Differences Between CuNi 90/10 and CuNi 70/30

• CuNi 90/10 is cost-effective and offers good corrosion resistance and thermal conductivity — ideal for standard marine piping and heat exchangers.

• CuNi 70/30 provides higher strength and superior resistance in aggressive or high-velocity seawater environments — preferred for offshore and desalination systems.

• Choosing the right alloy depends on the operating environment, mechanical demands, and budget considerations.

Copper-nickel (CuNi) alloys are renowned for their exceptional resistance to corrosion, especially in marine environments. Among these, the 90/10 and 70/30 compositions are the most prevalent, each offering distinct properties that make them suitable for specific applications. Understanding their differences is crucial for engineers and designers aiming to optimize performance and longevity in their projects.

• CuNi 90/10 (C70600): Comprises approximately 90% copper and 10% nickel, with small additions of iron and manganese to enhance corrosion resistance and mechanical strength.

• CuNi 70/30 (C71500): Contains about 70% copper and 30% nickel, along with slightly higher amounts of iron and manganese compared to the 90/10 alloy. This composition provides superior strength and resistance to aggressive environments.

The increased nickel content in the 70/30 alloy contributes to its enhanced mechanical properties and corrosion resistance, making it more suitable for demanding applications.

While both alloys exhibit excellent ductility and are easy to fabricate, the 70/30 alloy offers higher tensile and yield strengths, making it preferable for applications involving higher mechanical stresses.

Both CuNi 90/10 and 70/30 alloys are highly resistant to corrosion in seawater, a property enhanced by the formation of a protective oxide layer on their surfaces. However, their performance differs under specific conditions:

• CuNi 90/10: Suitable for environments with moderate flow rates and less aggressive conditions. It performs well in clean seawater applications.

• CuNi 70/30: Offers superior resistance to high-velocity seawater, polluted marine environments, and areas prone to biofouling. Its higher nickel content and alloying elements contribute to this enhanced performance.

In terms of maximum allowable flow velocities:

• CuNi 90/10: Up to 3.5 m/s for piping systems.

• CuNi 70/30: Up to 4.0 m/s for piping systems.

Exceeding these velocities can lead to erosion-corrosion, so selecting the appropriate alloy based on flow conditions is essential.

CuNi 90/10 has higher thermal conductivity, making it more efficient for heat transfer applications. However, CuNi 70/30’s lower thermal conductivity is offset by its superior strength and corrosion resistance, which are critical in more aggressive environments.

Both alloys are known for their excellent fabrication properties:

• Formability: CuNi 90/10 is more malleable, allowing for easier bending and forming, which is advantageous in complex installations.
  

• Weldability: Both alloys can be welded using standard techniques. However, it’s recommended to use 70/30 filler material when welding either alloy to ensure optimal joint strength and corrosion resistance.

• Work Hardening: Neither alloy can be strengthened by heat treatment, but their strength can be increased through cold working processes.

The cost difference between the two alloys is primarily due to their nickel content:

• CuNi 90/10: More cost-effective, making it suitable for large-scale projects where budget constraints are a concern.
  

• CuNi 70/30: Higher cost due to increased nickel content, but offers better performance in challenging environments, justifying the investment for critical applications.

The selection between the two alloys depends on the specific requirements of the application, including environmental conditions, mechanical stresses, and budget constraints.

CuNi 90/10 and 70/30 alloys have been extensively used in critical infrastructure projects across marine, power generation, and offshore sectors. For example, CuNi 90/10 is widely used in shipbuilding for seawater piping systems, bilge lines, and ballast systems. Its balance of corrosion resistance and cost-efficiency makes it ideal for large commercial vessels and naval ships where extensive piping is needed.

In contrast, CuNi 70/30 is often found in high-performance environments such as offshore oil rigs, FPSOs (Floating Production Storage and Offloading units), and desalination plants. These systems demand higher mechanical strength and better protection against harsh seawater and biological growth. In desalination plants, for instance, CuNi 70/30 is used in multi-stage flash (MSF) and reverse osmosis systems due to its excellent resistance to erosion from high-velocity brine.

Power plants located in coastal areas also use both alloys—CuNi 70/30 is typically reserved for condenser tubes that face direct exposure to seawater cooling loops, while CuNi 90/10 is used for less exposed systems. These real-world uses illustrate how critical the right alloy selection is for long-term performance and cost optimization.

Note: For detailed specifications and assistance in selecting the appropriate alloy for your application, please consult with our technical team at Admiralty Industries.