Vibration of FRP Bypass Piping of Sea Water Intake System in Offshore Platform

Severe vibration is observed at FRP (Glass-Fiber-Reinforced Thermosetting-Resin) bypass line connected to discharge of sea water intake pump which is installed on offshore platform. To find out characteristic of the flow, CFD (Computational fluid dynamics) analysis is conducted, and result shows that it is produced by complex pulsating two phase flow formed by the high speed water jet at the resistance orifice which passes through several elbows. After CFD analysis, the force-time history result from CFD analysis is used in transient structural analysis. Based on the numerical analysis result, mechanical response of the pipe and structure for the initial piping system and reinforced piping system are verified and compared with criteria of Energy Institute guideline and NORSOK S-002. Also in order to demonstrate a validity of the numerical analysis and check soundness of the whole reinforced piping and structure system with vibration, site measurement is performed. Moreover, in order to check the stress level of piping, dynamic strain measurement is undertaken. This paper discusses the details on history of bypass line design to avoid air entrapment not to damage on seawater pump, and how the vibration issue is approached, and finally compared with industry standard for safety. Further, the paper presents the numerical analysis result that makes design modifications implement for bypass piping and structure during a commissioning, and various evaluation method that verify the soundness of piping and structure based on field vibration measurement.