Metallurgical Failure Analysis Evaluation of a Hydroelectric Turbine Generator

A failure analysis investigation was conducted following a high-vibration incident sustained by a turbine generator at a hydroelectric power plant. Disassembly revealed that seven of the eighteen stud bolts connecting the turbine runner and shaft had fractured in service and became liberated prior to the incident. In addition, corrosion pits and cracking were observed on the turbine shaft and flange. Stress analysis suggested that the normal operating stresses were insufficient to result in fatigue fractures. Metallurgical evaluation of the stud bolts and turbine shaft confirmed that the fractures and cracking occurred by way of progressive cracking in the nature of corrosion fatigue on areas of these items that had been exposed to river water in service where corrosion pitting was observed.