Session: 04-01-03 Flexible Pipes III

Submission Number: 180579

Anti-FLIP Technology for Rough Bore Flexible Piping – 2” Experimental Study 

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.

 

Four different aluminium pipes with equal length and the same corrugation geometry were tested, with different levels of wall roughness. A flow sweep experiment was performed with air at three pressures (1, 4 and 6 bara). The first pipe tested was for all practical purposes smooth with a hydraulic roughness of 1.1 µm. The second and third pipes were roughened using sand blasting and had hydraulic roughness of 15 µm and 50 µm. The fourth pipe was roughened using knurling and had a hydraulic roughness of 275 µm. These hydraulic roughness values were based on measurements taken on the pipe walls.

 

Fluctuating pressure amplitudes were measured using 8 dynamic pressure sensors as the flow velocity was gradually increased. From this the peak amplitude was taken and used to estimate the onset velocity for FLIP. Results are also presented for the peak pressure frequency, pressure drop and upstream density. For 6 bara pressure, onset velocity for the 275 µm wall roughness pipe was measured at 31 m/s compared to 10 m/s for the smooth wall pipe, which was an increase of 310%. This was the largest increase in onset velocity, but significant increases were measured for the 50 µm roughness pipe and at other pressures.

 

A clear increase in FLIP onset velocity was measured as wall roughness was increased. The influence of the wall roughness effects both the losses and the source strength. It disturbs the shear layer instability by creating a thinner, but more turbulent boundary layer, which increases the wall shear stress. This not only affects the pressure drop and the acoustic attenuation, but also changes the velocity profile in the shear layer and therefore reduces the source strength. This technology forms part of a suite of Baker Hughes’ anti-FLIP solutions.

Presenting Author: Stefan Belfroid TNO

Presenting Author Biography: Stefan Belfroid is an experienced R&D engineer working as a senior scientist for the department of Heat Transfer and Fluid Dynamics at TNO, The Netherlands. His interests are in the fields of flow induced pulsations and vibrations and in the field of multiphase flow.

Authors:

Stefan Belfroid TNO
Paul Emmerson Baker Hughes
Michele Bonanni BakerHughes
Colin Russel BakerHughes
Janos Nasikas TNO