Coated Steel Pipe

Published:2025-07-24 | Last Updated: 2025-07-24    Views: 3

I. Definition of coated steel pipe

Coated steel pipe, as the name suggests, is a composite pipe material made by coating the inner and outer walls of steel pipe with one or more layers of plastic.

This innovative pipe material cleverly combines the high strength and pressure resistance of steel with the corrosion resistance and wear resistance of plastic.

It effectively addresses the drawbacks of traditional steel pipes, such as corrosion, scaling, and short service life, while overcoming the weaknesses of plastic pipes, such as low strength and poor pressure resistance. As a result, it offers broad application prospects in modern industrial and civil engineering fields.

II. The Composition of Coated Steel Pipes: Unveiling the Core Advantages of Composite Pipes  

The exceptional performance of coated steel pipes stems from their unique composite structure. This innovative pipe material is not made from a single material but cleverly combines the strength of steel pipes with the superior properties of plastic.

(1) Steel Pipe Base Material: A Sturdy Framework

The “framework” of coated steel pipes consists of carefully selected steel pipes, including:

Seamless steel pipes

Welded steel pipes (both straight seam welded and spiral welded)

Galvanized steel pipes

These steel pipes undergo rigorous pre-treatment before coating to ensure the subsequent coating adheres firmly.

(2) Plastic Coating: Comprehensive Protection

After the steel pipe substrate is pre-treated, advanced coating processes such as high-pressure electrostatic spraying, hot-dip coating, rotomolding, or fusion wrapping are used to uniformly and firmly apply high-performance polymer materials to the inner and outer walls of the steel pipe.  

Common plastic coating materials include:  

Polyethylene (PE)  

Epoxy resin (EP)  

Polyvinyl chloride (PVC)  

Polypropylene (PP)  

Nylon (PA)

(3) Internal and External Plastic Coating: The Secret of Performance Synergy

The final plastic-coated steel pipe is a composite pipe with both internal and external plastic coatings. This means it not only inherits the steel pipe's excellent pressure-bearing capacity but also gains the following superior properties of plastic:

Corrosion resistance

Scale prevention capability

Smooth low friction

This internal and external plastic coating structure enables the plastic-coated steel pipe to perform exceptionally well in various harsh environments, making it an ideal pipeline solution for modern engineering applications.

III. Production Process of Coated Steel Pipes: A Comprehensive Analysis from Base Pipe to Finished Product

The superior performance of coated steel pipes is closely tied to their complex and precise production process. Every step, from raw materials to the final product, is critical in ensuring the quality and durability of coated steel pipes.

(1) Base Pipe Pretreatment: Laying the Foundation for the Coating

Thorough pretreatment of the steel pipe is a crucial step before coating.

This process aims to:  

Remove contaminants: A combination of physical methods (such as sandblasting or shot blasting) and chemical methods (such as acid washing) is used to thoroughly remove oil, scale, and rust from the surface of the steel pipes. This ensures the surface achieves the required cleanliness, providing an ideal adhesion base for the subsequent coating.  

Enhance adhesion: Phosphating treatment is then performed. This creates a dense phosphating film on the surface of the steel pipe, significantly improving the adhesion between the coating and the steel pipe substrate and preventing the coating from peeling off.

(2) Heating and preheating: Preparing for coating

After pretreatment, the steel pipes must undergo precise preheating to reach the ideal temperature required for coating. The purpose of preheating is to ensure that the coating powder melts quickly upon contact with the pipe wall and adheres uniformly to the surface of the steel pipe, forming a continuous coating.

(3) Coating process: Diverse applications of core technology

The core of coated steel pipe manufacturing lies in diverse coating processes. Depending on the type of plastic material and application requirements, the most suitable coating method is selected:

High-pressure electrostatic spraying: Suitable for powder coatings such as epoxy resin and polyester. Through electrostatic force, charged powder is uniformly adsorbed onto the preheated steel pipe surface, followed by high-temperature curing to form a dense, smooth coating.

Hot-dip coating: Suitable for plastics such as polyethylene and polyvinyl chloride. The preheated steel pipe is immersed in molten plastic fluid, causing the plastic to uniformly coat the inner and outer walls of the steel pipe, then removed and cooled to cure. This method forms a coating with uniform thickness and strong adhesion.

Rotational molding: Primarily suitable for large, complex-shaped components. Plastic powder is placed into a mold, which is heated and rotated around two axes, causing the plastic to melt and evenly distribute along the inner walls of the mold. After cooling, the mold is removed to form the final shape.

Fusion winding: Suitable for materials such as PE and PP. Using specialized winding equipment, molten plastic strips are continuously wound around the surface of the steel pipe to form a dense coating.

Dip coating/spray coating: For liquid coatings (such as liquid epoxy coatings), dip coating or spray coating can be used to form a coating on the inner surface of steel pipes, ensuring corrosion resistance of the inner surface.  

(4) Curing and cooling: Stabilizing coating performance  

After coating, the coating must undergo high-temperature curing. This step aims to promote full cross-linking of the coating material, forming a stable physical and chemical structure to achieve optimal mechanical and corrosion-resistant properties. The cured coating must be gradually cooled to room temperature to avoid stress within the coating caused by sudden temperature drops, which could affect its service life.

(5) Quality Inspection: Ensuring Compliance with Standards

To ensure the exceptional quality and reliability of coated steel pipes, each pipe undergoes a series of rigorous inspections. The following are the main inspection items for coated steel pipes and their purposes:

IV. Coated Steel Pipes: Why They Are the Ideal Choice for Modern Engineering

Coated steel pipes, with their unique composite structure, offer a range of superior performance characteristics that traditional pipes cannot match.

(1) Exceptional Corrosion Resistance: Ensuring Long-Term Durability

The core advantage of coated steel pipes lies in their outstanding corrosion resistance. The plastic coating completely isolates the steel pipe substrate from corrosive media such as acids, alkalis, salts, and organic solvents. This not only effectively prevents the steel pipe from being corroded but also significantly extends the overall service life of the pipeline and reduces maintenance costs.  

(2) Superior Anti-scaling Performance: The Secret to Efficient Transportation  

Say goodbye to the hassle of pipeline scaling! The plastic coating surface of coated steel pipes is extremely smooth with a low friction coefficient. This effectively inhibits microbial adhesion and scaling on the inner walls of the pipeline, thereby reducing fluid resistance and ensuring transportation efficiency. For water supply, drainage, and fire protection systems, this means stable flow, reduced energy consumption, and avoidance of performance degradation caused by scaling.

(3) Inherits the Advantages of Steel Pipes: Combines High Mechanical Strength

Coated steel pipes perfectly inherit the inherent high mechanical strength and pressure-bearing capacity of steel pipes. They can withstand high working pressures and external impacts, are unlikely to deform or crack, and provide excellent safety assurance. This means the pipes remain stable and reliable even under harsh conditions.

(4) Hygienic and non-toxic: A safe choice for drinking water  

In the field of drinking water transportation, coated steel pipes are an ideal healthy choice. We use food-grade plastic coatings that meet drinking water standards, ensuring the product is non-toxic and odorless, and does not contaminate water quality. This safeguards residents' drinking water safety.

(5) Low fluid resistance: A model of energy efficiency  

The smoothness of the coated inner wall far exceeds that of traditional steel pipes, with a lower roughness coefficient. This significantly reduces fluid friction resistance within the pipeline, minimizes head loss, thereby markedly saving pumping energy consumption and improving system operational efficiency.  

(6) Excellent Insulation Performance: A Solution to Electrocution Corrosion  

The plastic coating itself possesses excellent insulation properties. This enables coated steel pipes to effectively prevent electrocution corrosion and interference from stray currents, making them particularly suitable as cable protection pipes to safeguard internal circuit safety.

(7) Easy installation: Ensuring efficient construction

The ease of installation of coated steel pipes is another reason for their popularity. They support various connection methods, including threaded, flanged, grooved, and welded connections, making the installation process convenient and quick, significantly improving construction efficiency and saving valuable time for engineering projects.

V. Coated Steel Pipes: Widely Used

Coated steel pipes, with their unique performance advantages, have become the preferred piping solution for many industries. Their versatility makes them indispensable in the following key areas:

(1) Urban and Rural Water Supply and Drainage Systems

Whether for potable water supply, industrial water supply and drainage, or fire protection systems, coated steel pipes are an ideal choice. Their excellent corrosion resistance, anti-scaling properties, and non-toxic characteristics make them the preferred material to replace traditional galvanized pipes and cast iron pipes, ensuring water quality safety and efficient fluid transportation.

(2) Petrochemical and Energy

In the transportation of corrosive media such as oil, natural gas, and chemicals, the corrosion resistance of coated steel pipes is critical to ensuring the safety and stability of production processes.

(3) Power, Communication, and Protection

As cable protection pipes, coated steel pipes offer excellent insulation and mechanical strength, effectively protecting cables from external damage and electromagnetic interference, ensuring the smooth operation of power and communication lines.

(4) Mining, Metallurgy, and Wear-Resistant Conveyance

When handling abrasive media such as slurry, tailings, and coal slurry, the wear resistance of coated steel pipes significantly extends pipeline lifespan and reduces maintenance costs.

(5) Agricultural Irrigation and Water Resource Management

In agricultural irrigation systems, the corrosion resistance and low flow resistance of coated steel pipes help improve water resource utilization efficiency and support sustainable agricultural development.

(6) Marine Engineering and Extreme Environments

In marine engineering fields such as seawater desalination and ship piping, coated steel pipes demonstrate unparalleled advantages due to their excellent resistance to seawater corrosion.

Coated Steel Pipes: Industry Standards and a Bright Future

The production and application of coated steel pipes adhere to strict industry standards, ensuring reliable quality. For example, national standards such as GB/T 28897-2012 “Plastic-Coated Composite Steel Pipes for Water Supply” and GB/T 5135.11-2009 “Automatic Sprinkler Extinguishing Systems—Part 11: Coated Steel Pipes” provide detailed specifications for product performance, testing methods, and acceptance criteria. These standards form the foundation of the quality of plastic-coated steel pipes.

VI. Market Prospects: Continuous Growth in Demand and Increasingly Wide Applications

Looking ahead, the market prospects for coated steel pipes are bright. With the global increase in environmental awareness and the growing demand for higher-performance pipeline systems, the demand for coated steel pipes will continue to rise.

Especially in the following key areas:  

Municipal engineering  

Building plumbing and drainage  

Fire protection systems  

Chemical industry  

Energy sector  

Coated steel pipes are gradually replacing traditional pipe materials and capturing a larger market share due to their superior performance advantages. Additionally, with ongoing innovations in coating technology and materials, the performance of coated steel pipes will continue to improve, enabling them to demonstrate their value in even more fields in the future.