What C71500 Really Is
UNS C71500 is the 70/30 copper-nickel alloy: roughly 70% copper, 29% to 33% nickel, with iron between 0.40% and 1.00% and manganese limited to 1.0% maximum. It is a single-phase wrought alloy with no hardening transformation, so its strength comes from cold work and its ductility from annealing. The accepted designations are CuNi30Mn1Fe under ISO naming, CW354H to EN 12451, material number 2.0882 in the German system, C7150 in JIS H3300, and BFe30-1-1 in the Chinese GB system.
It is important not to confuse the 70/30 grade with the 90/10 grade. A tube described as C71500 but supplied with 9% to 11% nickel is actually C70600, and the two materials have different strength, velocity tolerance and price. Purchasers should specify the UNS number in the purchase order and confirm the nickel range on the mill certificate.
Chemical Composition and Equivalent Grades
| Element | Composition (%) |
|---|---|
| Cu | Remainder |
| Ni | 29.0-33.0 |
| Fe | 0.40-1.00 |
| Mn | 1.0 max |
| Zn | 1.0 max |
| Pb | 0.05 max |
| System | Designation |
|---|---|
| UNS | C71500 |
| ISO | CuNi30Mn1Fe |
| EN 12451 | CW354H |
| DIN | 2.0882 |
| JIS H3300 | C7150 |
| GB | BFe30-1-1 |
Mechanical Properties
| Property | Annealed tube | Light drawn tube |
|---|---|---|
| Tensile strength | approx. 380-440 MPa | above 500 MPa |
| Yield strength, 0.2% offset | approx. 140-180 MPa | approx. 350 MPa and above |
| Elongation in 50 mm | 30% min, typically 45% | reduced, per temper code |
| Hardness | roughly 60-80 HRB | higher, per temper code |
The specification states minimum values for each temper code and the certified results usually exceed them, which is why range values are quoted here for design guidance. Physical data used in thermal design are a density of 8.94 g/cm³, a melting range of about 1170 °C to 1240 °C, thermal conductivity of about 29 W/m.K and electrical conductivity of approximately 4.6% IACS.
Corrosion Performance in Seawater
The 70/30 alloy forms a durable, iron-rich surface film that limits general corrosion to a very low rate in flowing seawater and protects the tube against impingement attack, pitting and crevice corrosion. It is not susceptible to chloride stress corrosion cracking, unlike the austenitic stainless steels, and it retains useful corrosion resistance in mildly polluted water where sulphides are present.
Velocity tolerance is higher than that of 90/10 tube, with clean seawater design velocities generally accepted up to about 3.5 m/s, and short-term excursions above that are tolerable in a well-designed system. Thermal conductivity is lower than 90/10, which is why the grade is chosen where the shell side fluid temperature must be preserved, and where thicker walls are wanted for pressure or mechanical strength. Erosion by sand or debris remains the main threat, and filtration upstream of the exchanger is the normal countermeasure.
Applications
Shipboard and offshore condensers, seawater piping and cooling systems.
Power station steam condenser and feedwater heater tube bundles.
Desalination plant heat exchanger and brine heater tubes.
Offshore platform seawater systems and brine heat exchangers.
Chemical and petrochemical units handling chloride-bearing process water.
Hydraulic and lubricating oil coolers in marine machinery.
Fabrication, Installation and Inspection
Tubes are supplied annealed for roller expansion and U-bending, or light drawn where stiffness is needed. Roller expansion must be controlled so that the tube wall is not over-reduced, and the tube sheet hole is drilled with non-graphitic lubricant. U-bends follow the radius, ovality and wall thinning limits of ASTM B395/B395M. Welding uses TIG or MIG with matching copper-nickel filler, clean surfaces and argon shielding on both sides where possible.
Inspection covers chemical analysis, tensile and flattening tests, eddy-current testing of every tube, hydrostatic or pneumatic pressure testing, dimensional verification and bore cleanliness. After installation, a flush with clean water removes debris before seawater is admitted, and commissioning at reduced flow helps the protective film form evenly across the whole bundle.
FAQ
Q: How can I confirm that a delivered tube is really C71500?
Check the nickel range on the mill certificate: 29.0% to 33.0% indicates 70/30 material. A certificate showing 9.0% to 11.0% nickel describes C70600, the 90/10 grade, whatever the order description says.
Q: Which applications need 70/30 rather than 90/10 copper-nickel?
Higher seawater velocities, sand-bearing or slightly polluted water, higher design pressures and applications where the process fluid temperature must be maintained are the usual reasons for selecting the 70/30 grade.
Q: Can C71500 tubes be welded to a steel tube sheet?
Yes, with a qualified procedure using a nickel-based or matching copper-nickel filler. Galvanic effects in the seawater circuit are managed by insulation, coating and cathodic protection as required by the system design.
Q: Is C71500 suitable for acidic or alkaline process fluids?
The alloy performs well in neutral and alkaline solutions and in many non-oxidising acids. Strongly oxidising acids such as nitric acid are not recommended, and each process duty should be assessed on its own chemistry.
Q: What temper is used for U-bent tube?
U-bend tube is formed from annealed O61 material, so that the bent section retains the required ductility and the bend is made without cracking; ASTM B395/B395M governs the bend dimensions and inspection.
Q: How should the tubes be stored before installation?
Keep them in the original cases or on timber dunnage indoors, with end caps fitted, away from steel racks and from chloride contamination, and free of standing water in the bore.
