When a piping system runs seawater, brackish cooling water, sour hydrocarbons or a hot brine stream, carbon and stainless steels often reach their limits. Engineers turn to copper nickel alloy tubing because it combines corrosion resistance, biofouling resistance, easy fabrication and excellent thermal conductivity in a single material. This guide walks procurement, project and quality teams through what to specify, what to ask a mill, and how to avoid the most common pitfalls when buying Cu-Ni tubes, plates and flanges for industrial projects.

Copper-nickel alloys (typically 90/10 Cu-Ni and 70/30 Cu-Ni) form a stable, adherent oxide film in seawater. This film is self-healing, resists biofouling and tolerates moderate flow velocities better than most stainless grades. Two consequences matter in real projects: lower lifetime maintenance cost, and fewer unplanned shutdowns caused by pitting or stress-corrosion cracking.

• 90/10 Cu-Ni (C70600): the most widely used grade for shipbuilding, seawater cooling, fire-fighting and desalination piping.
• 70/30 Cu-Ni (C71500): higher nickel content, used where the water is more aggressive or velocities are higher (e.g. high-pressure cooling, naval condensers).
• Alloy 400 (Monel) and high-nickel alloys (N06600, N08825): specified for HF service, hot alkaline media and offshore chemical processing where 90/10 is not enough.

A reliable mill should be able to deliver tubes and pipes against the standards the project actually calls out, not a vague "equivalent" grade. For industrial projects handled by EZ Steel Industrial, the most common specifications are:

• ASTM B111 / B111M – seamless condenser and heat-exchanger tubes (C70600, C71500, C12200).
• ASTM B466 / B466M – seamless and welded Cu-Ni pipe for general corrosion service.
• ASTM B619 / B622 / B729 – welded / seamless nickel and nickel-copper alloy pipe for pressure service.
• EEMUA 144 / 234 – the European standard for 90/10 and 70/30 Cu-Ni pipe used in shipbuilding and offshore.
• EN 12451 / EN 10216-5 – copper alloy and austenitic stainless seamless tubes for pressure and heat service.
• GB/T 8890, MIL-T-16420K(SH) – the standards referenced in Chinese shipbuilding and petrochemical projects.

Always ask the supplier which standard the mill test certificate is issued against. A 90/10 tube to EEMUA 144 is not the same procurement as a 90/10 tube to a generic GB equivalent; the testing, traceability and marking requirements differ.

Most Cu-Ni tubes used in pressure and process service are seamless, produced from hot-extruded or hot-pierced billets and then either cold-drawn (for tight tolerances) or hot-finished (for heavier wall sections). Welded Cu-Ni pipe is reserved for larger diameters, lower pressure service, and is often paired with pipe fittings designed for shipboard systems.

A qualified mill will document the full chain – billet heat, hot-working reduction ratio, final annealing, hydrostatic test and eddy current or ultrasonic NDT – and tie every test result back to a single heat number. The mill test report (MTR) is what an inspector will ask for first; if it is missing or does not match the marking on the tube, the material cannot be released to fabrication.

A Cu-Ni system is only as strong as its weakest flange, gasket or bolt. In practice, most in-service failures on seawater lines are traced to mixed-material flanges or incorrect gaskets, not to the tube itself. For a complete system, the procurement list should cover:

• pipe flanges and copper nickel flanges (90/10 or 70/30 to match the line), plus steel flanges for transition pieces.
• gasket stud bolt nut sets sized for the flange class, with spiral-wound gaskets for higher temperatures and RTJ gaskets where the project specification requires.
• industrial valves selected for the same service (gate, globe, ball, check) with trim and body materials compatible with the fluid.

For heat efficiency tubes in boilers and condensers, pairing Cu-Ni tubes with U-bend or finned assemblies from the same supplier reduces interface risk and shortens delivery.

• Mixed heats in one batch. A shipment that pulls tubes from several heats is harder to trace if an issue shows up at NDT. Ask for single-heat deliveries for critical lines.
• Velocity limits ignored. 90/10 is typically limited to about 3.0–3.5 m/s steady flow; above that, erosion-corrosion becomes a real risk. 70/30 tolerates higher velocities and is the safer choice for pump discharge and long cooling lines.
• Galvanic couples not engineered. Coupling Cu-Ni directly to carbon steel without a flange insulation kit or a zinc / iron sacrificial anode accelerates attack on the steel side. The whole system has to be specified together.
• Skipping hydrotest or NDT evidence. Pressure tubes for power and petrochemical service should be hydrostatically tested and have an NDT report (eddy current or ultrasonic) per the cited standard.

1. Confirm the design standard (EEMUA 144, ASTM B111, GB/T 8890, etc.) and the exact UNS / CN grade.
2. Lock the size range, tolerance class, length and end finish (plain end, bevelled, threaded).
3. Require a mill test certificate per heat, with chemical analysis, mechanical properties and NDT results.
4. Specify the matching flanges, gaskets, stud bolts and valves in the same purchase order to keep the system traceable.
5. Agree packaging, marking and shipping documents (heat number, batch number, project reference) up front.