Continuous monitoring as a tool for more accurate assessment of remaining lifetime for rotors and casings of steam turbines in service

The continuous monitoring of steam parameters and metal temperatures allows assessing the individual remaining lifetime for major high-temperature design components of steam turbines in service more accurately. Characteristic metal temperature differences and corresponding maximum thermal stresses and strains are calculated on-line to estimate the metal fatigue damage accumulated during the operation process. This can be one of the diagnostic functions of the power unit`s computerized Data Acquisition System (DAS) or special Subsystem of Diagnostic monitoring (SDM) for the turbine. In doing so, the remaining lifetime is assessed in terms of actual operating conditions and operation quality for the individual unit, and the problem of lifetime extension for each object is solved more accurately. Such an approach is considered as applied to a specific case of the supercritical-pressure steam turbine of 300-MW output. The applied mathematical models were developed on the basis of combined experimentation (field) and calculation investigations of the metal temperature and strain-stress fields in the high-temperature (HP and IP) rotors and casings under the most characteristic stationary and transient operating conditions. The monitoring results are used for revealing the operating conditions with the extreme thermal stresses and specific metal damage, as well as for making decisions about schedulingmore » the turbine`s overhauls and extension of the turbine lifetime beyond the limits having been set originally.« less