High-temperature-resistant 3pe anticorrosion pipeline resistant to cathode stripping and preparation method thereof

Abstract

The present application belongs to the technical field of 3PE anticorrosion, and particularly relates to a high-temperature-resistant and cathode-stripping-resistant 3PE anticorrosion pipeline and a preparation method thereof. The present application performs systematic chemical synergistic modification on the epoxy bottom layer, the intermediate adhesive layer and the polyethylene surface layer of the pipeline, specifically: the epoxy bottom layer is modified by phenolic resin and amino silane to form a heat-resistant dense barrier; the intermediate layer is reacted with maleic anhydride grafted polyethylene through amino silane to build a chemical bridge connecting the upper and lower layers; the surface layer is modified by fluorine primary amine to graft glycidyl methacrylate onto high-density polyethylene to introduce hydrophobic and oleophobic chains and reactive functional groups; the structure synergistically acts through the high-temperature stability of the bottom layer, the bidirectional chemical bridging ability of the intermediate layer and the inert hydrophobic characteristics of the surface layer to improve the upper limit of the long-term use temperature of the pipeline, the anti-stripping ability and the anti-medium permeation ability, and provides a solution for long-term protection of the pipeline in harsh environments.

Description

Technical Field

[0001] This invention belongs to the field of 3PE anti-corrosion technology, specifically relating to a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe and its preparation method. Background Technology

[0002] Steel pipelines are critical infrastructure for transporting oil and gas resources. They operate for extended periods in complex soil, electrolyte, and stress environments, making corrosion and protection crucial factors determining pipeline lifespan and operational safety. Three-layer polyethylene (3PE) anti-corrosion coating technology is the preferred solution for pipeline corrosion protection.

[0003] The standard 3PE anti-corrosion layer is a typical three-layer composite structure: the bottom layer is a fusion-bonded epoxy powder coating, which is electrostatically sprayed and fused to the surface of the preheated steel pipe to form a continuous anti-corrosion base layer with excellent insulation and compatibility with cathodic protection systems; the middle layer is an adhesive layer, usually made of polymers such as maleic anhydride-grafted polyethylene, which is co-extruded and wound onto the epoxy powder coating to achieve physical bonding and transition between the non-polar polyethylene surface layer and the polar epoxy bottom layer; the top layer is a high-density or medium-density polyethylene extruded layer, which provides the main mechanical protection against soil stress, rock scratches and water penetration.

[0004] Although 3PE anti-corrosion technology is mature, its performance still faces severe challenges under harsh conditions such as high temperature and complex corrosion: First, the intermediate adhesive layer mainly relies on the physical entanglement and polar adsorption of molecular chains with the upper and lower layers, lacking strong chemical bonds. Under long-term thermal aging, soil stress, or temperature difference cycling, interlayer delamination is prone to occur, leading to the failure of the protective system. Second, the long-term operating temperature of standard epoxy powder layer is usually no higher than 80℃. When the temperature of the transported medium is high or it is used in thermal pipelines, its adhesion and deformation resistance decrease sharply, while the adhesive layer softens and the interlayer bonding force is severely weakened. In addition, under high-temperature cathodic protection environments, the epoxy underlayer of the traditional 3PE structure is not sufficiently resistant to the penetration of corrosive media.

[0005] Therefore, developing a new type of 3PE anti-corrosion pipe that can enhance interlayer bonding, improve high-temperature resistance and cathodic disbondment resistance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe and its preparation method, so as to solve the above-mentioned technical problems.

[0007] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe includes the following steps:

[0009] S1. Select a complete steel pipe that is free from mechanical damage and oil stains. Perform shot blasting on the inside and outside of the steel pipe to remove rust, so that the rust removal grade of the steel pipe surface reaches Sa2.5. Use clean and dry air to blow the surface and preheat the steel pipe to 210~240℃ and hold for 1~3 minutes.

[0010] S2. Using electrostatic spraying process, silane-modified epoxy resin powder is evenly sprayed onto the preheated outer surface of the steel pipe, allowing it to melt, flow, and reach a gel-cured state to form an epoxy underlayer.

[0011] S3. When the temperature of the epoxy base layer drops to 100~150℃, use a co-extrusion winding equipment to melt-extrude silane-modified maleic anhydride-grafted polyethylene at 190~210℃ as the intermediate layer.

[0012] S4. When the intermediate layer is cooled to 150~180℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 200~220℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0013] S5. Further heat treatment is carried out on the steel pipe containing the three-layer composite structure at a temperature of 170~200℃ for 30~90s. After cooling to room temperature, a high-temperature resistant and cathodic disbondment resistant 3PE anti-corrosion pipe is obtained.

[0014] As a further improvement, the preparation method of the silane-modified epoxy resin powder is as follows: bisphenol A type epoxy resin, phenolic resin curing agent, aminosilane coupling agent, pigments, fillers and additives are placed in a high-speed mixer and premixed at 60~80℃ for 10~20min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder, with the extruder temperature set at 120~140℃ and the screw speed at 100~300rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0015] As a further improvement, the mass ratio of the bisphenol A type epoxy resin, phenolic resin curing agent, and aminosilane coupling agent is 100:20~35:1~5; the aminosilane coupling agent is γ-aminopropyltriethoxysilane or N-aminoethyl-γ-aminopropyltrimethoxysilane.

[0016] As a further improvement, the preparation method of the silane-modified maleic anhydride-grafted polyethylene is as follows: maleic anhydride-grafted polyethylene granules, aminosilane coupling agent and esterification reaction catalyst are premixed in a mixer to obtain a premix; the premix is ​​subjected to reactive melt extrusion through a twin-screw extruder, the extruder temperature is set to 170~200℃ and the material residence time is 1~3min; after cooling, it is granulated by a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0017] As a further improvement, the mass ratio of the maleic anhydride-grafted polyethylene granules to the aminosilane coupling agent is 100:3~6; the grafting rate of the maleic anhydride-grafted polyethylene granules is 0.8~1.5%; the aminosilane coupling agent is N-aminoethyl-γ-aminopropyltrimethoxysilane; and the esterification reaction catalyst is dibutyltin dilaurate, with an addition amount of 0.1~0.3% of the mass of the maleic anhydride-grafted polyethylene granules.

[0018] As a further improvement, the preparation method of the fluoroamine-modified GMA-grafted high-density polyethylene is as follows: high-density polyethylene granules, fluoroamine-modified glycidyl methacrylate, dicumyl peroxide, and antioxidant are mixed to obtain a mixture; under nitrogen protection, the mixture is subjected to a melt grafting reaction through a twin-screw extruder, with the extruder temperature controlled in stages along the screw, gradually increasing from 160~180℃ in the feeding section to 190~210℃ in the reaction section, and the material residence time is 2~5 minutes; after the extruded melt is subjected to a devolatilization device to remove unreacted monomers, it is then subjected to underwater pelletizing and drying to obtain fluoroamine-modified GMA-grafted high-density polyethylene.

[0019] As a further improvement, the mass ratio of the high-density polyethylene granules, fluoroprimary amine modified glycidyl methacrylate, and dicumyl peroxide is 100:1.5~4:0.1~0.3.

[0020] As a further improvement, the preparation method of the fluoroprimary amine modified glycidyl methacrylate is as follows: glycidyl methacrylate is mixed with a fluoroprimary amine and stirred for 5-8 hours under a nitrogen atmosphere at 65-75°C. After the reaction is completed, the mixture is cooled to room temperature to obtain a reaction solution. The reaction solution is added dropwise to n-hexane under stirring, the solid product is filtered out, washed 2-3 times with fresh n-hexane, and dried under vacuum at 40-50°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0021] As a further improvement, the fluorinated primary amine is 1H,1H-perfluoroheptylamine or 1H,1H-perfluorooctylamine, the molar ratio of glycidyl methacrylate to the fluorinated primary amine is 1:0.8~1.2, and the volume of n-hexane is 5~10 times the volume of the reaction liquid.

[0022] The present invention also provides a 3PE anti-corrosion pipe that is resistant to high temperature and cathodic disbondment.

[0023] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0024] By introducing phenolic resin curing agent and aminosilane coupling agent, a three-dimensional network with high cross-linking density is formed in the anti-corrosion substrate: phenolic resin significantly improves the glass transition temperature and thermal stability of the pipeline coating, while silane coupling agent enhances the adhesion between the coating and the steel pipe substrate through chemical bonding. On the other hand, the Si-O-Si inorganic network formed by its hydrolysis interpenetrates with the epoxy organic network, greatly improving the density, mechanical strength and resistance to media penetration of the coating.

[0025] By grafting fluorinated primary amine-modified glycidyl methacrylate onto high-density polyethylene chains, the introduced fluorocarbon long chains give the surface excellent hydrophobicity and oleophobicity, reducing the adsorption and penetration rate of corrosive media. In addition, the double bonds retained after the ring-opening reaction of glycidyl methacrylate ensure successful grafting, while the newly generated hydroxyl groups provide additional active reaction sites with the intermediate layer.

[0026] By utilizing the reaction of an aminosilane coupling agent with the anhydride ring on maleic anhydride-modified polyethylene, silane molecules are covalently linked to the polymer chain, generating new carboxyl groups. In subsequent co-extrusion and heat treatment processes, the intermediate layer undergoes esterification with the hydroxyl groups of the bottom and surface layers through its carboxyl groups. The silanols in the intermediate layer can also react with the hydroxyl groups, achieving a strong interfacial chemical bond between the three layers, mainly based on covalent bonds, thus solving the problem of interlayer delamination that easily occurs in traditional physical bonding. Attached Figure Description

[0027] Figure 1 This is an ATR-FTIR result of the silane-modified epoxy resin powder prepared in Example 1;

[0028] Figure 2 This is an ATR-FTIR result of the silane-modified maleic anhydride-grafted polyethylene prepared in Example 1.

[0029] Figure 3 This is an ATR-FTIR result of the fluoroprimary amine modified GMA grafted high-density polyethylene prepared in Example 1. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or manufacturer's conditions shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0031] In this invention, the pigments, fillers, additives and antioxidants involved are all conventional components in this technical field; the specific types can be conventionally adjusted according to the processing technology, physical properties and cost requirements of the final product, and usually will not have a substantial impact on the three-layer chemical modification system claimed by this invention and its core properties such as high temperature resistance, cathodic disbondment resistance and interlayer bonding strength.

[0032] In this invention, pigments and fillers may be selected from, but are not limited to, one or more of quartz powder, titanium dioxide, mica powder, barium sulfate, carbon black, or mica iron oxide; additives may include, but are not limited to, leveling agents (such as acrylates), defoamers (such as benzoin), wetting and dispersing agents, curing accelerators, or ultraviolet absorbers; antioxidants may be selected from, but are not limited to, one or more compound systems of hindered phenolic antioxidants and phosphite-based auxiliary antioxidants; unless otherwise specified, the references to these components in the embodiments and claims of this invention include the above conventional selections, and do not depart from the protection scope of this invention due to conventional substitution of their specific types.

[0033] The high-density polyethylene (HDPE) granules described in this invention are a conventional material suitable for pipeline anti-corrosion outer protective layers. Based on the common knowledge of those skilled in the art, pipeline-grade HDPE with a density of 0.940~0.965 g / cm³ and a melt flow rate (190℃ / 2.16kg) of 0.1~0.5 g / 10min can be selected. The weight-average molecular weight of the HDPE is in the range of 150,000~250,000 g / mol. HDPE with these parameters provides excellent mechanical protection while ensuring the smooth progress of the grafting reaction and good bonding with the intermediate layer. Those skilled in the art can select a suitable HDPE grade within this conventional range according to the specific pipeline specifications and service environment; such selection does not depart from the scope of protection of this invention.

[0034] In the following examples and comparative examples, the seamless steel pipes are all L245NS seamless steel pipes.

[0035] Example 1: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, comprising the following steps:

[0036] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0037] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0038] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude the silane-modified maleic anhydride grafted polyethylene at 190℃ as the intermediate layer.

[0039] S4. When the intermediate layer is cooled to 150℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 200℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0040] S5. Further heat treatment is carried out on the steel pipe containing the three-layer composite structure at a temperature of 170℃ for 30 seconds. After cooling to room temperature, a high-temperature resistant and cathodic disbondment resistant 3PE anti-corrosion pipe is obtained.

[0041] In this embodiment, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 100g of phenolic resin curing agent, 5g of γ-aminopropyltriethoxysilane, 150g of pigments and fillers, and 5g of additives are placed in a high-speed mixer and premixed at 60°C for 10 minutes to obtain a premix. The premix is ​​then melt-blended using a twin-screw extruder, with the extruder temperature set at 130°C and the screw speed at 100 rpm. After cooling and brittle fracture, the extruded material is pulverized using a micro-pulverizer to obtain silane-modified epoxy resin powder. The reaction equation between γ-aminopropyltriethoxysilane and bisphenol A type epoxy resin is:

[0042] ;

[0043] The ATR-FTIR image of the silane-modified epoxy resin powder prepared in this embodiment is as follows: Figure 1 As shown in the figure; it can be seen from the figure that 1100cm -1 The characteristic absorption peak of Si-OC appears at 1350 cm⁻¹. -1 The presence of a characteristic absorption peak for the CN bond at [location] indicates that the aminosilane undergoes a ring-opening reaction with the epoxy resin; the characteristic peak for the epoxy group (1250 cm⁻¹) [is also present]. -1 The relatively low intensity indicates that some epoxy groups participated in the reaction.

[0044] In this embodiment, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 0.8%), 15g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.0g of dibutyltin dilaurate (esterification reaction catalyst) are added to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation using a twin-screw extruder, with the extruder temperature set at 170℃, and the material is kept in the reaction zone for 3min by adjusting the screw speed; the material is then cooled in a water tank at 20℃, where it rapidly solidifies and sets, and is granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene. The reaction equation for N-aminoethyl-γ-aminopropyltrimethoxysilane and maleic anhydride-grafted polyethylene is:

[0045] ;

[0046] The ATR-FTIR image of the silane-modified maleic anhydride-grafted polyethylene prepared in this embodiment is as follows: Figure 2 As shown. From Figure 2 It can be seen that at 1690cm -1 The presence of a characteristic absorption peak nearby is consistent with the expected spectral characteristics of the reaction between amino groups and acid anhydrides to form amide bonds, indicating that silane has successfully modified maleic anhydride-grafted polyethylene. The reaction principle is as follows: the primary amino group in silane is a strong nucleophile, and the acid anhydride ring structure has high reactivity. After melt co-extrusion, the two undergo a nucleophilic ring-opening reaction, in which the amino group attacks the carbonyl carbon of the acid anhydride, and the acid anhydride ring-opens to form an amide bond and a carboxyl group.

[0047] In this embodiment, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0048] Preparation of fluoroprimary amine-modified glycidyl methacrylate: 1H,1H-perfluoroheptylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:0.8 and reacted at 65°C for 5 h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. While stirring, the reaction solution was added dropwise to n-hexane, with the volume of n-hexane being 5 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed twice with fresh n-hexane, and then dried under vacuum at 40°C to constant weight to obtain fluoroprimary amine-modified glycidyl methacrylate. The reaction equation is as follows:

[0049]

[0050] Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 7.5g of fluoroamine-modified glycidyl methacrylate, 0.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 160℃ in the feeding section to 190℃ in the reaction section. The material was kept in the reaction section for 5 minutes by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was granulated and dried underwater. The water temperature was controlled at 25℃. The granules were rapidly cooled and shaped, and after dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0051] The ATR-FTIR image of the fluoroamine-modified GMA-grafted high-density polyethylene prepared in this embodiment is as follows: Figure 3 As shown in the figure; it can be seen from the figure that 1200cm -1 A strong and broad characteristic absorption peak of the CF bond appears at 1730 cm⁻¹. -1 A characteristic peak of ester bond appears at 3300 cm⁻¹. -1 The presence of a characteristic absorption peak of hydroxyl groups at the point indicates that the fluoroprimary amine has successfully reacted with GMA and grafted onto the high-density polyethylene chain.

[0052] Example 2: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, comprising the following steps:

[0053] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 240℃ and hold for 3 minutes to ensure uniform heat penetration.

[0054] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0055] S3. When the epoxy base layer temperature drops to 150℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude silane-modified maleic anhydride-grafted polyethylene at 210℃ as the intermediate layer.

[0056] S4. When the intermediate layer is cooled to 180°C, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 220°C as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0057] S5. Further heat treatment is performed on the steel pipe containing the three-layer composite structure at a temperature of 200℃ for 90 seconds. After cooling to room temperature, a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe is obtained.

[0058] In this embodiment, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 175g of phenolic resin curing agent, 25g of N-aminoethyl-γ-aminopropyltrimethoxysilane, 200g of pigments and fillers, and 6.5g of additives are placed in a high-speed mixer and premixed at 80°C for 20 minutes to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 120°C and the screw speed at 300 rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0059] In this embodiment, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 1.5%), 30g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 0.5g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 200℃, and the material is kept in the reaction zone for 1min by adjusting the screw speed; the material is then cooled in a water tank at a cooling water temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0060] In this embodiment, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0061] Preparation of fluoroprimary amine modified glycidyl methacrylate: 1H,1H-perfluoroheptylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:1.2 and stirred at 75°C for 8 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. The reaction solution was added dropwise to n-hexane with stirring, the volume of n-hexane being 10 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed three times with fresh n-hexane, and then dried under vacuum at 50°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0062] Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 20g of fluoroamine-modified glycidyl methacrylate, 1.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 180℃ in the feeding section to 210℃ in the reaction section. The material was kept in the reaction section for 2 minutes by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was underwater pelletized and dried. The water temperature was controlled at 25℃. The pellets were rapidly cooled and shaped, and after dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0063] Example 3: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, comprising the following steps:

[0064] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 220℃ and hold for 2 minutes to ensure uniform heat penetration.

[0065] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0066] S3. When the epoxy base layer temperature drops to 120℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude silane-modified maleic anhydride grafted polyethylene at 200℃ as the intermediate layer.

[0067] S4. When the intermediate layer is cooled to 170℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 210℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0068] S5. Further heat treatment is carried out on the steel pipe containing the three-layer composite structure at a temperature of 190℃ for 60s. After cooling to room temperature, a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe is obtained.

[0069] In this embodiment, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 150g of phenolic resin curing agent, 15g of N-aminoethyl-γ-aminopropyltrimethoxysilane, 150g of pigments and fillers, and 6g of additives are placed in a high-speed mixer and premixed at 70°C for 15 minutes to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 140°C and the screw speed at 200 rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0070] In this embodiment, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 1.0%), 20g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.5g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 185℃, and the material is kept in the reaction zone for 2min by adjusting the screw speed; the material is then cooled in a water tank at a temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0071] In this embodiment, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0072] Preparation of fluoroprimary amine modified glycidyl methacrylate: 1H,1H-perfluorooctylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:1 and stirred at 70°C for 6.5 h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. The reaction solution was added dropwise to n-hexane with stirring, the volume of n-hexane being 8 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed three times with fresh n-hexane, and then dried under vacuum at 45°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0073] Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 12.5g of fluoroamine-modified glycidyl methacrylate, 1g of dicumyl peroxide (free radical initiator), and 1.3g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 170℃ in the feeding section to 200℃ in the reaction section. The material residence time in the reaction section was controlled to be 3.5min by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was subjected to underwater pelleting and drying. The water temperature was controlled at 25℃, and the pellets were rapidly cooled and shaped. After dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0074] Comparative Example 1: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, differing from Example 1 in that the epoxy resin powder used in the preparation of the base layer is not modified, and includes the following steps:

[0075] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0076] S2. Using high-voltage electrostatic spraying equipment, epoxy resin powder is evenly sprayed onto the outer surface of the preheated steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is evenly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0077] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude the silane-modified maleic anhydride grafted polyethylene at 190℃ as the intermediate layer.

[0078] S4. When the intermediate layer is cooled to 150℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 200℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0079] S5. Further heat treatment is performed on the steel pipe containing the three-layer composite structure at a temperature of 170℃ for 30 seconds. After cooling to room temperature, 3PE anti-corrosion pipe is obtained.

[0080] In this comparative example, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 0.8%), 15g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.0g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 170℃, and the material is kept in the reaction zone for 3min by adjusting the screw speed; the material is then cooled in a water tank at a cooling water temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0081] In this comparative example, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0082] Preparation of fluoroprimary amine modified glycidyl methacrylate: 1H,1H-perfluoroheptylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:0.8 and stirred at 65°C for 5 h under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. The reaction solution was added dropwise to n-hexane with stirring, the volume of n-hexane being 5 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed twice with fresh n-hexane, and then dried under vacuum at 40°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0083] Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 7.5g of fluoroamine-modified glycidyl methacrylate, 0.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 160℃ in the feeding section to 190℃ in the reaction section. The material was kept in the reaction section for 5 minutes by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was underwater pelletized and dried. The water temperature was controlled at 25℃. The pellets were rapidly cooled and shaped, and after dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0084] Comparative Example 2: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, differing from Example 1 in that the maleic anhydride-grafted polyethylene is not modified with silane, and includes the following steps:

[0085] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0086] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0087] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt and extrude the maleic anhydride grafted polyethylene granules at 190℃ as the intermediate layer.

[0088] S4. When the intermediate layer is cooled to 150℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 200℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0089] S5. Further heat treatment is performed on the steel pipe containing the three-layer composite structure at a temperature of 170℃ for 30 seconds. After cooling to room temperature, 3PE anti-corrosion pipe is obtained.

[0090] In this comparative example, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 100g of phenolic resin curing agent, 5g of γ-aminopropyltriethoxysilane, 150g of pigments and fillers, and 5g of additives are placed in a high-speed mixer and premixed at 60℃ for 10min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 130℃ and the screw speed at 100rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0091] In this comparative example, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0092] 1. Preparation of fluoroprimary amine modified glycidyl methacrylate: 1H,1H-perfluoroheptylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:0.8 and stirred at 65°C for 5 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. The reaction solution was added dropwise to n-hexane with stirring, the volume of n-hexane being 5 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed twice with fresh n-hexane, and then dried under vacuum at 40°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0093] 2. Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 7.5g of fluoroamine-modified glycidyl methacrylate, 0.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 160℃ in the feeding section to 190℃ in the reaction section. The material was kept in the reaction section for 5 minutes by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was granulated and dried underwater. The water temperature was controlled at 25℃. The granules were rapidly cooled and shaped, and after dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0094] Comparative Example 3: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, differing from Example 1 in that the high-density polyethylene is not grafted, and includes the following steps:

[0095] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0096] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0097] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude the silane-modified maleic anhydride grafted polyethylene at 190℃ as the intermediate layer.

[0098] S4. When the intermediate layer is cooled to 150°C, the co-extrusion winding equipment is used to melt and extrude high-density polyethylene granules at 200°C as the surface layer, which is then wound and wrapped around the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0099] S5. Further heat treatment is performed on the steel pipe containing the three-layer composite structure at a temperature of 170℃ for 30 seconds. After cooling to room temperature, 3PE anti-corrosion pipe is obtained.

[0100] In this comparative example, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 100g of phenolic resin curing agent, 5g of γ-aminopropyltriethoxysilane, 150g of pigments and fillers, and 5g of additives are placed in a high-speed mixer and premixed at 60℃ for 10min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 130℃ and the screw speed at 100rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0101] In this comparative example, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 0.8%), 15g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.0g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 170℃, and the material is kept in the reaction zone for 3min by adjusting the screw speed; the material is then cooled in a water tank at a cooling water temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0102] Comparative Example 4: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, differing from Example 1 in that the glycidyl methacrylate was not modified with fluoroprimary amine, and includes the following steps:

[0103] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0104] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0105] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude the silane-modified maleic anhydride grafted polyethylene at 190℃ as the intermediate layer.

[0106] S4. When the intermediate layer is cooled to 150°C, continue to use the co-extrusion winding equipment to melt and extrude GMA grafted high-density polyethylene at 200°C as the surface layer, and wrap it around the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure.

[0107] S5. Further heat treatment is performed on the steel pipe containing the three-layer composite structure at a temperature of 170℃ for 30 seconds. After cooling to room temperature, 3PE anti-corrosion pipe is obtained.

[0108] In this comparative example, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 100g of phenolic resin curing agent, 5g of γ-aminopropyltriethoxysilane, 150g of pigments and fillers, and 5g of additives are placed in a high-speed mixer and premixed at 60℃ for 10min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 130℃ and the screw speed at 100rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0109] In this comparative example, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 0.8%), 15g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.0g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 170℃, and the material is kept in the reaction zone for 3min by adjusting the screw speed; the material is then cooled in a water tank at a cooling water temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0110] In this comparative example, the preparation method of GMA-grafted high-density polyethylene is as follows: 500g of high-density polyethylene granules, 7.5g of glycidyl methacrylate, 0.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant are mixed to obtain a mixture. Under nitrogen protection, the mixture is subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature is controlled in stages along the screw, gradually increasing from 160℃ in the feeding section to 190℃ in the reaction section. The material is kept in the reaction section for 5 minutes by adjusting the screw speed. After unreacted monomers are removed by a devolatilization device, the extruded melt is granulated and dried underwater. The water temperature is controlled at 25℃. The granules are rapidly cooled and shaped, and after dehydration and drying, GMA-grafted high-density polyethylene is obtained.

[0111] Comparative Example 5: A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, differing from Example 1 in that the steel pipe containing the three-layer composite structure is not subjected to further heat treatment, and includes the following steps:

[0112] S1. Select seamless steel pipes with intact appearance, no mechanical damage, and no oil stains. Use a shot blasting machine to remove rust from the surface of the steel pipe. The abrasive used is a mixture of steel shot and steel grit. Continue until the rust removal grade of the steel pipe surface reaches Sa2.5. The anchor pattern depth is controlled at 50~90μm. Preheat to 210℃ and hold for 1 minute to ensure uniform heat penetration.

[0113] S2. Using high-voltage electrostatic spraying equipment, silane-modified epoxy resin powder is uniformly sprayed onto the preheated outer surface of the steel pipe. The electrostatic voltage is controlled at 60kV and the powder supply pressure is 0.3MPa, so that the powder is uniformly adsorbed under the action of the electric field. The spraying thickness is 200μm. The preheating of the steel pipe melts and levels the powder, and the coating reaches the gel curing state to form an epoxy underlayer.

[0114] S3. When the epoxy base layer temperature drops to 100℃, immediately use a co-extrusion winding device to wrap it, and melt-extrude the silane-modified maleic anhydride grafted polyethylene at 190℃ as the intermediate layer.

[0115] S4. When the intermediate layer is cooled to 150℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroamine-modified GMA-grafted high-density polyethylene at 200℃ as the surface layer, and wrap it around the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure, thus obtaining a 3PE anti-corrosion pipe.

[0116] In this comparative example, the preparation method of silane-modified epoxy resin powder is as follows: 500g of bisphenol A type epoxy resin, 100g of phenolic resin curing agent, 5g of γ-aminopropyltriethoxysilane, 150g of pigments and fillers, and 5g of additives are placed in a high-speed mixer and premixed at 60℃ for 10min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder with the extruder temperature set at 130℃ and the screw speed at 100rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder.

[0117] In this comparative example, the preparation method of silane-modified maleic anhydride-grafted polyethylene is as follows: 500g of maleic anhydride-grafted polyethylene granules (maleic anhydride grafting rate of 0.8%), 15g of liquid N-aminoethyl-γ-aminopropyltrimethoxysilane, and 1.0g of dibutyltin dilaurate (esterification reaction catalyst) are added together to a high-speed mixer and premixed at 1000rpm for 5min at room temperature to obtain a premix; the premix is ​​then subjected to reactive melt extrusion granulation through a twin-screw extruder, with the extruder temperature set at 170℃, and the material is kept in the reaction zone for 3min by adjusting the screw speed; the material is then cooled in a water tank at a cooling water temperature of 20℃, and the material is rapidly solidified and shaped, and then granulated using a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene.

[0118] In this comparative example, the preparation method of fluoroprimary amine modified GMA grafted high-density polyethylene is as follows:

[0119] 1. Preparation of fluoroprimary amine modified glycidyl methacrylate: 1H,1H-perfluoroheptylamine and glycidyl methacrylate (GMA) were mixed at a molar ratio of 1:0.8 and stirred at 65°C for 5 hours under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain a reaction solution. The reaction solution was added dropwise to n-hexane with stirring, the volume of n-hexane being 5 times the volume of the reaction solution. A solid product appeared. The solid product was collected by filtration, washed twice with fresh n-hexane, and then dried under vacuum at 40°C to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

[0120] 2. Preparation of fluoroamine-modified GMA-grafted high-density polyethylene: 500g of high-density polyethylene granules, 7.5g of fluoroamine-modified glycidyl methacrylate, 0.5g of dicumyl peroxide (free radical initiator), and 1.5g of antioxidant were mixed to obtain a mixture. Under nitrogen protection, the mixture was subjected to a melt grafting reaction through a twin-screw extruder. The extruder temperature was controlled in stages along the screw, gradually increasing from 160℃ in the feeding section to 190℃ in the reaction section. The material was kept in the reaction section for 5 minutes by adjusting the screw speed. After unreacted monomers were removed by a devolatilization device, the extruded melt was granulated and dried underwater. The water temperature was controlled at 25℃. The granules were rapidly cooled and shaped, and after dehydration and drying, fluoroamine-modified GMA-grafted high-density polyethylene was obtained.

[0121] Performance testing

[0122] 1. Resistance to cathodic disbondment

[0123] The 3PE anti-corrosion pipes prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to cathodic stripping radius tests, guided by the testing standard GB / T 23257-2017 "Polyethylene Anti-corrosion Coating for Buried Steel Pipelines".

[0124] First, a 25kV leak detection voltage was used to inspect the sample for pinholes, and samples without pinholes were selected for the experiment. Then, a hole with a radius of 6.4mm was drilled in the middle of the specimen, penetrating the anti-corrosion layer to expose the substrate. A plastic cylinder was glued to the pipe hole with sealant, and a 3% sodium chloride solution was added into the cylinder until it reached 4 / 5 of the tank height. Distilled water was added during the test to maintain the liquid level. A platinum electrode was inserted into the solution and connected to the positive terminal of a DC power supply. The bottom of the pipe was connected to the negative terminal of a DC power supply, and the potential was controlled at -1.5V. The samples were placed in environments of 55℃ and 85℃ for 30 days respectively.

[0125] After completion, the sample was removed and cooled to room temperature. Using a blade, the coating was scored 2 cm outwards in eight different directions along a 360° circumference, centered on the drilled hole, penetrating the anti-corrosion layer to expose the substrate. The blade was then inserted into the gap between the anti-corrosion layer and the steel pipe, and the anti-corrosion layer was pried open along the scored lines with horizontal force until the anti-corrosion layer showed obvious resistance to prying. Starting from the edge of the test hole, the peeling distance of each scored line was measured, which is the cathodic disbondment distance of the sample. The experimental results are shown in Table 1.

[0126]

[0127] As can be seen from Table 1, the embodiments of the present invention have excellent resistance to cathodic disbondment. Under the test condition of 55°C, the cathodic disbondment length of the three embodiments is stable within 5 mm. In the more stringent high-temperature test of 85°C, the cathodic disbondment length can still be maintained within 9 mm. The results show that the anti-corrosion system of the present invention has excellent resistance to cathodic disbondment. Moreover, the experimental results data of Examples 1 to 3 are relatively similar, indicating that stable and high-performance results can be obtained within the parameter range described in the claims of the present invention.

[0128] As can be seen from Table 1, the cathodic disbondment performance of samples 1-3 was significantly worse than that of samples 1-3, indicating that the chemical modification of each layer in this invention made a key contribution to the cathodic disbondment performance. Among them, the epoxy underlayer of Comparative Example 1 was not modified, resulting in a significant increase in cathodic disbondment length. The lack of silane groups led to insufficient crosslinking density and heat resistance. Under cathodic action, corrosive anions were more likely to penetrate and accumulate between the coating and the metal interface, affecting the adhesion of the anti-corrosion layer. Comparative Example 3 did not undergo surface grafting modification, resulting in weak bonding between the surface layer and the intermediate layer. The lack of fluorocarbon chains also reduced the anti-penetration ability, making it easier for corrosive media to reach the underlayer. The sample of Comparative Example 2 had the worst cathodic disbondment resistance, indicating that the intermediate layer, as an adhesive, lost its role as a bridge and could not form effective chemical bonds with the upper and lower layers, thus causing the anti-corrosion layer to peel off as a whole under penetration.

[0129] 2. Long-term stability at high temperatures

[0130] High-temperature aging adhesion tests were conducted on Examples 1-3 and Comparative Examples 1-3. A spark leak detector was used to check for leaks in the samples, and samples without leaks were selected for testing. The samples were placed in a heat-resistant container, with sufficient water added to fully immerse them, and subjected to heat aging at 95°C for 168 hours. After cooling for 1 hour, the adhesion of the anti-corrosion coating was tested using the pull-off method to evaluate the long-term bonding stability of the anti-corrosion coating at high temperatures. The experimental results are shown in Table 2.

[0131]

[0132] As shown in Table 2, Examples 1-3 exhibited excellent high-temperature bonding stability. After undergoing rigorous thermal aging at 95°C for 168 hours, the adhesion retention rate of all three examples remained stable at around 80%, significantly higher than Comparative Examples 1-3 and Comparative Example 5. Furthermore, the experiment revealed that the failure mode after aging in Examples 1-3 was cohesive failure. The results indicate that the highly cross-linked epoxy network formed by the curing of phenolic resin and the modification of the siloxane network exhibit excellent structural stability at high temperatures, effectively inhibiting polymer chain relaxation and degradation. The high bond energy of the chemical bonds connecting the three layers makes them resistant to breakage under long-term thermal action, thus enabling the pipeline to possess excellent thermal stability.

[0133] The results of Comparative Example 5 show that its initial adhesion is significantly lower than that of the Example, and the adhesion after aging decreases significantly. This indicates that the lack of further heat treatment steps means that the active functional groups preset in each layer of material cannot be fully activated to complete the interfacial chemical reaction. The interfacial chemical bond is not fully formed, so its initial adhesion mainly depends on physical bonding. A large number of strong chemical bonds cannot be formed between the layers. Under long-term thermal action, the physical bond will be rapidly weakened, affecting the long-term thermal stability of the pipeline.

[0134] 3. Basic corrosion resistance

[0135] To comprehensively evaluate the impermeability and corrosion resistance of the samples, chemical immersion tests were conducted on the samples of the examples and comparative examples to simulate harsh chemical corrosion environments. A 3.5 wt% sodium chloride solution was selected to simulate a neutral salt spray / soil corrosion environment, and a 10 vol% sulfuric acid solution was selected to simulate an acidic corrosion environment. The samples were immersed in the above solutions at a constant temperature of 40°C for 60 consecutive days. After immersion, the samples were removed, rinsed with deionized water, and dried. The presence of blistering, rust, discoloration, or peeling on the sample surface was observed and recorded. The results are shown in Table 3.

[0136]

[0137] As can be seen from Table 3, the embodiments of the present invention exhibit excellent chemical corrosion resistance. After immersion in two harsh corrosive media for 60 days, the coatings of Examples 1 to 3 remained intact. There was no change in 3.5% NaCl solution, and only slight discoloration without bubbling or peeling occurred in 10% H2SO4 solution. This indicates that the present invention constructs a dense, complete, and stable protective system through the synergistic effect of three layers: a high-density cross-linked bottom layer, a chemically bonded bridge in the middle layer, and an inert hydrophobic protective layer on the surface. This system can effectively block the penetration and erosion of corrosive media of different properties.

[0138] The sample in Comparative Example 1 lacked modification of the epoxy underlayer, resulting in insufficient density and adhesion of the underlayer. Corrosive media could easily penetrate from the edges or defects to the steel substrate interface, initiating matrix corrosion. The sample in Comparative Example 2 lacked modification of the middle layer, resulting in a lack of chemical bonding bridging effect. Therefore, corrosive media could easily diffuse between layers, exhibiting large-area interfacial blistering and delamination. The sample in Comparative Example 3 used ordinary high-density polyethylene, which has poor chemical resistance in acidic solutions and cannot provide effective protection for the underlying layer, leading to a significant decrease in overall protective performance. The sample in Comparative Example 4 performed well in salt water. Okay, this shows that the basis of chemical bonding exists. However, in an acidic environment, bubbling and discoloration occur, indicating that the lack of fluorocarbon chains reduces the chemical inertness and impermeability of the surface layer, thus affecting the overall protective effect. The sample in Comparative Example 5 used modified materials, but no further heat treatment was carried out during the pipe preparation process, and the reaction time was insufficient. Therefore, the chemical reaction between the interfaces could not be fully carried out, resulting in a loose interlayer bond. As a result, corrosive media can easily penetrate into the loose interlayer, causing multiple interlayer bubbling and delamination. This proves that a further heat treatment step is an indispensable and important step to achieve a tight bond between the layers.

[0139] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, characterized in that, Specifically, the following steps are included: S1. Select a complete steel pipe that is free from mechanical damage and oil stains. Perform shot blasting on the inside and outside of the steel pipe to remove rust, so that the rust removal grade of the steel pipe surface reaches Sa2.

5. Use clean and dry air to blow the surface and preheat the steel pipe to 210~240℃ and hold for 1~3 minutes. S2. Using electrostatic spraying process, silane-modified epoxy resin powder is evenly sprayed onto the preheated outer surface of the steel pipe, allowing it to melt, flow, and reach a gel-cured state to form an epoxy underlayer. S3. When the temperature of the epoxy base layer drops to 100~150℃, use a co-extrusion winding equipment to melt-extrude silane-modified maleic anhydride-grafted polyethylene at 190~210℃ as the intermediate layer. S4. When the intermediate layer is cooled to 150~180℃, continue to use the co-extrusion winding equipment to melt-extrude the fluoroprimary amine modified GMA grafted high-density polyethylene at 200~220℃ as the surface layer, and wind it onto the surface of the intermediate layer to obtain a steel pipe with a three-layer composite structure. S5. Further heat treatment is carried out on the steel pipe containing the three-layer composite structure at a temperature of 170~200℃ for 30~90s. After cooling to room temperature, a high-temperature resistant and cathodic disbondment resistant 3PE anti-corrosion pipe is obtained. The preparation method of the silane-modified epoxy resin powder is as follows: bisphenol A type epoxy resin, phenolic resin curing agent, aminosilane coupling agent, pigments, fillers and additives are placed in a high-speed mixer and premixed at 60~80℃ for 10~20min to obtain a premix. The premix is ​​then melt-blended through a twin-screw extruder, with the extruder temperature set at 120~140℃ and the screw speed at 100~300rpm. After the extruded material is cooled and broken into brittle fragments, it is pulverized by a micro-pulverizer to obtain silane-modified epoxy resin powder. The preparation method of the silane-modified maleic anhydride-grafted polyethylene is as follows: maleic anhydride-grafted polyethylene granules, aminosilane coupling agent and esterification reaction catalyst are premixed in a mixer to obtain a premix; the premix is ​​subjected to reactive melt extrusion through a twin-screw extruder, the extruder temperature is set to 170~200℃ and the material residence time is 1~3min; after cooling, it is granulated by a pelletizer to obtain silane-modified maleic anhydride-grafted polyethylene. The preparation method of the fluoroamine-modified GMA-grafted high-density polyethylene is as follows: high-density polyethylene granules, fluoroamine-modified glycidyl methacrylate, dicumyl peroxide, and antioxidant are mixed to obtain a mixture; under nitrogen protection, the mixture is subjected to a melt grafting reaction through a twin-screw extruder, with the extruder temperature controlled in stages along the screw, gradually increasing from 160~180℃ in the feeding section to 190~210℃ in the reaction section, and the material residence time is 2~5 minutes; after the extruded melt is subjected to a devolatilization device to remove unreacted monomers, it is then subjected to underwater pelletizing and drying to obtain fluoroamine-modified GMA-grafted high-density polyethylene; The preparation method of the fluoroprimary amine modified glycidyl methacrylate is as follows: glycidyl methacrylate is mixed with a fluoroprimary amine and stirred for 5-8 hours under nitrogen atmosphere at 65-75℃. After the reaction is completed, the mixture is cooled to room temperature to obtain a reaction solution. The reaction solution is added dropwise to n-hexane under stirring, the solid product is filtered out, washed 2-3 times with fresh n-hexane, and dried under vacuum at 40-50℃ to constant weight to obtain fluoroprimary amine modified glycidyl methacrylate.

2. The method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe according to claim 1, characterized in that, The mass ratio of the bisphenol A type epoxy resin, phenolic resin curing agent, and aminosilane coupling agent is 100:20~35:1~5; the aminosilane coupling agent is γ-aminopropyltriethoxysilane or N-aminoethyl-γ-aminopropyltrimethoxysilane.

3. The method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe according to claim 1, characterized in that, The mass ratio of maleic anhydride-grafted polyethylene granules to aminosilane coupling agent is 100:3~6; the grafting rate of the maleic anhydride-grafted polyethylene granules is 0.8~1.5%; the aminosilane coupling agent is N-aminoethyl-γ-aminopropyltrimethoxysilane; the esterification reaction catalyst is dibutyltin dilaurate, and the addition amount is 0.1~0.3% of the mass of maleic anhydride-grafted polyethylene granules.

4. The method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe according to claim 1, characterized in that, The mass ratio of the high-density polyethylene granules, fluoroprimary amine modified glycidyl methacrylate, and dicumyl peroxide is 100:1.5~4:0.1~0.

3.

5. The method for preparing a high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe according to claim 1, characterized in that, The fluorinated primary amine is 1H,1H-perfluoroheptylamine or 1H,1H-perfluorooctylamine, the molar ratio of glycidyl methacrylate to the fluorinated primary amine is 1:0.8~1.2, and the volume of n-hexane is 5~10 times the volume of the reaction liquid.

6. A high-temperature resistant and cathodic disbondment-resistant 3PE anti-corrosion pipe, characterized in that, The 3PE anti-corrosion pipe with high temperature resistance and cathodic disbondment resistance as described in any one of claims 1 to 5 is prepared.

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