C70600 Copper Nickel Tube Specifications and Properties

C70600 contains 88% minimum copper, 9-11% nickel, 1.0-1.8% iron, and 1.0% maximum manganese. The nickel provides corrosion resistance. The iron helps form the protective oxide film in seawater.

C70600 tube in annealed temper has a minimum tensile strength of 310 MPa, yield strength of 110 MPa, and elongation of 30%. These numbers tell you how strong and how ductile the tube is.

Which temper to choose：

Annealed (O60) – Most common. Easy to bend, flare, and roll into tube sheets.

Light drawn (H55) – Moderate strength. Used when tube needs some stiffness.

Hard drawn (H80) – Rarely used. Difficult to form. Only for straight runs with no bending.

For 95% of heat exchanger and condenser applications, order annealed (O60) C70600 tube. Do not order hard drawn unless you have a specific reason.

C70600 tube is covered by several ASTM standards depending on the application. ASTM B111 is the most common for heat exchangers and condensers.

ASTM B111 C70600 tube is available from 6.35mm to 76.2mm OD with wall thicknesses from BWG 22 (0.71mm) to BWG 10 (3.40mm). Tolerances are tight because tubes must fit into tube sheets.

Common dimensions：

Tolerances (for 1" OD and smaller)：

OD tolerance： ±0.004 inch (±0.10mm)

Wall tolerance： ±10% of nominal

Length tolerance： +6mm / -0mm for cut lengths under 6m

C70600 has a uniform corrosion rate of 0.025 mm/year or less in clean flowing seawater. This means a 1.24mm wall BWG 18 tube has a theoretical life of 40-50 years from uniform corrosion alone.

Corrosion rates by condition：

Corrosion types to know：

Uniform corrosion – Slow, predictable. Not a concern for normal life.

Impingement corrosion – Fast, localized at inlets. Caused by high velocity.

Pitting corrosion – Occurs in stagnant or sulfide polluted water.

Galvanic corrosion – Rare. C70600 is noble but can corrode if coupled with less noble metals.

C70600 tube is easy to bend, flare, and weld in the annealed temper. Hard drawn temper is difficult to form. Here are key fabrication limits.

Bending：

Minimum bend radius for annealed tube： 2-3 x OD

Use mandrel bends for tight radii

Hard drawn tube： minimum radius 5-6 x OD, or anneal first

Flaring：

30° flare is standard for annealed tube

Can flare to 45° with good technique

Hard drawn tube： flare before annealing, or not at all

Welding：

TIG and MIG both work

Filler metal： ERCuNi

No preheat needed for thin wall

Backing gas recommended for root pass

Threading：

Not recommended for thin wall B111 tube

Use B466 Schedule 40 pipe if threads are required

Order annealed C70600 tube if you need to bend, flare, or roll it into tube sheets. Order hard drawn only for straight, non‑formed applications.

Q1： What is the difference between C70600 and C71500 in terms of properties?

C71500 has higher strength and better erosion resistance but lower thermal conductivity. C71500 tensile strength is 450 MPa vs 310 MPa for C70600. Hardness is 75-90 HRB vs 40-80 HRB. Thermal conductivity is 40 W/m·K vs 45 W/m·K. C71500 contains 70% copper and 30% nickel. C70600 contains 90% copper and 10% nickel. Choose C70600 for normal service. Choose C71500 for high velocity or high temperature.

Q2： What is the maximum working temperature for C70600 tube in seawater?

60°C (140°F) is the recommended maximum for continuous seawater service. Above this temperature, corrosion rate increases sharply. At 80°C, corrosion rate may be 10-20 times higher than at 30°C. For seawater above 60°C, consider C71500 or titanium. For non‑seawater applications, C70600 can go higher but strength decreases.

Q3： Is C70600 magnetic?

No, C70600 is not magnetic. Copper nickel alloys with nickel content below 30% are non‑magnetic. C70600 has only 9-11% nickel, well below the threshold for magnetic behavior. This is important for applications near sensitive electronics or magnetic separation equipment.

Q4： What is the electrical conductivity of C70600 compared to pure copper?

C70600 has about 5-6% of the electrical conductivity of pure copper. Pure copper (C11000) has 101% IACS (International Annealed Copper Standard). C70600 has about 5-6% IACS. This is why C70600 is never used for electrical applications. It is a mechanical and corrosion alloy, not an electrical one.

Q5： Can C70600 be heat treated for higher strength?

No, C70600 is not heat treatable. Strength comes only from cold work. Unlike steel, copper nickel alloys do not respond to heat treatment. You cannot quench and temper C70600. The only way to increase strength is cold drawing (work hardening). Annealing softens the tube back to the O60 temper.

Q6： What is the fatigue strength of C70600?

Fatigue strength of C70600 is approximately 100-120 MPa for 10⁸ cycles. This is for annealed material. Light drawing increases fatigue strength slightly. For applications with vibration or cyclic pressure, design stresses should stay below fatigue limit. Full fatigue data is available from the Copper Development Association.

Q7： Does C70600 require stress corrosion cracking testing?

No, C70600 is not susceptible to stress corrosion cracking in normal seawater. However, in ammonia or sulfur environments, caution is needed. For most marine and power plant applications, stress corrosion is not a concern. This is one advantage over stainless steels, which can crack in chloride environments.

Q8： What is the creep resistance of C70600 at elevated temperature?

C70600 has moderate creep resistance up to 300°C. Above 300°C, creep becomes significant under sustained load. For most heat exchanger applications (below 200°C), creep is not a design factor. For high temperature process heat exchangers, consult detailed creep data or switch to a different alloy.

Q9： Can C70600 be used for cryogenic (low temperature) service?

Yes, C70600 maintains excellent ductility down to cryogenic temperatures (-200°C). Unlike carbon steel, which becomes brittle at low temperatures, copper alloys retain toughness. C70600 has been used in liquefied natural gas (LNG) and liquid nitrogen applications. No ductile to brittle transition occurs.

Q10： What is the surface finish of ASTM B111 C70600 tube?

Standard surface finish is annealed and pickled, with an oxide‑free exterior and interior. Internal surface must be clean for heat exchangers. No oil, no scale, no debris. Some mills also offer polished exterior or epoxy coating as options. For most heat exchanger applications, standard pickled finish is sufficient.

Q11： How does C70600 compare to 316L stainless steel in mechanical properties?

C70600 has lower strength but higher ductility than 316L stainless steel. 316L tensile strength is about 485 MPa vs 310 MPa for C70600. However, 316L elongation is 40% vs 30% for C70600. The bigger difference is in seawater corrosion： 316L pits. C70600 does not. In fresh water, either works. In seawater, choose C70600.

Q12： What is the thermal expansion coefficient of C70600 and why does it matter?

C70600 thermal expansion is 17.0 µm/m·K (20-300°C). This is higher than carbon steel (12 µm/m·K) but lower than many plastics. When welding C70600 tube to a carbon steel tube sheet, the difference in expansion can cause stress. Design for this differential. Preheating both materials before welding helps reduce mismatch stress.

Each tube batch goes through 5 checks before shipping：

Chemistry → Spectrometer confirms Ni 9-11%, Fe 1.0-1.8% (ASTM E1473)

Strength → Pull test until break. Must hit 310 MPa minimum (ASTM E8)

Flaws → Eddy current probe runs through every tube. Any signal = reject (ASTM E243)

Ductility → Flatten a ring to 3x wall. No cracks allowed (ASTM B968)

Leaks → Hydrostatic pressure 3000 psi, hold for 10 seconds (ASTM B111)

You get a Mill Test Report with every order. Third party inspection (SGS, BV, Lloyds) available.

Plastic caps on both ends

VCI paper between tube layers

Shrink wrap around each bundle

Steel strapping to secure bundle

Wooden case for small cut lengths or fragile sizes

Steel bundle + wooden pallet for 6-12m standard tubes

Waterproof label with grade, OD, wall, heat number, quantity

From raw material to finished tube in one plant：

Melting (3 furnaces, 5 tons each) → turns copper + nickel + iron into liquid alloy

Casting (2 lines) → pours liquid into solid billet, 80-220mm diameter

Extrusion (3500 ton press) → punches billet into hollow tube shell

Cold drawing (8 benches) → pulls shell through dies to shrink OD and wall

Annealing (4 furnaces) → heats tube to 600°C to soften after drawing

Straightening & cutting (3 lines) → makes tube straight and cuts to length

Testing (2 eddy current machines) → 100% inspection

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