Due to depleting sources of oil and gas reserves in shallow water depths, exploration and production activities have moved into ultra-deep offshore oil fields. Risers are an essential part of any offshore drilling facility. A riser tensioner located on the drilling platform has to provide an adequate vertical tension to maintain the stability of the riser. It is essential for a successful operation. Composite risers in deep sea conditions require much lower top vertical forces due to their high strength to weight ratio. Carbon/epoxy composite has been considered in the present study to carry out the burst analysis and to assess the safety of the composite riser under internal and external pressures and other environmental loads due to random sea currents. In order to ensure the permissible pressure and no fluid leakage, composite risers are provided with an internal steel liner. Initiation and propagation of debonding between the liner and composite has been studied and probability of failure is obtained. In burst analysis, maximum internal pressure is applied to a riser section and the stresses in all (hoop and longitudinal layers) the composite layers are checked against the failure. High pressures are incremented in small steps until fiber rupture occurs due to bursting. Maximum normal stress theory is employed for checking the failure. The same theory provides the limit-state to assess the safe pressure considering uncertainties associated with random input parameters involved. A finite element analysis has been carried out in ABAQUS/AQUA for random sea motion and fluctuating axial tension considering salient non-linearities. A small riser section modelled as a hybrid beam element (for global analysis) has been considered to study the bursting and debonding behavior. It is further discretized into thin shell elements (S4R). Steel liner and composite pipes are modeled separately and assembled together to ensure the overlapping various layers and sharing nodes. The composite body sustains the major stresses in the inner layers that diminish on moving outwards radially. An implicit time domain analysis has been carried out to obtain the response. The debonding through circumference and length are studied. The stresses obtained are compared with their ultimate strength.
Bursting Capacity and Debonding of Ultra Deep Composite Production Riser: A Safety Assessment
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Singh, M, & Ahmad, S. "Bursting Capacity and Debonding of Ultra Deep Composite Production Riser: A Safety Assessment." Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. Volume 6A: Pipeline and Riser Technology. San Francisco, California, USA. June 8–13, 2014. V06AT04A056. ASME. https://doi.org/10.1115/OMAE2014-23872
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