A corrosion-resistant plastic-coated composite steel pipe and its preparation process

Abstract

The present invention relates to the field of plastic-coated composite materials, and discloses a corrosion-resistant plastic-coated composite steel pipe, the surface of which includes the following layers: a base steel pipe, an interface treatment layer enhanced by nanomaterials, and a plastic coating layer; wherein the interface treatment layer is composed of nano silicon or nano aluminum oxide, and has a thickness of 10-20 μm, and the plastic coating layer is composed of a modified epoxy resin, a modified polyethylene and a polyvinyl chloride composite material, and has a thickness of 200-300 μm, and the surface of the steel pipe is treated with laser to increase the roughness, and the laser power is 800-1200 W. By adopting a special coating material and a composite structure, the corrosion resistance of the steel pipe is effectively improved. In salt spray tests and long-term immersion tests, the coating can effectively prevent the erosion of moisture, salt and acidic substances, and significantly prolong the service life of the steel pipe. The coating can maintain long-term and stable corrosion resistance in extreme environments, such as chemical, marine, mining and other highly corrosive places, and reduce the maintenance cost caused by corrosion.

Description

Technical Field

[0001] The invention relates to the field of plastic-coated composite materials, in particular to a corrosion-resistant plastic-coated composite steel pipe and a preparation process thereof. Background Art

[0002] In modern industry, steel pipes are widely used in the fields of oil, natural gas, chemical industry, water supply, gas supply, construction, energy, etc. as important transmission pipelines and supporting structures. However, due to the long-term exposure of steel pipes to complex natural and industrial environments, their surfaces are easily eroded by various factors, such as corrosion, oxidation, wear and chemical reactions, which will directly affect the service life and safety of steel pipes.

[0003] Traditional steel pipe anti-corrosion technologies, such as galvanizing, anti-corrosion coatings and electrochemical protection, can improve the corrosion resistance of steel pipes to a certain extent, but there are still many problems. For example, the corrosion resistance and adhesion of the galvanized layer are limited, and local corrosion is prone to occur; the adhesion of traditional coating materials is weak, and the coating is easy to peel or fall off in high temperature, humidity or mechanical impact environments; electrochemical anti-corrosion technology places high demands on the structure and cost of the steel pipe itself. In addition, many existing anti-corrosion technologies have problems such as high energy consumption, environmental pollution, uneven coating thickness, and complex processes during application.

[0004] In order to effectively solve the corrosion problem that may occur in steel pipes during long-term use, researchers have gradually begun to pay attention to the application of plastic-coated composite materials in steel pipe anti-corrosion. Plastic-coated composite steel pipe is a composite material that combines high-performance plastic materials with steel pipes. This structure can not only improve the corrosion resistance of steel pipes, but also improve their mechanical properties and processing performance. However, the current plastic-coated composite steel pipe technology still faces the following challenges:

[0005] Unstable coating adhesion: Existing coating technology has insufficient adhesion on the surface of steel pipes, especially under extreme conditions such as high temperature, humidity and mechanical shock. The coating is easy to peel off or detach, resulting in the failure to effectively solve the corrosion problem.

[0006] Uneven coating thickness: Due to the imperfect coating process of the coating material, the coating thickness is often uneven, and the coating is thinner in some areas, resulting in inconsistent anti-corrosion effects on the steel pipe, reducing the corrosion resistance and service life of the steel pipe.

[0007] The long-term stability of coating performance is poor: in extreme environments (such as high temperature, acid-base environment or highly corrosive medium), the corrosion resistance and mechanical properties of the coating are prone to decline, and the performance of the coating material may age or degrade, affecting the long-term application effect of the steel pipe.

[0008] High production cost and complex process: The existing plastic coating process usually involves complex processes such as multi-layer coating, heat treatment and curing, which not only increases production costs but also may pollute the environment, especially when using coatings containing volatile organic compounds (VOCs), which have a negative impact on air quality and the ecological environment.

[0009] Therefore, how to improve the adhesion, corrosion resistance and long-term stability of the coating while ensuring the anti-corrosion performance of the steel pipe, while reducing the production cost, has become an important direction for the development of plastic-coated composite steel pipe technology. In order to address the above problems, the present invention proposes a new corrosion-resistant plastic-coated composite steel pipe and its preparation process, which aims to achieve efficient anti-corrosion performance and long-term reliability of the steel pipe by optimizing the coating material, improving the coating process, and improving the adhesion of the coating, so as to adapt to various complex and harsh working environment requirements. Summary of the invention

[0010] In view of the deficiencies in the prior art, the present invention provides a corrosion-resistant plastic-coated composite steel pipe and a preparation process thereof, which solves the problems of insufficient coating adhesion, poor corrosion resistance, complex production process and high cost of the existing plastic-coated composite steel pipe.

[0011] To achieve the above objectives, the present invention is implemented through the following technical solutions: a corrosion-resistant plastic-coated composite steel pipe, a base steel pipe,

[0012] Nanomaterial-enhanced interface treatment layer,

[0013] Plastic coating;

[0014] The interface treatment layer is composed of nano silicon or nano aluminum oxide, with a thickness of 10-20 μm, and the plastic coating layer is composed of a composite material of modified epoxy resin, modified polyethylene and polyvinyl chloride, with a thickness of 200-300 μm.

[0015] Preferably, the surface of the steel pipe is roughened by laser treatment, the laser power is 800-1200W, and the scanning speed is 0.5-2m / min.

[0016] Preferably, the nano-material enhanced interface treatment layer uses ultrasonic dispersion technology to disperse nano-silicon or nano-aluminum oxide, the particle size of the nanoparticles in the solution is 20-50nm, and the thickness of the interface treatment layer is 10-20μm.

[0017] A process for preparing a corrosion-resistant plastic-coated composite steel pipe comprises the following steps:

[0018] Step 1: Surface pretreatment of the steel pipe, including pickling to remove scale, rust and contaminants;

[0019] Step 2: Surface laser treatment: Use laser to treat the surface of the steel pipe to form a micron-level rough texture;

[0020] Step 3: Interface treatment: coating the surface of the steel pipe with a nano-material-enhanced interface treatment layer to form a coating with a thickness of 10-20 μm;

[0021] Step 4: Plastic coating: Apply the coating material to the surface of the steel pipe by electrostatic spraying, cast coating or dipping, and then cure it after coating;

[0022] Step 5: Quality inspection, testing the coating adhesion, thickness and corrosion resistance to ensure that the product meets the requirements.

[0023] Preferably, the pickling step uses hydrochloric acid or sulfuric acid solution, the pickling temperature is 30-60° C., the pickling time is 5-15 minutes, and water washing and drying are performed after pickling.

[0024] Preferably, the laser power of the laser processing step is 800-1200 W, the scanning speed is 0.5-2 m / min, the processing depth is 5-10 μm, and a uniform roughness is formed.

[0025] Preferably, in the coating step, the coating material is composited from modified epoxy resin, modified polyethylene and polyvinyl chloride, the coating thickness is 200-300 μm, the curing temperature is 150-180° C., and the curing time is 20-30 minutes.

[0026] Preferably, the quality inspection step includes:

[0027] Use scanning electron microscopy to examine the coating surface condition;

[0028] The adhesion between the coating and the steel pipe substrate was evaluated using tensile and shear tests;

[0029] The corrosion resistance of the coating is evaluated by salt spray test and acid spray test;

[0030] Measure the coating thickness using a coating thickness gauge.

[0031] Preferably, after the coating is cured, the coating adhesion on the surface of the steel pipe is not less than 20MPa, and the corrosion resistance meets the requirements of the salt spray test. After 1000 hours of salt spray test, there is no obvious shedding or cracking of the coating.

[0032] The present invention provides a corrosion-resistant plastic-coated composite steel pipe and its preparation process.

[0033] Beneficial effects:

[0034] 1. The present invention effectively improves the corrosion resistance of steel pipes by using special coating materials and composite structures. In salt spray tests and long-term immersion tests, the coating can effectively prevent the erosion of moisture, salt and acidic substances, significantly extending the service life of the steel pipe. The coating can maintain long-term stable corrosion resistance in extreme environments such as chemical, marine, mining and other highly corrosive places, reducing maintenance costs caused by corrosion.

[0035] 2. The present invention significantly improves the adhesion of the coating by optimizing the bonding process between the coating material and the steel pipe surface. The coating can be evenly attached to the steel pipe surface, and even in high temperature, humidity and mechanical vibration environments, the coating can maintain stable adhesion to prevent falling off or peeling. This makes it less likely for the coating to be damaged during construction and long-term use of the steel pipe, thereby improving its reliability.

[0036] 3. The composite coating of the present invention has strong compression resistance, bending resistance and impact resistance, and the overall mechanical strength of the steel pipe is effectively improved. Even when encountering external force impact during transportation, installation or working environment, the coating can still remain intact without peeling, cracks or other damage. This high-strength coating enables the composite steel pipe to maintain long-term stable structural performance in complex and harsh environments.

[0037] 4. The coating preparation process of the present invention optimizes the curing process of the coating, adopts low-temperature curing or short curing time technology, effectively reduces energy consumption, and conforms to the concept of green environmental protection. At the same time, the coating materials used meet environmental protection standards, do not contain toxic substances, and can meet the requirements of modern industry for environmentally friendly products. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings of the present invention specification to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Embodiment 1:

[0041] Please see attached Figure 1 The embodiment of the present invention provides a corrosion-resistant plastic-coated composite steel pipe and a preparation process thereof, comprising:

[0042] S1. Selection and processing of base steel pipe.

[0043] Regarding step S1, pickling pretreatment is an important step in the preparation process of the plastic-coated composite steel pipe, which aims to remove the scale, rust and other surface contaminants on the surface of the steel pipe, and provide a good foundation for the subsequent coating adhesion and surface treatment. In this step, a chemical method is used to remove the contaminants on the surface of the steel pipe through the pickling solution to ensure that the surface of the steel pipe is clean and enhance its adhesion to the plastic coating layer.

[0044] In this embodiment, the surface of the steel pipe is first treated with a pickling solution, the main component of which is hydrochloric acid or sulfuric acid, the concentration is controlled between 10% and 20%, and the temperature is controlled between 30°C and 60°C to ensure that the surface oxide scale and rust can be effectively removed while avoiding excessive corrosion to the steel pipe matrix. The pickling time is controlled between 5 and 15 minutes, and the specific time varies depending on the degree of oxidation and rust on the surface of the steel pipe. In order to further improve the pickling effect, corrosion inhibitors can be appropriately added according to the surface condition of the steel pipe to reduce the corrosion of the steel pipe matrix by the acidic solution.

[0045] During the pickling process, the steel pipe is immersed in the pickling tank, and the solution reacts chemically with the surface of the steel pipe, dissolving the oxides and rust and falling off the surface. At this time, the pH value and temperature of the solution need to be checked regularly to ensure the continued effectiveness of the reaction. The surface of the steel pipe after pickling should show a metallic luster and be free of oxide scale, rust and other contaminants. After the pickling is completed, the steel pipe must be thoroughly neutralized and rinsed with clean water to ensure that there is no residual acid on the surface.

[0046] The pickling process uses the hydrogen ions in the acid solution to react with the iron oxide on the surface of the steel pipe to dissolve the oxide scale and rust to achieve a cleaning effect. This process can effectively remove the rust layer on the surface of the steel pipe, provide a clean surface for subsequent surface treatment processes (such as laser treatment and plastic coating adhesion), improve the adhesion of the coating, and thus enhance the overall performance of the plastic-coated composite steel pipe.

[0047] After pickling, the surface of the steel pipe is significantly improved, the oxide layer and rust are removed, and the surface cleanliness is high, which provides the necessary conditions for the subsequent laser treatment and the application of the nanomaterial interface layer. At this time, the surface of the steel pipe has a higher surface energy, which can effectively promote the combination of the subsequent laser treatment and the interface enhancement layer, thereby achieving the purpose of improving the coating adhesion and corrosion resistance. S2, neutralization and water washing

[0048] Regarding step S2, neutralization and water washing are an indispensable step in the preparation process of the plastic-coated composite steel pipe. The purpose is to remove the acidic substances that may remain during the pickling process, ensure that the surface of the steel pipe is no longer corroded, and provide adequate preparation for the subsequent drying treatment and plastic coating process. After completing the pickling step, a small amount of acidic solution or chemical reaction products may remain on the surface of the steel pipe. If they are not completely removed, they may affect the subsequent treatment effect and even cause corrosion. Therefore, the neutralization and water washing steps are to ensure that the surface of the steel pipe is completely clean and free of acidic residues.

[0049] In this embodiment, a weak alkaline solution is first used to neutralize the pickled steel pipe. Common neutralizing solutions include sodium carbonate solution (Na2CO3) or sodium hydroxide solution (NaOH), wherein the concentration of the sodium carbonate solution is usually controlled between 2% and 5%. During the neutralization reaction, the sodium carbonate ions in the solution react with the residual hydrogen ions in the acidic solution to generate carbon dioxide gas and water, thereby effectively removing the residual acidic substances. The neutralization treatment time is 2 to 5 minutes, and the specific time is appropriately adjusted according to the acid residue on the surface of the steel pipe and the concentration of the solution.

[0050] After neutralization, the steel pipe will be immediately transferred to the clean water flushing area, and the surface of the steel pipe will be thoroughly rinsed with clean water to ensure that there is no residual neutralizing liquid or acidic substances. The amount of clean water used and the flushing time need to ensure that there is no residue on the surface of the steel pipe. Usually the flushing time is controlled within 5 to 10 minutes. Appropriate inspections can be carried out during the flushing process to ensure that there is no obvious foam or acidic residue.

[0051] Principle and effect: The neutralization process removes the acidic substances remaining in the pickling process through chemical reactions, effectively avoiding secondary corrosion of the steel pipe matrix by the acidic solution. The water washing process further removes the neutralizing solution to ensure that the surface of the steel pipe is thoroughly clean, providing an ideal environment for subsequent drying and coating adhesion. The neutralization and water washing steps play an important protective role in this process, making the surface of the steel pipe completely free of acid and impurities, and improving the stability of subsequent processes.

[0052] After completing this step, there is no acidic substance or other residual pollution on the surface of the steel pipe, which ensures the prerequisite for coating adhesion and prevents corrosion caused by residual acidic substances. Neutralization and water washing can not only enhance the adhesion of the coating, but also lay the foundation for subsequent drying treatment. The successful implementation of this step plays a vital role in improving the surface quality of the steel pipe and extending the service life of the composite steel pipe.

[0053] S3. Drying.

[0054] Regarding step S3, drying is a key step that cannot be ignored in the preparation process of plastic-coated composite steel pipes. Its main purpose is to remove residual moisture on the surface of the steel pipe, prevent secondary oxidation and rust, and create ideal surface conditions for subsequent plastic coating processes. The surface of the steel pipe after pickling and neutralization treatment contains a certain amount of moisture. If it is not thoroughly dried, the moisture may react with oxygen in the air, causing the surface of the steel pipe to oxidize again, affecting the adhesion and quality of the coating. Therefore, the drying step needs to ensure that the surface of the steel pipe is completely dry in order to provide a good foundation for the smooth adhesion of the coating.

[0055] In this embodiment, the drying method adopts two methods: hot air drying and heating furnace drying. First, the steel pipe enters the drying system after neutralization and water washing. In this step, the steel pipe can be dried by hot air or heated in a heating furnace. During hot air drying, the surface of the steel pipe will be blown by continuous hot air, the wind temperature is generally set between 60℃ and 80℃, and the wind speed is controlled at about 3m / s. This method is suitable for drying small and medium batches of steel pipes.

[0056] For steel pipes on large-scale production lines, it is more efficient to use a heating furnace for drying. The heating furnace temperature is usually set between 80℃ and 100℃, and the drying time is 10 to 15 minutes, depending on the humidity of the steel pipe and the temperature in the furnace. The heating furnace uses a circulating hot air method to ensure that the surface of each steel pipe can be evenly heated and dried. The temperature and time during the drying process must be strictly controlled to avoid excessive temperatures that cause the oxide layer on the surface of the steel pipe to regenerate.

[0057] The combination of hot air drying and heating furnace drying can effectively remove moisture from the surface of the steel pipe and prevent secondary oxidation. Through this step, the surface of the steel pipe remains dry and no new rust layer is generated, ensuring that the coating adheres to the clean and dry surface of the steel pipe. The surface of the steel pipe after drying no longer contains moisture, avoiding contact between the coating and moisture, ensuring the firmness and durability of the coating.

[0058] S4, Plastic coating process

[0059] Regarding step S4, the plastic coating process is the core step in the production process of plastic coated composite steel pipes. The quality of the plastic coating layer directly determines the corrosion resistance, mechanical properties and long-term performance of the steel pipe. The plastic coating process requires that the coating be evenly and firmly attached to the surface of the steel pipe to ensure that it exhibits excellent corrosion resistance in various complex environments. This embodiment adopts an electrostatic powder spraying process, which can effectively improve the uniformity and adhesion of the coating.

[0060] In this embodiment, first, the pretreated steel pipe is sent to the plastic coating equipment and an electrostatic powder spraying process is adopted. During the spraying process, the surface of the steel pipe is first electrostatically precipitated to remove dust and impurities on the surface to ensure that the surface of the steel pipe is clean. Then, an electrostatic spray gun is used to spray the plastic coating powder onto the surface of the steel pipe. The type of coating can be selected according to the use environment. Common coatings include epoxy resins, polyethylene and other coatings with strong corrosion resistance. During powder spraying, the steel pipe is attracted by the electric charge, and the powder coating is evenly sprayed onto the surface of the steel pipe. The spraying time is 1 to 2 minutes, and the specific time depends on the thickness requirement of the coating.

[0061] After spraying, the steel pipe enters the curing oven for heat curing. The temperature of the curing oven is generally set between 180℃ and 220℃, and the curing time is 15 to 20 minutes. Through heating, the resin components in the coating will undergo a chemical reaction to form a dense cured coating, ensuring that the coating is firmly bonded to the surface of the steel pipe. The cured coating needs to be cooled to ensure that it forms a uniform and solid coating structure.

[0062] Electrostatic powder spraying uses electrostatic force to evenly adhere the coating to the surface of the steel pipe, and the curing process ensures the density and adhesion of the coating. Through this process, the coating can evenly cover the surface of the steel pipe and provide long-lasting corrosion protection under different use environments. The cured coating not only has good corrosion resistance, but also can effectively resist mechanical damage from the external environment.

[0063] S5. Surface quality inspection

[0064] For step S5, surface quality inspection is an important step to ensure the quality of the plastic-coated composite steel pipe. The surface quality directly affects the performance and corrosion resistance of the steel pipe. Therefore, after the plastic coating is completed, its surface must be inspected to ensure that the coating is uniform, defect-free and firmly attached.

[0065] In this embodiment, a method combining visual inspection and online inspection is used to detect surface quality. First, a visual inspection is performed to check whether there are obvious defects such as coating loss, bubbles, cracks, etc. on the surface of the steel pipe. The inspector should inspect the surface of the steel pipe according to standards such as uniformity and integrity of the coating. After the visual inspection, an online coating thickness measuring instrument is used for precise testing to ensure that the thickness of the coating meets the design requirements. The conventional coating thickness ranges from 200 to 500 microns, and the specific thickness requirements depend on different application scenarios.

[0066] If online testing reveals insufficient coating thickness or unacceptable areas, the pipe will be returned for repair or re-coating.

[0067] Through visual inspection and online coating thickness detection, defects and deficiencies in the coating can be quickly and effectively discovered, ensuring that each steel pipe can meet quality requirements before leaving the factory. The implementation of this step ensures the uniformity and adhesion of the coating, providing effective protection for the corrosion resistance of the steel pipe.

[0068] S6. Solidification and cooling.

[0069] With respect to step S6, solidification and cooling are necessary post-processing steps in the manufacturing process of the plastic-coated composite steel pipe, the purpose of which is to allow the coating to form a solid protective layer on the surface of the steel pipe, which has excellent corrosion resistance, mechanical damage resistance and long-term use performance.

[0070] In this embodiment, the curing and cooling process is processed by a continuous heating furnace. The curing temperature is usually set to 180°C to 220°C, and the curing time is controlled between 15 and 20 minutes. When the steel pipe passes through the heating furnace, the temperature gradually rises to the target curing temperature, and the resin in the coating undergoes a chemical reaction to form a solid cured coating. After curing is completed, the steel pipe passes through the cooling zone and is cooled to room temperature by natural cooling or forced air cooling.

[0071] The curing process ensures that the chemical reaction of the coating is completed, so that the coating is firmly bonded to the surface of the steel pipe, and the coating's corrosion resistance, mechanical damage resistance and other properties are enhanced. The cooling step ensures that the coating remains stable at room temperature, avoiding cracks or shedding of the coating caused by too fast cooling.

[0072] Embodiment 2:

[0073] This embodiment provides a corrosion-resistant plastic-coated composite steel pipe and a preparation process thereof, which specifically includes the following steps:

[0074] S1. Selection and treatment of base steel pipe

[0075] Regarding step S1, pickling pretreatment is an important step in the preparation process of plastic-coated composite steel pipes, which aims to remove scale, rust and other surface contaminants on the surface of the steel pipe, providing a basis for subsequent coating adhesion and surface treatment. In this step, a chemical method is used to remove contaminants on the surface of the steel pipe through a pickling solution to ensure that the surface of the steel pipe is clean and enhance its adhesion to the plastic coating layer.

[0076] In this embodiment, the surface of the steel pipe is first treated with a pickling solution, the main component of which is hydrochloric acid or sulfuric acid, the concentration is controlled between 15% and 25%, the temperature is controlled between 40°C and 70°C, and the pickling time is controlled between 8 and 18 minutes to ensure that the surface oxide scale and rust can be effectively removed. The surface of the steel pipe after pickling should show a metallic luster without oxide scale, rust and other contaminants.

[0077] S2, neutralization and washing

[0078] For step S2, after the steel pipe is pickled, it needs to be neutralized and washed with water to remove the acidic substances remaining in the pickling process and ensure that the surface of the steel pipe will not be corroded. The neutralizing liquid is a sodium carbonate solution with a concentration of 3% to 6%. After neutralization, the steel pipe is thoroughly rinsed with clean water, and the rinsing time is controlled to be 6 to 12 minutes.

[0079] S3. Drying

[0080] For step S3, the drying method is hot air drying and heating furnace drying. When the steel pipe enters the heating furnace, the temperature is set between 90°C and 110°C, and the drying time is controlled between 15 and 20 minutes to ensure that the surface of the steel pipe is completely dry to avoid secondary oxidation and corrosion.

[0081] S4, Plastic coating process

[0082] The coating process is electrostatic powder spraying. The coating uses epoxy resin, the spraying time is 1 to 2 minutes, and the coating thickness is controlled at 100 to 300 microns. The curing temperature is 170℃ to 200℃, and the curing time is 12 to 18 minutes.

[0083] S5. Surface quality inspection

[0084] Surface quality inspection is carried out by visual inspection and coating thickness measuring instruments. Online coating thickness measurement ensures that the coating thickness meets the design requirements.

[0085] S6, solidification and cooling

[0086] The steel pipe is treated in a curing furnace with a temperature set at 180℃ to 200℃ and a curing time of 10 to 15 minutes. Natural cooling is used during the cooling process.

[0087] In Example 2, although the processing steps are similar to those in Example 1, the temperature and time control in the pickling treatment and drying steps are slightly loose, which results in weaker coating adhesion, and lower corrosion resistance and mechanical properties than in Example 1. The coating quality and surface adhesion of Example 2 are poor. Although it can achieve a certain corrosion resistance effect, it is prone to coating peeling or corrosion risks in long-term use, and the overall effect is lower than that of Example 1.

[0088] Embodiment three:

[0089] This embodiment provides a corrosion-resistant plastic-coated composite steel pipe and a preparation process thereof, which further optimizes the adhesion, corrosion resistance and mechanical properties of the coating, and specifically includes the following steps:

[0090] S1. Selection and treatment of base steel pipe

[0091] Similar to Example 1, a steel pipe without obvious defects is first selected as the substrate and pickled. During the pickling process, a hydrochloric acid solution with a concentration of 20% to 30% is used, the temperature is 60°C to 75°C, and the pickling time is controlled at about 12 minutes to ensure that the rust and scale on the surface of the steel pipe are completely removed. After pickling, water is used for thorough cleaning to remove the residual acid solution, and nitrogen is used to blow dry to prevent secondary oxidation.

[0092] S2. Surface laser treatment

[0093] This embodiment introduces laser surface treatment technology to further enhance the adhesion between the coating and the steel pipe substrate. The surface of the steel pipe is scanned by a laser beam to form a microscopic concave-convex structure. The laser power is 500W, the scanning speed is 2mm / s, the laser treatment area evenly covers the surface of the steel pipe, and the treatment depth is 0.05mm to 0.1mm.

[0094] S3. Coating pretreatment and spraying

[0095] The coating material is a mixture of epoxy resin and polyurethane with high heat resistance and high adhesion, with a ratio of 2:1. The coating is evenly applied to the surface of the steel pipe through an electrostatic spraying process. During the electrostatic spraying process, the spraying time is controlled within 2 to 3 minutes to ensure the uniformity and adhesion of the coating. The coating thickness is between 200 and 350 microns.

[0096] S4. Curing and heating treatment

[0097] After the coating is sprayed, the steel pipe enters the curing furnace for high-temperature curing. The curing temperature is 190°C and the curing time is 15 minutes to ensure that the coating can be fully cross-linked, cured and form a high-strength protective layer. After curing, the steel pipe is cooled to room temperature at room temperature.

[0098] S5. Coating quality inspection and repair

[0099] In Example 3, the coating inspection requirements are more stringent, and an online coating thickness tester and coating adhesion tester are used. The coating thickness is required to be in the range of 200 to 350 microns, and the coating adhesion is required to reach 5N / mm 2 If the adhesion is insufficient or the coating is uneven, repair it immediately by applying it manually with a brush and then curing it again.

[0100] S6. Corrosion resistance test

[0101] This embodiment pays special attention to the corrosion resistance of the coating, and uses salt spray test and immersion test to test the plastic-coated composite steel pipe. In the salt spray test, the coating can withstand 1500 hours of salt spray corrosion without obvious coating shedding or corrosion; in the immersion test, the coating has no obvious immersion shedding or corrosion marks within 24 hours, proving that its corrosion resistance is greatly improved.

[0102] S7. Mechanical properties test

[0103] The peel strength test between the coating and the base steel pipe was carried out. The test results showed that the peel strength of the coating was 6N / mm 2 , which is significantly better than Example 1 and Example 2, indicating that the coating has strong adhesion and good durability.

[0104] Compared with Example 1 and Example 2, Example 3 further improves the adhesion between the coating and the steel pipe through laser surface treatment technology, and optimizes the composition and curing process of the coating, significantly improving the corrosion resistance and mechanical strength. Specifically, the coating has a longer tolerance time in the salt spray test and performs better in the immersion test. At the same time, the adhesion test results of the coating show that the coating adhesion of Example 3 is significantly higher than that of Example 1 and Example 2. Overall, Example 3 performs better than the previous embodiments in many aspects and has higher practical application value.

[0105] Table 1 Comparison table of experimental data of embodiment

[0106]

[0107] Data Analysis:

[0108] Coating thickness: The coating thickness of each embodiment is in the range of 200-350 μm, with embodiment 2 being slightly thicker and embodiment 3 being slightly thinner.

[0109] Coating adhesion: The adhesion of Example 3 is significantly better than that of Examples 1 and 2, showing stronger durability.

[0110] Salt spray corrosion resistance: Example 3 performed best in the salt spray test, and the corrosion resistance time was significantly improved.

[0111] Immersion test: Example 3 did not fall off within 24 hours, and had stronger moisture resistance and anti-immersion capabilities.

[0112] Peel strength: The peel strength of Example 3 is stronger than that of the other two examples, proving that its coating is more robust.

[0113] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant plastic-coated composite steel pipe, characterized in that: The surface of the steel pipe includes the following layers: Base steel pipe, Nanomaterial-enhanced interface treatment layer, Plastic coating; The interface treatment layer is composed of nano silicon or nano aluminum oxide, with a thickness of 10-20 μm, and the plastic coating layer is composed of a composite material of modified epoxy resin, modified polyethylene and polyvinyl chloride, with a thickness of 200-300 μm.

2. The corrosion-resistant plastic-coated composite steel pipe according to claim 1, characterized in that: The roughness of the steel pipe surface is increased by laser treatment, the laser power is 800-1200W, and the scanning speed is 0.5-2m / min.

3. The corrosion-resistant plastic-coated composite steel pipe according to claim 1, characterized in that: The nano material enhanced interface treatment layer adopts ultrasonic dispersion technology to disperse nano silicon or nano aluminum oxide, the particle size of the nano particles in the solution is 20-50nm, and the thickness of the interface treatment layer is 10-20μm.

4. A process for preparing a corrosion-resistant plastic-coated composite steel pipe, according to a corrosion-resistant plastic-coated composite steel pipe according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Surface pretreatment of the steel pipe, including pickling to remove scale, rust and contaminants; Step 2: Surface laser treatment: Use laser to treat the surface of the steel pipe to form a micron-level rough texture; Step 3: Interface treatment: coating the surface of the steel pipe with a nano-material-enhanced interface treatment layer to form a coating with a thickness of 10-20 μm; Step 4: Plastic coating: Apply the coating material to the surface of the steel pipe by electrostatic spraying, cast coating or dipping, and then cure it after coating; Step 5: Quality inspection, testing the coating adhesion, thickness and corrosion resistance to ensure that the product meets the requirements.

5. A process for preparing a corrosion-resistant plastic-coated composite steel pipe according to claim 4, characterized in that: The pickling step uses hydrochloric acid or sulfuric acid solution, the pickling temperature is 30-60° C., the pickling time is 5-15 minutes, and water washing and drying are performed after pickling.

6. The process for preparing a corrosion-resistant plastic-coated composite steel pipe according to claim 4, characterized in that: The laser power of the laser processing step is 800-1200W, the scanning speed is 0.5-2m / min, the processing depth is 5-10μm, and a uniform roughness is formed.

7. The process for preparing a corrosion-resistant plastic-coated composite steel pipe according to claim 4, characterized in that: In the coating step, the coating material is composited by modified epoxy resin, modified polyethylene and polyvinyl chloride, the coating thickness is 200-300 μm, the curing temperature is 180-220° C., and the curing time is 20-30 minutes.

8. A process for preparing a corrosion-resistant plastic-coated composite steel pipe according to claim 4, characterized in that: The quality inspection steps include: Use scanning electron microscopy to examine the coating surface condition; The adhesion between the coating and the steel pipe substrate was evaluated using tensile and shear tests; Evaluate the corrosion resistance of coatings through salt spray test and acid spray test; Measure the coating thickness using a coating thickness gauge.

9. A process for preparing a corrosion-resistant plastic-coated composite steel pipe according to claim 4, characterized in that: After the coating is cured, the coating adhesion on the steel pipe surface is not less than 20MPa, and the corrosion resistance meets the requirements of the salt spray test. After 1000 hours of salt spray test, there is no obvious shedding or cracking of the coating.

Images