Long Term Evaluation of Microbial Induced Corrosion Contribution to Underdeposit Sludge Corrosivity in a Heavy Crude Oil Pipeline

摘要

Internal corrosion has been observed in crude oil pipelines (<0.5% sediment and water(S&W)) at locations that facilitate the deposition and accumulation of entrained solids. The resulting sludges that form are composed of varying combination of hydrocarbons, sand, clay, corrosion by-products, biomass and water. The sludges are known to support robust microbial communities and these are suspected of contributing to the overall corrosivity of the sludge. This paper reports on the results of work done to evaluate the overall contribution of microbial induced corrosion (MIC) on the corrosion rates of steel coupons covered with a pipeline sludge extracted from a pigging operation. The sludge was applied to the coupons in both the as-received and sterilized condition and the coupons were extracted at 30 day intervals for 180 days. The results show that despite its high water content the corrosivity of the sludge was low (<20 μm/yr) and that weight loss after the initial 30 days was negligible. The activities of heterotrophic aerobic bacteria (HAB), acid producing bacteria (APB), and sulfate reducing bacteria (SRB) in the as-received sludge decreased during the experiment by 2, 1.5 and 1 order of magnitude, respectively. Overall there was no detectable contribution of MIC to the corrosion rates of the coupons during the experiment.