Why do steel pipes need corrosion prevention? As the name suggests, it is to prevent steel pipes from corrosion and prolong their service life. In pipeline projects for transporting oil, water, natural gas, etc., steel pipes are often used as economical transmission materials. However, the material composition and chemical elements of some steel pipes determine that they do not possess long-term corrosion resistance, significantly shortening their service life. This issue arises regardless of whether the pipes are buried underground or overhead. So, how to solve this problem? Later, people invented coating the outer or inner walls of steel pipes with anticorrosive materials to effectively control and prevent corrosion.
Currently, the main anticorrosive coatings for steel pipes include:
Grease Paint
Grease paint is a type of coating with dry oil as the primary film-forming material. It is convenient to produce, has good brushing and wetting properties, and is low in price with flexible paint films. However, its paint films dry slowly, are soft, have poor mechanical properties, and are not resistant to acids, alkalis, water, or organic solvents. Dry oil is often combined with rust-preventive pigments to form rust-preventive paint for use in atmospheric environments with low corrosion resistance.
Chinese Lacquer (Raw Lacquer)
Also known as raw lacquer or big lacquer, it is unique to China. Raw lacquer is a milky white viscous liquid obtained by cutting the bark of lacquer trees and filtering out impurities. When applied to an object's surface, its color quickly changes from white to red and then purple, eventually becoming a hard and shiny black paint film over time. Urushiol is the main component of raw lacquer, accounting for 30-70% (the higher the urushiol content, the better the quality of raw lacquer). Chinese lacquer has strong adhesion, a tough paint film, good gloss, and resistance to soil corrosion, water, and oil. However, it is toxic and can easily cause skin allergies. Additionally, it is not resistant to strong oxidants and has poor alkali resistance.
Phenolic Resin Paint
Includes alcohol-soluble phenolic resin, modified phenolic resin, and pure phenolic resin. Alcohol-soluble phenolic resin paint has good corrosion resistance but suffers from inconvenience in application, poor flexibility, and weak adhesion, limiting its use. Phenolic resin often requires modification during use. For example, rosin-modified phenolic resin refined with tung oil and mixed with various pigments can be ground into various magnetic paints. These paints have tough paint films, are low in price, and are widely used in furniture and door/window coatings. Pure phenolic resin paint has strong adhesion, water resistance, moisture resistance, heat resistance, corrosion resistance, and good weatherability.
Epoxy Resin Paint
Epoxy paint has good adhesion to metals, concrete, wood, glass, and other materials, excellent alkali resistance, and good insulation properties. However, it has poor aging resistance. Epoxy anticorrosive paint typically consists of epoxy resin and a curing agent, and the nature of the curing agent affects the paint film's properties. Epoxy resin paint is a single-component coating system using epoxy resin as the film-forming material. Compared to general epoxy paints, this type has lower costs but poorer alkali resistance. It is commonly used for various metal primers in chemical plants and as anticorrosive paint for outdoor equipment.
Polyurethane Paint
Polyurethane resin used in anticorrosive paint typically contains two components: isocyanate groups (-NCO) and hydroxyl groups. Polyurethane (PU) is formed by mixing and reacting these two components during application. PU paint has excellent physical and mechanical properties, with hard, flexible, bright, full, wear-resistant, strongly adhesive, corrosion-resistant, oil-resistant, acid-resistant, chemical-resistant, and industrial exhaust-resistant paint films. Its alkali resistance is slightly lower than epoxy paint but has better aging resistance. It is often used as a topcoat or primer. PU resin can be mixed with various resins, allowing for extensive formula adjustments to meet various requirements. It can be cured at room temperature or with heating, even at low temperatures (0°C). However, the storage stability of polyisocyanate components is poor, requiring moisture isolation and protection from freezing. PU paint is expensive but has a long service life.
Long Fiber Wound FRP Reinforced Epoxy Lining
Uses a unique embedded lining process to form a corrosion-resistant material within steel pipes. This material isolates corrosive liquids and gases from the steel pipes, providing an internal anticorrosive lining system for oilfield steel pipes and pipelines. For damaged downhole production tubing or subsea pipelines, replacement costs are high. This lining offers superior corrosion protection in harsh environments, unmatched by other products.
Polyethylene and Polypropylene Resin Paints
Polyethylene resin anticorrosive paint is a film-forming paint made from monomer resins. Polyethylene coatings are widely produced and applied. Polyethylene pipeline coatings have strong corrosion resistance, high mechanical strength, excellent waterproofing, stable quality, convenient construction, good applicability, and environmental friendliness. PE has low water absorption (less than 0.01%), high epoxy strength, low PE water absorption, good hot melt adhesive flexibility, and high anticorrosion reliability. However, its cost is higher than other joint coating materials. The raw materials for this paint are abundant and have been widely used in corrosion prevention.
Furan Resin Paint
Furan resin paint is resistant to various non-oxidizing inorganic acids, electrolyte solutions, and organic solvents. Its alkali resistance is also outstanding, but its oxidation resistance is poor. The furan resin series of anticorrosive paints includes furfuryl alcohol paint, furfural acetone formaldehyde paint, and modified furan resin paint.
Rubber Paint
Rubber anticorrosive paint is made from chemically treated or mechanically processed natural or synthetic rubber, with solvents, fillers, pigments, and catalysts added.
Asphalt Paint
Asphalt is one of the essential anticorrosive coatings, with coal tar pitch being the best. Coal tar pitch paint is low in price and has water resistance. After immersion in water for ten years, its water absorption rate is only 0.1% to 0.2%. It is resistant to some chemical media, has good wettability on steel surfaces with incomplete rust removal, high solid content for thick film formation, and low cost. However, it becomes brittle in winter and soft in summer. Exposure can cause some components to volatilize and escape, leading to paint film cracking. These drawbacks can be improved by adding other resins. For example, adding chlorinated rubber improves the drying properties of asphalt paint, addressing the issues of winter brittleness and summer softness. Epoxy asphalt paint made from epoxy resin combines the advantages of asphalt and epoxy paints, achieving satisfactory results in corrosion prevention. Asphalt paint has been used on container bottoms, ship hulls, dock gates, cofferdams, etc., with good anticorrosive effects.
Heavy-Duty Anticorrosive Paint
Heavy-duty anticorrosive paint is a type of coating with corrosion prevention effects several times higher than ordinary anticorrosive paint under severe corrosion conditions. It is characterized by excellent corrosion resistance to various media, outstanding durability, and a service life exceeding several years. It is primarily used in marine structures, chemical equipment, storage tanks, and pipelines.
