Heat recovery steam generator (HRSG) superheater outlet headers are exposed to cyclic stresses under varying transient operating conditions. Three different tube to header connections are analyzed. Cold, warm, and hot startup cycles are defined along with a load change cycle. These cycles are used to develop boundary conditions for a transient three dimensional finite element analysis of each detail. The results show that the highest stresses are away from the tube to header weld area. For the startup cycles analyzed, equations are presented for cycle life determination.

In the past, power plants for the most part did not operate in cyclic service. Today the demand for dispatchable operations is a common requirement for many new facilities. In this report practical considerations for evaluating and accommodating high cyclic operations of Heat Recover Stream Generators, (HRSG), are discussed. A general understanding of the difference between Low Cycle and High Cycle Fatigue is provided, how fatigue causes damage is discussed and the operating parameters that are most influential are identified. Non-analytical methods that can be used to minimize the effects of fatigue and how these options can greatly decrease damage are discussed. Typical HRSG operating cycles that should be considered in life evaluation are defined. Finally, a practical approach to evaluating the fitness of the equipment for high cyclic operations is presented along with an example of how this method can be used.