ASTM B466 and ASTM B111 C70600 copper-nickel tube, also written 90/10 cupronickel, is a standard wall material for seawater cooling circuits on ships, offshore platforms, desalination plants and coastal power stations. The alloy combines a nominal 90 % copper and 10 % nickel matrix with controlled iron and manganese additions that build a thin, stable surface film on the wetted side, and that film is what holds corrosion rates at very low levels in fast flowing seawater.
What Is C70600 90/10 Copper-Nickel Tube?
C70600 is the UNS designation of a copper-nickel alloy containing 9.0 % to 11.0 % nickel, 1.0 % to 1.8 % iron and up to 1.0 % manganese, with copper as the balance. Iron and manganese are not impurities in this grade; they are deliberate additions that make the protective film more adherent and more able to repair itself after local damage.
The alloy is supplied as seamless tube to ASTM B111 (ASME SB111), the specification for copper and copper alloy seamless condenser tubes and ferrule stock, and as pipe or tube to ASTM B466 (ASME SB466). The same material appears in defence and marine specifications as CN102, CW352H, CuNi10Fe1Mn and under naval engineering standards, so an existing drawing can usually be matched without changing the metallurgy.
Chemical Composition and Physical Properties
| Element / Property | Value |
|---|---|
| Nickel (Ni) | 9.0 – 11.0 % |
| Iron (Fe) | 1.0 – 1.8 % |
| Manganese (Mn) | 1.0 % max |
| Zinc (Zn) | 0.50 % max |
| Lead (Pb) | 0.02 % max |
| Carbon (C) | 0.05 % max |
| Phosphorus (P) / Sulphur (S) | 0.02 % max each |
| Copper (Cu) | Balance |
| Density | 8.94 g/cm³ |
| Thermal conductivity | about 45 W/(m·K) |
| Electrical conductivity | about 9 % IACS |
| Modulus of elasticity | about 124 GPa |
Thermal conductivity is far lower than that of pure copper, yet it remains adequate for condenser and heat exchanger duty; the design advantage of C70600 lies in the corrosion allowance it removes rather than in raw conductivity.
Dimensions and Wall Thickness
| Nominal size | Outside diameter | Standard wall | Heavier wall |
|---|---|---|---|
| DN 15 / 1/2 in | 16 – 20 mm | 1.0 mm | 1.5 mm |
| DN 25 / 1 in | 25 – 30 mm | 1.5 mm | 2.0 mm |
| DN 40 / 1-1/2 in | 40 – 44.5 mm | 1.5 mm | 2.0 mm |
| DN 50 / 2 in | 50 – 57 mm | 1.5 mm | 2.0 mm |
| DN 80 / 3 in | 80 – 88.9 mm | 2.0 mm | 2.5 mm |
| DN 100 / 4 in | 100 – 108 mm | 2.5 mm | 3.0 mm |
| DN 150 / 6 in | 150 – 159 mm | 2.5 mm | 3.0 mm |
| DN 200 / 8 in | 200 – 219 mm | 3.0 mm | 3.5 mm |
Tube for condensers is normally ordered by outside diameter and wall thickness rather than by nominal bore, because the heat transfer calculation depends on the actual wall and on the internal diameter after expansion into the tube sheet.
Mechanical Properties and Service Limits
Annealed tube: tensile strength approximately 275 MPa minimum, yield strength around 105 MPa, elongation about 30 %.
Hard drawn tube: tensile strength in the region of 420 MPa with lower elongation, used where mechanical stiffness is required.
Pressure: working pressure is governed by outside diameter, wall thickness and design temperature, and hydrostatic testing is performed to the stress level requested in the purchase order.
Flow velocity: clean seawater service is commonly designed at up to about 3 m/s, with lower limits where the water carries sand or entrained solids.
Temperature: the alloy is used continuously in seawater to roughly 300 °C, well beyond the range of most marine cooling circuits.
Joining: readily welded, brazed and expanded; tube to tube sheet joints are normally roller expanded and may be seal welded.
Typical Seawater Cooling Applications
Main and auxiliary seawater cooling circuits on commercial and naval vessels.
Condensers and heat exchanger tube bundles in coastal and offshore power generation.
Desalination plant evaporator and distiller tubes, where brine resistance is essential.
Ballast water lines, fire main and fire protection systems in marine service.
Offshore oil and gas process cooling, chemical and petrochemical seawater exchangers.
Finned tube and U-bend assemblies for air coolers and closed loop cooling skids.
FAQ
Q: What is the difference between ASTM B111 and ASTM B466 for C70600?
ASTM B111 covers seamless copper and copper alloy condenser tubes and ferrule stock, while ASTM B466 covers seamless copper-nickel pipe and tube in nominal sizes. The alloy is the same, but the dimensional and testing requirements differ with the end use.
Q: Why does 90/10 copper-nickel resist seawater?
The nickel content and the controlled iron addition form a thin, adherent oxide layer on the wetted surface. The film slows further attack, repairs itself after minor damage and keeps general corrosion rates very low even at flowing velocities.
Q: Can C70600 be used in polluted harbour water?
Performance falls where sulphides or ammonia are present, because these species disturb the protective film. In such service a higher nickel alloy or a different material is generally selected after water analysis.
Q: Does the alloy suffer stress corrosion cracking?
Copper-nickel 90/10 has good resistance to chloride stress corrosion cracking, and it is far less sensitive than the high zinc brasses. Residual stresses from manufacture should still be relieved on heavily cold formed parts.
Q: How are the tubes joined to a tube sheet?
Roller expansion is the standard method. Where leak tightness must be guaranteed, the joint is expanded and then seal welded, and the welded area is dye penetrant or radiographic tested.
Q: What tests are normally requested?
Common requirements include chemical analysis, tensile and hardness testing, flattening or flare testing for ductility, eddy current examination, hydrostatic test and grain size checks, with third party witness when specified.
