User:Cobdenstreet

The alloys are:

'''UNS Standard Compositions* of wrought alloys. Maximum or Range'''


 * These values may vary in other standards

There are subtle differences in corrosion resistance and strength which determine which alloy is selected. Descending the table, the maximum allowable flow rate in piping increases as does the strength.

Typical minimum mechanical properties and maximum velocities

In sea water, the alloys have excellent corrosion rates which remain low as long as the maximum design flow velocity is not exceeded. This velocity depends on geometry and pipe diameter. They have high resistance to crevice corrosion, stress corrosion cracking and hydrogen embrittlement that can be troublesome to other alloy systems. Copper-nickels naturally form a thin protective surface layer over the first several weeks of exposure to sea water and this provides its on-going resistance. Additionally, they have a high inherent biofouling resistance to attachment by macrofoulers ( e.g. sea grasses and molluscs) living in the sea water. To use this property to its full potential, the alloy needs to be free of the effects or insulated from any form of cathodic protection.



However, copper-nickels can show high corrosion rates in polluted or stagnant sea water when sulphides or ammonia are present. It is important therefore to avoid exposure to such conditions particularly during commissioning and refit while the surface films are maturing. Ferrous sulphate dosing to sea water systems can provide improved resistance.

As copper and nickel alloy with each other easily and have simple structures, the alloys are ductile and readily fabricated. Strength and hardness for each individual alloy is increased by cold working; they are not hardened by heat treatment. Joining of 90-10 (C70600) and 70-30 (C71500) is possible by both welding or brazing. They are both weldable by the majority of techniques although autogenous (welding without weld consumables) or oxy-acetylene methods are not recommended. 70-30 rather than 90-10 weld consumables are normally preferred for both alloys and no post weld heat treatment is required. They can also be welded directly to steel providing a 65% nickel-copper weld consumable is used to avoid iron dilution effects. Brazing requires appropriate silver-base brazing alloys. The C71640 alloy tends to be used as seamless tubing and expanded rather than welded into the tube plate.

Applications for copper-nickels have withstood the test of time as they are still widely used and range from sea water system piping, condensers and heat exchangers in naval vessels, commercial shipping, multi-stage flash desalination and power stations. They have also been used as splash zone cladding on offshore structures and protective cladding on boat hulls as well as for solid hulls themselves. A thorough overview of these and other copper-nickel alloys; their properties and applications can be found in www.coppernickel.org