How much do you know about fire-retardant coatings for steel structures?

The Importance of Fire-Resistant Coatings for Steel Structures

1. Addressing the fire-resistance shortcomings of steel structures: Although steel boasts high strength, it also has excellent thermal conductivity and tends to heat up and soften rapidly when exposed to fire. Under fire conditions, conventional steel structures typically lose their load-bearing capacity within about 15 minutes. However, fire-resistant coatings—by providing thermal insulation or expanding and foaming to form a protective layer—can slow down the heating of the steel, thereby buying valuable time for evacuating personnel and extinguishing the fire.

2. Meeting the requirements of building fire codes: According to the "Fire Protection Code for Building Design," steel structures in different types of buildings must achieve corresponding fire-resistance limits (for example, the fire-resistance limit for steel columns in high-rise buildings should be 2-3 hours). Fire-resistant coatings are a key measure for meeting these requirements.

3. Reducing fire damage: This can minimize the risk of steel structure collapse, protect the integrity of building facilities and structures, and lower post-disaster repair costs.

Classification of Fire-Retardant Coatings

Protection Objects and Fire-Resistant Performance

• Standard steel structure fire-retardant coating (Fp): For ordinary industrial and civil buildings (fibrous-type fires)

• Special steel structure fire-retardant coating (Ft): For special buildings such as petrochemical facilities and substations (hydrocarbon fires).

• Fire resistance rating: 0.5h, 1h, 1.5h, 2h, 2.5h, 3h

Fire-retardant coating markings

For example: GT-WRP-Ft2.00-A: Outdoor solvent-based intumescent fire-retardant coating, with a fire-resistance rating of 2 hours for special steel; Enterprise Code: AGT-NSF-Fp1.50-B: Indoor water-based non-intumescent fire-retardant coating, with a fire-resistance rating of 1.5 hours for ordinary steel; Enterprise Code: B

Design and Selection of Fire-Resistant Coatings

• The design of fire protection for steel structures shall, based on the intended use of the building or structure, the specific location, the type of fire, and the required fire-resistance rating, select the appropriate category of fire-retardant coating for steel structures.

• Intumescent fire-retardant coatings for steel structures typically contain binders, catalysts, foaming agents, and char-forming agents that are predominantly organic substances. When exposed to fire, the organic substances in the coating undergo a series of physicochemical reactions, causing the coating to rapidly expand and form a dense, honeycomb-like carbonaceous foam layer that serves as an insulating barrier. However, over time, certain organic components undergo irreversible processes such as decomposition, degradation, and leaching, leading to the “aging” and failure of the coating. This results in chalking, flaking, and poor durability, with a noticeable decline in performance. Tests have shown that within five years, the fire-resistance rating decreases by 21.7%.

Non-expanding fire-resistant coatings for steel structures are formulated using porous, lightweight, insulating materials (such as vermiculite, perlite, and mineral fibers) as aggregates and binders. Since the primary components are essentially inorganic, these coatings exhibit stable physicochemical properties and have a long service life; in projects where they have been applied for over 20 years, no instances of failure have yet been reported.

Summary

• For locations and components with high fire-resistance requirements—where the fire-resistance rating is ≥2 hours—it is advisable to use non-expanding fire-retardant coatings rather than non-epoxy expanding fire-retardant coatings for steel structures.

• Epoxy-based intumescent fire-retardant coatings for steel structures, thanks to their excellent adhesion, weather resistance, and fire-retardant performance, do not impose any restrictions on the application environment.

Mesh requirements during construction

(1) The type-test report for fire-retardant coatings indicates the presence of mesh reinforcement. When applying these coatings in construction projects, mesh reinforcement should be incorporated during the application process. The mesh materials recommended include wire mesh, alkali-resistant fiberglass mesh, or carbon fiber mesh.

(2) When the type-test report does not indicate the presence of mesh reinforcement, if the coating is relatively thick, it is advisable to adopt mesh-reinforced construction measures, which should comply with the following provisions: 1. For non-expanding steel structure fire-resistant coatings with a thickness of 25 mm or greater, mesh reinforcement is recommended within the steel structure fire-resistant coating. 2. For non-epoxy-based expanding steel structure fire-resistant coatings with a thickness of 3 mm or greater, and for epoxy-based expanding steel structure fire-resistant coatings with a thickness of 8 mm or greater, mesh reinforcement is recommended within the steel structure fire-resistant coating.

When applying fire-retardant coatings to galvanized steel structural components, a primer coat must be sprayed onto the galvanized surface to enhance the adhesion of the fire-retardant coating.

Comparison Chart of Advantages and Disadvantages of Fire-Retardant Coatings