Advancing Safety in Pumped Storage Hydropower Through Bolt Fatigue Analysis

A new study published in the Journal of Energy Storage examines the fatigue behavior of critical bolts in pumped storage units. The research, titled "Fatigue behavior simulation of the bolt connecting between head-cover and stay ring in pumped storage unit," appears in Volume 172 of the journal on 15 September 2026 as article 122986. Lead author Qiang Zhao and co-authors Tianyu Zhang, Xinbin Tu, Fengjiao Tang, Keyuan Wang, Kenan Du, Qingyuan Song, and Yongyao Luo detail an integrated experimental and simulation approach to assess bolt longevity under demanding operational conditions.

Pumped storage power stations play a key role in balancing energy grids by storing and releasing water to generate electricity during peak demand. The head-cover component, secured to the stay ring by high-strength bolts, experiences repeated cyclic loading from water pressure and operational transients. Fatigue damage in these bolts can lead to loosening, leakage, or unit shutdown, posing risks to station safety and increasing maintenance expenses.

Challenges in Load Prediction and Stress Analysis

Accurate fatigue life estimation for head-cover bolts has historically been constrained by difficulties in determining precise loads and accounting for complex structural interactions. The axial water thrust on the head-cover varies significantly during start-up, pump zero-flow conditions, and load rejection events. Traditional empirical methods often lack the quantitative precision needed for reliable predictions.

The study addresses these issues with a multi-scale mathematical model of the coupled flow in the pump-turbine passage. This model incorporates clearance flow and pressure-equalizing pipe effects, calibrated against experimental pressure measurements. It enables high-fidelity calculation of pressure pulsations and axial thrust across the system.

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Fluid-Structure Interaction Modeling

Researchers developed a nonlinear fluid-structure interaction (FSI) model for the head-cover, bolts, and stay ring system that explicitly accounts for threaded engagement. Conventional approaches frequently overlook thread geometry, yet engineering data show that fractures typically originate at the thread root—the area identified as highest stress in the new simulations.

The model captures dynamic stress responses under unsteady, non-uniform clearance flows and additional bending moments from the screw threads. Validation against dynamic stress tests confirms its accuracy in predicting bolt behavior during transient operations.

Integrated Fatigue Life Prediction Method

The team combined similarity-based fatigue tests on scaled bolt specimens with cumulative damage theory to predict service life. Preload application in test fixtures replicates real-world installation conditions, allowing extrapolation from laboratory cycles to field performance.

Results indicate a conditional fatigue safety factor of 1.775 for the head-cover bolts. Under the simulated conditions—including start-up, pump zero flow, and full load rejection—the bolts demonstrate infinite life potential when this safety margin is maintained.

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Implications for Hydropower Operations and Maintenance

Improved understanding of bolt force characteristics and fatigue mechanisms supports more robust safety assessments for pumped storage facilities worldwide. Operators can use these modeling techniques to refine inspection intervals, optimize preload specifications, and evaluate design modifications before implementation.

The work builds on prior publications by the same research group, including numerical simulations of bolt dynamic behavior and experimental fatigue testing protocols. Such sequential studies strengthen the evidence base for industry standards in high-head hydropower units.

Further details are available in the original publication at https://www.sciencedirect.com/science/article/abs/pii/S2352152X26026502.

Broader Context in Energy Storage Research

Pumped storage remains the dominant form of grid-scale energy storage, complementing intermittent renewables. Ensuring structural integrity of components like head-cover bolts directly contributes to reliable operation and cost-effective maintenance over decades-long service lives.

Related investigations into pressure fluctuations, rotor-stator interactions, and clearance flow dynamics continue to inform advances in pump-turbine design. The current simulation framework offers a template for similar analyses in other bolted connections subject to hydraulic loading.