What factor determines if corrosion is at Stage 4?

The determination of Stage 4 corrosion is based on the visible perforation of the base metal. At this stage, corrosion has progressed significantly, indicating a serious level of degradation. Perforation means that holes have formed in the metal, compromising the integrity and strength of the structure. This level of corrosion poses significant risks for safety and functionality, making it crucial to identify.

Minor surface rust alone does not indicate such advanced deterioration; it is typically an initial stage of corrosion and easily manageable. Blistering of the surface metal signifies rust beneath the surface but does not necessarily involve perforation, which is a clear sign of advanced corrosion. Major dents, while they can affect structural integrity, do not specifically relate to the corrosion process unless they lead to exposure and subsequent corrosion of unprotected metal. Identifying corrosion at Stage 4 focuses specifically on the presence of perforation, highlighting a critical need for repair or replacement of the affected component.