In modern infrastructure construction, industrial production, and various building projects, steel pipes serve as crucial carriers for transporting fluids, gases, and other substances. Their quality and performance directly impact the operational efficiency and reliability of the entire system. Plastic-coated steel pipes, a new type of steel pipe combining the high strength of metal steel with the excellent corrosion resistance and insulation properties of plastic coatings, have been widely used in numerous fields in recent years. They are gradually becoming a powerful alternative to traditional steel pipes, playing a vital role in promoting industry development and improving project quality.

First, the structure and principle of plastic-coated steel pipes
(I) Structural composition of plastic-coated steel pipes.
Plastic-coated steel pipes mainly consist of an inner metal pipe body and an outer plastic coating layer. The metal pipe body is typically made of high-quality welded steel pipes or seamless steel pipes, providing solid mechanical support and ensuring it can withstand certain internal pressure and external loads. The outer plastic coating layer can be made of PE, EP, PP, or other plastic materials, depending on the application. These plastic coatings adhere tightly to the surface of the metal pipe body, forming a continuous and dense protective barrier.
(II) Working Principle of Plastic-Coated Steel Pipes.
From a corrosion prevention perspective, the plastic coating effectively isolates the metal pipe body from external corrosive media, preventing direct contact between the metal and corrosive substances such as water, oxygen, acids, alkalis, and salts, thereby inhibiting electrochemical and chemical corrosion. In fluid transportation, the smooth plastic coating significantly reduces the frictional resistance between the fluid and the pipe wall, making the fluid flow more smoothly within the pipe, reducing energy loss, and improving transportation efficiency. Simultaneously, some plastic coatings also possess good insulation properties, effectively preventing stray current corrosion of the pipeline, further ensuring the pipeline’s service life.

Second, Production Process of Plastic-Coated Steel Pipes
(I) Raw Material Selection for Plastic-Coated Steel Pipes.
- Metal Pipe Body: For welded steel pipes, the quality of the steel strip directly affects the strength and welding performance of the steel pipe. Strict control of the chemical composition, mechanical properties, and surface quality of the steel strip is necessary. Seamless steel pipes require pure steel billet material and a uniform internal structure to ensure the reliability of the steel pipe during subsequent processing and use.
- Coating Material: Different types of plastic coating materials have their own unique performance characteristics. For example, polyethylene coatings possess good flexibility, impact resistance, and chemical corrosion resistance, making them suitable for general water and gas pipelines; epoxy resin coatings, on the other hand, offer excellent adhesion, hardness, and solvent resistance, and are commonly used in chemical, power, and other fields where high corrosion resistance is required. During production, the appropriate coating material must be precisely selected based on actual application needs.
(II) Pretreatment of Plastic-Coated Steel Pipes.
- Cleaning: Alkaline cleaning, ultrasonic cleaning, and other methods are used to remove oil, dust, cutting fluid, and other impurities from the steel pipe surface, ensuring the smooth progress of subsequent processing steps.
- Rust Removal: Through pickling, sandblasting, and other methods, rust, scale, and other impurities are thoroughly removed from the steel pipe surface, giving it a metallic luster and providing a good adhesion base for the plastic coating. Sandblasting effectively increases the surface roughness of the steel pipe, improving the mechanical bonding force between the coating and the substrate.
(III) Plastic Coating Process of Plastic-Coated Steel Pipes.
- Electrostatic Spraying: A high-voltage electrostatic generator is used to negatively charge the plastic powder. Under the action of an electric field, the plastic powder is uniformly adsorbed onto the grounded steel pipe surface. This method produces a uniform coating thickness, has high production efficiency, and is suitable for large-scale production.
- Dip Coating: Preheated steel pipes are immersed in a dip coating tank containing molten plastic, allowing the plastic to be evenly coated onto the surface of the steel pipe. The coating is then cured by heating. Dip coating can achieve a thicker coating with strong adhesion to the steel pipe.
- Rotational Molding: A measured amount of plastic powder is added to a rotating mold (steel pipe). Heating melts the plastic powder within the mold, causing it to adhere evenly to the inner wall of the mold. After cooling, a coating is formed. Rotational molding is suitable for manufacturing large-diameter, thick-walled plastic-coated steel pipes.
(IV) Curing Treatment of Plastic-Coated Steel Pipes.
The plastic-coated steel pipes require high-temperature curing to induce a cross-linking reaction in the plastic coating, forming a stable three-dimensional network structure, thereby improving the coating’s hardness, wear resistance, and chemical corrosion resistance. The curing temperature and time are precisely controlled according to the type of plastic coating material and the coating thickness to ensure optimal coating performance.

Third, Performance Characteristics of Plastic-Coated Steel Pipes
(I) Corrosion Resistance of Plastic-Coated Steel Pipes.
- Chemical Corrosion Resistance: In various chemical media environments, such as industrial wastewater containing acids, alkalis, and salts, and chemical reagent conveying pipelines, the plastic coating of plastic-coated steel pipes effectively resists the erosion of chemical substances, and its corrosion resistance is far superior to that of ordinary steel pipes. Experimental tests show that after prolonged immersion in strongly acidic (pH value approximately 2) or strongly alkaline (pH value approximately 12) solutions, the coating of plastic-coated steel pipes shows no obvious signs of corrosion, while ordinary steel pipes exhibit severe rust.
- Electrochemical Corrosion Resistance: Due to the insulating properties of the plastic coating, the electron conduction path between the metal pipe body and the external electrolyte solution is blocked, reducing the probability of electrochemical corrosion. In environments prone to electrochemical corrosion, such as damp soil and seawater, plastic-coated steel pipes exhibit good stability, greatly extending the service life of the pipeline.
(II) Mechanical Properties of Plastic-Coated Steel Pipes.
- High Strength: Relying on the high strength characteristics of the metal pipe body, plastic-coated steel pipes can withstand high internal pressure and external loads. Taking the common DN100 plastic-coated steel pipe as an example, its working pressure can reach 1.6MPa or even higher, meeting the high-pressure requirements of applications such as urban water supply and gas transmission.
- Impact Resistance: The plastic coating has a certain degree of flexibility and buffering effect, which can absorb and disperse external impact energy, making the plastic-coated steel pipe less prone to cracking or coating peeling when subjected to accidental impact. Even if the steel pipe is subjected to a certain degree of impact at the construction site, it can still maintain good performance.
(III) Fluid Transport Performance of Plastic-Coated Steel Pipes.
- Low Friction Resistance: The smooth plastic coating significantly reduces the coefficient of friction of fluid flowing inside the pipe. Compared with ordinary steel pipes, the hydraulic friction coefficient of plastic-coated steel pipes can be reduced by about 30%-40%, which means that under the same flow rate and transmission distance, using plastic-coated steel pipes can reduce the energy consumption of the transmission pump and lower operating costs.
- Anti-Scale Performance: The plastic coating surface is not prone to the adhesion of impurities and microorganisms, effectively preventing the occurrence of scale buildup inside the pipe. During long-term water transportation, the inner wall of the plastic-coated steel pipe remains smooth, and the cross-sectional area of ​​the water flow remains essentially constant, ensuring stable water delivery capacity and reducing the workload of pipe cleaning and maintenance.
(IV) Insulation and Weather Resistance.
- Insulation Performance: The plastic coating of the plastic-coated steel pipe has excellent insulation properties, effectively preventing stray current corrosion of the pipe and avoiding safety accidents caused by leakage. In fields with high insulation requirements, such as power cable protection conduits and communication pipelines, plastic-coated steel pipes have significant advantages.
- Weather Resistance: The specially formulated plastic coating can adapt to different climatic conditions. Under harsh environments such as high temperature, low temperature, and ultraviolet radiation, the coating performance remains stable, and it is not prone to aging or cracking. Whether in hot desert regions or cold polar environments, plastic-coated steel pipes can be used normally, demonstrating excellent weather resistance.

Fourth, Application Areas of Plastic-Coated Steel Pipes
(I) Building Water Supply and Drainage Systems.
- Domestic Water Supply: In residential and commercial buildings, plastic-coated steel pipes, due to their excellent corrosion resistance and hygienic properties, ensure water quality remains unpolluted, providing users with safe and clean domestic water. Their smooth inner walls reduce water flow resistance, making the water supply more stable and efficient.
- Firefighting Water Supply Systems: In fire protection engineering, the high strength and corrosion resistance of plastic-coated steel pipes enable them to withstand the impact of high-pressure water flow during a fire, while ensuring that the reliability of fire-fighting water supply is not affected by corrosion during long-term use. Their good flame-retardant properties also meet the safety requirements of fire-fighting pipelines.
(II) Municipal Engineering.
- Urban Water Supply and Sewage Treatment: Urban water supply pipeline networks require steel pipes with excellent corrosion resistance and long-term stability. Plastic-coated steel pipes meet these requirements, ensuring the safety and stability of urban water supply. In sewage treatment, plastic-coated steel pipes can effectively resist the erosion of various corrosive substances in sewage, ensuring the normal operation of sewage transportation and treatment systems.
- Gas Transmission: Gas transmission pipelines require extremely high safety and sealing performance from the steel pipes. Plastic-coated steel pipes not only possess excellent mechanical strength, capable of withstanding the pressure during gas transmission, but their plastic coating also prevents impurities in the gas from corroding the pipeline, thus improving the safety of gas transmission.
(III) Industrial Sector.
- Chemical Industry: In chemical production, various highly corrosive chemical media, such as acids, alkalis, and salt solutions, are frequently transported. Plastic-coated steel pipes, with their superior chemical corrosion resistance, are an ideal choice for chemical pipeline systems, effectively preventing pipeline leaks and ensuring the safety and stability of the production process.
- Power Industry: In power engineering, plastic-coated steel pipes can be used for cable protection conduits, circulating water pipelines, etc. Their insulation properties effectively protect cables from external electromagnetic interference and stray currents, while their corrosion resistance extends the service life of circulating water pipelines and reduces maintenance costs.
(IV) Agricultural Irrigation:
In agricultural irrigation systems, plastic-coated steel pipes can be used to transport irrigation water. Their corrosion resistance prevents impurities and chemicals in the water from corroding the pipeline, extending its service life. The smooth inner wall reduces water flow resistance, improves irrigation efficiency, and helps to achieve water-saving irrigation.