Laboratory biocide effectiveness testing is an important step in microbiologically influenced corrosion (MIC) management because it offers a controlled environment where numerous variables such as biocide type, concentration, and application method can be investigated for their effects on microbiological populations and corrosion rate. In this paper the results of biocide testing performed for a crude oil pipeline system are presented. Experiments were performed using biofilms grown from water collected from the pipeline system and comparisons were made between samples where no biocide was added and biocide addition at two different concentrations. The effects of the biocide were evaluated using corrosion rates, planktonic and sessile populations, and activity. A key finding from the experiments was that the addition of biocide resulted in an increase in general corrosion rates and pitting rates. These results further emphasize the need to consider the effects of biocide on corrosion and not just microbiological populations and that biocide addition could result in unintended and unexpected consequences.
Microbiologically influenced corrosion (MIC) is recognized as a significant corrosion threat to oil and gas pipelines.1 Biocides are commonly applied as a means of killing microorganisms with the goal of reducing both microbial concentrations and corrosion rates.2 Laboratory experiments are typically used in selecting an effective biocide prior to application to a pipeline system. In the past, biocide selection was informed primarily on the ability of a biocide to reduce the concentration of planktonic microbes with no consideration of the effects on sessile microbes or corrosion rate.3 However, a reduction in planktonic microbe concentration does not necessarily correspond to a reduction in corrosion rate4; therefore, evaluating biocide effectiveness solely on planktonic population changes is not likely to result in the selection of the biocide with the greatest reduction in corrosion rates. As a result, in recent years, a number of studies have been performed that incorporate assessments of the effects of biocide on sessile microbes and corrosion rate.5