Cathodic potential (CP) criteria have been used as a recommended minimum requirement for controlling external corrosion of buried or submerged steel piping systems. In the last part of a three-part paper field and laboratory data were evaluated to understand the effectiveness of the -100 mV polarization criterion which was compared with the effectiveness of the -850 mV on?potential criterion and various off-potential criteria in different soil resistivity ranges. The effectiveness of various CP criteria associated with elevated temperatures and soils with bacteria was also evaluated; the results are reported in this paper.