supported frangible roof and anchored tank roof slope

[inammanj123]

I am working on an anchored tank with frangible roof, and supported on rafter only.Its diameter is 9.5 m and a height of 16 m. This means that my tank must satisfy 5.10.2.6.d of API 650 My questions are:

1-As per 5.10.2.6.d all points of 5.10.2.6.a are applicable. this means that slope of frangible anchored tank can not be more than 1/6(9.5 degrees)??
2- can i lower my slope to 1/16, because my roof supported on rafters?
3- DLS used in the formula,5.10.2.6.a.5, has to be corroded weight of shell or nominal weight?

 

[JStephen]

1- Correct
2- Correct
3- DLS is defined in App. F as the nominal weight, which would be taken as the uncorroded weight.

 

[inammanj123]

thanks,

so to make my rafter supported roof frangible i can keep slope any where between 1/16 and 1/6, because if i keep slope of 1/6 maximum frangible area is just 950 mm2, which make it impractile to even the smalled angle(Ashell -Aroof Comes out to be very small). So i decrease the slope to 6 degree which increased to maximum area to 1500 mm2, enabling me to use apropriate angle.

jStephen some times client ask for calculations to be in corroded condition, and some other client says only unstiffened shell calcuationon(wind and vacuum) in corroded condition.

But when client does not say any thing about corroded condition we will use nomimnal values.