The effect of adding fresh nutrients to the growth of Sulfate-Reducing Bacteria (SRB), Desulfovibrio desulfuricans, in synthetic seawater was investigated by counting the planktonic cells in the solution. The corrosion of carbon steel exposed to mixed solution in the presence and absence of Desulfovibrio desulfuricans was characterized by Electrochemical Impedance Spectroscopy (EIS), linear polarization resistance (Rp) and open circuit potential (OCP) measurements. EIS spectra showed two time constants for the sterilized system of synthetic seawater and growth media. A high frequency constant is related to an outer layer due to the precipitates of chlorides, organic compound of the growth media and corrosion products. The constant at low frequency is a contribution of the metal dissolution reaction. The formation of biofilm by Desulfovibrio desulfuricans accelerates the corrosion rate and a diffusion controlled process appears as a result of sulfide-base iron corrosion products. The metal surface was examined by the Scanning Electron Microscopy (SEM) and the elemental composition of the corrosion products was estimated by X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and Energy Dispersive Spectroscopy (EDS). Experimental result revealed a substantial decrease in the Rp values for the coupon in the solution provided with fresh growth media in the presence of Desulfovibrio desulfuricans.
Microbiologically Influenced Corrosion (MIC) is the deterioration of metal by corrosion processes that occur, directly or indirectly, as a result of the metabolic activity of microorganisms. MIC occurs due to the effects of microorganisms on the kinetics of corrosion processes of metals1. Microbes may adhere to metal surfaces forming biofilms, which can alter the chemistry at the metal surface. Biofilms or microbial mats form complex ecosystems in the presence of the four prerequisite of life: a small amount of water, an electron donor, an electron acceptor and a carbon source2. MIC by the Sulfate-Reducing Bacteria (SRB) is a serious problem in installations and systems that use water in different areas of industry 3, 4. This heterogeneous group of anaerobic bacteria uses the sulfate as an electron acceptor in their metabolism. SRB are anaerobic microorganisms and can thrive in the temperature range of 25-60°C. Anaerobic condition can be developed in an environment like sea water. Several SRB can reduce nitrate, sulfite, thiosulfate and fumarate with H2 or organic compounds 5. The sulfate reduction can be indicated by the production of sulfide which oxidizes different types of metals6. The aim of this paper was to investigate the effects of the availability of nutrient for Desulfovibrio desulfuricans activity and the subsequent corrosion damage on carbon steel. Resulting corrosion products were examined by X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD). Biofilm and corrosion products were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) data complemented with the open circuit potential (OCP) and linear polarization resistance (RP) measurements were used to evaluate the corrosion behavior of the steel.
Samples Preparation Samples were prepared out of carbon steel pipe API5L-X52. Samples were cut by a water jet cutting machine.
