Monitoring the structural integrity of a flexible riser during dynamic loading with a combination of non-destructive testing methods

Flexible risers are composite structures consisting of several metal armours and polymeric layers, which are widely used in offshore oil exploration facilities due to their relatively simpler mounting, transportation and operation when compared to their rigid counterparts. Due to the nature of Brazilian oil reserves, a significant percentage of produce is transported through such structures, and their use is likely to increase in the near future. Hence, to maintain production levels and avoid environmental disasters it is essential to deepen the understanding of the behavior of these structures under loading and to quantify how incremental damage of the metal components affects overall structural integrity; furthermore, the development of techniques capable of giving early warning of structural damage is of utmost importance. In this work non-destructive testing (NDT) techniques were applied to a flexible riser in a full-scale dynamic loading test. Of the several techniques used during the test, readings from optical fiber sensors based on Bragg gratings and acoustic emission were selected for a direct comparison; these were validated by displacement values recorded by the mechanical actuator. A detection pattern is observed during forced rupture of the wires of one of the outer armor layers, and reliable identification of events is possible when information from the two NDT techniques is combined.