Correlation development of erosive wear and silt erosion failure mechanisms for pump as turbine

Abstract

One of the factors contributing to the gradual decline in the performance as well as the failure of hydropower plants over the years is silt erosion. Several researchers have developed empirical correlations for the prediction of erosive wear of hydro turbines, but these correlations are not directly applicable in practice as the materials examined for the impeller blades were different from the actual impeller material. In this study, an effort has been made to experimentally evaluate the silt erosion of the Pump as Turbine (PAT). The novelty of the study is to use the same material (SS304) for the specimens used for the analysis as well as for the impeller. The experiments were performed with three silt sizes of 100–350 μm, 350–700 μm, and 700–1000 μm; with three different silt concentrations of 0.75 %, 1 %, and 1.25 % for the duration of 18 hrs, 36 hrs, and 54 hrs. An empirical correlation is established for the assessment of normalized wear of the PAT impeller in terms of silt size, concentration, and operating time based on the experimental data. This correlation can be utilized to estimate normalized erosive wear of PAT impeller made up of SS304 material with an inaccuracy of ±15 %. According to the analysis, silt concentration was found to be a more significant parameter in causing erosion than silt size. Additionally, scanning electron microscopy was used to conduct a thorough analysis of the erosive failure mechanism of SS304 specimens. According to the analysis, silt size was observed to be an important factor in producing various types of erosive failures. The material removal from the substrate’s surface was found to be caused by plastic deformation and surface ploughing.