Abstract
Exposure tests were performed on low alloy steels in high Cl− and high SOx environment, and the structure of the rust were analyzed by TEM (Transmission Electron Microscopy) and Raman Spectroscopy. In the exposure test site, the concentrations of Cl− and SOx were found to be high, which caused the corrosion of the steels. The conventional weathering steel (SMA: 0.6% Cr-0.4% Cu-Fe) showed higher corrosion resistance as compared to the carbon steel (SM), and Ni bearing steel exhibited the highest one. Raman spectroscopy showed that the inner rust of Ni bearing steel was mainly composed of α-FeOOH and spinel oxides. On the other hand, SMA contained β- and γ-FeOOH in inner rust, which increased the corrosion. TEM showed that nano-scale complex iron oxides containing Ni or Cr were formed in the rust on the low alloy steels, which suppressed the corrosion of steels in high Cl− and high SOx environment.
Highlights
As the economy of East Asia grows rapidly, the corrosion of infrastructure is becoming a serious problem
There is no information on the corrosion behavior of steels under high Cl− and high SOx environment
The corrosion resistance of the steels was estimated after the exposure test for three years at the test site
Summary
As the economy of East Asia grows rapidly, the corrosion of infrastructure is becoming a serious problem. The corrosion in high SOx environment is thought to be heavy, there is little information on this case. There is no information on the corrosion behavior of steels under high Cl− and high SOx environment. As there are many cities located in high Cl− and high SOx environment in Asia, it is important to investigate the corrosion resistance of steels under this environment. The corrosivity and corrosion map was already identified in ISO 9223, where the exposure test using steel samples is conducted [1]. The adjustment of the classification system has been presented in progress based on ISO 9223 [2]. The characterization of the rust on steels at each site has not been conducted sufficiently
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