Session: 08-07-01 Internal Flows & FIV

Submission Number: 156774

Fatigue Life Assessment of an In-Service Subsea Riser Tower Subjected to Flow Induced Vibration: Part 1 of 2 – Measurement 

Flow induced vibration (FIV) can go undetected in subsea pipework, potentially leading to fatigue failures. Although FIV screening methods have been developed, these are deliberately conservative for multiphase pipe flows and do not accurately quantify the fatigue performance of subsea pipework already in situ.

The last few years has seen significant development of reliable simulation processes to predict the effects of multiphase flow induced vibration and they have been successfully compared with experimental data for a wide range of operating conditions.  However, there is limited in-situ vibration measurement data available from actual operating subsea equipment which would allow a direct verification of the analytical / numerical results.

As part of a routine ROV inspection, two spools on an in-service subsea riser tower were observed to be vibrating, and a combined simulation and measurement campaign was engaged upon to quantify the risk of fatigue failure.  This paper focussed on the measurement campaign.  Based on initial modal Finite Element Analysis, sensible locations were selected for placement of the accelerometers.  The extracted and processed data, covering 2 months of operations, suggested the following: there may be an interaction between the two adjacent riser towers which was unexpected but unlikely to cause significant damage; and the stresses based on the measured vibration were within 35% of the simulation results. Subsequently mitigations could be evaluated and implemented with confidence utilising a reasonably large safety margin.

Presenting Author: Mike Lewis Xodus Group

Presenting Author Biography: Mike has been working in the field of Computational Fluid Dynamics for 30 years. He became involved in Flow Induce Vibration studies 13 years ago. Since then, Mike has managed a Joint Industry Project on Multiphase Flow Induced Vibration, and continues to chair and manage a Special Interest Group on Flow Induced Vibration.