API 571 Certification (Corrosion & Materials) Practice Test

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Which materials are most resistant to Ammonium Bisulfide corrosion?

Carbon Steel
Super Duplex
Alloy 400
Alloy 20

The correct answer is: Super Duplex

Super Duplex is highly resistant to Ammonium Bisulfide corrosion due to its unique microstructure, which comprises both austenitic and ferritic phases. This combination provides enhanced strength and improved resistance to localized corrosion, such as pitting and crevice corrosion, which can occur in the presence of aggressive environments like Ammonium Bisulfide. The alloy's high chromium and molybdenum content further contribute to its corrosion resistance, making it well-suited for handling environments that can be harsh and corrosive. Super Duplex materials are specifically designed for applications where traditional stainless steels might fail, thus offering a greater durability and longevity in challenging conditions. In contrast, the other materials listed may not provide the same level of protection against Ammonium Bisulfide. Carbon steel is particularly vulnerable to corrosion in acidic environments, and while Alloy 400 and Alloy 20 are resistant to many types of corrosion, they do not have the same resistance levels to Ammonium Bisulfide as Super Duplex does. Therefore, for applications exposed to this specific corrosive agent, Super Duplex emerges as the superior choice.