ABSTRACT:

The main objective of this research was to evaluate the performance of thermosprayed coatings of zinc and aluminum (double layer) after 6 years of exposure, with and without the use of sealant (wash primer) in tropical marine environments of very high aggressiveness: La Voz (Cabo San Román / Falcón State) and Cruce del Lago de Maracaibo (Zulia State), in Venezuela. To that effect, carbon steel sheets (10 cm x 15 cm x 3 mm) were sprayed by flame. The sheets were characterized by means of initial weight, thickness, metallographic, adherence, roughness, being evaluated monthly by visual inspection and photographic during six years. After removal, the specimens were evaluated by microscopic analysis to determine the morphology of attack, microstructure, penetration of contaminants, composition and morphology of corrosion products. The results showed that after six years, the double layer system represents an excellent choice for corrosion protection of steel by combining the galvanic protection of zinc with the erosion resistance of aluminum. However, due to the erosion-corrosion effect, a sealant such as wash primer can be used in order to extend its service life.

INTRODUCTION

Worldwide, many organizations have made numerous efforts in terms of studies and research looking for new coating systems to improve the durability of structures exposed to marine and coastal marine environments, providing protection to the steel during its service life and producing a minimal impact on the environment. In marine and coastal marine environments, where a number of factors are present such as high chlorides concentrations, strong winds, changing conditions of relative humidity and temperature (especially in tropical climates like Venezuela), organic coatings do not perform properly. In this regard, thermo sprayed coatings appear as an alternative to protect steel structures in those environments. In countries like U.S., Europe, and Asia(1,2) these coatings are gaining importance for their promising corrosion resistance, durability, cost benefits, low environmental impact, and advantages over other conventional paint systems. One of the most important studies performed and also considered a pioneer in thermo sprayed was conducted by the American Welding Society(3). This study reported that thermo sprayed coatings with Zn and Al with and without sealer exposed in marine and industrial environments, provided protection against corrosion for 19 years. Moreover, in 1987, the Centre for Corrosion Technology Laque(4) reported that the degree of protection of the coatings, after 34 years of continuous exposure in a moderately aggressive marine atmosphere, varies considerably with alloy content, type of material applied, and method of application. In tropical marine environments such as in Venezuela little is known about the application and performance of this coating technology. Venezuela's environment is completely different from the above-mentioned countries given the high incidence of winds, and the changing conditions of temperature and relative humidity., Only the PATINA Network(5) is known to study the effect of this environments on coating systems. In it, the behavior under corrosion of a wide variety of conventional and new generation coatings in the atmospheres of the Ibero-American region was evaluated.

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