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The leakage accidents due to the corrosion on the internal bottom plates occurred frequently in the tanks which are involved in the first commercial direct coal liquefaction production line. For comprehending the corrosion, the compositions of the sedimentary liquids from diesel, hydro‐upgrading feed oil, heavy solvent oil, thick condensed oil and hydro‐stabilizing feed oil are surveyed in the first place, the results show that all the sedimentary liquids are almost neutral; the cations and anions in all sedimentary liquids are the same; the majority of ions are Ca2+, Cl−, and SO42− in these five sedimentary liquids. Then the immersion and electrochemical tests are implemented, it is represented that corrosion of same sedimentary liquid on Q235 steel coupon is severer than that on 16MnR steel coupon; the sedimentary liquid from hydro‐stabilizing feed oil has the most violent causticity; all the corrosives may hold the Fe2CO3 and Fe2O3; the polarization behavior of Q235 steel in the sedimentary liquid from hydro‐stabilizing feed oil is similar to that of 16MnR steel. Finally, the influences of different ions on the corrosivity of sedimentary liquids are also investigated, it can be concluded that the 672‐h general corrosion rates of Q235 and 16MnR steel coupons in all sedimentary liquids increase with improve of Cl‐ content but decrease with rising of SO42− content; in the sedimentary liquids containing large numbers of Cl‐ and Ca2+, the Ca2+ is the definitely vital ion which deeply influences the corrosivity of sedimentary liquids. The achievement of this research work also can be applied in the prevention for corrosion formed on the internal bottom plates of tanks referred to the direct coal liquefaction process. © 2018 American Institute of Chemical Engineers Process Saf Prog 37: 506–517, 2018 [ABSTRACT FROM AUTHOR]

In the coal direct liquefaction process line distribution of finished oil tanks and semifinished oil tanks, corrosion of tank reservoir parts and the gas phase are important. To prove the corrosion‐influencing factors and corrosion processes of various parts of the storage tank, further research was carried out based on the previous research. As the process of corrosion of the tank wall is affected by the sulfur element in oil, the sulfur content in refined oil and semi‐refined oil was analyzed first. The results show that: the sulfur content is high for hydro‐upgrading feed oil and hydro‐stabilizing feed oil, but the sulfur content is low for thick condensed oil and diesel. The tank is mainly made of 16MnR and Q235‐b steel in the process plant. In this article, 16MnR and Q235‐b steel coupons are used for static coupon experiments and electrochemical experiments to determine the influencing factors and processes that affect the corrosion of the reservoir and the gas phase. The static coupon tests show that the corrosion rates are similar for 16MnR and Q235‐b steel coupons in the reservoir location and for the gas‐phase parts. And, the corrosion rates decrease with time. The corrosion rates of 16MnR and Q235‐b steel in hydro‐stabilizing feed oil are relatively high, and the corrosion rates of 16MnR and Q235‐b steel are relatively low, though the difference is not significant. The 16MnR corrosion rate is relatively high in the reservoir location compared to that of the gas phase. The corrosion rate of Q235‐b steel in the gas‐phase space is relatively higher than that of the reservoir location. Electrochemical tests show that the corrosion rates of 16MnR and Q235‐b steel in hydro‐stabilizing feed oil are higher than those in the other three oils. Finally, the effect of temperature on the corrosion rate was studied by the static coupon experiment. The results show that the corrosion rates of 16MnR steel and Q235‐b steel in the four kinds of oil products increase first and then decrease when the temperature changes from 70 to 110°C. The corrosion rate reaches the maximum when the temperature is 90°C. The research of this article can provide some technical support and help for the corrosion protection and safety design of oil tanks in the direct liquefaction process. © 2018 American Institute of Chemical Engineers Process Process Saf Prog 37:419–426, 2018 [ABSTRACT FROM AUTHOR]