Crevice corrosion (Topic 11005)

Crevice corrosion occurs in narrow metal to metal or non-metal to metal gaps where the convection of water is hampered and a specific crevice chemistry different from the environment is allowed to develop. Aggressive ions like chlorides must be present in the electrolyte. The oxygen in the bottom of the crevice is consumed and an anodic area is developed adjacent to the oxygen depleted zone. Crevice corrosion develops quite similar to pitting corrosion after the initiation stage, with a gradual decrease of the pH and an increase of the chloride concentration within the crevice.

Crevice corrosion is normally not a serious problem on aluminium in the absence of aggressive ions, because of the very stable aluminiumoxide. However in a crevice there will be a possibility for accumulation of moisture because of capillary forces and deposits with corrosive or hygroscopic species. In this way there will be a constant corrosive environment in the crevice which eventually can break down the oxide layer.

Crevice corrosion can occur during storage of aluminium such as water-staining which creates dark stains as a result of a surface etching caused by water trapped between the adjacent surfaces. It is most commonly seen on sheet products and is mainly an aesthetic problem as the mechanical integrity of the water stained aluminium is rarely impaired. Another possible problem is accumulation of voluminous corrosion products in narrow crevices which can finally deform the construction in extreme cases.

Avoiding crevice corrosion is primarily a question of good design