Session: 04-01-03 Flexible Pipes III

Submission Number: 180595

Anti-FLIP Technology for Rough Bore Flexible Piping – CFD Analysis of 2 Inch Experimental Results 

Flow Induced Pulsation (FLIP) can occur under specific conditions when gas flows through rough bore flexible pipe systems and produces distinct tonal noise (singing riser). This is caused by the feedback between pressure waves generated from shear layer instability at the corrugation and the interaction with the acoustic field. This phenomenon can lead to environmental concerns and structural vibration in connected pipework or equipment.

Baker Hughes have proposed a low impact solution for FLIP mitigation in rough bore flexible pipe which, unlike any other solution, does not require the use of an insert covering the inward facing carcass gaps to provide FLIP protection. By controlling surface roughness on the carcass bore, the onset velocity for FLIP can be delayed. This paper provides an overview and results from testing on a small scale 49mm corrugated pipe.

A flow sweep experiment was performed on four different aluminium pipes with equal length and the same corrugation geometry, but with different levels of wall roughness (1, 15, 50, 275 µm hydraulic roughness). Peak amplitudes of the fluctuating pressures were used to estimate the onset velocity for FLIP. A clear increase in FLIP onset velocity was measured as wall roughness was increased. The largest increase was observed at 275 µm wall roughness (6 bara pressure), where the onset velocity was measured at 31 m/s compared to 10 m/s for the smooth wall pipe, which was an increase of 310%.

This paper presents analysis of the experimental results, including a comparison with Computational Fluid Dynamics (CFD) to predict the change in onset velocity with increasing wall roughness. CFD is used to predict the change in source strength, which reduces as the roughness increases, and this is compared to the source strength estimated from the measurement data. Wall roughness disturbs the shear layer instability by creating a thinner, but more turbulent boundary layer, which increases the wall shear stress. This changes the velocity profile in the shear layer and therefore reduces the source strength.

The influence of the wall roughness also effects the losses and these are estimated and compared against the predicted source strength to get the onset velocity. The delay in onset velocity due to wall roughness can mitigate FLIP, and this technology forms part of a suite of Baker Hughes’ anti-FLIP solutions.

Presenting Author: Paul Emmerson Baker Hughes

Presenting Author Biography: Paul has over 30 years of experience applying analytical and CFD modelling skills to solve complex fluid and thermal engineering problems. He is an expert in CFD, flow modelling and piping vibration and has published numerous papers at conferences and in technical journals.

Authors:

Paul Emmerson Baker Hughes
Stefan Belfroid TNO
Michele Bonanni Baker Hughes
Colin Russell Baker Hughes
Jannos Nasikas TNO