EFFECTS OF A CORROSION-INHIBITOR ON BACTERIA AND MICROBIOLOGICALLY INFLUENCED CORROSION

The effect of a corrosion inhibitor (CI) formulation on the population of sessile and planktonic field bacteria was measured and related to coupon pitting and general corrosion using controlled laboratory flow-through loops. Coupons were periodically removed from the flow loops, visually examined, scraped, and enumerated and subjected to epifluorescent microscopy and, in some instances, to scanning electron microscopy (SEM) before being cleaned and reweighed. For the most part, the presence of CI had no detectable effects on the populations of several types of sessile and planktonic bacteria. In one set of experiments, the populations of sulfate-reducing bacteria were more than one order of magnitude greater in the presence of the CI. In another instance, there was a generally higher population of planktonic anaerobic bacteria in the absence of CI. A lower Eh tended to coincide with higher populations of all types of bacteria. The presence of CI resulted in less coupon corrosion. There was only minor pitting corrosion. SEM scans of pit surfaces indicated varying concentrations of sulfur across the pits. There were many small tubercles present on the surface of the coupons. The tubercles appeared to be hollow, and SEM micrographs showed depressions in the coupons directly under the tubercles, indicating the possible beginning of microscopic pits.