51313-02568-Severe Pitting Corrosion Caused by Starving SRB Surviving on CS and Effect of Surface Roughness

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Product Number: 51313-02568-SG

ISBN: 02568 2013 CP

Author: Yajie Chen

Publication Date: 2013

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Sulfate reducing bacteria (SRB) are notorious in causing microbiologically influenced corrosion (MIC). Many researchers have studied the SRB-induced corrosion with supplemented organic nutrients. However many corroding environments do not always have SRB-metabolizable organic substrates. In this study we investigated (1) the biofilm development of a SRB on carbon steel coupons (2) the survival of the bacterium for 40 days after the organic substrates had been exhausted and (3) the associated progress of corrosion. The study was done in sterilized batch bioreactors with constant purge of nitrogen to ensure the anaerobic condition. Three stationary control (abiotic) systems and three SRB systems were included. N2 treated Postgate C medium was used and the carbon steel coupons were vertically hung and submerged in the medium. The coupons were polished on one side and not polished on the other side. Liquid samples were taken from the systems regularly for measurements of cell growth nutrient concentration and cell metabolites; four coupons from each system were removed at 3 21 and 43 days for MIC evaluation. The organic nutrients in the medium supported SRB growth and the biofilm developed for 3 days. Afterwards SRB cells were starved until 43 days. The 3D structure of biofilm with live and dead cell information was scanned by a Confocal Laser Scanning Microscope (CLSM). The electrochemical evolution was online monitored by Electrochemical Impedance Spectroscopy (EIS) and Open Circuit Potential (OCP) measurements. The surfaces of coupons before and after exposure to SRB culture or the abiotic medium were characterized by Scanning Electron Microscopy (SEM) and the elemental composition of the corrosion product was estimated by Energy Dispersive Spectroscopy (EDS). Pit morphology was characterized by Infinite Focus Microscope (IFM). Our study showed the SRB survived through the 40-day starvation presumably by iron oxidation coupled with sulfate reduction. SRB caused severe pitting corrosion with a maximum pit depth of 45 µm on both the polished and the rough side. Grain boundary also became increasingly more visible on the coupon surfaces. The rougher surface had earlier pit initiation and higher pit density. The finding of SRB’s ability to live and cause severe pitting corrosion under conditions of no organic food sources is very important to the understanding of SRB’s widespread presence in corroding environments. Further studies targeting at interfering/blocking this metabolism would allow the development of more effective methods for controlling the SRB induced corrosion.