Virtual testing of composite risers.

Abstract

Hydrocarbon reserves maintain high market demand for energy security reasons, while the world governments promote ramping up renewable energy production. Companies exploit deeper reservoirs as current reserves start to deplete. Composite risers, with their tailored high strength- to-weight ratio properties that reduce the effective tensions and bending moments, are lucrative options to transport hydrocarbons compared to conventional steel risers. However, there is limited research into composite risers’ full-scale behaviour. The main topic, that is missing from the literature, is the combined effect of far-field loading and mechanical properties uncertainties on composite risers’ integrity. Offshore complaint risers are exposed to dynamic vessel motion, environmental stochastic conditions, and high-pressure high temperature operational conditions. These complex multi-axial loadings result in non-linear riser response. The combined responses to these conditions with composite material in-situ, in addition to the environmental and manufacturing uncertainties are not well understood. Composites uncertainties due to material properties degradation associated with in-situ conditions, such as water absorption and manufacturing imperfections like voids and statistical variations require further investigation. This work aims to capture the far-field loading effects on composite risers, that contains imperfections that require full-scale testing and to develop a virtual testing multi-scale approach, that is lucrative to manufacturers to optimize the qualification testing processes. Three models are developed in a sequential multi-scale framework. A non-linear extensible algorithm is developed based on beam theory to capture the global riser response and to provide boundary conditions and loads to a meso scale composite FEA pipe model. The predicted principal strains, that are post-processed from the global riser response, are imposed to a microscopic peridynamics RVE model that incorporates the statistical void percentage and fibre distributions in the matrix. An integrity analysis is conducted using Monte Carlo method that reveals that mechanical properties variation due to moisture absorption reduces the riser reliability by two orders of magnitude. The increase in manufacturing voids percentage reduces the tensile and transverse strengths to less than half of its no-void values. Another integrity analysis is conducted to investigate the effect of manufacturing uncertainties using peridynamics. The predicted damages are benchmarked against Tsai-Wu failure criterion which is found to be matching the final failure conclusion. However, it is observed that the Tsai-Wu stress-based equality is invariant to the microscopic geometry imperfections such as, voids and fibre distribution and size. Although peridynamics micro modelling is a computationally expensive approach to composite risers failure predictions, however, it is a promising technique to investigate wider varieties of manufacturing uncertainties effect on the composite riser integrity when combined with far-field loading and harsh operational conditions. The methodology presented allows the composite riser manufacturers to optimize qualification tests to mimic full-scale testing and control the parameters that correlate with failure.

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Identifiers

ORCID for Adam Sobey: orcid.org/0000-0001-6880-8338

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