Abstract: The corrosion behavior of a X65MS pipeline steel in saturated H₂S/CO₂ environment is studied by simulating oil and gas delivery environment with high temperature and high pressure reactor. The corrosion rate under different immersion time periods is measured by the mass loss method， and the phase composition and morphology of corrosion products are analyzed by means of X-ray diffraction (XRD)， scanning electron microscope (SEM)， energy disperse spectroscopy (EDS) and electron probe microanalysis (EPMA)， respectively. The results show that the corrosion rate can be divided into three stages， i.e. the initial corrosion rate decreases rapidly， then changes slowly and finally flattens out. The corrosion process is mainly controlled by H₂S corrosion， and the products are dominated by ferrosulfur compound (Fe_○xS_○y). With the increase of immersion time， the proportion of iron decreases， the proportion of sulfur-rich phase increases， the film thickness of corrosion products increases， and the structure changes from loose to uniform and compact gradually. The corrosion products are mackinawite→troilite→pyrrhotite， and the stable pyrrhotite has a protective effect on the corrosion resistance of X65MS pipeline steel matrix.

Key words: X65MS pipeline steel, H₂S/CO₂ corrosion, corrosion rate, ferrosulfur compound, corrosion products