How to Perform Corrosion Protection on Steel Structures (Part I)

In fields such as construction, bridge engineering, and industrial equipment, steel structures are widely used due to their high strength and ease of construction. However, steel is susceptible to corrosion from environmental factors such as moisture, oxygen, and acidic or alkaline substances, which not only reduce the structure’s load-bearing capacity and shorten its service life but may also pose safety hazards. Therefore, effective corrosion protection is key to ensuring the long-term stable operation of steel structures. Currently, paint coating, hot-dip galvanizing, and metal spraying are the three most common corrosion protection solutions for steel structures. Each has its own characteristics and suitable applications, which will be compared and analyzed in detail below.

Paint Coating: A Widely Used Basic Corrosion Protection Solution

1. Corrosion Protection Principle

Paint coating involves applying multiple layers of anti-corrosion paint to the surface of the steel structure to form a continuous protective film that isolates the steel from contact with external corrosive media, thereby achieving the goal of corrosion protection. Anti-corrosion coatings primarily consist of film-forming agents, pigments, solvents, and additives. After drying, the film-forming agents form a tough paint film that provides protection; pigments enhance the paint film’s abrasion resistance, weather resistance, and hiding power; solvents aid in the uniform application of the coating; and additives improve the coating’s application performance and anti-corrosion effectiveness.

2. Application Process

Surface pretreatment: This is a critical step in the coating process and directly affects coating adhesion. Mechanical methods such as sandblasting or shot blasting are typically used to remove impurities—including rust, scale, and oil—from the steel surface, achieving a specific surface roughness (generally required to be between 40 and 75 μm) to increase the contact area between the coating and the steel.

Primer Application: The primer comes into direct contact with the steel, primarily serving to prevent rust and enhance adhesion. Select an appropriate primer based on the steel’s operating environment and corrosion protection requirements, such as epoxy zinc-rich primer or inorganic zinc-rich primer. Apply the primer evenly using spraying, brushing, or rolling methods. Typically, 1–2 coats are applied, with a dry film thickness controlled between 50–80 μm.

Intermediate Coat Application: The intermediate coat serves as a bridge between the primer and topcoat, increasing coating thickness and enhancing corrosion resistance and mechanical properties. Common intermediate coats include epoxy micaceous iron oxide intermediate coats, applied in 1–2 coats with a dry film thickness controlled between 80–150 μm.

Topcoat Application: The topcoat primarily serves decorative and protective functions, resisting erosion from UV rays, rain, and chemicals. Select the appropriate topcoat based on the operating environment, such as acrylic or polyurethane topcoats. Apply 1–2 coats, with a dry film thickness controlled between 60–100 μm.

3. Advantages, Disadvantages, and Suitable Applications

Advantages: Flexible and simple application that can be performed on-site; a wide variety of coatings available, allowing selection based on specific environmental conditions and requirements; relatively low cost, making it suitable for small- to medium-scale steel structure projects.

Disadvantages: The coating has a relatively short service life, typically requiring recoating every 5–10 years; it demands high standards for surface preparation, and improper preparation can lead to coating peeling; it offers poor wear resistance and impact resistance.

Suitable Applications: Indoor steel structures and environments with low corrosion levels, such as standard industrial plants and internal steel structures in commercial buildings; locations where high aesthetic appeal is required.