External microbiological influenced corrosion (MIC) underneath disbonded pipeline coating systems is a serious dilemma in the industry. In the past and even today, it has not been recognized as such because it has been primarily mistaken for galvanic corrosion. Due to the type of coating materials used in the past, the cleaning process or lack of it, and application methods used, all coating systems have the propensity to develop defects and pinholes where disbandment and this type of
microbial corrosion could occur. In addition, the pipeline may or may not have had cathodic protection initially and/or consistently applied. Given these factors and the interaction of bacteria from the soil, moisture availability, and temperature of the pipeline, this paper will discuss the role that microbes play in the disbandment process, thus resulting in corrosion of an underground pipeline. Several case histories, laboratory results, and field findings will be presented.
Keywords: microbiological influenced corrosion, galvanic corrosion, disbandment, coating materials