Cupronickel (also referred to as "cupernickel" or copper-nickel alloy) refers to a group of copper-nickel alloys that are used in saltwater environments due to their corrosion resistant properties.

The most common cupronickel alloys are:
  • 90/10 Cupro-nickel (copper-nickel-iron)
  • 70/30 Cupro-nickel (copper-nickel-iron)

These alloys have good working properties, are readily weldable and considered insensitive to stress corrosion. Cupronickel is also resistant to biofouling, crevice corrosion, stress corrosion cracking and hydrogen embrittlement.

Slight differences in corrosion resistance and strength generally determine which alloy grade is used for a particular application

Corrosion Resistance:

Cupronickel resists corrosion in seawater because its electrode potential is essentially neutral in such environments.

Consequently, it will not form electrolytic cells when placed in close proximity to other metals within an electrolyte, which is the main cause of galvanic corrosion.

Copper also naturally forms a protective oxide layer on its surface when exposed to seawater, which protects the metal from deterioration.

Applications:

Cupronickel is used in:

  • tubes for light-duty condensors, feedwater heaters and evaporators used in power stations and desalination plants
  • pipes carrying seawater to fire mains, cooling water systems and ship sanitary systems
  • underwater fencing
  • cabled tubes for hydraulic and pneumatic lines
  • fasteners, crankshafts, hulls and other marine hardware used in boats
  • silver-colored circulation coins
  • silver-plated cutlery
  • automobile parts
  • jewelry
  • cylinder cores in high-quality locks

Standard Cupronickel Compositions (Wt. %)

Cupronickel AlloyAlloy UNS No.CopperNickelIronManganese
90/10 CupronickelC70600Balance9.0-11.01.0-2.00.3-1.0
70/30 CupronickelC71500Balance29.0-32.00.5-1.50.4-1.0