Copper-Nickel Alloys for Marine Piping and Propellers

Guide to copper alloys in marine environments — Cu-Ni 90/10 and 70/30 for seawater piping, and nickel aluminum bronze (NAB) for propellers and valves.

Category: Materials · 11 min read · 2026-03-03

Copper alloys have served the marine industry for centuries due to their inherent resistance to seawater corrosion and biofouling. Modern applications range from seawater cooling systems on naval vessels to large ship propellers, where copper alloys remain irreplaceable.

Cu-Ni 90/10 (C70600) — The Marine Workhorse

Cu-Ni 90/10 (CW352H per EN) is the standard alloy for seawater piping systems on ships and offshore platforms. It combines good corrosion resistance with practical fabrication characteristics:

  • **Composition**: 90Cu-10Ni-1.5Fe-1Mn\n- **Seawater corrosion rate**: 0.02–0.05 mm/year in flowing seawater (1–2 m/s)\n- **Biofouling resistance**: Copper ions naturally inhibit marine organism attachment. Fouling rates are 10–20× lower than steel or titanium.\n- **Maximum velocity**: 3.5 m/s in straight pipe to avoid erosion-corrosion. Reduce to 2.5 m/s at bends and fittings.

Cu-Ni 70/30 (C71500) — Higher Performance

Cu-Ni 70/30 provides superior corrosion and erosion-corrosion resistance for more demanding applications:

  • **Composition**: 70Cu-30Ni-0.7Fe-0.7Mn\n- **Maximum velocity**: 4.5 m/s — significantly higher than 90/10, allowing smaller pipe diameters\n- **Temperature tolerance**: Better performance in hot seawater desalination systems (up to 120°C)\n- **Cost**: Approximately 40–50% more expensive than 90/10. Specified where long service life justifies the premium.

Nickel Aluminum Bronze (NAB)

Nickel aluminum bronze (CuAl10Ni5Fe5, C63000 / CW307G) is the premier alloy for marine propellers, seawater valves, and pump impellers. It combines high strength with exceptional seawater corrosion resistance:

  • **Tensile strength**: 630–750 MPa (cast), 700–850 MPa (wrought)\n- **Yield strength**: 250–330 MPa (cast)\n- **Elongation**: 13–18% — excellent toughness for propeller impact resistance\n- **Cavitation resistance**: Superior to all other copper alloys and most stainless steels

NAB propellers ranging from 500 kg to 80,000 kg are sand-cast in specialized foundries per national naval standards. Post-casting heat treatment (675°C for 6 hours, air cool) is applied to improve corrosion resistance by transforming the beta phase.

Welding Copper-Nickel Alloys

Cu-Ni alloys are readily welded by GTAW and SMAW using matching filler metals (e.g., ERCuNi for 90/10, CuNi30Mn1FeTi for 70/30). Critical precautions:

  • **Cleanliness**: Copper alloys are extremely sensitive to sulfur contamination. Use only markers, cutting fluids, and anti-spatter sprays certified sulfur-free.\n- **Shielding gas**: Pure argon for GTAW. CO₂-containing mixtures are not suitable for copper alloys.\n- **Preheating**: Generally not required for Cu-Ni alloys. Interpass temperature maximum 150°C to prevent hot cracking.

Galvanic Compatibility

When copper alloys are coupled with other metals in seawater, galvanic corrosion must be managed. Copper alloys are cathodic to steel, aluminum, and zinc — accelerating corrosion of the less noble metal. Use insulating flanges, sacrificial anodes, or impressed current cathodic protection per EN 12473.