Characterisation of the Property Profile of Newly Developed 600/620°C Steam Turbine Materials Based on Long-term Testing Data and the Correlation with Microstructure Analyses and Parameters
Project Number 314
The aim of the project is to determine the long-term properties of real production components made in new European 620°C steels which have been developed in COST522. Furthermore, the characterisation of the microstructure of long-term tested creep specimens of 600°C- and 620°C-materials will be made with the aim of installing correlations of strength to microstructure and proposals for residual life concepts.
The VGB projects 158, 217 and 259 already completed were performed to determine reliable material data of the newly developed 600°C steam turbine steels to validate the real long-term behaviour of highly stressed turbine rotors, turbine castings, and valve casings, and to enable a safe extrapolation for life times up to 200,000 h.
The new project 314 is now dealing with the next generation of steels containing Chromium, Boron and Cobalt (FB2, CB2 type) developed within the COST programs and resulting in new forging and casting alloys for application temperatures T > 600°C. First prototype components have already been made and qualified within the COST programs. The steels are now being introduced to new high temperature power plants under construction.
As in the new project real components made from the next generation of steels are available for long-term investigations, essential parameters for the long-term behaviour of the materials can be determined, i.e.
This information is required to enable a safe long-term operation and the subsequent residual life estimation in the power plant for deciding on revision intervals and life time prolongation measures.
The investigations on the new 600°C materials have shown that possible indications in the microstructure to be correlated with the life time consumption (e.g. pores detected in the component by replica technique), behave differently compared to low alloyed steels. For example, the number of pores, pore density, and the time to develop first pores, is very different. Therefore new and additional indicators are required to establish correlations to the life time consumption. Microstructure parameters which have to be measured very systematically by applying a defined testing and preparation technique are candidates for this approach.
Thus the new project VGB 314 is aiming for the following three topics:
The utilities involved will gain the following benefits from the project:
The project started in August 2008 is headed by Dr. Torsten-Ulf Kern, Siemens AG Energy Sector. The material investigations are carried out at the Darmstadt Technical University (Institut für Werkstoffkunde) and the Stuttgart University (Materialprüfungsanstalt).
The utilities involved,
provide components from the newly built European power plants and jointly finance the long-term project (planned duration: 6 years).
In addition, Alstom Switzerland (Ltd.) is a member of the steering committee.