Surface scales in sea water systems: Effects of their formation on corrosion behaviour of engineering steels

The formation of mineral scaling on engineering components can occur as a result of cathodic protection (CP). The consequences of such scale formation have been generally considered to be beneficial owing to the reduced current requirement and hence reduced costs of CP. This paper reports results of a study focusing on the type of scale compound precipitated during CP, its relation to applied potential and current levels, and the effect of scale formation on the subsequent corrosion resistance of stainless steel and carbon steel. Using dc electrochemical accelerated polarisation tests, the corrosion behaviour of UNS S31603 stainless steel and BS 4360 carbon-manganese steel was studied. Results have shown that scale formation can result in a significant decrease in the resistance of the passive stainless steel alloy to localised corrosion attack. The practical implications of these findings are discussed. © 1997 The Institute of Materials.