Deterioration of Protective Coating on Steel Structures in Harbor Attacked via Water and Sediment Erosion

Steel structures exposed to estuarine regions near the sea are susceptible to high-velocity and sediment-laden flows induced by runoff and tides, as well as storm surges, leading to significant erosion. This erosion causes defects in the protective coatings on steel surfaces, resulting in the accelerated corrosion of their components. However, damage to the protective coating of steel components is a relatively long process and is not easy to monitor in real time. This paper conducts an accelerated deterioration test of protective coatings under water and sediment erosion to explore the damage laws of the protective coatings of steel components under different test conditions. This study reveals that the adhesion of the protective coating decreased rapidly initially and then slowly with prolonged erosion time. In the early stage of erosion, scratches and pits are easily formed on the coating surface, while the damage tends to be uniform in the later stage. The damage characteristic values and damage rate of the protective coating were obtained based on the image recognition method. The characteristic value of scratch lengths ranged from 5 to 25 mm, and for pit diameters, they ranged from 1 to 4 mm. The maximum damage rate was 9.8%, and the damage rate showed a trend that approximately followed a logarithmic function with erosion time. It was also found that the sediment concentration had the greatest influence on the damage rate, followed by the erosion velocity, and the erosion angle had the least influence. Additionally, the relationships between adhesion and damage rate, as well as the relationship between adhesion and erosion depth, were established. It was found that the mean erosion depth exhibits a linear functional relationship with the damage rate, while adhesion exhibits a logarithmic functional relationship with both the damage rate and the erosion depth. The empirical formula proposed can provide a theoretical basis for quantitatively describing the surface defect conditions of the coating.