Effectiveness of aluminum anodes for cathodic protection in low chloride environments

Aluminum-based alloys are widely used in sea water as galvanic anodes. Conversely, their use in soil is not recommended because they tend to passivate when chloride content is low. However, there are chloride contaminated soil where the use of aluminum anodes may be of interest. The aim of this research is to evaluate the effectiveness of aluminum galvanic anodes in low salinity solutions at different chloride/sulfate ratios. The research followed two phases: electrochemical characterization of anodes through potentiodynamic and free corrosion potential tests in solution with different chloride/sulfate concentration, and galvanic coupling tests performed in soil saturated with chloride solutions (diluted natural or artificial seawater until reaching: 2,000, 6,000 and 19,000 ppm chlorides). The potentiodynamic tests showed that pitting potential decreased as chloride concentration increased; sulfate ions exhibited a passivating effect or a potential nobilisation as also observed on free corrosion potential tests. In coupling tests, anodes showed an acceptable working potential also at lowest tested chloride concentration.