Corrosion protection for large-diameter spiral steel pipes refers to the corrosion that occurs in pipelines during use and transportation due to chemical or electrochemical reactions caused by the operating environment and the transported medium. To effectively prevent or control corrosion of large-diameter spiral steel pipes, scientists are seeking new, more advanced, and more efficient methods.
New anti-corrosion technologies for large-diameter spiral steel pipes are constantly emerging, and can be broadly classified into the following types:
Main Types of Anti-corrosion Coatings for Large-Diameter Spiral Steel Pipes
1. Grease-based Coatings – Used in atmospheric environments with low corrosion resistance requirements.
Grease-based coatings are a type of coating with drying oil as the main film-forming agent. Their characteristics include ease of production, good brushability, good wetting properties, low cost, and a flexible film; however, the film dries slowly, is soft, has poor mechanical properties, and poor resistance to acids, alkalis, water, and organic solvents. Drying oils are often combined with anti-rust pigments to form anti-rust paints, used in atmospheric environments with low corrosion resistance requirements.
2. Raw Lacquer (also known as Chinese lacquer or raw lacquer) is a specialty of my country. It is a milky-white, viscous liquid that flows from the bark of a growing lacquer tree after the bark is cut. After being filtered through a fine cloth to remove impurities, it quickly changes color from white to red, then from red to purple, and eventually forms a hard, glossy black film. Urushiol is the main component of raw lacquer, accounting for 30% to 70%. Generally speaking, the higher the urushiol content, the better the quality of the raw lacquer. Raw lacquer has strong adhesion, a tough film, and good gloss. It is resistant to soil corrosion and relatively resistant to water and oil. Its disadvantages include toxicity and the potential for causing skin allergies. Furthermore, it is not resistant to strong oxidants and has poor alkali resistance. Currently, there are many modified raw lacquer coatings that overcome these shortcomings to varying degrees.
3. Phenolic Resin Coatings
These mainly include alcohol-soluble phenolic resins, modified phenolic resins, and pure phenolic resins. Alcohol-soluble phenolic resin coatings have good corrosion resistance, but are inconvenient to apply, and their flexibility and adhesion are not very good, limiting their application. Therefore, phenolic resins often need to be modified. For example, rosin-modified phenolic resin, refined with tung oil, and with the addition of various pigments, can be ground to produce various enamels. These enamels have tough films, are inexpensive, and are widely used for coating furniture, doors, and windows. Pure phenolic resin coatings have strong adhesion, are resistant to water and damp heat, are corrosion-resistant, and have good weather resistance.
4. Epoxy Resin Coatings
Epoxy coatings have good adhesion, exhibiting excellent adhesion to metals, concrete, wood, and glass; they are resistant to alkalis, oils, and water, and have excellent electrical insulation properties. However, they have poor aging resistance. Epoxy anti-corrosion coatings typically consist of two components: epoxy resin and a curing agent. The properties of the curing agent also affect the performance of the coating film. Commonly used curing agents include: ① Aliphatic amines and their modified forms. These are characterized by room temperature curing; unmodified aliphatic amines are highly toxic. ② Aromatic amines and their modified forms. The characteristics are slow reaction, often requiring heat curing, and relatively weak toxicity. ③ Polyamide resin. The characteristics are good weather resistance, low toxicity, good elasticity, and slightly poor corrosion resistance. ④ Phenolic resin, urea-formaldehyde resin, and other synthetic resins. These resins, when used in combination with epoxy resin and baked at high temperatures, crosslink to form a film. The paint film has outstanding corrosion resistance, good mechanical properties, and decorative properties. Epoxy ester resin coatings are a single-component coating system using epoxy ester resin as the film-forming agent. Epoxy ester resin is composed of epoxy resin and vegetable oil fatty acid esters. Compared with general epoxy coatings, this coating has a lower cost but poorer alkali resistance. It is commonly used as a primer for various metals and an anti-corrosion paint for outdoor equipment in chemical plants.
5. Polyurethane Coatings
Polyurethane resins used in anti-corrosion coatings often contain two components: isocyanate groups (NCO) and hydroxyl groups. During use, the two components are mixed and reacted to cure, forming polyurethane. The characteristics of polyurethane coatings are: ① Good physical and mechanical properties. The paint film is hard, flexible, glossy, full, wear-resistant, and has strong adhesion. ② Excellent corrosion resistance. Resistant to oil, acids, chemicals, and industrial waste gases. Alkali resistance is slightly lower than that of epoxy coatings. ③ Better aging resistance than epoxy coatings. Commonly used as a topcoat, but can also be used as a primer. ④ Polyurethane resin is miscible with many resins, and the formulation can be adjusted over a wide range to meet various application requirements. ⑤ Can be cured at room temperature or with heat, and can also be cured at low temperatures (0℃). ⑥ The storage stability of polyisocyanate components is poor; moisture must be avoided to prevent freezing. Polyurethane coatings are expensive, but have a long service life.
6. Polyethylene and Polypropylene Resin Coatings
Polyethylene resin anti-corrosion coatings are coatings made from monomers using resin as the film-forming agent. Polyethylene coatings are widely produced and used. Polyethylene pipes have strong anti-corrosion sealing properties, high mechanical strength, strong waterproofing, stable quality, convenient construction, good applicability, and do not pollute the environment. PE has a low water absorption rate (below 0.01%) and combines the high strength of epoxy with the low water absorption and good flexibility of hot melt adhesive, resulting in high corrosion resistance. Its disadvantage is its higher cost compared to other repair materials. The raw materials for this coating are abundant, and it is widely used in corrosion protection.
7. Furan Resin Coatings
Furan resin coatings are resistant to various non-oxidizing inorganic acids, electrolyte solutions, and various organic solvents. They also exhibit excellent alkali resistance, but poor oxidation resistance. Furan resin anti-corrosion coatings include furfuryl alcohol resin coatings, furfural acetone formaldehyde resin coatings, and modified furan resin coatings.
8. Rubber Coatings
Rubber anti-corrosion coatings use chemically treated or mechanically processed natural or synthetic rubber as the film-forming material, along with solvents, fillers, pigments, catalysts, etc.
⑴ Chlorinated Rubber Coatings. This coating has good water resistance, is resistant to salt water and salt spray; it has some resistance to acid and alkali corrosion, and can withstand 10% HCl, H2SO4, HNO3, different concentrations of NaOH, and wet Cl2 below 50℃. However, it is not solvent-resistant and has poor aging and heat resistance. This coating is widely used in shipbuilding, harbors, chemical plants, and other applications.
(2) Chloroprene rubber coating. This coating is resistant to ozone and chemicals, has excellent alkali resistance, good weather resistance, oil resistance, and heat resistance, and can be made into a peelable coating. Its disadvantages are poor storage stability; the coating is prone to discoloration and is not easily made into white or light-colored paint.
(3) Chlorosulfonated polyethylene rubber coating. It is made by reacting polyethylene resin with chlorine and sulfur dioxide (or chlorosulfonic acid). The coating has excellent ozone resistance, significant weather resistance, low water absorption, oil resistance, and temperature resistance; it can be used above 120℃ and does not become brittle at -50℃.
9. Asphalt coating.
Asphalt is one of the important anti-corrosion coatings. Coal tar pitch is particularly valuable, as its coatings are inexpensive and possess the following advantages: ① Water resistance, with a water absorption rate of only 0.1%–0.2% after immersion in water for 10 years; ② Resistance to corrosion from some chemical media; ③ Good wettability on steel surfaces that have not been adequately rusted; ④ High solids content, allowing for thick films; ⑤ Low price. Its disadvantages include brittleness in cold winters and softening in hot summers, and the potential for cracking due to the volatilization of some components after exposure to sunlight. These disadvantages can be mitigated by adding other resins. For example, adding chlorinated rubber can improve the drying properties of asphalt coatings, mitigating the winter brittleness and summer softening issues; adding epoxy resin to create epoxy asphalt coatings combines the advantages of both asphalt and epoxy coatings, achieving very satisfactory corrosion protection. Asphalt coatings have been used in container bottoms, ship bottoms, dock gates, and cofferdams, demonstrating excellent corrosion protection.
10. Heavy-duty Anti-corrosion Coatings
Heavy-duty anti-corrosion coatings are those used in contrast to general anti-corrosion coatings. It refers to anti-corrosion coatings that offer several times the corrosion resistance of ordinary anti-corrosion coatings under harsh corrosive conditions. Its characteristics include excellent resistance to strong corrosive media, outstanding durability, and a service life of several years or more. It is mainly used in marine structures, chemical equipment, storage tanks, and pipelines.
Post time: Apr-03-2026