Cathodic protection of stainless steel AISI 316L in sea water systems: Theoretical considerations and practical experience

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Cathodic protection of stainless steel AISI 316L in sea water systems: Theoretical considerations and practical experience

Drugli, J.M. / Steinsmo, U. / Valen, S.

Stainless steel AISI 316L when used in sea water suffers very often from local corrosion in narrow crevices or in welds. To mitigate this problem in piping systems built of this material, cathodic protection systems have been designed at SINTEF. Several of these systems have been in service for periods up to 15 years without problems. In some cases the cathodic currents and potential have been recorded and some of the data are presented in the paper. The current densities required to protect stainless steel in natural sea water are relatively high in certain period after start of exposure due to microbial activity on the steel surfaces. After a long exposure time the current demand decreases, partly as a result of calcareous deposits limiting the cathodic reaction. The current requirements for protection in chlorinated sea water are much lower and the so called Resistor controlled Cathodic Protection (RCP) method is well suited in this environment and can also be applied for use with stainless steel AISI 316L.