1.What is the reason why the quality of the galvanized layer foundation does not meet the standards?
Insufficient zinc coating thickness: If the actual zinc coating thickness is only 30-40μm (hot-dip) or 5-8μm (electroplating), corrosion resistance will be significantly reduced-the outdoor service life may be reduced from 15-20 years to 5-8 years, and white rust (zinc oxide) will easily appear on the surface within a short period of 1-2 years.
Poor zinc coating adhesion: The zinc coating will flake off during transportation or processing (such as cold bending and stamping), exposing the substrate to direct contact with air and causing rapid rusting.
2.What are the common types of surface defects in zinc layers?
Missing plating: Parts of the substrate are not covered with zinc, forming "black spots." These areas will rust preferentially (red rust will appear within 1-3 months).
Zinc particles/burrs: These are raised zinc particles on the surface of the zinc layer that can easily fall off due to friction, exposing a small area of the substrate.
Pinholes: Tiny holes in the zinc layer allow moisture to penetrate the substrate, causing "subcutaneous corrosion" (the surface may appear intact, but the substrate has rusted).
Causes: Unstable zinc bath temperature during hot-dip galvanizing (excessively high zinc bath temperature can easily cause zinc particles), scratches on the substrate surface (causing missing plating), and excessive impurities in the electroplating solution (causing pinholes).
3.What are the consequences if the usage scenario exceeds the tolerance range of the galvanized layer?
The zinc layer rapidly thins, and large areas of red rust appear on the surface.
White salt frost forms on the zinc surface, accompanied by red rust spots (base material corrosion).
Black mold spots appear on the zinc surface, and base material corrosion produces reddish-brown rust residue.
4.What are the consequences of improper post-maintenance?
Surface scratches not promptly addressed
Problem: If the zinc layer is scratched during transportation or installation (e.g., by impact or friction with hard objects), the exposed substrate will rust first, and the rust will spread to the surrounding zinc layer ("rust spread").
Proper maintenance: Within 24 hours of scratches, repair with zinc powder paint with a zinc content of ≥95% to form a "localized anti-corrosion layer."
Long-term stacking leading to poor ventilation
Problem: Galvanized coils or finished products are stacked and stored for long periods of time without elevated pads or ventilation gaps. This prevents moisture from evaporating between layers, creating a "localized humid environment" that causes white rust on the zinc layer and, in turn, corrosion of the substrate.
Galvanic corrosion caused by contact with other metals
Problem: If Q345B galvanized coils come into direct contact (without insulation) with metals of higher potential (such as stainless steel or copper) and are exposed to humidity, a "galvanic cell" will form, with the zinc layer acting as the anode and corroding first, accelerating failure.
5.What are the suggestions for improvement and remediation?
Zinc coating quality issues:
Minor defects (such as localized missing plating or thin zinc coating): Repair small areas with zinc powder paint; re-galvanize large areas (applicable only to unprocessed coils);
Severe defects (such as pinholes or large areas of peeling): Replace with qualified products and avoid use in load-bearing or critical outdoor structures.
Exceeding standards in certain environments:
Exposed to strong acids and alkalis/high salt spray: Perform additional anti-corrosion treatment (such as applying fluorocarbon paint or applying anti-corrosion tape), or switch to more corrosion-resistant materials (such as 304 stainless steel or weathering steel);
Humid environments: Add ventilation (such as installing exhaust fans in pipe corridors) and regularly inspect and remove moisture from the surface.
Improper maintenance:
Scratches should be promptly repaired with zinc powder paint;
Store stacked materials on raised platforms (≥10 cm above the ground) and leave 5-10 cm gaps between layers for ventilation;
Insulate materials from contact with other metals using insulating spacers (such as rubber or plastic) to prevent galvanic corrosion.