In seawater, cathodic protection systems for steel structures rely on the formation of a calcareous film to help polarize the surface and thereby reduce the current required to maintain the potential in the protection range. These models require experimental determination of the polarization behavior for the cathodically protected steel. The experiments have been carried out in a variety of electrolytes including artificial seawater, recirculated seawater, and once through fresh seawater. While the latter is obviously the preferred method, there are few research facilities capable of extensive testing in fresh flow-through seawater. This results in the use of the less preferred recirculated natural and artificial seawater procedures.
This paper presents the results of an investigation contrasting data obtained in a series of otherwise identical once-through and recirculating seawater experiments in which the current decay rates of cathodically protected steels were determined. The experiments were run in fresh Atlantic Ocean seawater at the Center for Marine Materials Laboratory at Florida Atlantic University and ASTM Specification for Substitute Ocean Water (D 1141) artificial seawater. Both once-through and recirculating experiments were run concurrently. Possible explanations for the observed polarization rate differences include the effect of dissolved organic carbons and ion depletion.