Risk-Based Operation and Maintenance Planning of Steam Turbine with the Long In-Service Time

In order to ensure the safety of power generation in Poland and to maintain energy production from coal-fired units with the long in-service time, it is required to develop a strategy for the further operation of the conventional power plants in conditions of increased flexibility. The presented research focuses on the critical component of the steam turbine, which is the high-pressure rotor. The methodology of the forecasting of crack propagation and growth of life-consumption processes was described, and the probability of a failure in subsequent years was estimated. The development of the identified phenomena depends mainly on the stress increases during start-ups; therefore, these increases were determined to ensure the safety of the turbine’s operation during the assumed period of operation (13 years). The permissible stress for rotor central bore (threatened with crack propagation) was 220 MPa for start-ups which were not carried out “on demand”, and for heat grooves (threatened with life-consumption processes) it was 420 MPa or 210 MPa, depending on the initial wear level of the material. An algorithm for online stress monitoring was presented, taking into account the variability of the heat transfer coefficients. The compiled method can be transformed into a real-time stress level control system. As a result, it is possible to obtain the desired increase in stress during start-up. For a longer service life (20 years), a method of selecting the optimal time interval to carry out preventive actions based on a risk analysis was additionally delineated. The optimal year to perform repair was between the 14th and 15th year of operation. The developed research allows presenting a strategy for further operation and maintenance (O&M) of the turbine, which can be adapted to a real unit.