Abstract
The synergistic effects of fluid flow, sand particles, and solution pH on erosion-corrosion of AISI 4330 steel alloy in saline-sand medium were studied through a rotating cylinder electrode (RCE) system by weight-loss and electrochemical measurements. The worn surface was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that, under all the test conditions assessed, the passivity of the steel alloy could not be maintained; as a result, an activation mechanism dominates the corrosion process of steel alloy. Furthermore, the potentiodynamic curves show that, with the increasing of the electrode flow rate and particle size, the anodic current density increased, which is due to deterioration of the electrode by the impacting slurry. Although the increase of particle size affects the anodic current density, the effect of particle size does not cause a significant change in the polarization behavior of the steel electrode. The electrochemical impedance and potentiodynamic curves suggest that erosion-corrosion phenomenon of the ASISI 4330 steel is under mixed control of mass transport and charge transfer. The inductive loops formed in the impedance plots are representative of an increase in roughness of the electrode caused by the particles impacting at the surface. The change in the passivity of the steel alloy as the pH is altered plays an important role in the corrosion rate.
Highlights
Erosion-corrosion is the metal deterioration that involves mechanical wear by impacting solid particles at the metal surface in conjunction with electrochemical dissolution of the metal by the corrosive solution, with both activities occurring synergistically in a dynamic two-phase fluid [1]
The electrochemical impedance spectroscopy (EIS) plots indicate that charge-transfer resistance (Rct), which is a characteristic magnitude for current flowing through electrochemical reactions that occur at the electrode surface, is determined by the diameter of the capacitive semicircle [14]
Corrosion related to electrochemical reactions at the metal/flowing-electrolyte interface and erosion related to particle impact will be enhanced as a result of the increment of rotation speed and acidification of the electrolyte
Summary
Erosion-corrosion is the metal deterioration that involves mechanical wear by impacting solid particles at the metal surface in conjunction with electrochemical dissolution of the metal by the corrosive solution, with both activities occurring synergistically in a dynamic two-phase fluid [1]. Corrosion may enhance erosion as the particle impacts the passive film and damages it, dissolution of the surface leads to the elimination of the work hardened layer and increases the surface roughness. Li et al [9] suggested another possible mechanism on how corrosion can enhance erosion, through localized attack at sites where the passive layer is ruptured during impact, leading to an increase in the electrochemical activity of these sites. Another study by Clark [11] pointed that the increase in the particle size will result in a greater impact kinetic energy This will lead to a higher corrosion rate. Weight-loss measurements and electrochemical tests were applied in this study to determinate the synergistic effect of erosion-corrosion phenomenon in an AISI SAE 4330 steel electrode. The influence of electrode rotating rate, erodent size, and pH were investigated to determine the roles of each parameter in the erosion-corrosion damage of an AISI SAE 4330 steel electrode
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