One of the main concerns regarding flexible pipe integrity is its annulus condition, as a flooded annulus can lead to excessive corrosion and reduce fatigue life of the armor layers. The current approach to address this is to periodically perform a vacuum or pressure test to check the annulus integrity and to measure its gas-filled volume, in order to detect an accumulation of condensation water, or the ingress of sea water (Bondevik, 2004). These measurements are sometimes complemented by a continuous measurement of the flow rate of gas escaping the flexible riser's vent ports (MCS International, October 2002). The vacuum or pressure test is a costly operation, performed intermittently, while the conventional vent-gas monitoring does not provide reliable information on gas diffusion rates or water vapor emissions. To address these issues, TOTAL and Schlumberger have developed the subC-racs* riser annulus condition surveillance system for continuous monitoring of flexible riser integrity, which eliminates the need for vacuum tests. The gas that permeates the riser pressure sheath is depressurized while measuring its pressure, temperature, and flow rate. As in a well production test, the pressure drawdown and buildup curves are analyzed to give detailed information about fluid content and connectivity. The instrument's resolution and accuracy allow frequent calculations of gas diffusion rate and of the volume of liquid that may have entered the annulus, weekly, daily, or more frequently, depending on gas diffusion rate and riser parameters. In this paper we describe the measurement principle and hardware, modeling of the gas diffusion in the annulus compared with experimental results, and field test results on various risers in a West Africa field. Emphasis is placed on the measurement results, but the implementation in hardware and real-time software for alarms and remote monitoring is also shown. Introduction Monitoring of flexible pipe integrity is a main concern for all offshore fields. It has become more significant as the number of flexible risers increases, and as they age. The main issues for flexible risers are the status of outer sheath and the presence of water in the annulus due either to condensation or by damage to the outer sheath (Figure 1).

The growth in deep water field developments and the need for increased oil recovery with reduced capital expenditure are pushing the technical boundaries of subsea asset design. One of the challenges facing these new developments is monitoring the structural health of their subsea production asset in an inherently inaccessible location. This is usually done through structural modeling and either spot monitoring campaigns using MEMS accelerometers or through subsea conventional strain gauges. Both technics present weaknesses: MEMS sensors usually require a great deal of data processing to obtain functional strain information at a desired location and strain gauges are complicated to install in a marine environment, many failing during pressure testing or installation. Both are also suseptible to electromagnetic fields which can biais their measurement. This paper presents details of a new non-intrusive integrity monitoring sensor systems recently deployed in the Gulf of Mexico and West Africa on production lines. Inherently reliable, as presenting no moving parts, these sensors use optical fibers embedded within a composite frame for their measurements. Using field proven subsea fiber optic mapping technology these systems have delivered high frequency un-biaised, on the pipe, strain from which is derived pipe bending and axial loading in addition to temperature and pressure monitoring.By providing electromagneticly immune, low noise, un-biaised, strain measurements to structural engineers to verify and improve their fatigue behaviour models, the non-intursive integrity monitoring system has proven a reliable alternative to MEMS and strain gauges. Furthermore unlike alternative solutions, this system also monitors pressure, illustrating this technology's capability at providing production and flow assurance data in addition to integrity data making it an ideal tool within a subsea production surveillance strategy.

The growth in deep water field developments and the need for increased oil recovery with reduced capital expenditure are pushing the technical boundaries of subsea asset design. One of the challenges facing these new developments is monitoring the structural health of their subsea production asset in an inherently inaccessible location. This is usually done through structural modeling and either spot monitoring campaigns using MEMS accelerometers or through subsea conventional strain gauges. Both technics present weaknesses: MEMS sensors usually require a great deal of data processing to obtain functional strain information at a desired location and strain gauges are complicated to install in a marine environment, many failing during pressure testing or installation. Both are also suseptible to electromagnetic fields which can biais their measurement. This paper presents details of a new non-intrusive integrity monitoring sensor systems recently deployed in the Gulf of Mexico and West Africa on production lines. Inherently reliable, as presenting no moving parts, these sensors use optical fibers embedded within a composite frame for their measurements. Using field proven subsea fiber optic mapping technology these systems have delivered high frequency un-biaised, on the pipe, strain from which is derived pipe bending and axial loading in addition to temperature and pressure monitoring.By providing electromagneticly immune, low noise, un-biaised, strain measurements to structural engineers to verify and improve their fatigue behaviour models, the non-intursive integrity monitoring system has proven a reliable alternative to MEMS and strain gauges. Furthermore unlike alternative solutions, this system also monitors pressure, illustrating this technology's capability at providing production and flow assurance data in addition to integrity data making it an ideal tool within a subsea production surveillance strategy.