Abstract
The stress–strain response of an offshore pipe riser subjected to combined internal pressure, tension and bending is studied. Finite element analysis was used to study three conditions of pipe riser – uncorroded, corroded and corroded and repaired with designated laminate orientation of carbon/epoxy or E-glass/epoxy fibre-reinforced composite. The behaviour of the pipe riser (grade API 5L X60 steel) was studied using Ramberg–Osgood model. Two composites laminate systems, a pre-cured prepreg (grade AS4 3501-6 carbon/epoxy) and a wet-layup filament-wounded composite (grade Gevetex LY556/HT917/DY063 E-glass/epoxy), were characterised. Design conditions were determined via a limit analysis known as the double-elastic slope method. The results showed that under combined hoop, tensile and bending loads, the riser tends to approach failure at a much lower strain compared with each of these loads being applied individually. The limiting design factor of the composite repair system was due to excessive tensile strain experienced in a bent riser while the compressive stress caused by reversing the bending load occurred well within the linear-elastic region. With respect to the types of composite repair system, carbon fibre displayed a much better strength rehabilitation over glass fibre. In the aspect of laminate orientation, off-axis plies [90°/ ± 30°]s and [90°/ ± 45°/0°]s laminates were found capable of restoring the strength of the corroded riser and provide superior reinforcement in both hoop and axial directions.
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