Estimated and Stationary Atmospheric Corrosion Rate of Carbon Steel, Galvanized Steel, Copper and Aluminum in Iran

Atmospheric corrosion of structural metals including aluminum, copper, carbon steel and galvanized steel has been investigated in various areas in Iran based on meteorological data and test coupon mass loss. Using annual average temperature and relative humidity (RH), the time of wetness (TOW, tau) of 51 cities in Iran was obtained in 2012. Coincidentally, sulfur dioxide (SO2) and chloride ion (Cl-) concentrations were measured in these cities; then, according to ISO 9223, the predicted corrosion rate (r(corr)) of aluminum, copper, carbon steel and galvanized steel was calculated. Geographical information system (GIS) modeling of TOW, air pollutants (sulfur dioxide and chloride ion) and estimated r(corr) were extracted. The mentioned metallic coupons were exposed to the outdoor atmosphere of 15 test sites for up to 12 months to measure the actual corrosion rate of metals. The corrosion products were characterized using scanning electron microscopy and an X-ray diffractometer. The results show that the atmospheric corrosivity of Iran as a developing country is mainly affected by the air temperature, RH and Cl- deposition rate. The atmosphere at shorelines is much more aggressive. Predicting the corrosion loss, the northern coastlines show a more corrosive atmosphere. On the contrary, coupons fixed at the southern coastlines are severely corroded compared with those fixed at the northern shorelines. Chabahar has the most corrosive atmosphere for carbon steel, galvanized steel and copper coupons where their actual corrosion rates (CRs) are 514.68, 10.25 and 11.01 mu m/year, respectively. Aluminum coupons presented the best corrosion resistance at all test sites, and their CR were approximately nil. The result shows that models developed by ISO 9223 are not appropriate for predicting the atmospheric corrosion of aluminum, copper, galvanized steel and carbon steel in most areas in Iran.