ASTM B111 C70600 covers seamless copper-nickel tube containing nominally 90% copper and 10% nickel, with iron and manganese additions that make the protective surface film durable in seawater. The tube is produced for surface condensers, evaporators, coolers and other heat exchangers where seawater, estuarine water or brine is the cooling medium, and it is supplied in the O61 annealed temper for rolling into tube sheets or the H55 light-drawn temper where higher strength is wanted. The same alloy is listed internationally as BFe10-1-1 in GB/T 8890, CN102 in BS 2871, C7060 in JIS H3300 and CuNi10Fe1Mn in DIN 1785.
Corrosion Behaviour in Seawater
The resistance of 90/10 copper-nickel depends on a thin, iron-containing oxide film that forms on the wetted surface once the tube is in service. Reported corrosion rates for the alloy illustrate how the film behaves:
| Static and low velocity conditions, below 1.5 m/s | about 0.02-0.03 mm/year in 3.5% sodium chloride solution |
| General seawater exposure | typically about 0.025 mm/year |
| Water velocity up to about 3 m/s | about 0.035 mm/year, with the film still intact |
Three conditions disturb this picture and must be considered at the design stage. Sulphide contamination in the cooling water breaks down the protective film and can raise local corrosion rates sharply, so sulphide-bearing water requires either a lower velocity limit or a higher alloy specification. Ammonia in the water attacks the alloy mainly in the vapour space and at high local velocities, so condenser air removal sections deserve separate review. Finally, stagnant or low flow conditions reduce the supply of oxygen needed to maintain the film, which is why drains and standby circuits are usually purged or vented rather than left full of seawater.
Chemical 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 |
Mechanical Properties
| 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 minimum values are those established for the tube form by ASTM B111, and they are reported on the material test certificate for each heat. Where a project specifies a light-drawn tube for its higher yield strength, the design should allow for the reduced expansion ductility of that temper when the joint is rolled.
Thermal and Physical Properties
Density: specific gravity 8.94, equivalent to about 8.9 g/cm³
Thermal conductivity: about 45 W/(m·K) at 20 °C, or about 26 Btu/(ft²·ft·h·°F) at 68 °F
Electrical conductivity: about 9% IACS at 68 °F
Melting range: 1100-1149 °C (2010-2100 °F)
Modulus of elasticity in tension: 18,000 ksi; modulus of rigidity: 6,800 ksi
Magnetic response: effectively non-magnetic
Conductivity figures quoted for copper-nickel vary between references because the properties depend on temper and on the temperature of measurement, so a design calculation should always state the temperature at which the value applies.
Tube Selection for Heat Exchanger Duty
Wall thickness should cover the expected general corrosion allowance plus the rolled joint, with additional allowance where the tube inlet faces abrasive water.
Velocity should be set high enough to keep the bore clean and low enough to stay inside the film stability window, and the inlet region should be reviewed separately from the bulk of the tube length.
Baffle spacing and support plate spacing control vibration; longer spans may justify the higher yield strength of the light-drawn temper.
Tube sheet material and water box coatings should be compatible with the tube to avoid galvanic acceleration at the joint.
Inspection and Testing
Every tube is eddy current tested over its full length to Practice E243, hydrostatically tested to the fibre stress established in ASTM B111, and sampled for expansion and flattening tests drawn from the lot. The material test certificate records the heat number, chemical analysis within the ranges above, the mechanical properties achieved against the temper minimums, and the non-destructive test results. For a retubing project the receiving inspection should compare the certificate with the specification for outside diameter, wall thickness and temper, and should record any handling damage to tube ends before installation begins.
Applications
Steam surface condensers in coastal and marine power plants
Desalination plant brine heaters, recovery sections and preheaters
Shipboard coolers, condensers and seawater service circuits
Offshore platform seawater cooling and process heat exchangers
Refinery and chemical plant heat exchangers using brackish or seawater cooling
FAQ
Q: What is ASTM B111 C70600 tube?
It is a seamless copper-nickel heat exchanger tube containing 9.0-11.0% nickel with iron and manganese additions, covered by ASTM B111 and its ASME counterpart SB111.
Q: How fast does C70600 corrode in seawater?
Typical reported rates are about 0.025 mm/year in seawater, with values around 0.02-0.03 mm/year at low velocity and about 0.035 mm/year at velocities up to 3 m/s while the protective film remains intact.
Q: What happens if the cooling water contains sulphide?
Sulphide disturbs the protective film and can raise localised corrosion significantly, so sulphide-bearing water calls for a reduced velocity limit or a higher alloy specification.
Q: What is the difference between the O61 and H55 tempers?
O61 is fully annealed with a minimum tensile strength of 40 ksi (275 MPa) and is used for expanded joints; H55 is light-drawn with 45 ksi (310 MPa) minimum tensile and 35 ksi (240 MPa) minimum yield strength for higher strength duty.
Q: Which equivalent grades exist in other standards?
GB/T 8890 lists BFe10-1-1, BS 2871 lists CN102, JIS H3300 lists C7060 and DIN 1785 lists CuNi10Fe1Mn for the same 90/10 composition.
Q: How is the tube tested before delivery?
Full length eddy current testing to Practice E243, hydrostatic testing to the standard, and expansion and flattening tests on lot samples, all documented on the material test certificate.
