When a piping system has to survive seawater, brines, condensates or aggressive chemicals for decades, copper nickel alloy is rarely an exotic choice — it is the default. From naval ships and offshore platforms to desalination plants and power station condensers, cupronickel tubes and pipes deliver a rare combination of corrosion resistance, biofouling resistance, workability and weldability. Yet the difference between a long, trouble-free service life and a costly retrofit often comes down to picking the right grade, the right standard and the right manufacturer.

EZ Steel Industrial has been producing copper nickel alloy tubes, pipes, fittings and flanges since 1994, and the questions our buyers ask are very consistent. This guide distills the practical answers we give every week.

A copper nickel alloy is a binary alloy of copper and nickel — typically with small additions of iron and manganese to improve corrosion resistance in seawater. The two workhorse grades are 90/10 (CuNi10Fe1Mn, UNS C70600) and 70/30 (CuNi30Fe1Mn, UNS C71500). They behave predictably in saline water, resist macrofouling because copper ions discourage marine growth, and tolerate moderate flow velocities without the localized attack that destroys many alternative materials. They are also easy to bend, weld and braze in the shop or on board.

Both grades are seawater-proven, but they are not interchangeable. Use the table below as a quick rule of thumb, then confirm with the relevant piping class.

In short: specify 90/10 for general shipboard and onshore cooling water, and move to 70/30 when the water is warmer, more aggressive or the design velocity is high. Both are stocked by EZ Steel Industrial in seamless and welded forms, and both are produced in our own facility.

A mill test certificate (MTC) is only useful if the listed standard actually matches the service. For copper nickel alloy tubes, pipes, fittings and flanges, the most commonly referenced specifications are:

• ASTM B111 / ASME SB111 — seamless condenser and heat exchanger tubes (C70600, C71500)
• ASTM B466 / ASME SB466 — seamless pipe and tube (C70600, C71500)
• ASTM B467 — welded pipe
• EEMUA 144 — 90/10 seamless and welded tubes for offshore
• EEMUA 234 — 90/10 and 70/30 pipe for marine and offshore
• DIN 86019 — 90/10 seamless pipes with metric dimensions
• MIL-T-16420K — naval shipboard piping
• EN 12451 — copper alloy tubes for heat transfer (condensers, refrigeration)

Don't accept an MTC that only states "C706" without naming the product form standard. A tube certified to B111 and a pipe certified to B466 look similar but are not interchangeable in classified systems.

Because cupronickel is so widely used, it is easy to forget how many services depend on it. Four typical application areas:

A cupronickel tube is only as reliable as the joint. Two practical recommendations from our project engineers:

• Use pipe fittings and pipe flanges made from the same alloy family (Cu-Ni body with Cu-Ni weld ends). Mixing a Cu-Ni tube to a carbon-steel BW fitting creates a galvanic cell where the steel becomes the sacrificial anode.
• For seawater manifolds, prefer copper nickel flanges over steel flanges — they are heavier, but they eliminate a major corrosion risk at the joint.
• Use compatible non-metallic gaskets (typically EPDM or graphite with stainless inserts) rather than compressed asbestos fibre. Gaskets, stud bolts and nuts can be supplied as a kit.

Cupronickel is forgiving in service but unforgiving of poor workmanship. Insist on the following as a baseline:

• Chemical composition report covering Cu, Ni, Fe, Mn, Zn, Pb (and residuals) on every heat
• Mechanical tests: tensile, yield, elongation per the cited standard
• Hydrostatic test for tubes and pipes, eddy current or ultrasonic NDT for the full length
• Metallographic check of grain size and absence of harmful carbides in 70/30
• Third-party inspection (SGS, BV, TUV, ABS) accepted on request

EZ Steel Industrial's ISO 9001-certified lab and ASME/AWS-qualified welders run all of the above in-house, and we issue EN 10204 3.1 certificates as standard. For nuclear or aerospace work, our Cu-Ni materials can also be supplied to RCC-M Part II for safety-critical applications.

After 30 years in the business, we see the same handful of issues over and over. Avoid them and your system will easily outlast its design life:

• Excessive flow velocity. Pushing 90/10 above ~3.5 m/s in seawater gradually strips the protective film and leads to erosion-corrosion. Specify 70/30 — or larger pipe — when flow is high.
• Sulphide- or ammonia-rich water. Polluted harbour water and stagnant cooling loops can drive attack on cupronickel. Add iron dosing or switch to 70/30.
• Galvanic mismatch. Avoid direct Cu-Ni to uncoated carbon-steel contact; use dielectric unions or Cu-Ni flanges throughout.
• Wrong filler metal. For welding, use a matching Cu-Ni filler (e.g. ERCuNi for 90/10). Brass or bronze fillers will fail in seawater.

The advantage of working with a manufacturer that produces tubes, pipes, fittings, flanges and industrial valves in compatible alloys is not just convenience — it is metallurgical consistency. Every component in your system comes from the same controlled supply chain, with matching MTCs and a single point of accountability. EZ Steel Industrial, founded in 1994 in Changsha, China, ships more than 480,000 tons a year of carbon, stainless and copper-nickel products to shipyards, power plants and EPC contractors in more than 60 countries.

Whether you are designing a new seawater cooling system, retrofitting a condenser, or quoting a desalination train, our engineering team can review your datasheet and recommend the right combination of copper nickel alloy tubes, copper nickel flanges and complementary products.