Electrochemically Active Biofilm on AISI 1020 Steel and Its Corrosion Potential

Abstract

Electroactive biofilms provide environments conducive to the occurrence of microbiologically influenced corrosion (MIC) in several industrial sectors. There are many distinct MIC mechanisms associated with different microbial groups and metabolism types. Most published research studies on MIC focus on bacteria, where sulfate-reducing bacteria (SRB) have the largest impact on corrosion because sulfate is widely distributed in anoxic environments, such as offshore oil reservoirs. This study investigated the role of an oilfield SRB-consortium in the AISI 1020 carbon steel corrosion immersed in hypersaline seawater (10% NaCl w/m) with low dissolved oxygen (>2 mg/L). This steel is globally used to build oil and gas industry facilities exposed to both onshore and offshore sites due to its low cost and good corrosion resistance. Each microcosm consisted of 100 mL seawater and one suspended metallic coupon of 6 cm² total surface area. Three identical microcosms were performed. Simultaneously, abiotic control assays without microbial consortium were also executed. The assays were analysed by weight loss method and scanning electron microscopy (SEM) after 10 days at 40°C. Additionally, SRB counts in the hypersaline seawater at diferent times are done. The planktonic population increased slow and its peak at 9.5× 106 MPN/mL appeared at day 10. This result suggest that the increased salt content was not an inhibiting factor since the SRB consortia grew well and remained metabolically active throughout the assay. Corrosion rates are shown in Table 1. The abiotic condition must have improved the corrosion rate because of the large amount of chloride ions (Cl−) in the hypersaline seawater (10% w/v salinity). Cl− enhances the electrical conductivity of aqueous solutions and consequently boosts the velocity of oxidation and reduction reactions of the corrosive process. Thus, it proceeds an homogeneous degradation over the entire surface area causing signifcant mass loss and well-proportioned corrosion rate. On the other hand, SRB-MIC consumes only a relatively small amount (mass) of material due to the localized corrosion (pits), corroborating the low corrosion rate. Many pits were detected in the steel surface with a maximum depth of 33 μm; it was 86% deeper than the maximum pit depth in abiotic condition.

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Identifiers

DOI

10.5006/lac23-20888

Journal

LatinCORR 2023

Year

2023