ASTM B111 C71500 is the 70/30 copper-nickel seamless tube grade: roughly 70% copper and 30% nickel, with iron and manganese additions that raise strength and stabilize the protective surface film. In marine condensers and heat exchangers the alloy is chosen because it tolerates high seawater velocity, resists pitting and stress corrosion cracking, and keeps a stable heat transfer coefficient over a long service life.
What C71500 Copper-Nickel Tube Is
C71500 tube, commonly called 70/30 tube, is produced seamlessly by piercing and drawing, so the tube wall is homogeneous and free of a longitudinal weld seam. The material is non-ferrous, lightweight relative to steel, and retains useful strength at low temperature, which makes it suitable not only for heat exchange equipment such as condensers but also for cryogenic piping in oxygen production plants. Small-diameter 70/30 tube is used for pressurized liquid lines such as lubrication and hydraulic circuits and for instrument impulse lines.
Chemical Composition of UNS C71500
| Element | Content (%) |
|---|---|
| Nickel, Ni | 29.0–33.0 |
| Iron, Fe | 0.40–1.0 |
| Manganese, Mn | 1.0 max |
| Zinc, Zn | 1.0 max |
| Lead, Pb | 0.05 max |
| Copper, Cu | Remainder |
The nickel content is the main corrosion variable; iron and manganese together control the formation of the protective oxide layer that limits attack in flowing seawater.
Mechanical Properties of UNS C71500 Tubes
| Temper | Tensile strength | Yield strength | Elongation | Hardness, Rockwell 30T |
|---|---|---|---|---|
| OS025 (annealed) | 414 MPa (60 ksi) | 172 MPa (25 ksi) | 45% | 45 |
| OS035 (annealed) | 372 MPa (54 ksi) | – | 45% | 36 |
Both tempers are supplied in the annealed condition, which is what allows the tube to be bent and roller expanded during bundle assembly without cracking.
Why 70/30 Tube Is Preferred for Marine Service
High resistance to seawater corrosion, including moving and aerated water
Effective resistance to stress corrosion cracking and ammonia attack in condenser environments
Natural resistance to biofouling, which helps keep the tube bore clean
Excellent thermal conductivity for compact heat exchanger designs
Good weldability and fabrication behavior for piping and header work
Long service life with low maintenance in salt-laden atmospheres
Compared with 90/10 copper-nickel, the 70/30 alloy offers higher strength and better tolerance of high water velocity and suspended solids, which is why it is specified for the more demanding condenser duties.
Applications of C71500 Tube
Marine condensers and heat exchangers on ships and offshore units
Tube bundles for power station condensers and turbine exhaust condensers
Desalination units and multi-stage flash evaporator tube banks
Seawater pipework and offshore fire water systems
Hydraulic lines and instrumentation pressure tubing
Fish cages and aquaculture hardware exposed to continuous seawater
Pumps, valves, sheathing and hull fittings
Cryogenic piping in air separation and oxygen production plants
Fabrication and Supply
Tubes are delivered in straight lengths or in coils, in the annealed tempers listed above, with clean ends suitable for expansion or welding. Dimensional inspection covers outside diameter, wall thickness, ovality and length, and the tube body is inspected before packing for sea transport so that the annealed surface arrives ready for bundle assembly.
Frequently Asked Questions
Q: What is the difference between C70600 and C71500 tube?
C70600 is the 90/10 copper-nickel grade with 9.0–11.0% nickel; C71500 is the 70/30 grade with 29.0–33.0% nickel, giving higher strength and better performance at high seawater velocity and in solids-bearing water.
Q: Which temper should be ordered for condenser bundles?
The annealed OS025 temper is the usual choice for roller expansion into tubesheets because it combines the higher 414 MPa tensile strength with 45% elongation; OS035 is used where lower strength is acceptable.
Q: Is C71500 tube welded or seamless?
For marine condensers and heat exchangers the tube is supplied seamless, produced by piercing and drawing so that no longitudinal weld seam is present in the wall.
Q: Why is iron added to C71500?
Iron in the 0.40–1.0% range, together with manganese, promotes a dense protective film on the inner tube surface, which is what limits corrosion under flowing seawater.
Q: Can 70/30 tube handle high seawater velocity?
Yes. The alloy is specified where water velocity and turbulence are high; it resists impingement and erosion far better than the lower-nickel grades and is therefore standard for high-duty marine condensers.
Q: Where else is C71500 tube used besides condensers?
It is used in desalination units, seawater pipework, offshore fire water systems, hydraulic lines, cryogenic piping and ship hull fittings such as pumps and sheathing.
