Atmospheric Corrosion of Stainless Steels in Thailand
Stainless steels are increasingly used outdoor. An important factor to be concerned is the appearance of stainless steel surfaces. The different appearances are produced by the different finishing processes. The stainless steel grades and surface finishes affect their corrosion resistance.
The atmospheric corrosion resistance of the different stainless steels and surface finishes which were AISI 304 HL (hairline finish), 304 MF (mirror finish), 316 HL, 316 2B, 430 HL and 430 BA (bright annealing finish) were studied. The specimens were prepared and exposed in 4 environments which were urban (Bangkok), rural (Ayuthaya), industrial (Maptaphut industrial estate, Rayong) and seaside (Kungkrabaen Bay Royal Development Study center, Chantaburi). The specimens were retrieved after 1, 3, 9, 15, 21, 27, 33 and 39 months of exposure. Pit depth, rating number (RN), weight change of the specimens were determined.
It was found that corrosion severity of seaside was 2 times higher than that of industrial, 3.3 times higher than that of urban and 10 times higher than that of rural environment. In mild environment the performance of all specimens was the same during 39 months of study. Surface finishes played a role on the corrosion resistance. MF gave the highest corrosion resistance. Rating number was a fast method to evaluate the appearance changes or atmospheric corrosion of the stainless steels. Weight change, roughness and brightness of specimens also were measured but they were insignificant different thus these parameters were not suitable for evaluating the atmospheric corrosion resistance of stainless steels.
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