The cathodic disbonding resistance and adhesion durability of three layer polyethylene coated steel pipe were studied from the viewpoint of water permeability and the water uptake of dicyandiamideimidazole cured epoxy primer. The reaction between the epoxy resin and dicyandiamide generates hydroxyl groups. Therefore, as the content of dicyandiamide increased, the water uptake of the primer increased and the water diffusion rate of the primer decreased because of the strong interaction between hydroxyl reaction product and water molecules. Excellent cathodic disbonding resistance and adhesion durability were observed when the primer had the lowest water permeability which was expressed as the product of the water uptake and water diffusion rate. On the other hand, the addition of a corrosion protective pigment to the primer
improved cathodic disbonding resistance and adhesion durability when the primer had high water uptake, which secured the sufficient solubility of the pigment. Keywords: cathodic disbonding, adhesion, water permeability, water uptake, diffusion rate, epoxy primer, polyethylene coating, corrosion protective pigment, hydroxyl group, passive state, elution