THERRI - Thermal fatigue crack growth

Determination of characteristic values for the evaluation of thermal growth of thermal fatigue cracks in power plants

Background / Aim

In the face of the energy transition and the associated changes in the energy market, the technical load requirements for fossil power plants have changed fundamentally nowadays. Modern power plants must now be able to operate flexibly to compensate the residual load, i.e. the load that cannot be provided by renewable energies.

Due to the increased and therefore necessary number of start-up and shut-down processes and the associated temperature and internal pressure fluctuations, the technical material is subjected to greater stress than ever before. Fatigue damage due to increasing alternating stress is thus of enormous importance for the power plant operator, whereas the influence of creep rupture stress is reduced due to shorter dwell times at high operating temperatures.

To ensure maximum safety and smooth operation, reliable predictions on components (e.g. failure probabilities or material status) are an important step towards modern power plants. The focus is on thick-walled power plant parts in the feed water and fresh steam system, as they are subject to particularly high loads.

The Project THERRI

Fracture mechanics crack growth analysis provides an effective way of assessing high degrees of fatigue of components subject to load cycling. In addition to the rule-based fatigue analysis, this allows additional service life reserves of the component and thus service life extensions to be tapped without reducing the required safety margins

In the project THERRI (THermal Fatigue RIS Growth), this subject area was dealt with starting from experimental engineering to finite element modelling up to the development of a new set of rules. The fracture mechanical tests on the IEK-2 were carried out both in air and in an atmosphere containing water vapour (H2O/Ar) in a temperature range of 300 to 600 °C in order to test the environmental influence on the crack growth behaviour of the steels examined and thus enable the laboratory results to be transferred to practical application in power plants.