Fatigue life prediction of steel spiral cases in pumped-storage power plants: Factors to be considered

Abstract

Pumped-storage power plants are playing an increasingly critical role in electricity grids by providing them with great operational flexibility. The flexibility requires frequent operation-mode switches of pump turbines, which leads to frequent variations in internal water pressure (IWP) resisted by steel spiral cases (SSCs). Such IWP variations are usually of large amplitudes due to their high design heads. Consequently, SSCs in pumped-storage power plants should be confronted with relatively high fatigue failure risks in their service lives. The specific objective of this study is therefore to identify key factors that significantly affect fatigue life prediction of SSCs in pumped-storage power plants. The authors perform a numerical simulation of a spiral case structure of the Liyang pumped-storage power plant on the finite element analysis platform ABAQUS, with its temporary-pressurization construction process carefully modeled using the complete simulation procedure. Then the finite element analysis results are used as input for fatigue analysis of the SSC on the ANSYS nCode DesignLife platform. The case study suggests that the concrete damage should be considered in fatigue life prediction of a SSC as the damage (even local) weakens the restraining effect on the SSC. The second major factor identified is the cyclic loading input strategy. The key to the loading strategy is to capture the essential features of IWP variations, i.e. to repeat the IWP loading roughly between the upper- and lower-reservoir heads. The study has also shown that the effect of the mean stress correction is less important than expected. The factors identified therefore assist in our understanding of the role of adequate fatigue design and analysis of SSCs in pumped-storage power plants.