What is Cupronickel?

What Is Cupronickel?

cupronickel
Cupronickel bars. Image copyright Gurudev Metal

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.

Cupronickel has been made and used for over a thousand years. Its first known use was in China in about 300 BCE. Chinese records describe the process for making "white copper," which involved heating and mixing copper, nickel, and saltpeter. Cupronickel was also used to make Greek coins. Later European "rediscovery" of cupronickel involved alchemical experiments.

Corrosion Resistance:

Cupronickel is naturally resistant to corrosion in seawater, making it a valuable metal for marine use. 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 has a wide array of uses. In some cases, it is valued for its strength and corrosion-resistance. In other cases, it is valued for its silver color and rust-free shine.

Some examples of cupronickel's uses include:

  • tubes for light-duty condensers, feedwater heaters, and evaporators used in power stations and desalination plants
  • pipes carrying seawater to fire mains, cooling water systems and ship sanitary systems
  • sheathing for wooden piles
  • 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
  • medical equipment
  • 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