Evaluación de acero galvanizado estructural frente a la corrosión en atmósfera marina. parte 1. resultados después de 1 año de exposición

In this study, the performance of the hot-dip galvanized steel in front of the marine environment corrosion and the corresponding runoff process observed in such environment are analysed. Therefore, 10x10x0.6cm galvanized steel samples, with a Zn coating thickness of 114 μm, were exposed in Valparaíso, V Region, Chile. Deterioration of the galvanized surface was evaluated measuring in situ corrosion potential and decreasing of zinc coating thickness; the attack morphology was analysed through scanning electron microscopy (SEM). The corrosion product composition was established through X-ray diffraction (XRD). Furthermore, different techniques were used to analyse the runoff solutions collected after rain events, in order to determine pH, Cl^-ion content and Zn⁺² ion concentration. The results after one year of exposure of the samples show that galvanized steel corrosion potential increased in time; this corroborates the formation of a protective layer of zinc corrosion products, which were identified as zincite (ZnO) and simonkoleite (Zn₅(OH)₈Cl₂·H₂O). On the other hand, the corrosion velocity determined in time was 16.4 μm/year. As for the rain events, the pH values of the runoff solutions were similar to the pH of the rain water. The chloride content also showed a tendency to decrease and stabilize in time; furthermore, the total zinc quantity lost as a soluble product is strongly influenced by the quantity, duration and periodicity among dry periods of fallen rain.