Schlumberger

Technical Paper: Field Test of a Flexible Pipe Integrity Monitoring System

Society: IBP
Paper Number: IBP2739-10
Presentation Date: 2010
 

Abstract

Flexible pipes are used in all offshore fields to transport high-pressure and high-temperature fluids while flexing with variable subsea currents and wave action. The monitoring of flexible pipe integrity is a main concern, growing more significant as they increase in number and age.

In a flexible pipe, gas from the transported fluids slowly diffuses into the pipe’s annulus, a space located between two concentric plastic layers where the armors that support the whole structure are also found. The annulus gas is vented at the surface and flared to prevent a pressure buildup that could burst the pipe’s outer sheath.

The main concern for flexible pipe integrity is the presence of water in the annulus, either due to condensation or damage to the outer sheath. Seawater, or condensation water in the presence of diffused CO2 or H2 S, can lead to excessive corrosion of the armor layers and can significantly reduce the service life of the line (MCS International, October 2002). It is also possible for oxygen and moisture from the air to enter the annulus if the vent ports are not equipped with check valves.

Currently, the only way to control the water tightness of the pipe’s outer sheath and the quantity of condensed water in the annulus is to perform vacuum or pressure testing of the annulus (Bondevik, 2004). This operation is infrequent and costly, and does not allow for continuous monitoring of the pipe. Sometimes, it is complemented by measuring the rate at which gas exits the vent ports. However, this measurement is sensitive to temperature variations in the annulus. A change in the rate of gas vent could be due to temperature effects, a change in gas diffusion rates, or water entry.

Technical Paper presented at 15th Rio Oil & Gas Conference, held on
Sep 13-16th 2010 at Rio Centro/RJ.

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