API 650 design liquid level

[EmilianoS87]

Hi everyone,


I have a question regarding the design liquid levels in an API 650 storage tank.


The tank will store a product with high relative density. The design liquid level (DLL) for the product is limited by some overflow nozzles, which are located below the top angle. However, for the hydrotest, the builder wants to fill the tank up to the top angle, blinding the overflows to test the shell joints.


Is it acceptable to define two different DLLs—one for the product (limited by the overflow nozzles) and one for the hydrotest (up to the top angle)? My concern is that if both are set to the top angle, the foundation would be unnecessarily penalized due to the high product density.


Has anyone dealt with a similar case?


Thanks in advance for your input!

 

[JStephen]

To avoid confusion, I would just define one DLL, but then go ahead and hydrotest it to the top of the shell, assuming design meets hydrotest requirements for that depth.
Also, see 7.3.6.1.1(b), (c) and (d), which allow the hydrotest depth to be different from the design depth in various cases.

 

[EmilianoS87]

Thanks for the quick response,

So, if I were to fill, let's say, 2 inches above the weld connecting to the roof plate, I would need to adjust the design calculations to account for this new level, correct?


For example, if testing according to 7.3.6.1.1 b), I would need to modify the equation in 5.6.3.2 for tt, setting H to the new value. In that case, I would effectively have two different H values.


If I test according to 7.3.6.1.1 d), would I need to include the test liquid’s specific gravity (G) in that equation?


That’s just for this specific paragraph and using the 1-foot method, but I assume I would need to review all relevant formulas to identify where this change in level has an impact—is that correct?

 

[JStephen]

You'd need to check it, but if the specific gravity is "high", then product loading should normally govern.

 

[pierreick]

Hi
Hydrotest should be using water, right?
In any case your design should cope with 100% storage filled in.
Pierre