Role of high-frequency loads in hydraulic unit destruction

High-frequency (HF) hydraulic loads go along with hydraulic unit’s (HU) operation throughout the operating range and cause stress pulsations in its components. The amplitudes of these pulsations are significantly lower than the amplitudes caused by low-frequency (LF) loads. Therefore, the lifetime estimation of hydropower units often ignores HF loads. This leads to overestimated lifetime expectations and to hydraulic unit components’ failures long before the predicted occurrence of hazardous cracks. Hydraulic unit lifetime estimation approach presented below relies upon fracture mechanics methods applied to lifetime-determining unit components and takes into account the combined effect of LF and HF loads. At first the lifetime estimation takes place in terms of crack length. Then the residual lifetime determined is the amount of operating hours left (taking into account the particular unit’s application). After a long period of operation, HF loads manifest themselves when the material damage reaches a certain critical level as well as the threshold for stress intensity factor (SIF) decreases. The proposed approach can be utilized as a convenient and effective tool to determine time for necessary repairs or replacement of worn components.