Highly alloyed stainless steel (SS) materials may be prone to local corrosion under certain conditions. To avoid corrosion in chlorinated seawater systems, a modified cathodic protection system called Resistor controlled Cathodic Protection (RCP) (1) has been developed. The method is based on having a resistor (or a diode) in series with the sacrificial anode to allow polarization of the SS steel to a potential level where corrosion does not occur, and where the current density requirement is small. The RCP method has been commercially available since 1995 and today RCP anodes protect stainless steels exposed to chlorinated seawater on more than 50 offshore and onshore facilities. Each RCP anode is uniquely designed for a specific location using a computer program that calculates potential variations, current density distribution, anode resistor values and anode consumption rates. This paper presents the principles and practical experience of the RCP method with emphasis on the importance of sufficient chlorination and the effect of deposits sometimes seen building up at the anode surface. Through the experience gained, continuous chlorination giving 0.5 ppm residual chlorine is generally recommended, and laboratory investigations to examine how deposits may affect the anodes have lead to an improved RCP anode design.
Keywords: stainless steels, resistor controlled cathodic protection, chlorinated seawater, biofouling