API 650 Self Supported Frangible Roof Cone 2

[wadavis]

API 650 5.10.2.6 limits the slope of frangible roofs to not greater than 2:12.
API 650 5.10.5.1 limits the slope of self supporting cone roofs to 2:12 or greater.

Am I missing something important or is it only 2:12 self supported cones than may be considered frangible.
This is in regard to a 15'-3" diameter tank.

wadavis
Structural EIT

 

[fegenbush]

wadavis,

You are correct that 2:12 is the only slope allowed.

Don't worry about a frangible roof on a 15'-3" diameter tank since it won't happen anyway. On a tank that small, it is not possible to meet the frangibility requirements. Specifically the allowable compression area requirement of 5.10.2.6(5). The tank does not weigh enough. The formula listed has some errors. It should read A = (Dls)/(2*pi*Fy*tan(theta)) The Dls is the dead load of the shell and attachments to the shell and Fy is the yield strength of the material. tan(theta) is the pitch of the roof.

If frangibility is required an cannot be met, an emergency pressure relief vent will be required per API 2000 calculations.

 

[wadavis]

Thanks for the reply fegenbuch,
That cleared things up and got me pointed and thinking in the right direction.

 

[MJCronin]

Generally speaking, an Emergency Pressure Relief device must be considered for any tank below 30 ft diameter. A frangible roof design will not work

I don't understand why API-650 doesn't simply state this...... It would save so many people a lot of time an agravation....

 

[IFRs]

Mr. Fegenbush - have you pointed out to the API committee that the formula needs work?

 

[fegenbush]

Dave,

It's on my list of agenda items to be processed. I will try to have it taken care of before the 12th edition is printed.

 

[IFRs]

Hmmm - I thought that was you!

 

[fegenbush]

IFRs,

Just wanted to update on the status of the formula. It appears this error has been corrected in the 12th edition of the standard.

 

[stookeyfpe]

Mr Fegenbush

Please transfer this knowledge to NFPA 30. This is knowledge base that I believe is lost in the fire code arena. This is important to professionals in my arena.