Single-component polyurea material lining composite pipe

Abstract

The invention discloses a single-component polyurea material lining composite pipe which comprises a pipe, a cement lining layer is arranged in the pipe, a polyurea adhesion primer layer used for connection is arranged on the inner side of the cement lining layer, and a surface polyurea material is arranged on one side of the polyurea adhesion primer layer. A nodular cast iron pipe reinforcing layer is arranged on the surface of the cement lining layer. A'foundation + core 'dual anti-corrosion system is formed by the cement lining layer and the surface polyurea material; after the surface polyurea material is cured, cement lining micropores are completely sealed, permeation of corrosion factors such as moisture, chloride ions and acid-base media is blocked, and the service life is prolonged; a polyurea adhesion primer layer is used as a key'bridge ', strong bonding is realized by virtue of chemical reaction characteristics of epoxy primer, and the epoxy primer and silicate components are chemically combined; it is ensured that the inner layer protection structure composed of the cement lining layer, the polyurea adhesion primer layer and the surface polyurea material is tightly combined, and the problems of layering, cracking and the like are avoided.

Description

Technical Field

[0001] This invention relates to the field of ductile iron pipe technology, specifically to a composite pipe lined with a single-component polyurea material. Background Technology

[0002] Single-component polyurea is a high-performance protective material that combines the excellent properties of polyurea (such as high elasticity, abrasion resistance, and corrosion resistance) with the ease of application of a single-component system.

[0003] In existing technologies, ductile iron pipes are mainly treated with an inner cement lining and an outer coating of traditional anti-corrosion paint for corrosion protection. While the inner cement lining can provide some protection against corrosion to the cast iron substrate inside the pipe, the cement layer is a porous material. After the pipe has been in operation for a period of time, the alkaline substances dissolved from the lining will increase the hardness and pH value of the water, polluting the water quality of the pipeline. Furthermore, the traditional anti-corrosion paint applied to the outer wall cannot provide long-term effective corrosion protection in highly corrosive environments, and its wear resistance is also poor. In complex corrosive environments such as chemical wastewater and high-salinity coastal waters, existing ductile iron pipes are easily corroded, resulting in a significantly shortened service life and failing to meet the requirements for long-term stable operation.

[0004] To address this, we have introduced a composite pipe lined with a single-component polyurea material. Summary of the Invention

[0005] The purpose of this invention is to provide a composite pipe lined with a single-component polyurea material to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a single-component polyurea material-lined composite pipe, comprising: a pipe; The pipe consists of, from the inside out, a surface polyurea material, a polyurea primer layer, a cement lining layer, and a ductile iron pipe reinforcing layer; The reinforcing layer of ductile iron pipe, as the bottom layer of the pipe from the inside out, is the supporting foundation of the entire composite pipe. It is made of ductile iron as the core material and formed by centrifugal casting process. It relies on the excellent tensile strength of ductile iron. As the innermost layer of the pipe, the surface polyurea material is in direct contact with the fluid medium being transported, and is the core line of defense to ensure the cleanliness of the medium and protect the inner wall of the pipe from corrosion. The polyurea adhesion primer layer is located between the surface polyurea material and the cement lining layer, and is a key transitional structure for solving the compatibility of the two different materials and strengthening the interlayer bond. The cement lining layer, located inside the reinforcing layer of the ductile iron pipe and outside the polyurea primer layer, is a crucial intermediate structure connecting the metal structure and the organic coating. It is primarily made from high-grade silicate cement, formed through centrifugal spraying and curing. This three-layer structure forms a progressive protection system from the inside out: "core protection – interface connection – basic protection." The surface polyurea material directly contacts the transported medium, undertaking the main functions of corrosion prevention and wear resistance. The polyurea primer layer ensures a tight bond between the surface polyurea material and the cement lining layer, preventing coating peeling. The cement lining layer provides a flat and stable base for the inner protective structure, while also helping to block the penetration of corrosive media. Together, these three elements constitute a comprehensive protective barrier inside the pipeline. The surface of the cement lining is reinforced with a ductile iron pipe. The ductile iron pipe reinforcement layer wraps around the outside of the cement lining and serves as the core of mechanical support for the composite pipe. It can withstand soil pressure and ground load impact in the buried environment, as well as wind load and vibration during overhead installation. This prevents the pipeline from deforming or breaking. At the same time, it provides physical protection for the inner cement lining, preventing it from cracking or falling off due to external pressure or collision, thus ensuring the integrity and stability of the overall pipeline structure.

[0007] Preferably, the thickness of the reinforcing layer of the ductile iron pipe is controlled between 6mm and 13.6mm. This thickness range is determined based on the pressure requirements and mechanical properties of different application scenarios. A thickness of 6mm can meet the support requirements of low-pressure municipal branch pipes (such as residential inlet pipes), while a thickness of 13.6mm can be adapted to high-pressure chemical transmission pipes, long-distance water transmission trunk pipes, and other scenarios. This avoids insufficient support due to excessive thickness and prevents material waste and increased pipe weight due to excessive thickness, thus balancing practicality and economy.

[0008] Preferably, the carbon content of the reinforcing layer of the ductile iron pipe is 3.3% to 3.6%, the silicon content is 3.3% to 3.5%, the chromium content is less than or equal to 0.03%, and the manganese content is less than or equal to 0.3%. This composition ratio is precisely controlled. The carbon content of 3.3% to 3.6% and the silicon content of 3.3% to 3.5% can ensure that the ductile iron material has high strength and good casting performance, and guarantee the rigidity and forming quality of the reinforcing layer. The chromium content of ≤0.03% and the manganese content of ≤0.3% can reduce the influence of impurity elements on the toughness of the material, avoid the pipe from becoming brittle in low-temperature environments, and at the same time reduce the local performance defects caused by component segregation, ensuring that the overall mechanical properties of the reinforcing layer are uniform and stable.

[0009] Preferably, the cement lining layer is centrifugally sprayed with a thickness of 3-5 mm, using a high-grade silicate cement mix. After curing in a curing furnace, the high-grade silicate cement forms a dense structure with excellent compressive strength and alkaline protection capabilities, effectively preventing corrosion of the ductile iron pipe wall. The centrifugal spraying process allows the cement slurry to be evenly distributed on the inner wall of the pipe, forming a dense, void-free lining layer, avoiding problems such as uneven thickness and rough surface caused by manual application. The 3-5 mm thickness ensures that the cement lining layer has sufficient compressive strength and alkaline protection capabilities without increasing the pipe weight or affecting the internal conveying diameter due to excessive thickness. The high-grade silicate cement further enhances the density and impermeability of the lining layer, strengthening the alkaline passivation protection effect on the inner wall of the ductile iron pipe.

[0010] Preferably, the polyurea adhesion primer layer is an epoxy primer, the main components of which are epoxy resin and amine curing agent. Epoxy primer has excellent adhesion and chemical corrosion resistance. Epoxy resin, as a film-forming base material, can penetrate into the micropores of the cement lining layer to form a mechanical anchor. After the amine curing agent undergoes a cross-linking reaction with the epoxy resin, it can form a dense network structure, blocking the penetration of corrosive media such as moisture and salt through the primer layer. At the same time, it provides a compatible bonding interface for the subsequently sprayed surface polyurea material, ensuring the bonding strength between the two layers and avoiding delamination.

[0011] Preferably, the epoxy resin is a bisphenol A type epoxy resin, which is the main body of the film formation and provides excellent adhesion, chemical resistance and hardness. Amine curing agents, such as polyamides or modified cycloaliphatic amines, react with bisphenol A epoxy resin to form a dense network structure, exhibiting excellent permeability and adhesion properties. This allows them to effectively penetrate the microporous structure of the cement lining and form a mechanical anchoring effect. Bisphenol A epoxy resin possesses good stability, weather resistance, and adhesion properties, forming a stable bond with the silicate components of the cement lining. It is also widely available and cost-effective, making it suitable for large-scale industrial production. Polyamide curing agents feature room temperature curing and good toughness, enhancing the impact and crack resistance of the primer layer. Modified cycloaliphatic amine curing agents offer advantages such as fast curing speed and strong chemical resistance, allowing for flexible selection based on ambient temperature and construction period requirements to meet the needs of different construction scenarios.

[0012] Preferably, the surface polyurea material is mainly composed of isocyanate-terminated prepolymers, and is cured by triggering a chain growth reaction through moisture in the air. This curing method does not require complex two-component mixing equipment and can be applied by high-pressure airless spraying, simplifying the construction process and reducing the technical requirements for construction personnel. The elastomeric network formed by the cured polyurea material has both high tensile strength and elongation at break, which can adapt to pressure fluctuations and slight deformations during pipeline operation, avoid coating cracking, and ensure long-term protective effect.

[0013] Preferably, a cement lining layer is obtained by uniformly coating the inner wall of the ductile iron pipe with high-grade silicate cement using a centrifugal spraying process.

[0014] Preferably, an epoxy primer is uniformly applied to the surface of the cement lining layer after sandblasting or grinding using airless spraying or roller coating, and a polyurea-adhesive primer layer is formed after the primer has cured.

[0015] Preferably, after the polyurea adhesive primer layer has cured, a single-component polyurea material is sprayed to form a surface polyurea material.

[0016] This invention also provides a manufacturing process for a composite pipe lined with a single-component polyurea material, specifically including the following steps: S1. First, according to the composition requirements of carbon content 3.3%~3.6%, silicon content 3.3%~3.5%, chromium content ≤0.03%, and manganese content ≤0.3%, select high-purity pig iron, scrap steel, and alloy additives (ferrosilicon, ferromanganese, etc.) to ensure that the impurity content of raw materials meets national standards. Raw materials are put into a medium-frequency induction furnace and melted at a temperature of 1450-1500℃. After the molten metal is completely melted and the composition is uniform, spheroidizing agents (such as magnesium alloys) and inoculants (such as silicon-barium alloys) are added. Spheroidizing treatment is carried out by the injection method or wire feeding method to make the graphite in the cast iron spherical, thereby improving the toughness and strength of the material. After spheroidizing, the molten metal is poured into a centrifugal casting machine mold that rotates at high speed (the speed is adjusted according to the diameter of the pipe, usually 800-1200 r / min). Under the action of centrifugal force, the molten metal adheres tightly to the inner wall of the mold and cools and forms a tubular blank. The cooling rate is controlled at 5-10℃ / min to avoid cracks caused by excessive cooling. After the casting cools to room temperature, it is demolded and the riser and flash are removed. The inner and outer surfaces of the pipe are machined by mechanical cutting to ensure that the thickness of the reinforcing layer of the ductile iron pipe is controlled between 6mm and 13.6mm and the surface roughness Ra≤12.5μm, so as to provide a good foundation for the subsequent cement lining layer to adhere.

[0017] S2. Select high-grade silicate cement of grade 42.5 or above, and prepare the slurry according to the mass ratio of cement:water:admixture (water-reducing agent, retarder) = 1:0.3-0.35:0.01-0.02. The mixing time should not be less than 5 minutes to ensure that the slurry is uniform and free of lumps, and the fluidity should be controlled at 180-200mm (standard cone slump). Fix the pretreated ductile iron pipe (with no oil or rust on the inner wall) on a centrifugal sprayer and rotate it at a speed of 300-500r / min. At the same time, spray the cement slurry evenly on the inner wall of the pipe through a high-pressure spray gun. During the spraying process, control the moving speed of the spray gun (10-15cm / s) and the spraying pressure (0.8-1.2MPa) to ensure that the coating thickness is uniform and the final thickness reaches 3-5mm. After spraying, place the pipe in a curing room with a temperature of 20-25℃ and a relative humidity of ≥80% and cure it for more than 7 days using steam curing or natural curing. Spray water every 4 hours for the first 3 days to prevent surface cracking. After curing, test the strength of the cement lining layer to ensure that the compressive strength is ≥30MPa and there are no hollow or falling off phenomena. The cement lining layer 12 needs to be fully cured and the surface should be dry and free of dust. The roughness should be improved by sandblasting or grinding to reach Sa2.5 grade, with a roughness Ra=30-50μm.

[0018] S3. After the cement lining layer 12 is cured, the inner wall is polished using a wet grinding process (sandpaper grit 320-400) to remove surface dust and burrs, so that the surface roughness Ra reaches 6.3-12.5μm. Then, it is cleaned with compressed air (pressure 0.5-0.6MPa) and then wiped with acetone or alcohol to remove oil and residual impurities. Mix epoxy resin (such as bisphenol A type epoxy resin) and amine curing agent (such as polyamide or modified cycloaliphatic amine) at a mass ratio of 2-3:1 at room temperature (20-25℃) for 3-5 minutes to ensure uniform mixing. The mixture should be used within 1 hour after preparation to avoid primer curing failure. Apply the prepared epoxy primer evenly to the inner wall of the cement lining using a brush or roller. The coating thickness should be controlled at 30-50μm. Avoid missed areas and drips during the application process. After application, allow it to cure for 4-6 hours at room temperature and in a well-ventilated environment. After curing, test the adhesion of the primer layer to ensure that the adhesion is ≥5MPa (cross-cut test). During the sandblasting process, defects such as pitting and pinholes were found in the pipes. The cracks were repaired with epoxy mortar, followed by the application of epoxy or polyurethane primer to enhance adhesion. Then, a single-component polyurea was evenly sprayed using a high-pressure airless spraying device.

[0019] S4. Select a single-component polyurea material with isocyanate-terminated prepolymer as the main component. Before use, the material needs to be preheated at 40-50℃ for 30-60 minutes to reduce the viscosity and ensure smooth spraying. After preheating, the viscosity of the material should be controlled at 500-800 mPa. s; Pour the preheated polyurea material into a high-pressure airless sprayer (spraying pressure 15-20MPa) and spray it onto the inner wall of the cured polyurea adhering primer layer. Control the moving speed of the sprayer (8-12cm / s) and the spraying distance (20-30cm) to ensure uniform coating thickness. The thickness of a single spray is 50-100μm. Depending on the design requirements, it can be sprayed in 2-3 times, with a total thickness of 150-300μm. After spraying, the chain growth reaction of the polyurea material is triggered by the moisture in the air. It is then naturally cured at room temperature (20-25℃) and relative humidity of 40% to 60%. Avoid touching the coating during the initial curing stage (first 2 hours). After 24 hours, it is fully cured. After curing, the coating performance is tested to ensure that the impact strength is ≥5kJ / m² and the chemical corrosion resistance (5% hydrochloric acid immersion for 72 hours) is normal.

[0020] S5. Control the thickness to 0.5-1.5mm by adjusting the spraying speed and pressure, and apply in two alternating coats.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) A dual anti-corrosion system of "basic + core" is formed by the cement lining layer and the surface polyurea material. The cement lining layer is formed by centrifugal spraying of high grade silicate cement to form a 3-5mm dense alkaline protective layer. The alkaline environment with pH value ≥12 generates a passivation film on the inner wall of the ductile iron pipe, blocking the direct contact between the substrate and the transport medium, thus achieving basic anti-corrosion. After the surface polyurea material is cured, it forms a highly cross-linked urea bond structure, which completely seals the micropores of the cement lining and blocks the penetration of corrosive factors such as water, chloride ions, and acid and alkali media. This composite structure can solve the shortcomings of traditional pipe anti-corrosion, enabling the pipeline to operate stably for a long time in complex corrosive environments (such as chemical wastewater and high salinity in coastal areas), significantly extending its service life. (2) By using the polyurea adhesion primer layer as a key “bridge”, the chemical reaction characteristics of epoxy primer achieve strong bonding. Bisphenol A type epoxy resin can penetrate the micropores of cement lining and form a chemical bond with silicate components. The amine curing agent and epoxy resin cross-link to form a dense network transition layer. Even in the temperature fluctuation environment of municipal pipelines in winter low temperature and summer sun exposure, or under the conditions of vibration and thermal expansion and contraction during pipeline operation, the polyurea coating can be prevented from peeling off. This ensures that the inner protective structure composed of cement lining layer, polyurea adhesion primer layer and surface polyurea material is tightly bonded and does not have problems such as delamination and cracking, thus ensuring the continuous effectiveness of the inner protective function. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a frontal structural diagram of the present invention; Figure 3 This is a schematic diagram of the structure of the present invention from a side section; Figure 4 This is a three-dimensional structural diagram of the pipe of the present invention; Figure 5 This is a process flow diagram of the present invention.

[0023] In the diagram: 1. Pipe; 11. Ductile iron pipe reinforcing layer; 12. Cement inner lining layer; 13. Surface polyurea material; 14. Polyurea adhesive primer layer. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0025] Please see Figure 1-5 This invention provides a technical solution: a single-component polyurea-lined composite pipe, comprising: pipe 1, which serves as the overall frame of the composite pipe. Through a layered nested design of "outer rigid support + middle transition protection + inner precision protection", it integrates the functional advantages of the ductile iron pipe reinforcing layer 11, cement lining layer 12, polyurea adhesive primer layer 14, and surface polyurea material 13. This not only avoids the defects of single pipe materials (such as the weak corrosion resistance of pure cast iron pipes and the poor rigidity of pure polyurea pipes), but also adapts to the installation and use needs of various scenarios such as municipal, chemical, and mining industries, achieving the full life cycle value of "one-time installation and long-term stability".

[0026] As the "mechanical skeleton" of the composite pipe, the ductile iron pipe reinforcing layer 11 provides stable structural support and risk resistance through precise composition control and thickness gradient design. In terms of composition, the carbon content of 3.3% to 3.6% and the silicon content of 3.3% to 3.5% ensure the high strength and rigidity of the material. Combined with ≤0.03% low chromium and ≤0.3% low manganese, the influence of impurities on toughness is reduced, and low-temperature brittleness or deformation due to external impact is avoided. In terms of thickness, the gradient range of 6mm to 13.6mm can be adapted to different pressure scenarios (from low-pressure branch pipes to high-pressure main pipes). It can withstand soil compression and high pressure of the medium, and can also provide a stable protective shell for the inner structure to prevent the inner layer from being damaged by external forces.

[0027] The cement lining layer 12 serves as a transitional layer between "basic corrosion protection and substrate optimization." Through process upgrades and material optimization, it lays the foundation for subsequent coating construction. A centrifugal spraying process is used in conjunction with high-grade silicate cement to form a dense alkaline protective layer of 3-5 mm. On the one hand, the alkalinity of the cement (pH≥12) generates a passivation film on the inner wall of the cast iron, preventing the substrate from rusting. On the other hand, the centrifugal process ensures that the surface is flat and crack-free with a moisture content of ≤6%, eliminating micropores and protrusions, and providing a uniform and rough bonding substrate for the polyurea adhesive primer layer 14, avoiding peeling of the subsequent coating due to substrate defects.

[0028] The polyurea adhesion primer layer 14 acts as a "functional link" between the cement lining and the polyurea layer, achieving strong adhesion and extended corrosion protection through the chemical properties of epoxy materials. Using an epoxy primer (bisphenol A type epoxy resin as the base material, polyamide or modified cycloaliphatic amine as the curing agent), the epoxy resin can penetrate the micropores of cement to form a "physical anchor". The curing agent and epoxy resin cross-link to form a dense network structure, and at the same time form a chemical bond with the cement components, so that the bonding strength between the polyurea layer and the cement lining is ≥2.5MPa. In addition, the primer layer can seal the micropores of cement, block the penetration of corrosive media, make up for the shortcomings of cement lining in corrosion protection, and form a "secondary anti-corrosion barrier" to adapt to complex working conditions such as temperature fluctuations and media immersion.

[0029] The surface polyurea material 13 serves as the "core protective layer" in direct contact with the medium, achieving efficient protection and performance optimization through its single-component moisture-curing properties. Based on isocyanate-terminated prepolymers, it does not require complex two-component mixing equipment. The chain growth reaction is triggered by moisture in the air, and it is surface dry in 10-30 minutes and fully dry within 2 hours, making it suitable for rapid on-site construction. After curing, it forms a dense elastomer that has excellent corrosion resistance (resistant to pH 1-14 media and 1000 hours of salt spray without damage), low friction surface (Ra<5μm) to reduce fluid resistance, and tensile strength of over 15MPa and elongation at break of over 400% to adapt to pipeline deformation and particle impact, achieving the triple function of "corrosion resistance + wear resistance + high-efficiency water delivery".

[0030] This invention also provides a manufacturing process for a composite pipe lined with a single-component polyurea material, specifically including the following steps: S1. First, according to the composition requirements of carbon content 3.3%~3.6%, silicon content 3.3%~3.5%, chromium content ≤0.03%, and manganese content ≤0.3%, select high-purity pig iron, scrap steel, and alloy additives (ferrosilicon, ferromanganese, etc.) to ensure that the impurity content of raw materials meets national standards. Raw materials are put into a medium-frequency induction furnace and melted at a temperature of 1450-1500℃. After the molten metal is completely melted and the composition is uniform, spheroidizing agents (such as magnesium alloys) and inoculants (such as silicon-barium alloys) are added. Spheroidizing treatment is carried out by the injection method or wire feeding method to make the graphite in the cast iron spherical, thereby improving the toughness and strength of the material. After spheroidizing, the molten metal is poured into a centrifugal casting machine mold that rotates at high speed (the speed is adjusted according to the diameter of the pipe, usually 800-1200 r / min). Under the action of centrifugal force, the molten metal adheres tightly to the inner wall of the mold and cools and forms a tubular blank. The cooling rate is controlled at 5-10℃ / min to avoid cracks caused by excessive cooling. After the casting cools to room temperature, it is demolded and the riser and flash are removed. The inner and outer surfaces of the pipe are machined by mechanical cutting to ensure that the thickness of the reinforcing layer of the ductile iron pipe is controlled between 6mm and 13.6mm and the surface roughness Ra≤12.5μm, so as to provide a good foundation for the subsequent cement lining layer to adhere. A cement lining layer is prepared by uniformly coating the inner wall of a ductile iron pipe with high-grade silicate cement using a centrifugal spraying process.

[0031] S2. Select high-grade silicate cement of grade 42.5 or above, and prepare the slurry according to the mass ratio of cement:water:admixture (water-reducing agent, retarder) = 1:0.3-0.35:0.01-0.02. The mixing time should not be less than 5 minutes to ensure that the slurry is uniform and free of lumps, and the fluidity should be controlled at 180-200mm (standard cone slump). Fix the pretreated ductile iron pipe (with no oil or rust on the inner wall) on a centrifugal sprayer and rotate it at a speed of 300-500r / min. At the same time, spray the cement slurry evenly on the inner wall of the pipe through a high-pressure spray gun. During the spraying process, control the moving speed of the spray gun (10-15cm / s) and the spraying pressure (0.8-1.2MPa) to ensure that the coating thickness is uniform and the final thickness reaches 3-5mm. After spraying, place the pipe in a curing room with a temperature of 20-25℃ and a relative humidity of ≥80% and cure it for more than 7 days using steam curing or natural curing. Spray water every 4 hours for the first 3 days to prevent surface cracking. After curing, test the strength of the cement lining layer to ensure that the compressive strength is ≥30MPa and there are no hollow or falling off phenomena. The cement lining layer 12 needs to be fully cured and the surface should be dry and free of dust. The roughness should be improved by sandblasting or grinding to reach Sa2.5 grade, with a roughness Ra=30-50μm. On the surface of the cement lining layer 12 after sandblasting or grinding, an epoxy primer is evenly applied by airless spraying or roller coating. After the primer cures, a polyurea-adhesive primer layer 14 is formed.

[0032] S3. After the cement lining layer 12 is cured, the inner wall is polished using a wet grinding process (sandpaper grit 320-400) to remove surface dust and burrs, so that the surface roughness Ra reaches 6.3-12.5μm. Then, it is cleaned with compressed air (pressure 0.5-0.6MPa) and then wiped with acetone or alcohol to remove oil and residual impurities. Mix epoxy resin (such as bisphenol A type epoxy resin) and amine curing agent (such as polyamide or modified cycloaliphatic amine) at a mass ratio of 2-3:1 at room temperature (20-25℃) for 3-5 minutes to ensure uniform mixing. The mixture should be used within 1 hour after preparation to avoid primer curing failure. Apply the prepared epoxy primer evenly to the inner wall of the cement lining using a brush or roller. The coating thickness should be controlled at 30-50μm. Avoid missed areas and drips during the application process. After application, allow it to cure for 4-6 hours at room temperature and in a well-ventilated environment. After curing, test the adhesion of the primer layer to ensure that the adhesion is ≥5MPa (cross-cut test). During the sandblasting process, defects such as pitting and pinholes were found in the pipes. The cracks were repaired with epoxy mortar, followed by the application of epoxy or polyurethane primer to enhance adhesion. Then, a single-component polyurea was evenly sprayed using a high-pressure airless spraying device.

[0033] S4. Select a single-component polyurea material with isocyanate-terminated prepolymer as the main component. Before use, the material needs to be preheated at 40-50℃ for 30-60 minutes to reduce the viscosity and ensure smooth spraying. After preheating, the viscosity of the material should be controlled at 500-800 mPa. s; Pour the preheated polyurea material into a high-pressure airless sprayer (spraying pressure 15-20MPa) and spray it onto the inner wall of the cured polyurea adhering primer layer. Control the moving speed of the sprayer (8-12cm / s) and the spraying distance (20-30cm) to ensure uniform coating thickness. The thickness of a single spray is 50-100μm. Depending on the design requirements, it can be sprayed in 2-3 times, with a total thickness of 150-300μm. After spraying, the chain growth reaction of the polyurea material is triggered by the moisture in the air. It is then naturally cured at room temperature (20-25℃) and relative humidity of 40% to 60%. During the initial curing stage (the first 2 hours), the coating should not be touched. After 24 hours, it is fully cured. After curing, the coating performance is tested to ensure that the impact strength is ≥5kJ / m² and the chemical corrosion resistance (5% hydrochloric acid immersion for 72 hours) is normal. The sprayed single-component polyurea material forms a surface polyurea material 13.

[0034] S5. Control the thickness to 0.5-1.5mm by adjusting the spraying speed and pressure, and apply in two alternating coats.

[0035] This process balances ease of construction with coating reliability, making it particularly suitable for complex pipe diameters and on-site operations.

[0036] Ductile iron pipe reinforcement layer 11: structural support and rigidity assurance As the outermost structure of the composite pipe, the ductile iron pipe reinforcing layer 11 is designed with specific composition and thickness to provide mechanical support for the entire pipeline. Its carbon content is controlled at 3.3% to 3.6% and silicon content at 3.3% to 3.5%, which not only ensures the high strength and rigidity of the material, but also reduces the impact of impurities on the toughness of the pipe through composition optimization of low chromium (≤0.03%) and low manganese (≤0.3%), thus preventing the pipeline from deforming or breaking due to external impact or soil pressure during buried or overhead installation. At the same time, the thickness range of 6mm to 13.6mm has been mechanically calculated to adapt to the pressure requirements of different scenarios such as municipal water supply and chemical transportation, providing a stable external protective shell for the inner structure and preventing damage to the inner cement lining layer 12 and polyurea coating due to external extrusion.

[0037] Cement lining layer 12: Foundation corrosion protection and surface leveling The cement lining layer 12 is attached to the inner side of the reinforcing layer 11 of the ductile iron pipe by centrifugal spraying. The thickness of 3-5 mm is mixed with high-grade silicate cement to form a dense alkaline protective layer. On the one hand, the alkaline environment of cement (pH value ≥ 12) can form a passivation film on the inner wall of the ductile iron pipe, inhibiting iron ion oxidation and blocking direct contact between the pipe substrate and the transport medium, thus playing a basic anti-corrosion role. On the other hand, the centrifugal spraying process ensures that the surface of the cement lining is flat and free of cracks. After curing in a curing furnace, it can eliminate surface micropores and protrusions, providing a uniform and rough base surface for the subsequent polyurea primer layer 14. This process can control the surface moisture content of the cement lining to below 6%, avoiding the failure of the primer and cement layer due to residual moisture. At the same time, the flat surface can reduce the thickness deviation during polyurea coating spraying and ensure uniform protective effect.

[0038] Polyurea Adhesion Primer Layer 14: Interfacial Bonding and Penetration Anchoring The polyurea adhesion primer layer 14 serves as a "bridge" between the cement lining layer 12 and the surface polyurea material 13. It achieves strong adhesion through the chemical reaction characteristics of the epoxy primer (bisphenol A type epoxy resin + polyamide / modified cycloaliphatic amine curing agent). The epoxy resin, as the base material, can penetrate into the microporous structure of the cement lining and form a chemical bond with the silicate components in the cement. The amine curing agent undergoes a cross-linking reaction with the epoxy resin to form a dense network structure, creating a transition layer on the cement surface that combines adhesion and chemical resistance. According to the JC / T2435-2018 standard, this primer layer can enable the polyurea coating to achieve a bonding strength of more than 2.5 MPa with the cement lining. It can not only resist long-term immersion in the transported medium and temperature changes (such as temperature fluctuations in municipal pipelines during winter low temperatures and summer sun exposure), but also prevent the polyurea coating from peeling off due to pipeline vibration and thermal expansion and contraction, ensuring the stability of the inner protective structure.

[0039] Surface polyurea materials 13: Core protection and performance optimization The surface polyurea material 13, serving as the innermost protective layer, is primarily composed of isocyanate-terminated prepolymers and achieves high-efficiency protection through a unique moisture-curing mechanism. When the material is sprayed onto the primer layer, the isocyanate groups in the prepolymer undergo a chain-growth reaction with moisture in the air, gradually curing to form an elastomer network. This process eliminates the need for complex two-component mixing equipment, and the surface drying time can be controlled within 10-30 minutes by adjusting the amount of catalyst (such as dibutyltin dilaurate or amine catalysts), adapting to the efficiency requirements of on-site construction. The cured polyurea layer has two core functions: firstly, it promotes… Firstly, it provides airtight protection. The highly cross-linked urea bonds in its molecular structure can completely seal the micropores of the cement lining, preventing corrosive factors such as moisture, chloride ions, and acid and alkali media from penetrating into the cement layer and ductile iron substrate, fundamentally solving the problem of traditional cement linings easily failing in corrosive water. Secondly, it optimizes performance. The smooth surface of the polyurea layer (friction coefficient ≤0.01) can reduce fluid resistance and improve water conveyance efficiency. At the same time, its tensile strength of over 15MPa and elongation at break of over 400% can adapt to pressure fluctuations and slight deformations during pipeline operation, avoiding coating cracking caused by water flow impact and pipeline settlement.

[0040] (a) Structural integration and size adaptation: meeting the installation needs of multiple scenarios Pipe Material 1, with its precise layer thickness ratio (6mm-13.6mm ductile iron pipe reinforcing layer + 3-5mm cement lining layer + 80-120μm primer layer + 1.5-2.5mm polyurea layer), can flexibly adapt to different pipe diameters from DN100 to DN2000, covering the full range of needs from small-diameter municipal branch pipes (such as residential inlet pipes) to large-scale water transmission trunk pipes (such as intercity water transmission pipes). At the same time, the interface design of both ends of Pipe Material 1 (such as socket type and flange type) is compatible with existing pipe installation standards, and can be directly connected to traditional ductile iron pipes, steel pipes, etc., without the need for additional customized adapter accessories, reducing the difficulty of engineering modification. For example, in municipal pipe network upgrade projects, it can directly replace old cement pipes, reduce construction delays caused by interface incompatibility, and improve installation efficiency by more than 30%.

[0041] (ii) Performance balance and risk avoidance: avoiding single structural defects Relying solely on the performance of a single layer can easily lead to significant shortcomings (such as poor corrosion resistance of pure ductile iron pipes and insufficient rigidity of pure polyurea pipes). Pipe material 1, through layered complementarity, completely avoids these risks: the ductile iron reinforcing layer compensates for the insufficient rigidity of polyurea and cement, preventing the pipe from deforming under external pressure; the cement lining and polyurea layer solve the corrosion problem of cast iron pipes, preventing leaks due to rust. Taking pipelines in chemical industrial parks as an example, if pure cast iron pipes are used, perforation will occur due to media corrosion within 3 to 5 years; if pure polyurea pipes are used, they are prone to bending under soil pressure; while the composite structure of pipe material 1 can operate stably for more than 15 years in corrosive environments without the risk of deformation, significantly improving the reliability of pipeline operation.

[0042] (III) Full life cycle management: Facilitates maintenance and testing The overall structural design of pipe 1 takes into account the convenience of later operation and maintenance: the outer ductile iron pipe reinforcement layer can be coated with anti-corrosion topcoat, forming a double guarantee of "external anti-corrosion + internal protection", and the cast iron material has strong weather resistance, with no obvious rust after 10 years of outdoor exposure, reducing the maintenance cost of the external surface; the inner polyurea layer is smooth and seamless, and the condition of the inner wall can be directly inspected through a pipe endoscope without disassembling the pipe, improving the inspection efficiency by 50%; in addition, if the polyurea layer is damaged in a certain area, it can be repaired through a simple process of "grinding - applying primer - spraying polyurea", and the repair time for a single point is controlled within 2 hours, which is far lower than the overall replacement cost of traditional pipes.

[0043] II. Cement Lining Layer 12: A foundational protection and performance optimization layer that serves as a bridge between the upper and lower layers. The cement lining layer 12 is not a simple "filling layer," but rather, through material proportioning and process optimization, it forms a crucial transition between the ductile iron pipe reinforcing layer and the polyurea adhesive primer layer. Its function and effect can be broken down into four aspects: (a) Substrate protection: Building the first line of defense against corrosion The high-grade silicate cement (such as P.O42.5R) used, after centrifugal spraying, forms a dense structure with strong alkalinity (pH 12-13), which can react with the iron elements on the inner wall of the reinforcing layer of ductile iron pipe to generate a passivation film of iron(III) oxide (Fe3O4). This passivation film is about 5-10 μm thick and can prevent iron ions from contacting oxygen and moisture in the transport medium, thus delaying the corrosion process of cast iron pipe from the source. Comparative experiments show that ductile iron pipes without cement lining have a rusted area of ​​up to 30% on the inner wall after being soaked in tap water for 1 year; while pipes with cement lining have a rusted area of ​​only 1% to 2%, improving the anti-corrosion effect by more than 28 times.

[0044] (ii) Surface pretreatment: to provide a high-quality substrate for the primer layer Centrifugal spraying creates a uniform rough texture (surface roughness Ra 8-12μm) on the surface of the cement lining layer 12. This texture significantly increases the contact area with the polyurea primer layer, enhancing interfacial adhesion like "serrations." If the cement surface is smooth (Ra < 5μm), the primer layer's adhesion strength is only 1.0-1.5MPa, while after centrifugal spraying, the adhesion strength can be increased to 2.5-3.0MPa, fully meeting the requirement of "coating-substrate adhesion strength ≥ 2.0MPa" in GB50268 "Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering". Simultaneously, after 24 hours of steam curing, the moisture content of the cement lining can be controlled at 3%–5%, preventing bubbles and pinholes in the primer layer due to moisture evaporation and ensuring the quality of subsequent coating applications.

[0045] (iii) Pressure buffering: Relieves the impact of media and temperature stress The cement lining layer is designed to be 3-5mm thick, providing a certain degree of elasticity (elastic modulus 2.5×10). 4 When transporting high-pressure media (such as municipal water supply pressure of 1.0-1.6 MPa) in pipelines, it can absorb some of the fluid impact force, reduce the direct pressure on the reinforcing layer of ductile iron pipes, and avoid fatigue damage to the pipe material due to long-term high pressure; at the same time, cement material has a low thermal conductivity (0.93 W / (m²)). K) can slow down the freezing rate of the medium inside the pipe in winter when the temperature is low and reduce the transfer of external heat in summer when the temperature is high, thereby reducing the thermal expansion and contraction stress caused by the sudden temperature change in the pipe. For example, in northern winters, pipes without cement lining are prone to cracking due to the volume expansion of the medium when it freezes, while pipes with cement lining delay the freezing time by 4 to 6 hours, greatly reducing the risk of freezing and cracking.

[0046] (iv) Cost balance: finding the optimal solution between performance and economy Compared to full polyurea lining (which requires a polyurea layer thickness of 5-6mm to achieve the same protective effect), the raw material cost of cement lining layer 12 is only 1 / 5 to 1 / 8 of that of polyurea material, which can significantly reduce the overall pipe cost. Taking DN1000 pipe as an example, the cost of full polyurea lining is about 800 yuan per meter, while the combination of "cement lining + thin polyurea layer" can control the cost per meter to 450-500 yuan, reducing the cost by 37% to 43%. At the same time, it takes into account both corrosion resistance and economy, making it more suitable for large-scale municipal engineering projects.

[0047] III. Polyurea Adhesion Primer Layer 14: A Strong Bond for Interfacial Bonding and an Extended Anti-corrosion Layer Although the polyurea adhesion primer layer 14 is only 80-120μm thick (about the thickness of a sheet of A4 paper), it is the key to determining the protective effect of the inner layer of the composite pipe. Its role and effect far exceed "simple bonding", which can be divided into three aspects: (i) Penetration anchoring: Achieving "molecular-level bonding" with the cement lining. Bisphenol A epoxy resin in epoxy primers possesses excellent penetration properties. After application, it can penetrate into the micropores (approximately 0.1-0.5 μm in diameter) and microcracks of the cement lining, forming an "anchor" structure. Simultaneously, when amine curing agents (such as polyamide) undergo a cross-linking reaction with the epoxy resin, they form chemical bonds (such as ether bonds and hydroxyl groups) with components in the cement, such as Ca(OH)2 and SiO2. This dual effect of "physical anchoring + chemical bonding" enables the adhesion strength between the primer layer and the cement lining to reach over 3.0 MPa, far exceeding the industry average of 2.0 MPa. Even if the pipeline is subjected to long-term vibration (such as municipal pipelines near highways), the primer layer will not peel off from the cement lining, ensuring the stability of the inner layer structure.

[0048] (ii) Extended Corrosion Protection: Blocking the "Secondary Penetration" of Corrosive Media Although the cement lining already possesses basic corrosion protection capabilities, chloride and sulfate ions in the transported medium can still slowly penetrate through the micropores of the cement during long-term use. The dense network structure (crosslinking density ≥1.5×10³mol / m³) of the polyurea primer layer 14 can completely seal these micropores, forming a "corrosion protection barrier." Experimental data shows that in a 3% NaCl solution immersion environment, the chloride ion penetration depth of the composite pipe without the primer layer reaches 2mm (after 1 month), while the penetration depth of the composite pipe with the primer layer is only 0.2mm, improving the corrosion protection effect by 10 times. In addition, the primer layer has excellent chemical resistance and can withstand the corrosion of media with pH values ​​of 2-12. In chemical wastewater transport scenarios, it can prevent corrosive media from eroding the cement lining and extend the service life of the inner layer protection.

[0049] (III) Interface transition: Solving the "performance incompatibility" problem between cement and polyurea. The performance of the cement lining (rigid material, elongation at break <0.1%) and the surface polyurea material (elastic material, elongation at break >400%) differs significantly. Direct bonding is prone to problems due to the different coefficients of thermal expansion and contraction (cement's coefficient of thermal expansion is 12×10). -6 / ℃, polyurea thermal expansion coefficient 25×10 -6 Interface cracking occurs at temperatures ranging from 60°C to 15°C. The elongation at break of the polyurea-coated primer layer 14 is approximately 50%–80%, falling between these two values, thus acting as an "elastic buffer": when temperatures change, the primer layer can absorb the stress difference between the cement and the polyurea, preventing interface cracking. For example, in high summer temperatures (pipe surface temperature 60°C), the interface cracking rate of composite pipes without a primer layer reaches 15%, while the cracking rate of composite pipes with a primer layer is only 1%, significantly improving structural compatibility.

[0050] IV. Surface Polyurea Material 13 (original description "Surface Polyurea Material 1" revised): The "Ultimate Barrier" of Inner Layer Protection and the Core of Functional Optimization As the innermost layer of the composite pipe, the surface polyurea material 13 is in direct contact with the transported medium. Its performance determines the core indicators of the pipeline, such as corrosion resistance, wear resistance, and water transport efficiency. Its role and effect can be further broken down into four aspects: (i) Ultra-dense corrosion protection: resisting corrosion risks in all scenarios The surface polyurea material is mainly composed of isocyanate-terminated prepolymers. After curing, the urea bond structure (-NH-CO-NH-) formed is dense and non-porous (porosity <0.1%), which can completely block the penetration of moisture, oxygen, and corrosive ions; its performance is particularly outstanding in different corrosive environments. For municipal drinking water applications: Polyurea materials comply with GB / T17219 "Safety Evaluation Standard for Drinking Water Transmission and Distribution Equipment and Protective Materials", and the content of harmful substances (such as heavy metals and VOCs) in the water after immersion is <0.001mg / L, ensuring drinking water safety; Marine engineering scenario: After immersion in 5% NaCl solution for 1000 hours, the polyurea layer showed no blistering or peeling, and the tensile strength retention rate was >90%, which is far superior to traditional epoxy coatings (retention rate <60%). Chemical application: It can withstand corrosion from 30% sulfuric acid and 50% sodium hydroxide solution (immersion for 30 days, weight change rate <1%), and is suitable for conveying acid and alkali media.

[0051] (ii) High elasticity and crack resistance: adaptable to pipeline deformation and impact The surface polyurea material has an elongation at break of >400% and a tensile strength of >15MPa, exhibiting excellent elasticity and toughness. When the pipeline undergoes slight deformation due to soil settlement (bending degree ≤3°), the polyurea layer can deform synchronously with the pipeline without the risk of cracking. When transporting media containing particles (such as mine tailings), the elasticity of the polyurea layer can absorb the impact energy of the particles (impact strength >50kJ / m²), avoiding lining wear caused by particle erosion. Comparative experiments show that in tailings transportation scenarios, the wear of traditional cement linings reaches 0.5mm / year, while the wear of polyurea linings is only 0.03mm / year, improving wear resistance by 16 times.

[0052] (III) Low-resistance and high-efficiency water conveyance: reducing energy consumption and operating costs After curing, polyurea material has a smooth surface (surface roughness Ra < 5μm), which is much lower than that of cement lining (Ra ≥ 20μm) and steel pipe (Ra ≥ 15μm). According to Manning's formula, under the same pipe diameter (DN1000) and the same flow rate (1.5m³ / s): The head loss along the pipe with cement lining is 0.025 m / km; The head loss along the pipe lined with polyurea is only 0.012 m / km, a reduction of 52%.

[0053] This means that the required pump head can be reduced by about 2 meters. Based on a daily water delivery of 100,000 tons and an electricity cost of 0.6 yuan / kWh, the annual electricity saving can reach 180,000 kWh, and the operating cost can be reduced by 25% to 30%. It is especially suitable for long-distance, high-flow water delivery projects.

[0054] (iv) Rapid curing construction: suitable for efficient production and emergency repair The surface polyurea material is a one-component moisture-curing system, requiring no two-component mixing. Surface drying time after spraying is only 10-30 minutes (controllable by adjusting catalyst dosage), and complete drying time is less than 2 hours, significantly shortening the production cycle. In mass production scenarios: In assembly line production, the polyurea spraying time for each DN1000 pipe is only 5 to 8 minutes, and the daily production capacity can reach 100 to 120 pipes, which is twice as efficient as two-component polyurea (spraying time 15 to 20 minutes). Emergency repair scenario: If a section of the pipeline is damaged, water supply can be restored within 2 hours after spraying polyurea on site, which is much faster than traditional cement lining repair (which requires 72 hours of curing), reducing the impact of water outages on residents' lives and industrial production.

[0055] V. Ductile Iron Pipe Reinforcement Layer 11: The "Rigid Skeleton" and Safety Guarantee of Composite Pipes The ductile iron pipe reinforcing layer 11 serves as the outer support of the composite pipe. Through composition optimization and thickness design, it provides mechanical protection for the entire pipe. Its functions and effects can be divided into four aspects: (i) High-strength pressure resistance: meets the requirements of multiple pressure levels The carbon content (3.3%–3.6%) and silicon content (3.3%–3.5%) of the reinforcing layer in ductile iron pipes are precisely proportioned, resulting in a tensile strength >420MPa and a yield strength >300MPa, far exceeding that of ordinary gray cast iron (tensile strength <200MPa). Different thicknesses are available to suit different pressure scenarios. Thickness 6-8mm: Suitable for low-pressure scenarios (such as municipal branch pipes, working pressure ≤0.6MPa). Thickness 9-11mm: Suitable for medium pressure scenarios (such as municipal main pipelines, working pressure 0.8-1.2MPa). Thickness 12~13.6mm: Suitable for high-pressure scenarios (such as long-distance water transmission, chemical high-pressure pipelines, working pressure 1.6-2.0MPa).

[0056] In the water pressure test, the 13.6mm thick reinforcing layer can withstand a water pressure of 3.0MPa (1.5 times the working pressure) without leakage or deformation, ensuring the safe operation of the pipeline.

[0057] (ii) Impact and deformation resistance: adaptable to complex installation environments The low-chromium (≤0.03%) and low-manganese (≤0.3%) composition of the reinforcing layer of ductile iron pipe reduces the impact of impurities on the material's toughness. Its impact toughness (-20℃) is >15J / cm², far exceeding that of ordinary cast iron (<5J / cm²). In buried installation scenarios: During the soil compaction process, even when subjected to mechanical rolling (pressure ≤50kN), the reinforcing layer will not sink or crack; In overhead installation scenarios: Under the influence of external forces such as strong winds and earthquakes, the rigidity of the reinforcement layer can maintain the straightness of the pipe and prevent the joints from loosening and leaking due to shaking.

[0058] (iii) Weather resistance and aging resistance: extending outdoor service life The reinforcing layer of ductile iron pipes undergoes a double external anti-corrosion system, treated with a zinc-aluminum coating (80-100μm thick) and an asphalt topcoat (50-80μm thick). Weather resistance: In outdoor exposure environments, after 10 years of exposure to sunlight and rain, the coating shows no peeling or rust, and the substrate corrosion rate is <0.01mm / year; Resistant to soil corrosion: In acidic soils (pH 4-5) or alkaline soils (pH 9-10), the zinc-aluminum coating can form a sacrificial anode protection, preventing the cast iron substrate from being corroded and extending the life of the reinforcing layer to more than 50 years.

[0059] (iv) Dimensional stability: Ensure installation accuracy and sealing performance The reinforcing layer of the ductile iron pipe is made using centrifugal casting, ensuring high dimensional accuracy (outer diameter tolerance ±0.5mm, wall thickness tolerance ±0.3mm). The roundness error of both ends (such as T-type socket joints) is <0.2mm, allowing for a perfect fit with the sealing ring and ensuring a tight seal. In municipal pipeline installation, the interface leakage rate is less than 0.1%, far below the industry standard of 1%; Even with temperature variations (-30℃ to 60℃), the coefficient of thermal expansion of the reinforcing layer (11×10⁻⁶) remains relatively constant. -6 The interface is stable at ℃, and the interface will not develop gaps due to deformation, thus avoiding the risk of water leakage.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composite pipe lined with a single-component polyurea material, characterized in that, include: Pipe (1) includes, from the inside out, a surface polyurea material (13), a polyurea adhesive primer layer (14), a cement lining layer (12), and a ductile iron pipe reinforcing layer (11). The ductile iron pipe reinforcement layer (11) is the bottom layer structure of the pipe (1) from the inside to the outside. It is the supporting foundation of the entire composite pipe. It is made of ductile iron as the core material and formed by centrifugal casting process. The surface polyurea material (13) serves as the innermost layer of the pipe (1) and is in direct contact with the fluid medium being transported. The polyurea adhesion primer layer (14) is located between the surface polyurea material (13) and the cement lining layer (12), and is a key transition structure for solving the compatibility of the two different materials and strengthening the interlayer bonding. The cement lining layer (12) is located inside the ductile iron pipe reinforcing layer (11) and outside the polyurea adhesive primer layer (14), and is an important intermediate structure connecting the metal structure and the organic coating.

2. The composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: The thickness of the ductile iron pipe reinforcing layer (11) is controlled between 6 mm and 13.6 mm.

3. The composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: The carbon content of the reinforcing layer (11) of the ductile iron pipe is 3.3% to 3.6%, the silicon content is 3.3% to 3.5%, the chromium content is less than or equal to 0.03%, and the manganese content is less than or equal to 0.3%.

4. The composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: The cement lining layer (12) is centrifugally sprayed with a thickness of 3-5 mm. It uses high-grade silicate cement and forms a dense structure after being cured in a curing furnace.

5. A composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: The polyurea adhesion primer layer (14) is an epoxy primer, the main components of which are epoxy resin and amine curing agent.

6. A composite pipe with a single-component polyurea material lining according to claim 5, characterized in that: The epoxy resin is a bisphenol A type epoxy resin; The amine curing agent is polyamide or modified cycloaliphatic amine. The polyamide or modified cycloaliphatic amine reacts with bisphenol A type epoxy resin to form a dense network structure, which can effectively penetrate into the microporous structure of the cement lining layer (12) and form a mechanical anchoring effect.

7. The composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: The surface polyurea material (13) is mainly composed of isocyanate-terminated prepolymer, and is cured by triggering a chain growth reaction through moisture in the air.

8. A composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: A cement lining layer (12) is prepared by uniformly coating the inner wall of a ductile iron pipe with high-grade silicate cement using a centrifugal spraying process.

9. A composite pipe with a single-component polyurea material lining according to claim 1, characterized in that: On the surface of the cement lining layer (12) after sandblasting or grinding, an epoxy primer is uniformly applied by airless spraying or roller coating. After the primer cures, a polyurea-adhesive primer layer (14) is formed.

10. A single-component polyurea material-lined composite pipe according to claim 1, characterized in that: After the polyurea adhesive primer layer (14) has cured, a single-component polyurea material is sprayed to form a surface polyurea material (13).

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