Pressure Warnings & HR 235 Material for API 650 Tank

[risankhan]

Dear Members,

I am working on an inquiry of API 650, 15,000 bbls Crude Oil Tank. The design data is under;
Design Pressure: 1 psig, Vacuum Pressure: 0.5 psig, Design Temperature: 200 °F, Sp.Gr: 0.7, Roof Type: Conical Supported

I have Etank software. Firstly I worked on 54.1 ft diameter & 37.72 ft height. But because of (1) greater value of design vacuum from max. allowable working vacuum pressure and (2) greater value of design pressure from max. allowable working pressure I changed the sizes & used 49 ft diameter & 46 ft height. The (1) warning was cleared because of change in diameter but the (2) was still active. To control on (2) warning, I used the heavy crub angle (Top Course Stiffener) 8" x 8" x 32 mm thk. The top shell course thk. is 6 mm and the thk. of curb angle is 32 mm.

My question is that " I choosed the correct method to get control on these problems or not?" and if someone have a better way to delete this warning then please share/guide me.

Secondly, Is HR 235 material is equivalent to A-36 or A 283 Gr. C material. If not then guide me how to put & from where the values of HR-235 material. (attached)

Thanks & Regards,

Nasir Khan

 

[JStephen]

Quite often, a design pressure like that will be specified because the person writing the specification did not realize what a major impact it would have on the cost. Most crude oil tanks are not designed for pressures or vacuums that high, and those values could quite likely be reduced.

 

[risankhan]

Yes JStephen, I am also agreed with you. But I have no proper reference of any code/ standard to guide client.

Please also guide me on my question regarding attachment of heavy crub angle with top shell course and HR 235 material.

 

[JStephen]

Increasing the roof slope will reduce the angle size required. Using a flat plate will likely be more economical than a large rolled angle- check rolling capabilities in the area.

Check the requirements of API-650 in regards to a "National Standard" in 4.2.6, which I think will cover your material. You may also be able to get dual-certified material if that simplifies things.

 

[risankhan]

Thanks JStephen.

Let me clear one thing, is that we already quoted for this project. In initially design we did not used vacuum pressure in our calculations by mistake. Now I am tried to balance the new design (With Design Vacuum Pressure) with the design we quoted. To reduce the shell courses thicknesses I used shell stiffeners.

I am doing tank designing on Etank software. As you advised to use flat plate, I did not find flat plate option in Top Stiffener in Etank. Clear it to me that if I go for 8" x 8" x 1.25" thk. angle which will be weld as a top stiffener with top shell course 6 mm thk, it will fine on not. 8" x 8" x 1.25" angle is easily available from Pakistan local market.

 

[MJCronin]

JStephen...

I agree with your comments.....but

What, in your experience, would be a reasonable design pressure and design vacuum for a crude storage tank of this size ?

Do you have any references to guide us ?

I believe that about +10 IWC and -5 IWC would be about right.

A lot would depend on the nature of the crude and the tank location.

Anyone ??????

 

[Duwe6]

Over and above the static pressure of the fluid, and hydrostatic load per 650, there is no need to go much over 2-4 ounces per sq. inch pressure, and 1/2 to 1 ounce per square inch vacuum. You are building an *Atmospheric* storage tank. Trying to get one rated for significant pressure gets expensive.

 

[JStephen]

risankhan- I'm not familiar with the software in question- but if it doesn't allow enough choices, it might be prudent to switch to hand calculations.

With the angle, the problem isn't just buying the material but also getting it rolled to the radius.

MJ- a typical US installation would be an atmospheric tank with internal floater- if pressurized, it could vary, but usually wouldn't be that high.