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 offer an excellent balance between mechanical properties, corrosion behaviour and a good attractive cost. As martensitic structures are susceptible to hydrogen embrittlement, it is important to determine a safe potential range for cathodic protection and to avoid overprotection that could cause failure. In consequence, the influence of cathodic protection is investigated on supermartensitic steel without and with the use of artificial crevices (ASTM G78 and modified). 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. Crevice free parts do not corrode if they are polarised at -550 mVsce or lower. Samples protected at -750 mVsce do not develop corrosion even if they are equipped with artificial crevices. Nevertheless, some results suggest that crevice corrosion can be prevented or slowed down at -550 mVsce. Practical implementation methods of moderate cathodic protection are also suggested.
Moderate cathodic protection of supermartensitic stainless steels
2000
10 Seiten, 8 Bilder, 4 Tabellen, 7 Quellen
Conference paper
Storage medium
English
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