Predicting the Chemistry and Corrosion Rates in a Coating Disbonded Region With or Without Cathodic Current Penetrating in via the Holiday and Coating

Understanding conditions in a coating disbonded region on buried pipelines is technically challenging and yet important because it is believed that shielding of cathodic protection (CP) current by a disbonded coating can be a large source of pipe external corrosion. A model is developed that enables predicting the chemistry, corrosion potential and rate of a pipe steel in a coating disbonded region. The model is built upon fundamental principles and is flexible to treat various conditions associated with a disbonded region. In this paper, the fundamental principles of the model, some key model results and the practical implications of the results will be reported and discussed. This work has been supported by the U.S. PHMSA under Contract: DTPH56-08-T-000003.