Cathodic protection is the main technique for corrosion protection of steel in the submerged zones of ships, harbour installations, offshore structures and internal surface of plants that operate in direct contact with seawater. The combination of cathodic protection and corrosion resistant alloys may be a convenient solution. The cathodic protection of stainless steel can avoid localized corrosion induced by chlorides and makes possible the use of alloys with lower contents of chromium and molybdenum compared to the levels needed for ensuring the corrosion resistance in seawater. Natural seawater is a unique environment in which aerobic bacterial settlement acts as a cathodic depolarizer towards the oxygen reduction on stainless steel surfaces immersed at ambient temperature. In addition, microbial colonization increases the probability of localized corrosion initiation and propagation. The paper is aimed to the definition of suitable boundary conditions for cathodic protection modelling of stainless steels in natural seawater. The boundary conditions have been derived by measurements performed in field on several corrosion resistant alloys immersed in natural seawater. Finite element method (FEM) has been used to evaluate the potential and current distribution under cathodic protection to assess the corrosion risk under general conditions of exposure.
展开▼
