Grade Background
ASTM B111/B111M is the standard specification for seamless copper and copper-alloy condenser tubes, evaporator tubes and ferrule stock. UNS C71500 is the 70/30 copper-nickel grade within that specification, also written CuNi 70/30, CuNi30Mn1Fe, BFe30-1-1, CW354H or 2.0882. It contains about 30% nickel with small but critical iron and manganese additions; the iron develops the protective surface film in seawater, and the manganese stabilises the microstructure after hot working.
Compared with the 90/10 grade, C71500 offers higher strength, better performance at higher seawater velocity and a lower thermal conductivity, which is an advantage when the shell side fluid temperature must be preserved. It is the grade selected for condensers and exchanger shells in demanding marine, power and desalination duty.
Chemical Composition
| Element | Composition (%) | Function |
|---|---|---|
| Cu | Remainder | Base metal |
| Ni | 29.0-33.0 | Strength and seawater corrosion resistance |
| Fe | 0.40-1.00 | Protective film formation |
| Mn | 1.0 max | Deoxidation, structural stability |
| Zn | 1.0 max | Residual control |
| Pb | 0.05 max | Impurity limit |
Because the nickel range is narrow and the iron range is low, the analysis of each heat is verified against the specification before the tube is released. Residual zinc and lead are controlled for the same reason: both disturb the protective film and both impair weld quality.
Mechanical and Physical Properties
| Form and temper | Tensile strength | Yield strength | Elongation |
|---|---|---|---|
| Tube, annealed (O61 / OS025) | approx. 415 MPa typical | approx. 170 MPa typical | 45% typical |
| Tube, light drawn | higher, per temper code | higher, per temper code | lower, per temper code |
| Flat product, annealed (M20) | approx. 380 MPa typical | approx. 140 MPa typical | 45% typical |
The specification fixes minimum values for each temper code, so the purchase order states the temper and the certificate reports the measured results. Physical design data are a density of 8.94 g/cm³, a melting range of about 1170 °C to 1240 °C, thermal conductivity of roughly 29 W/m.K to 37 W/m.K, electrical conductivity of about 4.6% IACS, and a modulus of elasticity of approximately 150 GPa to 155 GPa.
Service Behaviour in Seawater
The 70/30 alloy tolerates higher flow velocities than 90/10, and published design guidance for clean seawater commonly allows up to about 3.5 m/s to 4 m/s. It resists impingement attack, chloride pitting, crevice corrosion and stress corrosion cracking, and it is less sensitive than the 90/10 grade to temporary sulphide contamination in polluted harbours or estuaries. Biofouling resistance is lower than that of 90/10 because less copper is released at the surface, so filtration and cleaning schedules matter more in warm seawater.
As with all copper-nickel grades, the protective film is established during the first weeks of service. Commissioning at reduced flow, with clean filtered water, helps the film to form evenly. Repeated drying and rewetting, or long stagnant periods, disturb the film and should be avoided.
Applications and Product Forms
Condenser and heat exchanger tubes in power stations and marine propulsion plants.
Exchanger shells, waterboxes and heavy-wall pipe for seawater systems.
Desalination plant brine heaters and evaporator tube bundles.
Offshore platform cooling systems and firefighting water systems.
Hydraulic and lube oil cooler tube bundles on board ship.
Chemical process exchangers handling chlorides and alkaline solutions.
Fabrication, Welding and Inspection Points
C71500 is readily cold formed and welded. Annealed tube is roller expanded into the tube sheet with a controlled expansion torque, and U-bends are produced to the radius and ovality limits of ASTM B395/B395M. Welding is carried out by TIG or MIG with matching copper-nickel filler metal; the joint is shielded and purged to prevent oxidation, the interpass temperature is kept low, and carbon, sulphur and lead contamination from marking inks, grease and graphite lubricants must be excluded because these elements cause hot cracking.
When C71500 tube is joined to steel components, the joint is designed and the procedure qualified for the dissimilar combination, and electrical insulation or coating is used at connections to limit galvanic effects in the seawater circuit. Tube sheets, waterboxes and any steel parts in contact with copper-nickel are cathodically protected in accordance with the system design.
Acceptance testing normally covers chemical analysis of the heat, tensile tests, flattening or expansion tests, eddy-current testing of all tubes, hydrostatic or pneumatic pressure tests, dimensional checks and a visual examination of the bore and outside diameter. Tubes are shipped with end caps in wooden cases and labelled with heat number, size and temper.
FAQ
Q: What is the difference between C71500 and C70600?
C71500 contains about 30% nickel and C70600 contains about 10%. The 70/30 grade is stronger, tolerates higher seawater velocity and resists polluted water better, while the 90/10 grade offers higher thermal conductivity and lower cost.
Q: Is C71500 tube weldable in the workshop?
Yes. Welding is performed by TIG or MIG with matching copper-nickel filler under argon shielding. Contamination by carbon, sulphur or lead must be avoided, so greases, graphite lubricants and ordinary marking inks are kept away from joint areas.
Q: Can C71500 be bent and formed?
Yes. The alloy has good ductility, and the annealed temper is used for severe forming such as U-bending. Cold forming is done with tooling that keeps surface damage to a minimum because deep scratches concentrate stress.
Q: Which typical applications use C71500 tube?
Marine and offshore condensers, exchanger shells, seawater piping, hydraulic lines, firefighting systems and desalination brine heaters are the traditional applications, together with power plant steam condensers.
Q: Why is the thermal conductivity lower than that of 90/10 copper-nickel?
Nickel additions reduce thermal conductivity. In exchangers where the process fluid temperature must be maintained, or where a thicker wall is needed for pressure, the lower conductivity of 70/30 is a benefit rather than a drawback.
Q: What documentation should come with the tubes?
A mill certificate showing heat number, chemical analysis, tensile results, eddy-current and pressure test records, dimensional records and the packing list matched to the bundle labels.
