Static and Dynamic Analysis of a Piping System

Abstract

This project work includes static and fluid induced vibration analysis, for a given piping system. Model was created as per actual configuration for resonance frequency and water hammer induced vibration analysis. The natural frequencies, static, thermal and dynamic stresses of the piping system were obtained in different 34 applied load cases. The static analysis demonstrates that the wrong boundary condition at one support location increases thermal stress and also responsible for higher moment then allowable at nozzle shell junction. Actual calculated equipment stiffness value makes this nozzle moment safer side but it is not recommended solution as design must sustained the stresses in the worst conditions. The effects of supports were analyzed during the thermal analysis in different temperature range, to obtain maximum thermal stresses. As a result none of the segments were close to the actual thermal and allowable stresses ratio of 1.0 so it was acceptable.

In the vibration resonance analysis the first, second and third natural frequency of system was found at 3.70 Hz, 4.37 Hz and 4.98 Hz with its corresponding mode shapes and it was compared with fluid’s excitation frequency to find out resonance region. As a result middle segment of model was found in resonance condition at a maximum flow rate of 110.66 feet3/sec. In the water hammer analysis failure prediction was found and the time of valve closing and opening were obtained as a parameter to control the crest of wave pressure. The result shows that with adequate time of valve operation, the wave crest will not reach to the pressure of failure. The pressure reducer may be kept before the valve in order to reduce the impact of this traveling wave. Redesign and relocation of trunion support also decreases the dynamic stresses as well as nozzle moment. Hence in this project work, the possible causes of nozzle failure were identified and appropriate suggestions were given.