Prediction of the lifetime behaviour for C/C-SiC tubes as high and ultrahigh temperature heat exchangers (HITHEX) - material characterisation and qualification

Heat exchangers for high and ultrahigh temperatures are a need and a precondition to realise high efficient fossil fired power plants based on the so-called Externally Fired Combined Cycle (EFCC) or the Indirect Fired Gas Turbines (IFGT). The main target of both processes is to increase the thermal efficiency of existing power plants by approximately 25% resulting in the same decrease in fuel consumption and, therefore, in the same reduction of CO2 formation. The main activities of the MPA University of Stuttgart in this project is focused on the characterisation and qualification of the structural material of the ultrahigh temperature heat exchanger (UHTHE) necessary in the above mentioned processes. The influence of the temperature and load on the material behaviour have been analysed by means of tensile tests and creep tests. The effectiveness of different coating systems and the interaction between coating system and basic material was also investigated. Additionally a set of leakage tests with tubes were performed at room temperature. The results of these experimental investigations have been compared with the design needs and also reflect the basis for the further material development and optimization. (orig.)