In Situ and Real Time X-Ray Computed Tomography for the Micromechanics Based Constitutive Modelling of the Unbonded Flexible Riser

Abstract

The failure mechanism of the composite flexible riser, comprising a pipe with melt fused carbon fiber tape or pultruded composite rods, is not well understood. As there is change in the configuration of the composite layers and its manufacturing methods, so the bulk material property also changes significantly. To capture the correct material model for global FE analysis, real time x-ray computed tomography was performed while the flexible pipe was being compressed. For developing a constitutive model for the composites, a time series of 3D volume images were analyzed quantifying the local strains responsible for the debonding of the layers and the crack development. These values were then used to understand the inter-layer adhesion leading to correlation between the FE global modelling and experiments capable of capturing the progressive delamination. The resulting global modelling was used to determine the area under compressive loading. The effect of global sea conditions and cumulative damage was noted. A correlation between the global model and experiments can be used to optimize riser performance. This method hopes to capture the overall behavior of flexible pipe under compressive loading.

The Effect of Ice Floe on the Strength, Stability, and Fatigue of Hybrid Flexible Risers in the Arctic Sea

“…The hybrid riser system, incorporating the CFRP composite layer serving as a pressure armour, is instrumental in the conveyance of fluids from the subsea manifold to the vessel located in a deep-water setup [4]. This innovative system, if employed as a key component of floating offshore facilities, can be utilised in deep waters such as the Arctic Sea due to its lightweight per metre length [5][6][7][8]. These flexible risers are also characterised by a smooth bore, eliminating the problem of slug flow-induced vibrations [9].…”

“…However, the harsh conditions in the Arctic regions, such as the presence of floating ice and low temperatures, present additional challenges for its implementation. The impact of ice on the hybrid riser can result in the formation of microcracks, leading to its failure [5,7]. A self-healing concept has been proposed to address this issue by recovering the microcracks and restoring their fatigue life [10,11].…”