The Study of Diffusion Ions and Water in Powder and Liquid Epoxy Coatings of Pipeline with Using Fluorescence Microscopy and AFM Methodology

ABSTRACT

FBE coatings are known to absorb moisture and pass current. They allow current to pass and exhibit a reduced electrical resistance under cathodic protection. The results of cathodic disbonding and EIS tests for FBE coatings show that with increasing of permittivity factor of coating, the radius of cathodic disbondment increases. When epoxy exposes in electrolyte, the diffusion of ions and water in coating caused of reduction of electrical resistance. The cathodic disbonding radius (r) decreases with diminish passing ions and water from epoxy coating. The precise mode by which water and ions enter organic coatings when subjected to corrosive environments remains unresolved. Local electrochemical methods have provided insight into the local nature of the under film degradation process. But these local electrochemical methods have not provided conclusive evidence as to whether the transport of water and ions occur through discrete or regional heterogeneities within the organic film. The mode of water diffusion and interaction with liquid and powder epoxy coatings that used for internal and external coating of pipe line with fluorescence microscopy and AFM methodology was investigated. It seems that the flux of  water and ions across the film  by the presence of small imperfections or pores which extend through the thickness of  coating and have cross-sections that are larger than  free areas typically present between the molecular chains of  matrix for the ions passing  through the bulk matrix of  the polymer film. Furthermore, there are regional differences within a single coating with regards to ion selectivity.