Corrosion behavior about tubing steel in environment with high H₂S and CO₂ content

Abstract

The corrosion behavior of C100 steel in simulated environments with high H₂S and CO₂ content was studied through high-temperature and high-pressure autoclave, and the H2S stress corrosion cracking (SSC) resistance of C100 steel was evaluated by SSC tests. Scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD) technique were employed to characterize the corrosion products and the metal matrix. The results indicate that all of the corrosion products in this investigation are mainly composed of different types of iron sulfide such as Fe_0.95S, FeS_0.9, Fe_0.985S, Fe₇S₈ and FeS, and the absence of iron carbonate in the corrosion scales suggests that the corrosion process is governed by H₂S corrosion. The corrosion rate decreases in the initial stage and then increases with the enhancement of the temperature. There exists a minimum corrosion rate at about 110 °C. Under the partial pressure of H₂S lower than 9 MPa, the corrosion rate decreases with the increase of $P_{H_2 S} $ While over 9 MPa, a higher $P_{H_2 S} $ will result in a faster corrosion process. When the applied stress is 72%, 80% and 85% of actual yield strength (AYS), all tested specimens show no crack, which reveals a superior SSC resistance.

Keywords

C100 steel / H₂S / CO₂ / corrosion rate / stress corrosion cracking

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