corrosion and stress corrosion cracking (SCC) problems. This results in high costs for corrosion inhibitor injection and frequent maintenance and replacement, resulting in high total life-cycle costs. Furthermore, metal pipelines are heavy and lack flexibility, making installation extremely difficult in complex terrain and deep-sea environments.

[0003] To address the aforementioned issues, steel-reinforced polyethylene composite pipes have emerged. These pipes combine the high strength of steel with the corrosion resistance of polyethylene, forming a composite structure by using steel wire or steel plate mesh as a reinforcing layer and covering it with high-density polyethylene (HDPE). This results in excellent performance at specific pressure ratings. However, existing technologies have revealed a series of core defects during long-term service, severely limiting their application in critical fields:

[0004] First, interface failure is the core problem. The fundamental issue with existing steel-reinforced polyethylene composite pipes lies in the weak bonding between the steel and plastic interfaces. During manufacturing, the steel wires or strips are only physically interlocked with the polyethylene matrix or simply bonded by heat fusion. When the pipe is subjected to internal pressure, axial tension, or cyclic thermal cycling, the significant difference in the elastic modulus and coefficients of thermal expansion between the two materials makes it highly susceptible to microcracks and stress concentration at the interface, leading to interface debonding. Once interface debonding occurs, the reinforcing layer cannot effectively bear the load, resulting in the loss of the overall structural integrity of the pipe and causing internal pressure bulging or axial necking failure.

[0005] Secondly, the electrofusion welded joint is the weakest point in the structure. In existing technologies, pipe connections typically use electrofusion fittings. However, in traditional electrofusion fittings, the resistance wire is only embedded in the pure polyethylene layer. During welding, the molten zone is limited to the polyethylene material. For steel-reinforced polyethylene composite pipes, continuous connection of the reinforcing layer (steel skeleton) cannot be achieved during welding. Therefore, the welded joint becomes an unreinforced pure plastic area, and its pressure-bearing capacity is typically only 60%-70% of the pipe body. This structural characteristic of "strong pipe, weak joint" locks the pressure-bearing bottleneck of the entire pipeline system at the joint, posing a significant safety hazard.

[0006] Secondly, rubber ring seals are not adaptable to complex operating conditions. To address the needs of pipeline systems for flexible sealing and axial displacement compensation, some products have introduced rubber ring sealing structures. However, existing rubber rings are mostly made of a single rubber material. When transporting high-temperature (e.g., above 60°C) oil and gas media or exposed to ultraviolet radiation and ozone for extended periods, the rubber material is prone to aging, hardening, permanent deformation, and even cracking, leading to seal failure. In addition, the sealing interface between traditional rubber rings and the pipe body lacks an effective stress relief structure, making them prone to "creeping" leaks under pressure fluctuations.

[0007] Finally, the manufacturing process struggles to achieve integrated structural synergy. Currently, the production of steel-reinforced polyethylene composite pipes often employs an offline process of "first winding the skeleton, then coating with plastic," or a stepwise composite process of "inner pipe-skeleton-outer pipe." These processes struggle to effectively control the chemical bonding at the "steel-plastic" interface at the microscopic level, and even more so to form an integrated reinforcing structure that runs through the pipe body and joints.

[0008] In summary, there is an urgent need for a new type of composite pipe and its preparation method that can fundamentally solve the failure of the "steel-plastic" interface, achieve equal strength between the joint and the body, and improve the long-term reliability of the sealing system under extreme working conditions. Summary of the Invention

[0009] To achieve the above objectives, this invention provides an interface-reinforced electrofused steel-reinforced polyethylene composite pipe, its preparation method, and its application. The interface-reinforced electrofused steel-reinforced polyethylene composite pipe comprises:

[0010] The composite pipe base material consists of, from the inside out, an inner high-density polyethylene layer, an interface-reinforced adhesive layer, a steel skeleton reinforcement layer, and an outer high-density polyethylene layer.

[0011] The outer surface of the inner high-density polyethylene layer is introduced with carboxyl and amino polar functional groups after being subjected to online plasma activation treatment by a plasma jet treatment device.

[0012] The interface-reinforced adhesive layer is a blend of maleic anhydride-grafted polyethylene and ethylene-acrylic acid copolymer. The interface-reinforced adhesive layer covers the outer surface of the inner high-density polyethylene layer. The maleic anhydride groups in the interface-reinforced adhesive layer react chemically with the amino groups on the outer surface of the inner high-density polyethylene layer to form amide bonds.

[0013] The steel skeleton reinforcement layer is formed by winding copper-plated steel wire coated with nano-silica modified epoxy resin. During the winding process, the nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire undergoes physical interlocking and chemical reaction with the interface reinforcement bonding layer.

[0014] The outer protective layer, a high-density polyethylene layer, covers the outer surface of the steel skeleton reinforcement layer.

[0015] Accordingly, this invention also provides a method for preparing an interface-reinforced electrofused steel-reinforced polyethylene composite pipe, comprising the following steps:

[0016] Step 1: Preparation of the composite pipe base material, specifically including the following sub-steps:

[0017] Step 1.1: Extrusion molding and surface activation treatment of the inner high-density polyethylene layer: High-density polyethylene resin is mixed with carbon black masterbatch, antioxidant and ultraviolet absorber to form an inner layer mixture. The inner layer mixture is extruded into an inner high-density polyethylene pipe blank through a first single screw extruder. After the inner high-density polyethylene pipe blank is extruded from the die and the surface temperature is maintained in the molten range, the outer surface of the inner high-density polyethylene pipe blank is subjected to online plasma activation treatment using a plasma jet treatment device.

[0018] Step 1.2: Online co-extrusion of the interface-reinforced adhesive layer: Within 0.5 seconds after completing the plasma activation treatment in Step 1.1, the activated inner high-density polyethylene pipe blank is sized by a vacuum sizing sleeve. Then, the interface-reinforced adhesive layer material formed by blending maleic anhydride grafted polyethylene and ethylene-acrylic acid copolymer is uniformly coated on the outer surface of the inner high-density polyethylene pipe blank through a co-extrusion die using a second single-screw extruder.

[0019] Step 1.3: Winding and simultaneous curing of the steel skeleton reinforcement layer and the interface: After the interface reinforcement adhesive layer described in step 1.2 is extruded and covers the outer surface of the inner high-density polyethylene pipe blank, copper-plated steel wire coated with nano-silica modified epoxy resin is immediately cross-wound by a winding machine to form a double-layer symmetrical steel skeleton reinforcement layer. During the winding process, the copper-plated steel wire being wound is heated online by a medium-frequency induction heating device, so that the nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire softens and partially cures, and undergoes physical interlocking and chemical reaction with the interface reinforcement adhesive layer in the molten state.

[0020] Step 1.4: Coating and shaping of the outer sheath with high-density polyethylene: The outer sheath with high-density polyethylene material is extruded and coated on the outer surface of the pipe blank that has been wound with the steel skeleton reinforcement layer through a third single screw extruder. Then, the composite pipe is cooled to below 60°C through a vacuum cooling and shaping device to complete the preparation of the composite pipe base material.

[0021] Step 2: Prefabrication of integrated electrofusion welded pipe fittings, specifically including the following sub-steps:

[0022] Step 2.1: Embedding of stress relief groove structure and conductive mesh on the inner wall of the pipe fitting: High-density polyethylene material is injected into the mold using injection molding process to form an integral electrofusion welded pipe fitting blank with a socket on one end and a flat end on the other. In the mold design, multiple spiral stress relief grooves are formed on the inner wall of the socket of the pipe fitting. During the injection molding process, the pre-made mesh conductive layer is accurately positioned by the positioning pins in the mold and embedded in the inner wall surface of the socket of the pipe fitting.

[0023] Step 2.2: Preparation of interface matching layer between pipe fitting welding area and pipe body: A layer of interface matching layer slurry is coated on the inner wall surface of the pipe fitting socket by screen printing process, and then dried after coating.

[0024] Step 2.3: Installation and activation of the pre-embedded rubber ring: Install the fluorosilicone rubber ring in the annular groove on the inner wall of the socket of the pipe fitting. Before installation, immerse the fluorosilicone rubber ring in an ethanol solution containing silane coupling agent for surface activation treatment.

[0025] Step 3: Electrofusion welding and sealing system construction of composite pipes and fittings, specifically including the following sub-steps:

[0026] Step 3.1: Pretreatment and positioning of the welding end face: Remove the outer high-density polyethylene layer of the composite pipe base material prepared in Step 1 to expose the steel skeleton reinforcement layer and the inner high-density polyethylene layer. Grind the exposed end of the steel skeleton reinforcement layer flat and clean the outer surface of the composite pipe in this end area. Then clean the inner wall of the socket of the integrated electrofusion welded pipe fitting prepared in Step 2 and insert the pretreated end of the composite pipe base material into the socket of the integrated electrofusion welded pipe fitting.

[0027] Step 3.2: Implementation of the graded electrofusion welding process: Connect the output electrode of the electrofusion welding machine to the terminal block on the outside of the integrated electrofusion welding pipe fitting, start the welding program, and perform welding using a graded welding process, which includes a preheating stage, a fusion welding stage, and a pressure holding and cooling stage in sequence.

[0028] Step 3.3: Stress activation of the rubber ring sealing system: In the pressure holding and cooling stage after the electrofusion welding in step 3.2, axial pressure is applied to the integrated electrofusion welded pipe fitting and the composite pipe base material by a hydraulic clamp. This causes the end of the composite pipe base material to apply a continuous axial extrusion force to the fluorosilicone rubber ring pre-embedded in the annular groove of the integrated electrofusion welded pipe fitting. This causes the fluorosilicone rubber ring to undergo elastic deformation and tightly adhere to the spiral stress relief groove on the outer wall of the composite pipe base material and the inner wall of the integrated electrofusion welded pipe fitting.

[0029] Preferably, the working gas of the plasma jet treatment device in step 1.1 is a mixture of nitrogen and acrylic acid, wherein the volume percentage of acrylic acid in the mixture is 8%, the output power of the plasma jet treatment device is 450 watts, the treatment distance is 15 mm, and the treatment time is 2 seconds.

[0030] In step 1.2, the mass ratio of maleic anhydride-grafted polyethylene to ethylene-acrylic acid copolymer in the interface-reinforced adhesive layer material is 65:35, and the extrusion thickness of the interface-reinforced adhesive layer is controlled between 0.3 mm and 0.5 mm.

[0031] In step 1.3, the diameter of the copper-plated steel wire is 0.8 mm. The nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire is composed of bisphenol A type epoxy resin, methyl hexahydrophthalic anhydride curing agent, and silica particles with a particle size of 30 nanometers in a mass ratio of 100:80:5. The thickness of the nano-silica modified epoxy resin coating is 30 micrometers. The winding angle of the copper-plated steel wire is 58 degrees. The temperature of the copper-plated steel wire being wound by the medium frequency induction heating device is controlled between 140°C and 150°C.

[0032] The outer sheath high-density polyethylene material mentioned in step 1.4 has the same composition as the inner layer mixture of the inner high-density polyethylene layer mentioned in step 1.1.

[0033] Preferably, the spiral stress relief groove in step 2.1 has a semi-circular cross-sectional shape with a radius of 0.5 mm and a groove depth of 0.4 mm, and the pitch between two adjacent spiral stress relief grooves is 2 mm; the mesh conductive layer is woven from tin-plated copper wire with a diameter of 0.3 mm, the mesh conductive layer has a mesh count of 20 mesh, the resistance of the mesh conductive layer at 20°C is 0.02 ohms / cm², and after the mesh conductive layer is embedded in the inner wall surface of the pipe fitting socket, the distance between the mesh conductive layer and the inner wall surface of the pipe fitting socket is 0.2 mm;

[0034] The interface matching layer slurry in step 2.2 is composed of maleic anhydride grafted polyethylene, conductive carbon black and coupling agent in a mass ratio of 100:15:3, wherein the coupling agent is γ-aminopropyltriethoxysilane, the coating thickness of the interface matching layer slurry is 0.1 mm, and the drying treatment is drying at 80°C for 30 minutes.

[0035] The cross-section of the fluorosilicone rubber ring in step 2.3 is "X" shaped. The Shore A hardness of the fluorosilicone rubber ring is 75 degrees, and the compression set is less than 15% under the condition of 150℃×70 hours. The surface activation treatment is to immerse the fluorosilicone rubber ring in an ethanol solution containing 1.5% by mass of silane coupling agent and sonicate it at 40℃ for 30 minutes. The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0036] Preferably, in step 3.1, the length of the outer sheath high-density polyethylene layer removed from the end of the composite pipe base is 80 mm. After the pre-treated end of the composite pipe base is inserted into the socket of the integrated electrofusion welded pipe fitting, the fitting gap between the outer wall of the composite pipe base and the inner wall of the integrated electrofusion welded pipe fitting is 0.2 mm to 0.3 mm.

[0037] In step 3.2, the preheating stage of the graded welding process involves linearly increasing the welding voltage to 32 volts within 30 seconds and maintaining this voltage for 20 seconds. The fusion welding stage of the graded welding process involves linearly increasing the welding voltage from 32 volts to 39.5 volts within 15 seconds and maintaining this voltage for 60 seconds. The pressure holding and cooling stage of the graded welding process involves applying an axial pressure of 0.2 MPa to the integrated electrofusion welded pipe fitting and the composite pipe base material using a hydraulic clamp while the welding voltage is cut off, and continuing to cool for 300 seconds until the welding interface temperature drops below 80°C.

[0038] In step 3.3, the elastic deformation of the fluorosilicone rubber ring causes the four lips of the fluorosilicone rubber ring to fit tightly against the spiral stress relief groove on the outer wall of the composite pipe base and the inner wall of the integrated electrofusion welded pipe fitting.

[0039] Preferably, after step 3, step 4 is further included: finished product performance testing and parameter calibration, which specifically includes the following sub-steps:

[0040] Step 4.1: Axial Tensile Performance Testing and Feedback Calibration of Welded Joints: A specimen containing the complete welded joint is cut from the completed welded composite pipe system. The specimen is mounted on a universal testing machine for axial tensile testing, and the maximum tensile load of the welded joint is recorded. The axial tensile load of the composite pipe matrix material was tested at the fracture location. If the value is lower than 95%, the welding voltage curve in step 3.2 is adjusted according to the test results.

[0041] Step 4.2: High-temperature and high-pressure cyclic aging test and calibration of the sealing system: The pipe section with joints prepared in Step 3 is installed in the high-temperature and high-pressure cyclic test device. Nitrogen gas containing 10% H2S by mass is used as the test medium. The test pressure is 1.2 times the nominal pressure of the pipe and the test temperature is 85℃. Pressure cyclic fatigue test is carried out at a cycle frequency of 6 times / minute for a total of 5000 cycles. During the test, the leakage rate of the sealing system is monitored in real time by a pressure sensor and a helium gas spectrometer. If the leakage rate exceeds Pa·m³ / s within the test cycle, the surface activation treatment time of the fluorosilicone rubber ring in Step 2.3 or the pretreatment accuracy of the composite pipe end in Step 3.1 is adjusted according to the failure analysis results.

[0042] Preferably, the axial tensile test described in step 4.1 is performed at an ambient temperature of 23℃±2℃ with a loading rate of 5 mm / min;

[0043] The specific method for adjusting the welding voltage curve in step 3.2 based on the test results in step 4.1 is as follows: when the ratio of the voltage to the voltage is in the range of 85% to 95%, increase the holding voltage of the fusion welding stage in step 3.2 by 0.5 volts; when the ratio of the voltage to the voltage is below 85%, increase the holding voltage of the fusion welding stage in step 3.2 by 1.0 volt, and extend the holding and cooling time of the holding and cooling stage in step 3.2 by 60 seconds.

[0044] Preferably, the inner layer mixture in step 1.1 is formed by mixing high-density polyethylene resin with 1.2% carbon black masterbatch, 0.5% antioxidant, and 0.3% ultraviolet absorber by a high-speed mixer at 85°C for 10 minutes. The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the ultraviolet absorber is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole.

[0045] In step 1.1, the extruder temperature of the first single-screw extruder is controlled between 190°C and 210°C. The online plasma activation treatment is performed within 3 seconds after the inner high-density polyethylene pipe blank is extruded from the die head and the surface temperature is maintained in the molten state range of 185°C to 195°C.

[0046] In step 1.2, the processing temperature of the second single-screw extruder is controlled between 210°C and 230°C;

[0047] The processing temperature of the third single-screw extruder described in step 1.4 is controlled between 190°C and 210°C.

[0048] Preferably, in step 1.3, when the nano-silica modified epoxy resin coating undergoes physical interlocking and chemical reaction with the interface-reinforced adhesive layer in the molten state under softened and partially cured conditions, the nano-silica particles in the nano-silica modified epoxy resin coating act as nucleating agents, inducing a change in the crystalline morphology of the polyethylene in the interface-reinforced adhesive layer, forming a dense transverse crystalline layer.

[0049] Accordingly, this invention also provides an application of the interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe, which is used in gathering and transportation pipeline systems of high-sulfur oil and gas fields or in deep-sea oil and gas extraction riser systems at water depths of 1500 meters or more.

[0050] The beneficial effects of this invention are:

[0051] 1. This invention introduces carboxyl and amino polar functional groups onto the surface of the inner high-density polyethylene layer through plasma activation. These groups react chemically with maleic anhydride groups in the interface-reinforced adhesive layer to form amide bonds, achieving interfacial chemical bonding. Simultaneously, copper-plated steel wire coated with nano-silica-modified epoxy resin undergoes physical interlocking and chemical reaction with the molten interface-reinforced adhesive layer during winding via medium-frequency induction heating. The nano-silica particles in the coating induce the formation of a dense, transverse crystalline layer in the interface-reinforced adhesive layer. The synergistic effect of the multi-level reinforcement system increases the interfacial bonding strength between the steel skeleton and the polyethylene matrix by more than three times, fundamentally preventing pipeline failure caused by interfacial debonding.

[0052] 2. This invention embeds a mesh-like conductive layer and coats an interface matching layer within an integrated electrofusion welded pipe fitting. Through a staged electrofusion welding process, voltage and pressure are precisely controlled in three stages: preheating, fusion welding, and pressure holding and cooling. This allows for deep molecular chain entanglement and covalent bond reactions between the maleic anhydride-grafted polyethylene in the interface matching layer and the interface-reinforced adhesive layer on the outer wall of the composite pipe. After welding, the axial tensile strength of the welded joint can reach over 98% of the strength of the pipe body, completely changing the traditional situation where the strength of electrofusion welded joints is only 60%-70% of the pipe body strength. This ensures that the pressure-bearing capacity of the entire pipeline system is no longer limited by the joint.

[0053] 3. This invention employs an "X"-shaped fluorosilicone rubber ring, which undergoes surface activation treatment with a silane coupling agent. During the welding pressure holding and cooling stage, the axial pressure causes the rubber ring to elastically deform, and the four lips tightly adhere to the spiral stress relief grooves on the outer wall of the composite pipe and the inner wall of the fitting, forming multiple sealing barriers. Simultaneously, the silane coupling agent forms a chemical bond with the polyethylene material under the residual heat of welding, achieving permanent adhesion at the sealing interface. This sealing system exhibits a leakage rate of less than 1×10⁻⁻⁻⁶ in a rigorous test at 85℃, with a medium containing 10% H₂S, 1.2 times the nominal pressure, and 5000 cycles. 6 Pa·m³ / s, extending the lifespan by more than 3 times compared to traditional rubber sealing systems. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0055] Figure 1 This is a flowchart of the steps of the method of the present invention;

[0056] Figure 2 This is a schematic diagram of the structure of the inner wall of the socket of the integrated electrofusion welded pipe fitting of the present invention;

[0057] In the diagram: 1-Inner high-density polyethylene layer; 2-Interface reinforced adhesive layer; 3-Steel skeleton reinforcement layer; 4-Outer protective high-density polyethylene layer. Detailed Implementation

[0058] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0059] Please see Figures 1-2 This invention provides an interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe, its preparation method, and its application.

[0060] Step 1: Preparation of composite pipe base material

[0061] Step 1 aims to prepare the base pipe portion of the interface-reinforced electrofused steel-reinforced polyethylene composite pipe described in this invention. This step, through the synergistic effect of multiple sub-steps including extrusion molding, surface activation, co-extrusion, winding molding, and coating shaping, constructs a composite pipe base with a multi-level interface-reinforced structure of "chemical bonding-physical interlocking." Specifically, Step 1 includes the following sub-steps:

[0062] Step 1.1: Extrusion molding and surface activation treatment of the inner high-density polyethylene layer

[0063] The purpose of step 1.1 is to prepare the inner layer structure of the composite tube and introduce active functional groups on its outer surface, so as to provide a basis for subsequent chemical bonding with the interface-enhanced adhesive layer.

[0064] High-density polyethylene resin is mixed with carbon black masterbatch, antioxidant, and ultraviolet absorber to form an inner layer mixture. Specifically, high-density polyethylene resin is mixed with 1.2% carbon black masterbatch, 0.5% antioxidant, and 0.3% ultraviolet absorber by mass using a high-speed mixer at 85°C for 10 minutes. The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the ultraviolet absorber is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole. Through the above mixing process, the components are uniformly dispersed to form the inner layer mixture.

[0065] The inner layer mixture is extruded through a single-screw extruder at a temperature between 190°C and 210°C to form an inner layer high-density polyethylene (HDPE) pipe blank. Within 3 seconds of extrusion from the die, while the surface temperature of the HDPE pipe blank remains in the molten state between 185°C and 195°C, an online plasma activation treatment is performed on the outer surface of the HDPE pipe blank using a plasma jet treatment device. The working gas of the plasma jet treatment device is a mixture of nitrogen and acrylic acid, with acrylic acid comprising 8% by volume. The output power of the plasma jet treatment device is 450 watts, the distance between the treatment nozzle and the outer surface of the pipe blank is 15 mm, and the treatment time is 2 seconds. Under these conditions, high-energy particles in the plasma bombard and activate the molecular chains on the surface of the pipe blank, while the acrylic acid monomers undergo graft polymerization under the action of the plasma, introducing carboxyl and amino polar functional groups onto the outer surface of the HDPE pipe blank.

[0066] Step 1.2: Online co-extrusion of the interface-reinforced adhesive layer

[0067] The purpose of step 1.2 is to coat the outer surface of the activated inner high-density polyethylene layer with an adhesive layer that can chemically react with both the polyethylene layer and the metal reinforcement layer, thus constructing a "chemical bond bridge".

[0068] Within 0.5 seconds of completing the plasma activation treatment in step 1.1, the activated inner high-density polyethylene (HDPE) tube blank is sized using a vacuum sizing sleeve. Subsequently, using a second single-screw extruder at a processing temperature of 210°C to 230°C, an interface-reinforced adhesive layer material formed by blending maleic anhydride-grafted polyethylene and ethylene-acrylic acid copolymer at a mass ratio of 65:35 is uniformly coated onto the outer surface of the inner HDPE tube blank through a co-extrusion die. The extrusion thickness of the interface-reinforced adhesive layer is controlled between 0.3 mm and 0.5 mm. During this process, the maleic anhydride groups in the interface-reinforced adhesive layer material chemically react with the amino groups introduced into the outer surface of the inner HDPE tube blank in the aforementioned steps to form amide bonds, achieving interfacial chemical bonding.

[0069] Step 1.3: Simultaneous curing of the steel frame reinforcement layer by winding and interface.

[0070] The purpose of step 1.3 is to construct a steel skeleton reinforcement structure on the outer surface of the interface reinforcement adhesive layer, and to achieve synchronous curing and reinforcement of the interface between the reinforcement layer and the substrate by physically interlocking and chemically reacting the active coating on the surface of the steel wire with the interface reinforcement adhesive layer through online heating.

[0071] After the interface-reinforced adhesive layer described in step 1.2 is extruded and covers the outer surface of the inner high-density polyethylene pipe blank, copper-plated steel wire coated with nano-silica-modified epoxy resin is immediately cross-wound at a winding angle of 58 degrees using a precisely controlled winding machine to form a double-layer symmetrical steel skeleton reinforcement layer. The diameter of the copper-plated steel wire is 0.8 mm. The nano-silica-modified epoxy resin coating on the surface of the copper-plated steel wire is composed of bisphenol A type epoxy resin, methyl hexahydrophthalic anhydride curing agent, and silica particles with a particle size of 30 nanometers in a mass ratio of 100:80:5, and the thickness of the nano-silica-modified epoxy resin coating is 30 micrometers. During the winding process, the copper-plated steel wire being wound is heated online using a medium-frequency induction heating device, with the heating temperature controlled between 140°C and 150°C, causing the nano-silica-modified epoxy resin coating on the surface of the copper-plated steel wire to soften rapidly and partially cure. In its softened state, the coating physically interlocks with the molten interface-reinforced adhesive layer. Simultaneously, the epoxy groups in the coating chemically react with the carboxyl groups in the interface-reinforced adhesive layer to form covalent bonds. The nano-silica particles in the nano-silica-modified epoxy resin coating act as nucleating agents, inducing changes in the crystalline morphology of the polyethylene in the interface-reinforced adhesive layer, forming a dense transverse crystalline layer.

[0072] Step 1.4: Coating and shaping of the outer sheath with high-density polyethylene

[0073] The purpose of step 1.4 is to cover the outer surface of the steel skeleton reinforcement layer with an outer protective layer to form protection for the internal structure and to complete the shaping of the composite pipe base material.

[0074] Using a third single-screw extruder, at a temperature of 190°C to 210°C, the outer sheath high-density polyethylene material is extruded through a crosshead and coated onto the outer surface of the tube blank with the steel skeleton reinforcement layer already wound. The outer sheath high-density polyethylene material has the same composition as the inner layer mixture of the inner high-density polyethylene layer described in step 1.1. Subsequently, the composite pipe is cooled to below 60°C using a vacuum cooling and shaping device, completing the preparation of the composite pipe base material.

[0075] Step 2: Prefabrication of integrated electrofusion welded pipe fittings

[0076] Step 2 aims to prefabricate an integrated electrofusion welded pipe fitting that matches the composite pipe base material prepared in Step 1. This fitting integrates a stress-relieving structure, a conductive heating structure, and a pre-embedded sealing structure, laying the foundation for subsequent equal-strength welding and reliable sealing. Specifically, Step 2 includes the following sub-steps:

[0077] Step 2.1: Embedding the stress relief groove structure and conductive mesh on the inner wall of the pipe fitting

[0078] The purpose of step 2.1 is to form a microstructure that can disperse stress on the inner wall of the fitting socket and to precisely embed the conductive element used to generate welding heat into the inner wall surface of the fitting.

[0079] Using injection molding, high-density polyethylene material is injected into a mold to form an integral electrofusion welded pipe fitting blank with a socket at one end and a flat end at the other. In the mold design, multiple spiral stress-relieving grooves are formed on the inner wall of the socket. Each spiral stress-relieving groove has a semi-circular cross-section with a radius of 0.5 mm and a depth of 0.4 mm, and the pitch between adjacent spiral stress-relieving grooves is 2 mm. During injection molding, a pre-fabricated mesh-like conductive layer, woven from 0.3 mm diameter tin-plated copper wire, is precisely positioned and embedded in the inner wall surface of the socket using positioning pins within the mold. The mesh-like conductive layer has a mesh size of 20 and a resistance of 0.02 ohms / cm² at 20°C. The distance between the mesh-like conductive layer and the inner wall surface of the socket is 0.2 mm.

[0080] Step 2.2: Preparation of the interface matching layer between the fitting welding area and the pipe body

[0081] The purpose of step 2.2 is to coat the inner wall of the fitting socket with a matching layer that can chemically react with the interface reinforcement adhesive layer on the outer wall of the composite pipe substrate, so as to enhance the bonding strength of the welding interface.

[0082] A 0.1 mm thick interface matching layer slurry is coated onto the inner wall surface of the pipe fitting socket using a screen printing process. The interface matching layer slurry is composed of maleic anhydride-grafted polyethylene, conductive carbon black, and a coupling agent in a mass ratio of 100:15:3, wherein the coupling agent is γ-aminopropyltriethoxysilane. After coating, it is dried at 80°C for 30 minutes.

[0083] Step 2.3: Installation and activation of the pre-embedded rubber ring

[0084] The purpose of step 2.3 is to install the specially made sealing ring inside the pipe fitting and to improve the interfacial adhesion between the sealing ring and the polyethylene material through surface activation treatment.

[0085] The fluorosilicone rubber ring is installed in the annular groove on the inner wall of the pipe fitting socket. The fluorosilicone rubber ring has an "X" shaped cross-section, a Shore A hardness of 75, and a compression set of less than 15% at 150℃ for 70 hours. Before installation, the fluorosilicone rubber ring is immersed in an ethanol solution containing 1.5% by mass of a silane coupling agent and ultrasonically treated at 40℃ for 30 minutes for surface activation. The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0086] Step 3: Construction of the electrofusion welding and sealing system for composite pipes and fittings

[0087] Step 3 aims to weld the composite pipe matrix prepared in Step 1 to the prefabricated integrated electrofusion welded pipe fitting in Step 2, and simultaneously activate the sealing system to form a complete pipe connection structure. Specifically, Step 3 includes the following sub-steps:

[0088] Step 3.1: Pretreatment and positioning of the welding end face

[0089] The purpose of step 3.1 is to pre-treat the welding end face of the composite pipe base material, remove the outer protective layer and expose the reinforcing layer, and then precisely insert the pipe into the fitting to prepare for welding.

[0090] At the end of the composite pipe substrate prepared in step 1, the outer high-density polyethylene layer is removed using a scraper, exposing an 80 mm long steel skeleton reinforcement layer and an inner high-density polyethylene layer. The exposed end of the steel skeleton reinforcement layer is ground smooth using an angle grinder, and the outer surface of the composite pipe in this end area is cleaned with acetone. Subsequently, the inner wall of the socket of the integrated electrofusion welded pipe fitting prepared in step 2 is wiped clean with ethanol. The pre-treated end of the composite pipe substrate is inserted into the socket of the integrated electrofusion welded pipe fitting until the positioning step at the bottom of the socket is reached, ensuring that the fit clearance between the outer wall of the composite pipe substrate and the inner wall of the integrated electrofusion welded pipe fitting is 0.2 mm to 0.3 mm.

[0091] Step 3.2: Implementation of the staged electrofusion welding process

[0092] The purpose of step 3.2 is to achieve uniform melting, full reaction and dense solidification of the welding interface by controlling the welding voltage and holding pressure in stages, so as to form a high-strength integrated welded joint.

[0093] Connect the output electrode of the electrofusion welding machine to the terminal block on the outside of the integrated electrofusion welding fitting. The terminal block is electrically connected to the internal mesh-like conductive layer of the fitting. Start the welding program using a step-by-step welding process.

[0094] The first stage is the preheating stage: within 30 seconds, the welding voltage is linearly increased to 32 volts and maintained at that voltage for 20 seconds.

[0095] The second stage is the fusion welding stage: within 15 seconds, the welding voltage is linearly increased from 32 volts to 39.5 volts and held at that voltage for 60 seconds.

[0096] The third stage is the pressure holding and cooling stage: while the welding voltage is cut off, an axial pressure of 0.2 MPa is applied to the integrated electrofusion welded pipe fitting and the composite pipe base material through a hydraulic clamp, and cooling is continued for 300 seconds until the welding interface temperature drops below 80°C.

[0097] Step 3.3: Stress activation of the rubber ring sealing system

[0098] The purpose of step 3.3 is to activate the pre-embedded sealing ring by using the axial holding pressure applied during the welding process, so that it undergoes elastic deformation and fits tightly against the sealing interface, while using the residual heat of welding to promote the chemical bonding between the sealing ring and the polyethylene interface.

[0099] During the pressure holding and cooling stage after the electrofusion welding in step 3.2, the axial pressure applies a continuous axial compressive force to the end of the composite pipe base material against the fluorosilicone rubber ring pre-embedded in the annular groove of the integrated electrofusion welded pipe fitting. This compressive force causes the fluorosilicone rubber ring with the "X"-shaped cross-section to undergo elastic deformation, and its four lips tightly adhere to the spiral stress relief groove on the outer wall of the composite pipe base material and the inner wall of the integrated electrofusion welded pipe fitting.

[0100] Step 4: Finished Product Performance Testing and Parameter Calibration

[0101] Step 4 aims to perform performance testing on the welded composite pipe system and calibrate the process parameters based on the test results to ensure the performance stability and consistency of the product. Specifically, Step 4 includes the following sub-steps:

[0102] Step 4.1: Axial tensile performance testing and feedback calibration of welded joints

[0103] The purpose of step 4.1 is to test the axial tensile strength of the welded joint and compare it with the strength of the pipe body, and to ensure that the joint and the body have the same strength through feedback calibration.

[0104] A specimen containing the complete welded joint was cut from the welded composite pipe system. The specimen was mounted on a universal testing machine and subjected to axial tensile testing at an ambient temperature of 23℃±2℃ and a loading rate of 5 mm / min until specimen failure. The maximum tensile load of the welded joint was recorded. and the location of the fracture. The test results obtained... Axial tensile load of composite pipe base material Compare. If the above Below the If the value is 95%, then the welding process parameters are determined to be deviated. Based on the test results, the welding voltage curve in step 3.2 is adjusted through finite element analysis inversion, specifically: when the... With the When the ratio is in the range of 85% to 95%, increase the holding voltage of the fusion welding stage described in step 3.2 by 0.5 volts; when the With the When the ratio is less than 85%, the holding voltage of the fusion welding stage described in step 3.2 is increased by 1.0 volt, and the holding cooling time of the holding cooling stage described in step 3.2 is extended by 60 seconds.

[0105] Step 4.2: High-temperature and high-pressure cyclic aging test and calibration of the sealing system

[0106] The purpose of step 4.2 is to test the long-term reliability of the sealing system under simulated extreme operating conditions and to calibrate the sealing structure and material processing technology based on the test results.

[0107] The pipe section with joints prepared in step 3 was installed in a high-temperature and high-pressure cyclic testing apparatus. The test medium was nitrogen gas containing 10% H2S by mass, the test pressure was 1.2 times the nominal pressure of the pipe, and the test temperature was 85℃. Pressure cyclic fatigue testing was conducted at a cycle frequency of 6 cycles / minute, for a total of 5000 cycles. During the test, the leakage rate of the sealing system was monitored in real time using a high-precision pressure sensor and a helium gas spectrometer leak detector. If the leakage rate exceeded [a certain threshold] within the test cycle, [further testing would be conducted]. If the pressure is measured in Pa·m³ / s, the sealing system structure or material is deemed defective. Based on the failure analysis results, adjust the surface activation treatment time of the fluorosilicone rubber ring in step 2.3 or the pretreatment accuracy of the composite pipe end in step 3.1.

[0108] Step 5: Application

[0109] Step 5 involves applying the prepared and tested interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe to specific engineering scenarios.

[0110] The interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe that has passed the performance test in step 4 can be used in the gathering and transportation pipeline system of high-sulfur oil and gas fields, or in the riser system of deep-sea oil and gas extraction at a water depth of more than 1,500 meters.

[0111] In summary, this invention provides an interface-reinforced electrofusion steel-reinforced polyethylene composite pipe with an adhesive ring, its preparation method, and its application. Through the complete technical solution of steps 1 to 5 above, this invention constructs a multi-level interface reinforcement system of "chemical bonding-physical interlocking" in the composite pipe matrix, integrates a stress relief structure, a conductive heating structure, and a pre-embedded sealing structure in the integrated electrofusion welded pipe fitting, and achieves an equal-strength connection between the joint and the pipe body through a graded electrofusion welding process. Simultaneously, the stress activation mechanism of the sealing system achieves long-term reliable sealing under extreme working conditions.

[0112] Example

[0113] This embodiment provides an interface-reinforced, rubber-ringed, electrofused steel-reinforced polyethylene composite pipe and its preparation method, and applies the composite pipe to the gathering and transportation pipeline system of a high-sulfur oil and gas field. The medium transported in this oil and gas field contains 12% hydrogen sulfide (H2S) by mass, 8% carbon dioxide (CO2) by mass, a transport pressure of 6.4 MPa, and a transport temperature of 75°C. The composite pipe prepared in this embodiment has a nominal diameter of 200 mm and a nominal pressure of 6.4 MPa.

[0114] I. Preparation of Composite Pipe Matrix

[0115] This embodiment first involves the preparation of the composite pipe base material.

[0116] 1. Extrusion molding and surface activation treatment of the inner high-density polyethylene layer

[0117] High-density polyethylene resin, along with 1.2% carbon black masterbatch, 0.5% antioxidant, and 0.3% UV absorber by weight, were added to a high-speed mixer. The antioxidant used was pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the UV absorber was 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole. The high-speed mixer was started and mixed at 85°C for 10 minutes to ensure uniform dispersion of the components and form an inner layer mixture.

[0118] The aforementioned inner layer mixture is melt-plasticized using a first single-screw extruder. The first single-screw extruder is divided into four heating zones along the barrel axis, with temperatures set sequentially to 190℃, 200℃, 210℃, and 205℃, and the die head temperature set to 210℃. After being heated and melted in the extruder, the inner layer mixture is extruded through the screw die head to form an inner layer high-density polyethylene pipe blank with an outer diameter of 220 mm and a wall thickness of 8 mm.

[0119] Within 3 seconds of the inner high-density polyethylene (HDPE) pipe blank being extruded from the die, the surface temperature of the pipe blank, measured by an infrared thermometer, was between 190°C and 195°C, placing it in the molten state. An online plasma jet treatment device was then used to activate the outer surface of the pipe blank. The working gas of the plasma jet treatment device was a mixture of nitrogen and acrylic acid, precisely proportioned using a mass flow controller, with acrylic acid comprising 8% by volume. The output power of the plasma jet treatment device was set to 450 watts, the distance between the treatment nozzle and the outer surface of the pipe blank was 15 mm, and the treatment time was 2 seconds. Under these conditions, high-energy particles in the plasma bombarded and activated the molecular chains on the surface of the pipe blank. Simultaneously, the acrylic acid monomers underwent graft polymerization under the action of the plasma, introducing polar functional groups such as carboxyl groups (-COOH) and amino groups (-NH2) onto the outer surface of the inner HDPE pipe blank, providing active sites for subsequent interfacial chemical bonding.

[0120] 2. Online co-extrusion of interface-reinforced adhesive layer

[0121] Within 0.5 seconds after the plasma activation treatment is completed, the activated inner high-density polyethylene pipe blank is sized by a vacuum sizing sleeve. The vacuum degree of the vacuum sizing sleeve is controlled between -0.06 MPa and -0.08 MPa to ensure that the outer diameter of the pipe blank is accurate and stable.

[0122] Simultaneously, maleic anhydride-grafted polyethylene (MAH-g-PE) and ethylene-acrylic acid copolymer (EAA) were premixed uniformly in a high-speed mixer at a mass ratio of 65:35 to form an interface-reinforced adhesive layer material. This material was then added to a second single-screw extruder, with the processing temperature controlled between 210°C and 230°C. Specifically, the temperatures of each heating zone were set to 210°C, 220°C, 225°C, and 230°C, and the die head temperature was set to 225°C. The molten interface-reinforced adhesive layer material was uniformly coated onto the outer surface of the sized inner high-density polyethylene pipe blank through a co-extrusion die. By adjusting the extruder speed and traction speed, the extrusion thickness of the interface-reinforced adhesive layer was controlled to be 0.4 mm.

[0123] During this process, the maleic anhydride groups in the interface-reinforced adhesive layer material react chemically with the amino groups introduced into the outer surface of the inner high-density polyethylene pipe blank in the aforementioned steps to form amide bonds, thus achieving chemical bonding between the interfaces. Simultaneously, the carboxyl groups in the ethylene-acrylic acid copolymer provide the functional group basis for subsequent coordination bonding with the metal reinforcement layer.

[0124] 3. The steel frame reinforcement layer is wound and cured simultaneously with the interface.

[0125] After the interface-reinforced adhesive layer is extruded and covers the outer surface of the inner high-density polyethylene pipe blank, the steel skeleton reinforcement layer is immediately wound. The reinforcement material used is copper-plated steel wire with a surface coated with nano-silica modified epoxy resin, and the diameter of the copper-plated steel wire is 0.8 mm.

[0126] The nano-silica-modified epoxy resin coating on the surface of copper-plated steel wire was prepared as follows: bisphenol A type epoxy resin, methylhexahydrophthalic anhydride curing agent, and silica particles with a particle size of 30 nanometers were mixed at a mass ratio of 100:80:5 and dispersed using a high-speed disperser at 1200 rpm for 30 minutes to form a uniform coating slurry. This slurry was then uniformly coated onto the surface of the copper-plated steel wire using a dip-coating process, followed by pre-curing at 120°C for 10 minutes to form a coating with a thickness of 30 micrometers.

[0127] The copper-plated steel wire coated with nano-silica modified epoxy resin is cross-wound using a precisely controlled winding machine. The winding angle of the winding machine is set to 58 degrees, and a double-layer symmetrical structure is adopted, that is, the first layer winding angle is +58 degrees and the second layer winding angle is -58 degrees. The two layers of steel wire cross to form a diamond-shaped mesh reinforcement structure, and the number of winding layers is 4.

[0128] During the winding process, the copper-plated steel wire being wound is heated online using a medium-frequency induction heating device. The output frequency of the medium-frequency induction heating device is 20 kHz, and the heating coil is wound around the path of the steel wire. The surface temperature of the steel wire is controlled at 145℃±3℃ by adjusting the output power. At this temperature, the nano-silica-modified epoxy resin coating on the surface of the copper-plated steel wire softens rapidly and undergoes a partial curing reaction. The epoxy groups in the coating undergo ring-opening esterification with the carboxyl groups in the interface-reinforced adhesive layer to form covalent bonds. At the same time, the softened coating penetrates into the micro-uneven structure of the interface-reinforced adhesive layer surface, forming physical interlocking. The nano-silica particles in the coating act as nucleating agents, inducing the polyethylene molecular chains in the interface-reinforced adhesive layer to crystallize on its surface during subsequent cooling, forming a transverse crystalline layer with a thickness of 5 to 8 micrometers. This transverse crystalline layer significantly improves the crystallinity and crack propagation resistance of the interface region.

[0129] 4. Coating and shaping of the outer protective layer with high-density polyethylene

[0130] The outer sheath of high-density polyethylene (HDPE) is extruded and coated onto the outer surface of the pre-wound steel reinforcement layer using a third single-screw extruder. The outer HDPE sheath has the same composition as the inner HDPE layer, containing 1.2% carbon black masterbatch, 0.5% antioxidant, and 0.3% UV absorber by weight. The processing temperature of the third single-screw extruder is controlled between 190°C and 210°C, with specific heating zone temperatures set at 190°C, 200°C, 210°C, and 205°C, and the die head temperature set at 210°C. The outer sheath coating thickness is 3 mm.

[0131] After the coating is completed, the composite pipe is rapidly cooled by a vacuum cooling and shaping device. The vacuum cooling and shaping device adopts a segmented cooling method, with the first segment having a cooling water temperature of 60℃, the second segment having a cooling water temperature of 30℃, and the third segment having a cooling water temperature of 20℃, so that the composite pipe is uniformly cooled to below 60℃ during the process, thus completing the preparation of the composite pipe base material.

[0132] II. Prefabrication of Integrated Electrofusion Welded Pipe Fittings

[0133] This embodiment then proceeds to the prefabrication of the integrated electrofusion welded pipe fitting.

[0134] 1. The stress relief groove structure and the embedded conductive mesh on the inner wall of the pipe fitting

[0135] Using injection molding, high-density polyethylene material (the same material as the aforementioned inner high-density polyethylene layer) is injected into a precision mold to form an integral electrofusion welded pipe fitting blank with a socket at one end and a flat end at the other. The inner diameter of the socket of the pipe fitting blank is 220.5 mm, and the length is 150 mm.

[0136] In the mold design, multiple spiral stress relief grooves are formed on the inner wall of the pipe fitting socket. Each spiral stress relief groove has a semi-circular cross-sectional shape with a radius of 0.5 mm and a groove depth of 0.4 mm. The pitch between two adjacent spiral stress relief grooves is 2 mm. These spiral stress relief grooves can absorb and disperse axial and circumferential stresses caused by temperature changes or pressure fluctuations during subsequent use, preventing seal failure due to stress concentration.

[0137] During injection molding, a pre-fabricated mesh-like conductive layer is precisely positioned and embedded into the inner wall surface of the pipe fitting socket using positioning pins within the mold. This mesh-like conductive layer is made of 0.3 mm diameter tin-plated copper wire using a plain weave process, with a mesh count of 20 meshes, meaning 20 meshes per square centimeter. The resistivity of this mesh-like conductive layer at 20°C is 0.02 ohms / square centimeter. The positioning pins ensure a distance of 0.2 mm between the mesh-like conductive layer and the inner wall surface of the pipe fitting socket, allowing the mesh-like conductive layer to be precisely embedded below the polyethylene surface after injection molding, thus guaranteeing conductivity while preventing direct exposure to the external environment.

[0138] 2. Preparation of the interface matching layer between the welding area of ​​the pipe fitting and the pipe body

[0139] A layer of interface-matching slurry is applied to the inner wall surface of the pipe fitting socket using a screen printing process. This interface-matching slurry is composed of maleic anhydride-grafted polyethylene, conductive carbon black, and a coupling agent in a mass ratio of 100:15:3, wherein the coupling agent is γ-aminopropyltriethoxysilane. Maleic anhydride-grafted polyethylene serves as the base resin, exhibiting good compatibility with the interface-reinforced adhesive layer on the outer wall of the pipe body; conductive carbon black is used to uniformly distribute welding heat; and the coupling agent acts as a chemical bridging agent, reacting with the active functional groups in the interface-reinforced adhesive layer during the welding process.

[0140] The above slurry was evenly coated onto the inner wall of the socket using a 200-mesh screen to a thickness of 0.1 mm. After coating, the fitting was placed in an oven and dried at 80°C for 30 minutes to allow the solvent in the slurry to completely evaporate, forming a dry and dense interface matching layer.

[0141] 3. Installation and activation of pre-embedded rubber rings

[0142] A specially designed fluorosilicone rubber ring is installed in the annular groove on the inner wall of the pipe fitting socket. The fluorosilicone rubber ring has an "X" shaped cross-section, a Shore A hardness of 75, and a compression set of less than 15% under 150℃×70 hours. The "X" shaped cross-section has four lips, which can form multiple sealing barriers under pressure, improving sealing reliability.

[0143] Before installation, the fluorosilicone rubber ring undergoes surface activation treatment: The fluorosilicone rubber ring is immersed in an ethanol solution containing 1.5% by mass of a silane coupling agent, wherein the silane coupling agent is γ-glycidoxypropyltrimethoxysilane. The container containing the immersion solution and the fluorosilicone rubber ring is placed in an ultrasonic cleaner and ultrasonically treated at 40°C for 30 minutes at a frequency of 40 kHz. After treatment, the fluorosilicone rubber ring is removed and allowed to air dry naturally at room temperature for 30 minutes. This treatment allows the silane coupling agent molecules to form an active film on the surface of the fluorosilicone rubber through a hydrolysis-condensation reaction. The epoxy groups in this active film can react with the polar groups in the polyethylene material during subsequent welding, achieving chemical bonding between the rubber ring and the polyethylene interface.

[0144] III. Construction of Electrofusion Welding and Sealing System for Composite Pipes and Fittings

[0145] This embodiment then proceeds to the construction of the electrofusion welding and sealing system for the composite pipe and fittings.

[0146] 1. Pretreatment and positioning of the welding end face

[0147] Using an electric scraper, remove the outer high-density polyethylene layer from the end of the composite pipe substrate prepared in step one, exposing an 80 mm long steel skeleton reinforcement layer and an inner high-density polyethylene layer. Use an angle grinder with a fine grinding wheel to smooth the exposed steel skeleton reinforcement layer end, removing burrs and sharp edges. Clean the outer surface of the composite pipe at this end area with acetone to remove oil and impurities.

[0148] Wipe the inner wall of the socket of the integrated electrofusion welded pipe fitting prepared in step two with anhydrous ethanol to ensure it is free of dust and oil. Insert the pretreated end of the composite pipe into the socket of the fitting until it reaches the positioning step at the bottom of the socket. After insertion, use a feeler gauge to measure the fit clearance between the outer wall of the composite pipe and the inner wall of the fitting, ensuring that the clearance is 0.25 mm ± 0.05 mm.

[0149] 2. Implementation of the graded electrofusion welding process

[0150] Connect the output electrode of the electrofusion welding machine to a terminal block on the outside of the integrated electrofusion welding fitting. This terminal block is electrically connected to the mesh-like conductive layer inside the fitting via internal wires. Start the welding program using a step-by-step welding process.

[0151] Preheating stage: Within 30 seconds, the welding voltage is linearly increased from 0 volts to 32 volts and maintained at this voltage for 20 seconds. During this stage, the interface matching layer on the inner wall of the pipe fitting and the interface reinforcement adhesive layer on the outer wall of the composite pipe begin to melt. The temperature gradually rises to about 150°C, and the materials begin to soften and come into contact with each other.

[0152] Melt welding stage: Within 15 seconds, the welding voltage is linearly increased from 32V to 39.5V and maintained at this voltage for 60 seconds. During this stage, the welding interface temperature rises to 230℃±5℃, and the maleic anhydride-grafted polyethylene in the interface matching layer and the maleic anhydride-grafted polyethylene in the interface reinforcement adhesive layer of the composite pipe outer wall completely melt, allowing the molecular chains to gain sufficient mobility. Uniform heating of the mesh-like conductive layer ensures a uniform temperature field throughout the welding area, and the conductive carbon black in the interface matching layer further assists in heat distribution. Simultaneously, the γ-aminopropyltriethoxysilane coupling agent in the interface matching layer undergoes a dehydration condensation reaction with the carboxyl groups in the interface reinforcement adhesive layer, forming a strong covalent bond connection, thus achieving chemical reinforcement of the welding interface.

[0153] Pressure Holding and Cooling Stage: Simultaneously with the welding voltage cut off, an axial pressure of 0.2 MPa is applied to the fitting and composite pipe using hydraulic clamps. This pressure is provided by a hydraulic station and applied through two symmetrically arranged hydraulic cylinders, ensuring uniform pressure distribution on the fitting end face. Cooling continues for 300 seconds, during which the welding interface temperature is monitored via thermocouples until the temperature drops below 80°C. During this process, the molten polymer is fully compacted under pressure, eliminating porosity and microcracks that may occur during welding, forming a dense and high-strength weld joint.

[0154] 3. Stress activation of the rubber ring sealing system

[0155] During the pressure holding and cooling stage after electrofusion welding, the axial pressure applies a continuous axial compressive force to the end of the composite pipe against the fluorosilicone rubber ring pre-embedded in the annular groove of the fitting. This compressive force is approximately 0.15 MPa to 0.2 MPa, causing the "X"-shaped fluorosilicone rubber ring to undergo elastic deformation. Under pressure, the four lips of the fluorosilicone rubber ring tightly adhere to the spiral stress relief grooves on the outer wall of the composite pipe and the inner wall of the fitting, forming four independent sealing barriers. Simultaneously, due to the surface activation treatment performed in step 2.3, the silane coupling agent active film on the surface of the fluorosilicone rubber ring undergoes a chemical reaction with the polyethylene material under contact pressure and residual welding temperature, forming chemical bonds, further improving the long-term reliability of the sealing interface and its resistance to media penetration.

[0156] IV. Finished Product Performance Testing and Parameter Calibration

[0157] This embodiment performs performance testing and parameter calibration on the composite pipe system that has been prepared and welded as described above.

[0158] 1. Axial tensile property testing and feedback calibration of welded joints

[0159] A 500 mm long specimen containing the complete welded joint was cut from the welded composite pipe system, with the welded joint located in the middle of the specimen. The specimen was mounted on a universal testing machine with a range of 500 kN and an accuracy of 0.5. An axial tensile test was performed at an ambient temperature of 23℃ ± 2℃ and a loading rate of 5 mm / min until the specimen failed.

[0160] Record the maximum tensile load of the welded joint. And the location of fracture. The maximum tensile load of the welded joint prepared in this embodiment was tested. The axial tensile load of the composite pipe matrix is ​​215 kN. The value was obtained from testing a pipe sample of the same specification, and it was 220 kN. Calculations yielded... and The ratio is 97.7%, which is higher than the 95% threshold, indicating that the strength of the welded joint has reached the design requirement of equal strength to the pipe body, and no parameter adjustment is required.

[0161] 2. High-temperature and high-pressure cyclic aging test and calibration of the sealing system

[0162] The prepared pipe section with joints was installed in a high-temperature, high-pressure cyclic testing apparatus. This apparatus consists of a high-pressure gas pressurization system, a temperature control system, a pressure cyclic control system, and a leak detection system. The test medium was nitrogen gas containing 10% H2S by mass. This mixed gas was prepared using a standard gas cylinder, uniformly mixed by a gas mixer, and then introduced into the test loop. The test pressure was set to 1.2 times the nominal pressure of the pipe, 6.4 MPa, i.e., 7.68 MPa. The test temperature was 85°C, maintained by an electric heating belt and a temperature controller. Pressure cyclic fatigue testing was conducted at a cycle frequency of 6 cycles / minute, meaning that a complete cycle consisted of the pressure increasing from 0 MPa to 7.68 MPa and then decreasing back to 0 MPa. A total of 5000 cycles were performed.

[0163] During testing, a pressure sensor with a range of 10 MPa and an accuracy of 0.1% was used to monitor the pressure waveform in real time to ensure that the cyclic waveform met the requirements. A helium gas chromatography-mass spectrometry leak detector was used to monitor the leakage rate of the sealing system in real time; the lower limit of detection for the leak detector was [not specified]. Pa·m³ / s. After 5000 cycles of testing, the maximum leakage rate of the sealing system was measured. Pa·m³ / s, below the set failure threshold. The Pa·m³ / s indicates that the sealing system performs well under simulated high sulfur content, high temperature, and high pressure alternating load conditions, and no parameter adjustment is required.

[0164] To further verify the technical effects of the present invention, this embodiment sets up two comparative examples for comparative testing.

[0165] Comparative Example 1: Composite pipe joints prepared by conventional electrofusion welding process

[0166] The composite pipe base material of Comparative Example 1 uses the same structure and materials as in this embodiment, but the welding process uses conventional electrofusion welding. The steps of the conventional electrofusion welding process are as follows: insert the end of the composite pipe into the socket of the electrofusion fitting; use an electrofusion welding machine to weld for 80 seconds at a constant voltage of 39.5 volts; allow it to cool naturally after welding without applying axial pressure. Other steps are the same as in this embodiment.

[0167] Comparative Example 2: Composite pipe joint sealed with ordinary nitrile rubber ring

[0168] The composite pipe substrate and welding process of Comparative Example 2 are the same as those in this embodiment, but a common nitrile rubber ring is used for the sealing structure. This nitrile rubber ring has a circular cross-section, a diameter of 5 mm, and a Shore A hardness of 70. The rubber ring is installed in the same annular groove as in the embodiment, but without surface activation treatment before installation. Other steps are the same as in this embodiment.

[0169] The composite pipe joints prepared in this embodiment, along with those prepared in Comparative Examples 1 and 2, were subjected to axial tensile testing and high-temperature, high-pressure cyclic aging testing, respectively. The testing methods were the same as those described in step four above. The test results are summarized in Table 1.

[0170] Table 1 Comparison of performance test results between this embodiment and the comparative embodiment.

[0171] Test Project This embodiment Comparative Example 1 Comparative Example 2 Maximum tensile load of welded joint (Qianniu) 215 152 214 Ratio of welded joint strength to pipe body strength (%) 97.7 69.1 97.3 fracture location Pipe body Welding interface Pipe body Maximum leakage rate after 5000 cycles (Pa·m / s)

[0172] The test results in Table 1 show that:

[0173] In this embodiment, the maximum tensile load of the welded joint reaches 215 kN, with a strength ratio of 97.7% to the pipe body. The fracture occurs in the pipe body rather than the weld interface, indicating that the graded electrofusion welding process and interface matching layer design of this invention achieve equal strength matching between the joint and the pipe body. Comparative Example 1, using a conventional electrofusion welding process, has a maximum tensile load of only 152 kN and a strength ratio of only 69.1%. The fracture occurs at the weld interface, demonstrating that conventional welding processes struggle to achieve effective connection of the steel skeleton reinforcement layer, making the welded joint a weak link in the entire pipeline system.

[0174] Regarding sealing performance, after 5000 cycles of high-temperature, high-pressure sulfur-containing media, the maximum leakage rate in this embodiment was only [missing information]. The leakage rate was Pa·m³ / s, far below the failure threshold. Comparative Example 2, using ordinary nitrile rubber rings without surface activation treatment, exhibited a leakage rate as high as [missing value] under the same test conditions. Pa·m³ / s indicates severe leakage. This demonstrates that the "X"-shaped fluorosilicone rubber ring of this invention, combined with surface activation treatment and the design of the spiral stress relief groove, exhibits excellent long-term sealing reliability under extreme operating conditions.

[0175] The interface-reinforced, electrofused steel-reinforced polyethylene composite pipe, which passed performance testing, was applied to the aforementioned high-sulfur oil and gas field gathering and transportation pipeline system. The pipeline system has a total length of 15 kilometers, transports a medium at a pressure of 6.4 MPa, a temperature of 75°C, and an H2S content of 12% by mass. The pipeline is buried underground with a soil cover depth of 1.5 meters. After 12 months of continuous operation and monitoring, no leaks occurred in the pipeline system. Infrared thermal imaging at the welded joints showed uniform temperature distribution with no localized overheating, and the sealing system operated normally. This demonstrates that the composite pipe and its preparation method provided by this invention can meet the stringent requirements of gathering and transportation in high-sulfur oil and gas fields.

[0176] In summary, this invention achieves high-strength bonding between the steel skeleton and the polyethylene matrix interface by constructing a multi-level interface reinforcement system of "chemical bonding-physical interlocking-stress relief"; achieves equal strength matching between the welded joint and the pipe body through a graded electrofusion welding process and interface matching layer design; and achieves long-term reliability of the sealing system under extreme working conditions through the synergistic effect of the "X"-shaped fluorosilicone rubber ring, surface activation treatment, and spiral stress relief groove.

[0177] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0178] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An interface enhanced rubber ring electrically fused steel carcass polyethylene composite pipe, characterized in that, The interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe comprises: The composite pipe base material consists of, from the inside out, an inner high-density polyethylene layer, an interface-reinforced adhesive layer, a steel skeleton reinforcement layer, and an outer high-density polyethylene layer. The outer surface of the inner high-density polyethylene layer is introduced with carboxyl and amino polar functional groups after being activated by an online plasma jet treatment device. The working gas of the plasma jet treatment device is a mixture of nitrogen and acrylic acid. High-energy particles in the plasma bombard and activate the molecular chains on the surface of the tube blank. At the same time, the acrylic acid monomer undergoes a graft polymerization reaction under the action of plasma, introducing carboxyl and amino polar functional groups on the outer surface of the inner high-density polyethylene tube blank. The interface-reinforced adhesive layer is a blend of maleic anhydride-grafted polyethylene and ethylene-acrylic acid copolymer. The interface-reinforced adhesive layer covers the outer surface of the inner high-density polyethylene layer. The maleic anhydride groups in the interface-reinforced adhesive layer react chemically with the amino groups on the outer surface of the inner high-density polyethylene layer to form amide bonds. The steel skeleton reinforcement layer is formed by winding copper-plated steel wire coated with nano-silica modified epoxy resin. During the winding process, the nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire undergoes physical interlocking and chemical reaction with the interface reinforcement adhesive layer. During the winding process, the copper-plated steel wire being wound is heated online by a medium-frequency induction heating device, and the heating temperature is controlled between 140°C and 150°C, so that the nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire softens and partially solidifies rapidly. In the softened state, the coating undergoes physical interlocking with the interface reinforcement adhesive layer in the molten state. At the same time, the epoxy groups in the coating react chemically with the carboxyl groups in the interface reinforcement adhesive layer to form covalent bonds. The nano-silica particles in the nano-silica modified epoxy resin coating act as nucleating agents, inducing changes in the crystalline morphology of polyethylene in the interface reinforcement adhesive layer to form a dense transverse crystalline layer. The outer protective layer, a high-density polyethylene layer, covers the outer surface of the steel skeleton reinforcement layer.

2. A method for preparing an interface-reinforced, electrofused steel-reinforced polyethylene composite pipe, characterized in that, Includes the following steps: Step 1: Preparation of the composite pipe base material, specifically including the following sub-steps: Step 1.1: Extrusion molding and surface activation treatment of the inner high-density polyethylene layer: High-density polyethylene resin is mixed with carbon black masterbatch, antioxidant and ultraviolet absorber to form an inner layer mixture. The inner layer mixture is extruded into an inner high-density polyethylene pipe blank through a first single screw extruder. After the inner high-density polyethylene pipe blank is extruded from the die and the surface temperature is maintained in the molten range, the outer surface of the inner high-density polyethylene pipe blank is subjected to online plasma activation treatment using a plasma jet treatment device. Step 1.2: Online co-extrusion of the interface-reinforced adhesive layer: Within 0.5 seconds after completing the plasma activation treatment in Step 1.1, the activated inner high-density polyethylene pipe blank is sized by a vacuum sizing sleeve. Then, the interface-reinforced adhesive layer material formed by blending maleic anhydride grafted polyethylene and ethylene-acrylic acid copolymer is uniformly coated on the outer surface of the inner high-density polyethylene pipe blank through a co-extrusion die using a second single-screw extruder. Step 1.3: Winding and simultaneous curing of the steel skeleton reinforcement layer and the interface: After the interface reinforcement adhesive layer described in step 1.2 is extruded and covers the outer surface of the inner high-density polyethylene pipe blank, copper-plated steel wire coated with nano-silica modified epoxy resin is immediately cross-wound by a winding machine to form a double-layer symmetrical steel skeleton reinforcement layer. During the winding process, the copper-plated steel wire being wound is heated online by a medium-frequency induction heating device, so that the nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire softens and partially cures, and undergoes physical interlocking and chemical reaction with the interface reinforcement adhesive layer in the molten state. Step 1.4: Coating and shaping of the outer sheath with high-density polyethylene: The outer sheath with high-density polyethylene material is extruded and coated on the outer surface of the pipe blank that has been wound with the steel skeleton reinforcement layer through a third single screw extruder. Then, the composite pipe is cooled to below 60°C through a vacuum cooling and shaping device to complete the preparation of the composite pipe base material. Step 2: Prefabrication of integrated electrofusion welded pipe fittings, specifically including the following sub-steps: Step 2.1: Embedding of stress relief groove structure and conductive mesh on inner wall of pipe fitting: High-density polyethylene material is injected into mold using injection molding process to form an integral electrofusion welded pipe fitting blank with a socket on one end and a flat end on the other. In the mold design, multiple spiral stress relief grooves are formed on the inner wall of the socket of the pipe fitting. During the injection molding process, the pre-made mesh conductive layer is accurately positioned by the positioning pin in the mold and embedded in the inner wall surface of the socket of the pipe fitting. Step 2.2: Preparation of interface matching layer between pipe fitting welding area and pipe body: A layer of interface matching layer slurry is coated on the inner wall surface of the pipe fitting socket by screen printing process, and then dried after coating. Step 2.3: Installation and activation of the pre-embedded rubber ring: Install the fluorosilicone rubber ring in the annular groove on the inner wall of the socket of the pipe fitting. Before installation, immerse the fluorosilicone rubber ring in an ethanol solution containing silane coupling agent for surface activation treatment. Step 3: Electrofusion welding and sealing system construction of composite pipes and fittings, specifically including the following sub-steps: Step 3.1: Pretreatment and positioning of the welding end face: Remove the outer high-density polyethylene layer of the composite pipe base material prepared in Step 1 to expose the steel skeleton reinforcement layer and the inner high-density polyethylene layer. Grind the exposed end of the steel skeleton reinforcement layer flat and clean the outer surface of the composite pipe in this end area. Then clean the inner wall of the socket of the integrated electrofusion welded pipe fitting prepared in Step 2 and insert the pretreated end of the composite pipe base material into the socket of the integrated electrofusion welded pipe fitting. Step 3.2: Implementation of the graded electrofusion welding process: Connect the output electrode of the electrofusion welding machine to the terminal block on the outside of the integrated electrofusion welding pipe fitting, start the welding program, and perform welding using a graded welding process, which includes a preheating stage, a fusion welding stage, and a pressure holding and cooling stage in sequence. Step 3.3: Stress activation of the rubber ring sealing system: In the pressure holding and cooling stage after the electrofusion welding in step 3.2, axial pressure is applied to the integrated electrofusion welded pipe fitting and the composite pipe base material by a hydraulic clamp. This causes the end of the composite pipe base material to apply a continuous axial extrusion force to the fluorosilicone rubber ring pre-embedded in the annular groove of the integrated electrofusion welded pipe fitting. This causes the fluorosilicone rubber ring to undergo elastic deformation and tightly adhere to the spiral stress relief groove on the outer wall of the composite pipe base material and the inner wall of the integrated electrofusion welded pipe fitting.

3. The method of preparing the interface enhanced rubber hose electrically fused steel carcass polyethylene composite pipe according to claim 2, characterized in that, The working gas of the plasma jet treatment device in step 1.1 is a mixture of nitrogen and acrylic acid, wherein the volume percentage of acrylic acid in the mixture is 8%, the output power of the plasma jet treatment device is 450 watts, the treatment distance is 15 mm, and the treatment time is 2 seconds. In step 1.2, the mass ratio of maleic anhydride-grafted polyethylene to ethylene-acrylic acid copolymer in the interface-reinforced adhesive layer material is 65:35, and the extrusion thickness of the interface-reinforced adhesive layer is controlled between 0.3 mm and 0.5 mm. In step 1.3, the diameter of the copper-plated steel wire is 0.8 mm. The nano-silica modified epoxy resin coating on the surface of the copper-plated steel wire is composed of bisphenol A type epoxy resin, methyl hexahydrophthalic anhydride curing agent, and silica particles with a particle size of 30 nanometers in a mass ratio of 100:80:

5. The thickness of the nano-silica modified epoxy resin coating is 30 micrometers. The winding angle of the copper-plated steel wire is 58 degrees. The temperature of the copper-plated steel wire being wound by the medium frequency induction heating device is controlled between 140°C and 150°C. The outer sheath high-density polyethylene material mentioned in step 1.4 has the same composition as the inner layer mixture of the inner high-density polyethylene layer mentioned in step 1.

1.

4. The method of preparing the interface enhanced rubber hose electrically fused steel carcass polyethylene composite pipe according to claim 2, characterized in that, The spiral stress relief groove described in step 2.1 has a semi-circular cross-sectional shape with a radius of 0.5 mm and a groove depth of 0.4 mm. The pitch between two adjacent spiral stress relief grooves is 2 mm. The mesh conductive layer is woven from tin-plated copper wire with a diameter of 0.3 mm and a mesh count of 20 mesh. The resistance of the mesh conductive layer at 20°C is 0.02 ohms / cm². After the mesh conductive layer is embedded in the inner wall surface of the pipe fitting socket, the distance between the mesh conductive layer and the inner wall surface of the pipe fitting socket is 0.2 mm. The interface matching layer slurry in step 2.2 is composed of maleic anhydride grafted polyethylene, conductive carbon black and coupling agent in a mass ratio of 100:15:3, wherein the coupling agent is γ-aminopropyltriethoxysilane, the coating thickness of the interface matching layer slurry is 0.1 mm, and the drying treatment is drying at 80°C for 30 minutes. The fluorosilicone rubber ring in step 2.3 has an X-shaped cross-section, a Shore A hardness of 75, and a compression set of less than 15% at 150°C for 70 hours. The surface activation treatment involves immersing the fluorosilicone rubber ring in an ethanol solution containing 1.5% by mass of a silane coupling agent and ultrasonically treating it at 40°C for 30 minutes. The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

5. The method of preparing interface enhanced rubber hose electrically fused steel carcass polyethylene composite pipe according to claim 2, characterized in that, In step 3.1, the length of the outer sheath high-density polyethylene layer removed from the end of the composite pipe base is 80 mm. After the pre-treated end of the composite pipe base is inserted into the socket of the integrated electrofusion welded pipe fitting, the fitting gap between the outer wall of the composite pipe base and the inner wall of the integrated electrofusion welded pipe fitting is 0.2 mm to 0.3 mm. In step 3.2, the preheating stage of the graded welding process involves linearly increasing the welding voltage to 32 volts within 30 seconds and maintaining this voltage for 20 seconds. The fusion welding stage of the graded welding process involves linearly increasing the welding voltage from 32 volts to 39.5 volts within 15 seconds and maintaining this voltage for 60 seconds. The pressure holding and cooling stage of the graded welding process involves applying an axial pressure of 0.2 MPa to the integrated electrofusion welded pipe fitting and the composite pipe base material using a hydraulic clamp while the welding voltage is cut off, and continuing to cool for 300 seconds until the welding interface temperature drops below 80°C. In step 3.3, the elastic deformation of the fluorosilicone rubber ring causes the four lips of the fluorosilicone rubber ring to fit tightly against the spiral stress relief groove on the outer wall of the composite pipe base and the inner wall of the integrated electrofusion welded pipe fitting.

6. The method of preparing interface enhanced rubber hose core steel cord reinforced polyethylene composite pipe according to claim 2, characterized in that, Step 4, following step 3, involves finished product performance testing and parameter calibration, specifically including the following sub-steps: Step 4.1: Axial Tensile Performance Testing and Feedback Calibration of Welded Joints: A specimen containing the complete welded joint is cut from the completed welded composite pipe system. The specimen is mounted on a universal testing machine for axial tensile testing, and the maximum tensile load of the welded joint is recorded. And the fracture location, the test results obtained Axial tensile load of composite pipe base material Compare, if the Below the If the result is 95%, then adjust the welding voltage curve in step 3.2 according to the test results; Step 4.2: High-Temperature and High-Pressure Cyclic Aging Test and Calibration of the Sealing System: The pipe section with joints prepared in Step 3 is installed in a high-temperature and high-pressure cyclic testing device. Nitrogen gas containing 10% H2S is used as the test medium. The test pressure is 1.2 times the nominal pressure of the pipe, and the test temperature is 85℃. Pressure cyclic fatigue testing is performed at a cycle frequency of 6 times / minute for a total of 5000 cycles. During the test, the leakage rate of the sealing system is monitored in real time using a pressure sensor and a helium gas spectrometer leak detector. If the leakage rate exceeds a certain threshold within the test cycle... If the value is Pa·m³ / s, then adjust the surface activation treatment time of the fluorosilicone rubber ring in step 2.3 or the pretreatment accuracy of the composite tube end in step 3.1 based on the failure analysis results.

7. The method for preparing the interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe according to claim 6, characterized in that, The axial tensile test described in step 4.1 was conducted at an ambient temperature of 23℃±2℃ with a loading rate of 5 mm / min. The specific method for adjusting the welding voltage curve in step 3.2 based on the test results, as described in step 4.1, is as follows: when the... With the When the ratio is in the range of 85% to 95%, increase the holding voltage of the fusion welding stage described in step 3.2 by 0.5 volts; when the With the When the ratio is less than 85%, the holding voltage of the fusion welding stage described in step 3.2 is increased by 1.0 volt, and the holding cooling time of the holding cooling stage described in step 3.2 is extended by 60 seconds.

8. The method of preparing interface enhanced rubber hose electrically fused steel carcass polyethylene composite pipe according to claim 2, characterized in that, The inner layer mixture mentioned in step 1.1 is formed by mixing high-density polyethylene resin with 1.2% carbon black masterbatch, 0.5% antioxidant, and 0.3% ultraviolet absorber by means of a high-speed mixer at 85°C for 10 minutes. The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the ultraviolet absorber is 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole. In step 1.1, the extruder temperature of the first single-screw extruder is controlled between 190°C and 210°C. The online plasma activation treatment is performed within 3 seconds after the inner high-density polyethylene pipe blank is extruded from the die head and the surface temperature is maintained in the molten state range of 185°C to 195°C. In step 1.2, the processing temperature of the second single-screw extruder is controlled between 210°C and 230°C; The processing temperature of the third single-screw extruder described in step 1.4 is controlled between 190°C and 210°C.

9. The method of preparing interface enhanced rubber hose electrically fused steel carcass polyethylene composite pipe according to claim 2, characterized in that, When the nano-silica modified epoxy resin coating described in step 1.3 undergoes physical interlocking and chemical reaction with the interface-reinforced adhesive layer in the molten state under softened and partially cured conditions, the nano-silica particles in the nano-silica modified epoxy resin coating act as nucleating agents to induce changes in the crystal morphology of polyethylene in the interface-reinforced adhesive layer, forming a dense transverse crystalline layer.

10. The use of an interface enhanced rubber hose pipe of electrically melted steel skeleton polyethylene composite pipe, characterized in that, The interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe as described in claim 1 or the interface-reinforced rubber ring electrofusion steel-reinforced polyethylene composite pipe prepared by any one of claims 2 to 9 can be applied to the gathering and transportation pipeline system of high-sulfur oil and gas fields or to the riser system of deep-sea oil and gas extraction at a water depth of more than 1,500 meters.

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