| Cathodic protection is used in oil and gas industries to mitigate corrosion associated with defective coatings on coated pipelines. A disbonded coating is a defect that includes a coating break exposing a bare metal surface, the holiday, with the surrounding coating totally disbonded from the metal. A mathematical model of the steady-state conditions in a disbonded coating system is presented in this dissertation. The model explicitly accounted for electroneutrality and the transport of species by diffusion and migration. The electrochemical reactions considered were corrosion, oxygen reduction, and hydrogen evolution. The influences of applied potential, bulk electrolyte resistivity, and geometric parameters on the system were determined. The model presented is more sophisticated than previous steady-state models for disbonded coating systems presented in literature.;A cathodic delamination system comprises a defect where the coating surrounding a holiday is partially disbonded. This system involves the propagation of a front along the metal-coating interface. The spatial distributions of potential at the buried metal-coating interface for experimental cathodic delamination systems have been reported. These results have been interpreted in literature in terms of a qualitative mechanism for cathodic delamination. A mathematical model is presented in this dissertation that simulated the propagation of the front during cathodic delamination at a zinc-coating interface. The key to this model involved the hypotheses that the porosity and the polarization kinetics at the metal-coating interface were pH dependent. The simulations provided qualitative agreement with published experimental results. This model is the first mathematical model proposed for the propagation of the front during cathodic delamination and provides a foundation for more sophisticated models. |
