Effects of H₂S/CO₂ Partial Pressures on Pitting Behavior of Super Duplex Stainless Steel UNS S32750 in a Environment of High Temperature and High Chloride Content

Corrosion immersion tests were conducted on super duplex stainless steel (SDSS) UNS S32750 in a environment of high temperature, high chloride concentration and different partial pressures of H₂S and CO₂. The general corrosion rate, pitting corrosion morphology of SDSS UNS S32750 and composition of passive film on its surface by the methods of mass loss, laser confocal microscopy and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the SDSS UNS S32750 had a good general corrosion resistance and pitting corrosion resistance when the partial pressures of H₂S and CO₂ were no higher than 30 kPa and 150 kPa respectively under the test condition. When the partial pressures of H₂S and CO₂ were 100 kPa and 500 kPa respectively, pitting corrosion happened to the SDSS UNS S32750 due to the localized loss of the passive film and consequent anodic dissolution. The passive film was mainly composed of FeS₂, NiO, NiS, Cr₂O₃ and Fe(OH)₂.