The experiment research of corrosion behavior about tubing steel in environment with high H_2S and CO_2 content

摘要

The corrosion behavior of C100 steel in simulated environments with high H_2S and CO_2 content was studied through high-temperature and high-pressure autoclave, and the H_2S 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 Fe0.95S, FeS0.9, Fe0.985S, Fe7S8 and FeS, and the absence of iron carbonate in the corrosion scales suggests that the corrosion process is governed by H_2S corrosion. The corrosion rate decreases in the initial stage and then increases with the enhance of the temperature. There exists a minimum corrosion rate at about 110°C. Under the partial pressure of H_2S lower than 9MPa, the corrosion rate decreases with the increase of P_(H_2S). While over 9MPa, a higher P_(H_2S) 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. The precipitation of the second phase particles at the grain boundary or in crystal grain, the dislocation tangle and the dislocation pinning of the dispersion carbonide hinder the SSC cracks to propagate.