API 571 Certification (Corrosion & Materials) Practice Test

What type of alloys typically undergo denickelification?

1. Copper-Nickel alloys

2. Aluminum alloys

3. Stainless steels

4. Wrought iron

The correct answer is: Copper-Nickel alloys

Denickelification is a specific form of corrosion that primarily affects copper-nickel alloys, particularly those containing nickel as a significant component. This phenomenon occurs when the nickel is selectively leached out from the alloy, leading to a reduction in the nickel content and a potential deterioration of the material's mechanical properties and corrosion resistance. Copper-nickel alloys are known for their excellent resistance to maritime corrosion, but in certain environments, such as seawater or when exposed to certain chemical agents, the nickel can be preferentially dissolved. This not only alters the composition but also impacts the corrosion performance of the remaining copper component. In contrast, aluminum alloys, stainless steels, and wrought iron do not typically experience denickelification. Aluminum alloys are more prone to pitting and localized corrosion, while stainless steels may undergo different types of corrosion like stress corrosion cracking or intergranular corrosion depending on their alloying elements and service conditions. Wrought iron is generally more susceptible to uniform corrosion in the presence of moisture and oxygen, rather than the selective leaching seen in denickelification. Understanding the unique susceptibility of copper-nickel alloys to this specific corrosion mechanism is crucial for materials engineers and corrosion specialists when assessing environments where these alloys will be used