Integrity Monitoring of Flexible Risers by Optical Fibres

The use of fibre optic sensing technology for integrity monitoring of flexible risers has been demonstrated. A technique for integration of the sensors along the tensile armouring has been developed and used in testing of a full-scale riser where the strain in the tensile armour was measured. The integration technique is also applicable to fibre optic sensors for other measurands. The test riser was exposed to a fatigue test of 612 000 bending cycles. The strain measurements provided new and important data about the conditions in the annulus of a riser during operation. The small diameter of optical fibres (OD = 0.125mm) and the multiplexing features of sensors based on fibre Bragg gratings (FBG) make it possible to realise various sensing systems in the riser annulus. A possible combination of different fibre optic sensors is outlined.