Pitting Corrosion (2)

ASTM-G46 has a standard visual chart for rating of pitting corrosion

The shape of pitting corrosion can only be identified through metallography where a pitted sample is cross-sectioned and the shape the size and the depth of penetration can be determined.

Source: http://www.corrosionclinic.com/types_of_corrosion/pitting_corrosion.htm