New Monitoring Technology for Detection of Flexible Armor Wire Failure

Abstract

Flexible risers have been one of the preferred riser solution for many floating production systems in shallow to deepwater in many regions of the world for their good dynamic behavior and their reliability. The flexible pipe is composed of several plastic and steel layers. The weight of the riser is carried by a large number of steel wires (called tensile armours) that are essential to the integrity of the pipe. It is therefore important to be able to ensure the integrity of those armour wires and to detect a possible failure early enough to intervene in time, inspect the riser and if needed plan to re-terminate or partially replace it.To answer to this operational and safety issue, Technip and Schlumberger Subsea Surveillance (SSS) have a joint effort to develop a new technology allowing to detect failure or conditions likely to lead to failure of tensile armour wires. This new monitoring technology is based on a clamped composite structure with embedded optical fiber using among others Fiber Optics Bragg Gratings technologies (FBG). The developed device allows capturing armour failure monitoring the permanent deformation (torsion and elongation) results from an unbalanced equilibrium of the tensile armour layers. These crossed informations increase reliability of integrity assurance.The paper will present the essentials of the behaviour of the armour wires in a flexible riser, and the resulting requirements that need to be taken into account for the development of a system monitoring their possible breakage. The selected technologies and their optimization are presented as well as the way they are integrated in the riser system. The pipe and monitoring equipment prototypes are presented.

Flexible Riser Monitoring Using Hybrid Magnetic/Optical Strain Gage Techniques through RLS Adaptive Filtering

“…Another scheme using FBG strain gages was proposed in [1]. It is based on a retrofit clamp that monitors axial elongation and torsion of a flexible riser.…”

“…They are used to link subsea pipelines to floating installations, such as FPSOs (floating production/storage/off-loading unit). Flexible risers have been one of the preferred deepwater riser solutions in many regions of the world due to their good dynamic behavior and reliability [1].…”

Real time continuous structural integrity monitoring of flexible risers with optical fiber sensors

“…Marinho et al [7] have described the use of superficial monitoring techniques for continuous flexible riser integrity assessment, reporting field trials involving percolated gas monitoring, nitrogen injection in the annular space, deformation monitoring, and visual inspection with a video camera. Even though all these methods have been yielding encouraging results, it is the technique based on optical fiber sensors that is closer to reach a mature status [12][13][14][15][16][17][18]. Non-invasive magnetic inspection is also undergoing a series of laboratory experiments and is now ready to be tested in the field [11].…”

“…The first is through measurement of strains in the flexible pipe's outer sheath. A similar approach has been proposed by Corrignan et al [16] who have employed an optically instrumented clamp to measure longitudinal and torsional strains in the outer sheath. Morikawa et al [15] presented results of laboratory and field tests where a thin steel collar instrumented with fiber optic strain sensors was clamped to the riser outer surface measuring circumferential strains and therefore changes in its diameter.…”