The cathodic protection (CP) of on-grade coated steel storage tanks deployed on reinforced concrete slabs in soils of 20-30 kΩ cm resistivity was evaluated for two different time periods 9 years apart. The required CP current was calculated and the ohmic drop was measured using the instant-off potential method. The resulting polarisation shift is a useful indicator of the level of protection afforded and whether the potential criterion or the polarisation shift criterion is fulfilled. It was also noted that the greater the ground resistivity, the less corrosive the environment for an on-grade steel structure.
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