Fatigue Life Assessment of Boiler Components Under Cyclic Operating Conditions

A fatigue life assessment application has been implemented using the methodology given in the European Standard EN 12952-3. The assessment application can use data from the Distributed Control System (DCS) of the plant or, to improve accuracy, use component metal temperatures if thermocouples have been fitted across the component of interest. Fatigue assessments have been carried out on typical high temperature components in Heat Recovery Steam Generators (HRSGs) and a large coal fired boiler which were subject to cyclic operation. The assessments carried out used recorded plant operating DCS and thermocouple data and examined main cyclic events, e.g. shutdown/cold start-up cycle, etc. Detailed finite element analyses have also been conducted on a typical superheater header using as input the plant operating data. Calculated fatigue damage levels for both methods are compared and it is shown that comparable values are obtained. In addition, further assessment has been performed on a component where the period of operation included several shutdown/cold start cycles and many sub-cycles. On completion of the above studies, Mitsui Babcock have implemented the fatigue assessment method into a simple plant life monitoring system.