In modern industry and infrastructure construction, pipes serve as core components for conveying media and providing structural support. Their performance directly impacts project quality and operational efficiency. With continuous technological advancements, single-material pipes are increasingly unable to meet the diverse demands of complex working conditions. Composite steel pipe, with its core characteristics of "complementary advantages and combined performance," has become a key development direction in the pipe industry in recent years. Made by combining two or more different metallic or non-metallic materials through a specialized process, composite steel pipe retains the high strength and ease of processing of the base material while also offering key properties such as corrosion resistance and wear resistance of the cladding. It is widely used in a variety of fields, including petrochemicals, municipal water supply, and energy transportation.

I. Definition and Classification of Composite Steel Pipe

Composite steel pipe is not a single product, but rather a product system based on a "composite structure." Academically, it refers to a tubular product formed by firmly bonding two or more materials with different properties using physical, chemical, or mechanical methods. The structural support portion is called the "base material," while the corrosion and wear resistance portion is called the "cladding." Based on the material combination of the base material and the cladding, composite steel pipes can be divided into three main categories, each corresponding to a distinct application scenario.

(I) Metal-Metal Composite Steel Pipes

This is currently the most widely used category, with the core principle being "strength guaranteed by a low-cost base material and longevity enhanced by a highly corrosion-resistant cladding." Common combinations include stainless steel composite pipes (carbon steel/low-alloy steel as the base material, copper/brass as the cladding), and nickel-based alloy composite pipes (carbon steel as the base material, Hastelloy and Monel as the cladding). For example, stainless steel composite pipes: their carbon steel base material ensures mechanical strength and impact resistance, meeting the requirements of high-pressure transmission; while the stainless steel cladding provides resistance to corrosive environments such as acidic and alkaline media and seawater, addressing the high cost and corrosion susceptibility of pure stainless steel pipes. These pipes are widely used in chemical wastewater transportation and municipal pipelines in coastal areas. (2) Metal-Non-Metal Composite Steel Pipes
This type of pipe combines the strength of metals with the corrosion resistance of non-metals, making it suitable for applications with high corrosion and low pressure. Typical examples include steel-plastic composite steel pipes (carbon steel base material, polyethylene or polypropylene cladding) and steel-glass composite steel pipes (carbon steel base material, glass fiber reinforced plastic cladding). Steel-plastic composite steel pipes combine the rigidity of carbon steel with the chemical resistance of plastic, while offering a smooth inner wall, low fluid resistance, and minimal maintenance. They have become a preferred material for building water supply and drainage, and for transporting chemical liquids. Steel-glass composite steel pipes further enhance heat resistance and insulation, making them suitable for specialized applications such as high-temperature corrosive gas transportation and insulated piping in the power industry.
(3) Non-Metal-Non-Metal Composite Steel Pipes
Primarily addressing performance requirements in extreme environments, they combine different non-metallic materials to compensate for the shortcomings of single non-metallic pipes. Examples include glass fiber-carbon fiber composite steel pipes (glass fiber as the base material ensures toughness, carbon fiber as the reinforcement layer enhances strength) and polyethylene-polytetrafluoroethylene composite steel pipes (polyethylene provides structural support, while polytetrafluoroethylene provides resistance to ultra-high and low temperatures and severe corrosion). These pipes are lightweight, weather-resistant, and offer excellent insulation properties. They are commonly used in high-end applications such as lightweight aerospace piping, high-purity media transportation in the semiconductor industry, and piping for polar research equipment.

II. Core Production Processes for Composite Steel Pipes

The performance of composite steel pipes depends critically on the "bonding strength of the composite interface." Only a firm, seamless bond between the base material and the cladding prevents delamination and shedding during use, ensuring overall stable performance. Currently, mainstream production processes can be divided into three categories, each with significant differences in their principles, advantages, and applicable scenarios.

(I) Mechanical Composite Processes

Mechanical composite processes rely on "physical pressure" to force the two materials into a close fit, creating a mechanical interlock or interference fit. Core processes include cold rolling composite, explosive composite, and hydraulic bulging composite. Cold rolling cladding involves rolling a cladding metal strip and a base steel pipe through multiple sets of rollers, causing the cladding metal to plastically deform and tightly wrap around the base. This mature process is low-cost and suitable for mass production of small and medium-diameter stainless steel composite pipes. Explosive cladding utilizes the instantaneous high pressure generated by explosive detonation to plastically deform and bond the cladding metal and base steel pipe under high temperature and pressure. This creates an extremely strong bond and can be used for large-diameter, thick-walled nickel-based alloy composite steel pipes. However, production efficiency is low and cost is high, making it primarily used for pipes used in special applications. Hydraulic bulging cladding involves injecting high-pressure liquid into a double-layered tube billet, causing the inner tube to plastically expand and tightly fit the outer tube. This method is suitable for composite steel pipes with special cross-sections or thin walls, resulting in high precision and a smooth inner wall.

(II) Metallurgical Composite Process

Metallurgical composite processes use high-temperature heating to induce metallurgical reactions in the materials, forming an atomic-level bond between the base and cladding. This creates a distinct interface and overall performance closer to that of a single alloy. Mainstream processes include hot-dip cladding, overlay welding, and laser cladding. Hot-dip cladding involves immersing the base steel pipe in molten cladding metal (such as zinc, aluminum, or stainless steel alloys), forming an alloy layer through diffusion reaction. This simple and cost-effective process is widely used for municipal guardrails and low-pressure water pipes, where corrosion protection requirements are low. Overlay welding uses heat sources such as arcs and plasma arcs to melt cladding metal powder or welding wire onto the inner or outer wall of the base pipe. The cladding thickness can be adjusted as needed, making it suitable for thick-walled chemical reactor pipes and oil and gas well casings that require high corrosion resistance. Laser cladding utilizes a high-energy-density laser to rapidly melt and solidify the cladding material and the base pipe surface, forming a thin, uniform, high-performance coating with a minimal heat-affected zone and high cladding purity. It is commonly used for precision equipment piping and radiation-resistant composite steel pipes for nuclear power plants.

(III) Chemical cladding processes
Chemical cladding processes rely on chemical reactions or diffusion to form chemical bonds between the cladding material and the base pipe. These processes primarily include chemical vapor deposition (CVD) and sol-gel methods. Chemical vapor deposition is a process in which a gas containing coating elements is introduced into a high-temperature substrate pipe. The gas decomposes and deposits on the substrate surface to form a coating. This method can produce ultra-thin, high-purity ceramic or metal coatings, which are suitable for high-purity pipelines and high-temperature anti-oxidation pipelines in the semiconductor industry. The sol-gel method is a process in which the coating material is made into a sol, which is then coated on the substrate surface and dried and sintered to form a gel coating. The process is flexible and can achieve the composite of complex-shaped pipes. It is often used in the preparation of non-metal-non-metal composite steel pipes, such as ceramic-glass composite pipes.