| LI Jinling,MA Wenjun,ZHU Shidong,QU Chengtun,FU Anqing.Adsorption and Corrosion Mechanism of CO2-H2S on α-Fe(110) Close-packed Plane in Humid Environment[J],53(20):82-93 |
| Adsorption and Corrosion Mechanism of CO2-H2S on α-Fe(110) Close-packed Plane in Humid Environment |
| Received:November 01, 2023 Revised:January 04, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.20.007 |
| KeyWord:CO2-H2S Cl− first principles α-Fe(110) close-packed plane adsorption characteristic corrosion mechanism |
| Author | Institution |
| LI Jinling |
Shaanxi Province Key Laboratory of Environmental Pollution Control and Reservoir Protection Technology of Oilfields, College of Chemistry and Chemical Engineering,Xi'an , China ;Shaanxi University Engineering Research Center of Oil and Gas Field Chemistry,Xi'an , China |
| MA Wenjun |
Shaanxi Province Key Laboratory of Environmental Pollution Control and Reservoir Protection Technology of Oilfields, College of Chemistry and Chemical Engineering,Xi'an , China |
| ZHU Shidong |
School of Materials Science and Engineering,Xi'an , China ;Key Laboratory of Corrosion Protection and New Materials for Oil and Gas Fields of Shaanxi Higher Education Institutes, Xi'an Shiyou University, Xi'an , China |
| QU Chengtun |
Shaanxi Province Key Laboratory of Environmental Pollution Control and Reservoir Protection Technology of Oilfields, College of Chemistry and Chemical Engineering,Xi'an , China ;Shaanxi University Engineering Research Center of Oil and Gas Field Chemistry,Xi'an , China |
| FU Anqing |
National Key Laboratory of Oil and Gas Drilling and Transportation Equipment, CNPC Tubular Goods Research Institute, Xi'an , China |
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| Abstract: |
| CO2 and H2S gas and the droplets containing Cl− often co-exist on the top of the pipelines used for transporting oil and gas, which is different from the bottom environment of the pipelines, resulting that the corrosion processes are complex and the pipelines suffer from more serious local corrosion. Up to now, there are numerous studies about the effects of CO2 or/and H2S on pipeline corrosion, but most of them mainly focus on the corrosion protection and control, material selection and corrosion protection systems, etc., there are relatively few reports on the generation and evolution of corrosion from the perspective of theory, especially from the electron structure at the microscopic level. While revealing the mechanism of corrosion occurrence and evolution from the microscopic level is an important basis for formulating effective anti-corrosion measures. In this paper, the adsorption and corrosion characteristics of CO2-H2S on the α-Fe(110) close-packed plane in the humid environment containing Cl− were studied, and the adsorption and pitting mechanism was explored from the microscopic scale, in order to provide theoretical basis for the corrosion mechanism study and effective protection technology application of pipelines in oil and gas fields. Based on the first-principle method of Density Functional Theory (DFT), Materials Studio software was applied to establish an adsorption model of CO2, H2S and Cl− on α-Fe (110) surface. The adsorption energy, local density of states (LODS), partial density of states (PDOS) and differential charge density of CO2, H2S, CO2-H2S and CO2-H2S-Cl− on α-Fe(110) surface were calculated, respectively. The results showed that the adsorption energy of CO2, H2S, CO2-H2S and CO2-H2S-Cl− at the most stable position of α-Fe(110) was −4.065 eV, −3.961 eV, −8.538 eV and −12.775 eV, respectively indicating that the adsorption energy of CO2-H2S on the α-Fe(110) surface was more negative than that of CO2 and H2S alone, and Cl− further reduced the adsorption energy of CO2-H2S. When CO2 or H2S were adsorbed on α-Fe(110) surface, for CO2, the 2p orbital of C and the 2p orbital of O overlap with the 3d orbital of Fe was in the energy range of 1.6-4.7 eV and −6.4-5.2 eV, respectively, indicating that adsorption energy of CO2-H2S on α-Fe(110) surface was smaller than that of CO2 and H2S alone, and Cl− further reduced the adsorption energy of CO2-H2S; While for H2S, the 2p orbital of S overlaps with the 3d orbital of Fe was in the range of −6.7-−3.1 eV; However, when CO2 and H2S were co-absorbed on the α-Fe(110) surface, there was a certain competitive effect between CO2 and H2S for electrons in the corrosion environment, and CO2 had an advantage, the adsorption energy of CO2-H2S on α-Fe(110) surface was smaller compared with the adsorption of CO2 and H2S alone, Cl− further decreased the adsorption energy of the system. The presence of Cl− not only further complicated the corrosion environment but also generated soluble chloride. Therefore, Cl− reduced the peak of LODS of CO2, H2S, and CO2-H2S, and the transfer trend was to lose electrons, the electrons of the matrix and corrosive medium could release more energy, and transition to lower energy level, thus the chemical bond strength between Fe and CO2 or H2S was strengthened. In addition, the 2p orbitals of Cl− overlaps with the 3d orbitals of Fe were at −6.8 eV and −5.7 eV, Cl− would be adsorbed to the surface of Fe and form chemical bonds, forming soluble chloride. Then the structure and composition of the corrosion product film were changed, and the density and stability would also be weakened, leading to more severe corrosion of the metal. In addition, the corrosion behavior of L360 steel in the humid environment containing CO2-H2S and different Cl− concentration was studied with a high temperature and high pressure autoclave. The results showed that with the increase of Cl− concentration, not only did the average corrosion rate increase gradually, even up to 2.935 mm/a, but also the pitting corrosion would become more and more serious, which was in good accordance with the simulated results mentioned above. Therefore, the co-adsorption of CO2 and H2S on α-Fe(110) close-packed plane has a certain synergistic and competition effect, and increases metal corrosion, FeCO3 will form preferentially, while the growth of FeCO3 is effected by H2S. And the presence of Cl− enhances the force between CO2 or/and H2S and α-Fe(110) surface, and weakens the protection of corrosion product film, further accelerating metal corrosion, especially pitting corrosion. |
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