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

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

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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 variousproblems such as medical infections, fouling of water cooling system, productcontamination, and microbiologically influenced corrosion (MIC)[1].MIC accounts for as much as 20% of all forms of corrosion, amounting tobillions of dollars in losses each year[2]. Among bacteria relatedto 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 largequantities of H2S. SRB are the main reason tocause the MIC by accelerating corrosion rate, inducing stress corrosion andpitting corrosion [4-6]. The aim of this study was to evaluate thecorrosion associated with the formation of SRB biofilms on carbon steelsurfaces. The bacterial strain used in the experiments was Desulfovibrio vulgaris cultured in Postgate´s C medium. Carbonsteel coupons of SAE 1010 were placed in the cultures for biofilm developmentduring 7 days. Then, coupons were extracted and bacterial adherence and biofilmformation were measured by viable bacteria counts, epifluorescence microscopyand by the crystal violet assay. Surface attack of carbon steel and biofilmmorphology were analyzed by scanning electron microscopy (SEM). The corrosionbehavior of the carbon steel during biofilm formation was analyzed byelectrochemical impedance spectroscopy (EIS) after 1, 3 and 7 days of immersionin the culture. Studies carried out allowed correlating the biofilm formation withthe 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. Thenumber of viable SRB found in the biofilm after 7 days was 102-103bacteria/cm2 as determined by the dilution to extinction method,while the number of planktonic bacteria was 103-104bacteria/mL. The impedance spectra (Figure 2) show that the charge transferresistance increases with time due to the action of the microorganism under  study.