Pipe-in-Pipe |
 
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Pipe-in-Pipe |
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A useful feature in Flexcom is the ability to model pipe-in-pipe configurations. Internal and external sections are modelled separately, and interact with each other by means of special connections simulating linear and non-linear resistance to relative motion as well as internal fluid hydrodynamic forces. Although the capability is called ‘pipe-in-pipe’, it can also be used in the modelling of ‘pipe-on-pipe’ or piggy-backed systems - there is no requirement for one section to be physically contained within another.
When referring to pipe-in-pipe sections, the terms ‘outer’ and ‘inner’ are used regularly. This makes sense as the purpose of the *PIP SECTION keyword is to identify which pipe sections are contained within other pipe sections. When referring to pipe-in-pipe connections, the terms ‘primary’ and ‘secondary’ are used, reflecting the fact the connections may represent either pipe-in-pipe or pipe-on-pipe configurations (indeed the same *PIP CONNECTION keyword is used to define both).
•Model Set-up Guidelines provides guidance to assist new users with model creation and help to avoid common pitfalls.
•Pipe-in-Pipe Sections describes how one pipe is contained within another, and explains the implications of this for buoyancy and hydrodynamic forces.
•Standard Connections outlines the operation of the standard pipe-in-pipe contact model at a high level.
•Sliding Connections explains the additional functionality offered by sliding connections, and suggests scenarios for which it is appropriate.
•Contact Modelling discusses the operation of the pipe-in-pipe contact modelling algorithm in detail.
•Hydrodynamic Forces outlines the main fluid forces modelled by Flexcom (including buoyancy, hydrodynamic and internal fluid) and how these are affected by the presence of pipe-in-pipe configurations.
Flexcom’s pipe-in-pipe facility has been used extensively by Wood engineering services division. For example, Flexcom was an integral part of the FEED and detailed engineering design phases for a Bundled Hybrid Offset Riser (BHOR) configuration deployed offshore west of Africa, and the software was also central to the complicated installation process involving shallow water tow out and deep water upending.
Liu et al. (2013) compare Flexcom and Abaqus for a pipe-in-pipe configuration, outlining independent research conducted by IntecSea and FloaTEC. A static in-situ analysis of an SCR within a pull-tube, and a dynamic pull-through analysis are considered. The results show very close agreement for the static case, and strong agreement for the dynamic case (including sliding pipe-in-pipe contact) in terms of the bending response. Flexcom does not yet model frictional effects in the pipe-in-pipe model, but this was not an issue in this case study, as bending is typically the principle design driver for pull-tube scenarios rather than tension. Furthermore, the authors conclude that the solution offered by Flexcom offers greater computational efficiency than the Abaqus simulation (i.e. shorter run-times).
•*PIP SECTION is used to define internal and external pipe sections when part of a pipe-in-pipe model is contained within another.
•*PIP CONNECTION is used to define pipe-in-pipe connections between nodes of the finite element model.
•*NO PIP SLIDING is used to disable the interchangeable nature of sliding pipe-in-pipe connections.
•*PIP STIFFNESS is used to define force-deflection curves for non-linear pipe-in-pipe connection stiffnesses.
•*LINES PIP is used to specify that two lines are connected in a pipe-in-pipe (or pipe-on-pipe) configuration.
If you would like to see an example of how these keywords are used in practice, refer to A03 - Pipe-in-Pipe Production Riser (Standard Connections) and H02 - J-Tube Pull-In (Sliding Connections).