Avaliação de biocidas naturais no controle da biocorrosão em aço carbono 1020 por bactérias redutoras de sulfato

Abstract

The growing industrial development has favored, during time, the employment of metalicinstalationsburried and submerged, such as oil and gas pipelines, ships, storage tanks and oil platforms. Consequently, the problems related to corrosion increased and encouraged the development and the improvement of techniques for control and combat this process.This dissertation's goal is to evaluate the use of natural biocides in the control of the MIC of carbon steel AISI 1020 by sulfate reducing bacteria (SRB). Initially, the MIC behavior in steel was evaluated in synthetic sea water, in anaerobiosis with a culture of Sulfate Reducting Bacteria (SRB).Some natural biocides (garlic oil, hop and neem extract) and olther commercial (glutaraldehyde) will be used to control corrocion caused by those bacteria. The scanning of potential biocidal products was realized through analysis of microbial growth in steel surface, with quantification of SRB by the most probable number (MPN) method. This inicial scan consists in inoculation of reactors containing the test specimens and the natural biocides by periods varying from 0 to 7 days for the selection of those most promising biocides. The results show that the biocides: hop and neem extract had better response in inhibition of microbial growth.Subsequently, the electrochemical behavior of the steel in environment with the selected biocides and the commercial biocide as well, were studied by electrochemical impedance spectroscopy (EIS), always using synthetic sea water as electrolytic environment. When analyzing the results, hop presented better response comparing to neem extract. It kept the OCP relatively unchanged, minimizing 'ennobling' of the samples and making biofilm formation difficult. Besides that, in the most accentuated phase of microbial growth it showed bigger resistance to charge transfer and smaller values of double layer electric capacitance suggesting the formation of a protective biofilm on the sample surface.In addition, scanning electron microscopy were realized in order toto visualize the presence or not of biofilm in sample surface in the tests with biocide in 4 and 7 days. In those tests, different morphologies of the films were observed between the hop and neem extract. In the glutaraldehyde's case, observed a surface with difficulty in the adhesion and formation of the biofilms was observed.