API 571 Certification (Corrosion & Materials) Practice Test

What happens to nickel alloys with high nickel contents when exposed to temperatures above 1193F?

1. They become more ductile

2. They suffer from sulfidation and metal loss

3. They resist all forms of corrosion

4. They increase in tensile strength

The correct answer is: They suffer from sulfidation and metal loss

Nickel alloys with high nickel contents experience sulfidation and subsequent metal loss when subjected to elevated temperatures above 1193°F. At these temperatures, the interaction between the alloy and sulfur-containing environments can lead to the formation of nickel sulfide. This process not only depletes the nickel from the alloy but also compromises its structural integrity, resulting in a reduction of mass and deterioration of the material's mechanical properties. In contrast, while some metals may exhibit increased ductility or tensile strength at certain temperatures, this specific behavior is not characteristic of high nickel alloys under the stated conditions. Additionally, no material can resist all forms of corrosion at elevated temperatures; thus, it's essential to understand the context of the environmental conditions when evaluating corrosion resistance. These factors collectively support the conclusion that sulfidation and metal loss are critical concerns for nickel alloys in high-temperature applications.