Corrosion of construction metals under simulated acid rain/fog conditions with high salinity

Abstract

Corrosion of 1,312 specimens of five common construction metals were examined in a salt-spray chamber under simulated conditions of acid rain/fog with high salinity. When specimens were exposed to a condition simulating the acid rain/fog during summer in Hong Kong, i.e. pH 3.5, 1% of salt and 35 °C, the average corrosion rates were 735, 330, 2, 97 and 9 µm yr⁻¹, respectively, for mild steel, galvanized steel, stainless steel 304, red brass and aluminum. Relative effects of pH, salt concentration and temperature on the corrosion of these five metals were analyzed based on tests conducted at nine designed conditions. For the first four metals, the corrosion rate appears to increase linearly with the increase of ‘acidity’, salinity and temperature, according to regression analysis. Corrosion rate of SS 304 is almost independent of salinity and temperature, but is slightly affected by pH. Red brass is more susceptible than SS 304, but its susceptibilities to pH and salinity are one order of magnitude lower than those of mild steel and galvanized steel. Mild steel is about five times more susceptible to pH than galvanized steel; whereas the latter is about three times more susceptible to salinity than the former. Aluminum's corrosion rate increases as pH decreases; however, the effects of salinity and temperature are inconclusive.