Two Designations, Two Nickel Levels
The copper-nickel family is defined by nickel content. 90/10 copper nickel is UNS C70600, containing about 10 percent nickel, while 70/30 copper nickel is UNS C71500, containing about 30 percent nickel. Correct designation matters: C70600 is the 90/10 grade and C71500 is the 70/30 grade. Both alloys are used for piping in seawater systems because of their strength, ductility, and resistance to saltwater corrosion.
Chemical Composition
| Element | C70600 (90/10) | C71500 (70/30) |
|---|---|---|
| Copper | About 90 percent | About 70 percent |
| Nickel | 9.0-11.0 percent | 29.0-33.0 percent |
| Iron | 1.0-1.8 percent | 0.40-1.0 percent |
| Manganese | 1.0 percent max | 1.0 percent max |
Strength and Erosion Resistance
The higher nickel content of C71500 raises strength and improves resistance to erosion and impingement attack, particularly in high-velocity or turbulent seawater. C71500 is the better choice where flow velocities are high or where abrasive particles are present. C70600, with its lower nickel content, is more formable, slightly lighter on cost, and has marginally higher thermal conductivity.
Corrosion and Biofouling Behavior
Both alloys form a stable protective film in seawater and resist biofouling, so marine growth does not attach readily. C70600 is noted for excellent anti-fouling characteristics and is the most common copper-nickel alloy for seawater piping. C71500 extends service capability in more aggressive conditions, including polluted or sulfide-bearing waters at elevated temperature.
Applications
Marine: seawater cooling systems, saltwater transfer lines, shipboard piping, and hull sheathing.
Offshore: subsea systems, firewater lines, and platform piping.
Power generation: condenser and heat exchanger tubing in coastal plants.
Desalination: evaporator tubes, brine heaters, and distiller tubing.
Industrial: chemical processing, heat exchangers, and evaporators.
How to Choose
For general seawater piping, heat exchangers, and systems with moderate flow velocity, C70600 90/10 delivers the best balance of cost, corrosion resistance, and formability. For high-velocity seawater, elevated temperatures, aggressive media, or maximum erosion resistance, C71500 70/30 is the appropriate upgrade.
Frequently Asked Questions
Q: Is C70600 70/30 or 90/10?
A: C70600 is the 90/10 grade with about 10 percent nickel; C71500 is the 70/30 grade with about 30 percent nickel.
Q: Which copper nickel is stronger?
A: C71500 70/30 has higher strength and better erosion resistance in fast seawater.
Q: Is 90/10 suitable for seawater piping?
A: Yes, C70600 90/10 is the most widely used copper-nickel alloy for seawater piping and heat exchangers.
Q: Do these alloys resist biofouling?
A: Yes, both resist marine growth attachment, and C70600 is especially noted for anti-fouling behavior.
Q: What standards apply?
A: ASTM B111 for condenser tubes, B466 for pipe, B171 for plate, and B151 for rod and bar, with ASME SB equivalents.
Q: Which alloy should I choose?
A: Use C70600 for standard seawater service and C71500 where velocity, temperature, or aggressive media demand higher performance.
