Relationship between the existence of microbes and early corrosion behavior of mild steel in fresh waters

The relationship between existence of microbes and early corrosion behavior of mild steel in fresh waters was studied using immersion tests, electrochemical measurements and surface analysis techniques. In the field immersion test at Dan Jiangkou reservoir in China, mild steel had less corrosion weight loss in the upper layer of water, where more microbes existed. The accumulation of microbes on the surface of coupons was thought to slow down the corrosion rate by restricting the oxygen diffusion and other factors. This hypothesis was confirmed by the electrochemical measurements and immersion test in natural freshwater. The results of the Scanning Electron Microscopy (SEM) and Fourier Transform Infra-red (FT-IR) spectra further confirmed that the existence of microbes could affect the formation of the corrosion products. Furthermore, the surface film formed in microbes-contained freshwater was thicker and with more complex corrosion products.