Microbial Influenced Corrosion of Carbon Steel Exposed to Desalinized Seawater

摘要

Microbial Influenced Corrosion (MIC) is an aggressive type of corrosion that produces deteriorationof metal surfaces exposed to aqueous environments as a consequence of the development of acomplex biological matrix. Pipelines of carbon steel (CS) used to transport desalinized seawaterare susceptible to MIC due to failures in the plant of desalinization such as membrane damage orfiltration through toric joints and in the operation of pipelines including improper hydrostatic tests,water with low flow rate, and prolonged period of water stagnation that reduce the dissolved oxygenconcentration. Although CS has an active behavior in a wide range of environments, when it isexposed to low oxygen concentration a passive magnetite layer can be formed. The passivationproduced by magnetite decreases the homogenous corrosion rate, but it made susceptible topitting corrosion. The MIC of CS with a magnetite layer has been reported only by the iron-reducingbacteria Shewanella oneidensis, but its capacity to reduce solid iron is not widely distributed innature. However, other bacterial metabolisms could be related to the MIC of carbon steel with amagnetite layer. Fermenting acidifying bacteria could break the magnetite film or increase itsporosity due to dissolution of magnetite, previously reported in abiotic acid environments. In thisstudy, a biofilm with the capacity to decrease pH was obtained from a system affected by MIC andits effect on pitting corrosion of CS API 5L X65 with magnetite layer was evaluated. Corrosion wasevaluated using microscopic techniques and electrochemical tools such as open circuit potential,polarization curves, and electrochemical impedance spectroscopy. Additionally,exopolysaccharides were analyzed to determine the fermentable compounds presents in thebiofilms, and a mathematical model of the MIC of carbon steel with a magnetite layer based onfinite element and implemented in COMSOL coupled with MATLAB is proposed to understand theMIC mechanisms. The results of this research are the first steps to highlight the relevance of acidproducing bacteria in MIC of CS with a magnetite layer.