Introduction The aim of this publication is to provide engineers with an appreciation of copper alloys commonly used in marine applications. It will provide an overview of the range of alloys and their properties, and give references and sources for further information. Copper is a metal that is extracted from the earth, is essential to the development of all forms of life and has been vital in the progress of civilisation. Alongside gold, it is the oldest metal used by man and its history of use dates back more than 10,000 years. Since antiquity, both wrought and cast forms of copper alloys have shown high resistance to the ravages of the marine environment, like the bronze cannon in Figure 1. Seawater is corrosive to most construction materials and, with properties which have been developed and modified to meet today’s exacting engineering challenges, copper alloys continue to offer solutions to a range of industries requiring reliability in seawater.
The metal copper is very versatile, having good resistance to corrosion in marine atmospheres and in seawater with moderate flow velocities. Its properties, both in terms of corrosion resistance and mechanical strength, can be further improved by alloying. There are many copper alloys suitable for marine service and the main groups are: Coppers Copper-nickels Bronzes Brasses Copper-beryllium All copper alloys can be machined accurately and cost-effectively and to a good standard of tolerance and surface finish. Some copper alloys have excellent machinability as a primary attribute – specifically leaded brasses, which set the standard by which all other metals are judged. Other copper alloys are made with a variety of combinations of properties such as strength, wear resistance, anti-galling and cold formability. These may be less easily machined, but are still easier to machine than many other types of material. For seawater systems, copper-nickel and aluminium bronze are often preferred, although other copper alloys are used in marine service and have their specific advantages. Copper alloys differ from other metals in that they have an inherent high resistance to biofouling, particularly macrofouling, which can eliminate the need for antifouling coatings or water treatment.
There are many copper alloys which fall within each group and a selection are examined here. Copper Development Association publication 120 Copper and Copper Alloys(1) gives a more comprehensive breakdown of standards, compositions and properties. Typical applications for marine environments include heat exchangers and condensers, seawater piping, hydraulic tubing, pump and valve components, bearings, fasteners, marine fittings, propellers, shafts, offshore sheathing and aquaculture cages.