Study On Stress Corrosion Of P110 Steel In Solution Containing Cl^- Under CO₂/O₂ Environment

In recent years,the oil field environment is becoming more and more complicated with the oil field production period goes on,and corrosion of casing pipe is much worse now.Working environment of casing pipe becomes worse,leading to appearance of stress corrosion cracking(SCC).At the same time,NaCl solution is the main component of drilling fluid,which is highly corrosive to the casing.In the process of drilling,sometimes according to the needs of the production uses air drilling.Injecting oxygen to the underground,which will cause corrosion of the tubing.Stress corrosion is the most devastating in a variety of corrosion behavior,owing to its hige corrosion rate which often brings catastrophic accidents suddenly,and the production and the economy suffer huge losses.Among of them stress corrosion cracking is the most serious.Therefore,it is importent for the safety of oil casing steel to study the P110 steel SCC corrosion behavior.In the present work,the basic mechanical properties of P110 steel were studied,including chemical composition,hardness,impact and tensile test,which provided the basic data for the subsequent experimental analysis.The mechanism of SCC of different dissolved oxygen and different rate of O2/CO2(saturated CO2,10%O2+90%CO2,50%O2+50%CO2,saturated O3)on P110 steel were discussed by slow tensile test.By means of calculating the stress corrosion susceptibility index amount of P110 casing steel in saturated CO2,dissolved oxygen 10.5 mg/L,saturated O2(dissolved oxygen 19.5 mg/L),10%O2+90%CO2,50%O2+50%CO2,dissolved oxygen 12.5 mg/L and other corrosion environment.The microstructure of fracture and the mechanism of stress corrosion cracking were studied.The tensile strength,elongation and shrinkage of various corrosive environments were obtained by the slow tensile test and impact test under the simulating corrosion environment.The results showed that with the increase of the rate of O2/CO2,the value of the impact strength,the tensile strength,elongation and shrinkage of P110 steel in saturated CO2,10 O2+90%CO2,50%O2+50%CO2 and saturated O2 system gradually reduced.Similarly,under the corrosion environment of different dissolved oxygen concentration(19.5 mg/L,12.5 mg/L and 10.5 mg/L),the value of the impact strength,tensile strength,elongation,shrinkage of P110 steel gradually increased with the decrease of O2 concentration rate.The influence of the SCC of P110 steel in CO2 environment filled with saturated oxygen was studied by the slow tensile test.The results showed that with the increase of O2 concentration,the tensile strength,elongation,shrinkage and fracture time of P110 steel decreased and the stress corrosion index increased,and the fracture characteristics were changed from the toughness to the brittle gradually.It was seen that O2 significantly promoted the occurrence of P110 steel SCC in CO2 environment.The influence of the SCC of P110 steel in 3.5%NaCl solution filled with different dissolved oxygen was studied by slow tensile test.The results showed that with the increase of O2 content,the value of the tensile strength,elongation,shrinkage and fracture time of P110 steel decreased,the stress corrosion index and the stress corrosion susceptibility gradually increased,and the fracture brittleness characteristics became more and more obvious,which showed that O2 significantly promoted the occurrence of P110 steel SCC in 3.5%NaCl solution.