Evaluation of structural dynamic response of piping subjected to multiphase flow-induced vibration

Abstract

Flow-induced Vibration (FIV) in piping systems pose a problem for the energy infrastructure, where maintaining the integrity of pipelines is essential to ensure stable provision of power supply. In the petrochemical industry, large volumes of multiphase flow, consisting of oil, gas, and water, are transported. Predicting the dynamic responses of piping carrying multiphase flow is therefore useful for assessing whether the piping can withstand the fluctuating forces arising from the unstable flow within. To reduce the risk of large vibrations, resonance should be avoided. Both the dominant multiphase excitation frequencies and the natural frequencies of the structure must be identified to ensure that resonant conditions are prevented. Numerical modal analysis is widely used in structural dynamics to identify the modal parameters, including the resonant frequencies.

In this research, a comparison between numerical and experimental analyses of a 6 inch (168 mm) piping structure has been performed. The onshore piping assembly was selected as the structure under test because it operates under various multiphase flow conditions. The experimental modal analysis was used to verify and modify the numerical model. The analyses were performed with the aim of identifying the piping’s natural frequencies and modes. The numerical modal analysis was performed using the finite element solver in the Ansys Mechanical simulation software. The experimental data was collected using DeweSoft’s Krypton Data Acquisition (DAQ) modules and analyzed with the DewesoftX data acquisition software. The numerical model computed satisfactory results when updated based on experimental results.

Structural vibration of the piping was also measured while the piping transported multiphase flow with various flow conditions. The measurements were used to identify which natural frequencies were excited by the multiphase excitation forces. The anticipated increase of structural response for increased flow rates was confirmed. Comparison of computed frequency responses across varying flow conditions revealed that regimes with increased flow rates resulted in greater amplitudes at resonances. At resonant frequencies, the operational deflection shapes matched the mode shape patterns corresponding to those frequencies. This confirms that modal parameters also can be obtained through operational modal analysis.