Surface treatment of spiral steel pipe

Surface treatment is an essential process in the manufacturing of spiral steel pipes to enhance their durability, corrosion resistance, and overall performance. The following are common surface treatment methods for spiral steel pipes.

1. Cleaning

Mechanical Cleaning: This involves the use of tools like wire brushes, abrasive wheels, and grinding machines to remove rust, scale, and old coatings from the pipe surface. It is effective for eliminating loose contaminants.

Chemical Cleaning: Chemical solutions such as acids and alkalis are used to clean the pipe surface by dissolving and removing contaminants. This process is also known as pickling.

2. Surface Preparation

Blasting: Abrasive blasting (sandblasting, shot blasting) is used to clean and roughen the surface of the steel pipe. This process helps to remove rust, scale, and old paint, providing a better surface for the application of coatings. It is one of the most effective methods for achieving a clean and textured surface.

Grinding: Grinding can be used for finer surface preparation, especially in areas that require precision. It is commonly used to smooth weld seams and other surface imperfections.

3. Coating

Primer Application: A primer is applied to the cleaned and prepared surface to provide a protective base layer. This helps improve the adhesion of subsequent coatings and provides initial corrosion protection.

Painting: Multiple layers of paint are applied to provide additional corrosion resistance and aesthetic appeal. The types of paints used include epoxy, polyurethane, and other anti-corrosive coatings.

FBE Coating (Fusion Bonded Epoxy): This is a powder coating process where epoxy powder is applied to the heated surface of the steel pipe, forming a durable and protective layer that offers excellent resistance to corrosion and chemicals.

4. Galvanizing

Hot-Dip Galvanizing: The steel pipe is dipped into a bath of molten zinc, forming a protective zinc coating that provides excellent corrosion resistance. This process ensures that the entire surface, including internal areas, is coated.

Cold Galvanizing (Zinc Rich Paint): Zinc-rich paint is applied to the steel pipe surface, providing a protective coating that offers some of the benefits of galvanizing without the need for hot-dip processes.

5. Passivation

Chemical Passivation: A passivation solution, typically containing nitric acid or other oxidizing agents, is applied to the steel surface to form a protective oxide layer. This layer enhances corrosion resistance and prolongs the lifespan of the steel pipe.

6. Polyethylene Coating

3LPE Coating (Three-Layer Polyethylene): This consists of an epoxy primer, a copolymer adhesive, and a polyethylene topcoat. It provides superior corrosion protection and mechanical resistance.

7. Inspection and Testing

Quality Control: After surface treatment, the pipes undergo rigorous inspection and testing to ensure that the coating is uniform, adheres well, and provides the necessary protection. This includes visual inspections, adhesion tests, thickness measurements, and other non-destructive testing methods.

By undergoing these surface treatment processes, spiral steel pipes are better equipped to withstand harsh environmental conditions, extend their service life, and maintain their structural integrity in various applications.