On the extension of CP models to address cathodic protection under a delaminated coating
Cathodic protection models for pipeline and other metallic structures developed to address the presence of coating flaws or holidays do not account explicitly for the presence of a delaminated region surrounding a holiday. The potential drop in the delaminated region was obtained by solving the coupled, non-linear, partial differential, governing equations that describe transport and electrochemical reactions within the delaminated region. The results were used to develop an analytic expression for the potential drop across the delaminated region as a function of delaminated region length and the resistivity of the bulk environment exterior to the holiday. Expressions developed using this approach can be utilized by existing cathodic protection models to deliver improved potential distributions along protected metallic surfaces. The simulations were used to test the commonly employed assumption that transport by diffusion can be neglected in the delaminated region. The influence of diffusion on current was shown to be significant.
The Location of Cathodic Reaction during Localized Corrosion
A theoretical model for predicting the current and potential distribution within a prototypic pit was used to estimate conditions under which cathodic reaction occurs in the occluded region. The model is developed for a long, narrow occluded cell where the anode is localized in the tip region. Cathodic reaction (hydrogen reduction) on the side walls and external surface is predicted by assuming metal‐ion hydrolysis, diffusion of hydrogen ions, Ohm's law, cathodic reduction via Tafel kinetics, and constriction of current lines entering the occluded region. Results indicate that cathodic reaction within occluded regions is favored for deep narrow regions in solutions of low hydrogen ion concentration. Dimensionless groupings of system parameters are used to scan behavior over wide ranges of parameter space and to compile conditions under which appreciable cathodic reaction can be anticipated within occluded cells.
Anodic passivation of iron in alkaline solutions containing halides
Passivation of Fe in pure NaOH solutions, and in alkaline solutions containing Clt-, Brt-, and It- ions has been studied by measuring the galvanostatic relations during anodic polarization to the O2-evolution potential, followed by cathodic polarization to the H2evolution potential. Halides decrease the charge needed for each of the two arrests observed in the anodic curve, and for the arrest in the cathodic curve. At the same halide concentration, the effect increases with increase of atomic number. However, it increases with increase of concentration for the same halide. The phenomena are explained on the basis of adsorption. 
 
The possible role of XOt- ions has been also considered. In pure NaOH solutions, the effect of pH on the potential E of the two anodic arrests is given by dE/dpH = -70 to -75 mV, in agreement with the suggested mechanisms for iron dissolution in alkaline solutions.