Stress Cracking Corrosion For 13cr Stainless Steel In High Temperature And High Pressure CO₂ Environment

13Cr stainless steel is a corrosion-resistant alloy steel with martensitic microstructures,which has strong resistance to CO₂ corrosion.It has been widely used in high temperature and high pressure oil and gas fields containing CO₂.However,in the course of service,oil pipelines also suffer from corrosion or even stress cracking in varying degrees.In this paper,the effects of Cl-concentration,CO₂ partial pressure and tension/compression stress on stress corrosion cracking of 13Cr stainless steel in high temperature and high pressure CO₂ were studied by means of high temperature electrochemistry,slow strain rate tension,four-point bending test and SEM and XPS.The results provide data and theoretical support for the application of 13Cr stainless steel in CO₂ environment.The results of slow strain rate tensile tests in different Cl-concentration and high pressure CO₂ environments show that the stress corrosion susceptibility decreases first and then increases in 5%NaCl solution.The stress corrosion susceptibility in different solutions is the highest,and the order is 5%>20%>10%.Cl-concentration had no effect on the composition of passive film.SEM and XPS analysis showed that the main components of passive film were Cr₂O₃ and FeO.High temperature electrochemistry showed that the passive film of 13Cr stainless steel immersed in 10%NaCl solution had the best corrosion resistance.High temperature electrochemistry and slow strain rate tension under different CO₂ partial pressures show that with the increase of CO₂ partial pressures,the concentration of passive film defects on the surface of 13Cr stainless steel increases,and the ability to resist ion intrusion in solution decreases,the corrosion resistance decreases,and the stress corrosion sensitivity increases.The effects of 3MPaCO₂ partial pressure and tension and compression stress in 5%NaCl solution on stress corrosion of 13Cr stainless steel were studied by four-point bending test and surface analysis.Both tensile stress and compressive stress increase the corrosion reaction rate and the damage degree of passive film.Under the same stress value,the damage effect of tensile stress on passive film is obviously greater than that of compressive stress.The failure modes of passive film are different between tensile stress and compressive stress.Under the action of tensile stress,micro-cracks are formed on the surface of the sample.When the tensile stress increases to a certain value,crack propagation causes the failure of passive film,and stress concentration at the failure site leads to stress corrosion cracking.Under the action of compressive stress,the bonding between the sample and the matrix is poor,and when the compressive stress increases to a certain value,a very small part of passive film will be detached.Stress corrosion cracking is caused by stress concentration at the falling place.