Introduction
This article explains the C70600 copper-nickel pipe specification. The 90/10 copper-nickel family, principally C70600 with the related C70400 grade, contains about 90 percent copper and 10 percent nickel. It is the standard material for seawater piping, heat exchanger tubing and offshore engineering because of its outstanding resistance to marine corrosion and biofouling.
Composition
C70600 contains 9.0 to 11.0 percent nickel and 1.0 to 1.8 percent iron with the balance copper, while C70400 carries 4.8 to 6.2 percent nickel with 1.3 to 1.7 percent iron. Iron is a deliberate addition: at these levels it improves the corrosion resistance of the protective film, particularly against impingement attack in flowing seawater.
Why 90/10 Is Used in Seawater
The nickel stabilizes the protective surface film that forms on the alloy, and the film self-heals quickly when damaged. This gives the material excellent resistance to uniform corrosion, pitting, crevice attack and erosion-corrosion at flow velocities up to about 3 m/s in seawater. The alloy also resists macrofouling better than many metals, which reduces cleaning frequency in heat exchangers.
| Property | C70600 | C70400 |
|---|---|---|
| Nickel | 9.0 - 11.0% | 4.8 - 6.2% |
| Iron | 1.0 - 1.8% | 1.3 - 1.7% |
| Tensile strength | 275 - 365 MPa | About 270 - 340 MPa |
| Seawater velocity | Up to about 3 m/s | Moderate flows |
Properties
90/10 cupronickel has a tensile strength of about 275 to 365 MPa in the annealed condition with elongation above 30 percent, a thermal conductivity of roughly 40 to 45 W/(m·K) and a density of about 8.94 g/cm3. It can be welded by all common processes and retains good ductility at low temperatures, which suits refrigeration and cryogenic piping.
Applications and Standards
Typical uses are seawater cooling and fire mains, heat exchanger and condenser tubes, oil cooler tubes, low-finned tubes, shipboard piping, desalination plants and offshore platforms. The alloys are covered by ASTM B111, B466, B171 and B151, with the ASME counterparts SB111 and SB466 for pressure service.
Verification
Confirm the nickel and iron ranges, temper and dimensions on the mill certificate, and check the pressure test requirements for pipe and tube service. For seawater duty, verify that the delivered analysis matches the corrosion-resistant grade specified.
