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.
