Maximum Design Pressure for API 650 Tank

[ak1965]

Dear Fellow Members,

We are ordering an API 650 tank for storing Hydrocarbons.

Please confirma the maximum design pressure a dome roof tank can be designed ?

API 650 describes at page 5-5 under the deisgn considerations for loads that maximum internal deisgn pressure is 2.5 psi. but does not specify the type of roof.

Is it the maximum pressure a tank can be designed as per API650 irrespective of the type of roof?

 

[JStephen]

Tanks designed under API-650 can be designed for up to 2.5 PSI. On a tank of any size, designing for 2.5 PSI will have a major effect on the structural design, the anchorage, the foundation, and the cost. The pressure should be specified to reflect actual operating conditions, rather than as an arbitrary figure. Note that API-650 assumes that the normal operating pressure is 40% of the design pressure.

Theoretically, any roof can be designed for pressure, but steep self-supporting cones or domes lend themselves to pressurized use better. Before specifying domes, check with your tank suppliers for availability.

 

[ak1965]

Thanks Jstephen...

That is what I also thought....however, in the mean time. I referred API 620 as well for Tank design pressure.

It dictates in the scope itslef i.e. page 1-1 point no.1.2.2

Quote:

"The tanks described in this standard are designed for metal temperature not greater than 250 DegF and with pressures in their gas or spaces not more than 15 lbf/in.2"

How do u signify this pressure stated by API 620 which is almost 06 times of pressure in tanks as guided by API 650?

This is very cruicial to understand as it has a severe impact on deciding the design pressure.

See the attachments of excerpts from standards

 

[JoeTank]

The difference comes from the intent of the Code committee. API-620 has always been the primary Code for pressurized tanks. It shares alot of similarities with the joint ASME-API pressure vessel Code (discontinued in the mid-1950s). The low pressures (up to 2.5 psi) of API-650 was added to accomodate the low operating pressures for vapor recovery systems while maintaining the overall economy of API-650 vs API-620. API-620 tanks historically were not just simple flat bottom tanks, but rather spheres, globoids and noded spheroids... all of which are more appropriate for higher pressures. That's why API-620 allows much higher pressures.

Joe Tank

 

[ak1965]

Thanks JoeTank,,,

If API-620 has always been the primary Code for pressurized tanks. Why the title of API620 appears as:-

"Design and Construction of Large, Welded, Low Pressure Storage Tanks"

I wonder the versatility of standards sometimes confusing too.

 

[JoeTank]

What don't you understand? 15 psi is a low pressure.

Joe Tank

 

[ak1965]

okkk...I am sorry....Infact I compared 15 psi with 2.5 psi and considered it relatively higher pressure while compared to API 650 2.5 psi...and for me low pressure meant something like 500 mm water column or so.....!!

It is all relative......drawing a bigger line in front of a small line.......2nd line automatcially becomes larger...and hence happened to my thoughts....!!

Thanks any ways...!!

 

[LOUDOG]

Greater than 15 psi is a pressure vessel.

Anything less can be designed to any code you wish, unless in your locale there is a law against it. API-650 just helps to make more economic choices. If you wanted I could design you up a tank with a design pressure of 14.9 psi with a flat roof. It would just be fairly expensive.

 

[JoeTank]

ak1965,
My sincere apologies if I sounded rude in my response. I did not intend to be so rude.

Joe Tank

 

[Unotec]

ak1965, I think what you're missing is the definition for low and high pressure.
Anything below 15psi (in this part of the world) is considered low pressure. High pressure above.
So, 620 allow for building tanks to withstand the low-high pressures, 650 for closer to ambient.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[JStephen]

There is a difference in how some of the standards approach design pressure.

For example, in API-12F, the tank designs are stated to be good for 1.0 PSI, so the assumption is that any API-12F tank is adequate for that pressure, whether required for a particular application or not.

In contrast, most API-650 tanks are not designed for any pressure. Of those that are designed for pressure, it is very seldom the full 2.5 PSI that is designed for.

If you have a small vessel, the difference between a 20 psi and a 40 psi design may be negligible, and it's not unreasonable to specify a 50 psi pressure when you only really need 20 psi. But if you have a large tank (say 150' diameter), raising the pressure from atmospheric to 2.0 PSI may cost thousands and thousands of dollars.

 

[JoeTank]

ak1965,
What is the capacity of the tanks you are considering?

Joe Tank

 

[LOUDOG]

API-12F 750 BBL tanks are only good for 0.5 psi. However these same tanks can be built using API 650 and be good for 1.0 psi, but will most likely need anchors for uplift.

 

[ak1965]

Thanks to all tech.contributors.....Loudog, Joetank, Jstephen,Unotec

JoeTank,

we are planning for a 400m3 tank.

 

[JoeTank]

400m3 is not a very large tank. Why are you wanting to go with a double wall tank? That is actually quite a rare thing in a field erected ASTs.

Joe Tank

 

[ak1965]

The design is already under review and shall be changed suitably.

My query was raised at very initial stage.

Thanks for the suggestions and advice.

 

[LOUDOG]

I have design 750 BBL double walls. It was for a location where the lack of secondary containment was grandfathered in. Then they needed new tanks, but the location was too congested to make putting up secondary conatainment around the tanks too expensive, so they decided to go with double walled tanks.

 

[Unotec]

In Alberta the double wall for secondary containment has become an iffy issue. Whereas I do not agree with what the Board is claiming, double wall as secondary containment is not the way to go for the time being.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>