Synergistic Corrosion Mitigation Appraisal of Coal Tar Epoxy Duplex Coating System by Spectroscopic and Microscopic Techniques

Epoxy-polyamide primer and coal tar epoxy topcoat system were tested to evaluate preservation of electrogalvanized mild steel (EGMS) under various naturally stimulated exposures including marine, industrial and urban test sites of Karachi city, while salt spray 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 (EDX) analysis and oxygen–carbon ratio techniques. Results indicated that the natural exposure testing (particularly at marine and industrial test sites) caused extremely high degradation of coal tar epoxy duplex coating systems as compared to accelerated testing. SEM has also revealed high degradation in the surface characteristics of the coating applied on EGMS after natural exposure testing. This is most likely due to the presence of several corrosive components of environment, emerging from the mist of salt spray in the atmosphere and pollution due to industry and automobiles. In addition to this, it was also found that the major modes of degradation were completely different in accelerated and natural exposure testing. Comparison of the results of coal tar epoxy coating systems applied on EGMS with our previous study on mild steel revealed high photodegradation of the coating systems applied on EGMS in natural exposure testing, i.e., oxygen/carbon ratios as determined by (EDX) analysis were higher for the coating systems applied on EGMS.