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Dynamic Liquid Hoop Forces

Thursday, May 18, 2017   By: ADI HAR-SHOSHAN [93] 4 Stars
When claculating shell courses thickness as per 1 foot method ,does the Dynamic Liquid Hoop Forces or stresses that created during seimic event should be taken into account for the thickness of the first course?

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Monday, May 22, 2017   By: ITS [1678] 4 Stars
This is a difficult subject, but I hope it is simple for others to understand to issues.

So the dynamic liquid hoop forces or hydrodynamic pressures from a seismic event must be taken into consideration through out tank to include the first shell course to the highest shell course.

The horizontal acceleration influences the sloshing of the upper two thirds of the tank -worse case full tank - shell course that puts pressure against the shell courses on the side of the slosh and needs to be thicker because of this.

The lower third is trickier for the critical zone where the shell and annular plate meets gets highly stressed. So the pressure from sloshing against the shell courses in the lower third requires additional thickness to over come that pressure from the added liquid level and weight of the slosh.

The floor gets additional pressure too from the added liquid height from the slosh. This also means the ground under half of the tank will be highly pressurized and the other half will be under pressurized trying to cause over turning. So, the ring wall foundation must be robust enough to handle this dynamic shift of the mass above and maybe a concrete floor is under the tank steel floor to stiffen the structure.

So, you should take into account the thickness of the first course and more.

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Monday, May 22, 2017   By: ITS [1678] 4 Stars
I meant to say acceleration of the weight and not plain weight.

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Wednesday, June 21, 2017   By: davidr@fast.net [39] 5 Stars
This is covered in API 650 Annex E.6.1.4 but seldom are the controlling condition.

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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