Why this guide exists

Most articles on copper-nickel stop at the textbook line that it is "an alloy of copper and nickel, used in coins and condenser tubes." That sentence is correct, and almost useless on a Friday afternoon when an inspector is rejecting your heat-exchanger tube bundle because the iron content drifted above 1.8%.

This walkthrough is built for the people who actually buy, specify, and sign off on the material. We will move from chemistry to project delivery, and tie every section back to the copper nickel alloy inventory and mill test reports you can pull from a single shipment at EZ Steel Industrial.

1. The two grades that do 95% of the work

When you order copper nickel alloy tube, pipe, plate, or fittings, you are almost always choosing between two UNS designations. The rest of the spec sheet is the same chemistry, the same family of standards, and the same welding procedure — only the nickel content shifts.

The 90/10 grade is the workhorse: cheaper, easier to weld, and more than adequate for most ship and offshore piping at velocities below 3.5 m/s. The 70/30 grade earns its premium where the fluid is hotter, faster, or more aggressive — and where a 30-year inspection cycle is non-negotiable. Both grades gain their corrosion resistance from a thin, self-healing oxide film that forms on the inner surface in clean seawater; that film is the reason no internal lining or cathodic-protection coupon is normally required.

2. Reading the chemistry the way an inspector reads it

A mill test certificate for cupronickel looks like a generic metal cert, but three numbers actually drive acceptance. Get these right and the rest is paperwork.

• Iron (Fe): 1.0–1.8% for C70600, 0.4–1.0% for C71500. Iron is the corrosion-resistance modifier. Too little and the protective film is too soft; too much and you lose ductility for bending. Reject the heat if Fe is outside the band.
• Manganese (Mn): 0.5–1.0%. Manganese ties up residual sulfur so the alloy can be hot-worked cleanly. Outside this range, expect cracking during tube bending.
• Nickel (Ni) plus cobalt. For 90/10, Ni must sit in 9.0–11.0%; for 70/30, 29.0–33.0%. This is the spec-defining number — every other element supports it.

Anything else on the cert is informational. A good supplier will hand you a heat-by-heat breakdown and a statement of compliance to the named standard. If the cert only shows "composition meets specification" without numbers, send it back.

3. Matching the form to the service

Specifying the alloy is the easy part. The harder question is which product form the project actually needs. The wrong form costs you fabrication hours you never get back.

Seamless tube for heat exchangers and condensers

Condenser and heat-exchanger tube bundles are almost always seamless per ASTM B111 or B395. The wall is thin, the bends are tight, and any weld seam becomes a preferential corrosion site in the first five years. For U-tube bundles, confirm that the mill can deliver the bend radius you need with full solution annealing after bending — cold work on cupronickel is fine, but it must be heat-treated back to the soft temper before it goes into service.

Welded pipe for ship and offshore piping

For above 100 mm nominal bore, welded pipe per ASTM B467 or EEMUA 144 is the economic choice. The weld must be made with the matching Cu-Ni filler (e.g., ERCuNi for 90/10) and the joint must be fully radiographed. Welded pipe is also where your pipe fittings package starts to matter: elbows, tees, and reducers in the same UNS grade, with the same MTC traceability, in the same shipment.

Plate and sheet for heat-exchanger tube sheets and baffles

Plate to ASTM B122 is common for tube sheets in copper-nickel exchangers. The trick is welding it to a carbon-steel shell without galvanic corrosion — the joint is almost always fitted with a thin weld-deposited nickel-aluminum-bronze transition. Spec this transition in the drawing, not in the field.

4. The four service environments where cupronickel wins

If the project is not on this list, cupronickel is probably the wrong answer. The alloy is excellent at a narrow set of jobs and expensive at everything else.

Seawater cooling loops on ships and offshore platforms

This is the canonical use. The combination of biofouling resistance, tolerance to chlorides, and stable heat-transfer coefficient makes 90/10 the default for engine-room coolers, firewater mains, and ballast piping. The alloy tolerates stagnant seawater for the brief shutdown windows that occur in real operations — it is not, however, a substitute for proper lay-up procedures during long outages.

Desalination plants (MSF, MED, SWRO)

Multi-stage flash and multi-effect distillation still rely on 70/30 for the brine heater and the high-temperature evaporator stages. The alloy resists the localized pitting that hits stainless steel once chloride concentration climbs past 60,000 ppm.

Refinery overhead condensers

The first condenser after the crude column is a chloride-corrosion and ammonium-bisulfide attack zone. Cu-Ni 70/30 has been the workhorse here for decades because it tolerates both attack modes simultaneously. Pair the tube bundle with matching pipe flanges and a proper gasket stud bolt nut set so the joint integrity matches the tube integrity.

Coastal power plant condensers

Coastal and offshore power plants use Cu-Ni for the same reason ships do: a thin wall tube that survives 30+ years of once-through seawater with no internal coating to fail. For thermal optimization, finned tubes in aluminum or copper-nickel are often integrated on the air-cooled side of the auxiliary systems.

5. The fabrication rules that prevent field failures

The most expensive copper-nickel failures are not material defects — they are the result of breaking fabrication rules. Five habits separate projects that stay on the water from projects that come back to the shipyard in year three.

• Use matching fillers only. ERCuNi (90/10) for 90/10 base, ERCuNi30 for 70/30. Stainless or aluminum-bronze fillers on cupronickel base metals will fail at the fusion line.
• Solution-anneal after heavy bending. U-bends and rolled tube ends need a 600–700 °C soak to restore corrosion resistance in the cold-worked zone.
• Keep iron contamination off the surface. Cut with non-ferrous tools or dedicated carbide. Embedded carbon-steel filings become local corrosion cells the moment the system sees seawater.
• Avoid threaded joints below 50 mm. Use butt-welded or flanged connections. Threading thins the wall and destroys the protective film locally.
• Hydrotest with clean, low-sulfide water. Sour hydrotest water will sulfide-stress-crack cupronickel that has not been in service yet.

6. What a clean procurement package looks like

Whether you are sourcing for a shipyard, an EPC contractor, or a refinery turnaround, the package structure is the same. The list below is the minimum that arrives in a single shipment from a mill that actually understands cupronickel:

• Tubes, pipes, or plates in the named UNS grade, with heat numbers stenciled on each piece.
• Matching fittings (elbows, tees, reducers) and pipe flanges in the same heat or a fully traceable sub-heat.
• Gasket stud bolt nut sets sized to the flange class, with the bolt torque values on the MTC.
• Heat-by-heat mill test reports showing the iron, manganese, and nickel numbers from section 2 above.
• Welding procedure specifications (WPS) and procedure qualification records (PQR) for the matching filler metal.
• Third-party inspection release from the nominated agency, with photos of the heat-marked material before packing.

If your supplier sends the tubes and a generic cert, the fittings and flanges come from a second vendor three weeks later, and the stud bolts ship from a third — you do not have a project package. You have a parts list.

7. Common pitfalls and how to avoid them

Across two decades of cupronickel orders, the same five problems show up at almost every new shipyard or refinery. They are all avoidable at the procurement stage.

Specifying C71500 where C70600 would do

Engineers often default to the higher-nickel grade "to be safe." For 90% of seawater service, C70600 is the correct answer. The 70/30 grade should be reserved for elevated temperature, high velocity, or specific corrosion environments — not as a blanket upgrade.

Forgetting the matching flange standard

A cupronickel pipe welded to a carbon-steel flange works, but it accelerates corrosion on the carbon-steel side. Either upgrade the flanges to copper nickel flanges or fit a dielectric gasket and isolation kit. Decide this in engineering, not in the field.

Mixing suppliers within one system

Each supplier uses its own melt practice. Two heats from two mills, even at the same UNS grade, can behave differently in the same electrolyte. The cleanest projects single-source the heat and the traceable downstream components.

8. How EZ Steel Industrial supplies this package

EZ Steel Industrial has been producing copper nickel alloy tube, pipe, plate, fittings, and flanges since 1994. The cupronickel line is backed by API, EN, and ASME certifications, with an ISO 9001-accredited laboratory issuing heat-by-heat MTCs in English.

For projects, the supply scope is built around four questions: which UNS grade, which product form, which standard (ASTM, EEMUA, GB/T, JIS), and which downstream components must be in the same shipment. The answer is typically a bundle that includes the tubes, the pipe fittings, the pipe flanges, and the stud-bolt sets — with one MTC package covering the whole system.

Capacity sits at 480,000 metric tons per year, with 500+ technical and production staff, and documented deliveries into South-to-North Water Diversion, West-East Gas Pipeline, and major shipyards. When a project needs more than cupronickel — carbon steel, stainless steel, or heat efficiency tubes for the exchanger side of the same plant — the same mill can supply the lot.