Dear Sirs,

I have designed a tank (API 650, 11th edition, Addendum 1 Nov 2008), in which I want frangible roof joint, so I considered the slope of 1:6.

While deciding the self-supporting cone roof thickness as per 5.10.5.1, it becomes greater than 13 mm.

1)How to determine the thickness of self-supporting cone roof to keep the joint as a frangible roof joint?

2)What is the definition of “DL” which is mentioned in the Appendix R - e (1) & e (2)? As per 5.2.1.a it is the weight of the tank or tank component including any corrosion allowance. But does it mean that it include the weight of the nozzles on tank shell courses & roof, weight of the wind girder, weight of the curb angle, ladders, platforms, & any other accessories which are located on the tank shell & roof (bottom plate is not considered)?

1) The thickness is based on the tank diameter, the roof slope, and the roof load. You'll have to alter one of these parameters.

2) Usually "DL" is the tank shell plus any weight supported by the shell.

Dear Richard Sir,

If "DL" is the tank shell plus any weight supported by the shell, then does it mean that the weight of the nozzles on the roof, roof structure (rafters & girders), handrails on the roof & any other weight supported by the roof do not have to consider?

As per 5.10.5.1 (API 650, 11th edition, Addendum 1 Nov 2008),
T = greater of load combinations (e)(1) & (e)(2) of Appendix R (kPa).
Now i have the weight "DL" in "kg" & i have to convert this weight into "kPa" to get the value of "T" in "kPa".

My concern is, while converting "DL" from "kg" to "kPa", which area should have to consider?
Is that area will be "[(Pi / 4) x (tank diameter)^2]" or "surface area of total shell" or "any other as per your opinion"?

The weight would be the weight supported by the shell, so that would include nozzles, stairs, etc. Be careful with the weight of the roof plates and framing - some sections of the Code want you to include one but not the other.

The area is the surface area of the roof - you're after the roof loading.