Types of Copper-Nickel Alloys

Alloys for marine environments include general engineering and high-strength grades:

• 90-10 Copper-Nickel (C70600,CW352H) has 10% nickel and is the most commonly used wrought copper alloy for marine engineering applications. It has small but important additions of iron and manganese to improve its resistance to localized corrosion and seawater flow. It is found in seawater systems for naval and commercial shipping and offshore oil and gas production, as well as in desalination and aquaculture.
• 70-30 Copper-Nickel (C71500, CW354H) has 30% nickel. It is stronger than 90-10 copper-nickel and can resist higher flow rates. It too has small but controlled amounts of iron and manganese to optimize its corrosion properties. It was originally developed for naval applications but is now in wider use particularly in multistage flash desalination units.
• 66-30-2-2 Cu-Ni (C71640, CW353H) This modified 70-30 alloy contains 2% iron and 2% Mn and can withstand higher flow rates than 90-10 and 70-30. However, its relative resistance to localized corrosion is slightly less. The alloy is successfully used as condenser tubing. Commercially, this is its main product form. It was originally developed for higher resistance to erosion corrosion in the presence of suspended solids and has been extremely successful in multi-stage flash desalination plants, particularly in the heat rejection and brine heater sections.
• Copper-Nickel-Chromium: A wrought Cu-Ni-Cr alloy with 16% Ni and 0.5% Cr (UNS C72200) was developed to allow higher flow velocities in condenser tubing. A cast alloy with 30% Ni and 2% Cr by the UK Royal Navy (UK Defence Standard 02-824) is used as an alternative to nickel aluminum bronze for cast valve bodies and pump components.
• High-Strength Copper-Nickel Alloys:
  • The addition of aluminum can increase the strength of copper-nickel by conventional precipitation hardening mechanisms. Cu-Ni-Al alloys, principally consisting of Ni₃Al and known as gamma prime, are used in shafts and bearing brushes, bolting, pump and valve trim, gears and fasteners.
  • The addition of tin displays spinodal strengthening via sub-microscopic chemical composition fluctuations. Cu-Ni-Sn alloys are used subsea where bearing performance, non-magnetic, low-fouling, anti-galling or high strength properties are required. Example applications include subsea manifold and ROV lock-on devices and seawater pump components, stems, bushes and bearings, drill components, subsea connectors and lifting nuts.

• 75-25 Copper-Nickel: This alloy, which contains a trace amount of Mn, is commonly used in today's silver-colored coins.
• 55-45 Copper-Nickel: This alloy is commonly used in thermocouples and resistors because its resistivity is relatively constant over a wide range of temperatures.
• Other alloys: Some of the marine alloys mentioned above have found non-marine applications (e.g., 90-10 Cu-Ni for brake tubing and antimicrobial applications.

Variations in the common national and international specifications for the 90-10, 70-30 and 66-30-2-2 copper-nickel alloys are shown in the table below. From this, the extent to which various standard materials overlap may be compared. In some standards, the impurities are more closely controlled than in others. In cases of doubt, the supplier's advice should be obtained.

Small amounts of other elements are often added to copper-nickel to achieve specific desirable properties. But certain impurity elements, such as lead, sulfur, carbon, bismuth, antimony and phosphorus may impair weldability and hot workability. Therefore, chemical concentrations must be carefully controlled. Common additives and impurities in copper-nickel alloys include the following:

• Manganese is invariably present in the commercial alloys as a de-oxidant and de-sulfurizer. It improves working characteristics and contributes to corrosion resistance in seawater.
• Iron is added (up to about 2.5%) to alloys required for marine applications. Iron confers resistance to impingement attack by flowing seawater and increases the strength. Initial development of the optimum compositions of the copper-30%nickel-iron alloys took place in the 1930's. This work was carried out to meet naval requirements for improved corrosion-resistant materials for condenser tubes and other applications involving contact with seawater. (NOTE: the term "copper-nickel (Cu-Ni)" refers to copper-nickel-iron alloys.)
• Chromium improves resistance to erosion in fast-flowing seawater. It can replace some of the iron content. At 1% or more, chromium increases strength. Chromium is used in a 30% nickel casting alloy (UK Defence Standard 02-824) and in a lower chromium, 16% nickel, wrought alloy (C72200).
• Niobium (Columbium) can increase strength. It also improves the weldability of cast alloys.
• Aluminum is used in the age-hardening process for high-strength copper-nickels.
• Silicon is a deoxidant that improves castability, increases strength and reduces ductility.
• Tin confers an improved resistance to atmospheric tarnishing. At 2%, it is used with 9% nickel to produce the alloy C72500. This alloy has useful stress relaxation and spring properties and is used in the electronics industry. Alloys with 4-10% tin can provide hardening to provide high strength, wear and galling characteristics.
• Titanium is essential in welding consumables. It promotes the formation of pore-free welds.
• Zinc is a primary constituent in Cu-Ni-Zn alloys, also known as nickel-silvers. In contrast, zinc in Cu-Ni alloys are restricted to less than 1%.
• Antimony, arsenic, lead, sulphur, phosphorus, tellurium and bismuth alone or in combination have little effect on corrosion resistance. Because of their influence on hot ductility, they may impair weldabilty. Therefore, they are carefully controlled to low levels.

• International standards of wrought and cast copper-nickel forms (Copper-Nickel Standards section)
• Design Standards
• Standard Compositions of Wrought Copper-Nickel Alloys (UNS copper alloy numbers)
• Forms and Sizes of Copper-Nickel Alloys

A useful Cross-Reference Table of copper-nickel alloys was prepared by Deutsches Kupferinstitut.