Copper-nickel Welding and Fabrication
“Copper-nickel alloys have a remarkable combination of good resistance to both corrosion and biofouling in seawater. As they are also readily welded and fabricated, they are an obvious choice for pipe systems, heat exchangers and structures engineered for marine use.
Copper-nickels have been specified for seawater use for over 50 years; they are the materials of first choice for seawater pipework and condenser/heat exchanger service for many of the world’s navies, floating production storage and offloading vessels and merchant ships. They are used in desalination, power plants and offshore fire water systems, and for the sheathed splash zone protection of oil and gas platform legs. In all such applications, their durability is proven.
Fabrication of copper-nickels is not difficult, although a higher degree of cleanliness is required than for steel. They are ductile and easily formed. Their machinability is similar to that of aluminium bronzes, phosphor bronzes and other copper alloys that do not have special free-cutting additions. Copper-nickels can be welded by most standard processes. The core of this book is welding and fabrication. General engineering properties, corrosion and biofouling resistance and applications are included only where they influence decisions on fabrication. It provides an informed understanding of the two primary copper-nickel alloys, to allow good fabrication and operation.
There are two main grades of copper-nickel alloy used in marine service – 90-10 (10% nickel) and 70-30 (30% nickel). The 70-30 alloy is stronger and has greater resistance to seawater flow; but 90-10 will provide good service for most applications and, being less expensive, tends to be more widely used. Both alloys contain small but important additions of iron and manganese, which have been chosen to provide the best combination of resistance to flowing seawater and to overall corrosion.
Copper-nickels are stronger than copper but lower in strength than steels. Their ductility, toughness and formability are all excellent. They do not embrittle at low temperatures and retain their mechanical strength and ductility down to cryogenic temperatures. ”
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