Types of anti-corrosion coatings for large-diameter spiral steel pipes

New anti-corrosion technologies for large-diameter spiral pipes continue to emerge. The main types of anti-corrosion coatings for pipelines are:

1. Raw lacquer
Raw lacquer is a kind of milky white viscous liquid that flows out from the bark of the growing lacquer tree. It is filtered through fine cloth to remove impurities. After it is applied on the surface of the object, the color will quickly change from white to red, and from red to purple, and it will become a hard and bright black paint film after a long time.

Raw lacquer has strong adhesion, tough paint film and good gloss. It is resistant to soil corrosion, water and oil. The disadvantage is that it is toxic and easy to cause skin allergies. In addition, it is not resistant to strong oxidants and has poor alkali resistance. There are many modified raw lacquer coatings that overcome the above-mentioned shortcomings to varying degrees.

2. Epoxy resin coating
Epoxy ester resin coating is a one-component coating system with epoxy ester resin as the film former. Epoxy ester resin is formed by compounding epoxy resin and vegetable oil fatty acid ester. Compared with general epoxy coatings, this coating has lower cost and poor alkali resistance. It is often used as a variety of metal primers and anti-corrosion paints for outdoor equipment in chemical plants.

3. Polyurethane coating
Polyurethane resins used in anti-corrosion coatings often contain two components: isocyanate groups-NCO and hydroxyl groups. When used, mix the two components and react to cure to form polyurethane (polyurethane).

Features of polyurethane coatings: ① Good physical and mechanical properties. The paint film is hard, flexible, bright, plump, wear-resistant and has strong adhesion. ②Excellent corrosion resistance. Resistant to oils, acids, chemicals and industrial fumes. Alkali resistance is slightly lower than epoxy coatings. ③Aging resistance is better than epoxy coating. Often used as a top coat, it can also be used as a primer. ④Polyurethane resin can be miscible with various resins, and the formula can be adjusted in a wide range to meet various application requirements. ⑤It can be cured at room temperature or by heating, and it can also be cured at a lower temperature (0°C). ⑥The storage stability of the polyisocyanate component is poor, and moisture must be isolated to avoid jelly. Polyurethane coatings are expensive, but have a long service life.

4. Polyethylene, polypropylene resin coating
Polyethylene pipes have strong anti-corrosion and sealing properties, high mechanical strength, strong water resistance, stable quality, convenient construction, good applicability, and do not pollute the environment. PE has low water absorption (less than 0.01%), high epoxy strength, low water absorption of PE and good softness of hot melt adhesive, etc., and has high anti-corrosion reliability. The disadvantage is: compared with the cost of other filling materials ,costly. The raw material of the coating is abundant and has been widely used in corrosion. Polyethylene resin anti-corrosion coating is a coating made of monomer resin as a film-former. Among them, polyethylene coatings have been mass-produced and applied.

5. Asphalt paint
Asphalt is one of the important anti-corrosion coatings. Especially coal tar pitch is the best. Coal tar pitch paint is cheap and has the following advantages: ① water resistance, its water absorption rate is only 0.1% to 0.2% after being immersed in water for 10 years; ② resistant to erosion by some chemical media; Rust steel surface still has good wettability; ④ high solid content, thick film can be obtained; ⑤ low price. The disadvantage is that it becomes brittle in cold winter and soft in summer, and some components volatilize and escape after exposure to the sun, which will cause cracks in the paint film. These shortcomings can be improved by adding some other resins.

The anticorrosion of large-diameter spiral steel pipe pipelines refers to the chemical or electrochemical reaction of the pipelines in the use and transportation of large-diameter spiral pipelines due to the influence of the use environment and the conveying medium.

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