Why Copper-Nickel Keeps Showing Up in Three Very Different Plants

Copper-nickel alloys (UNS C70600 for 90/10 and UNS C71500 for 70/30, plus the related EEMUA 144 and 234 grades) are unusual in the non-ferrous world because they resist three failure mechanisms at once: general seawater corrosion, biofouling-driven under-deposit attack, and stress-corrosion cracking in brackish or polluted cooling water. The 90/10 grade is the workhorse for ship piping, offshore seawater systems, and coastal power plant auxiliary cooling. The 70/30 grade carries the higher temperature, higher velocity, and more aggressive water-chemistry duties, including refinery overhead condensing and desalination plant brine circuits.

The economic logic is consistent across all three. The installed cost of a Cu-Ni tube bundle is higher than carbon steel, but the life-cycle cost is lower because the bundle does not need cathodic-protection retrofits, internal linings, or a mid-life replacement. For projects that design for 20 to 30 year service intervals — and almost every refinery, ship, and coastal power plant does — that is the only calculation that matters.

Service Environment 1 — Marine and Offshore Seawater Systems

Ship bilge, ballast, fire-fighting, and seawater cooling circuits are the original home of 90/10 Cu-Ni. EEMUA 234 and the related ASTM B466 / B467 standards govern the tube chemistry, dimensional envelope, and hydrostatic test pressure. A 90/10 specification written for a 30,000 DWT chemical tanker should also lock down the following five items, which together decide whether the system will pass class survey on the first drydock:

• Maximum water velocity cap (commonly 3.5 m/s for 90/10 in clean seawater, 2.5 m/s in silty or shallow-water harbours) to prevent erosion-corrosion at fittings.
• Sulphide and ammonia limits in service water, since polluted harbour water can break the protective surface film and trigger pitting.
• Joint method: TIG or MIG with matching Cu-Ni filler (e.g. ERCuNi for 90/10), or mechanical grooved coupling where class society allows.
• Cathodic compatibility: zinc or aluminium anodes sized for the structure, because stray current from incorrectly isolated steel hulls will attack the Cu-Ni.
• Class society documentation: full MTR per heat, hydrostatic test report, and traceability sheet per the IACS or the relevant flag administration.

For offshore wind substations and FPSO seawater modules, the same 90/10 specification is used with a tighter velocity limit (typically 2.5 m/s) and an additional oxygen-content check, because the closed-loop cooling on those platforms often runs at higher dissolved oxygen than ship-side systems.

Service Environment 2 — Petrochemical and Refinery Condensers

In refinery service, copper-nickel appears mainly in overhead condensers, sour-water stripper reboilers, and amine unit heat exchangers, where the combination of hydrocarbon vapour, condensed water, and trace chloride makes carbon steel a one-to-three-year story. 70/30 (UNS C71500) is the standard for those duties. ASTM B111, B395, and B466 cover the tube; ASME SA179 and SB111 cover the bundle; and the welding procedure specification is typically written to ASME Section IX.

A 70/30 specification written for a CDU overhead condenser should pin down the operating window, not just the alloy. The key parameters that an experienced refinery buyer puts in writing are:

• Tube-side and shell-side design pressure and temperature, with explicit corrosion allowance on the shell-side (commonly 1.5 mm for 70/30 in overhead service).
• Water-chemistry envelope: chloride limit (typically < 50 ppm for 70/30 to avoid SCC), pH window 7.0 to 9.0, and total suspended solids < 10 ppm to keep the film intact.
• Bimetallic isolation at tube-to-tubesheet joints, to prevent galvanic attack when the tubesheet is stainless or titanium-clad.
• Tubesheet cladding material matching the tube alloy, or a qualified explosive-bonded transition joint, with full traceability on the cladding chemistry.
• Cleaning regime: sponge-ball or chemical cleaning cycle, with documented compatibility from the supplier — because a Cu-Ni tube that is cleaned with the wrong acid will pit within a single turnaround.

For an LNG plant or an ethylene plant cooler running brackish cooling water, the same 70/30 specification is extended with a chloride-controlled service-water analysis report attached to the MTR file. That single attachment has ended more procurement disputes than any other document, because it puts a number on the side of the spec that is most often left vague.

Service Environment 3 — Coastal Power Plant and Desalination Cooling

Coastal and offshore power plants, including the auxiliary cooling systems on offshore wind converter stations, run their main and auxiliary condensers on once-through or closed-loop seawater. Here the design driver is biofouling: barnacle, mussel, and algal growth on the water-side wall is what determines the actual cleaning interval, not the corrosion rate. 90/10 is the standard, with 70/30 reserved for the higher-temperature, higher-velocity auxiliary coolers where biofouling is mitigated by chlorination or sponge-ball cleaning.

The specification language a power-plant buyer should insist on is essentially a pairing of the marine and the petrochemical language above, with the addition of:

• Intermittent chlorination compatibility: free chlorine residual not exceeding 0.5 ppm continuous or 1.0 ppm intermittent, since Cu-Ni tolerates chlorination but not peroxide or bromide-based alternatives.
• Maximum sand and silt content on the inlet, because erosion at the tube ends accounts for a large share of the unplanned outages on coastal units.
• Tube-sheet and water-box material pairing, since the water box is almost always carbon steel with a rubber or epoxy liner — and the Cu-Ni tube-to-liner seal is the leak path that triggers a scheduled outage.
• For desalination plants: a clear statement of brine temperature, salinity range, and recovery ratio, because the Cu-Ni film behaves differently at 8% brine versus open seawater.

The result is a specification that, in writing, looks very similar across all three environments. The differences are in the four or five quantitative limits that the spec sets on the service envelope. That is by design, because a mill that can meet the strictest version of those limits will also meet the others.

The Common Specification Backbone: Chemistry, Mechanical, and Documentation

Whatever the service environment, three items belong in every copper nickel alloy specification. They are also the three items most often left out of "industry standard" RFQs:

Pairing Copper-Nickel Tubes with the Rest of the Heat Exchanger Package

A Cu-Ni bundle is only as reliable as the joints, the channel covers, the inlet and outlet valves, and the structural pipe that connects it to the rest of the plant. Sourcing each of those from a separate vendor is how projects end up with a 90/10 tube paired to a carbon steel flange that fails the bimetallic isolation check, or a industrial valve trim that is incompatible with the cooling-water chemistry.

A single-source package from one quality system eliminates those risks. The matching copper nickel flanges are supplied in the same heat, with the same MTR chain, the same surface finish, and the same delivery schedule as the tubes. The gasket stud bolt nut set is sized for the flange class and the bolt-loading curve of the joint, not a generic catalogue pick. The connecting pipeline works scope — including any transition to the plant carbon steel or stainless line — is engineered in the same drawing set. The heat exchanger fabricator and the end client audit one file instead of five, and the field erection crew opens one crate of matched parts instead of five.

For shipyards, the same logic extends to the supporting structure works scope, including the tube supports, the pipe racks, and the sea-chest penetrations. For power plants, it extends to the structural pipe supports and the condenser saddles. In every case, the engineering question is the same: which other line items have to move in the same MTR chain as the Cu-Ni tube, and is the supplier able to deliver that file as one document set?

A Field-Tested RFQ Checklist for Copper-Nickel Alloys

Before a Cu-Ni RFQ goes out, the procurement engineer should be able to answer all eight items below without leaving the datasheet. A supplier that answers them all in the first round is a supplier that will also meet the inspection plan and the delivery window.

• Alloy and temper: 90/10 (C70600) or 70/30 (C71500), annealed or light-drawn, with the standard printed (ASTM B466, B111, EEMUA 234, GB/T 8890, JIS H 3300).
• Service envelope: tube-side fluid, shell-side fluid, design temperature, design pressure, maximum velocity, chloride and sulphide limits, cleaning regime.
• Dimensional envelope: OD, wall, length, straightness, and for U-bent bundle applications, leg length and bend radius tolerance.
• Joining method: welding procedure (TIG / MIG / brazing), filler metal grade, post-weld stress relief, and bimetallic isolation at the tubesheet.
• NDT scope: hydrostatic, eddy current, ultrasonic, PMI, with the sampling rate per lot and the acceptance criteria written into the spec.
• Documentation set: 3.1 MTR, dimensional report, NDT report, heat-treatment chart, traceability code, and any class society or ASME data reports that apply.
• Surface protection, end capping, and sea-freight packaging suitable for annealed non-ferrous tubes.
• Bundled scope: matching Cu-Ni flanges, gasket and stud-bolt set, isolation valves, and the connecting pipeline / structure work from the same quality file.

From Specification to Commissioning: A Single-File Supply Model

The reason a single-file supply model matters for copper-nickel more than for any other non-ferrous is simple: a Cu-Ni bundle is usually the highest-cost line item in a heat exchanger, and it is also the line item with the longest lead time and the largest field-replacement penalty if the order goes wrong. Spending an extra 10 to 15 percent on the specification and the mill audit, and choosing a supplier that can deliver the matched flanges, gaskets, valves, and connecting piping in the same documentation file, is what keeps that line item from becoming the project's most expensive unplanned outage.

That is the supply model we have refined since 1994 at EZ STEEL INDUSTRIAL: a single quality file, a single MTR chain, a single delivery schedule, and a single point of accountability from raw tube to assembled bundle. The same documentation discipline that holds on a 30,000 DWT chemical tanker holds on a 200,000 bpd refinery and on a 1,000 MW coastal power plant. That is what makes the difference between a copper nickel alloy order and a copper nickel alloy project.