WC-Co and WC-Co-Cr coatings for the protection of API pipeline steel from corrosion in 4% NaCl solution

Abstract

Two inorganic coatings, namely 88%WC-12%Co (PSC1) and 86%WC-10%Co-4%Cr (PSC2), were deposited on the surface of an API-2H pipeline steel using high velocity oxy-fuel deposition. The corrosion of the uncoated and coated API-2H steel after their immersion in a solution of 4.0% NaCl for 1 h, 24 h, and 48 h has been studied. Various electrochemical measurements such cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and potentiostatic current versus time were employed. The surface morphology and analysis were carried out via the use of scanning electron microscopy and energy dispersive X-ray examinations. All experiments have revealed that the deposited coatings decreased the cathodic current, anodic current, corrosion current density (jCorr), absolute current versus time, and the corrosion rate (RCorr) compared to the uncoated API-2H steel. The value of jCorr decreased from 47 μA/cm2 for uncoated steel to 38 μA/cm2 for the PSC1-coated steel and 29 μA/cm2 for the PSC2-coated steel. Moreover, prolonging the time of exposure decreases the jCorr and RCorr values. The jCorr values obtained after 48 h recorded 32, 26, and 20 μA/cm2 for the uncoated, PSC1, and PSC2 samples, respectively. Moreover, applying these coatings also led to increasing the corrosion resistance (RP) after all the exposure periods of time. In addition, the PSC2 coating was found to be more protective against corrosion for the surface of the steel than the PSC1 coating.