API 571 Certification (Corrosion & Materials) Practice Test

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What is the primary cause of crack initiation in ammonia SCC?

Material defects
Environmental factors
Design flaws
Alloy composition

The correct answer is: Alloy composition

The primary cause of crack initiation in ammonia stress corrosion cracking (SCC) is largely attributed to the specific alloy composition. Certain materials exhibit greater susceptibility to SCC when exposed to ammonia, particularly those that contain a higher percentage of certain elements or have specific microstructural characteristics. In environments containing ammonia, which can be highly corrosive, the alloy composition plays a critical role in determining how well the material can resist the combined effects of stress and corrosion. For instance, stainless steels with lower molybdenum content may be more prone to SCC in ammonia than those with higher alloying elements designed to enhance resistance. While material defects, environmental factors, and design flaws can all contribute to the risk of SCC, the intrinsic properties of the alloy itself dictate the initial susceptibility to cracking when faced with ammonia exposure. Therefore, understanding and selecting appropriate alloy compositions becomes essential in mitigating the risk of crack initiation in such environments.