VESSELS AND TANKS

[Eabrar]

HI

CAN ANYONE TELL ME THAT FOR STORAGE PURPOSE WHY SOMETIME VESSELS ARE DESIGNED WHILE OTHER TIME TANKS ARE DESIGNED?

THANKS

 

[JoeTank]

Generally speaking PRESSURE VESSELS are used for storage at pressures exceeding 15psig. Oherwise, a TANK is used.

ASME VIII is often used for PVs in North America, per local regulatory requirements. API-650 and API-620 are typically used for tanks in the oil and chemical industry.


Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[zdas04]

15 psig???????? A 15-ft diameter tank with 15 psi on it would have 380,000 lbf of force trying to lift the top. I've seen tanks lose their tops with 3 psi on them and the design point is generally less than 1 psi.

David

 

[JStephen]

Steve is correct.

ASME B&PV Code is for 15 PSI and up. Below 15 PSI, there is usually not a specific legal requirement for one standard or another. But normally, API-620 would be used for pressures between 2.5 and 15 PSI, and API-650 for pressures below 2.5 PSI. AWWA D100 and NFPA-22 are other atmospheric tank codes. There are others for UL tanks, bolted or concrete tanks, etc.

For a tank to hold 15 PSI, it has to be designed for that pressure. You can't just take any old tank, and put 15 PSI into it. And designing a tank of some size for 15 PSI will usually require a dome roof or steep cone roof, anchor bolts, etc.

Eabrar, as to your question- a tank is always cheaper than a pressure vessel of the same capacity. So for any product that can be stored in an atmospheric tank, that's the way to go. And when the nature of the product, or the process conditions require pressurized storage, then you go with the pressure vessel and pay the price.

 

[Eabrar]

why the price is less in case of a tank?

 

[JStephen]

Why a tank is cheaper than a vessel of the same size:
-Tank shell will usually be thinner, less steel required
-Tank roof and bottom (or ends if horizontal) can be flat or field-formed cone shapes instead of dished heads
-Tank roof and bottom will usually be thinner than the dished heads on a vessel
-Large tanks can be constructed vertically, with a flat bottom resting on the soil. With internal pressure, this construction becomes awkward or impossible due to uplift of the shell.
-Vessel construction (in the US) requires increased inspection, increased paperwork, etc. You have to have an ASME stamp to build an ASME vessel, for example. Not so with atmospheric tanks.