Purpose – The purpose of this paper is to characterize the surface of steel under cathodic protection while submerged in seawater, to understand the mechanism that controls the operation of the protection system. Design/methodology/approach – Steel rods were immersed in seawater and NaCl solution with applied cathodic protection. The experimental methodology included monitoring of corrosion potential (E corr ), galvanic current (I galv ) protection potential (E protection ) and the depolarization potential of steel during the time of exposure. In addition, the chemical composition of the steel surface was assessed using a Scanning Electron Microscope (SEM). Findings – In this research it was determined that the effectiveness of the CP system was mainly attributable to the formation of an iron oxide film on the steel surface. Research limitations/implications – It is necessary to carry out analysis of the chemical composition of deposits formed on the steel surface, perhaps using X‐ray diffraction (XRD), to verify the presence of a protective oxide. Practical implications – Deposits on the steel surface have the beneficial effect of reducing the current required for efficient protection. Deposit formation therefore is of economic interest, as it decreases the cost of protection. Originality/value – A unique feature of cathodic protection in seawater is the formation of calcareous deposits on metal surfaces. Advantageous aspects of these deposits, such as decrease in cathodic current requirement, have been investigated by various authors from various viewpoints. However, very little attention has been paid to the impact of any iron corrosion product films; the present paper contributes useful understanding and explains the importance of the mechanism that controls the operation of the protection system.
Anti-Corrosion Methods and Materials – Emerald Publishing
Published: May 17, 2013
Keywords: Steel; Cathodic protection; Films (states of matter); Seawater; Steel rods; Galvanic current; Surface properties of materials