What are the effects of coating on large diameter spiral steel pipe?

1. Characteristics and Anti-Corrosion Properties

For large-diameter spiral steel pipes, particularly those with an outer protective polyethylene pipe, additional anti-corrosion polyethylene coating is unnecessary. This type of steel pipe is odorless, non-toxic, wax-like, and boasts excellent low-temperature resistance (operating temperatures as low as -70 to -100°C). It offers:

Chemical Stability: Resistant to most acids and bases (except oxidizing acids).

Low Solubility: Insoluble in common solvents at room temperature with low water absorption.

Electrical Insulation: Excellent performance due to its linear molecular structure, though it can slowly dissolve in some organic solvents without swelling.

Coating Anti-Corrosion: This method involves uniformly applying paint to the surface of derusted metal pipes to isolate them from corrosive media. Composite materials or structures with good dielectric properties, stable physical and chemical properties, and a wide temperature range are increasingly used for anti-corrosion coatings on large-diameter spiral steel pipes.

2. Types and Conditions of Anti-Corrosion Coatings

Outer Wall Coatings: Different coatings are applied based on the specific needs of the pipe’s inner and outer walls.

- Inner Wall Anti-Corrosion Coating

Purpose: Prevents internal corrosion, reduces frictional resistance, and increases throughput.

Common Coatings: Amine-cured epoxy resin and polyamide epoxy resin.

Coating Thickness: Typically ranges from 0.038 to 0.2 mm.

Surface Treatment: Essential for ensuring the coating bonds firmly to the pipe wall. Since the 1970s, the same material has been used for both inner and outer wall coatings to allow simultaneous application.

- Outer Wall Anti-Corrosion and Thermal Insulation Coating

Application: Used on medium and small-caliber OCTG pipes for transporting crude oil or fuel oil thermally to reduce heat dissipation to the soil.

Common Insulation Material: Rigid polyurethane foam, suitable for temperatures ranging from -185 to 95°C.

Composite Structure: A layer of high-density polyethylene is applied over the insulation layer to enhance strength and prevent groundwater penetration into the insulation layer.

By employing these techniques and materials, large-diameter spiral steel pipes can achieve effective corrosion resistance and thermal insulation, ensuring their durability and reliability in various industrial applications.