Corrosion and Fire Protection: Durability Solutions for Steel Structures

While steel structures offer high strength and lightweight advantages, they remain vulnerable to corrosion and fire hazards in humid or high-temperature environments. Systematic protective measures are essential to extend their service life.

1. Corrosion Prevention Solutions

The essence of steel corrosion lies in the electrochemical reaction between steel and oxygen/moisture. Thus, the core principle of corrosion prevention is to isolate the steel from corrosive agents (water, oxygen, corrosive ions).

(1) Coating Systems

A mature anti-corrosion coating system typically comprises multiple layers, forming a complete protective system:

Primer: This critical layer directly contacts the steel and often contains rust-inhibiting pigments (e.g., zinc powder).

Zinc-rich Epoxy Primer: The most commonly used type. Zinc powder provides “cathodic protection,” sacrificing itself to corrosion before the steel, thereby shielding the substrate. It also forms a dense physical barrier.

Intermediate Coat: Bridges the primer and topcoat, increasing overall coating thickness and enhancing shielding.

Epoxy Micronite Intermediate Coat: Contains flake-like micronite pigments. These overlapping flakes, like roof tiles, effectively extend the penetration path for water and oxygen, providing excellent shielding.

Topcoat: The outermost layer primarily provides weather resistance, aging resistance, UV protection, aesthetics, and desired color.
Polyurethane Topcoat, Fluorocarbon Topcoat: Offers outstanding gloss retention, color stability, and durability. Fluorocarbon topcoats, in particular, boast exceptionally long service life and are commonly used in harsh environments or landmark structures.

Cross-sea bridges (e.g., Hong Kong-Zhuhai-Macao Bridge)

Operating in highly saline, humid marine corrosion environments, their coating systems face extreme demands: employing an ultra-long-term anti-corrosion system of “epoxy zinc-rich primer + epoxy micaceous iron oxide intermediate coat + fluorocarbon topcoat,” designed for over 30 years of protection.

(2) Long-Term Corrosion Protection Technologies

For critical areas difficult to maintain or exposed to extreme environments, more fundamental technologies are employed:

Hot-Dip Galvanizing: Steel components are immersed in molten zinc to form a metallurgically bonded zinc-iron alloy coating. This provides both cathodic protection and a physical barrier, offering exceptional durability. Commonly used on transmission towers and small components.

Thermal Sprayed Zinc/Aluminum: Molten zinc/aluminum wire is sprayed onto steel surfaces via arc or flame, forming a porous metallic coating. Pores are then filled with a sealing agent. This provides over 50 years of protection and is used for exposed primary structures in large bridges and stadiums.

2. Fire Protection Solutions

The goal of fire protection for steel structures is not to prevent combustion, but to delay temperature rise through thermal insulation. This prevents the steel from reaching critical temperatures within a specified fire duration (e.g., 1 hour, 2 hours), thereby buying valuable time for evacuation and firefighting.
Primary fire protection methods:

(1) Fireproof Coatings (Most Common, Economical, and Flexible)

Thick-film Fireproof Coatings: Primarily inorganic thermal insulation materials applied in thick layers (up to several centimeters). They delay heat transfer through low thermal conductivity. They offer high fire resistance ratings (up to 3+ hours) but have a rough appearance, making them suitable for concealed structural areas (e.g., stadium roof trusses).

Thin/Ultra-thin fireproof coatings:

Expandable coatings with thin layers (millimeters thick) that rapidly expand into carbonized foam insulation dozens of times thicker when exposed to fire. Aesthetically pleasing, they can be exposed and finished with decorative paint, widely used on visible beams and columns in shopping malls, office buildings, etc.

(2) Fireproof Board Cladding

Encasing steel components with fire-resistant panels like gypsum board, vermiculite board, or fiber cement board. Advantages include resistance to structural deformation, excellent durability, ease of dry construction, and a smooth surface ready for final finishes. Commonly used for standardized columns and beams.

(3) Concrete Encasing or Masonry

Encasing steel columns in concrete or embedding steel beams within concrete slabs. This is one of the most traditional and reliable methods, providing both fire protection and increased structural rigidity. However, it has the heaviest self-weight and slower construction pace.

(4) Internal Water-Cooling Systems (Active Fire Protection)

Employed in critically important structures (e.g., supertall building cores). Large box-shaped steel columns are filled with water, which circulates to dissipate heat during fires. Technically complex and extremely costly, yet highly effective.

Application Example: Supertall Office Tower (e.g., Shanghai Tower)

Its core’s massive steel columns may be clad with fireproof panels or thick fireproof coatings, while exposed decorative trusses use ultra-thin fireproof coatings. This approach meets fire resistance requirements while preserving interior aesthetics.

3. Maintenance Cycle

Protective systems require periodic maintenance to repair wear and prevent localized damage from causing overall failure. Maintenance schedules should be determined based on environmental corrosivity and protection type:

(1) Routine Inspections

Check for coating cracks, peeling, or blistering, and inspect fireproof layers for damage. Focus on rainwater collection points, high-temperature zones, and bolt connections. Repair minor damage promptly with matching coatings or fireproof materials.

(2) Mid-Term Inspections

Use coating thickness gauges to measure anti-corrosion coating thickness and ultrasonic flaw detectors to assess weld corrosion. Conduct adhesion tests on fireproof coatings. If adhesion ≤ 0.3MPa, perform full recoating.

(3) Overhaul Maintenance

Adjust cycles based on environmental differences:

General industrial environments: Every 8-10 years

Port/chemical environments: Every 5-8 years

Thoroughly remove old coatings and rust, reapply corrosion and fireproofing systems, and perform stress testing on steel structures to ensure structural safety.

Corrosion and fire protection for steel structures is a systematic project spanning the entire lifecycle of design, construction, and operation. During the design phase, scientifically select the most cost-effective protection system based on the building’s importance, environmental corrosion level, and required fire resistance duration. Strictly adhere to specifications during construction and conduct regular maintenance inspections. LF engineers provide guidance and training tailored to your project requirements. For related project needs, feel free to leave a message.