Localized Corrosion of UNS A95052 Aluminum Alloy for Application in Multi-Effect Desalinator Plants

摘要

Aluminum alloy UNS A95052 (AA5052) is very attractive for desalination applications because of its good corrosion resistance in seawater at temperatures up to 125 degrees C, low cost, good thermal conductivity, and non-toxicity of its corrosion products. The pitting corrosion potential, E-ptt, and the pit repassivation potential, Er, pit, of AA5052 were measured in deaerated 65,000 ppm sodium chloride (NaCl) solutions at 30 degrees C, 60 degrees C, and 85 degrees C. E-ptt decreased with temperature, in accord with literature results. Er, pit was a function of anodic charge passed during pit growth stage. A complete evaluation of suitability of this alloy from a corrosion perspective requires also studies of crevice corrosion at different temperatures, considering that multi-plate designs of desalinators have metal plates in contact with rubber gaskets and seals. Cyclic potentiodynamic polarization was used to estimate crevice repassivation potentials, Er, crev, at 30 degrees C, 60 degrees C, and 85 degrees C, in specimens with an attached rubber O-ring as a crevice former. This crevice former simulated the partially occluded geometry expected in desalination plants. Stable crevice corrosion potentials, Ecrev, were similar to E-pit, and, when polarized to a similar anodic charge density, E-r, crev were similar to E-r, (pit). Based on this result, from a corrosion perspective, the presence of crevices in the desalination plant is not expected to present an additional risk during operation of the plant. Electrochemical tests were also performed in saturated AlCl3 solutions to explain the results using Galvele's localized acidification model.