End cap effect calculation? 3

The end cap effect is the pressure effect in the pipe in the axial direction.

The pressure x pipe cross section area in the ID = end cap force.

This end cap force is also called thrust force which genrally acts on the pipeline bends and anchors.



Narendranath R
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The End Cap Force is an force introduced in pipelines formulation for the effective axial force. It derives from the fact that the pipeline is immersed in pressure fields. You have to recall the Archimede law. In the Archimede law you can replace the integration of the pressure field on an immersed body with the submerged mass of the body provided the field of pressure around the body is closed.
In the case of pipeline we have 2 fields :
- external hydrostatic
- internal pressure
for simplificity of relationships (static equilibrium etc...) the submerged weight of the pipe is usually considered. This implies that the pressure field acting on the pipe wall has already been accounted - BUT the end cross section are most of the time NOT closed (the pipe gets in air, gets connected to other structures etc...)
which means that you have to add/remove it from your resulting axial force (true/effective). See DnV OS-F101 section 5 you ll find the definition of the axial force. The above explanation is very rarely clarified althought very simple. I have met so many pipeline engineer ignoring this point !
To convince yourself do the integration of pressure field on a square cross section pipe immersed vertically in water.
calculate all pressure resulting force and compare to the submerged weight + external force equation -

Regards
Jean-Francois DUROCH
Principal Pipeline Engineer