Control of microbial corrosion using coatings and natural additives

One of the major concerns in the oil and gas industry is corrosion. Microbial-influenced corrosion (MIC) can be defined as the deterioration of metals by natural processes directly or indirectly related to the activity of microorganisms. MIC affects many industries, such as petrochemical, ships and marine structures, power generating, aircraft fuel systems, waste water facilities, cooling water systems, process industries, paper mills, and water supply and distribution systems. In this study, the influence of sulfate-reducing bacteria (SRB), grown in a lactate/sulfate culture medium, on the corrosion of both uncoated and coated mild steel was evaluated in the presence and absence of natural additives. To achieve this, an oil-based coating (alkyd) was used with and without the addition of natural additives to protect mild steel in a sulfate-reducing bacteria environment. Another objective of this study was to investigate the effects of SRB and/or their metabolites on the used coatings and the adverse effects of those coatings and additives on biofilm formation and bacteria growth rate. In this paper, 2 natural additives were identified for effective MIC protection. Natural products were selected based on the environmental appeal of the products. Two additives, derived from olive oil and Manhaden fish oil, were found to be effective in reducing MIC. In general, 2-3% of a natural additive was deemed adequate for effective MIC protection. Bacteria populations were counted at the beginning and at the end of the tests using the plate count method. After immersing the different coupons for 3 months in the SRB medium, it was noticed that the number of bacteria and their colonies were highly affected by both the environment and the used coating systems. A series of corrosion tests was performed to study the effectiveness of various natural additives. Visual observations, scanning electron microscopy (SEM) analyses, and computer image analyzer techniques were used to study the effects of SRB on the different coupon surfaces. It was observed that the presence of coatings inhibited both the biofilm growth and biocorrosion effects. The results revealed that the addition of some natural additives improved the protection ability of commercial coatings, with the best result with Manhaden fish oil.