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Conference Article: Comparison of mechanical and corrosion behaviour of Alloy 800 H and the new alloy AC 66

Pelz, W. (Bergbau-Forschung GmbH, Essen (Germany, F.R.)); Schendler, W.; Weber, H. (Mannesmann-Roehrenwerke AG, Duisburg (Germany, F.R.))

Abstract

In coal gasification plants based on nuclear process heat, materials are subjected to high temperature corrosion in process gas atmosphere at 750 to 900 deg. C. The process gas consists of steam, CO, CH4, CO2 and, depending on the gasified coal, low or high H2S-concentrations. The service problems can be divided as follows: 1. Gas-metal interaction: (a) high temperature corrosion. (B) sulphidation. (C) carburization. (D) internal oxidation or internal sulphidation. 2. Ash (slag)-metal interaction: (a) corrosion in molten salts. (B) erosion. 3. Mechanical loading: (a) embrittlement. (B) thermal fluctuations/strain fluctuations. (C) low cycle fatigue. (D) high temperature creep. Therefore materials for heat exchangers must be resistant to these types of high temperature corrosion and they should also have adequate creep rupture strength. Some commercial alloys and various model alloys were exposed to a process gas atmosphere to determine the corrosion behaviour and also stressed mechanically to investigate the interaction of high temperature creep behaviour and corrosion. The tests were carried out for a total period of 10,000 h and specimens were taken out after periods of 1000, 3000, 5000 and 10,000 h. A programme for the development of alloys was started with the aim of optimizing the chemical composition resulting in a good high temperature corrosion resistance and adequate mechanical properties, particularly high creep strength. However, the material must be such that it can be deformed to tubes. Compared with Incoloy 800, one of the new and optimized model alloys (30-32% Ni, 25-27% Cr, and Ce, Fe-balance) exhibits a very good corrosion resistance even when sulphur rich coal is gasified. The creep rupture strength at 900 deg. C is in the range of the creep strength for Incoloy 800.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
High temperature metallic materials for gas-cooled reactors. Proceedings of a specialists meeting held in Cracow, 20-23 June 1988
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--18, pp:176-183