Why copper nickel alloy still dominates seawater service

For more than half a century, 90/10 (UNS C70600) and 70/30 (UNS C71500) copper-nickel tubes have been the default choice for shipboard piping, offshore cooling water, and desalination plant brine systems. The reasons are well documented: a self-healing protective oxide film that forms in clean seawater, excellent resistance to biofouling compared with carbon alternatives, good thermal conductivity for heat-exchanger duty, and a predictable corrosion rate below 0.025 mm/year under typical flow conditions.

What is less often discussed is that the system only performs as well as its weakest link. A perfectly specified 90/10 tube welded to a carbon-steel flange with no isolation gasket will suffer galvanic attack at the joint. A 70/30 tube installed in a stagnant section will pit, regardless of how clean the bulk supply is. Procurement plays a direct role in preventing both failure modes by bundling the right materials together.

Step 1: Define the service envelope before you quote

Engineers who jump straight to a 90/10 vs. 70/30 comparison before they know their velocity, temperature, and chloride range usually over-specify on alloy content and under-specify on joint design. Before requesting a quote, lock down the following five parameters:

• Fluid: seawater, brackish water, treated brine, or a chemical mix with chlorides and sulfides.
• Design temperature and pressure: including any upset cases, not just the normal operating point.
• Flow velocity: target 2.0–3.5 m/s for 90/10, up to 4.0 m/s for 70/30, to stay within EEMUA 234 guidance.
• Service life expectation: 20 years for naval hull service, 30+ years for onshore desalination skids.
• Inspection and certification level: EN 10204 3.1 vs. 3.2, third-party hold points, and PMI requirements.

These five numbers set every other decision: alloy ratio, temper, flange class, gasket style, and the type of bolting. Sharing them up front in your RFQ prevents suppliers from quoting to the wrong standard.

Step 2: Choose the right alloy and temper

Both common grades of copper nickel alloy work in seawater, but they answer different questions. The table below is the decision matrix we use with most of our marine and offshore customers.

Temper selection: annealed vs. as-drawn

Annealed (O temper) is the default for tube bundles that need bending, flaring, or expansion into tube sheets — most heat-exchanger and U-bend applications. As-drawn (H temper) gives higher strength for straight pipe runs in engine rooms or pump suction lines. For U-bend service specifically, confirm that the mill supplies bend radii to EEMUA 144 and provides post-bend stress relief, otherwise the cold-worked outer wall can be a corrosion initiation site.

Step 3: Pair the tube with the right flanges and gaskets

A copper-nickel tube welded to a carbon-steel flange is the single most common cause of accelerated galvanic attack in seawater systems. Two practical approaches solve this:

For the bolting itself, specify stainless-steel stud bolts to ASTM A193 B8/B8M with B8M nuts in chloride service, and use a compatible gasket — spiral-wound with non-asbestos filler, or RTJ for higher classes. These items all live under the same gasket stud bolt nut product line and are easiest to procure as a single bundle.

Step 4: Decide what actually belongs in the bundle

One of the most expensive mistakes on a copper-nickel project is splitting procurement by material family, then trying to coordinate four different suppliers at site. A bundled scope — one PO, one MTR pack, one delivery — typically reduces interface defects by half on hull and platform projects. The standard bundle covers:

• Copper-nickel tubes and pipes to ASTM B466 / EEMUA 234, in seamless or welded form as required.
• Butt-weld fittings (elbows, tees, reducers) matched to the tube grade and temper.
• Copper-nickel pipe flanges in weld-neck or slip-on style to ASME B16.5, in 150# to 600# classes.
• Gaskets, stud bolts, and nuts that are compatible with both Cu-Ni and any stainless transition pieces.
• For heat-exchanger service, the matching U-bend tubes and finned tubes, drawn from the same heat lot where possible.

"Most field failures in seawater systems are not material failures. They are coordination failures between the tube, the flange, and the bolting."

Step 5: Insist on documentation that protects you in service

Paperwork is not bureaucracy — in a copper-nickel system it is the only way to confirm twenty years later what is actually in the pipe. The minimum documentation set for a procurement order should include:

• Mill test certificate to EN 10204 3.1 (or 3.2 if third-party witnessed).
• Chemical composition including the critical iron and manganese ranges for 90/10 (1.0–1.8% Fe, 0.5–1.0% Mn) — these control the protective film.
• Mechanical properties: tensile strength, yield, elongation, hardness.
• Hydrostatic or eddy-current test report for every tube length.
• PMI (positive material identification) results on flanges and fittings, to prevent mix-ups at receipt.
• Heat-number traceability linking tubes, flanges, fittings, and bolting back to the same production batches.

A supplier that can deliver this as a single indexed PDF — not twenty separate attachments — will save your QA team hours per shipment.

Step 6: Match the supplier to the project, not the other way around

A copper-nickel tube mill is not automatically a copper-nickel system supplier. When you are running a multi-discipline project — ship, platform, desalination skid, petrochemical cooling loop — what you need is one accountable source that can deliver the tubes, the pipe flanges, the fittings, and the bolting as a coordinated package. That means a mill with a broad inventory of ASTM A106, A312, and B466 grades, in-house NDT, and a track record of MTR packs that have already been accepted by classification societies and EPCs.

EZ STEEL INDUSTRIAL has been producing industrial steel and copper-nickel piping since 1994, with an annual capacity above 480,000 tons and a documented product line spanning carbon, stainless, and copper-nickel alloy tube, plus the full flange, fitting, gasket, and industrial valves range that typically travels with a seawater scope. For buyers who want one RFQ, one PO, and one delivery that holds together under audit, that bundle model is usually the difference between a clean commissioning and a six-month punch list.

A short checklist for your next RFQ

• Fluid, temperature, pressure, velocity, and target service life.
• Alloy choice with a written reason (90/10 vs. 70/30).
• Standard reference: ASTM B466 / EEMUA 234 / EN 12451.
• Flange material matched to tube or with an explicit transition plan.
• Gasket, stud bolt, and nut material specified together.
• EN 10204 3.1 or 3.2 certification, with PMI on flanges and fittings.
• Single-bundle delivery scope where the project allows it.