What Copper Nickel 90/10 Tubing Is
Copper nickel 90/10, designated UNS C70600 under ASTM B111/B111M and known internationally as CuNi10Fe1Mn, is a wrought copper alloy containing about 90 % copper and 10 % nickel with deliberate additions of iron and manganese. It is used as seamless heat exchanger tubing, condenser tubing and seawater piping because a thin, tenacious copper oxide film forms on the surface and stays in place under flowing water, protecting the wall from general corrosion and from impingement attack.
The iron addition is not incidental. Iron is what makes the protective film durable in fast flowing seawater, so the specification sets a minimum as well as a maximum for it. Tubes that meet the nickel and iron ranges of ASTM B111/B111M behave very differently from low-cost material in which the iron has been allowed to fall away.
Chemical Composition of UNS C70600
| Element | Requirement |
|---|---|
| Nickel (Ni) | 9.0 to 11.0 % |
| Iron (Fe) | 1.0 to 1.8 % |
| Manganese (Mn) | 1.0 % maximum |
| Zinc (Zn) | 1.0 % maximum |
| Lead (Pb) | 0.05 % maximum |
| Copper (Cu) | Remainder, nominal 88.6 % |
All other elements are restricted as individual and total residuals. The narrow iron window is the single most important composition check for seawater service, because it controls resistance to erosion-corrosion at the tube inlet.
Mechanical and Physical Properties
| Property | Value |
|---|---|
| Tensile strength, annealed O61 | 275 MPa (40 ksi) minimum |
| Yield strength at 0.5 % extension, annealed O61 | 105 MPa (15 ksi) minimum |
| Elongation, annealed | 30 % minimum |
| Density | 8.94 g/cm³ |
| Melting range | About 1100 to 1145 C |
| Thermal conductivity | About 45 W/(m·K) |
| Electrical conductivity | About 9 % IACS |
| Modulus of elasticity | About 152 GPa |
Light drawn and hard drawn tempers are produced for applications that do not require bending, and they deliver higher tensile and yield values than the annealed condition. Tubes ordered for roller expansion or U-bending are supplied annealed to a nominal grain size such as OS025 so that the wall deforms plastically without cracking in the tubesheet.
Standard Sizes and Delivery Forms
| Outside diameter | Typical wall | Common use |
|---|---|---|
| 9.53 mm (3/8 in) | 0.9 to 1.24 mm | Small condensers, oil coolers |
| 12.70 mm (1/2 in) | 0.9 to 1.65 mm | General heat exchangers |
| 15.88 mm (5/8 in) | 1.24 to 1.65 mm | Power plant condensers |
| 19.05 mm (3/4 in) | 1.24 to 2.11 mm | Desalination and marine exchangers |
| 25.40 mm (1 in) | 1.65 to 2.77 mm | Seawater piping and large coolers |
Tube is delivered straight in lengths up to 12 m, coiled for small diameters, or U-bent. Annealed tube is capped and packed in wooden cases or bundles with end protection so that the bore stays clean and the surface film is not damaged by handling. Eddy current examination to ASTM E243 and hydrostatic proof testing are the usual non-destructive checks.
Applications in Marine and Process Service
Surface condensers and auxiliary coolers on ships and offshore platforms.
Multi-stage flash and multi-effect distillation plants for seawater desalination.
Seawater piping, firewater lines and hydraulic heat exchangers.
Power station condensers, oil coolers and high-pressure feedwater heaters.
Air coolers and process exchangers in coastal chemical plants.
Heat exchangers handling brackish water with suspended sand.
Because thermal conductivity is lower than that of plain copper, 90/10 tubes are often specified with a thinner wall or additional tubes to achieve the same duty. The trade-off is a large gain in corrosion allowance, which normally governs the life of seawater-cooled equipment.
Fabrication and Installation Guidance
The alloy is readily expanded into tubesheets, bent, flared and swaged. Soldering and brazing are both rated good to excellent, gas shielded arc welding is excellent and coated metal arc welding is good, while oxyacetylene welding gives only fair results because of the heat input involved. Welding copper nickel requires clean, dry surfaces and a matching copper nickel filler; carbon contamination from marking pens or steel tooling is the most common cause of weld cracking.
During installation the tubes should not be allowed to rub against carbon steel supports, and residual welding spatter or mill scale should be removed from the water side, because deposits create the crevices where localised attack begins. Design velocity is usually capped near 3 m/s for clean seawater, with a lower figure where the water carries sand. Inlet ends of condensers commonly receive a thicker wall or a protective ferrule to resist impingement attack.
FAQ
Q: Why is iron specified in a copper nickel alloy?
Iron is the element that makes the protective surface film durable in flowing seawater. ASTM B111/B111M requires 1.0 to 1.8 % iron, and material below the minimum corrodes faster at the tube inlet.
Q: What is the maximum seawater velocity for 90/10 tube?
Clean seawater designs normally keep velocity near 3 m/s. Where the water carries sand or the tube inlet is close to a pump, velocity is reduced and thicker inlet walls are used.
Q: Can 90/10 tubes be welded instead of expanded?
Yes. Gas shielded arc welding with matching copper nickel filler gives excellent results, and welded joints are common in seawater piping. Welded tube-to-tubesheet joints are used on high pressure exchangers, though roller expansion remains more common.
Q: Which temper should be ordered?
Order soft annealed tube to a nominal grain size, such as OS025, when the tube will be U-bent or roller expanded. Choose a drawn temper only when the tube stays straight and higher strength is required.
Q: How does 90/10 compare with 70/30 cupro nickel?
70/30 contains more nickel and tolerates higher velocity and more polluted water, but it costs more. 90/10 is the economical grade for clean seawater and brackish water at moderate flow.
Q: Is 90/10 tube suitable for fresh water systems?
It is, but plain copper or admiralty brass is usually more economical there. Cupro nickel is specified where chloride content, flow velocity or contamination rules out the simpler alloys.
