| ZHAO Guoxian,LIU Ranran,LI Qiongwei,YANG Lihua,SUN Yulai,DING Langyong,WANG Yingchao,ZHANG Siqi,SONG Yang.Corrosion Characteristics of 5Cr Oil Casing Steel in Cl−-containing CO2 Environment[J],53(6):55-66 |
| Corrosion Characteristics of 5Cr Oil Casing Steel in Cl−-containing CO2 Environment |
| Received:March 27, 2023 Revised:November 06, 2023 |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2024.06.005 |
| KeyWord:5Cr oil casing steel CO2 corrosion corrosion product film Cr element enrichment electrochemical impedance spectroscopy wire beam electrode |
| Author | Institution |
| ZHAO Guoxian |
School of Material Science and Technology, Xi'an Shiyou University, Xi'an , China |
| LIU Ranran |
School of Material Science and Technology, Xi'an Shiyou University, Xi'an , China |
| LI Qiongwei |
Research Institute of Oil & Gas Technology, Changqing Oilfield, Xi'an , China;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Field, Xi'an , China |
| YANG Lihua |
Research Institute of Oil & Gas Technology, Changqing Oilfield, Xi'an , China;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Field, Xi'an , China |
| SUN Yulai |
Research Institute of Oil & Gas Technology, Changqing Oilfield, Xi'an , China;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Field, Xi'an , China |
| DING Langyong |
School of Material Science and Technology, Xi'an Shiyou University, Xi'an , China |
| WANG Yingchao |
School of Material Science and Technology, Xi'an Shiyou University, Xi'an , China |
| ZHANG Siqi |
Xi'an Moore Petroleum Engineering Laboratory Limited Company, Xi'an , China |
| SONG Yang |
Xi'an Moore Petroleum Engineering Laboratory Limited Company, Xi'an , China |
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| Abstract: |
| Wire beam electrode (WBE) technology can accurately describe the corrosion potential and current density distribution of the electrode surface, and EIS technology can obtain the corrosion electrochemical information of the metal substrate under the cover of the corrosion product film, and combine the advantages of the two to study and analyze the CO2 corrosion characteristics of 5Cr oil casing steel at different temperature accurately and in detail. Among them, the corrosion products form a barrier film on the inner wall of the pipeline have a great degree of protection for the pipe body itself and reduce the overall corrosion rate. However, there will be rupture and regeneration of the product film at different stages of corrosion, and the pores of the corrosion product film will cause the active site of the substrate to react, and local corrosion is prone to occur here, and there is a tendency to form pitting corrosion, and the effect of local damage on local corrosion of the substrate has not gotten much enough attention, so it is necessary to study it. The corrosion characteristics of 5Cr oil casing steel in the environment of 0.1 MPa CO2 and 65 g/L Cl− were studied by immersion test and electrochemical test. The corrosion product layer for different corrosion time was analyzed by XRD, XPS, SEM and EDS and the polarization curves and impendence spectroscopy test were used to analyze electrochemical characteristics of 5Cr oil casing steel. The results showed that the corrosion product layer on 5Cr oil casing steel surface was composed of FeCO3 and Cr(OH)3 inlays in inner layer and the grainy CaCO3 in outside layer. After 14 d, the Cr enrichment in the corrosion product layer reached more than 30%, and the mass fraction ratio of Cr/Fe in the product layer reached higher, which was about 15 times of the substrate. As the corrosion progressed, the overall resistance caused by the fitted charge transfer resistance and the product film coverage in the circuit became larger, so that the anode reaction was inhibited, the charge transfer process became more and more difficult, and the resistance of the electrochemical reaction increased significantly. In the early stage of corrosion, there was local inhomogeneity, and with the progress of corrosion, the electrode corrosion potential had a negative shift, and the final distribution range was −0.59-−0.61 V, and the anode current area on the electrode surface was greatly reduced. The capacitive impedance arc with a large radius is formed in the electrochemical impedance spectrum of 5Cr oil casing steel, the film coverage degree and compactness of the corrosion product increase, the resistance caused by the charge transfer resistance in the equivalent circuit tends to increase, and the resistance of the electrochemical reaction increases significantly. The formation and expansion of the local anode zone on the surface of 5Cr oil casing steel have the tendency to cause pitting corrosion, and it is formed at the void channel of the film in the early stage of corrosion. The corrosion products are gradually deposited on the inner wall of the pit, and a protective surface layer with obvious Cr enrichment is formed on the inner wall of the pit, and the original pitting corrosion area is transformed from the original anode active point to the cathode area, which inhibits its development. The polar transformation phenomenon of the 5Cr oil casing steel area current under the corrosion product film occurs from the cathode to the anode, and the pores in the product film make the 5Cr oil casing steel base metal corroded, resulting in the appearance of anode current. |
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