ABSTRACT
In addition, modern shipbuilding also makes use of the high strength to weight ratio of aluminium alloys for the construction of specialist vessels. These alloys, likewise, can be vulnerable to corrosion in seawater. Sometimes, however, the degree of corrosion resistance errs towards the marginal, in which case internal cathodic protection might offer an option. Pitting corrosion is a phenomenon that applies to passive metals. Like the nature of the passive film itself, the mechanisms and morphologies of pitting have been widely studied by corrosion scientists. As a generalisation, most passive alloys will undergo crevice corrosion at slightly lower temperatures in seawater than they undergo pitting corrosion. Since it is very difficult to avoid crevices in the construction of offshore equipment using corrosion-resistant alloys, crevice corrosion is, in practice, a more dominant threat than pitting. Both thermodynamic and electrode kinetic analyses lead to the conclusion that different metals have different protection potentials to that of steel.
