Why Copper-Nickel Still Runs Today's Seawater Service

For more than seventy years, the two workhorse grades of copper nickel alloy — 90/10 (CuNi10Fe1Mn) and 70/30 (CuNi30Fe1Mn) — have been the default material for piping, heat-exchanger water boxes, and ship hulls that live in seawater. The reason is practical: a thin, self-healing oxide film forms on the inner surface within the first few months of service, then drives the long-term corrosion rate down to a few thousandths of a millimetre per year, while keeping biofouling lower than almost any other metal option.

That single property — predictable, low-rate corrosion in clean, aerated seawater — is what keeps 90/10 and 70/30 at the top of the procurement list for shipyards, FPSO builders, and offshore platform designers. The challenge is not whether to use copper-nickel; it is which grade, which product form, and which fabrication partner can deliver to project specification without surprises on the quayside.

Quick Selection: 90/10 or 70/30?

A common mistake is to assume 70/30 is simply a "stronger 90/10." It is, but it is also a different beast in the workshop and on the order form. The table below covers the differences engineers most often need in writing specs.

Rule of thumb: if the design velocity stays under 2.5 m/s and the service is hull-side seawater, shipboard sanitary, or platform firemain under 100 mm, 90/10 saves money without giving up performance. When the spec demands higher velocity, higher temperature, or stricter corrosion margins, 70/30 is the safer call.

Standards You Will Be Quoted Against

Copper-nickel buyers tend to be a standards-literate group, because the spec sheet drives which heat, which mechanical test certificate, and which dimensional tolerance the mill will produce. Make sure your inquiry references the right combination of standards rather than a generic "seawater grade":

• ASTM B466 / B467 — seamless and welded pipe (C70600 for 90-10, C71500 for 70-30). For products that will be welded downstream, specify C70620 / C71520 instead.
• ASTM B111 — seamless condenser and heat-exchanger tubes in copper-nickel.
• ASTM B552 — seamless and welded Cu-Ni tubes for desalination and marine service.
• EEMUA 234 — the de facto offshore standard for 90/10 piping, including bend geometry, weld prep, and hydrostatic test requirements.
• EN 12451 / EN 1652 — European designations for tubes and plate/sheet; useful when shipping into EU yards.
• BS MA18 — older but still cited for salt-water piping in some ship classes; it sets the maximum design velocity figures that many specifiers still rely on.

When suppliers quote "to standard," ask for the specific number plus the condition (annealed, light drawn, etc.). The wrong condition is the single most common cause of rejected shipments.

Designing the System, Not Just the Pipe

Pipe is the headline product, but most seawater systems fail first at the joints. For a coordinated package, look at three product groups together:

Pipe and tube. Specify ASTM B466 seamless or welded pipe for line pipe, ASTM B111 for condenser and heat-exchanger tube, and ASTM B552 when the project is desalination or marine water treatment. Wall thickness and dimensional tolerance need to be matched to the joining method — flanged, butt-welded, or brazed — not chosen independently.

Copper nickel flanges and complementary steel flanges. 90/10 and 70/30 flanges are commonly delivered to ASME B16.5 / B16.47 dimensions, but offshore projects frequently default to EEMUA 234 flange geometry. When you mix Cu-Ni pipe runs with steel branch connections, lock down the dissimilar-metal weld procedure (65% Ni-Cu consumable is the industry default) at the inquiry stage, not during fabrication.

Supporting fittings and bolting. Elbows, tees, reducers, and stud-bolt-and-gasket sets should be ordered as one engineering package rather than as separate line items. Pipe fittings and gasket stud bolt nut assemblies sourced from the same mill reduce paperwork and remove one of the most common sources of MRO downtime — the wrong gasket on a Cu-Ni flange face.

Fabrication Notes That Save Shipyard Time

Copper-nickel is unforgiving of contaminated surfaces. The first three rules below look mundane and are the reason most pre-fabrication NDT failures are avoided:

• Keep an area of the workshop clean and dry that is dedicated to Cu-Ni. Do not share grinding discs or stainless wire brushes between Cu-Ni and carbon-steel jobs.
• Store sheets vertically, not flat, and keep them in original packing until they go into the lay-up. Marking crayons and paint overspray must be removed before any joint fit-up.
• Use 70-30 Cu-Ni filler for both 90-10 and 70-30 welds; interpass temperature below 150 °C to avoid microfissuring; backing gas (argon) on the root run for pipe welds.

Bending is well within reach of most yards: rotary draw and 3-roll bending will produce tube bend radii down to twice the tube diameter; tighter radii need prefabricated bends. Cold work above 20% will roughly halve elongation and double proof strength, so plan intermediate anneals into heavy fabrication work rather than discovering the issue at the hydrostatic test.

Bringing It Together: A Practical Project Workflow

For a typical FPSO seawater cooling or a platform firemain upgrade, the workflow below keeps engineering, procurement, and fabrication in step:

1. Lock the design conditions — fluid, max continuous velocity, design temperature, biofouling control method, and any chlorination or sulfide exposure.
2. Pick the alloy grade (90/10 or 70/30) and reference the standards on the datasheet (ASTM B466, EEMUA 234, EN 12451, etc.).
3. Issue one inquiry for pipe, flanges, fittings, gaskets, and stud-bolting — not five separate RFQs — to keep the MTR trail clean.
4. Validate the WPS for similar-metal and dissimilar-metal welds at the first-article stage, not at the production stage.
5. During commissioning, avoid running sulfide-polluted water through fresh Cu-Ni lines for the first 3 months; the protective film needs clean, aerated seawater to mature.

Buyers who follow that sequence end up with systems that hit 25–30 year service intervals with predictable, low-rate corrosion — which is the whole point of choosing copper-nickel in the first place.

Where EZ Steel Industrial Fits

EZ Steel Industrial has produced industrial pipe, fittings, and flanges from its base in Changsha, China since 1994, and now runs more than 500 employees across eight product lines. The copper and nickel alloy range covers petrochemical, marine and shipbuilding, and power-and-aerospace grades, with 90/10 and 70/30 available in seamless and welded pipe, condenser tube, plate, and flanges to ASTM B466, B467, B111, B552, EN 12451, and EEMUA 234.

Marine and shipbuilding buyers can move directly to the stainless steel pipe and Cu-Ni product range on the marine category page, where 90/10 and 70/30 tube, pipe, and flanges are listed with their governing standards. For the broader package — steel flanges, butt-weld fittings, gasket sets, and stud bolts — the pipe flanges and fittings pages carry the matching inventory. Coordinating the full seawater package through a single mill removes the MTR-traceability gaps that cause the most paperwork during FAT and class survey.