Thermal Stress Analysis in Structural Elements of HRSG Casing

Heat recovery steam generators (HRSGs) are arranged at the tail end of gas turbines in combined cycle power plants (CCPPs), and are designed to withstand the hot gas environment approaching 600℃. In addition to higher thermal to power efficiency, CCPPs show superior response characteristics compared to those of other conventional steam power plants. For that reason, frequent load changes on the system, which sometimes include daily start and stop (DSS) operation, would impose additional burden on the structural elements. The main objective of this work is to analyze the thermal stress conditions as related to the observed failure on the structural elements of HRSG casing, and to find root causes of failure of mechanical integrity. To achieve this goal, field measurements were performed to record temperatures of wall and stiffener of the casing from a real plant in operation. To consider the effect of hot gas on the casing, computational fluid dynamic (CFD) analysis of gas flow inside the HRSG with appropriate wall conditions using FLUENT V12. Thermal stress analysis on the thin wall of the casing and stiffeners of HRSG was conducted with the temperature data from the CFD results, using ANSYS Workbench V12. Summarizing the computational results, some limited ideas were presented which would be useful to prevent damages.