Installation new Al.Dome room on existing floating roof tank

[farzam]

Dear All,

Our client is going to install a new Al.dome roof on the existing floating roof(ID=18.31m,H=14.64,Design pressure=10/-2.5mbarg, medium density=880 kg/m3), regarding their inspection the actual thickness of some shell courses are lower than required thk. as per test condition.according to API650-3.6.3 the weight of rood is not related to shell thk.now I need to know the roof weight is important for shell thk.?otherwise which items shall be checked?
Thanks in Advance
Farzam

 

[JoeTank]

Farzam,
The dome roof supplier must advise you of the concenteated point loading that the dome will impose on the shell. You must then determine if the shell is adequate to prevent buckling of the thin areas. If it is not adequate, the shell must be replaced or stiffened. likewise you must evaluate the lateral loads on the top shell stiffener. A competent dome supplier should be able to assist you with this evaluation or you should obtain help from a storage tank engineer. Unfortunately some dome suppliers are willing to put their dome on any tank out there.

Joe Tank

 

[IFRs]

Farzam - the tank roof weight is normally not used when calculating the tank shell thickness. JoeTank has covered the other important issues quite well.

 

[JoeTank]

Mr. IFRs,
I believe that roof weight is in fact a design factor for the splsate thickness when checking a tank shell. The roof weight, whether steel, aluminum (or whatever) is not part of the shell calculation when checking hoop stress, but it is a design factor. Although the minimum thicknesses of the API Standard will give adequate thickness for vertical compression due to roof loads, Mr Farzam mentioned that the shell plates were thinner than required by API. Assuming that the plates are corroded, I suspect that the roof weights plus design loads will require some level of remedial action.

Joe Tank

 

[farzam]

Dear JoeTank,

Thank you verymuch for your complete advise
Farzam

 

[jaydees]

You might also have to look at whether the tank will need anchoring. The dome roof manufacturer should be giving you some vertical uplift loads due to wind. This will increase the overturning moment which might then require anchorage.

 

[farzam]

Dear JoeTank,

Our domeroof contractor is going to make stress analysis for shell courses, but he wants to apply analysis only for 3top courses, because he beleives that main forces act on these 3courses, but the reduction thickness was happened at lower courses. whats your idea?

Thanks in advance
Farzam