Cupronickel or copper nickel is an alloy of copper that contains nickel and strengthening iron and manganese. The copper content typically varies from 60 to 90 percent. Despite its high copper content, cupronickel is silver in colour. Cupronickel is highly resistant to corrosion by salt water, and is therefore used for piping, heat exchangers and condensers in seawater systems, as well as for marine hardware. It is sometimes used for the propellers, propeller shafts, and hulls of high-quality boats. Other uses include military equipment and chemical, petrochemical, and electrical industries.