Galvanic Properties

Copper nickel alloys lie mid-way in the galvanic series being compatible with other copper alloys but more noble than zinc, aluminium, steel and aluminium bronze and less noble than passivated stainless steel, nickel alloys and titanium. The 70-30 alloy is slightly more noble than the 90-10 alloy. As with all bimetallic couples careful attention should be given to avoiding unfavourable galvanic area ratios.

Galvanic contact with less noble copper-alloys, carbon steel and zinc negates the biofouling resistance of copper-nickel. Therefore, in applications requiring the full biofouling resistance of copper-nickel, such as boat hulls, the use of anodes and impressed current cathodic protection systems should be avoided.

Splash zone sheathing on steel offshore platforms in 90-10 copper-nickel should at least span from below mean tide level to well into the atmospheric zone. Potential galvanic corrosion on the adjacent steel is addressed by coating the top section with paint; the bottom, submerged junction will be protected by the cathodic protection system normally applied to the structure.

On copper-nickel boat hulls, careful attention is required for all hull fittings, and propellers as the hull will not require cathodic protection. Hull fittings should be in copper-nickel or a more slightly noble alloy. This is not only to protect the fittings but also to achieve optimum biofouling resistance of the copper-nickel, as will be discussed later. Nickel aluminium bronze is preferred to manganese bronze for the propeller, since it is the more noble alloy. Corrosion, particularly dezincification is probable if the less noble manganese bronze is used as experience in the first 90-10 copper-nickel hulled boat, the Copper Mariner and more recently in New Zealand on a copper-nickel sheathed vessel.

Directory | Standard | Heat | Heat Exchanger | Temperature | Pressure | Corrosion | Hardness | Surface | Properties | Select Stainless Steel | Contact US