Definition of C70600 Copper Nickel 90/10 Pipe
C70600 is the UNS designation for the copper-nickel alloy containing nominally 90% copper and 10% nickel, commonly called 90/10 cupronickel. Because of the 10% nickel addition the alloy forms a stable, self-repairing protective film in seawater and therefore resists general corrosion, pitting, crevice corrosion and galvanic attack far better than unalloyed copper or brass. ASTM B111/B111M covers the seamless condenser and heat exchanger tube form, while ASTM B466/B466M covers seamless copper-nickel pipe and tube.
The material is one of the standard choices for seawater piping, condenser and cooler tubing, desalination plant equipment and offshore systems. It combines moderate strength with excellent ductility, so it can be bent, flared, expanded and welded without difficulty.
Chemical Composition
| Element | Requirement, % |
|---|---|
| Nickel (Ni), including cobalt | 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 |
The iron range is intentional and important: iron incorporated into the surface film is what makes the alloy resistant to impingement and erosion-corrosion in flowing seawater. Manganese supports the same film, and the nickel content sets the level of general corrosion resistance.
Tensile Requirements and Physical Data
| Property | Value |
|---|---|
| Tensile strength, temper O61 annealed | 275 MPa (40 ksi) min |
| Yield strength, temper O61 annealed | 105 MPa (15 ksi) min |
| Tensile strength, temper H55 light drawn | 310 MPa (45 ksi) min |
| Yield strength, temper H55 light drawn | 240 MPa (35 ksi) min |
| Density | 8.94 g/cm³ |
Annealed tube is specified where the tube has to be bent or rolled into a tube sheet; light-drawn tube is used where a stiffer wall is needed to resist vibration or where the tube-to-tube sheet joint has to carry higher load. Thermal conductivity of the 90/10 alloy is markedly lower than that of pure copper, a trade-off accepted for the large gain in seawater durability.
Why 90/10 Cupronickel Performs in Seawater
Film formation: in aerated seawater the alloy develops a thin, adherent oxide film containing nickel and iron, which limits the access of oxygen to the metal surface.
Erosion resistance: the film reforms quickly after mechanical damage, so the alloy tolerates considerably higher water velocities than brass or aluminium bronze in the same circuit.
Biofouling control: copper ions released at very low concentrations discourage the settlement of marine organisms, which helps to keep heat transfer surfaces clean and reduces the need for chemical dosing.
Galvanic tolerance: the alloy sits close to copper in the galvanic series and is compatible with copper-based and most stainless tube-sheet materials.
Weldability: gas tungsten arc, gas metal arc and laser welding can all be used with matching copper-nickel filler, which allows pipe systems and fabricated headers to be built without difficulty.
Applications
Seawater cooling and ballast piping on ships and offshore units, including firewater and deluge lines.
Condensers, coolers and heat exchangers in coastal power stations, refineries and chemical plants.
Desalination plants, brine heaters and evaporator tubing.
Water treatment, process cooling and heat recovery equipment in industrial plants.
Power station condensers, nuclear auxiliary cooling circuits and oil and gas topside equipment.
Specifications and Ordering
The applicable standards are ASTM B111/B111M for seamless condenser and heat exchanger tube, ASTM B466/B466M for seamless copper-nickel pipe and tube, EN 12451 for European heat exchanger tube orders, EEMUA 144 for offshore and marine copper-nickel tube recommendations, and MIL-T-16420K for military tube requirements. Both specifications allow a broad range of outside diameters and wall thicknesses, with pipe sizes up to about 6 in nominal bore and ends supplied plain, beveled or threaded; U-bends, coiled lengths and pancake coils can be produced to drawing.
An order should state the grade, temper, outside diameter, wall thickness and tolerance, length or bend data, end finish, the testing required and the applicable revision of the standard. Where seawater velocity is high, the engineering drawings should confirm that the selected wall allows for the expected erosion allowance over the design life.
Inspection and Quality Control
Heat analysis must fall inside the C70600 ranges, and the finished product is checked for outside diameter, wall thickness, eccentricity, length and straightness. Eddy-current examination to ASTM E243 is the routine method for detecting longitudinal and transverse defects in copper-nickel tube, and the expansion and flattening tests of ASTM B153 verify ductility of the finished tube. A hydrostatic or pneumatic pressure test is carried out at the pressure agreed in the order, and each consignment is normally documented with a mill certificate recording chemistry, tensile results, non-destructive test results and conformity to the specification.
FAQ
Q: What is C70600 copper nickel pipe?
A seamless copper-nickel alloy pipe and tube containing about 90% copper and 10% nickel, selected for seawater and other corrosive duties.
Q: Why does the specification require iron and manganese?
Iron in the range 1.0 - 1.8% and manganese up to 1.0% stabilise the protective film that gives the alloy its seawater and erosion-corrosion resistance.
Q: What is the strength of 90/10 cupronickel tube?
In the annealed O61 temper the minimum tensile strength is 275 MPa with minimum yield strength of 105 MPa; the light-drawn H55 temper raises these minima to 310 MPa and 240 MPa.
Q: Which standards apply?
ASTM B111/B111M for seamless condenser and heat exchanger tube and ASTM B466/B466M for seamless copper-nickel pipe and tube, with EN 12451, EEMUA 144 and MIL-T-16420K used for specific markets.
Q: Is C70600 suitable for welded seawater piping systems?
Yes. The alloy welds readily by gas tungsten arc or gas metal arc processes with matching copper-nickel filler, and welded fabrication is common for seawater piping.
Q: How does 90/10 compare with 70/30 copper nickel?
C70600 is the general-purpose seawater grade and is more economical; C71500 contains about 30% nickel and is chosen for higher velocity, polluted water and more severe service.
Q: What tests are carried out before despatch?
Chemical analysis, tensile testing, eddy-current examination to ASTM E243, expansion and flattening tests to ASTM B153, plus a pressure test when specified.
