Copper-nickel (CUNI or Cupronickel) alloys are widely used in marine systems, including seawater cooling systems, desalination plants, and offshore structures. Their unique properties make them ideal for harsh underwater environments.

While copper itself is highly resistant to corrosion in the atmosphere and fresh water, copper-nickel alloys offer even greater resistance when exposed to seawater. The addition of nickel enhances the alloy’s strength, durability, and ability to resist corrosion and erosion in various natural waters, such as seawater, brackish water, and treated water. These materials also exhibit excellent mechanical performance, including resistance to stress corrosion cracking and corrosion fatigue.

Many navies and commercial ships rely on copper-nickel alloys for critical components due to their long-term reliability and performance in marine settings.

Copper-nickel alloys were first developed over fifty years ago specifically for use in seawater environments. Initially, they were used in condensers and piping systems, and their effectiveness has been proven through decades of continued use in a wide range of marine applications. Today, these alloys are extensively used in the offshore, power generation, and desalination industries, and remain a key material for many naval and commercial vessels.

In addition to their corrosion resistance, copper-nickel alloys have an inherent ability to resist macrofouling—such as the buildup of marine organisms. This natural resistance helps reduce the need for biocides in condenser and seawater systems, and minimizes drag and cleaning requirements on ship hulls and offshore platforms.

Copper-nickel alloys provide the best balance of resistance to flowing seawater and overall corrosion protection. Two main grades are commonly used in marine applications: 90-10 (90/10) and 70-30 (70/30), which contain 10% and 30% nickel, respectively. Both alloys include small amounts of iron and manganese, which enhance their performance in seawater. The 30% nickel alloy is stronger and better suited for high-flow applications, but the 90-10 grade is often preferred for its cost-effectiveness and widespread use.

A modified version of the 30% nickel alloy, containing 2% manganese and 2% iron, is specifically used for condenser tubes in multi-stage flash desalination units. This alloy offers improved impact resistance and is designed for heat rejection systems. However, due to the effects of impurities on hot ductility and weldability, strict limits are placed on certain elements. Contamination during forming and welding must be carefully controlled. These special grades are typically produced as seamless tubes, allowing them to be expanded into tube sheets without the need for welding.

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