Petrobras oil and gas production in the deep and ultra deepwater fields in Campos Basin and other provinces off the Brazilian coast heavily relies on flexible pipes. Maximizing the availability and reliability of an extensive offshore pipeline network poses innumerous challenges to the Company, which is steadily moving towards a condition based approach to maintenance of their flexible risers. In this context, Petrobras, in cooperation with its academic partners, has launched a comprehensive R&D program named MONFLEX, focusing on novel techniques for structural monitoring of flexible risers.
Years of field experience have demonstrated that one of the most frequent failure modes of flexible pipes is the sequential rupture of wires in their tensile armor layers [1]. The MONFLEX Program has explored a range of different technologies in order to timely detect and monitor the growth of this class of progressive structural damage. Some of the proposed approaches have relied on video cameras pointed towards fixedly mounted targets on the riser outer sheath, vibration and acoustic methods, these in a wide frequency range, and techniques based on fiber optic strain sensors. All three have been experimentally deployed in the field and are currently being evaluated. Among those, fiber optic monitoring is the one that has shown the better promise of becoming the chosen method for detecting wire ruptures in the riser’s armor layers.
The fiber optic based monitoring system developed in the MONFLEX R&D Program has been named MODA, which, in Portuguese, stands for Direct Wire Optical Monitoring. The MODA system consists in instrumenting all the wires of the riser’s external tensile armor layer with fiber Bragg grating strain sensors. In flexible risers already in operation, a window in the polymeric outer sheath of the pipe is temporarily opened in order to allow the sensors installation, and then repaired with a protective, anticorrosive layer. Even though in MODA the strain sensors are installed in the external armor layer, full scale laboratory tests have demonstrated that the algorithm employed to treat and analyze the real time data provided by the system is capable of instantaneously detecting ruptures of wires either in the external or internal layers of the tensile armor. The proposed contribution will report the later results of extensive laboratory tests and field trials performed with the MODA system.
