Copper Nickel Alloys: 90/10 vs 70/30 Cupronickel Comparison
Copper-nickel alloys (cupronickels) are among the most important materials for marine and seawater applications. The two most common grades — 90/10 Cu-Ni (C70600) and 70/30 Cu-Ni (C71500) — offer exceptional resistance to seawater corrosion, biofouling, and erosion. This guide compares these two alloys to help you select the right grade for your application.
Cupronickel alloys have been the material of choice for naval vessels, offshore platforms, desalination plants, and power station cooling systems for over a century. Understanding the differences between 90/10 and 70/30 grades ensures optimal performance and cost-effectiveness.
Basic Composition
| Element | 90/10 (C70600) | 70/30 (C71500) |
|---|---|---|
| Copper (Cu) | Balance (~88.6%) | Balance (~65%) |
| Nickel (Ni) | 9-11% | 29-33% |
| Iron (Fe) | 1.0-1.8% | 0.40-1.0% |
| Manganese (Mn) | 1.0% max | 1.0% max |
| Zinc (Zn) | 0.50% max | 0.50% max |
Mechanical Properties Comparison
| Property | 90/10 Cu-Ni | 70/30 Cu-Ni |
|---|---|---|
| Density | 8.94 g/cm³ | 8.94 g/cm³ |
| Melting Point | 1080°C | 1170°C |
| Tensile Strength (annealed) | 310 MPa | 370 MPa |
| Yield Strength (0.2%) | 105 MPa | 130 MPa |
| Elongation | 40% | 35% |
| Hardness (HV) | 80 | 100 |
| Thermal Conductivity | 40 W/m·K | 29 W/m·K |
| Electrical Conductivity | 7% IACS | 4% IACS |
Corrosion Resistance
| Environment | 90/10 | 70/30 |
|---|---|---|
| Seawater (flowing) | Excellent | Excellent |
| Seawater (stagnant) | Good | Excellent |
| Velocity limit (m/s) | 2.5 (clean) | 3.5+ (clean) |
| Sulfide pollution | Good | Better |
| Ammoniacal solutions | Fair | Fair |
| Stress corrosion cracking | Resistant | Resistant |
| Biofouling resistance | Excellent | Excellent |
Key Differences
70/30 Cu-Ni advantages over 90/10:
- Higher strength — allows thinner walls or higher pressure ratings
- Superior resistance to high-velocity seawater (important for pump impellers, fast vessel hulls)
- Better resistance to sulfide-contaminated seawater
- Higher nickel content provides better overall corrosion resistance
90/10 Cu-Ni advantages over 70/30:
- Lower cost (significantly less nickel)
- Better thermal conductivity (preferred for heat exchangers)
- Better workability and formability
- Higher electrical conductivity (relevant for electrical applications)
- More readily available in standard sizes
Application Selection Guide
| Application | Recommended Grade | Rationale |
|---|---|---|
| Seawater piping (general) | 90/10 | Cost-effective, adequate performance |
| Seawater piping (high velocity) | 70/30 | Better erosion resistance |
| Heat exchanger tubes | 90/10 | Better thermal conductivity |
| Condenser tubes | 90/10 or 70/30 | Depends on cooling water conditions |
| Naval vessel hulls | 90/10 | Biofouling resistance, cost |
| Desalination plant | 70/30 | Maximum corrosion resistance |
| Offshore platform splash zone | 70/30 | High velocity wave impact |
| Fire water systems | 90/10 | Cost-effective for large quantities |
| Power station cooling | 90/10 | Thermal conductivity + corrosion resistance |
Fabrication Considerations
Both alloys are readily fabricated using standard methods:
- Welding: GTAW (TIG), GMAW (MIG), SMAW, and submerged arc all work well
- Brazing: Silver brazing alloys recommended
- Forming: Both are ductile and can be cold-formed; 90/10 is more formable
- Machining: Good machinability, though gummy compared to brass
Service Life Expectancy
In typical seawater service with proper design and installation:
- 90/10 Cu-Ni: 20-30+ years
- 70/30 Cu-Ni: 25-40+ years
Both alloys significantly outperform carbon steel, stainless steel (in stagnant seawater), and most copper alloys in marine environments.
Conclusion
Both 90/10 and 70/30 cupronickel are proven materials for seawater service. The choice between them comes down to balancing performance requirements against cost. For most seawater piping and heat exchanger applications, 90/10 provides excellent performance at lower cost. Reserve 70/30 for high-velocity service, polluted seawater, or critical applications where maximum corrosion resistance justifies the premium. Both alloys deliver decades of reliable service when properly specified and installed.
Need copper nickel products? CoreMetal Steel supplies 90/10 and 70/30 Cu-Ni in pipe, tube, plate, and sheet forms. Contact Tracy at tracy@coremetalsteel.com or +86 18291910632 for competitive pricing and fast delivery.