Structural reliability and ageing of multistage pumps during start-up: A fracture mechanics-based experimental assessment

As the energy transition progresses, pumped-storage power plants are playing an increasingly critical role in ensuring reliable and efficient power grid operation. However, the growing operational variability induces structural degradation in mechanical components, primarily due to fatigue-related damage. This study presents an experimental framework for assessing the structural reliability and ageing of multistage pumps operating in ternary units during start-up procedures of pumped-storage power plants through a fracture mechanics approach. A reduced scale model of a multistage pump is instrumented with strain gauges at the blade-crown intersection and tested under transient conditions on a dedicated test rig. Start-up sequences, where the pump is driven to synchronous speed via the turbine, are investigated. Using linear-elastic fracture mechanics, the propagation of hypothetical cracks in a full scale impeller is modeled and analyzed to evaluate fatigue-induced degradation. For the investigated case study, the results indicate a crack propagation in the full-scale impeller of the order of 10−7m per start-up for crack lengths in the millimetric range, and enhance the understanding of structural damage mechanisms in multistage pumps during start-up by demonstrating a strong correlation between crack propagation and the occurrence of hydrodynamic phenomena. Moreover, the study highlights the impact of turbine-side operational strategies on pump ageing, showing that the most detrimental start-up sequence induces crack propagation levels approximately 20% higher than those associated with the least damaging trajectory, and supports the development of operational strategies aimed at ensuring the structural reliability of pumps to extend their lifetime.