In addition to serving as water supply pipelines, galvanized steel pipes are also used to transport warm water, boiling water, and steam. These media induce distinct corrosion mechanisms on zinc coatings compared to cold tap water. For instance, calcium bicarbonate (Ca(HCO₃)₂), which is beneficial in cold water, becomes detrimental under elevated temperatures. When heated, calcium bicarbonate decomposes into calcium carbonate (CaCO₃) and releases free carbon dioxide (CO₂). The resulting CO₂ gas adheres to the zinc surface in the form of bubbles, creating localized acidic environments that significantly accelerate corrosion.
Furthermore, the electrochemical potential difference between iron and zinc reverses in hot water conditions. This inversion promotes oxygen enrichment at the zinc coating surface, exacerbating corrosion through galvanic effects. The combined action of thermal decomposition products and altered electrochemical conditions leads to more aggressive corrosion of zinc coatings in hot water systems compared to cold water environments.
