Cupronickel alloys provide excellent corrosion resistance in seawater, and that resistance increases with nickel content. In rapidly moving seawater in particular they are widely used for connectors, fasteners and shafts.
In seawater, metals and alloys can suffer several forms of corrosion: general wastage, impingement attack, and localised corrosion such as pitting, crevice corrosion, stress corrosion cracking and intergranular attack. Cupronickels resist these well.
General corrosion rates for 90-10 and 70-30 cupronickel alloys in seawater are very low, ranging between 0.025 and 0.0025 mm/yr. For most applications these rates let the alloys last their required lifetime, with little probability of premature failure from corrosion.