ASTM B111 C70600 is the seamless 90/10 copper-nickel tube specified for boiler heat exchangers, steam condensers and air condenser coils where the cooling medium is seawater, brackish water or a corrosive process stream. The alloy carries 9.0-11.0% nickel with 1.0-1.8% iron and a manganese addition, producing a protective surface film that survives flowing water and repeated thermal cycling. Tubes are supplied in the O61 annealed temper for expansion into tube sheets and in the H55 light-drawn temper where the extra yield strength is needed for long spans or higher pressure duty.
Where the Grade Fits in Exchanger Duty
Two service patterns dominate this application. In boiler plant the tube carries cooling water on one side and condensate or feedwater on the other, so the tube must resist water-side corrosion while staying clean enough to maintain heat transfer. In air cooled condenser and refrigeration coils the tube carries refrigerant or process fluid and is exposed to ambient moisture, salt air and condensate, so external surface corrosion resistance matters as much as internal performance. In both cases the 90/10 composition provides a combination of corrosion resistance, thermal conductivity and fabricability that heavier stainless or higher nickel alloys cannot match at equivalent cost.
Composition and Strength
| Nickel, Ni (including Co) | 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 |
| Copper, Cu | remainder |
| O61 annealed, tensile strength, min | 40 ksi (275 MPa) |
| O61 annealed, yield strength, min | 15 ksi (105 MPa) |
| H55 light-drawn, tensile strength, min | 45 ksi (310 MPa) |
| H55 light-drawn, yield strength, min | 35 ksi (240 MPa) |
The H55 temper is the usual answer when a specification calls for a high strength copper-nickel tube: the light-drawn condition raises the yield strength from 105 MPa to 240 MPa, which improves resistance to vibration fatigue and allows a wider baffle spacing. The trade-off is lower expansion ductility, so a light-drawn tube should be rolled with a torque suited to the temper and should not be substituted for an annealed tube in an existing tube sheet without review.
Dimensions and Tolerances
ASTM B111 tabulates tolerances against the specified outside diameter, wall thickness and length. The values below apply to the light and medium condenser sizes:
| Outside diameter up to 12 mm | plus or minus 0.076 mm |
| Outside diameter over 12 to 18 mm | plus or minus 0.10 mm |
| Outside diameter over 18 to 25 mm | plus or minus 0.15 mm |
| Wall thickness 0.50 to 0.90 mm | plus or minus 0.08 mm |
| Wall thickness 0.90 to 1.5 mm | plus or minus 0.11 mm |
| Wall thickness 1.5 to 2.1 mm | plus or minus 0.13 mm |
| Length up to 4500 mm | plus 2.4 mm, minus 0 |
| Length over 4500 to 6000 mm | plus 3.2 mm, minus 0 |
Wall thickness selection should combine the corrosion allowance for the design life with the material needed for the joint and for the tube's own pressure rating. Where a specification quotes a minimum wall rather than a nominal wall, the specified tolerance must be added to the corrosion allowance so that the tube still meets the minimum at the thinnest permissible point.
Thermal and Physical Properties
Density: specific gravity about 8.9
Thermal conductivity: about 45 W/(m·K) at 20 °C
Electrical conductivity: about 9% IACS
Melting range: 1100-1149 °C
Modulus of elasticity in tension: 18,000 ksi; modulus of rigidity: 6,800 ksi
Magnetic response: effectively non-magnetic
Inspection and Testing Requirements
Eddy current testing of the full tube length to Practice E243, providing information on the suitability of the tube for its intended duty.
Hydrostatic testing to the fibre stress set in ASTM B111, using the thin-cylinder relationship given in the standard.
Expansion and flattening tests on samples from the lot, both of which must show no visible cracks.
Chemical analysis of the cast, and mechanical testing of the finished tube to confirm the temper minimums.
Material test certificate recording heat number, composition, properties and non-destructive test results.
Installation and Maintenance Notes
Roll the tube with a torque matched to the temper and wall thickness, and check several joints at the start of the rolling programme so that the setting is proven before the bulk of the tube sheet is completed. Keep the water side clean during commissioning, because deposits formed before the protective film stabilises can lead to under-deposit attack. On the air side, keep fins and supports free of trapped moisture and avoid direct contact between the copper-nickel tube and carbon steel supports in wet locations. Where a boiler condenser is laid up for long periods, drain and dry the tube side or use a lay-up regime that keeps oxygenated water moving.
FAQ
Q: Is C70600 suitable for boiler heat exchanger tube?
Yes. The 90/10 copper-nickel composition is widely used for boiler plant condensers and coolers, particularly where cooling water is seawater or brackish.
Q: Can C70600 tube be used in air cooled condensers?
Yes. The alloy is used for air condenser and refrigeration coils because it resists atmospheric and condensate corrosion while providing good heat transfer.
Q: What does high strength mean for this tube?
The H55 light-drawn temper is specified with minimum values of 45 ksi (310 MPa) tensile and 35 ksi (240 MPa) yield strength, compared with 40 ksi (275 MPa) and 15 ksi (105 MPa) for the O61 annealed temper.
Q: Which temper should be ordered for a retubing job?
Match the temper of the original tube where the design permits, because a light-drawn tube expands differently from an annealed tube and the rolling procedure must be adjusted accordingly.
Q: What tolerances apply to the delivered tube?
ASTM B111 sets tolerances by diameter, wall thickness and length; for common condenser sizes the outside diameter tolerance is between 0.076 mm and 0.15 mm and the wall thickness tolerance between 0.08 mm and 0.13 mm.
Q: How is the tube verified before shipment?
Full length eddy current testing, hydrostatic testing, and lot based expansion and flattening tests are carried out, and the material test certificate documents the results for each heat.
