If you are sizing pipework for a seawater cooling loop, a firefighting main on a chemical tanker, or a platform sea-water lift, the conversation almost always comes back to one alloy family: copper nickel alloy. The reason is simple. Seawater is a uniquely aggressive service: chlorides, biofouling, galvanic coupling and erosion in one. Few materials survive the full mix without either exotic cost or coating maintenance. 90/10 and 70/30 Cu-Ni have been doing that job for more than half a century, and modern procurement still leans on them — provided the specification is written correctly.

This guide distils what an engineer really needs to lock down before placing a mill order: which grade fits the service, which standards to reference, how the tube package connects to flanges and fittings, and what to verify on the test certificates. The recommendations below reflect the working portfolio of ezindustrialtube.com and the way its buyers actually bundle Cu-Ni with the rest of the pressure boundary.

Why Copper Nickel Alloy Is Still the Default Seawater Material

The two production grades that do most of the work are 90/10 (UNS C70600, CN102) and 70/30 (UNS C71500, CN107). They share the same corrosion mechanism — a thin, self-healing oxide film that reforms if the surface is scratched — but they trade off mechanical strength against resistance to higher-velocity flow.

For most newbuild and offshore packages, 90/10 is the right default: it is cheaper, easier to weld and accepted by every major class society. Step up to 70/30 only when design flow velocity is high, when the line is carrying brackish or polluted water, or when the upstream system includes hot brine or sour condensates.

The Standards You Actually Cite in the Purchase Order

A clean Cu-Ni specification should reference the producing mill standard, the testing standard, and a recognised fabrication or class standard. The most common combination for marine and offshore buyers is:

• Tube / pipe: ASTM B466 (seamless), B467 (welded), B552 (U-bend); EN 12451; BS 2871; GB/T 8890; JIS H 3300.
• Flanges: ASME B16.5 / B16.47 with Cu-Ni material per ASME SB151 or EEMUA 234.
• Class / fabrication: EEMUA Publication 144 for offshore, plus class society rules from DNV, Lloyd's Register, ABS or CCS.
• Quality system: EN 10204 type 3.1 mill certificate, with option 3.2 for class-notified work.

On the customer side, this is exactly the bundle available in the Copper & Nickel Alloy category: tubes to ASTM B466 / B467 / B552, complemented by flanges, fittings and the pressure-boundary gaskets, stud bolts and nuts needed to complete a line.

Matching the Tube Package to the Rest of the Pressure Boundary

The most common specification mistake is buying a beautiful Cu-Ni tube, then connecting it with carbon-steel flanges and standard graphite gaskets. Galvanic corrosion will attack the tube at the joint, and a paper-graphite gasket will fail when the line warms. Treat the run as a system:

• Flanges: Specify copper nickel flanges in 90/10 or 70/30 to ASME B16.5; for higher pressures or offshore headers step up to B16.47 Series A. Avoid galvanic couples to carbon steel — they will consume the Cu-Ni stub end first.
• Fittings: Use Cu-Ni elbows, tees and reducers with the same UNS designation as the tube. Brazed joints use silver-bearing fillers (e.g. BCuP-3 for Cu-Ni to Cu-Ni); welded joints use a matching filler such as ERCuNi.
• Gasket, stud bolt & nut: Specify non-asbestos compressed fibre or PTFE for cold service, spiral-wound with graphite for hot or firewater duty. Bolting should be naval brass or Cu-Ni–clad where a fully matched system is required, otherwise aluminium bronze (ASTM F468) is a common compromise. The matching parts sit in the gasket stud bolt nut range.
• Valves: Gate, globe and check valves on Cu-Ni lines should be bronze or Cu-Ni bodied with the same seat material, to avoid the same galvanic issue at the trim.

What to Check on the Mill Test Certificate

A correct EN 10204 3.1 certificate for a Cu-Ni tube should show, at minimum, the following information matched to the order:

• UNS designation (C70600 or C71500) and the producing standard (B466 / B467 / B552 / EN 12451).
• Heat number and chemical composition, including Fe (1.0–1.8 % for 90/10) and Mn (0.5–1.0 %) — these are the corrosion-resisting additions, not residuals.
• Mechanical results: tensile strength, yield (0.2 % offset) and elongation, tested on the lot.
• Hydrostatic or eddy-current test confirmation per the standard cited.
• For class work, an independent 3.2 certificate signed by an IACS surveyor.

If a mill can only deliver a 2.1 or 2.2 certificate for a class-notified line, that is a stop-the-clock finding. Push back before the pipe is shipped.

Bundling the Order So the Project Stays on Schedule

Seawater systems on vessels and offshore modules are usually small in tonnage but large in line-item count: a few hundred metres of tube, a few dozen flanges, a few hundred gaskets, and several hundred stud bolts. If those arrive on six different trucks from six different suppliers, the site spends more time chasing paperwork than installing. The faster workflow is to procure the whole pressure boundary from one source, on one purchase order, with one certificate pack.

This is the logic behind a bundled procurement approach: align the Cu-Ni tube, the Cu-Ni flanges, the matching gaskets and stud bolts, and the line valves into a single shipment. Inventory holding drops, the MTR cross-references are cleaner, and the receiving inspection is done once instead of five times.

Where EZ STEEL INDUSTRIAL Fits

EZ STEEL INDUSTRIAL has been producing and exporting industrial pipe, fittings, flanges, valves and bolting from Changsha, China since 1994, with API, EN and ASME-certified output and ISO 9001-accredited lab testing. For seawater work specifically, the relevant inventory lines are:

• Seamless and welded Cu-Ni tube per ASTM B466 / B467 / B552, EN 12451, BS 2871 and JIS H 3300.
• Cu-Ni flanges (90/10 and 70/30) to ASME B16.5 / B16.47.
• Monel, Inconel and nickel-alloy tubes for the higher-temperature ends of the system.
• Non-metallic and spiral-wound gaskets, plus naval brass and aluminium bronze stud bolts, to complete the joint.