API 620 conical roof thickness calculation questions
API 620 conical roof thickness calculation questions
(OP)
Should the roof live load and snow load be included in the roof weight when calculating the unit force T1 (equation 8 of 5.10.2.5)?
For example, suppose I have a tank with a 100 foot diameter tank with conical roof with alpha = 80, plate density = 0.2833, and internal pressure of 0.1 psi. The roof plate weight is 81337 lbs. T1 using this weight is 48.516 and T2 is 345.5. The required thickness per 5.10.3.2 is 0.0466. If I add a roof live load of 20 lb/ft^2, the weight jumps to 238416.5 and T1 is now negative at -191.433. After iterating several times for 5.10.3.3, I came up with a required thickness of 0.273. Quite a big difference.
A second question: What if the internal pressure is zero? T2 is then zero. Which section then applies for calculating thickness?
For example, suppose I have a tank with a 100 foot diameter tank with conical roof with alpha = 80, plate density = 0.2833, and internal pressure of 0.1 psi. The roof plate weight is 81337 lbs. T1 using this weight is 48.516 and T2 is 345.5. The required thickness per 5.10.3.2 is 0.0466. If I add a roof live load of 20 lb/ft^2, the weight jumps to 238416.5 and T1 is now negative at -191.433. After iterating several times for 5.10.3.3, I came up with a required thickness of 0.273. Quite a big difference.
A second question: What if the internal pressure is zero? T2 is then zero. Which section then applies for calculating thickness?





RE: API 620 conical roof thickness calculation questions
If the roof is a self-supporting cone (not expected with 100' diameter!), then you could take the design vacuum as a negative number, and roof plate weight, snow load, live load, all as negative numbers, and calculate a negative T1 from it. I don't think API-620 address the allowable stress for T2 in compression in a cone, though.
If internal pressure is zero, you just have a self-supporting or supported cone roof.
RE: API 620 conical roof thickness calculation questions
For the zero internal pressure case, it doesn't look like any of the 5.10.3 sections apply. Would it be best to use 5.10.3.3 in this case?
RE: API 620 conical roof thickness calculation questions
RE: API 620 conical roof thickness calculation questions