Effect of CO₂ Partial Pressure on the Corrosion Behavior of S135 Steel in CO₂/H₂S Coexistence Systems

Abstract

In order to clarify the influence and regularity of CO2 partial pressure on the corrosion behavior of S135 steel in the CO2/H2S coexistence system， the corrosion simulation test of S135 steel in CO2/H2S coexistence systems was conducted by using high temperature and high pressure reactors.Meanwhile， the weight loss method， constant load method， X - ray diffraction (XRD)， scanning electron microscope(SEM)， energy spectroscopy (EDS) and three-dimensional profile scanner were used to study the effects of different CO2 partial pressures on the corrosion behavior rules of S135 steel in CO2/H2 S coexistence systems at 100 ℃.Results showed that as the CO2 partial pressure increased， the corrosion rate of S135 steel increased， and the yield strength damage became intensified.When the CO2 partial pressures were 5， 10， 15， and 20 MPa， the yield strength (σs) damage rate were 1.4%， 3.6%， 4.5%， and 15.9%， respectively.Additionally， the tensile strength (σb) damage rates were 1.2%， 3.4%， 5.2%and 15.4%， respectively.S135 steel underwent general corrosion under low CO2 partial pressure， and with the increase of CO2 partial pressure， the corrosion behavior developed into mainly general corrosion， supplemented by local corrosion.In the initiation stage， the stress corrosion cracking was dominated by local anodic dissolution (pitting corrosion).As the CO2 partial pressure increased， stress corrosion cracks were more likely to grow， and the stress corrosion sensitivity increased， which caused the corrosion process of the substrate became aggravated.

Keywords

• co2 partial pressure|s135 steel|co2/h2s|weightlessness corrosion|stress corrosion