Corrosion Control Issues for Marine Vessel Copper-Nickel Boxcoolers

Copper-Nickel (CuNi) alloys (sometimes referred to as Cunifer) have good corrosion resistance and natural fouling resistance in seawater and are used extensively for seawater systems, including heat exchangers. For smaller marine vessels (for example tugs, support vessels, etc.) the heat exchanger tubes are simply placed inside a seachest, open to the sea, to allow cooling creating a box cooler arrangement. To maintain the natural anti-fouling properties the CuNi needs to be isolated from the vessel’s cathodic protection (CP) system. However, depending on the configuration of the cooler and seachest as well as the position of the cathodic protection anodes within the seachest, isolated coolers can be at risk of stray current corrosion problems. As the tube walls are thin, even low rates of corrosion should be avoided. The paper will describe the overall problems encountered and methods developed to prevent stray current corrosion damage, whilst maintaining the natural marine fouling resistance of the CuNi.