ABSTRACT
UNS A95052 (AA 5052) results very attractive for desalination applications due to its good corrosion resistance in seawater at temperatures up to 125°C, low cost, good thermal conductivity, and non-toxic corrosion products. The pitting potential, Epit, and the pit repassivation potential, Er, pit, of AA 5052 were measured in deaerated 65,000 ppm sodium chloride solutions at 30, 60 and 85°C. Pitting potential 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 the metal plates for desalinators are usually in contact with rubber gaskets and seals. Different techniques were used to estimate crevice repassivation potential at 30, 60 and 85°C, in samples with an attached rubber O-ring as a crevice former. Some samples were exposed at the corrosion potential in deaerated 65,000 ppm sodium chloride (normal operation) and in aerated 65,000 ppm sodium chloride solution with 5 ppm Cu++ ions (possible contaminants in feed water), in order to predict corrosion performance of the alloy.
INTRODUCTION
Seawater desalination with waste heat from nuclear or fossil power plants is an attractive alternative for the production of potable water.1 Multi-effect desalination process (MED) relies on the evaporation of water from a thin film of seawater.2 The heat of condensation is used in the evaporation of water from a subsequent film of seawater, achieving an efficient production of distillate. Materials for use in such plants must have an adequate corrosion resistance in seawater at 70°C or higher, 1,2 depending on the design and type of plant. Aluminum alloys, in particular UNS A95052(1) (referred hereafter as AA 5052), possess several advantages for this application, including a good thermal conductivity, 3,4 low cost when compared to copper or titanium alloys, 5 the non-toxicity of the alloy or its corrosion products6 and good wettability in seawater at high temperature. 3 Therefore, they are often the chosen material for this application. 1-3,6-9
