Corrosion of Zinc Coatings in Hot Water

Galvanized steel pipes are used not only for tap water but also for transporting warm water, boiling water, steam, and other media, which exhibit different corrosion effects on zinc coatings compared to cold tap water. For instance, calcium bicarbonate in cold tap water is beneficial to zinc coatings, but it becomes harmful in hot water. This is because calcium bicarbonate decomposes into calcium carbonate and free carbon dioxide when heated. Consequently, carbon dioxide and air bubbles adhere to the zinc coating, leading to accelerated corrosion. Additionally, the iron-zinc potential difference behaves oppositely in hot water, making it easier for oxygen to accumulate on the surface of the zinc coating, which also accelerates its corrosion.