Abstract
The corrosion behavior and characteristics of 3Cr steel in coexisting H2S- and CO2-containing solution at temperature from 25 to 65 °C were investigated by potentiodynamic polarization sweep, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) with energy-dispersive x-ray (EDX). The EIS data fitted by ZsimpWin software were analyzed and discussed. The experimental results indicated that corrosion potential (Ecorr) became more negative and that corrosion current density (icorr) decreased as the Na2S·9H2O concentration (i.e., H2S/HS−) increased from 0 to 1.6%, with the obvious passivation characteristics occurring in anodic polarization branch curve in 1.6% Na2S·9H2O case. Warburg impedance characteristics of diffusion process in low-frequency region following a depressed capacitive semicircle in the intermediate frequency region were observed with the addition of certain Na2S·9H2O concentration or temperature, with the phase angle peaks for H2S-containing cases in the intermediate frequency region shifting to low-frequency direction and raising toward −90° significantly. Severe corrosion pits or cavities or river-liking platform could be observed after removing the corrosion products. The contents of S element in the “first deposition” black corrosion product layer were higher than those in the “second deposition” gray corrosion product crystals. All result displayed the inhibition effect with the addition of Na2S·9H2O. In addition, one four-stage corrosion model involving H2S and CO2 corrosion was proposed.
Published Version
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