Optimization of the Cathodic Protection Design in Consideration of the Temperature Variation for Offshore Structures

The temperature effect on the current density which closely related to cathodic protection (CP) design was examined using electrochemical tests. A case study of an optimized CP design for the floating production storage and offloading using a computational analysis tool was also performed. The electrochemical test results showed that the current density and the surface resistance of the specimen (EH36) at 28°C are lower and higher, respectively, compared with the 5°C condition; this phenomenon is the result of a calcareous deposit that was verified by scanning electron microscopy and energy dispersive x-ray spectroscopy surface analyses. The polarization curves which contained the effect of calcareous deposits according to the temperature were used as the computational analysis input data. The simulation results showed that the structure under the 5°C condition did not satisfy the CP criteria (−800 mVSCE to −1,050 mVSCE) at the bottom shell and the mooring chain. It had higher potential than −800 mVSCE. Although the structure at 28°C satisfied the protective potential range, it was sufficiently unstable for the prediction of the corrosion damage. To optimize and resolve the identified problems, the CP design was changed by CP methods, anodes quantities, and anodes distribution. Consequently, the structure at 5°C is sufficient for the satisfaction of the protective-potential criteria (< −800 mVSCE) at the bottom shell and the mooring chain. In the case of the structure at 28°C, a more-even potential distribution was achieved.