Corrosion Behavior and Characteristics of 3Cr Steel in Coexisting H 2 S- and CO 2 -Containing Solutions
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JMEPEG https://doi.org/10.1007/s11665-020-05023-1
Corrosion Behavior and Characteristics of 3Cr Steel in Coexisting H2S- and CO2-Containing Solutions Z.F. Yin, Y.L. Zhang, G.R. Chang, and T.Q. Yang (Submitted March 31, 2020; in revised form May 26, 2020) 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 Na2SÆ9H2O concentration (i.e., H2S/HS2) increased from 0 to 1.6%, with the obvious passivation characteristics occurring in anodic polarization branch curve in 1.6% Na2SÆ9H2O 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 Na2SÆ9H2O 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 290° 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 Na2SÆ9H2O. In addition, one four-stage corrosion model involving H2S and CO2 corrosion was proposed. Keywords
3Cr steel, corrosion model, corrosion product layer, EIS, H2S and CO2 corrosion, polarization curve
1. Introduction The control of internal corrosion of metal pipes and facility materials damaged by the corrosive gases containing H2S and CO2 in oil and gas production environments is a very serious issue all the time, and often the inadequate protection leads to costly repairs, shutdowns, and human safety and environmental hazards which is caused by corrosion failure (Ref 1-3). In oil and gas environments containing H2S and CO2, the corrosion behavior of metal materials is influenced by temperature, pressure, fluid velocity and flow type, gas partial pressure, gasto-liquid ratio, oil–water chemical composition and microorganization of materials. However, the strongly corrosive H2S will cause the deterioration of metal materials due to the hydrogen induced cracking, stress corrosion cracking, and other localized corrosion by CO2 corrosion (Ref 4-6). Several researches have investigated in the CO2-H2S-H2O corrosion system to better understand the corrosion behavior Z.F. Yin, School of Mechanical and Material Engineering, Xian University, No.1 in Keji 6th Road, Xian 710065, Peoples Republic of China; and Shaanxi Key Labor
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