Study On Corrosion Resistance Of 2205 Duplex Stainless Steel In Underground Environment

Based on the review of previous research and development for 2205 duplex stainless steel tubes,the physical and chemical properties analysis,simulating corrosion test,and electrochemical test analysis for such tube,combined with modern analysis techniques,i.e.SEM,EDS,XRD,and XPS,were performed to analyze the corrosion resistance of 2205 duplex stainless steel in harsh corrosive environments.The corrosion resistance mechanism was also explored in this thesis.The simulating corrosion test results show that the 2205 duplex stainless steel exhibited high corrosion resistance during the simulated CO2 corrosion test due to Cr element enriched on the surface and then Cr2O3 passivation film formed.The corrosion rate was as low as 0.0076 mm/a.The corrosion resistance decreased with the increase of temperature and Clconcentration.When the CO2 partial pressure increased,the carrosion rate rised fisrt and then remained constant.In the CO2 and CO2 + H2 S environment,2205 duplex stainless steel has good SCC resistance.However,in the corrosion environment containing CO2+H2S+ elemental sulfur,the addition of elemental sulfur lead to stress corrosion cracking.Under the corrosion condition of fresh acid,the corrosion rate of 2205 is still within the standard prescribed level,even it increases a bit;By comparison,the corrosion of 2205 in the corrosion environment of independent residual acid containing CO2 and independent formation water is very slight.In the whole process of acidizing completion,the deeper the depth of the well,the greater the corrosion rate of 2205 duplex stainless steel,and the maximum pitting depth showed a decreasing trend.In the corrosion environment of completion fluid,the uniform corrosion rate increases with the increase of CO2 content,but it still belongs to slight corrosion.The electrochemical test results show that the corrosion resistance of 2205 has been obvious improved because of the addition of corrosion inhibitor in the corrosion environment of fresh acid.Meanwhile,the self-corrosion current density increases and also the corrosion ratewhile the corrosion resistance decreases with the temperature increases.In the residual acid,formation water CO2,and completion fluid corrosion environments,the anode polarization curve of 2205 presents a clear passivation zone.The corrosion reaction is controlled by the anode reaction process,and the corrosion rate is maintained at lower levels.In the acid-corrosion environment,as the temperature increases,the corrosion inhibitor particles first adsorbed on the metal surface and then fall off.The adsorption capacity gradually weakens and the corrosion process is obviously aggravated.In the residual acid,formation water CO2 and completion fluid corrosion environment corrosion environments,2205 polarization resistance showed a downward trend with the increase of temperature,but it still own good corrosion resistance.