In a new industrial process, an existing floating head heat exchanger is being repurposed. The operational conditions involve cyclic loading, which were not originally considered during its design phase. To evaluate the impact of these cyclic loads on the heat exchanger, Dynaflow Research Group conducted a comprehensive fatigue analysis.
Analysis
The analysis focused on critical areas including tubes, tubesheets near tube holes, flange-to-shell connections, shell near support brackets, expansion bellows connecting to the floating head, shell-side and tube-side nozzles, and outer heads including the floating head. Finite Element models were developed for each critical area, utilizing appropriate analysis tools such as FE/Pipe and Pro Mechanica. The fatigue assessment was conducted in accordance with the Dutch code RToD (Regels voor Toestellen onder Druk), considering both Low Cycle and High Cycle fatigue.
For a projected operational lifespan of 20 years, future cyclic pressures, temperatures, and nozzle loads were simulated. Historical cyclic loads were also analyzed to account for past fatigue damage. The combined results from these analyses provided insight into the cumulative fatigue damage over the heat exchanger’s entire lifespan.
Results
The analysis revealed that all critical areas, except for the shell-side inlet and outlet nozzles, met the fatigue requirements outlined by RToD. Due to their fatigue history, these nozzles did not have sufficient remaining fatigue capacity to accommodate all future load cycles without exceeding allowable limits. Following discussions with the client, it was determined that the nozzle loads specified in standard requirements could be adjusted downwards to ensure they fall within acceptable limits.
