Automated Design Life Evaluation for a Gas Turbine HRSG

Many combined cycle plants operate only during peak demand hours and start/stop at least once a day, Exposure of the HRSG to the repeated thermal gradients experienced during start-up has raised questions about fatigue durability. Additionally, portions of the superheater and reheater sections operate in the creep range and owners want assurance that these parts will provide 25–30 years of life. This paper illustrates the development of an automated process to evaluate the effects of creep and cycling induced fatigue. The process employs a dynamic thermal analysis computer program, spreadsheets, and finite element analysis to complete a comprehensive fatigue/creep evaluation of every significant pressure part in the HRSG. An automated life evaluation process offers many advantages to the owner. During the design stage of the project, the analysis allows designers to provide for correct materials and adequate strength. Once the plant is in operation, changed operating conditions can be easily evaluated to determine their effect on HRSG life.