Copper-Nickel Alloys: A Comprehensive Guide

by AMC

HPE Product Page

Posted on September 05, at 12:40 PM

In this blog, we’ll explore copper-nickel alloys—an important material that often goes unnoticed. Recognized for their remarkable resistance to corrosion and wear, copper-nickel alloys are perfect for challenging environments such as ships, cooling systems, and chemical facilities. Learn why these alloys are a preferred selection for dependable and enduring performance in tough conditions.

Copper-nickel alloy, also referred to as cupronickel, is a blend of metals that primarily consists of copper and nickel, along with trace amounts of iron and manganese. This alloy is prized for its superior corrosion resistance, especially in marine settings, and its longevity. Typically, the nickel content ranges from 10% to 40%, enhancing the strength and wear resistance of the alloy. Copper-nickel alloys find common usage in applications such as marine equipment, heat exchangers, and a variety of industrial piping systems due to their durability and resistance to biofouling and oxidation.

General Information on Copper Nickel Alloys

The most widely utilized copper-nickel alloys feature either 10% or 30% nickel content, labeled as 90-10 and 70-30 alloys, respectively. These alloys incorporate minute quantities of iron and manganese to elevate rust resistance. They demonstrate great flexibility and can be strengthened through cold working processes, with the 70-30 alloy showcasing increased strength suitable for managing higher flow rates. Additionally, these alloys exhibit excellent thermal conductivity, making them beneficial for heat exchangers and condensers. Their workability extends to shaping and welding, where they can also be welded to steel.

Other types of copper-nickel alloys exist, including one that contains 2% manganese and 2% iron (66-30-2-2), ideal for tubing in high flow and abrasive environments. A newer chromium-enhanced alloy (Cu-30Ni-Cr) is also available for even greater flow capabilities.

Cast copper-nickel alloys have their applications as well, although nickel-aluminum bronzes are typically favored for pumps and valves. For instance, the UK Royal Navy employs a cast Cu-30Ni-Cr alloy as an alternative to nickel-aluminum bronze.

High-strength copper-nickel alloys come in two varieties: those strengthened through aging (Cu-Ni-Al alloys) and those enhanced via specialized heat treatment (Cu-Ni-Sn and Cu-30Ni-Cr). Some of these alloys boast strength comparable to that of high-strength steel and include beneficial attributes like anti-galling and non-sparking qualities.

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Copper Nickel Alloy Corrosion

Copper-nickel alloys such as the 90-10 and 70-30 grades utilize a protective surface film to fend off corrosion. Unlike certain alloys that form a protective oxide layer in air, these alloys develop a sophisticated, multi-layered film in seawater, composed of oxides, chlorides, and hydroxy-chlorides. This film forms rapidly and improves over time, resulting in low rates of corrosion. Consequently, short-term corrosion tests might not accurately represent their long-term performance. It is essential to ensure that the alloys are subjected to optimal seawater conditions during initial use to facilitate an effective protective film.

Additionally, copper-nickel alloys do not encounter problems such as chloride-induced pitting, crevice corrosion, or stress corrosion cracking, which are common with certain stainless steels. However, they may be influenced by sulfides and ammonia. While sulfide stress corrosion and hydrogen embrittlement are generally not issues, sulfides can alter the protective film, potentially leading to pitting and elevated corrosion rates. Thus, long-term exposure to polluted seawater containing sulfides or environments with sulfate-reducing bacteria (SRBs) should be avoided. In contrast to brass, copper-nickel alloys resist ammonia stress cracking, although ammonia may escalate corrosion rates.

In scenarios involving high velocity or turbulence, the protective film may erode, prompting erosion-corrosion. However, this is less concerning for copper-nickel alloys compared to other copper variants, making it imperative to adhere to design and operation guidelines to mitigate issues, such as steering clear of partially throttled valves and tight bends in pipe systems.

Copper-nickel alloys generally exhibit compatibility with other copper alloys and feature greater corrosion resistance compared to steel and aluminum. Nonetheless, they might corrode more swiftly when connected to passive stainless steels, high-nickel alloys, and titanium.

Copper Nickel Alloy Chemical Composition

Mechanical Properties of Copper-Nickel Alloys

Effects of Nickel Content in Copper-Nickel Alloys

Nickel plays a significant role in determining the characteristics of copper-nickel (Cu-Ni) alloys. As the nickel content increases, so does the alloy's tensile strength, resistance to corrosion, and heat endurance. However, the capacity to conduct heat and electricity diminishes. For instance, while tensile strength increases with a higher nickel percentage, the material's ability to stretch (elongation) remains relatively stable after a slight initial decrease at up to 5% nickel.

Heat Treatment of Copper Nickel Alloys

Cu-Ni alloys are primarily heat-treated to achieve soft annealing and stress relief. Recrystallization annealing takes place at temperatures between 620°C and 900°C, with higher temperatures necessitating shorter treatment durations. Stress-relief annealing occurs within the range of 280°C to 500°C.

Annealing should be performed in an air-free or slightly reduced atmosphere to avoid contamination and to eliminate the need for pickling. Certain alloys can undergo age-hardening, such as CuNi30Cr and CuNi5Al4Mn2, each requiring specific heat treatment procedures.

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Conclusion

Copper-nickel alloys, particularly the 90-10 and 70-30 variants, deliver outstanding durability and corrosion resistance, making them suitable for demanding environments like maritime applications and industrial systems. These alloys, enhanced with components like manganese and chromium, provide remarkable performance and adaptability. Proper heat treatment and mindful design practices contribute to their sustained effectiveness. In summary, copper-nickel alloys emerge as a trustworthy selection for rigorous conditions, showcasing long-lasting performance alongside robust resistance to corrosion and wear.

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FAQ

What are the uses of copper-nickel alloy?

Copper-nickel alloys are utilized in marine hardware, heat exchangers, hydraulic tubing, cooling systems, and in surfaces requiring antimicrobial properties due to their strength and resistance to corrosion.

What is the difference between copper and copper-nickel?

Copper-nickel alloys, such as 70/30 cupronickel, are silver-colored and consist of 70% copper and 30% nickel, enhancing strength and corrosion resistance, while pure copper appears reddish-brown and is primarily used for its conductivity.

Is copper-nickel better than stainless steel?

Copper-nickel alloys outperform stainless steel in marine settings due to their superior resistance to corrosion in seawater, while stainless steel might be preferable for applications involving harsh chemicals and acids.

What is the price of copper-nickel alloy?

The price of copper-nickel alloy varies based on factors like alloy grade and market fluctuations. For the most accurate and current pricing, please feel free to reach out to us.

What temperature is copper-nickel alloy?

Copper-nickel alloys are suitable for applications with maximum operating temperatures up to 600°C (1,110°F). They maintain consistent performance due to their low-temperature coefficient of electrical resistance.

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