In principle, a cupronickel can contain between 1% and 49% nickel, such that copper remains the main element (otherwise you would call it a nickel-copper alloy). Both copper and nickel are completely soluble in each other, which supports this very wide range of compositions.
The most commonly produced cupronickel is the 90/10 (90% Cu, 10% Ni). Increasing the nickel content towards 30% (as found in alloys such as UNS C71640) will increase the abrasion resistance, which will also apply to the flow rates in seawater that parts may be exposed to.
Hiduron 130 (DTD 900/4805, 2.1504) and Hiduron 191 (DEFSTAN 02-835, NES835) both contain c.15% nickel, which is an optimum level to achieve excellent mechanical and physical properties. Both alloys have been used successfully for >50 years since their original development for naval applications, although today they are used in more varied applications such as subsea connectors, valve trim, fasteners and couplings, generally in seawater.
Here are some other applications which require cupronickel alloys –
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