Copper Nickel 70/30

Copper nickel alloy 70/30 is a mixture of 70% copper and 30% nickel with contents of iron and manganese. These content additions make copper nickel even more resistant to corrosion & erosion and with a slightly enhanced strength level than alloy 90/10, making it a perfect fit for more demanding applications.

Copper nickel alloy 70/30 has better resistance to oxidation and stress corrosion cracking. Cupronickel has high oxidation resistance which is seen in moist air and steam. This alloy is thermally stable and has mid-level strength even when at a high temperature.

Physical properties of copper nickel

Fabrication and Heat Treatment 

Alloy copper nickel 70/30 reacts well to most fabrication processes and can be readily hot and cold worked. It is also easily joined by brazing, soldering, or even with other welding methods. With good hot and cold forming ability and malleability approaching that of copper, copper nickel 70/30 does not harden instantly, letting the material draw and spin. 

CuNi 70/30 or UNS C71500 alloy can be annealed at specific temperatures between 649°C and 816°C (1200°F and 1500°F). In the annealed condition, copper nickel alloy offers moderate strength levels which makes it perfectly suitable in more demanding applications. Copper nickel alloy also has good fabricability as mentioned above and high inherent resistance to biofouling.

Corrosion Resistance of copper nickel alloy

Copper nickel alloy – 70/30 or cupronickel is one of the most corrosion-resistant and durable types of copper-based alloys for condensing and heat exchanging tubes in seawater. Copper nickel alloy 70/30 is noted for its excellent resistance properties to corrosion, erosion and pitting along with good strength, workability and weldability.

Chemical composition

The corrosion-resistant properties of 70/30 alloy are improved in higher velocity waters (up to 4.5m/s) and contaminated or polluted seawater. It has also high resistance to stress corrosion cracking, corrosion fatigue and has a high retention of mechanical properties from sub-zero temperatures to ~300°C. 

CuNi 70/30 alloy or copper nickel alloy has better resistance to attack by freshwater, boiler feedwater, and steam. It can also withstand the attack of phosphoric, sulfuric, and mild organic acids. Copper nickel alloy has greater resistance to alkaline chlorides, chromates, nitrates and sulfates. CuNi alloy 70/30 is resistant to wet and dry chlorine, bromine, and carbon dioxide at ambient temperatures.

Specifications 

Applications of copper nickel alloy

UNS C71500 alloy is used in applications where stainless steel cannot be utilized as chloride stress-corrosion cracking may occur and other parts may require high corrosion resistance.

Cupronickel alloy has widely been used in the marine sector that has since extended to industries including:

• Offshore oil and gas
• Power generation
• Desalination
• Cooling plants.

The alloy is commonly used for seawater service as forged and machined valve and pump components, flanges, fittings, and hardware due to its inherent corrosion resistance and also areas where high corrosion resistance is needed and the issue of chloride stress-corrosion cracking limiting the use of stainless steels.

Copper nickel is also used in: 

• Submarine and seawater pipework
• Offshore firewater systems
• Heat exchangers
• Condensers
• Sheathing of legs and risers on offshore platforms 
• Boat hulls
• Hydraulic lines
• Desalination units  

NOTE: Copper nickel 70/30 is a registered trademark of  Special Metals Corporation