On-line fatigue–creep monitoring system for high-temperature components of power plants

A system has been developed for on-line monitoring of various aging effects, such as fatigue, creep and fatigue–creep interaction. This can take care of the fluctuations of the process fluid temperature, pressure and flow rate and the piping loads such as axial forces and bending moments. The system converts the plant transients to temperature/stress responses using the finite element method and the transfer function approach. The fatigue usage factor is computed using the rainflow cycle counting algorithm. The creep damage index is evaluated from the computed temperature and stress histories and the material creep rupture curve. Examples of a thick pipe and a shell–nozzle junction under mechanical and thermal loads are studied. This system is useful in life estimation and life extension programs of thermal power plants, nuclear power plants, chemical process industries, and so on.