| Abstract | The atmospheric corrosion of carbon steel and weathering steel under 3 different Thailand atmospheric conditions was evaluated. Exposure time was divided into 3 periods which are 2 months of rainy season, 2 months of dry season and 4 months through exposures. To clarify the effects of rain, sheltered exposure stands have been utilized. Pollutants (chloride ions and SO2) are determined according to ISO standard and meteorological data were obtained from Meteorological Department of Thailand. In AIT and TISTR, the amounts of corrosion in direct exposure tests were higher than sheltered exposure tests. The corrosion rates of both direct and sheltered exposures were greater in rainy season than those in dry season. These results indicate that the corrosion rate increases with an increasing TOW (Time Of Wetness). In these sites, the amounts of pollutants are smaller, and, therefore, the TOW has a predominant effect on the corrosion rate. At Rayong exposure site, the corrosion phenomenon is complicated due to the high pollutant deposition on steels. In this case, corrosion rate cannot be classified only by TOW, but must consider the degree of pollution. In direct exposure, the corrosion rate is affected by washing out of pollutant effect in wet season by rainfall. Furthermore, the specimens under the shelter is not cleaned up from pollutants. The steel surface highly contaminated with er would easily adsorb water vapor and get into wet state, and thus the real time of wetness in Rayong would be longer than that estimated by ISO. At Rayong, the highest corrosion rate is observed from weathering steel directly exposed in dry season. This is interpreted by high deposition of er, compared to the low er by washing-out in wet season. It is, therefore, realized that the atmospheric corrosion might not be determined by the simple category of corrosivity factors which are classified by ISO standard, especially in marine atmosphere. |