Flow Induced Vibration in Multi Phase Piping Systems - Successful Mitigation
Authors: Locharla Haribabu , Al Awadhi Ibrahim , Narayana Sathyanath , Al Ahmad Alya , Miranda Robert 
Published: November 2017

Ideal process/piping design is based on consistent and steady operating parameters. Sometimes these parameters varies significantly due to capacity or performance enhancements during operation. These flow changes from an ideal design to actual operating conditions are often resulting in flow induced vibrations. Excessive Vibrations in piping systems pose potential threats to plant safety and integrity. This paper presents the challenges to mitigate flow induced piping vibration due to multi-phase flow in rich amine systems with successful measures.

A comprehensive study was conducted to identify the root cause for piping vibration in rich amine piping system (20″ pipe) from plate type heat exchanger to amine regenerator. The vibration measurement was carried out where the vibrations are visually high. The vibration screening and likelihood calculations were carried out based on Energy Institute's guidelines and those were identified in concern/problem zones.

The process study including the review of hydraulics and piping stress analysis was carried out with actual operating conditions. The multiphase density/forces was simulated to identify root cause and to propose suitable recommendations for mitigation of piping vibration.

Process study reveals that the fluid flow type is multi-phase where the sudden pressure drop occurs at control valve. The flow regimes were reviewed along the section of pipe to identify the major flow turbulences. The alteration in the operational modes shall reduce the impact of load due to slug flow and shall minimize the vibration. But, since it results in loss of energy, it was suggested to provide adequate piping supports to mitigate the piping vibration.

Static/dynamic piping stress analysis reveals that the piping system needs better supporting arrangement to cater slug loads conditions. The natural frequency of existing system was calculated and found to be low with existing supports. The design of existing supports was reviewed and accordingly suggested suitable additional supports such as holddown and axial stop to increase the natural frequency of piping vibration. Since the piping vibration source is control valve where there is sudden change in pressure, the guides and axial stop restraints were proposed to control lateral/axial movements by keeping the stresses in safe limits.

The proposed modification were implemented while plant is in operation. The post implementation vibration survey was carried out and the readings were found to be within acceptable limits.

The challenges such as balancing the stresses in piping system with appropriate minimum natural frequency levels to make system rigid enough and implementation of proposed modifications without shutdown were successfully achieved. The novel information from this study is, by identifying exact root cause of piping vibration, it is easy to mitigate the same from source level by application of best design/analysis practices with successful measures.