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Recent Developments of Techniques for the Life Assessment of Hot Parts

pubblicazioni - Articolo

Recent Developments of Techniques for the Life Assessment of Hot Parts

The Future of Gas Turbine Technology RECENT DEVELOPMENTS of TECHNIQUES for the LIFE ASSESSMENT of HOT PARTS C. Rinaldi, P. Broglia, L. De Maria, F. Cernuschi CESI RICERCA ( MILAN – ITALY) Claudia.rinaldi@cesiricerca.it Tel. +39 02 3992 4747 The life assessment of service exposed blades is a common concern to OEMs and operators not only on new models of gas turbines but also on proven gas turbines when operated in cycling conditions as recently more and more required in the present energy market. In the last three years these topics have been addressed in the frame of a wide research and development project dedicated to gas turbine technology , supported by the Italian government this Several aspects were studied, as single crystal material characterization, development of damage models to be used in life management systems, coating degradation studies and innovative NDTs development (such as frequency scanning eddy current method (F-SECT), photoluminescence piezospectroscopy and pulsed thermography). In this paper some of the main results will be described: currency1 an electrochemical technique able to give a quantitative integral indication of the nbase material degradation, which was studied on the single crystal CMSX-4 superalloy, after laboratory aging at two temperatures for times untill 3000h and also on the gauge length of specimens after interrupted creep tests. The electrochemical method is simlar to the well known EPR test on stainless steels. A good correlation was found between the spent creep life and the measured electrochemical parameter. currency1 The photoluminescence piezospectroscopy technique measures the compressive residual stress of the thermally grown oxide of EB-PVD TBCs. An innovative portable instrument was developed and validated comparing measurements on specimens aged in the laboratory in cyclic oxidation tests; it was applied also on components both new and after a plant operation period. The measurements performed with this technique were compared with those of other NDTs ( F-SECT and pulsed thermography) so that a comprehensive evaluation of the coating degradation level could be obtained. The assessment was verified with metallographic analyses done on metallographic sections. currency1 Some literature TBC degradation models were implemented with the results of cyclic oxidation tests performed in the laboratory, so that a Life Managment system could be improved with a routine for TBC coated blades. Some life prediction could be successfully compared with the results of an in situ (open case) inspection performed with thermography applied to mounted blades. Finally a discussion of the state of the art of NDTs applicable today to the TBC coated hot parts will be done and possibilities of further improvements enlighted, starting from the experience gained till now. PUBBLICATO 06004666 (PAD – 739349)PUBBLICATO 06004666 (PAD – 739349)

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