What Is ASTM B111 C70600 Tube?
ASTM B111 is the standard for copper and copper-alloy seamless condenser tubes and ferrule stock. UNS C70600, the 90/10 copper-nickel alloy, is one of its principal grades. The tube contains approximately 90 percent copper and 10 percent nickel, with iron and manganese additions for strength and corrosion resistance. It is manufactured by extrusion or piercing of billets followed by cold drawing and annealing, producing a homogeneous seamless structure with no welded seam. C70600 is a copper-nickel alloy, not a steel; specifying it as an alloy steel tube is incorrect.
Chemical Composition
| Element | Content (%) |
|---|---|
| Copper (Cu) | Balance |
| Nickel (Ni) | 9.0 - 11.0 |
| Iron (Fe) | 1.0 - 1.8 |
| Manganese (Mn) | 1.0 max |
| Zinc (Zn) | 1.0 max |
| Lead (Pb) | 0.05 max |
| Carbon (C) | 0.05 max |
| Sulfur (S) | 0.02 max |
| Phosphorus (P) | 0.02 max |
Mechanical Properties (Annealed)
| Property | Typical Value |
|---|---|
| Tensile strength | 300 - 410 MPa (44 - 60 ksi) |
| Yield strength, 0.2% offset | 110 - 210 MPa (16 - 30 ksi) |
| Elongation | 30 - 45% in 2 in |
| Hardness | 55 - 75 HRB |
| Modulus of elasticity | 135 GPa |
| Density | 8.94 g/cm3 |
Corrosion Resistance in Water Treatment Service
Uniform corrosion: very low rates in clean and moderately polluted seawater.
Pitting and crevice corrosion: resistant because the protective film self-repairs in flowing water.
Impingement attack: withstands design seawater velocities, typically up to about 2.5 to 3 m/s for 90/10.
Biofouling: copper ions released at a controlled rate prevent barnacle and mussel attachment.
Stress corrosion: immune to chloride stress-corrosion cracking.
Applications in Water Treatment
C70600 tubes are engineered for demanding water environments: heat exchangers and condensers in desalination plants, cooling-water circuits for power and process plants, seawater intake and brine lines, and water conveyance systems handling raw or brackish water. The alloy also serves fire mains, sanitary lines, and hydraulic lines on vessels and offshore platforms, where long life in seawater is the decisive requirement.
Frequently Asked Questions
Q: Is C70600 a steel alloy?
A: No. C70600 is a copper-nickel alloy with 90 percent copper and 10 percent nickel. It contains no iron as a base element, only a small iron addition for corrosion performance.
Q: What does 90/10 mean?
A: The nominal copper-to-nickel ratio: 90 percent copper and 10 percent nickel, with iron and manganese additions.
Q: Why is C70600 used in desalination plants?
A: It resists the corrosive effects of seawater and brine, withstands the high velocities in evaporator and heat recovery circuits, and resists biofouling that would otherwise reduce heat transfer.
Q: Can C70600 tubes handle brackish water?
A: Yes. It is well suited to brackish and estuary water where chloride levels are too aggressive for many other copper alloys.
Q: How is C70600 tube welded or joined?
A: Tubes are roller-expanded into tube sheets and may be seal-welded with matching copper-nickel filler; TIG and MIG welding are both established procedures.
Q: What tests are performed per ASTM B111?
A: Chemical analysis, tensile testing, flattening, expansion, and eddy-current or hydrostatic testing, with hardness and residual-stress tests when specified.
