Copper-Nickel (CuNi) (Cu+Ni)
Copper-nickel alloys combine the inherent biofouling resistance and seawater corrosion resistance of copper with the strength and erosion resistance contributed by nickel. The two workhorse grades — 90/10 (90% Cu, 10% Ni) and 70/30 (70% Cu, 30% Ni) — dominate marine piping, desalination, and offshore platform applications. Their natural antifouling properties reduce maintenance costs compared to coated alternatives.
Properties
- Density
- 8,900–8,950 kg/m³
- Melting Point
- 1,100–1,240 °C
- Boiling Point
- ~2,300 °C
- Thermal Conductivity
- 29–40 W/(m·K)
- Electrical Resistivity
- 1.9–3.8 × 10⁻⁷ Ω·m
- Tensile Strength
- 275–500 MPa
- Yield Strength
- 105–250 MPa
- Hardness
- 80–160 HB
- Elongation
- 25–45%
- Crystal Structure
- FCC
Common Grades
- C70600 (CuNi10Fe1Mn): 90/10 copper-nickel — the standard marine piping alloy. Good seawater resistance at moderate velocities.
- C71500 (CuNi30Fe0.5Mn): 70/30 copper-nickel — higher strength and superior resistance to high-velocity seawater erosion-corrosion.
- C71640 (CuNi30Fe2Mn2): Iron-enriched 70/30 grade for enhanced erosion resistance in condenser tubes and heat exchangers.
- C72200 (CuNi16Cr): Chromium-bearing CuNi for improved strength and erosion resistance in aggressive marine conditions.
Applications
- Marine/Naval: Seawater piping systems, hull cladding, propellers, ship fire mains, sea chests
- Desalination: MSF and MED evaporator tubes, brine heater tubes, condensers
- Offshore Oil & Gas: Platform seawater cooling systems, fire-water piping, subsea hydraulic lines
- Power Generation: Steam condenser tubes, feedwater heater tubes, cooling water systems
- Aquaculture: Fish farm pen netting (antifouling), cage frames, underwater structures
FAQ
Why is copper-nickel preferred over stainless steel for seawater piping?
Copper-nickel offers three key advantages over stainless steel in seawater: 1) inherent biofouling resistance that eliminates the need for antifouling coatings, 2) immunity to chloride-induced stress corrosion cracking that threatens austenitic stainless steels, and 3) predictable, uniform corrosion behavior with no risk of sudden pitting failure. CuNi piping systems typically last 30+ years in seawater service.
What is the difference between 90/10 and 70/30 copper-nickel?
70/30 CuNi has higher nickel content, providing greater strength (tensile ~500 MPa vs ~350 MPa), better resistance to high-velocity erosion-corrosion, and higher maximum service temperature. However, it costs 30–40% more than 90/10. Most marine piping uses 90/10; 70/30 is reserved for condensers, high-velocity systems, and more demanding environments.
Do copper-nickel alloys prevent biofouling?
Yes, copper-nickel alloys release copper ions at a controlled rate that is toxic to marine organisms. This provides inherent resistance to macro-fouling (barnacles, mussels, algae) without antifouling paints. Studies show 70–90% reduction in fouling compared to unprotected steel. This natural antifouling property is the main reason CuNi is chosen for seawater intakes, aquaculture nets, and platform legs.