Assessment of structural and mechanical heterogeneity of the material of turbine runners based on the results of hardness measurements

The article presents an assessment of the structural heterogeneity and mechanical properties of the turbine runners of hydroelectric power plants in the presence of operational defects based on the hardness measurements. The article presents the design features and structure of the turbine runner’s metal. The chemical composition of the steel was determined by laser spark emission spectrometry using a portable laser steeloscope. The mechanical properties were determined based on the static tension testing of the samples using an tensile testing machine. The impact work and impact toughness characteristics were obtained based on the impact bending testing of samples with a U-shaped concentrator using a pendulum impact test machine in the temperature range from +20 to –30°C. The crack resistance characteristics were obtained based on the crack resistance testing of samples using a testing machine. The samples for all tests were cut from a fragment of the turbine runner’s blade. The metal hardness values were obtained using the dynamic portable hardness tester by measuring the Brinell hardness on four blades from the non-pressure side in the areas of cavitation damage. The main problems of hydraulic turbine operation associated with cavitation damage to the metal are described. The division of the turbine runner’s blades into zones according to the degree of cavitation damage is shown. Based on the results of Brinell hardness measurements, the characteristics of mechanical properties — the yield strength and tensile strength — were calculated. Based on their values, statistical processing was made and histograms of distributions were constructed with the determination of the characteristic law of distribution of a random variable, the heterogeneity coefficients were determined and graphs of the statistical distributions of the values of the characteristics of mechanical properties were constructed.