51316-7772-Use of Carbon Steel Beads to Determine Microbially-Influenced Corrosion Under Flow Conditions

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Product Number: 51316-7772-SG

ISBN: 7772 2016 CP

Author: Tijan Pinnock

Publication Date: 2016

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Microbially influenced corrosion (MIC) in oil and gas transporting and production facilities is caused predominantly by the activity of sulfate reducing bacteria (SRB). SRB can oxidize iron in carbon steel and use the electrons obtained to reduce sulfate to sulfide and accelerate general corrosion rates. Carbon steel coupons are commonly used to determine MIC-associated general corrosion rates and pitting corrosion following surface examination of the coupons. In this study we have used spherical carbon steel beads (? = 0.238 cm) to monitor corrosion. An attractive feature of these beads is that they are very homogeneous in size with an average weight of 55.0 + 0.3 mg. Significant general corrosion rates of up to 1 mm/yr have been observed during one month incubations of 5 to 20 beads in serum bottles with either field samples or with cultures containing SRB. In order to study and quantify SRB-mediated MIC under flow conditions as observed in many oil and gas facilities and pipelines aqueous medium containing SRB from an oilfield in southern Alberta was pumped into an up-flow bioreactor containing 35 beads. The SRB-containing medium was the outflow of a continuous culture vessel mimicking the produced water output from the oil field. SRB activity was monitored by determining the concentrations of sulfate sulfide and organic electron donors at different points along the flow path. Little iron was found in the bioreactor effluent suggesting that most was retained as corrosion product. After 256 days of continuous flow the carbon-steel beads were removed from the bioreactor and treated according to NACE RP0775-2005. Weight loss was determined to derive an industrially significant general corrosion rate of 0.11 mm/yr. Bead mass ranged from 36.5 to 51.4 mg with an average of 44.0 + 3.3 mg. Surface examination indicated deep pitting in the most heavily corroded beads. However the significant 11-fold increase in standard deviation from 0.3 to 3.3 mg is also a proxy for the unevenness of the corrosion i.e. for pitting corrosion. Hence an effective system for studying SRB-mediated general and pitting corrosion under flow conditions has been designed and this is now being used to determine the efficacy of various biocides and corrosion inhibitors in preventing MIC-associated general and pitting corrosion.