API 571 Certification (Corrosion & Materials) Practice Test

Intergranular corrosion describes a specific type of corrosion that occurs along the grain boundaries of metallic materials. This phenomenon is particularly significant in materials such as stainless steels and aluminum alloys, where the integrity of grain boundaries can be compromised due to factors like sensitization, temperature exposure, or chemical contamination.

The corrosion process occurs because the grain boundaries often have different properties compared to the bulk material due to variations in chemical composition, phase distribution, or microstructural features. During intergranular corrosion, corrosive agents penetrate the spaces between grains, leading to selective attack and potential weakening of the material without affecting the overall material thickness significantly. This localized attack can eventually result in severe damage to the component, even if the outer appearance seems normal.

In contrast, corrosion through the entire material thickness represents a uniform corrosion process rather than localized attack. Surface-level corrosion typically refers to degradation occurring only on the surface, without affecting the grain boundaries. Lastly, while corrosive environments like humid conditions can promote various corrosion types, they do not specifically define intergranular corrosion, which is characterized by the attack along grain boundaries, making this the most accurate description.