Why Copper Nickel Alloy Stays on the Short List

Two grades do almost all of the work in marine and exchanger service: Cu-Ni 90/10 (UNS C70600) and Cu-Ni 70/30 (UNS C71500). The iron and manganese additions are not incidental — they form a stable, self-healing surface film in chloride-rich water that resists both general corrosion and bio-fouling. In flowing seawater at typical design velocities, 90/10 shows negligible general-corrosion loss, which is why shipyards and offshore platforms return to the alloy generation after generation.

The trade-off is mechanical strength and high-temperature performance. Cu-Ni does not pretend to be a high-pressure alloy; it is a corrosion-resistant alloy that happens to handle moderate pressure very predictably. If your design temperature pushes into the sustained high-temperature range, or your pressure pushes you toward creep-rated materials, the conversation shifts to nickel-iron-chromium grades such as Inconel or Monel — which EZ Steel also supplies as part of the same product family.

90/10 vs 70/30: How to Choose Without Re-Specifying the Whole System

The two grades are similar in fabrication but very different in duty. Use the table below as a starting point, then confirm with your project’s flow, velocity, and water-chemistry data.

A practical rule of thumb from the field: if the line is on the cold side, in clean seawater, and runs at moderate velocity, specify 90/10 and invest the savings in better flange facings and gasket materials. If the line sees warmer water, occasional sand or silt, or higher design velocities, jump to 70/30 and accept the cost premium as insurance against unplanned shutdowns.

The Tubing Is Only Half the Spec — Match the Joints

Most premature failures in Cu-Ni systems are not the tube itself. They start at the flange, the gasket, or the stud bolt. The tube can be perfect in every metallurgical sense, but if the joint leaks, the asset is down. That is why a serious procurement walkthrough treats the tube and the joining components as one package.

Flanges: use Cu-Ni when the line is Cu-Ni

Bolting carbon-steel flanges to a Cu-Ni pipe in a chloride-rich splash zone is asking for galvanic trouble. For marine service, specify copper nickel flanges with the same UNS designation as the tube, or use a proper isolation gasket kit. For process and structural lines, our steel flanges range covers ASME B16.5 and related standards when the duty permits.

Fittings: keep the joining method consistent with the duty

Butt-weld fittings give the strongest joint and are preferred for high-pressure and high-temperature runs. For small-bore, instrument, and lower-pressure branches, socket-weld and threaded fittings are faster to install and easier to rework. Our butt weld fittings and threaded fittings ranges are produced in matching Cu-Ni grades so the metallurgical continuity is preserved across every change of direction.

Gaskets, stud bolts and nuts: the quietest failure mode

Spiral-wound and ring-type joint gaskets, paired with the correct stud bolt grade and nut, are the workhorses of any Cu-Ni piping package. Sourcing them from a single supplier alongside the tube eliminates the excuse that "the gaskets were not on the truck" when the joint is being made up on site. Browse the full gasket stud bolt nut range to spec the joint correctly the first time.

Reading the Standard Stack Correctly

EEMUA 234 and EEMUA 144 are the most commonly cited standards for offshore Cu-Ni tube. They do not contradict ASTM B466; they layer on top of it with ordering, traceability, and inspection requirements specific to offshore service. When a project specification says "EEMUA 234", the supplier must demonstrate control of chemical composition, mechanical properties, dimensional tolerances, and the test regime — not just material origin. EN 10204 3.1 certificates should be the minimum expectation, with 3.2 available for third-party witnessed orders.

For the heat-exchanger side, EN 12451 is the European reference for copper and copper-alloy tubes for condensers and heat exchangers. The grade codes (CW 352H for 90/10, CW 354H for 70/30) are the right way to anchor a European spec, while UNS numbers anchor an American spec. Both point to the same alloy; what changes is the paperwork.

From Spec to Site: How a Bundled Package Cuts Project Risk

The most common reason a Cu-Ni package goes wrong is fragmentation. The tube arrives from one supplier, flanges from another, gaskets from a third, and studs from a fourth. Every handover is a chance for a mismatch — wrong facing, wrong bolt length, missing traceability. A bundled package from a single source closes those gaps.

EZ Steel Industrial supplies this exact bundle for marine, offshore, and exchanger projects: Cu-Ni tubes and pipes, Cu-Ni and steel flanges, butt-weld, socket-weld and threaded fittings, plus the complete gasket, stud bolt and nut set. We also supply the carbon steel pipe side of the system (for structural piling and pipeline construction) and the stainless steel pipe side where duty demands it. One PO, one set of MTRs, one delivery.

Where Cu-Ni Tubing Fits in Real Projects

Cu-Ni 90/10 dominates commercial shipbuilding: seawater cooling, firefighting, ballast, and sanitary lines. 70/30 is the default for the tube bundle inside condensers and for offshore process cooling where waters are warmer and less predictable. Power plants running once-through cooling on estuarine or coastal water use 70/30 tube in the condenser bundle precisely because the alloy tolerates the higher inlet temperatures and the suspended solids.

In desalination, Cu-Ni remains a default evaporator material because the protective film tolerates the cleaning routines that other alloys struggle with. Petrochemical facilities use Cu-Ni for utility water and for the cooler side of exchanger bundles, while the hot hydrocarbon side often steps up to Inconel and Monel tubes in the same project. In aerospace and nuclear service, RCC-M Section II governs the source of nuclear-grade material; our RCC-M Section II nuclear tube programme covers that side of the duty.

Common Engineering Mistakes to Avoid

Three mistakes show up over and over in Cu-Ni procurement:

• Specifying a 90/10 tube and a C71500 flange. The alloy mismatch invites galvanic trouble; match UNS designations across tube, flange, and fitting.
• Allowing high design velocities. Once seawater velocity exceeds the limit published in the project standard (commonly in the low single-digit metres per second for 90/10), the protective film is at risk. 70/30 tolerates higher velocities but is not a licence to ignore them.
• Treating gaskets and studs as consumables. They are not. They are engineered components with the same traceability expectations as the tube.