414Corrosion is one of the leading causes of failures in on- and offshore pipelines. Microbiologically influenced corrosion (MIC) has been identified as one of the major origins of corrosion and can result in locally high metal loss rates. Despite advances in the understanding of MIC, it remains difficult to accurately detect MIC and to predict where and when it will occur. External MIC is strongly affected by local environmental conditions. Relevant factors include soil and groundwater conditions as well as protective measures, like coatings and cathodic protection (CP). In this chapter, case studies are presented of the application of ER bioprobes to assess the effects of environmental conditions on external MIC.
An ER bioprobe was developed based on an electrical resistance (ER) probe. On the metal coupon of an ER probe, a corroding biofilm of sulfate-reducing microorganisms is grown under laboratory conditions. The bioprobe is subsequently inserted in groundwater or soil. Corrosion rates are instantaneously measured with the ER bioprobe, making it possible to simulate and study the development of external MIC of buried pipelines under realistic field conditions.
The effects of soil and groundwater composition on MIC rates were determined both in controlled laboratory conditions as well as in the field. Availability of organic matter, sulfate, and nitrate were shown to be key parameters for MIC. Fluctuating conditions, like the sequential exposure to groundwater with and without oxygen, resulted in a large increase of MIC rates. Groundwater flow had a strong impact on the MIC rates, showing the importance of mass transfer of nutrients and oxygen as a rate-determining factor. The ER bioprobes were also used to study the effectiveness of various levels of CP on MIC.
This research provides practical tools to assess the risk of MIC in specific types of groundwater. Also, the detailed information obtained provides mechanistic understanding enabling the prediction of MIC risk under varying conditions.