EVALUATION OF BIOFILM FORMATION AND CORROSION BEHAVIOUR OF SAE 1010 CARBON STEEL IN SRB CULTURES BY MICROSCOPIC TECHNIQUES AND ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

VIERA MARISA; RASTELLI SILVIA E.; GÓMEZ DE SARAVIA SANDRA

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Congreso; 17° Congreso Internacional de Metalurgia y Materiales. CONAMET-SAM; 2017

Soc. Chilena de Materiales y Metalurgia, Soc.Argentina de Metalurgia, Univ.de Atacama,,

Biofilms cause various problems such as medical infections, fouling of water cooling system, product contamination, and microbiologically influenced corrosion (MIC)[1]. MIC accounts for as much as 20% of all forms of corrosion, amounting to billions of dollars in losses each year[2]. Among bacteria related to MIC, sulfate reducing bacteria (SRB) are most often blamed [3]. The ubiquity of these bacteria leads to a variety of impressive industrial, economic and ecological effects because of their proneness to generate large quantities of H2S. SRB are the main reason to cause the MIC by accelerating corrosion rate, inducing stress corrosion and pitting corrosion [4-6]. The aim of this study was to evaluate the corrosion associated with the formation of SRB biofilms on carbon steel surfaces. The bacterial strain used in the experiments was Desulfovibrio vulgaris cultured in Postgate´s C medium. Carbon steel coupons of SAE 1010 were placed in the cultures for biofilm development during 7 days. Then, coupons were extracted and bacterial adherence and biofilm formation were measured by viable bacteria counts, epifluorescence microscopy and by the crystal violet assay. Surface attack of carbon steel and biofilm morphology were analyzed by scanning electron microscopy (SEM). The corrosion behavior of the carbon steel during biofilm formation was analyzed by electrochemical impedance spectroscopy (EIS) after 1, 3 and 7 days of immersion in the culture. Studies carried out allowed correlating the biofilm formation with the different degree of attack suffered by the SAE 1010 carbon steel coupons. In Figure 1 it is possible to observe the adhesion of D. vulgaris to the steel surface and abundant corrosion products. The number of viable SRB found in the biofilm after 7 days was 102-103 bacteria/cm2 as determined by the dilution to extinction method, while the number of planktonic bacteria was 103-104 bacteria/mL. The impedance spectra (Figure 2) show that the charge transfer resistance increases with time due to the action of the microorganism under study.