Pressure Difference in Spherical Tank: 1.01bar to 15.65bar

[Dell]

a spherical tank with an inner radius of 1.2m is filled with gas,
the barometric pressure is 1.01bar
the absolute pressure in the tank is 15.65bar

1)what is the thickness of the tank if the stress in the tank is 80Mpa?
2)what is the difference in the pressure between the top and bottom of the tank?

to find the thickness of the tank i used an analysis on half of the tank
(15.65-1.01)*pi*1.2^2 = 80*pi*(R^2-1.2^2)

from this i found the outer radius R=1.21093m
therefore t=0.01093m


2)what is the difference in the pressure between the top and bottom of the tank?

i think that this is a kind of trick question, i think that the pressure in the tank is constant but i am not sure, just a gut feeling. can someone please verify/correct me, with an explanation. thanks

 

[mgb_phys]

Unless it's a really trick question - like you are supposed to consider the sag weight of the tank pressing down on the top of the gas - then it's the same

 

[Dell]

thanks, can you give me an explanation,?? that's what i thought, just from my logic, but a friend of mine says he thinks it is density*g*2.4 (rho*g*delta_H),

(i had already calculated the density for another part of the question not showed here, was 222kg/m3)