Spatial Evaluation of Preservability of Mild Steel by Coal Tar Epoxy Coatings Via Spectroscopic and Microscopic Techniques

Abstract

Generally film coatings are formulated by accounting average weather conditions, corrosivity level and any metal substrate, while accelerated (salt spray) test usually considered adequate to predict performance of a coating system. This established a need to evaluate compatibility of a coating system to a particular operational conditions for preservation of underlaying substrate metal. In this communication, epoxy-polyamide primer and coal tar epoxy topcoat system were tested for preservation of mild steel under various natural exposures including marine, industrial and urban test sites of Karachi city, while accelerated test was also conducted for comparison. Condition of coating was assessed by visual morphological inspection, gloss measurements, scanning electron microscopy (SEM), energy-dispersive X-ray analysis and by oxygen/carbon ratios. Resulted data were statistically analyzed through principal component analysis and explained a variance of 99.82 % when two components were considered. Severe blistering, acute loss of gloss and high degradation in the surface characteristics of coal tar epoxy coating systems were noticed after natural exposure testing at marine and industrial sites as compared to accelerated (salt spray) testing. However, comparison of performance of coal tar epoxy coating systems applied on mild steel with our previous study on electrogalvanized mild steel has shown faintly better preservability of mild steel samples by coal tar epoxy coating systems. This was also proved by relatively lower oxygen/carbon ratios for the coating systems applied on mild steel which correspond to lower coating degradation products.