Laboratory studies involving corrosion in complex, multi-component gaseous environments at elevated temperatures

Abstract

The basis for the development of laboratory test programmes to provide data relevant to the selection and design of alloys for use in complex, multi-component gases, such as those produced during coal gasification, is discussed and some of the advantages and disadvantages are considered. The results from recent laboratory studies involving exposures of alloys in environments of low oxygen and high sulphur partial pressures at 300–700°C are reviewed and compared, with emphasis on non-equilibrium gases that approximate to those of gasifier systems. Conventional Cr₂O₃−forming alloys develop sulphide scales in this temperature range, but these do not necessarily lead to unacceptable rates of metal loss. The corrosion rate is usually determined by the composition and integrity of the inner scale layer, and can be very low if the layer consists of an oxide or a mixture of oxides and acceptably low if it consists of a refractory metal sulphide or a chromium-rich sulphide, such as FeCr₂S₄. However, mixed oxides plus sulphides are much less protective, often giving unacceptably high corrosion rates. The additions of oxide-forming elements, particularly silicon or aluminium, to iron (nickel)—chromium—base alloys can facilitate the formation of the oxide layer, thereby giving improved corrosion resistance.

Keywords:

• sulphidation
• oxidation
• coal gasification
• laboratory study