Current lateral buckling (LB) methodologies can be very expensive to implement and in some cases can have unsatisfactory trigger reliability. Imposing a designed Residual Curvature (RC) to provide an initiation point for lateral buckling, by appropriate modification to the straightener settings during reel-lay installation, is a relatively new and efficient method for LB initiation and has been applied in the field to single pipelines to date. The logical progression for this is to apply the RC methodology to the installation of reeled pipe in pipe (PiP).
PiP systems which are laid by reel-lay require detailed finite element analysis to determine vessel pipelay settings which ensure that the product is straightened as it leaves the vessel. In addition, imposing an RC section has further technical requirements over standard pipeline installation, i.e. meeting residual strain requirements over a specified length to deliver the required in-situ curvature needed for LB initiation. It is important to identify and optimise the solution to ensure that both installation and in-service requirements can be met and are practically achievable. Therefore, justification for use of the RC methodology for reeled PiP requires a portfolio of in-depth reeling and installation analyses to understand the application of this method for a complex reeled system, and how vessel and environmental influences may impact on the final solution.
To justify the implementation of the RC methodology for PiP, advanced non-linear FE analyses were used to assess vessel capabilities, the installation of PiP with RC and to determine the achievable in-situ RC for PiP. The effect and impact of reeling on the PiP is discussed in relation to both standard and RC pipelay. The paper discusses the technical challenges involved in the installation of an RC section for reeled PiP by presenting the methodologies employed in determining the achievable RC for PiP, the potential impact from environmental loading during installation and the resultant in-situ residual curvature that is expected.