API 571 Certification (Corrosion & Materials) Practice Test

Which of the following factors contributes to corrosion fatigue in metals?

1. Temperature fluctuations

2. Mechanical stress

3. Alloy reactivity

4. Environmental conditions

The correct answer is: Mechanical stress

Corrosion fatigue in metals is primarily influenced by mechanical stress, making it a critical factor to consider. When metals are subjected to fluctuating loads or constant mechanical stress, they become more susceptible to cracking and failure, particularly in corrosive environments. The combination of tensile stresses—whether they are due to external loads or residual stresses—and the presence of a corrosive medium accelerates the degradation of the material, leading to fatigue failure. In the context of corrosion fatigue, mechanical stress can initiate and propagate cracks within the material. The presence of a corrosive environment further reduces the material's resistance to these stresses, allowing tiny cracks to grow more rapidly than they would under mechanical loading alone. This synergistic effect can significantly reduce the lifespan of components, making the understanding of mechanical stress crucial in managing materials in engineering applications. While temperature fluctuations, alloy reactivity, and environmental conditions can all play roles in corrosion processes, they do not directly contribute to the specific mechanism of corrosion fatigue as fundamentally as mechanical stress does. Instead, these factors could influence the rate of corrosion or the types of corrosion present but are secondary to the impact that mechanical loads have on material integrity under fatigue conditions.