API 650 Appendix E - How do you figure"Nh" ?

[jcoots]

I am looking to get some confirmation on the calculation for (Nh - the Product hydrostatic membrane force) in API 650 App. E

I think it is the head pressure at the elevation in question divided by the thickness at that elevation.
(Head Press/shell thk.)

My second guess is that it could be
(Head Press/circumference)


Thanks in advanced.

 

[TankDude]

I interpret it the same as your first guess. I feel that the method used to determine the hydrodynamic hoop forces, when used in combination with this value, verifies this interpretation since the analysis point is the distance "Y" located vertically downward from the liquid surface.

 

[JStephen]

It's the hydrostatic stress times the thickness. Take the 2.6D(H-1)G/S equation and remove the stress from the denominator and you have Nh. It's also equal to radius in inches times pressure at the point.

Nh=PR = 62.4(H-1)G/144 x D/2 x 12"/ft = 2.6(H-1)DG

 

[jcoots]

Thanks for the confirmation.