What Is Copper Nickel Alloy?

Copper nickel alloys are solid-solution alloys in which copper is the base element and nickel is the principal alloying addition, typically ranging from 5% to 30% by weight. Iron and manganese are added in controlled amounts to improve corrosion resistance and strength without sacrificing ductility. The most commercially important grades are CuNi 90/10 (UNS C70600, ~10% Ni) and CuNi 70/30 (UNS C71500, ~30% Ni).

Unlike brass or bronze, copper nickel does not rely on zinc or tin. Its performance comes from the nickel content stabilizing the face-centered-cubic copper matrix, which is why the alloy remains tough and ductile even after decades of submersion in seawater. The protective dark brown oxide film that forms on the surface regenerates continuously when scratched, which is the secret behind its long service life.

The Two Grades That Run the Industry

CuNi 90/10 (C70600) — The Workhorse

90/10 is the default choice for shipboard piping, heat exchanger tubing, and offshore cooling systems. It combines good strength (yield typically 105–110 MPa for annealed tube) with excellent resistance to flowing seawater up to about 1.5 m/s. It is also easier to bend and weld than 70/30, which is why it dominates shipbuilding specifications.

CuNi 70/30 (C71500) — The High-Performance Option

70/30 is specified when service conditions are more aggressive — higher velocities, polluted or sulfide-containing water, or higher design temperatures. Its corrosion rate in seawater is roughly half that of 90/10, and it tolerates velocities up to about 3.5 m/s before erosion-corrosion becomes a concern. It is the preferred grade for power plant condensers using brackish or estuary water.

Where Copper Nickel Alloy Excels

The single biggest reason engineers pick copper nickel is seawater. In flowing seawater, 90/10 corrodes at roughly 0.025 mm/year and 70/30 at about 0.015 mm/year — values that translate into multi-decade service life for properly designed systems. Equally important, the alloy resists biofouling: barnacles, mussels, and algal mats struggle to adhere to the protective oxide film, which keeps flow paths clear and reduces cleaning outages.

Marine and shipbuilding

Seawater cooling lines, bilge and ballast systems, firewater mains, and sanitary drains on commercial vessels are almost universally built from CuNi 90/10 to EEMUA 144 or MIL-T-16420K. Naval specifications such as DEF STAN 02-780 also rely on the same alloy family. The combination of weldability, predictable expansion, and documented 30+ year service records is hard to beat.

Heat exchangers and condensers

Power plant and desalination condensers use copper nickel tubes because the alloy tolerates a wide range of water qualities and recovers gracefully from flow excursions. For boiler-side service and high-pressure steam systems, manufacturers typically switch to stainless steel or nickel-based tubes, but the waterbox and connecting piping remain copper nickel.

Petrochemical and chemical processing

In refineries and chemical plants, copper nickel is used for heat exchanger bundles handling brackish cooling water, for overhead condenser systems, and for piping in processes where chloride stress-corrosion cracking rules out stainless steel. It is also a reliable material for desalination evaporators in multi-stage flash and multi-effect distillation plants.

Aerospace and nuclear

Special high-nickel copper alloys and related cupronickels are referenced in RCC-M Section II for safety-related components in pressurized water reactors, and in aerospace specifications for fluid systems where galvanic compatibility with copper-based heat exchangers is critical. These applications demand tight chemistry control and full traceability — something only experienced mills can deliver.

Standards You Will See on a Drawing

Specifying copper nickel is mostly a matter of choosing the right combination of material, dimensional, and testing standards. The most common references are:

• ASTM B466 / B467 — seamless and welded pipe (UNS C70600, C71500, C71640)
• ASTM B111 — seamless condenser tubes and ferrule stock
• EEMUA 144 — 90/10 seamless tube for offshore and marine use
• EEMUA 234 — 70/30 seamless tube, same applications, higher performance
• DIN 86019 — welded 90/10 pipe for shipbuilding
• MIL-T-16420K — U.S. Navy tube specification
• JIS H 3300 — Japanese standard for copper and copper alloy tubes
• GB/T 8890 — Chinese standard for condenser and heat-exchanger tubes

A reliable mill will trace every heat to a 3.1 certificate per EN 10204, including chemical composition, mechanical properties, hydrostatic test results, and where required, NDT reports.

Specifying the Complete System: Pipes, Fittings, and Flanges

Copper nickel is rarely used as bare pipe. A working system needs matching pipe fittings, flanges, gaskets, and fasteners — and all of those components need to share the same alloy family to avoid galvanic problems.

For ship and offshore systems, 90/10 butt-weld fittings are the standard. Socket-weld and threaded variants are reserved for smaller instrument connections. Flanges are typically supplied to ASME B16.5 or EN 1092-1, in either flat-face or raised-face styles, with the same UNS designation as the pipe. Pipe flanges made from CuNi 90/10 mate cleanly with carbon steel flanges when the gasket and bolt materials are chosen to control galvanic potential — typically PTFE or non-asbestos gaskets with monel or stainless bolts.

Bundling all these items from a single supplier is the fastest way to keep chemistry consistent across a project and avoid mix-ups on site.

Common Mistakes When Specifying Copper Nickel

• Confusing CuNi with cupro-nickel plated steel. Only solid alloy gives you the corrosion performance — cladding will fail once the surface is breached.
• Pushing velocity too high. Beyond the recommended limits, even 70/30 can suffer erosion-corrosion. Use larger pipe diameters or a different material when velocities exceed 3.5 m/s.
• Mixing with incompatible gaskets. Graphite and certain rubber compounds can cause crevice corrosion in stagnant seawater. Use spiral-wound gaskets with a CuNi or monel winding, paired with PTFE filler.
• Forgetting about the waterbox. The transition from CuNi tubes to the waterbox is the most common leak point. Specify a CuNi-clad or CuNi-bolted waterbox from the outset.

Sourcing Copper Nickel From a Single Source

Copper nickel systems work best when pipes, tubes, fittings, flanges, and gaskets are ordered together from a mill that controls the entire supply chain. That is the model EZ Steel Industrial has used since 1994: full-cycle manufacturing, comprehensive inventory of common grades (ASTM B466, EEMUA 144/234, JIS H 3300, GB/T 8890), and bundled solutions shipped to shipyards, refineries, and power plant sites worldwide.

With an annual capacity above 480,000 tons, ISO 9001-certified laboratories, and full EN 10204 3.1 traceability, EZ Steel Industrial supports everything from a single replacement condenser tube bundle to a complete seawater cooling package for a new offshore platform. Whether the project calls for 90/10 piping to EEMUA 144, 70/30 heat-exchanger tubes to ASTM B111, or matching CuNi flanges and gaskets, getting the bundle from one source eliminates the most common field failures — chemistry mismatches between components.