ASTM B111 C70400 is a seamless copper-nickel tube grade, commonly called 95-5 copper-nickel, in which the copper base is alloyed with about 5% nickel together with controlled iron and manganese additions. The alloy sits between the simple brasses and the 90-10 and 70-30 copper-nickel grades: it retains much of the thermal conductivity of copper while gaining the seawater resistance that the nickel, iron and manganese combination provides. Tube is supplied in the O61 annealed temper or the H55 light-drawn temper for surface condensers, evaporators, heat exchangers and condenser coils.
Alloy Character
Nickel in solid solution raises the corrosion potential of the matrix and helps form a dense, adherent oxide film; the iron addition stabilises that film against breakdown under flowing water; and manganese improves castability and film stability. The result is a tube that resists seawater, salt spray and mildly acidic process media, with a typical corrosion rate below 0.1 mm/year in marine exposure, which is why 95-5 copper-nickel is widely used for seawater circuits and heat transfer equipment where full 90-10 specification is not required. In trade documents the alloy is often written as BFe5-1.5-0.5 following the Chinese material designation system, and it corresponds to UNS C70400 in the ASTM system.
Composition and Mechanical Behaviour
| Copper, Cu | 90-93% nominal balance |
| Nickel, Ni (including Co) | 5-7% |
| Iron, Fe | 1.0-1.8% |
| Manganese, Mn | controlled addition for film stability |
| Zinc, Zn | 1.0% max |
| Lead, Pb | 0.05% max |
| Temper | O61 annealed or H55 light-drawn |
| Tensile strength | about 380 MPa annealed, rising to about 585 MPa in harder tempers |
| Yield strength | about 120 MPa annealed, rising to about 380 MPa in harder tempers |
| Elongation | about 40% annealed, reducing to about 15% in harder tempers |
| Density | about 8.8 g/cm³ |
The strength values above describe the range normally achieved by the alloy across tempers and are quoted to support preliminary design. The binding acceptance values are the minimum tensile strength, minimum yield strength and minimum elongation that ASTM B111 sets for the specific UNS number and temper, and these are stated on the material test certificate issued with each lot.
Dimensional Tolerances
ASTM B111 tabulates dimensional tolerances by outside diameter and wall thickness. For the small and medium diameters used in condenser and heat exchanger service the following values apply:
| 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 0.80 mm | plus or minus 0.08 mm |
| Wall thickness 0.80 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 |
| Wall thickness 2.1 to 3.0 mm | plus or minus 0.17 mm |
| Length up to 4500 mm | plus 2.4 mm, minus 0 |
| Length over 4500 to 6000 mm | plus 3.2 mm, minus 0 |
| Length over 6000 to 10000 mm | plus 4.0 mm, minus 0 |
Physical and Thermal Properties
Density: about 8.8 g/cm³, giving a lighter tube line than an equivalent 90-10 or 70-30 specification
Thermal conductivity: about 50 W/(m·K) at room temperature, well above stainless steel
Electrical conductivity: low compared with pure copper, as expected for a copper-nickel alloy, which is not a limitation for heat transfer duty
Magnetic response: essentially non-magnetic, so magnetic inspection and separation methods can be applied without interference
Fabrication: readily cold formed, expanded, soldered and brazed, with gas shielded arc welding giving the best welded joint quality
Testing and Quality Control
Tubes are supplied against the test requirements of ASTM B111: eddy current testing of the full length to Practice E243, hydrostatic testing to the fibre stress set by the standard, and expansion and flattening tests on samples drawn from the lot. Chemical analysis is taken from the cast or from the finished tube as required, and the heat number marked on each tube links it back to the material test certificate. For seawater service the certificate should be reviewed together with the iron and manganese contents, because it is the combination of nickel with those two elements that determines how well the protective film survives in the actual cooling water.
Applications
Marine engineering: seawater pipework, condenser and heat exchanger tube bundles, and lube and jacket water coolers on vessels.
Offshore installations: seawater lift lines and heat transfer equipment on platforms exposed to continuous salt spray.
Desalination and water treatment: evaporator and preheater tube where a lower alloy content is sufficient.
Energy and chemical plants: condenser and cooler duty in power generation and petrochemical units handling mildly aggressive water.
Refrigeration and air conditioning: condenser and evaporator coils, where the alloy's thermal conductivity and corrosion resistance are both used.
Selection and Fabrication Guidance
Choose C70400 when the cooling water is seawater or brackish but the duty is moderate, and move to 90-10 C70600 or 70-30 C71500 when the water is polluted, the velocity is high, or the tube must survive sulphide contamination. During fabrication, keep the tube in the annealed condition for expansion into tube sheets, protect the bore from site dirt, and avoid mixing this alloy with steel components in a wet circuit without attention to galvanic coupling. Welded connections should be made after the rolling operation where the design permits, and heat input should be controlled to avoid loss of the annealed temper in the joint region.
FAQ
Q: What is ASTM B111 C70400?
It is the 95-5 copper-nickel grade covered by ASTM B111 for seamless condenser tubes and ferrule stock, with about 5% nickel and 1.4% iron in a copper base.
Q: What is the difference between C70400 and C70600?
C70400 contains about 5% nickel and C70600 contains 9.0-11.0% nickel. The higher nickel content of C70600 gives better resistance to polluted and higher velocity seawater, while C70400 remains suitable for moderate marine duty at lower alloy cost.
Q: Which tempers are available?
O61 annealed for tube that will be expanded into a tube sheet, and H55 light-drawn for tube that needs higher strength. The temper determines the minimum mechanical properties certified for the lot.
Q: How thick does the tube usually need to be?
Condenser and heat exchanger service commonly uses wall thicknesses between about 0.5 mm and 1.5 mm, and the choice should leave allowance for the expected corrosion rate over the design life.
Q: Can the tube be welded?
Yes, with a technique suited to copper-nickel, and gas shielded arc welding gives the best results. Soldering and brazing are also used widely for this alloy, particularly for fittings and small coils.
Q: How is the delivered tube verified?
Full length eddy current testing, hydrostatic testing and lot based expansion and flattening tests are performed, and the material test certificate reports composition, mechanical properties and the non-destructive test results.
