CORROSION OF Y, FE AND FE-15Y IN H-2-H2S MIXTURE UNDER 10(-3) PA S-2 AT 600-SIMILAR-TO-800-DEGREES-C

The corrosion of an Fe-based alloy containing 15 wt pet Y in H-2-H2S m ixtures under 10(-3) Pa S-2 was studied at 600 similar to 800 degrees C in an attempt to find materials with improved sulphidation resistanc e with respect to pure Fe. The presence of Y has been shown to be bene ficial, but not sufficient to the level expected. In fact, the alloy i s able to form at all tested temperatures an external FeS layer, benea th which a zone containing a mixture of the two sulphides is also pres ent. Thus, Fe can still diffuse through this region to form the outer FeS layer with non-negligible rate. The corrosion rate of Fe is consid erably reduced by the Y addition, but the alloy corrodes still much mo re rapidly than Y. The sulphidation kinetics is generally rather irreg ular for both the pure metals, while the corrosion rate of the alloy d ecreases with time and tends to become parabolic after an initial peri od of 12 similar to 17 h. The sulphidation behaviour of the alloys is discussed by taking into account the presence of an intermetallic comp ound Fe17Y2 and the limited solubility of Y in Fe.