Typical API-650 Tank - Vacuum Rating for Oil Storage?

[ChEMatt]

I've lost all references to previous instances, and am trying to recall what the typical criteria is for vacuum rating for an oilfield tank corresponding to API-650. I want to say it's -4 inches of H2O, but I don't want to say that to an engineering certainty.

For that matter, what typically drives such a value?

This would be for a tank installed in, say, North Dakota. Crude oil. RVP less than 10. Positive pressure rating would be 1 psig.

Thanks!

-CheMatt

 

[LittleInch]

Section 5.2.1 - 1 " water !!

You should get a copy of API 650 and BTW, this would be better in the storage tank forum, not the PV forum....

The resistance to collapse of a thin shell due to external pressure is very low

Design External Pressure (Pe): Shall not be less than 0.25 kPa (1 in. of water) except that the Design External
Pressure (Pe) shall be considered as 0 kPa (0 in. of water) for tanks with circulation vents meeting Annex H
requirements. Refer to Annex V for design external pressure greater than 0.25 kPa (1 in. of water). Requirements
for design external pressure exceeding this value and design requirements to resist flotation and external fluid
pressure shall be a matter of agreement between the Purchaser and the Manufacturer (see Annex V). Tanks that
meet the requirements of this standard may be subjected to a partial vacuum of 0.25 kPa (1 in. of water), without
the need to provide any additional supporting calculations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

The default is 1" water column as noted above. You can design the tank per Annex V for higher vacuum ratings. It will depend on the size and configuration as to what the maximum rating you could get out of a typical tank.
The default pressure is atmospheric. API-650 tanks can be designed for up to 2.5 psi under Annex F, but unless specifically designed for it, wouldn't be adequate for the 1 psi.
Also, note that Annex V is fairly new, and that the wind/pressure/seismic overturning criteria have been revised with each addendum, so those ratings could vary depending on the year of the standard in use.

 

[r6155]

Calculate the minimum shell thickness required for the combined loading from design external pressure
and WIND.

Regards
r6155

 

[MJCronin]

Suggest that you finalize your complete tank venting scheme and your maximum pumpout rate for the range of products that you expect to store.

Tank design for vacuum should consider maximum pumpout rate, temperature swings AND MINUMUM ACTUATION PRESSURE FOR THE TYPE OF VACUUM PROTECTION DEVICE THAT YOU WILL INSTALL

I have worked on projects where the tank designer has to guess on a vacuum rating only to learn months later that the relief device engineer has other ideas ..... consider these things early in project design !!!


MJCronin
Sr. Process Engineer

 

[georgeverghese]

Agreed, a well thought out pressure control / safety relief and vacuum breaking setting diagram will help to give you an idea of what operating pressure range is required. Also include adequate room for pressure control in case volatile vapor recovery is requested in the Company HSE regulations for this project.