| Along with exploition of high acid oil and gas wells, H2S, CO2corrosion problem had extremely restrained exploition and transportation. The existence of H2S, CO2would enhance the possibility of hydrogen induced cracking (HIC) of pipeline steel.X52pipeline steel has been used frequently in exploring and transporting oils andnatural gases.so study on hydrogen permeation and the possibility of hydrogen induced cracking of this kind of material is of great importance in exploring and transporting oil and natural gas safely and it helps manager to take some measures to avoid disaster events.In this paper, X52pipeline steel was used as experimental materials.The hydrogen permeation behaviors of X52steel in CO2, H2S and H2S/CO2environments were studied by Devnathan-Stachurski double cell method, and the influence of acidic gases,temperature and pH on hydrogen permeation was summarized further. The hydrogen induced cracking of the X52steel in different acidic gases, different temperatures was investigated by immersion experiments. The corrosion scales were studied by scanning electron microscopy (SEM) and energy disperses spectroscopy (EDS).The results showed that the steady state permeation current in solutions dissolved acid gases decreased with the order of H2S, H2S/CO2and CO2. H2S in the corrosive medium had "poisonous effect" to prevent hydrogen atom complexing, which led to steady state hydrogen permeation current in H2S and H2S/CO2environment were greater than the CO2environment. In H2S/CO2environment, due to the competitive adsorption of CO2on the surface of the material, the role of "poisonous effect" was reduced, so the steady state hydrogen permeation current in H2S environment was greater than that in H2S/CO2coexist environment. In CO2, H2S and H2S/CO2environment, the hydrogen permeation behaviors of X52steel mainly affected by the ambient temperature and pH value.The permeation current increased with increasing ambient temperature, while increasing pH value mitigated the permeation current. The relationship of hydrogen diffusion coefficient and temperature conforms to the Arrhenius equation.Diffusion activation energy values measured in CO2, H2S, H2S/CO2gas environment diffusion activation energy values were26105J·mol-1,27727J·mol-1and27935J·mol-1respectively. Specimen surface in the three different corrosive environments generated different types of corrosion product films, which would hinder the diffusion of hydrogen atoms at different degrees, so diffusion activation energy in CO2, H2S and H2S/CO2environment is different. However, diffusion activation energy of pure iron was7710J· mol-1as reported by literature, because alloying elements of X52steel hindered the diffusion of hydrogen atom, diffusion activation energy of X52steel in the three kinds of atmospheres were far greater than that of pure iron. At the same temperature, the corrosion scales of X52steel in H2S environment were denser than that in H2S/CO2coexistence environment. Increasing temperatures would increase the content of depleted S-type corrosion product (FeS1-x) of corrosion product films, structure of corrosion product film containing a large amount of FeS1-x was relatively loose, which enhanced the severity of pitting. Comparative analysis of the crack length ratio (CLR), the crack width ratio (CTR) and crack sensitivity ratio (CSR) of X52steel specimens in H2S environments at20℃, H2S environments at50℃, H2S/CO2environments at20℃and H2S/CO2environments at50℃, hydrogen induced cracking parameters in H2S/CO2environment were lower than that in H2S environment, while temperatures promoted the nucleation and propagation of hydrogen induced crack. According to API standards that CLR≤15%, CTR≤3%-5%, CSR≤1.5%-2%are found, the material is not sensitive to hydrogen induced cracking. In this study, the crack length ratio (CLR), the crack width ratio (CTR) and crack sensitivity ratio (CSR) of X52steel in H2S environments at50℃was respectively5.5%,1.5%and0.12%, which was the maximum value of the four kinds of environments.However they were far less than the upper limit requirements, so X52pipeline steel is not sensitive to hydrogen induced cracking. |
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