Improvement of corrosion protection properties of calcareous deposits on carbon steel by pulse cathodic protection in artificial sea water

Purpose - This study aims to evaluate the influence of pulsed cathodic protection on calcareous deposit formation on structures submerged in the synthetic sea water. Design/methodology/approach - Chronoamperometric and C-HF methods have been used to evaluate the influence of pulsed cathodic protection on decreasing the required cathodic current for protection and also decreasing the surface coverage. The morphology of the formed deposits was evaluated using scanning electron microscopy. Chemical analyses of the formed deposits were performed using energy dispersive X-ray spectrometer and X-ray diffraction. Findings - It was observed that pulse frequency influenced both the structure and the composition of the deposits. The most compact aragonite layer was obtained at high frequencies and at a high off-time. It was clearly shown that by applying currents with less than 100 Hz frequency, the deposits formed on the sample involved CaCO3 (aragonite) and Mg(OH)(2) (brucite). However, the kinetics of deposits formed when applying pulse current have been improved, compared to deposits formed by conventional cathodic protection. The reason is that large electrode overpotential favors nucleation through a decrease in the energy of nucleus formation. On the other hand, by intensive decrease of surface potential, repulsion of aggressive anions such as SO42- and Cl- occurs. These anions inhibit the formation of aragonite deposits. Research limitations/implications - In order to have a better investigation of electrodeposition processes in the shorter time, the use of more advanced techniques and analysis methods such as XPS is recommended. Furthermore, EHD techniques could be used for measurements of thickness of the layers. Practical implications - The pulsed cathodic protection method is a relatively new method for the protection of buried and submerged structures. Recently, many researches have investigated that the influence of this technique on increasing the throwing power, decreasing interference effects on neighboring structures and increasing the uniformity of current distribution under cathodic protection. Originality/value - Very little attention has been paid in the past to the effect of pulsed CP on deposit formation. The present paper, therefore, contributes useful understanding of the mechanism and advantages of such deposits in improving the effectiveness and lowering the operational cost of cathodic protection in use on offshore structures.