5. Common Problems and Solutions for Galvanizing Steel
Processing galvanized metal presents practical challenges due to the physical and chemical properties of the galvanized coating. By identifying these challenges early in the project planning phase and implementing appropriate processing methods, they can be effectively addressed.
1. Cut Edge Corrosion Problem
● Description: The cut edges of pre-galvanized or formed sheets expose bare steel, and the protective effect of the zinc coating diminishes beyond about 2-3 mm from the edge, which may lead to corrosion on these steel surfaces.
● Risk: Edges are prone to corrosion and rusting, which affects product lifespan and appearance.
● Solution: Immediately after processing, applying zinc primer or cold galvanizing compounds to the cut edges can provide localized protection.
2. Welding Fumes and Strength Issues
● Description: When welding galvanized steel, zinc volatilizes at temperatures above 900°C, generating zinc oxide fumes that pose a health hazard and may contaminate the weld metal, resulting in porosity and reduced joint strength.
● Risk: Fumes pose health risks, cause welding porosity, and reduce joint strength.
● Solution: Adequate ventilation and proper respiratory protection should be provided during welding operations. Before welding, remove 25-50 mm of the zinc layer around the weld seam, then restore protection using zinc paint or thermal sprayed zinc. Alternatively, specify the use of galvannealed materials for welding.
3. Degradation in High-Corrosion Environments
● Description: Exposure to chlorides, industrial pollution, or high-humidity environments accelerates zinc consumption. In coastal or industrial environments, hot-dip galvanized products may only last for 15-20 years.
● Risk: Accelerated corrosion, increased maintenance frequency, and shortened service life.
● Solution: For harsh environments, the coating thickness should be increased to at least 100 micrometers instead of the standard 85 micrometers. Consider combining hot-dip galvanizing with high-performance topcoats, which can extend the service life significantly compared to single-layer galvanizing.
