On the feasibility of a novel concept for a free-standing riser

Abstract

This work consists of investigating the feasibility of a novel concept for the freestanding riser, where the pipeline is integrated to the riser by means of a transition section that is kept in place by a multiple line mooring system, developed to keep the functionality and integrity of the entire riser along its lifetime. A steel jumper is also evaluated as a potential alternative to the traditional jumper made up of flexible pipe. The work applies a finite element simulation software, Orcaflex, dedicated to global analysis of risers. As part of the feasibility investigation, screening static analysis is performed to identify the most promises configurations for the multiple line mooring system, followed by a series of dynamic analyzes to evaluate the behavior of the riser in extreme conditions. Moreover, several investigations are performed to assess the functionality and the robustness of the system, including the development of a methodology for wall thickness selection that minimizes the required upthrust for the buoyancy tank, parametric studies to check possible installation and dimensional tolerances, assessment of fatigue damage by comparison with conventional risers, development of methodology for determination of the jumper configuration, and checking how the pipe sizes impact the definitions within the design. The results show great potential of application, assuming the utilization of circumscriptive lines for mooring the riser.