Define "intergranular corrosion" as it relates to NDT.

Intergranular corrosion refers specifically to the localized attack along the grain boundaries of a material. This type of corrosion can occur in various metals and alloys, particularly in certain stainless steels and aluminum alloys, and is often a concern in welds and heat-affected zones. It happens when the metal’s crystal structure becomes susceptible to environmental elements, leading to the degradation of the material at these pivotal locations where the grains meet.

Understanding intergranular corrosion is particularly important in non-destructive testing (NDT) because this type of corrosion can significantly affect the mechanical properties and integrity of a material without being easily detectable through conventional inspection methods. Unlike uniform corrosion, which affects the entire surface evenly and can be assessed more readily, intergranular corrosion can compromise a material’s strength while maintaining an intact outer surface.

In examining the context of the other choices, surface coatings, uniform corrosion, and corrosion caused by environmental exposure each describe different phenomena that do not specifically highlight the significance of grain boundaries in the corrosion process. By identifying intergranular corrosion correctly, one can better assess the potential risks and implement suitable inspection techniques to ensure material integrity.