What Is 90/10 Copper Nickel?
90/10 copper nickel is a copper-rich, nickel-alloyed material containing roughly 90% copper and 10% nickel, standardised as UNS C70600 and, in European wrought designation, as CuNi10Fe1Mn. Small controlled additions of iron and manganese give the alloy its characteristic resistance to fast-flowing seawater, which is why it has been the reference material for marine piping, condenser and heat exchanger tubing for decades.
The alloy sits between two extremes. It is far more corrosion resistant than pure copper or brass in seawater, yet it costs considerably less than 70/30 copper nickel or high-nickel copper alloys because it contains only about half the nickel. That balance of performance and cost is the core reason it is chosen for large cooling water systems, desalination plants and shipboard seawater circuits.
Chemical Composition and Applicable Standards
The composition window is narrow because iron and manganese control the stability of the protective surface film. Typical values for UNS C70600 are shown below.
| Element | Typical content | Function |
|---|---|---|
| Copper (Cu) | Balance, 86.5% minimum | Base metal; thermal and electrical conduction |
| Nickel (Ni) | 9.0-11.0% | Corrosion resistance, strength |
| Iron (Fe) | 1.0-1.8% | Improves impingement resistance in seawater |
| Manganese (Mn) | 1.0% maximum | Deoxidation, film stability |
| Zinc (Zn), lead (Pb) | 1.0% and 0.05% maximum | Controlled as residual impurities |
Common product specifications include ASTM B111 for condenser and heat exchanger tubes, ASTM B466 for seamless pipe and tube, ASTM B171 for plate and sheet, and ASTM B467 for welded pipe, together with the matching ASME SB-111 and SB-466 designations. Buyers should quote the specification, temper and test requirements together, because the same composition supplied in a different temper behaves differently in service.
Mechanical and Physical Properties
| Property | Annealed 90/10 copper nickel |
|---|---|
| Density | about 8.94 g/cm3 |
| Tensile strength | 275-345 MPa |
| 0.2% yield strength | 105-170 MPa |
| Elongation | 30% minimum in 50 mm |
| Hardness | about 60-80 HB |
| Thermal conductivity at 20 °C | about 45 W/mK |
| Thermal expansion, 20-300 °C | about 17 x 10-6 per °C |
| Modulus of elasticity | about 130-140 GPa |
Two points deserve emphasis. First, the thermal conductivity of about 45 W/mK is roughly ten times lower than that of pure copper but still around three times higher than austenitic stainless steel, which is precisely why the alloy is competitive in heat transfer duty. Second, its thermal expansion is higher than carbon steel, so pipe runs and tube-to-tubesheet joints must be designed to tolerate movement.
Seawater and Marine Corrosion Performance
Exposure to aerated seawater causes the alloy to form a thin, adherent oxide film of nickel and copper oxides that is self-repairing in flowing, oxygen-bearing water. Once formed, the film restricts further attack, and general corrosion rates in normal seawater service are typically of the order of 0.02-0.05 mm per year, far below the rates seen on carbon steel in the same environment.
Impingement and erosion resistance: the iron addition allows the alloy to withstand seawater velocities that would rapidly erode pure copper. Tubes are usually designed for a maximum water velocity of about 2.5-3 m/s to limit impingement attack.
Pitting and crevice corrosion: resistance is good in clean, flowing seawater up to about 60 °C; deposits and stagnant pockets should be avoided because they create oxygen-depleted zones.
Biofouling: marine organisms attach less readily than on steel or aluminium, which reduces cleaning frequency in cooling water circuits.
Fresh and brackish water: corrosion rates generally remain below 0.1 mm per year, covering water treatment plants, cooling towers and coastal freshwater piping.
Atmospheric and salt spray: the alloy resists tarnishing and pitting in coastal and mildly industrial atmospheres, which suits outdoor equipment and architectural components.
Two environments remain outside the alloy's capability: reducing acids such as hydrochloric or non-aerated sulphuric acid, and sulphide-bearing fluids, where hydrogen sulphide reacts with copper to form a non-protective film and accelerates attack. Ammoniacal and ammonium-containing environments should also be avoided, as copper alloys are sensitive to stress corrosion cracking in those conditions.
Fabrication, Cost and Design Considerations
The alloy is readily hot and cold formed, and in the annealed condition it can be bent, flared, expanded into tubesheets and machined without difficulty. Welding is normally done by gas tungsten arc or gas metal arc welding with matching copper-nickel filler metal; controlled heat input limits oxidation, and post-weld cleaning to remove oxide scale is required to preserve corrosion resistance. Brazing and soldering are also practical, though the joint should be protected from preferential attack in seawater.
Compared with carbon steel the material cost is higher, and compared with 70/30 copper nickel it is lower for the same wall thickness. In practice the alloy wins on total cost of ownership in marine cooling and desalination duty, where the alternative is frequent replacement. Limitations to plan around are its moderate strength, which rules out highly loaded structural or fastener applications, and its sensitivity to selective leaching in stagnant, low-oxygen systems, which is managed by avoiding dead legs and by keeping flow rates in the recommended range.
FAQ
Q: What is 90/10 copper nickel used for?
It is used mainly for seawater and cooling water systems: condenser and heat exchanger tubes, seawater intake and discharge lines, shipboard sanitary and ballast piping, desalination plant pipework, pump and valve components and offshore platform seawater circuits.
Q: How does it compare with 70/30 copper nickel?
The 70/30 grade has higher nickel content, giving greater strength, higher erosion resistance at high seawater velocity and better tolerance of polluted water at a higher material cost. The 90/10 grade is preferred where conditions are moderate and cost efficiency matters.
Q: Is 90/10 copper nickel resistant to all corrosion?
No. It performs very well in aerated seawater, fresh water and mild industrial atmospheres, but it is attacked by reducing acids and sulphide-bearing fluids, and it is sensitive to ammonia-related stress corrosion cracking. Service conditions must always be reviewed before selection.
Q: What standards cover the alloy?
UNS C70600 material is commonly supplied to ASTM B111 for tubes, ASTM B466 for seamless pipe and tube, ASTM B171 for plate and ASTM B467 for welded pipe, with equivalent ASME designations SB-111, SB-466, SB-171 and SB-467.
Q: Can 90/10 copper nickel be welded?
Yes, by gas tungsten arc or gas metal arc welding using matching copper-nickel filler metal, without preheating. Heat input should be controlled to limit oxidation, and the weld and adjacent area must be cleaned after welding to restore the protective film.
Q: What is the maximum service temperature?
In seawater, long-term immersion service is generally limited to about 60 °C to avoid film breakdown and deposit-related attack. In clean fresh water and steam condensate the alloy can be used at considerably higher temperatures, subject to a project-specific assessment.
