The Effect of Coating Procedure on the Strength and Corrosion Resistance of Epoxy Coatings on A36 Steel: Pull-Out and Potentiodynamic Analysis

In harsh environments with a high chloride ion content, a high-performance coating must be applied to steel. For the latter to be protected in such conditions epoxy coating is often used. The performance of this coating depends on its type and the application process. Corrosion resistance and adhesion are considered important parameters in this process. This study investigates the impact of coating application methods (spray (S), handroll (H), and combinations (S+H)) on the epoxy coating performance on ASTM A36 steel substrates. A mathematical model of void formation during the drying processes is also presented. A combined garnet blasting and high-pressure water blasting method was employed to achieve optimal substrate cleanliness and roughness prior to the coating processes. The coating quality and mechanical integrity were characterized by pull-out adhesion testing and potentiodynamic polarization analysis in chloride-rich water. The results demonstrated notable differences influenced by the coating application technique. The H+S showed the highest adhesion strength (13.05 MPa), primarily due to improved primer-substrate, mechanical interlocking, and minimized void content. On the other hand, S+H showed the lowest adhesion strength, which was explained by weaker primer-substrate bonding and increased porosity. Testing using potentiodynamic polarization revealed that the coatings applied only by (H+H) had the best corrosion resistance, as evidenced by their lowest corrosion current density and most positive corrosion potential. The (S+S), on the other hand, produced the least amount of corrosion resistance.