Influence Of Microbes On Corrosion Of Carbon Steel In Seawater

The microbes exist extensively in seawater, submarine sediment and corrosion product. They can influence the corrosion of metals, especially to carbon steel in seawater. Microbiologically influenced corrosion of carbon steel in seawater has been given severe attention. Compared with effects made by temperature, the dissolved oxygen, flow velocity, Salinity, pH etc, the effect of microbiologically influenced corrosion to carbon steel is more complex. The species and numbers, the spatial relationship with surface of carbon steel, the extent of influencing corrosion, and function mechanism of microbes vary with exposed time.Samples of carbon steel were exposed to seawater. The numbers of Sulfate-reducing Bacteria, Heterotrophic Bacteria, Iron Bacteria and Sulfide-oxidizing Bacteria in internal rust layers were analyzed. Modality and distribution of the bacteria was observed by SEM; Content of FeS in internal rust layers was measured. The effect of microorganisms on corrosion of carbon steel in seawater was discussed. The relation of the corrosive bacteria in internal rust layer and corrosion influenced by them to fouling, rust layer and temperature was analyzed. The results showed that for carbon steel exposed to sea for 1-120 month, there were large quantities of SRB congregating in internal rust layer, and synchronously were different numbers of Heterotropic bacteria, iron bacteria and sulfide-oxidizing bacteria. Content of FeS in internal rust layer is high, and it increased with the increase of exposure time. For carbon steel exposed to seawater for 1 month at Yulin and Qingdao test sites, bacteria had influenced markedly corrosion, especially SRB.Samples of carbon steel were exposed to seawater and 3.5% NaCl respectively to prepare rust layers with and without microbes. Corrosion appearance was observed in different corrosion phase after exposing different time(1-340days).Electrochemical techniques such as measurement of open corrosion potential, Weak polarization curves, Polarization curves and Electrochemical impedance spectroscopy were...