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THERRI (THermisches ERmüdungsRIsswachstum)

A joint research project for flexible power plant operation

Nowadays the requirements on fossil fuel power plants have fundamentally changed. Modern power plants must be capable of flexible operation, to compensate for power requirements which cannot be provided by renewable sources of energy. Due to frequent startup and shutdown cycles and the associated temperature and pressure fluctuations, the applied materials face by far more demanding loading scenarios than in the past. Due to increased cycling fatigue damage enormously gains in importance, whereas the impact of creep lowers due to shorter operation at constant high temperature. In order to ensure maximum safety and sustainable operation reliable predictive tools for component performance are an important step towards modern flexible power plants. Thick-walled components of the feed water and live steam systems present the most heavily loaded parts and thus are in the focus of particular interest. Fracture mechanics provide an effective way to evaluate fatigue life exhaustion on the basis of crack growth analysis and thus component life may be extended beyond state of the design code based fatigue analysis without a reduction in safety and reliability.
The THERRI project covers the whole field from experimental work over finite element modeling to the proposal of a new regulatory framework for fatigue life evaluation. At IEK-2 fracture mechanics experiments are carried out in the temperature range from 300 to 600 °C both in air and in water vapor containing atmosphere (H2O / Ar) in order to examine the environmental impact on the crack growth behavior of the examined steels, to enable the transfer of laboratory results to practical application in power plants.

In power plant application fatigue and creep cracking do interact. Fatigue cracking occurs due to frequent load changes, whereas creep cracks arise from constant high temperature loading. For this reason fatigue cracks dominate at low temperature and creep cracks come into play at approximately 500 to 600 °C. An important goal of the THERRI project is the identification of the lower temperature limit of the relevance of creep crack propagation.
Another goal is to tailor inspection intervals related to current or planned operation strategies. In addition, an assessment methodology shall be developed, which in contrast to classical fatigue life analysis is largely independent of the knowledge of the previous operating history. This leads to international versatility, since many thermal power plants are operated with only few on-line monitoring for the detection of life consumption all over the world.

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Participating partners of the research project THERRI

Forschungszentrum Jülich GmbH - Institute of Energy and Climate Research (IEK-2)
Universität Rostock - Fakultät für Maschinenbau und Schiffstechnik - Lehrstuhl für Technische Thermodynamik
Universität Rostock - Fakultät für Maschinenbau und Schiffstechnik - Lehrstuhl für Strukturmechanik
TÜV NORD SysTec GmbH & Co. KG - Abt. Entwurfsprüfung, Festigkeit und Konstruktion