3 replies to this topic

[WilliamN]

Dear peers,

I want to check with our peers out there if it is practical (eg, cost? API guideline? etc.) to specify a storage tank (API 620 or API 650) with design pressure of 3 psig/Full vacuum. One of our procedures is steaming out the tank for inspection. due to certain environmental requirements, we might need close all openings while steaming the tank. This will create a huge vacuum when steam condenses. so if the tank is designed with full vacuum, steaming out with closed openings then is feasible.

 

Thanks.

 

WilliamN

[ankur2061]

Hi,

 

The latest edition of API STD 650 (13th) addresses vacuum design or design for external pressure in Annex V but mentions that the procedures in the Annex are limited to an external pressure of 1 psi (-1 psig). Full vacuum conditions are not addressed. API STD 620 also does not address full vacuum design. Essentially based on these two standards a full vacuum design is not available.

 

Only the PV code ASME Section VIII is the one that includes a full vacuum design.

 

So going strictly from codes and standards limits you in the design of a suitable tank for your application. However, special designs can be done with due testing and certification from the fabricator wherein the tank is certified to operate under deep vacuum conditions (full vacuum is a hypothetical value). You will have to find a fabricator who can provide such a special design and who can provide you references for a similar installed tank working satisfactorily and with due certification of the design conditions of the tank. Cost would be an unknown factor for such a design (probably quite expensive).

 

BTW, you can hookup your tank vent or multiple tank openings to some kind of a closed system so that you don't have to worry about environmental release during steam-out and avoid going for such a special design of full vacuum. My 2 cents.

 

Regards,

Ankur.

[WilliamN]

Ankur,

Thanks for your valuable comments. Indeed certain environmental rules have pushed the envelop to an extent that it is challenging to find a suitable engineering solution. Probably closed system as you mentioned is a more practical way to go.

 

WilliamN. 

[fallah]

 

I want to check with our peers out there if it is practical (eg, cost? API guideline? etc.) to specify a storage tank (API 620 or API 650) with design pressure of 3 psig/Full vacuum. One of our procedures is steaming out the tank for inspection. due to certain environmental requirements, we might need close all openings while steaming the tank. This will create a huge vacuum when steam condenses. so if the tank is designed with full vacuum, steaming out with closed openings then is feasible.

 

 

WilliamN,

 

It's not inherently practical to consider full vacuum for atmospheric and low pressure storage tanks nor in relevant codes have been forecasted such design consideration.

 

Despite sudden condensation due to heavy rain fall which can be well managed by operation team, a proper vacuum vent can handle the partial condensation during steaming out operation.