What SB111 UNS C70600 Seamless Pipe Is
ASME SB111 UNS C70600 is the CuNi 90/10 grade of the seamless copper-nickel tube specification. The alloy contains nominally 10% nickel with deliberate additions of iron and manganese, and it is the workhorse material for seawater piping, condensers and desalination plant where chloride stress corrosion cracking rules out stainless steel. ASME SB111 and ASTM B111/B111M are technically identical documents; the same composition is also supplied as seamless pipe and tube under ASTM B466/B466M.
C70600 combines high resistance to flowing seawater with good fatigue strength, low susceptibility to pitting and a thermal conductivity high enough to make it efficient in heat transfer service. It is equally at home as a machined, forged or tubular component: valve bodies, pump parts, hull sheathing, fire water mains and heat exchanger tubes are all routine applications.
Chemical Composition Limits
| Element | Range or limit |
|---|---|
| Ni (nickel) | 9.0-11.0% |
| Fe (iron) | 1.0-1.8% |
| Mn (manganese) | 1.0% max |
| Zn (zinc) | 1.0% max |
| Pb (lead) | 0.05% max |
| Cu (copper) | Remainder |
A typical commercial heat contains about 10% nickel, 1.3% iron and 88.7% copper. The iron addition is what separates a seawater copper-nickel from a plain copper-nickel: it builds a durable protective film that resists impingement attack, and manganese is added to stabilise it and to improve hot working behaviour.
Mechanical and Physical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.94 g/cm3 | 0.323 lb/in3 |
| Tensile strength, ultimate | 303-414 MPa | 43900-60000 psi |
| Tensile strength, yield (temper dependent) | 110-393 MPa | 16000-57000 psi |
| Elongation at break, 254 mm gauge | 42% | 42% |
| Elastic modulus | 140 GPa | 20300 ksi |
| Shear modulus | 52.0 GPa | 7540 ksi |
| Poisson ratio | 0.34 | 0.34 |
| Machinability, free-cutting brass = 100% | 20% | 20% |
The wide tensile range reflects temper: soft annealed tube sits near the lower end, while drawn or light-drawn product reaches the upper values. Allowable stresses for pressure design are taken from the relevant ASME code rather than from these tensile figures.
Surface Finish: What the Galvanized Description Means
Copper-nickel tube is not hot-dip galvanized, because zinc coatings are applied to steel and do not form a sound metallurgical coating on a copper-based alloy. Where a supplier catalogue describes C70600 copper-nickel pipe as galvanized, the wording normally refers to a protective finish applied to the outside diameter for transit or for a specific installation: bright drawn finish, light oil or lacquer coating, or tin plating. Buyers should confirm the required finish in writing and state whether the tube is to be supplied bare, bright annealed, or coated, since this determines both the appearance and the storage requirements of the delivered pipe.
Corrosion, Heat Resistance and Heat Treatment
Copper-nickel alloys have very good resistance to seawater, brine, organic compounds, salts and diluted non-oxidising acids. CuNi 90/10 with iron and manganese offers excellent resistance to sea water and brackish water, and it is less prone to impingement attack than pure copper or admiralty brass. CuNi 70/30 offers the best aqueous corrosion resistance of the commercial copper alloys, together with higher strength for high-pressure circuits, so the two grades are often used side by side in one plant.
Hot strength increases with only a small nickel addition, and the iron addition improves mechanical properties at both room and elevated temperature. CuNi10Fe1Mn such as C70600 is used in pressure vessel construction up to about 300 °C, and CuNi30Mn1Fe up to about 350 °C, above which strength drops markedly, particularly creep strength and the creep strain limit.
Heat treatment of copper-nickel is normally limited to soft annealing and stress relief. Recrystallisation annealing temperatures vary widely between about 620 °C and 900 °C depending on the degree of cold work, the nickel content and the additional constituents: high temperatures go with short continuous annealing cycles, low temperatures with long static cycles. Stress relief annealing is carried out between about 280 °C and 500 °C. Annealing should be done in a protective or slightly reducing atmosphere, or in vacuum, to avoid the oxide scale that would otherwise require pickling.
Applications of C70600 Pipe and Tube
Heat exchangers, condensers and distillation columns
Sea water pipework, hydraulic lines and offshore fire water systems
Desalination units and power plant cooling circuits
Fish cages and other aquaculture structures
Pumps, valves, sheathing and fittings for ship hulls
Machined and forged valve and pump components used in seawater service
Feedwater heater and condenser tubing in power stations and ships
These duties share one requirement: long service life in chloride-bearing water without the chloride stress corrosion cracking and pitting that would affect stainless steel under the same conditions.
Frequently Asked Questions
Q: What does UNS C70600 mean?
C70600 is the UNS number for the 90/10 copper-nickel alloy containing 9.0-11.0% nickel, 1.0-1.8% iron and up to 1.0% manganese, with copper as the remainder. It is the same material as CuNi 90/10 and CuNi10Fe1Mn.
Q: Is C70600 pipe seamless or welded?
SB111 and B111/B111M tube is seamless by definition, produced by piercing, drawing and annealing. Welded copper-nickel tube is available for some duties, but seamless product is normally specified for high-pressure and critical seawater service.
Q: Why is iron added to 90/10 copper-nickel?
Iron in the 1.0-1.8% range forms a protective oxide film on the inner surface of the tube that resists impingement attack from fast-flowing seawater and extends service life considerably compared with iron-free copper-nickel.
Q: Can C70600 be used at elevated temperature?
Yes, within limits. CuNi10Fe1Mn is used in pressure equipment up to about 300 °C, and the higher-alloyed CuNi30Mn1Fe up to about 350 °C. Above those temperatures creep strength and creep strain limits fall away rapidly.
Q: How is copper-nickel tube annealed?
Recrystallisation annealing is carried out between roughly 620 °C and 900 °C depending on cold work and composition, and stress relief between 280 °C and 500 °C. A protective or slightly reducing atmosphere avoids oxide scale and the pickling that would follow.
Q: Which industries use C70600 pipe?
Shipbuilding, offshore oil and gas, power generation, desalination, chemical processing, aquaculture and HVAC cooling water systems all rely on it for chloride-bearing water and moderate-temperature heat transfer duties.
