7 replies to this topic

[Shailesh kshirsagar]

I want to how to select positive design pressure of API stroage tank between 0 to 18 kPag.

As per API 650 , positive design pressure for API tanks should be between 0 to 18 kPag (2.5 PSI g). As per Appendix F of API 650 specified that internal pressure should be such that it should not exceed nominal weight of the metal in Shell or roof.
How the process engg. know the approximate weight of the tank as it will depend upon thickness of tank. And thickness will depend upon design pressure.

is there any approximate fig. of design pressure versus thickness are available.
for ex. 3/18" CS plate tank = XX weight = XX design pressure.

Presently, I am doing priliminary tankage flare header study. for this purpose I want storage desing pressure effects on the weight of tank ( on cost).

I have checked below link, below I not got any answer regarding this.

http://www.cheresour...esign-pressure/

Please guide.

[fallah]

Hi,

Process engineer will specify the design pressure of the tanks, subject to a small internal pressure, as per the specifications of the fluid to be stored regardless of the roof plate thickness.

Then, as per equations in F.4.1 and F.4.2 the nominal roof thickness could be calculated along with subsequent design pressure modification.

Fallah

Edited by fallah, 20 May 2012 - 05:54 AM.

[Shailesh kshirsagar]

Thanks for reply Fallah.
Actually, I am performing tankage flare header calculations in BFD stage.
If I considered design pressure of tank as a 2 kPag then my flare header become too high rather if I considered 6 kPag.
I want to know 3~4 kPa increase in design pressure has any impact on tank cost. that is why I asked approximate weight of the tank w.r.t tank design pressure.

[fallah]

Hi,

As per API 650, the force due to Internal pressure of the storage tank acting on its roof area not to be exceeded the weight of the roof plates. then, for increasing internal design pressure you should increase the roof's plate thickness with having impact on tank cost.

You can derive the relationship between roof weight and internal pressure in your case and compare the weights of the roof before and after increasing internal pressure. With having the cost of various thickness plates, you can estimate the subsequent cost impact due to this pressure change.

Fallah

[jrtailor09]

Dear Shailesh,

I have not seen API Storage tank relief outlet connect to flare header. API storage tank to be provided with safety device like Emergency vent, PVRV (pressure vacuum relief valve).

Can u tell me what is back pressure of flare header ?

As flare header back pressure is very high compare to the Storage tank design pressure / Relieving pressure.

Kindly recheck & confirm for any such facility provided any where in the world before the starting Flare header calculation for tankage.

Regards,

Jatin

Edited by jrtailor09, 24 May 2012 - 06:38 AM.

[fallah]

jatin,

It would be possible. Actually in some oil and gas facilities there is LLP (low low presure) flare network dedicated to such low pressure relieving sources. The back pressure in such network with large pipe sizing would be adjusted below 50-60 mbarg (as typical).

Fallah

Edited by fallah, 24 May 2012 - 09:57 AM.

[jrtailor09]

Fallah,

5-6 kpag is very less for the flare system component sizing. This will covers Flare tip, molecular seal, water seal riser & flare header etc. Do u feel this is enough pressure drop for the component sizing?

Capital cost will be very high in that case for the flare system componenet.

Regards,

jatin

[fallah]

jatin,

Your evaluation is generally right, but in some cases you have to release some very low pressure sources of relieving fluids into flare network and in such situations you have to consider a dedicated LLP flare network for mentioned sources.

Fallah