Microbiologically influenced corrosion (MIC) is a type of corrosion affected by the activity of the microorganism. The attachment of microorganisms and biofilm adhesion are strongly related to the metal surface finish. This makes the influence of MIC more aggressive as the roughness increases. In this study, the effect of different surface roughness on corrosion rate of X65 carbon steel and stainless steel 304 and 306 was studied. The corrosion properties were compared using electrochemical testing such as potentiodynamic polarization method and electrochemical impedance spectroscopy. The weight loss of the steel samples in seawater for a 47-day period and in seawater with Scenedesmus oblique algae for 31-day periods was assessed. In addition, a qualitative assessment for corrosion was done via optical microscopy. Corrosion was highest on carbon steel with the rougher surface of 60 grit and lowest in the smoother surface of 800 grit. Carbon steel was highly susceptible to corrosion while stainless steel had the best corrosion resistance.
Microbial influenced corrosion is a type of corrosion caused by microorganisms attached to the metal surface or by their activity. The first one who noted the MIC was Gaines in 1910 [1], followed by research about the graphitization of cast irons in anaerobic soils in 1934 [2]. Nowadays, attention to MIC problems increased significantly. Many researches focused on understanding and explanation of the interactions that happened between the metal and the biofilm. MIC can attack metallic and non-metallic materials, either with the presence of oxygen or not. In the first case when there is oxygen, iron-oxidizing bacteria directly oxidize iron to produce iron oxides or iron hydroxides. In the second case when there is no oxygen, sulfate-reducing bacteria produce hydrogen sulfide causing sulfide stress cracking. Beside the direct way to cause corrosion, microorganisms can cause corrosion by attacking the corrosion inhibitors [3]. It is difficult to differentiate the MIC costs independently from abiotic corrosion because microorganisms can be found in any environment with water activity. Hence, microorganisms can contribute to all corrosion sites. MIC is usually found in stationary or low-flow environments. Because in fast fluid flow environments, the speed of the flow will wash away the bacterial species which causes the MIC [4]. The estimated global cost of corrosion was approximately 3.4% of the global gross domestic product (GDP) [5]. 20% of all corrosion costs could be attributed to MIC [6]. MIC may be prevented by reducing biofilm formation on the surface of the metal. It could be prevented with chemical treatment by using biocides which are applied to the metal surface to reduce the formation of biofilm. But many environmental issues are associated with the application of chemical biocides, which makes the development of eco-friendly inhibitors very important.
