Technical note Atmospheric corrosion of aluminium conductor

The failure of an aluminium conductor situated 40 m from the coast of the Mediterranean Sea in an area polluted with SO₂ and CO₂ was investigated. The pollution is caused by combustion of light fuel and oils and by sand blown from the desert, which were responsible for the severe atmospheric corrosion. Mechanical tests, chemical analysis, and visual and microscopic examination showed that the aluminium conductor had suffered severe localised corrosion as a result of galvanic corrosion between the zinc coating on the steel sheathing and the aluminium conductor wires in the presence of electrolyte deposited from the surrounding humid atmosphere. After a period of time, all the zinc coating on the steel wires had disappeared in the attacked areas and a new galvanic cell then developed between the steel wire (cathode) and the aluminium wire (anode). Reduction in the cross sectional area of the aluminium wires, owing to severe pitting corrosion, resulted in overheating of the surrounding area which in turn led to evaporation of the volatile components present in the grease used to insulate the steel from the aluminium. As a result, the hard grease lost its beneficial effect as an insulator and severe localised corrosion (pitting) occurred.