C70600 Copper Nickel 90/10 CuNi Heat Exchanger Tubes

What Is C70600 Copper Nickel 90/10?

C70600 is a copper nickel alloy in which nickel is the principal alloying addition, present at about ten percent, with copper making up almost all of the remainder and small controlled additions of iron and manganese. The alloy is also written as CuNi 90/10 or 90/10 cupronickel, and it is the most widely used tube material for seawater cooled condensers, heat exchangers and marine piping systems.

The combination of copper and nickel produces a single phase, face centred cubic structure that is tough, ductile and highly resistant to seawater, and the iron addition improves resistance to impingement and to flowing seawater attack. The alloy does not rely on a brittle protective layer: its corrosion resistance comes from the alloy itself and from a thin, stable surface film that forms in service, which is why it tolerates the bends, expansions and welding that a heat exchanger requires.

Chemical Composition

All values are percentages by mass. The iron and manganese limits are not incidental: iron content within the specified range is what gives 90/10 cupronickel its resistance to erosion corrosion in fast flowing seawater, and manganese supports the same effect, so a heat outside those limits should be questioned even if the nickel and copper figures look correct.

Standards and Designation Equivalents

The 70/30 alloy, C71500, follows the same pattern in the standards and is chosen where higher strength and greater resistance to high velocity seawater are needed, at higher cost. Tubing for seawater service is generally ordered against ASTM B111/B111M, which sets the composition range, the temper and the mechanical property requirements, and which defines the pressure testing and electric non-destructive testing that the tube must pass.

Fabrication and Joining Properties

This profile is what makes 90/10 cupronickel such a practical heat exchanger material. Tube can be bent, expanded and welded on site, and joints can be made by brazing where welding heat would be inconvenient. Welding should still respect the usual rules for copper nickel: clean, dry joint faces free of marking ink and grease, low heat input, high purity shielding gas and a matching copper nickel filler, followed by removal of heat tint and weld spatter.

Service in Heat Exchangers and Marine Systems

Power station condensers and auxiliary coolers using seawater or brackish water.

Desalination plant evaporator and distiller tubes, where the alloy has been the standard choice for decades.

Marine piping, sea water systems, tube sheets, baffles, ferrules and fittings.

Refinery condenser and cooler tubes, including service where hydrogen sulphide may be present.

Automotive and industrial heat transfer components such as brake lines and power steering tubing.

Service life is decided less by the alloy than by how it is used. Clean surfaces and a design velocity that avoids both stagnation and excessive erosion keep the protective film intact, while deposits, biological growth, chloride rich stagnant water and entrained sand all shorten life. Tube sheets and water boxes should be designed for even flow distribution, cleaning methods should avoid scoring the bore, and dissimilar metals should be separated wherever the transfer of water between them could set up galvanic attack.

Inspection, Supply Condition and Documentation

Seamless condenser tube is supplied in straight lengths or in coils in the ordered temper, normally soft annealed for bending and expanding. It is tested for pressure tightness and examined by an electric non-destructive method such as eddy current testing as required by the product standard, and is checked for dimensions including outside diameter, wall thickness concentricity and length. Chemical analysis and tensile testing confirm the grade and temper.

Documentation is issued as a mill test certificate listing the chemical, mechanical and non-destructive test results, and can be provided to EN 10204 type 3.1 where full traceability is required, with third-party inspection arranged at the works when the contract calls for it. Tube is protected with caps and wrapping and packed in strapped bundles or wooden cases for sea transport so that the bore arrives clean and undamaged.

FAQ

Q: What does 90/10 mean in CuNi 90/10?
It describes the approximate proportions of the two main elements, about ninety percent copper and ten percent nickel, with iron and manganese additions that improve resistance to flowing seawater.

Q: What is the composition of C70600?
Nickel 9.0 to 11.0 percent, iron 1.0 to 1.8 percent, manganese up to 1.0 percent, zinc up to 1.0 percent, lead up to 0.05 percent and copper as the remainder, with a nominal analysis of about 88.6 percent copper and 10 percent nickel.

Q: Which standard governs C70600 heat exchanger tube?
ASTM B111/B111M, with ASME SB111 used for code work; pipe is covered by ASTM B466 for the seamless form and ASTM B467 for the welded form.

Q: Can C70600 tube be welded on site?
Yes. Gas shielded arc and butt welding both give excellent results, and brazing and soldering are also suitable where welding heat would be undesirable.

Q: How does the 70/30 alloy compare?
C71500, the 70/30 cupronickel, offers higher strength and better resistance to high velocity seawater than C70600, and is selected where those conditions justify its higher cost.

Q: What causes premature tube failure in seawater service?
Deposits and stagnant water leading to under-deposit corrosion, excessive velocity and entrained solids causing erosion corrosion, and poor cleaning practice that damages the protective film.