Abstract

Standard cathodic protection design is predicated on the attainment of the minimum structural protective potential of −0.80 volt with respect to the silver-silver chloride electrode. The resulting net driving potential, that is the difference in potential between the polarized structure and the sacrificial anode, is 0.25 volt. The design criteria presented herein provide for an initially high current density such that polarization is significantly greater than that corresponding to the minimum protective potential. This results in substantially reducing the net driving potential and as a consequence reduces the current required to protect the structure during its lifetime. Field measurements are being carried out on platforms in the Arabian Gulf as part of a comprehensive program to achieve cathodic protection with a minimum number and weight of sacrificial anodes. In the first phase of this program the design was based on providing an initial current density of 310 milliamperes per square meter of metal exposed to sea water. Field measurements are presented that show that a structure potential of −0.98 volt with respect to the silver-silver chloride electrode has been achieved. Although the design life was 20 years, the lifetime calculated using the field measurements, was 39 years. The second phase of the program involves utilization of anodes with a greater current output, that is anodes of lower weight with a greater surface area. The design for this phase, which involves a 40 percent weight reduction, will be discussed.