Failure analysis of a steam turbine rotor

A large and growing portion of electricity is being produced by aging thermal power plants, and although steam turbines are being constructed with excellent high quality materials such as CrMoNiV steel, varying forms of metallurgical degradation due to creep and/or fatigue could still affect the parts and components during long-term operation at high temperatures [1]. Moreover, the de-regulated electricity market, which has existed for approximately 15 years, has led to energy companies operating their power plants in a flexible manner, as opposed to continuous operation, in order to maintain profitability in a very competitive commercial environment [2]. This paper investigates the rotor turbine failure of a 60 MW unit of a thermal power plant. The rotor was made of CrMoNiV steel, and the failure occurred after approximately 10 years in operation. Several different analyses were carried out in order to identify the failure’s root cause: visual examination, SEM fractography, micro-hardness measurement, and microstructural characterization. The fracture of the shaft was located at the first stage [2] and the fatigue fracture extended over roughly 75% of the initial cross section. Primary failure causes were identified by the analyses performed, and the observed fracture mechanism was traced back to high cycle fatigue damage. The origin of the fatigue phenomenon can be traced to the stress field generated on the rotor surface by both the frequent startup cycles and the blade fixing method.