Overview of Copper-Nickel Alloys for Marine Service
Copper-nickel alloys have been the material of choice for seawater systems for over a century. The two most important grades – 90/10 (C70600) and 70/30 (C71500) – offer excellent seawater corrosion resistance, biofouling resistance, and good mechanical properties.
Chemical Composition and Properties Comparison
| Property | C70600 (90/10) | C71500 (70/30) |
|---|---|---|
| Copper | 88.6% min | 65.0% min |
| Nickel | 9.0-11.0% | 29.0-33.0% |
| Density | 8.94 g/cm3 | 8.90 g/cm3 |
| Thermal Conductivity | 40 W/mK | 29 W/mK |
| Tensile Strength (annealed) | 276-352 MPa | 345-448 MPa |
| Yield Strength (annealed) | 103-276 MPa | 138-345 MPa |
| Elongation | 30% min | 30% min |
Corrosion Resistance in Seawater
General Corrosion: 90/10: 0.025-0.05 mm/year; 70/30: 0.01-0.025 mm/year
Erosion-Corrosion: 90/10 max velocity ~2.4 m/s; 70/30 max velocity ~3.0-3.7 m/s
Stress Corrosion Cracking: Both alloys highly resistant – major advantage over austenitic stainless steels.
Biofouling: 90/10 has slightly better biofouling resistance due to higher copper content.
Application-Specific Selection Guide
| Application | Recommended | Rationale |
|---|---|---|
| Seawater cooling pipes (ships) | C70600 (90/10) | Cost-effective, good flow velocities |
| Condenser tubes | C71500 (70/30) | Higher strength for thin-wall tubes |
| Offshore platform piping | C71500 (70/30) | Maximum corrosion life |
| Fire water systems | C70600 (90/10) | Adequate for intermittent use |
| Desalination intake | C71500 (70/30) | High velocity, critical uptime |
Sourcing Copper-Nickel Products
CoreMetal Steel supplies copper-nickel pipe, tube, fittings, and flanges in both C70600 and C71500 grades, with full mill certification and class society approval.
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