Studies in Accelerated (Predicted) Versus Observed Anticorrosive Performance for Coastal Industrialized Location

摘要

Accelerated test for corrosion protection is an industrially accepted norm. Even though no correlations are claimed by the coating manufacturers or the users, the users specify and manufacturers comply with the specifications. Coating's performance in actual use conditions may be unrelated to its accelerated test results. In this work, visual examinations and Scanning electron microscopy (SEM)/Energy dispersive X-ray (EDX) analysis were used to study accelerated (predicted) versus observed anticorrosive performance for coastal industrialized location. Commercially available coating systems based on epoxy-polyamide/polyurefhane (P1), epoxy-polyamide/epoxy-amine (P2) and alkyd/alkyd (P3) formulations were applied on mild steel test panels (4"× 6" sizes). Then accelerated testing (ASTM B-117) and natural exposure testing at marine test site in Karachi, Pakistan was performed. It was found that the accelerated corrosion testing showed much less severity of corrosion compared to natural exposure testing for all the coatings tested. Severe blistering, filiform corrosion spread of corrosion around the scribe and loss of gloss was noticed in natural exposure testing. SEM micrographs suggested that the accelerated testing did not show surface features similar to those noticed after natural exposure testing. Principal component analysis explained a variance of 99.98 %, 99.97 % and 99.29 % for P1, P2 and P3 coating systems respectively. These results clearly indicate that no correlation exists between accelerated test method ASTM B117 and natural testing carned out at coastal industrialized location. Based on the results it is suggested to follow a more stringent protocol (inclusion of highly coitosive bromide, sulfite and nitrate ions in acidic pH (6 to 6.5) of the salt solution) for coastal industrialized locations.