Virtue anchor point is the point where the expansion force is equivalent to the soil frictional force.
End Expansion/Movement
Pipeline end expansion is movement at the hot end or cold end of linepipe. Expansion spool is recommended if the hot end expansion is significant.
Expansion Spool
Expansion spool is spool piece installed to prevent pipeline from overstress risers and bends at platform during expansion that normally occurs at the hot end. Conventional expansion spool is in L or N-shape.
Pipeline Walking
Pipeline walking is pipeline axial displacement due to increment or decrement of operating temperature and pressure.
Reversed Movement
Pipeline tends to expand during increment of operating temperature and pressure. Reversed movement is the contraction of pipeline during the reduction of operating temperature and pressure.
Residual Movement
Residual movement = end expansion (forward movement) – reversed movement
When the operating temperature and pressure increase, the linepipe will experience end expansion. If the operating temperature and pressure are reduced, the linepipe will experience contraction (reversed movement). Even if the operating temperature and pressure of linepipe are returned to initial values, partial of the movement towards the platform still remain (residual movement). This is because friction always opposes motion, and prevented the pipeline from fully contract when the operating temperature and pressure falls to ambient temperature,[Ref. 1].
References:
- 1. A.C. Palmer (1981) Movements of Submarine Pipelines Close to Platforms, Offshore Technology Conference, Houston, Texas, OTC 4067, May 1981.
- 2. DNV OS-F101 (2007) Submarine Pipeline Systems.
