The corrosion at buried metal-coating interfaces under an open circuit condition occurs through the galvanic interaction between anodic and cathodic sites. The requirements include pathways for electronic conductivity and ionic transport between the sites and a driving electrochemical force for the electrochemical reactions that exceeds the iR drop. A mathematical model of a galvanic cell is presented that addresses the ionic transport between anodic and cathodic sites beneath an organic coating on an aluminum substrate.