Design and protection criteria for cathodic protection of seawater intake structures in petrochemical plants

Impressed current cathodic protection (ICCP) and sacrificial anode cathodic protection (SACP) systems were designed and installed to control chloride-induced corrosion of the steel reinforcement in the atmospherically exposed and submerged parts of the seawater structures, respectively. The design and long-term performance assessment of these systems are described and discussed. The monitoring data collected have suggested that all ICCP systems are performing satisfactorily and meeting the design objectives in controlling the corrosion of the steel reinforcement. The SACP systems generally did not meet the specified criterion of -800 mV Ag/AgCl current-on steel potentials; however, there have been no signs of corrosion or concrete distress in submerged areas since application of SACP system. The results showed that a steel current density ranging between 8 and 14 mA/m(2) was sufficient to afford required protection to the steel reinforcement in different structures. The protection afforded to these structures has residual effect and could last up to 2 months or so when the CP system is turned off. As a result of CP application, the corrosion potentials of the steel reinforcement have been shifted by some 100 to 200 mV in the positive direction.