The effect of materials properties on the reliability of hydraulic turbine runners

Abstract

The failure of hydraulic turbine runners is a rare event. So in order to assess the reliability of these components one cannot rely solely on the number of observed failures in a given population. However, as there is a limited number of degradation mechanisms involved, it is possible to use physically-based reliability models. Such models are often more complicated but are able to account for physical parameters in the degradation process. They can therefore help provide solutions to improve reliability. With such models, the effect of materials properties on runner reliability can be highlighted. This paper presents a brief review of the Kitagawa-Takahashi diagram which links the damage tolerance approach, based on fracture mechanics, to the stress or strainlife approaches. Using simplified response spectra based on runner stress measurements, we will show how fatigue reliability is sensitive to materials fatigue properties, namely fatigue crack propagation behaviour and fatigue limit obtained on S-N curves. Furthermore, we will review the influence of the main microstructural features observed in 13%Cr-4%Ni stainless steels commonly used for runner manufacturing. The goal is ultimately to identify the most influential microstructural features and to quantify their effect on fatigue reliability of runners.

The Impact of Water Hammer on Hydraulic Power Units

“…Regarding interest in asset management, Gagnon et al [38] show that cyclical loadings in the transient mode have a major impact on equipment reliability. The influence of the load spectrum derived from turbine strain measurements and operation history [39] and the main microstructural features observed in stainless steels commonly used for runner manufacturing [40] are examined to properly evaluate the risks associated with operation. A synoptic view of the loading features and the key issues during hydraulic turbine transient operating conditions and the impact on fatigue damage is provided in the review paper by Liu et al [41] These effects shorten the lifetime [42], increase hydropower plant operation costs [43] and power generation loss.…”

Fatigue life estimation of Francis turbines based on experimental strain measurements: Review of the actual data and future trends

“…to the rapid grow after HCF onset) and therefore repair costs will be very high. Therefore, according to the work made by Gagnon et al [125][126][127][128][129] the failure criteria is defined as the HCF onset and the reliability of the runner is defined as the probability of not exceeding this point. In order to define the state limit, where the HCF onset occurs, the Kitagawa-Takahashi diagram [130] with the correction proposed by El Haddad et al [131] was used in those studies.…”

“…24). In this context, the reliability is defined as the probability of not exceeding the limits defined in this diagram considering all the possible uncertainties [125][126][127][128][129].…”

Investigation on the Impact of Air Admission in a Prototype Francis Turbine at Low-Load Operation

“…Although this approach is widely used for fatigue assessments by academic and industrial researches, it is not suitable to treat crack growth and consider the influence of high cycle fatigue onset. Consequently, Gagnon et al [48,49] proposed a more complex way according to the linear elastic fracture mechanics. However, the paper limits itself to an improvement of the numerical methodology and comparison with air injection.…”