This work was carried out within a research program on the materials for a coal liquefaction plant. One of the most critical problems of this technology is the selection of construction materials for the reactor and the hot separator. Corrosion tests were performed in an autoclave under conditions similar to those met in a hydrogenation reactor at a temperature of 723°K and a pressure of 25 MPa. Investigations were performed on ferritic and austenitic steels in an environment containing H2, H2S, H20, and hydrogenation production vapors. The corrosion rates of the steels were calculated and compared to those obtained at several coal liquefaction plants. The scales were analysed using various metallographic methods, i.e., optical microscopy, scanning electron microscopy, x-ray spectrometry, wavelength dispersive x-ray spectrometry and others. Thermochemical diagrams for Fe-Cr-Ni-S-O systems were constructed, and the experimental results are discussed in relation to the diagrams. Based on this information, the processes taking place on the surface of construction materials in the reactor and hot separator at the coal liquefaction plant were interpreted.
The investigations prove that the corrosion products on the low-chromium steels are composed of sulfides that do not serve as a sufficient barrier against corrosion.
In addition to sulfide corrosion products on 17% chromium, ferritic steels and Cr-Ni steels also contain Cr2O3 oxide. For these steels, corrosion rates are lower by an order of magnitude than those for low-chromium steels.
