Cathodic protection is the main tool used for the protection of steels exposed to natural seawater for offshore applications. Since the last decade, 13% Cr martensitic and supermartensitic components have
been developed for slightly sour gas transport and processing. They l offer an excellent balance between mechanical properties, corrosion behavior and a good attractive cost. As 13 Cr steels have a limited corrosion resistance to seawater and as martensitic structures are
susceptible to hydrogen embrittlement, it is important to determine a safe potential range altogether for corrosion protection and to avoid overprotection that could cause failure 2. In consequence, this safe potential range was investigated for supermartensitic steel with and without artificial crevices (ASTM G78, modified, elastic rubber). Laboratory demonstration of the concept of "protection potential" is presented.
Supermartensitic steels are passive in artificial sea water in a limited potential range. Moreover, their passive state can be perfectly maintained by a moderate cathodic protection. This is facilitated if a good quality oxide film is present on the steel surface. Supermartensitic steels can be protected at -550 mV/SCE in artificial seawater. If active crevices are
initially present, corrosion in these crevices can be slowed down at -550 mV/SCE. All the experimental results show a favorable influence of moderate cathodic protection on supermartensitic steels exposed to
seawater.
Keywords : moderate cathodic protection, supermartensitic stainless steels, seawater