Sulphate reducing bacteria (SRB) can regulate environmental pH because of their metabolism. Since local acidification results in pitting corrosion, the potential capacity of pH regulation by SRB would have important consequences for electrochemical aspects of the bio-corrosion process. This study focussed on identifying the effect of pH on the corrosion of duplex stainless steel (DSS) 2205 in a nutrient rich artificial seawater medium containing SRB species, Desulfovibrio vulgaris. DSS samples were exposed to the medium for 13 days at 37 0C at pH ranging from 4.0 to 7.4. The open circuit potential value (OCP), sulphide level, pH and number of bacteria in the medium were recorded daily. Electrochemical impedance spectroscopy (EIS) and potential dynamic polarization were used to study the properties of the films and corrosion behaviour of the material. Inductively coupled plasma mass spectrometry (ICPMS) was used to measure the concentration of cations Cr, Fe, Ni, Mo, Mn in the experimental solution after 13 days. Scanning electron microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) were used for surface analysis. The results showed the pH changed from acidic values set at the beginning of the experiment to approximately pH 7.5 after 5 days due to bacterial metabolism. After 13 days, the highest iron concentration was in the solution that was initially at pH 4 accompanied by pitting on the stainless steel. Sulphide was present on all specimens but with more sulphide corrosion products at pH 4. The results of this study suggest that the corrosion process for the first few days exposure at low pH was driven by pH in solution rather than by bacteria. The increasing pH during the course of the experiment slowed down the corrosion process of materials originally at low pH. The nature and mechanism of SRB attack on duplex stainless steel at different acidic environments are discussed.
The data was collected by experiments.
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