Abstract
The concept of cathodic protection, as applicable to corrosion control of offshore structures, is reviewed and discussed within the context of a new design approach, which is based upon parametric features of the linear potential versus current density decay with time and which has utility to both new and retrofit systems. Evaluation of literature data pertaining to two Gulf of Mexico structures, both before and after retrofit, indicated that the cp systems upon these may have provided continued protection despite the fact that the anodes were largely expired. Also, the retrofit cp designs that were evaluated may not be capable by themselves of repolarizing the respective structures in the event that calcareous deposits are removed by storm activity. Parameters identified as particularly important with regard to performance of original and retrofit anodes are 1) shape of the long-term sigmoidal potential-current density curve and 2) the likelihood that original anodes that have passivated or partially passivated due to low current output will be activated in the event of storm related depolarization. Other questions and considerations relevant to qualification of a particular structure for cp retrofit and design of retrofits are presented and discussed.
