**7.4 Pitting corrosion or localized corrosion**

Pitting corrosion is a localized attack resulting in the formation of holes in the metals. These holes are relatively small and they are looks like a rough surface (**Figure 5**), they were sometimes isolated or so close together. Pitting is one of the most destructive and insidious forms of corrosion [22].

## **7.5 Intergranular corrosion**

Most of the metals and alloys are susceptible to intergranular corrosion, when exposed to specific corrosion environment which is shown in the **Figure 6**. Grain boundaries are usually more reactive than grain matrix. Hence localized attack occurs at and adjacent to grain boundaries with relatively little corrosion of the matrix. This type of attack is usually rapid and penetrates deep into the metal resulting in loss of strength and causes catastrophic failures. It is caused by,

