Investigation of Initial Atmospheric Corrosion of Carbon and Weathering Steels Exposed to Urban Atmospheres in Myanmar

This research is aimed at studying the corrosion rates of carbon and weathering steels due to exposure at three urban exposure sites and the characteristics of corrosion products of carbon steel in Yangon, Myanmar. The ISO 9223 standard was used to classify the corrosion aggressiveness of the atmosphere. There is a high level of time of wetness (TOW) class which is <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:msub> <a:mrow> <a:mi>τ</a:mi> </a:mrow> <a:mrow> <a:mn>4</a:mn> </a:mrow> </a:msub> </a:math> in the south and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:msub> <c:mrow> <c:mi>τ</c:mi> </c:mrow> <c:mrow> <c:mn>3</c:mn> </c:mrow> </c:msub> </c:math> in the central part of Myanmar. At the recent exposure sites in Myanmar, the atmospheric impurities are low, so the corrosion rates of carbon and weathering steels are mainly governed by TOW. The corrosion rates of test sites fall into the ISO C2 category. It appears that corrosion kinetics fit the power model well, since the correlation coefficient is high. Various morphologies of corrosion products including globular, flowery, and sandy lepidocrocite emerged in the early stage of exposure. The longer TOW conditions resulted in the formation of lepidocrocite and goethite. The growth of goethite products on carbon steel was discovered after nine months of exposure.