How is Level 4 Rust defined?

Level 4 Rust is characterized by perforation, which indicates a serious level of corrosion that has resulted in actual holes in the metal substrate. This level of rust signifies a significant deterioration of the material, typically affecting its structural integrity and requiring immediate attention or replacement.

In contrast to minor discoloration and moderate corrosion, which involve less severe forms of rust that do not compromise the integrity of the material, perforation indicates that the rusting process has advanced to a point where it has compromised the surface entirely. Deep pitting, while also a significant concern, refers specifically to the formation of pits or cavities that do not necessarily penetrate through the material, distinguishing it from the complete perforation seen at Level 4. Therefore, defining Level 4 Rust by perforation effectively captures the extent of damage and the urgency of intervention needed.