Monitoring the structural integrity of a flexible riser during a full-scale fatigue test

Flexible risers are presently seen as an attractive alternative to their rigid counterparts in the offshore oil exploration industry, mainly because of their relatively simpler mounting and transportation. However, the complex multi-layered structure which guarantees high flexural compliance is not favorable for inspection with most non-destructive testing (NDT) techniques, which makes structural integrity evaluation difficult. Initial efforts concentrated on the search for a single technique which would ensure reliable detection of armor failure, but recent studies have shown that the safest approach may be to take advantage of the redundancy obtained when different instruments are combined. This work presents results of a full-scale dynamic loading test of a 6 m-long section of a flexible pipe with end-fittings which was instrumented with a range of sensors. Of these, measurements of torsional angle variation, axial displacement and Acoustic Emission were selected for a direct comparison. 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 three techniques is combined.