1. Assess the Cause of Peeling
• Environmental Factors: Check for excessive chloride exposure (coastal areas), acid rain (industrial zones), or constant moisture (poor drainage).
• Mechanical Damage: Inspect for abrasion, impact, or stress cracks disrupting the patina.
• Material Defects: Verify if the steel meets GB/T 4171 standards (low Cu/Cr/Ni content can weaken the patina).
2. Surface Preparation
• Remove Loose Rust:
◦ Light grinding or soft abrasive blasting (e.g., walnut shells) to avoid damaging sound steel.
◦ Avoid sandblasting to bare metal unless repainting (retain intact patina areas).
• Clean Contaminants: Use phosphoric acid (5–10%) to dissolve residual salts/chlorides, then rinse with fresh water.
3. Restore the Protective Patina
• Accelerated Re-rusting:
◦ Apply copper sulfate solution (5%) or commercial rust accelerators to promote uniform re-oxidation.
◦ Cycle wet/dry conditions (spray with deionized water 2–3× daily for 1–2 weeks).
• Rust Stabilizers: Brush on tannic acid or proprietary converters to bond loose rust into a stable layer.
4. Protective Coatings (Optional)
• For Critical Areas: Use breathable acrylic coatings or silane sealers to lock in the patina while allowing moisture escape.
• Avoid Epoxy/Paint: Non-breathable coatings trap moisture and worsen corrosion underneath.
5. Prevent Recurrence
• Improve Drainage: Eliminate water pooling near the steel.
• Isolate from Chlorides: In coastal zones, install splash barriers or rinse surfaces periodically.
• Monitor Welds/Edges: These areas are prone to patina failure; apply rust inhibitors locally.
6. Structural Evaluation
• Measure thickness loss with ultrasonic testing; if >10% of original thickness, consider reinforcement or replacement.
