Permeability of Fusion-bonded epoxy coating to cathodic current: Pulsed current vs. direct current cathodic protection

Abstract

This work aimed at investigating the permeability of Fusion-Bonded Epoxy (FBE) coating to cathodic current resulting from pulsed current cathodic protection (PCCP) in comparison to direct-current cathodic protection (DCCP). To accomplish this objective, a series of experimental techniques were employed, including chronoamperometry, chronopotentiometry, electrochemical impedance spectroscopy (EIS), and in-situ pH measurements. Subsequently, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and, X-ray photoelectron spectroscopy (XPS) analyses were conducted to examine the alterations in the chemistry of FBE. The FBE coating exhibits slight permeability to the cathodic current generated by the DCCP method, whereas it is relatively permeable and permeable to the cathodic current generated through the PCCP method at frequencies of 5 kHz and 10 kHz, respectively. Thus, the permeability of the FBE coating to the cathodic current was determined to be 7.23 %, 10.94 %, and 14.83 % after applying DCCP, PCCP-5 kHz, and PCCP-10 kHz, respectively. The use of the PCCP approach, as opposed to the DCCP method, results in more alterations to the FBE coating's chemistry. This new approach, in particular, leads to an increased absorption of water within the coating structure, which then enhances the formation of ion-conductive channels on the surface of the FBE coating. It is notable to state that, within the framework of the PCCP approach, the cathodic current permeability of the FBE coating exhibits enhancement as the frequency increases.