The Real Challenge of Seawater Service

Seawater is not just "corrosive." It is a living, biofouling, chloride-rich, velocity-sensitive fluid that punishes most engineering metals in subtle ways. Stainless steels that look perfect on day one can suffer pitting, crevice attack, and stress corrosion cracking once chloride concentration, temperature, and flow velocity combine in real operating conditions.

That is why, for shipbuilding, offshore platforms, and coastal power plants, engineers have relied on copper-nickel alloys since the 1950s. The 90/10 and 70/30 grades offer a rare combination: high resistance to seawater corrosion, natural resistance to biofouling, excellent ductility for bending and flaring, and predictable long-term performance.

How Copper-Nickel Alloy Resists Seawater

The corrosion resistance of Cu-Ni alloys comes from a thin, adherent, self-healing oxide film that forms on the inner surface in contact with seawater. Once this film is established, it protects the base metal even under high flow velocity and stops biofouling organisms from attaching to the wall.

In practical terms, this means:

• Stable corrosion rates below 0.05 mm/year in clean seawater, even after years of service
• Resistance to pitting and crevice corrosion in chloride-rich environments
• Tolerance to velocities up to 3.5 m/s for 90/10 and higher burst strength from 70/30
• No need for cathodic protection of the tube itself, simplifying installation

For comparison, common 304/316 stainless steel tubes can suffer pitting once temperatures rise above 40 掳C combined with chlorides, a routine condition in engine rooms and heat-exchanger service.

90/10 vs 70/30: Choosing the Right Grade

Both grades belong to the same Cu-Ni family, but they are designed for different pressure and velocity envelopes. Selecting the correct one up front prevents over-specifying cost or under-specifying safety.

If your system is a standard seawater cooling line or a shipboard fire-fighting main, 90/10 is the most economical and widely specified choice. If the line sees higher pressure, elevated temperature, or aggressive brine, 70/30 earns its premium.

Standards You Will See on Every Datasheet

A trustworthy copper-nickel tube supplier should be fluent in the standards your engineer writes into the spec. At our facility, every marine Cu-Ni tube is produced and tested against the following specifications:

• GB/T 26291 — Chinese standard for marine Cu-Ni seamless tubes
• MIL-T-16420K(SH) — U.S. military specification for shipboard Cu-Ni piping
• ASTM B466 / B467 — seamless and welded Cu-Ni pipe
• DIN 86019 — German standard for Cu-Ni butt-weld fittings
• EN 2871 / BS 2871 — European copper and copper alloy tubes
• EEMUA 144 / 234 — the offshore industry's reference for 90/10 and 70/30 Cu-Ni

When a project mixes standards — for example, EEMUA tubes with DIN fittings — sourcing from a single manufacturer removes the dimensional and metallurgical mismatch that often causes installation delays.

Why One Project, One Supplier Matters

Tube is only half the package. A working seawater system also needs flanges, elbows, tees, gaskets, stud bolts, and isolation valves — all in materials that match the corrosion environment. Specifying each line item separately is a recipe for mismatches.

As a single source for the full piping package, EZ Steel Industrial can deliver Cu-Ni tubes together with the matching pipe fittings (butt-weld, socket-weld, and threaded), Cu-Ni and steel flanges, spiral-wound gaskets with stud bolts, and the industrial valves that close the loop. One heat number, one mill test certificate file, one delivery — all traceable back to the original heat.

Our marine and shipbuilding tube line covers cold-finished and hot-finished seamless Cu-Ni pipe, plus welded Cu-Ni tube in standard sizes, with full dimensional and wall-thickness tolerance tables available on request.

Where EZ Steel Industrial's Cu-Ni Tubes Are Already Working

Over the past thirty years, our copper-nickel tubing has been specified into:

• Shipboard seawater cooling systems and bilge lines for commercial and naval vessels
• Offshore platform fire-fighting and ballast piping, built to EEMUA 144/234
• Coastal power plant once-through cooling circuits
• Refinery overhead condensers and desalination plant heat exchangers
• Marine heat-exchanger bundles using U-bend Cu-Ni tubes

Each shipment leaves our facility with full EN 10204 3.1 mill certificates, hydrostatic or eddy-current test records, and, where required, third-party inspection reports from organizations named in the purchase order.

How to Specify Cu-Ni Tubing on Your Next RFQ

To get a fast, accurate quotation, include the following six items in your inquiry:

• Material grade (for example C70600 / 90/10 or C71500 / 70/30)
• Standard (EEMUA 144, ASTM B466, MIL-T-16420K, GB/T 26291, etc.)
• Outer diameter and wall thickness, or the size table reference
• Service condition: seawater, brackish water, brine, or chemical duty
• Required testing: hydrostatic, eddy current, PMI, or third-party witness
• Matching fittings, flanges, and valves if you want a single shipment

With these in hand, our engineering team can return a technical offer, a price, and a realistic delivery window in days, not weeks.