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The corrosion behavior of the Xinjiang oil field (China) gathering pipeline steel was studied by a weight-loss technique, microscopic characterization, an X-ray diffractometer, and a three-dimensional microscope. When the CO2/O2/H2S system contains a low H2S concentration (100 ppm), the CO2 and O2 concentrations increase and the corrosion rate of 20# steel increases. When the CO2 concentration increases (10–30%), the corrosion rate increases by 8.84%, and the corrosion product film thickness increases significantly by 231.01%, while when the O2 concentration increases (0.5–2.5%), the corrosion rate increases by 29.24%, and the thickness of the product film increased by 29.21%. The two mechanisms that promote the increase in the corrosion rate are different. CO2 promotes the cathodic reaction to increase the corrosion rate, while O2 accelerates the corrosion process by destroying the structure of the corrosion film. The morphology of corrosion products is more complex. The increase in O2 concentration increases the number of corrosion defects, and the change in CO2 concentration has little effect on local corrosion. The corrosion products mainly include FeCO3, Fe2O3, and FeS2, but S and FeS are not formed. The reason is that CO2 controls the corrosion process, and a large amount of O2 is consumed, which weakens the interaction between H2S and O2. [ABSTRACT FROM AUTHOR]

Multi-component thermal fluid flooding is an efficient thermal technology for heavy oil recovery. However, the oil and gas transported by the gathering pipeline exhibit the large temperature difference along with high O2, H2S and CO2 contents, which may easily bring serious corrosion problems to the pipeline. In this article, the present work aims to study corrosion behavior and corrosion mechanisms in a CO2/H2S/O2 coexistence system using a Huning 4 block gathering pipeline material, particularly clarifying the influence of temperature on the corrosion behavior and localized corrosion mechanism. The high-temperature autoclave was used to simulate the corrosion environments. The corrosion products at various temperatures were examined via three-dimensional optical microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The maximum uniform corrosion rate of L245NS is 0.5149 mm/a (at 333 K), and the maximum local corrosion rate is 4.6258 mm/a (at 363 K). At lower temperatures (303–333 K), the corrosion product film possessed a double-layered membrane, where the bottom layer was enriched with S-based elements, mainly FeS or FeS2 and the upper layer was mainly covered by FeCO3 with the uniform corrosion state. Applying the higher temperatures (363–393 K) made the FeCO3 grain coverage more continuous and dense, leading to the formation of a dense double-layered film, where the uniform corrosion was suppressed, while localized corrosion emerged. The thermodynamics shows that an increase in the temperature was found to decrease the solubility product coefficient of FeS and FeCO3, inducing the appearance of a protective layer and inhibiting the corrosion process. [ABSTRACT FROM AUTHOR]

The aim of this work was to understand the synergistic effect of O2 and H2S on the corrosion behavior of N80 steel in a simulated high-pressure flue gas injection system. Weight loss measurements show that the presence of O2 and an increase in temperature significantly accelerated the general corrosion rate of the N80 steel. We calculated a gray relational grade between different impact factors and the general corrosion rate from the results of an orthogonal experimental corrosion rate. The grade ranking of impact factors was: O2 concentration (0.817) > temperature (0.706) > total pressure (0.689) > H2S concentration (0.665) > CO2 concentration (0.517). Surface characterization of corrosion scales was done using scanning electron microscopy, energy-dispersive spectroscopy, x-ray powder diffraction, and 3D optical microscope analysis. The results show that in the O2-H2S-CO2-H2O coexistence system the products were composed mainly of FeCO3, FeS, Fe2O3, Fe3O4, and elemental sulfur. The results of the corrosion rate test and the characterization show that the presence of O2 greatly accelerated the corrosion process and changed the corrosion mechanism. Elemental sulfur, which was generated by the reaction between the H2S and the O2, participated in the corrosion process of the N80 steel. It could be considered that the synergistic effect of O2 and H2S accelerated the corrosion of the N80 steel. In addition, the porous structures of the corrosion scales and the severe local pits show that the high content of O2 inhibited the formation of FeCO3 and aggravated the corrosion of N80 steel. [ABSTRACT FROM AUTHOR]

Fire-driven technology has triggered significant interest as an effective technology to improve oil recovery. However, corrosion can easily occur since fire-drive tail gas usually contains corrosive gases, such as CO 2 and O 2. In this work, the corrosion behavior of several 35CrMo steel samples in a fire-drive tail gas environment was studied using weightlessness measurements, surface characterization techniques, and high temperature-pressure electrochemical tests. The research results show that the average corrosion rate of 35CrMo steel in a CO 2 –O 2 coexisting environment is much higher than the average corrosion rate in a CO 2 -containing environment or O 2 -containing environment. The localized corrosion rate of 35CrMo steel in an O 2 -containing environment is higher than the localized corrosion rate in both the case of a CO 2 -containing environment or a CO 2 –O 2 one. The pitting factor shows that 35CrMo steel exhibits a localized corrosion in an O 2 -containing environment. The surface characterization results demonstrate that, in a typical fire-drive tail gas environment, the corrosion products are composed of Fe 2 O 3 , FeOOH, and Fe 3 O 4. The high temperature-pressure electrochemistry test data shows that in a CO 2 –O 2 -oexisting environment, the membrane resistance decreases upon an increase in the O 2 content. [Display omitted] • Forming an acidic microstructure in CO 2 /O 2 coexisting environment. • The aggregation of corrosion products and H 2 makes the upper products crack. • The constant phase angle element after film formation is capacitive. [ABSTRACT FROM AUTHOR]