A 90/10 copper nickel tube in a refinery seawater cooling loop quietly does the job at 3.5 to 4.5 metres per second flow, in chloride-rich water, in temperatures that would pit 304 stainless within a single turnaround. A 70/30 tube, with the same nickel-copper backbone but more nickel, holds higher velocities and tolerates hotter, more aggressive fluids. Both have been on datasheets for decades, and both remain the first call for many refinery, marine, and power plant duties. The reason is not nostalgia; it is that copper nickel alloy does something most alloys cannot: it resists chloride pitting, resists macrofouling, and stays ductile under thermal cycling, all at the same time.

Most Cu-Ni failures in the field are not alloy failures. They are system failures — a Cu-Ni tube welded into a carbon steel flange stack, a tube ordered to the wrong standard for the destination, or a heat number traceability gap that surfaces at site reception. EZ STEEL INDUSTRIAL has been manufacturing alloy pipe, tube, fittings, and flanges from its base in Changsha, Hunan, since 1994. With more than 500 staff and annual output above 480,000 tons, the mill supplies API, EN, and ASME certified product into more than 40 countries. What follows is the working framework our engineering team uses when a Cu-Ni project lands on the desk.

"Copper nickel" is a family, not a single grade. Buyers who treat it as one material end up overpaying for one duty and under-specifying for the next.

Composition families you will meet in the field

• 90/10 (UNS C70600, CuNi10Fe1Mn): the workhorse grade for ship seawater systems, refinery cooling loops, and offshore platform piping. Roughly 90% copper, 10% nickel, with 1 to 1.8% iron and 0.5 to 1% manganese to stabilize the structure against impingement attack.
• 70/30 (UNS C71500, CuNi30Fe1Mn): higher nickel content, higher strength, and tolerance for higher seawater velocities. Used in more demanding condenser and heat exchanger service.
• Other grades in the family: Cu-Ni with tin additions (for improved erosion resistance), aluminum brass for special condenser tubes, and Monel 400 (Ni-Cu 70/30) and Inconel variants when the service leaves the Cu-Ni envelope entirely.

Common forms on a project

The same chemistry is delivered as tubes, pipes, plate, sheet, fittings, and flanges. On a real project, tube is rarely the only line item: a condenser bundle includes the tubes, the tubesheets, the baffles, the headers, and the transition pieces. A ship seawater system includes pipe, elbows, tee branches, flanges, and valves. The material discipline at every joint has to match the tube, which is why the article returns to fittings and flanges later.

Cu-Ni is not a substitute for stainless. It is a specialist. The cases below are where the alloy consistently delivers the lowest lifecycle cost on duty where stainless either fails or requires expensive protection.

Seawater and brackish service

90/10 is the default for piping and tubing in seawater service: firemain, ballast, bilge, and cooling loops. 70/30 is used where the duty pushes velocities or temperatures higher. The alloy's iron and manganese content forms a stable, adherent surface film that resists both pitting and biofouling, which is why cruise ships, naval vessels, and offshore platforms have kept the material on their drawings for half a century.

Heat exchange and condensation

Refinery overhead condensers, power plant main condensers, and desalination evaporators all use heat efficiency tubes in Cu-Ni or aluminium brass. The combination of thermal conductivity, fouling resistance, and corrosion tolerance in brackish or contaminated cooling water is what makes the grade the default for these bundles. Enhanced surface variants — finned, rifled, or grooved — are used where the heat duty pushes the limits of plain tube.

Hydrocarbon, chemical, and refinery service

Cu-Ni shows up on the shell side of overhead condensers and on cooling coils in atmospheric and vacuum columns. The alloy handles chloride-bearing cooling water, sour condensates, and the thermal cycling of a unit that swings between feed and turnaround duty. Where the process side requires something more aggressive, the alloy is often selected only for the exchanger tube side and paired with a different alloy on the shell side.

Subsea, offshore, and shipbuilding

Platform cooling loops, firewater systems, and ship seawater systems are still the most common Cu-Ni installations. Standards here are EEMUA 234 and the older MIL-T-16420K for naval work, plus national standards such as GB/T 8890 and JIS H 3300 for shipyards in Asia. EZ STEEL INDUSTRIAL manufactures the full range of Cu-Ni tubes and pipes for shipbuilding and offshore work in 90/10, 70/30, and matching Cu-Ni flanges to ASME B16.5.

A single Cu-Ni tube can be ordered to half a dozen standards depending on the project location, the vessel flag, and the buyer's existing QA system. The matrix below is the one our export team uses to map an enquiry to the right product reference.

For 90/10 and 70/30 in seamless form, ASTM B466 covers the refinery and process market. For condensers, ASTM B111 and EN 12451 are the most referenced. For shipbuilding and offshore, the relevant copper nickel alloy program at EZ STEEL INDUSTRIAL covers GB/T 8890, EEMUA 234, and JIS H 3300 side by side. Where the project requires nuclear-grade traceability, RCC-M II is the governing standard and is supplied with the documentation depth that the safety authorities expect.

The first decision on a Cu-Ni project is almost always 90/10 versus 70/30. Both resist seawater corrosion, but they do not do it the same way.

90/10 is the more economical grade, easier to form, and tolerates typical seawater velocities up to 3.5 to 4.5 metres per second in clean service. 70/30 is the stronger grade, with roughly 50% higher yield strength, and tolerates higher velocities and slightly hotter service. 70/30 also tolerates more aggressive chemistries, including higher sulphide and ammonia content, and is the grade specified for many main condenser bundles in power plants.

Cost runs roughly 90/10 < 70/30 < Monel 400 < Inconel 600 < Inconel 690. The decision is not "which is best" but "which is the lowest-cost material that survives the duty." When the service demands even higher temperature or higher corrosion resistance, the next step is Monel 400 or the Inconel 600 / 690 / 693 family, all of which are part of the wider alloy program that EZ STEEL INDUSTRIAL produces under the same quality system as the Cu-Ni line.

One detail that gets missed in the lab and surfaces in service is galvanic compatibility. Cu-Ni is noble relative to carbon steel. A Cu-Ni tube welded into a carbon steel flange stack, or routed through a steel support without isolation, will drive galvanic corrosion at the joint. The way to avoid this is to keep the joint in the same alloy family — Cu-Ni flanges on Cu-Ni pipe, Cu-Ni transition fittings where the material changes — and to electrically isolate any contact with dissimilar metals.

A Cu-Ni tube is only as reliable as the components around it. The most common procurement mistake on Cu-Ni projects is buying the tube from one supplier and the fittings and flanges from another. The result is a system with two or three different heat numbers, two or three different mill certificates, and a QA package that takes days to reconcile at site reception.

Why the tube is only half the answer

Galvanic compatibility at the joint decides whether the line sees a 30-year service life or a 5-year one. Material discipline at the joint — the same alloy family, the same heat number where possible, and the same surface condition — is what keeps the system corrosion-stable over time. The way to control this is to source tube, fittings, and flanges from a single qualified mill with full traceability.

Pipe fittings and pipe flanges

For Cu-Ni lines, butt-weld fittings to ASME B16.9 are the standard for high-pressure service. Socket-weld and threaded fittings are used on smaller-diameter instrument and utility lines. Pipe fittings in the same Cu-Ni grade eliminate the galvanic mismatch that a carbon steel elbow introduces at every change of direction. At the joint to a vessel or a header, the matching pipe flanges are typically weld neck to ASME B16.5, in the same alloy as the pipe, with the correct facing (RF for most service, RTJ for higher pressure class) and the matching stud bolt and gasket specification.

Copper nickel flanges for full-system compatibility

When the project specification calls for full Cu-Ni compatibility at the joint — which it should for ship seawater systems, offshore platform piping, and refinery cooling loops — copper nickel flanges are the cleanest answer. 90/10 and 70/30 flanges are forged to the same ASME B16.5 dimensional envelope as steel flanges, so they interchange with existing steel piping where isolation gaskets are used, and they match the chemistry of the Cu-Ni pipe exactly. Forged in matched heat numbers, the joint avoids the galvanic cell that drives most Cu-Ni field failures.

Heat efficiency tubes for higher duty

Where the heat duty is at the edge of plain Cu-Ni tube capability, the next move is not a higher alloy but a different tube geometry. Heat efficiency tubes with finned, low-finned, or rifled outer surfaces increase the heat-transfer area on the shell side and break up the boundary layer on the inner side, which is often where the thermal bottleneck sits. The alloy stays 90/10 or 70/30 Cu-Ni; what changes is the geometry and the heat-transfer coefficient.

The Cu-Ni program at EZ STEEL INDUSTRIAL is built on the same full-cycle manufacturing chain as the rest of the mill: incoming raw material inspection, hot extrusion, cold drawing, solution annealing where required, dimensional and surface inspection, and finished-goods packaging for export.

Mill capability

Annual output above 480,000 tons and a workforce of more than 500 staff support a deep inventory program in Cu-Ni 90/10 and 70/30 seamless pipe, welded pipe, condenser tube, and the matching fittings and flanges. The plant holds API, EN, and ASME certifications, with an ISO 9001 certified laboratory for in-house chemistry, mechanical, and corrosion testing. The export program is structured to ship from Changsha in seaworthy packaging, with customs paperwork and on-time dispatch handled in-house.

Test regime

Every Cu-Ni lot is released against a defined test program: chemical composition by spectrometer, mechanical properties (tensile, hardness, flattening, drift expansion), hydrostatic test, eddy current or ultrasonic test as the standard requires, and intergranular corrosion testing on request for nuclear and refinery critical service. Third-party inspection by ABS, SGS, BV, or the customer's nominated agency is available on every order and is recommended for first-time supply.

Documentation buyers actually ask for

The standard documentation bundle is a mill test certificate to EN 10204 3.1 (3.2 is supplied where the project specification requires it), a dimensional report, a surface finish report where relevant, packaging and marking photographs, and full traceability of heat number through the production route. For RCC-M II nuclear orders, the documentation depth is stepped up to match the safety authority's requirements and includes the additional traceability and audit records that nuclear procurement requires.

The savings from splitting a Cu-Ni order across two or three suppliers look attractive on a spreadsheet and almost never survive first contact with site. Three suppliers mean three quality systems, three delivery schedules, three mill test certificates, and three different approaches to packaging. When a discrepancy shows up at site, the contractor absorbs the cost of resolution, the delay, and the rework.

Sourcing tube, fittings, flanges, and the heat efficiency variant from a single qualified mill compresses the QA package into one document set, aligns the heat numbers where the project requires it, and produces one shipment plan that the project logistics team can act on. For refinery turnarounds, shipyard block deliveries, and modular power plant skids, this is the difference between a clean reception and a week of phone calls. EZ STEEL INDUSTRIAL was built around that bundle model, and the Cu-Ni program is one of the lines where it shows the most clearly.

Copper nickel alloy succeeds when alloy choice, joint system, and supplier discipline are aligned. 90/10 carries most seawater and refinery cooling duties economically. 70/30 steps in where velocity, temperature, or chemistry demand more. The fittings, flanges, and tube geometry need to be specified in the same conversation as the tube. The documentation bundle needs to be set at the RFQ, not at delivery. When all of that is done by a single qualified mill, the result is a system that installs on schedule and runs for the design life without drama.

For a Cu-Ni project quotation, the engineering team at EZ STEEL INDUSTRIAL works from a standard enquiry package: material standard (ASTM B466, EN 12451, GB/T 8890, EEMUA 234, JIS H 3300, or RCC-M II), grade (90/10, 70/30, or a higher nickel alloy), size (OD × wall × length), quantity, end use, and destination port. A mill-traceable quote is returned within one business day, and a project-bundle quote covering tube, pipe, fittings, flanges, and the heat efficiency variant follows within five working days.