A Framework for Conducting Analysis of Microbiologically Influenced Corrosion Failures

Overview of MIC

Microbiologically influenced corrosion (MIC) is corrosion that is affected by the presence and/or activity of microorganisms, including bacteria, archaea and fungi.^[1] MIC is experienced by assets in the oil and gas industry, paper production, cooling water systems, waste water handling, manufacturing, infrastructure, and many other places. Problems with MIC and fouling in aviation jet fuel tanks and biodiesel storage and delivery systems by bacteria, yeast and filamentous fungi are also well-documented. Since microorganisms require water to demonstrate activity, the potential for MIC is logically associated with locations where exposed metal is in contact with water or solids containing sufficient moisture. 

On wetted surfaces, microorganisms typically exist in a diverse biofilm that consists of extracellular polymeric substances (EPS), various types of cells, and organic and inorganic material. Biofilms formed by microorganisms create a microenvironment on the metal surface that can differ significantly from the overall environment, leading to local differences in electrochemical potential resulting in corrosion. Microbial activities in biofilms can also facilitate corrosion by producing corrosive metabolites (acids, elemental sulfur), changing the nature or kinetics of rate controlling reactions, forming mineral scales, and direct uptake of electrons from the steel surface. 

Microorganisms and their activities are affected by many environmental factors, including most prominently, temperature, salinity, oxygen concentration, pH, and availability of nutrient compounds. Although most microorganisms can exist over a range of these environmental conditions, they commonly have a set of conditions at which growth is optimal. When conditions are unfavorable, cells may become dormant or die, or transition to a spore form that can last a long time until conditions once again become favorable for growth. 

While the chemical and physical environments have a significant effect on microbiology, they also have an equally significant effect on corrosion mechanisms and forms of damage. When diagnosing MIC, the abiotic (i.e., non-biological) effects of the environment must also be considered. Distinguishing the degree to which abiotic or biotic conditions lead to a corrosion failure is one of the greatest challenges in MIC failure investigation. The use of a MIC diagnostic framework; however, can help provide the insight needed to sort out the actual cause.

MIC Failures

In the oil and gas industry, a significant number of pipeline failures due to either external or internal corrosion have resulted from MIC, some with catastrophic consequences. One widely publicized case occurred in August of 2000 when a 30” diameter high pressure natural gas pipeline near Carlsbad, New Mexico ruptured and caught fire, killing 12 individuals. The rupture was determined in part to be the result of internal MIC. Another high-profile crude oil pipeline leak due to MIC occurred in 2006, leading to a temporary shutdown of most of the crude oil production on the North Slope of Alaska.^[2] Where natural gas and crude oil are gathered from producing wells, water (brine) is often comingled, exposing the gathering systems to the threat of MIC.