High energy boiler feed discharge piping can lead to operational problems especially in a dynamic environment. While a flexible system is preferred from thermal considerations, it can pose problems when exposed to transients such as water hammer. This paper presents a study of one such problem and the remedial measures suggested therein. Discharge piping of a combined cycle power plant has shown severe vibrations whenever the second boiler comes into operation while the first one is in normal operation. Force time histories at all elbows have been generated for the event i.e., partial opening of the valve using the computer code based on method of characteristics. FFT analysis of a typical force time history has been performed to obtain frequency content. Dynamic response of the system has been computed using modal time history approach including 150 modes and the convergence was checked. Results of the analysis indicate displacements much larger than the maximum width of the bottom support slide plate, when dynamic displacements are superimposed on displacements from thermal loading in the lateral direction confirming the prevailing situation at site. Pipe supports have been suitably modified and this has helped in reducing the vibrations drastically.
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