Failure Analysis of a Kaplan Turbine Runner Blade by Metallographic and Numerical Methods

The paper presents the results of the failure analysis of a Kaplan turbine runner blade from a hydropower station in Romania. In order to determine the causes that led to the crack, the authors carried out metallographic investigations on a sample obtained from the damaged blade. They led to the conclusion, that the cracking of the blade was caused by fatigue, initiated by the numerous non metallic inclusions, which were discovered in the vicinity of the blade surface. The results obtained by metallographic investigations were completed by numerical analysis regarding the resistance of the blade and service life estimations. The calculations showed that the cracking of the blade started and developed from the stress concentrator placed between the blade and blade flange. In order to avoid further damages, the blade geometry and the number of blades have to be reconsidered.