ABSTRACT

Localized environments in fuel grade ethanol (FGE) transportation systems, where conditions are suitable for microbial growth, may promote microbiologically influenced corrosion (MIC) of steel components. Interstate pipeline transportation of ethanol fuels increases the potential impact of a MIC related failure. A laboratory investigation is conducted to evaluate the susceptibility of linepipe steels to MIC when low concentrations of ethanol and acetic acid are present. Acetic acid producing bacteria (APB) and a sulfate-reducing bacterial (SRB) consortium are cultivated from storage tanks used to capture ethanol spillage and runoff water at fueling terminals. Electrochemical corrosion testing and electron microscopy is applied to study MIC of API 5L X52 and API 5L X70 linepipe steels by these bacteria. Electrochemical techniques including open circuit potential (OCP), polarization resistance (PR), and electrochemical impedance spectroscopy (EIS) evaluate electrochemical properties of the steel-solution interface. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) are applied to study biofilm, corrosion products, and morphology. Electrochemical corrosion data indicate acceleration of steel corrosion rates due to SRB in ethanol and acetic acid environments. Localized corrosion is identified on API 5L X52 and X70 steels exposed to APB and on API 5L X70 exposed to SRB.

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