Predicting Conditions in Coating Disbonded Regions on Buried Pipelines in Nuclear Plants

Corrosion would not be a large concern if the coating on a buried pipe is intact or it is disbonded but without a holiday in it. The dangerous form of corrosion is believed to occur when the coating is disbonded, has a holiday and shields cathodic protection (CP) current. The corrosion severity in the coating disbonded region is determined by the local corrosive environment and the ability of CP current penetration into the disbonded region. Unfortunately, the pipeline industry has so far been incapable of or lacking field techniques or procedures for measuring the corroding conditions in a coating-disbonded region irrespective of the presence of CP. A model is developed that is capable of making predictions of the corroding conditions in the coating disbonded region, including chemistry, potential and corrosion rate. This model is built upon fundamental principles and reduced to simple algorithms that can allow for field application. This paper reports the fundamentals behind the model, the model results and implications for practical application.