INTEGRITY ANALYSIS OF FLEXIBLE PIPES TENSILE ARMOUR WIRES USING NON-DESTRUCTIVE METHOD OF INVERSE MAGNETOSTRICTION: A METHOD COMPARISON

Abstract

Flexible pipes have been used for decades for conveying produced fluids from oil wells to floating production, for storing and offloading units, and for flowing injection fluids inside wells under the seabed. Over the years, with an increase in oil demand globally, the exploration of new and deeper oil reservoirs has become a reality. With greater water depths, the top tension of the risers has increased significantly, as well as the pressure from the water column on the pipe structure, demanding the application of bigger pipes and the use of stronger materials. Pre-salt reservoirs on the Brazilian basins are rich in carbon dioxide (CO2) and hydrogen sulfide (H2S), which are great contributors to the premature fragilization of armour wires on the top section of the flexible risers and are capable of compromising the integrity of the structure. The wire fragilization and possible breakages cannot be avoided once the riser is connected to the floating unit, but they can be monitored, to avoid a complete riser structural failure. Several systems have been developed to monitor tensile armour wires integrity, such as visual monitoring, which visually detects torsion on the structure, acoustic waves, and magnetic collar systems, which have failed to provide reliable results. As the armour wires provide axial resistance to the structures, Fiber Bragg grating is being used in modern flexibles to monitor armour wire deformation and has been delivering reliable results. Another method, the inverse magnetostriction, is being tested using an anisotropic magneto sensor to detect wire deformation and generate a 2D stress map of the measured area. In this article, two tests are performed using the same equipment, but in different specimen. One test was performed on the wires without being applied on the flexible structure. The other test was performed on a window opened on a 6” nominal bore flexible pipe, with the objective of identifying if the method is reliable in detecting armour wire failures on flexible risers. This method could read stresses variations on the armour wires, but a larger sensor could penetrate deeper on the structure and provide a sharper stress map.