ASTM B111 C70600 is the seamless 90/10 copper-nickel tube grade used for seawater desalination plants, marine cooling circuits and offshore process heat exchangers. The alloy contains 9.0-11.0% nickel together with 1.0-1.8% iron and a manganese addition, and it is often called cupronickel in trade documents. The nickel content forms a dense protective oxide film, the iron stabilises that film against removal by flowing water, and the result is a tube that keeps a low corrosion rate in seawater across a wide range of velocities. It is supplied in the O61 annealed temper for expanding duty or the H55 light-drawn temper where additional strength is needed.
Why 90/10 Copper-Nickel Is Used in Desalination
Desalination trains circulate large volumes of seawater and brine through heat transfer tube at temperatures that accelerate most corrosion processes. Three properties make the 90/10 composition the default choice for this duty: a low and predictable corrosion rate in seawater, tolerance of the higher velocities used to keep tube bores clean, and low macrofouling rates that reduce the frequency and cost of mechanical cleaning. The alloy also tolerates the chlorination used to control biological growth in intake systems, and it does not suffer the dezincification that affects brasses.
Composition
| Nickel, Ni (including Co) | 9.0-11.0% |
| Iron, Fe | 1.0-1.8% |
| Manganese, Mn | 1.0% max |
| Zinc, Zn | 1.0% max |
| Lead, Pb | 0.05% max |
| Copper, Cu | remainder, with copper plus named elements 99.5% min |
The nickel range and the iron minimum are the two values that most directly control performance in seawater, so both should be confirmed on the mill certificate. The manganese and zinc limits keep the matrix clean and prevent the formation of phases that would reduce ductility during expansion.
Mechanical Properties by Temper
| O61 annealed, tensile strength, min | 40 ksi (275 MPa) |
| O61 annealed, yield strength, min | 15 ksi (105 MPa) |
| H55 light-drawn, tensile strength, min | 45 ksi (310 MPa) |
| H55 light-drawn, yield strength, min | 35 ksi (240 MPa) |
The annealed temper is the normal delivery condition for tubes that will be rolled into a tube sheet, because it expands without cracking. The light-drawn temper is selected where the tube spans a longer unsupported length between baffles or where vibration is a design concern, and the higher yield strength of that temper improves fatigue resistance at the cost of some expansion ductility.
Physical Data
Specific gravity: 8.94, giving a density of 0.323 lb/in³ at 68 °F
Melting range: 2010-2100 °F (1100-1149 °C)
Electrical conductivity: about 9% IACS at 68 °F
Thermal conductivity: about 26 Btu/(ft²·ft·h·°F) at 68 °F, equivalent to roughly 45 W/(m·K)
Coefficient of thermal expansion: 9.5 × 10-6 per °F over 68-572 °F
Modulus of elasticity in tension: 18,000 ksi; modulus of rigidity: 6,800 ksi
Reported conductivity values for this alloy vary between data sources because they depend on temper, temperature and measurement method, so design calculations should quote the value together with its test temperature.
Fabrication Characteristics
| Soldering | Excellent |
| Brazing | Excellent |
| Gas shielded arc welding | Excellent |
| Coated metal arc welding | Good |
| Butt welding | Excellent |
| Spot and seam welding | Good |
| Capacity for cold working | Good |
| Capacity for hot forming | Good |
The alloy is normally joined to tube sheets by expansion, sometimes followed by seal welding. Where welded pipe connections are used, filler metal matched to the copper-nickel family and a controlled heat input keep the joint corrosion resistant.
Applications
Multi-stage flash and multi-effect desalination plants, including brine heater and recovery section tube
Seawater cooling systems and marine heat exchangers on ships and offshore units
Offshore oil and gas production, where seawater is used for cooling and injection support systems
Power generation condensers and auxiliary coolers operating on seawater or estuarine water
Engine cooling, wastewater handling and fire suppression circuits on commercial and naval vessels
Selection and Handling Guidance
Specify the outside diameter, wall thickness, length and temper, and state whether the tube is to be expanded, welded or both; these decisions drive the temper selection and the allowed dimensional tolerance. Confirm the nickel and iron contents on the certificate before release of the lot, keep tube capped and dry in store, and avoid contact with steel during site handling to prevent iron contamination that would disturb the protective film. In service, maintain the velocity inside the range established for the circuit and avoid stagnant conditions, since the film depends on a supply of oxygenated flowing water.
FAQ
Q: What is ASTM B111 C70600?
It is the 90/10 copper-nickel seamless tube grade in ASTM B111, containing 9.0-11.0% nickel with iron and manganese additions, supplied for condenser, evaporator and heat exchanger duty.
Q: Why is 90/10 copper-nickel preferred for desalination plants?
It maintains a low corrosion rate in seawater and brine, tolerates the higher water velocities used to keep tube bores clean, resists biofouling and accepts the chlorination used in intake systems.
Q: Which temper should be ordered?
O61 annealed for tube that will be expanded into a tube sheet, and H55 light-drawn where higher strength or better vibration performance is required.
Q: What mechanical minimums apply?
The O61 temper is specified with minimum values of 40 ksi (275 MPa) tensile and 15 ksi (105 MPa) yield strength, and the H55 temper with 45 ksi (310 MPa) tensile and 35 ksi (240 MPa) yield strength.
Q: Can C70600 tube be welded?
Yes. Soldering, brazing, gas shielded arc welding and butt welding are all well suited to this alloy, and welded joints should use filler metal from the copper-nickel family.
Q: How should tube be stored before installation?
Keep it indoors and dry with end caps in place, and avoid contact with carbon steel, which can transfer iron to the tube surface and interfere with formation of the protective film in service.
