1.What is the destructive mechanism of acid rain on galvanized coating?
The main components of acid rain are sulfuric acid and nitric acid. The H⁺ concentration is much higher than that in a neutral environment. The zinc sulfate and nitrate generated are both soluble salts, which will be washed away from the surface of the zinc layer by rainwater, causing the zinc layer to continuously "dissolve and lose". This type of corrosion is uniform corrosion, which is directly manifested as the linear thinning of the zinc layer over time.
2.What are the differences in corrosion rates under different acid rain intensities?
Non-acid rain areas: The annual corrosion rate of the zinc layer is about 0.5-2μm;
Weak acid rain areas: The corrosion rate increases to 2-5μm/year;
Strong acid rain areas: The corrosion rate can reach 5-15μm/year. If accompanied by high humidity or industrial pollutants, the rate may be higher.
3.What is the relationship between zinc layer thickness and lifespan?
Zinc layer weight 60g/m² (about 8.4μm):
Non-acid rain area: lifespan ≈60÷5=12 years (conservative value);
Weak acid rain area: lifespan ≈60÷15=4 years;
Strong acid rain area: lifespan ≈60÷40=1.5 years.
Zinc layer weight 275g/m² (about 38.5μm):
Non-acid rain area: lifespan ≈275÷5=55 years;
Weak acid rain area: lifespan ≈275÷15≈18 years;
Strong acid rain area: lifespan ≈275÷40≈6.9 years.
4.What are the other exacerbating factors?
High humidity and precipitation frequency: Acid rain areas are usually rainy and have high air humidity, which keeps the zinc layer moist for a long time. Acidic substances continue to react with zinc, leaving no chance for "drying repair";
Synergistic effects of atmospheric pollutants: Acid rain is often mixed with industrial waste gas and coastal salt spray. Cl⁻ will penetrate the passivation film of the zinc layer, causing pitting corrosion, leading to "local premature exhaustion" of the zinc layer;
Temperature fluctuations: In acid rain areas with large temperature differences between day and night, the acidic water film on the surface of the zinc layer will be concentrated due to evaporation, and the H⁺ concentration will increase, aggravating corrosion.
5.What are the measures to extend the life of galvanized steel in acid rain areas?
Thickening the zinc layer: Choose a high zinc layer specification to extend the service life by increasing the "corrosion allowance";
Passivation and coating treatment: Chromate passivation is performed on the zinc layer to form an acid-resistant passivation film; or additional acid-resistant coating is applied to physically block acid rain erosion;
Regular maintenance: In areas where acid rain occurs frequently, clean the galvanized steel surface every 1-3 years to remove acidic residues and apply an anti-corrosion coating.