| During the process of exploitation via fire-drive technology,oxygen is depleted because of combustion,while nitrogen and other gases are ejected through producing well,engendering fire-drive tail gas.Fire-drive tail gas in Xinjiang Oil Field contains hydrogen sulfide and carbon dioxide,and there may be oxygen left,resulting in corrosion of metallic materials of pipelines and equipment.At present,research of corrosion mechanism about fire-drive tail gas and materials of fire drive flue gas refilling technology was absent.Besides,the interaction between oxygen,hydrogen sulfide and carbon dioxide and corrosion mechanism of them were studied more deficiently.Therefore,it’s necessary to study corrosion mechanism of metallic materials in fire-drive tail gas environment to provide oil field with theoretical basis about corrosion research and protection.Based on field conditions of relevant links of fire drive flue gas refilling technology including pressure and temperature,four experimental conditions were set up comprising O2 and CO2,H2S and CO2,O2 and H2S and O2,H2S and CO2 so as to search corrosion mechanism of metallic materials under various corrosive gases coexistence systems.Moreover,different oxygen partial pressure was selected to study the effect of oxygen partial pressure on corrosion behaviour of metallic materials when O2,H2S and CO2 coexisted.The partial pressure or content of corrosive gases above was set up according to the composition of fire-drive tail gas in Xinjiang Oil Field.20G steel and 316L steel were chosen as experimental materials,which were commonly used for gas injection pipeline and compressor in injection station.Corrosion environment was simulated by means of high temperature and high pressure experiment in gas phase and liquid phase respectively,and weight-loss method was combined to measuer general corrosion rates.Then corrosion morphology and corrosion product were tested by microscopic analysis.Among the surface analysis technologies,3-D Profiler was applied to test localized corrosion,SEM to test surface and cross section micromorphology,EDS to test energy spectrum of elements of corrosion product and XRD to test chemical composition of corrosion product.For 316L steel,XPS was further used to test chemical composition more accurately because its corrosion product film was too thin.Through the methods above,corrosion behaviour could be understood,and interaction of gases and corrosion mechanism of metallic materials were obtained.By this thesis,some conclusions about corrosion of 20G steel and 316L steel under various conditions of fire-drive tail gas in Xinjiang Oil Field were reached:20G steel was severely corroded under conditions of fire-drive tail gas.Fe2+or Fe(OH)2 was oxidized by O2.When coexisting with CO2,oxygen restrained precipitation of ferrous carbonate and destroyed its integrity.The precipitation of sulfide was suppressed as well when O2 coexist with H2S.O2 also reacted with H2S,generating S or S8.After reacting between CO2,H2S and steel,corrosion product consisted of a a great deal of FeCO3 and a small quantity of sulfide.At last,when three types of corrosive gases coexisted,they all precipitated in corrosive reaction directly and corrosion product was oxidized by O2 and deoxidized by H2S repeatedly.And the increase of O2 partial pressure added complexity of structure and composition of corrosion product,decreasing the compactness and accelerated the corrosion.316L steel showed excellent general corrosion resistance.There were alloy elements depositing in the corrosion product scale and passivation occurred.However,when O2 partial pressure became sufficiently high,S8 precipitated locally,resulting in breaking point in the film,and pitting corrosion occurred.At last,aimed at the findings of this thesis about corrosion mechanism,some advice about corrosive observation and protection was offered,which had implications for corrosion protection and safety of field operation and decrease of cost of metallic materials. |
PDF Full Text Request