Hello,


I am designing one tank with internal pressure as atmospheric + full of liquid as per API 650.

Generally, tanks under 18 kPa internal pressure falls under this code category.

Anyone please tell me what will be the exact internal pressure value for atmospheric tanks??

Initially i assumed zero pressure by considering the tank is operating under atmospheric conditions. But while doing this, the required roof to shell junction value (as per appendix F) comes as negative value.

Now i considered 0.75 kPa after referring some tank guide books. Please tell me that the considered internal pressure value is correct??


Thanks in advance for your response.

Raja.

About the "problem" of negative area as calculated under Appendix F, you may see
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=46484

The internal pressure may be by gas blanketing or by other operational conditions. There isn't an "exact internal pressure value for atmospheric tanks", rather you/ your company as Subcontractor/ your Contractor must establish the internal pressure for your specific tank.

Hello Mariog..


Appreciate your time..

Thanks for the reply..

Hello rajarajan

The only pressure the tank will see is the hydrostatic pressure from the liquid. You are probably aware if the One-Foot formula in API 650. It looks like this:

td = 2.6D(H-1)G/Sd + CA.

The H in that formula determines the pressure acting in the tank at each shell course. As there is no internal pressure, there is not tendency for the tank to lift, thus no bolting is required.

Hello rajararjan

I did not answer the last part of your question, for which I apologise. API 650 does not require you to consider an internal pressure if you are sure that there is none. Adding a pressure could make you tank more expensive because there might be the necessity of adding foundation bolts.

API 650 has a normative appendix namely Appendix F with title "Design of Tanks for Small Internal Pressures".

By paragraph F.2 it is required to modify one-foot formula, taking into account that "in calculating shell thickness", H- the design liquid height- must be increased with a term that is proportional with the design internal pressure.

Hello rajararjan

The TANK programme takes care of all the contingencies associated with tank design. That includes Appendix F.

Thank for the suggestions..

Now it was almost clear. Can i apply zero internal pressure in tank software for atmospheric tanks. Is it correct procedure?

Yes rajarajan.

Tanks often have zero pressure. They are in the main atmospheric tanks, but are permitted to have a very small internal pressure of 2.5 psi (18 kPa)