Papers
REAL TIME CONTINUOUS STRUCTURAL INTEGRITY MONITORING OF FLEXIBLE RISERS WITH OPTICAL FIBER SENSORS
Abstract
Even though the armor layers play a major role in the structural integrity of flexible risers, operators and service providers worldwide are still in search of reliable inspection or monitoring techniques capable of detecting the presence of cracks or other defects in the metallic wires that compose the internal and external armor layers of the pipe. In the present contribution, we report the effort undertaken by Petrobras in order to face this challenge. Novel inspection and monitoring systems, based on acoustic emission, measurement of residual magnetic field, optical sensing, or employing visual monitoring cameras, are being developed and tested. Among these techniques, the one relying on optical fiber sensors has provided the best results so far. The use of fiber Bragg grating sensors for directly measuring strains in each wire of the external traction layer offers an accurate and reliable real-time, continuous monitoring technique, providing the operator with valuable information and early warning if any deviation from the expected wire's structural behavior is detected. The paper describes the technique and presents results from full scale laboratory tests as well as from the first field trial conducted in an offshore platform operated by Petrobras in Campos Basin.
NEW ADVANCES IN FLEXIBLE RISER MONITORING TECHNIQUES USING OPTICAL FIBER SENSORS
Abstract
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.
MONITORING FLEXIBLE RISERS WITH OPTICAL SENSORS – OPERATIONAL EXPERIENCE AND FUTURE PERSPECTIVES
Abstract
Most of the subsea production systems in Brazil are developed using flexible pipes, including pre-salt fields and their challenging scenarios in ultra deepwater, with CO2 and H2S contaminants, high internal pressure and severe metocean conditions. The integrity management of these flexible pipes plays a major role in maximizing the availability of the production systems while minimizing both safety and environmental risks. One of the key areas for the integrity management is the riser top section, where high tensions and curvatures result in high stresses and may lead to fatigue issues in the tensile armors.
In order to better assess the integrity of the tensile armor at the top section of flexible risers Petrobras has developed a monitoring technique known as MODA (Monitoring based on Optical fiber attached Directly on Armor wires). As the name implies, this technique uses optical sensors — strain gauges based on Fiber Bragg Grating (FBG) technology — attached to each wire of the outer tensile armor. The strain measurements provided by these sensors make it possible to identify broken wires and detect events associated with wire ruptures.
Many components and steps are required to transform the wire strain measurements in integrity data. The main components are the riser end-fitting, adhesives, FBG sensors, submersible optical connectors, optical distribution panels, FBG interrogators and server computers. The main steps are the strain sensor bonding procedure, infrastructure commissioning, equipment installation, data acquisition, data processing and data analysis. The coordination of interfaces between different players involved in each of these steps is crucial for a successful implementation of the MODA.
This paper will discuss Petrobras operational experience with of the MODA and its challenges, lessons learned and future perspectives.
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