Fatigue Life Estimation of Pelton Turbine Using Local Strain Approach

This paper studies the fatigue life estimation of the 12 MW Pelton turbine of Khimti Hydropower. The material of turbine is 13Cr–4Ni SS. Pelton turbines are widely used hydraulic machines that efficiently extract energy from high head and low discharge flow. These turbines are subject to repeated load/stress amplitude mainly due to water jet impact from jet nozzles. Finite element analysis indicated that the maximum stress and strain occur at the root of the Pelton bucket. During the long operating hours, these bucket roots initiate micro-cracks which eventually grow to considerable crack size. This paper focuses on fatigue life estimation of Pelton turbines using a local strain approach. Structural analysis of the Pelton runner sector was carried out to determine the maximum local strain value. Modified universal slope and hardness methods were used to obtain strain–life curve for fully reversible load. The Haigh diagram was used to obtain the strain–life curve for pulsating load. The maximum value of local strain was calculated to be 2.38 ×  10–3 mm/mm. For this maximum local strain, fatigue life was calculated as 2.67 × 106 cycles, which falls in the high-cycle fatigue region. This study concluded that the Pelton turbines are designed for infinite life and hence damage tolerance approaches are necessary to investigate the crack growth rates.