Copper-Nickel (CuNi) alloys — particularly the 90/10 and 70/30 compositions — have long been recognized as the premier material for seawater piping systems in offshore oil & gas platforms, naval vessels, and coastal power plants.

Why CuNi?

The unique properties of Copper-Nickel alloys make them ideally suited for marine service:

Corrosion Resistance — CuNi alloys form a thin, adherent protective film when exposed to seawater. This film is self-healing, meaning minor damage repairs itself over time, providing decades of reliable service without the need for additional coatings or cathodic protection.

Biofouling Resistance — Unlike carbon steel or even stainless steel, CuNi alloys naturally resist the attachment of marine organisms such as barnacles, mussels, and algae. This reduces maintenance costs and maintains flow efficiency in piping systems.

Mechanical Properties — With tensile strengths ranging from 275 to 400 MPa depending on composition, CuNi alloys offer excellent strength while maintaining good ductility and formability. They can be readily welded, brazed, and fabricated using standard techniques.

90/10 vs. 70/30

The two most common CuNi compositions each serve distinct roles:

• 90/10 (C70600) — The workhorse alloy for general seawater service. Cost-effective with good corrosion resistance up to moderate flow velocities. Widely used in condenser tubes, heat exchangers, and general piping.

• 70/30 (C71500) — The premium choice for demanding applications. Superior resistance to high-velocity seawater, impingement attack, and stress corrosion cracking. Preferred for critical systems and higher-temperature service.

Sourcing Quality CuNi Products

At Gulf Coast Alloys, we partner directly with specialized manufacturers like HAE WON (S. Korea) for CuNi fittings and BM MEtal (S. Korea) for CuNi flanges. These direct mill relationships ensure consistent quality, competitive pricing, and reliable delivery schedules for your marine and offshore projects.

Whether you need standard CuNi fittings and flanges or custom specifications for a specialized application, our team can help you source the right products for your project requirements.