Mechanisms of Corrosion of Structural Materials in Contact with Coal Chars in Coal Gasifier Atmospheres. Semi-Annual Progress Report

摘要

Five chromia-former alloys, Inconel 671, Hastelloy X, 310 stainless steel, Incoloy 800, and Haynes 188, have been exposed to both FMC char (2.7% S) and th Husky char (0.9% S) at 1600 and 1800 exp 0 F for 96 hours. Inconel 671 and 310 stainless corroded the most rapidly, Haynes 188 and Hastelloy had the best corrosion resistance, and Incoloy 800 was intermediate. Corrosion in the higher sulfur char (FMC) was generally more severe than that in the lower sulfur char (Husky), although the more corrosion-resistant alloys (Haynes 188 and Hastelloy X) showed minimal differences from one char to another. Hastelloy X showed an unusual effect of temperature, the corrosion rate being higher at 1600 than at 1800 exp 0 F in FMC char. The effect of preoxidation on FeCrAlY was to retard corrosion. However, an incubation period was observed, during wich sulfur penetrated the alumina film, followed by linear corrosion kinetics. The beneficial effect increased with increasing film thickness up to a critical value, beyond which corrosion was greater than for thinner films. It is believed that mechanical breakdown of the film caused this effect. A coating of 63Al-33Cr-4Hf on Incoloy 800 markedly retarded corrosion in FMC char at 1800 exp 0 F. Protection was attributed to the formation of Cr sub 2 S sub 3 and Al sub 2 S sub 3 in the reaction product. Corrosion in a mixture of H sub 2 -10% H sub 2 S at 950 exp 0 C (conditions giving a comparable sulfur activity as that in the FMC char at 1800 exp 0 F) was 6 times more rapid for Inconel 671 and over 3000 times more rapid for Hastelloy X. The scale structures were considerably different than those formed in char. 21 figures. (ERA citation 08:025315)