Abstract
Microbially-influenced corrosion (MIC) contributes to the general corrosion rate (CR), which is typically measured with carbon steel coupons. Here we explore the use of carbon steel ball bearings, referred to as beads (55.0 ± 0.3 mg; Ø = 0.238 cm), for determining CRs. CRs for samples from an oil field in Oceania incubated with beads were determined by the weight loss method, using acid treatment to remove corrosion products. The release of ferrous and ferric iron was also measured and CRs based on weight loss and iron determination were in good agreement. Average CRs were 0.022 mm/yr for eight produced waters with high numbers (105/ml) of acid-producing bacteria (APB), but no sulfate-reducing bacteria (SRB). Average CRs were 0.009 mm/yr for five central processing facility (CPF) waters, which had no APB or SRB due to weekly biocide treatment and 0.036 mm/yr for 2 CPF tank bottom sludges, which had high numbers of APB (106/ml) and SRB (108/ml). Hence, corrosion monitoring with carbon steel beads indicated that biocide treatment of CPF waters decreased the CR, except where biocide did not penetrate. The CR for incubations with 20 ml of a produced water decreased from 0.061 to 0.007 mm/yr when increasing the number of beads from 1 to 40. CRs determined with beads were higher than those with coupons, possibly also due to a higher weight of iron per unit volume used in incubations with coupons. Use of 1 ml syringe columns, containing carbon steel beads, and injected with 10 ml/day of SRB-containing medium for 256 days gave a CR of 0.11 mm/yr under flow conditions. The standard deviation of the distribution of residual bead weights, a measure for the unevenness of the corrosion, increased with increasing CR. The most heavily corroded beads showed significant pitting. Hence the use of uniformly sized carbon steel beads offers new opportunities for screening and monitoring of corrosion including determination of the distribution of corrosion rates, which allows estimation of the probability of high rate events that may lead to failure.
Highlights
Corrosion of carbon steel is caused by physical, chemical, and microbiological factors (Beech and Sunner, 2004; Gieg et al, 2011; Enning and Garrelfs, 2014)
Water samples from the central processing facility (CPF) and injection waters had no significant Most probable numbers (MPNs) of acid-producing bacteria (APB) or sulfate-reducing bacteria (SRB)
Determination of corrosion rate (CR) is typically done with coupons by electrochemical methods (Dexter et al, 1991) or by determining weight loss
Summary
Corrosion of carbon steel is caused by physical, chemical, and microbiological factors (Beech and Sunner, 2004; Gieg et al, 2011; Enning and Garrelfs, 2014). It is a serious and expensive problem, which can lead for instance to failure of pipelines. When corrosion is uneven localized pits can form These can be narrow and deep or shallow and wide (https://www.nace.org/ Pitting-Corrosion/) and may eventually span the entire pipeline wall causing a failure. In the laboratory and in the field flat metal coupons are typically used to evaluate general and pitting corrosion by metal weight loss and by surface examination of the coupons, respectively. This allows definition of the pitting factor (P) as the ratio of the corrosion rate of the deepest pit (mm/yr) divided by the general corrosion rate (mm/yr)
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