Why Copper-Nickel Still Wins in Seawater Service

Decades after the first offshore platform was commissioned, 90/10 and 70/30 Cu-Ni remain the default choice for shipbuilding seawater cooling, firewater mains, and desalination intake lines. The reason is not nostalgia — it is iron content. The small but controlled iron and manganese additions in C70600 (90/10) and C71500 (70/30) form a stable, self-healing oxide film that resists biofouling and impingement attack in flowing seawater far better than austenitic stainless grades.

In practice, this means a Cu-Ni line on a platform or a chemical tanker can run for decades with only flushing and minor anode replacement, where a stainless steel pipe in the same service often suffers from crevice and pitting corrosion in under five years. For procurement engineers, that reliability translates directly into OPEX, inspection intervals, and class-society survey costs.

90/10 vs 70/30: Pick the Alloy for the Service, Not the Catalog

The most common engineering error on copper-nickel procurement is treating 90/10 and 70/30 as interchangeable. They are not. 90/10 (UNS C70600) is the default for general seawater service — firewater, ballast, cooling, and HVAC — where flow velocity stays below roughly 3.7 m/s and temperatures are moderate. 70/30 (UNS C71500) is the upgrade you specify when salinity is high, water is polluted or stagnant, or velocities run higher and erosion risk increases.

For offshore platforms, the safer reference is EEMUA Publication 234, which covers 90/10 and 70/30 seamless and welded tube, dimensional tolerances, and the inspection regime expected for North Sea and Middle East operators. The equivalent ASME and ASTM route — B466 (seamless) and B467 (welded) — is the preferred path for shipyards working to naval or commercial class rules.

What a Tight Cu-Ni Specification Actually Contains

A specification that survives a third-party audit has six non-negotiable blocks. Each one protects a different failure mode and each one must be in writing before the mill test certificate is issued.

• Alloy designation with UNS number and temper (annealed, as-drawn, or hot-finished)
• Outside diameter, wall thickness, length, and end finish (plain, beveled, grooved)
• Chemical composition limits, especially Fe, Mn, Zn, Pb and S for marine service
• Mechanical properties — tensile, yield, elongation, hardness — referenced to ASTM B466, B467, or EEMUA 234
• Inspection and testing — eddy current or hydrostatic NDT, with EN 10204 3.1 or 3.2 certification
• Marking, traceability, and packaging requirements to survive containerized export

Skipping any one of these blocks is how a project ends up with tubes that look identical on the dock but carry the wrong heat number, the wrong temper, or no traceability at all.

A Cu-Ni Line Is Never Just Tubes

Field experience shows that the corrosion and leak path in a seawater system rarely lives in the straight pipe — it lives in the joint. A serious Cu-Ni procurement bundle therefore pulls in the components that actually touch the tube ends, not just the line item on the requisition.

Bundling these items under one supplier removes the classic failure mode of mismatched delivery dates — where the tubes arrive on site and the flanges sit on a dock in another port. It also gives the engineer a single point of accountability for MTC, traceability, and any non-conformance raised at the receiving inspection.

Inside a 32-Year-Old Cu-Ni Supply Program

EZ Steel Industrial has been producing and exporting copper-nickel tubes, pipe flanges, and matched industrial valves since 1994 from a 480,000-tonne annual capacity base in Hunan, China. The program covers the standards the marine and petrochemical market actually specifies — GB/T 26291, MIL-T-16420K(SH), ASTM B466/B467/B165, DIN 86019, EN/BS 2871, and EEMUA 144/234 — and ships seamless and welded Cu-Ni tubes in cold-finished and hot-finished conditions with full EN 10204 3.1 mill certification.

What sets a project-grade supply apart from a commodity shipment is the documentation chain: heat-number traceability from the melt, controlled chemical limits for Fe and Mn, hydrostatic or eddy-current NDT on every tube, and packaging that survives six weeks in a sea-freight container. When that chain is in place, the receiving inspector signs the MTC on the first pass and the project avoids the 4–8 week rework loop that quietly kills Cu-Ni schedules.

A Practical Pre-Order Checklist for Buyers

Before releasing a copper-nickel RFQ, walk through these checks. They are the difference between a clean order and a multi-month correspondence cycle with the mill.

• Confirm service fluid, maximum velocity, temperature, and chloride profile — these decide 90/10 vs 70/30
• Lock the standard family (EEMUA 234, ASTM B466/B467, EN 12451) before the quotation round
• Specify temper, end finish, and length tolerance in the RFQ — not as a follow-up email
• Require MTC to EN 10204 3.1 (or 3.2 for third-party witnessed lots)
• Bundle flanges, valves, and bolting to the same supplier and the same shipment window
• State marking, packaging, and containerization requirements in writing