70/30 is a copper nickel alloy that is known for its exceptional resistance to erosion, corrosion and pitting. It also has good strength, weldability and workability.
The alloy has experienced a long, successful history in the marine industry that has since extended to other industries such as desalination and cooling plants, power generation, and offshore oil and gas.
CN107 and C71500 designations are the most popular specifications covering the 70/30 cupronickel alloy, although the Defence Standard DEF STAN 02-879 Annex B (superseding NES 780 and DEF STAN 02-780) provides tighter controls on mechanical properties and impurities along with a mandatory impact value.
Properties of 70/30 Cupronickel
70/30 is well known for its excellent resistance to erosion and corrosion, particularly in marine environments. Its corrosion resistance property is enhanced in polluted seawater and higher velocity waters (up to 4.5 m/s). In addition, 70/30 has excellent resistance against corrosion fatigue and stress corrosion cracking and possesses a high retention of mechanical properties from sub-zero temperatures to ~300 °C.
In the annealed condition, the 70/30 copper-nickel alloy has moderate strength levels making it suitable for use in more demanding applications. It also has an inherent resistance to biofouling. During the initial period of use, a protective oxide film naturally develops over the material and creates an unfavorable surface that prevents marine growth.
70/30 can be readily hot and cold worked and is amenable to most fabrication processes. Further, it can be easily joined by a wide range of welding methods including soldering and brazing. With a malleability approaching that of copper and good hot and cold formability, the 70/30 alloy does not harden quickly, lending itself to spinning and drawing.
Applications of 70/30 Cupronickel
Thanks to its inherent corrosion resistance, 70/30 is predominantly used for seawater service as machined and forged valve and pump components, flanges, fittings and hardware.
It is even used in offshore firewater systems, seawater, and submarine pipework, condensers, heat exchangers, sheathing of risers and legs on boat hulls and offshore platforms, desalination units, hydraulic lines. And in areas where concern over chloride stress-corrosion cracking hinders the use of stainless steels and also in areas where high corrosion resistance is needed.
|Fabrication properties of 70/30 cupronickel
|Hot & cold workability
|Machinability rating (free-cutting brass=100)
||925 - 1025 °C
||650 - 850 °C
|Soldering & brazing
|Gas shielded arc welding
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NB Weight data for guidance only
This information has been sourced, reviewed and adapted from materials provided by Columbia Metals Ltd.
For more information on this source, please visit Columbia Metals Ltd.