NovaStark
Mechanical
- Feb 11, 2013
- 250
Hi,
For learning purposes I'm looking over a calculation done for one of our tanks designed to API 620 with the following information:
Max design pressure = 1 psi
Min design pressure = 2" WC
Tank Radius = 1044 inches
Pressure due to liquid = 27 psi
Pressure due to gas = 1 psi
P = 28 psi
Weight of tank shell = 1,346,000 lbs
Weight of roof = 621,400 lbs
Live Loads:
Pressure: 1 psi = 253,150 lbs
2" WC = -3,425,150 lbs
Roof Load = 25 psf = 596,600
Now for the thickness calculation for shell course 1, we have to find W which is the total weight of the tank
W = weight of shell + weight of roof + weight of live loads.
Next they have max W(live) = 253,150 + 596,000 = +849,150 lbs (which is the 1 psi load + roof live load)
and then min W (live) = -3,425,150 lbs (which is the 2" WC load).
then
max W(comp) = 1,346,000 + 621,400 + 849,150 = 2,816,550 lbs
min W(tension) = 1,346,000 + 621,400 -3,425,150 = -1,457,750 lbs.
My confusion comes into why is the 2" WC load negative as this should be acting opposite to the weight whilst the 1 psi load should be in the same direction.
Also confusing is the calculation of the compressive load and tensile load. Shouldn't the 2: WC be causing compression of the tank as it is making a vacuum within the tank and the 1 psi does the opposite?
Yet to calculate the unit forces T1 and T2, in the equation for T1, then used W = + 1,457,750. Shouldn't they have used the larger load of 2,816,550 ?
I suspect my confusion is possibly to do with the direction of the forces based on the free body diagram. Can anyone shed some light to help me understand better?
For learning purposes I'm looking over a calculation done for one of our tanks designed to API 620 with the following information:
Max design pressure = 1 psi
Min design pressure = 2" WC
Tank Radius = 1044 inches
Pressure due to liquid = 27 psi
Pressure due to gas = 1 psi
P = 28 psi
Weight of tank shell = 1,346,000 lbs
Weight of roof = 621,400 lbs
Live Loads:
Pressure: 1 psi = 253,150 lbs
2" WC = -3,425,150 lbs
Roof Load = 25 psf = 596,600
Now for the thickness calculation for shell course 1, we have to find W which is the total weight of the tank
W = weight of shell + weight of roof + weight of live loads.
Next they have max W(live) = 253,150 + 596,000 = +849,150 lbs (which is the 1 psi load + roof live load)
and then min W (live) = -3,425,150 lbs (which is the 2" WC load).
then
max W(comp) = 1,346,000 + 621,400 + 849,150 = 2,816,550 lbs
min W(tension) = 1,346,000 + 621,400 -3,425,150 = -1,457,750 lbs.
My confusion comes into why is the 2" WC load negative as this should be acting opposite to the weight whilst the 1 psi load should be in the same direction.
Also confusing is the calculation of the compressive load and tensile load. Shouldn't the 2: WC be causing compression of the tank as it is making a vacuum within the tank and the 1 psi does the opposite?
Yet to calculate the unit forces T1 and T2, in the equation for T1, then used W = + 1,457,750. Shouldn't they have used the larger load of 2,816,550 ?
I suspect my confusion is possibly to do with the direction of the forces based on the free body diagram. Can anyone shed some light to help me understand better?
