API 650 - E.6.1.4 Dynamic Liquid Hoop Forces

[EmilianoS87]

I was reviewing some calculation notes on this topic and noticed that when the test point is above the design liquid level, the Y value becomes negative. If I proceed with the equations using a negative Y value, I sometimes end up with unusual and excessively high thickness requirements for shell courses that may not even be in contact with the liquid.

In your experience, how do you handle this? Should this check be skipped for shell courses located above the design liquid level, or is there a specific approach to account for this scenario?

 

[HTURKAK]

noticed that when the test point is above the design liquid level, the Y value becomes negative.

What is the test point? Definition of Y=Distance from liquid surface to analysis point, (positive down), m (ft).
Will you pls post a sketch and calculation showing your interpretation ?
Apparently there is misunderstanding.

 

[JStephen]

You don't normally check hoop stresses in the shell above the design liquid level.
Note that if you try to check static hoop stresses above the liquid surface using the regular equations, you'll similarly get meaningless negative values.

 

[EmilianoS87]

What is the test point? Definition of Y=Distance from liquid surface to analysis point, (positive down), m (ft).
Will you pls post a sketch and calculation showing your interpretation ?
Apparently there is misunderstanding.

I believe as JStephen is saying if I try to check static hoop stresses above the liquid surface Y is negative and I would get strange values that does not represent the actual shell stresses. I am thinking to only check for hoop stress if Y is positive. Am I correct?

 

[HTURKAK]

If the analysis point above the liquid level, then the hoop stresses will diminish and will be meaningless to calculate . However, the max. liquid level needs to be discussed .
Test height and max. operation height could be different. Definition of H,
H is the design liquid level, in m: is the height from the bottom of the course under consideration to the top of the shell including the top
angle, if any; to the bottom of any overflow that limits the tank filling height; or to any other level specified by
the Purchaser, restricted by an internal floating roof, or controlled to allow for seismic wave action.
That is , if there is no restriction or any overfill slot to dictate the max. product level , the max. height should be height of the tank.

 

[EmilianoS87]

I understand, thank you both. You've been a great help