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External Floating Roof Design

External Floating Roof Design

External Floating Roof Design

(OP)
Hello all,

I am looking at Annex C External floating roofs in API 650 - 12th Edition.

Clause C.3.4.1 (a) states that floating roofs shall have sufficient buoyancy to remain afloat with 250mm of rain fall over the full horizontal tank area. i.e. total volume of rainwater in m³ = 0.25 x Pi*D²/4, where D is the full inside diameter of the tank (in m).

Clause C.3.4.2 states for pontoons with single decks, the pontoons must have adequate strength to prevent distortion when the centre deck is loaded by the design rainwater (as above).

Does it seems excessive to assume that the total volume of rainwater based on the full tank diameter acts on the centre deck area only?
What if say for example you had a scenario for a floating roof where the deck area is not large enough to contain the full volume of the rainwater calculated. I.e the rainwater would then overspill onto the pontoon area?

With regards to calculating the stresses in the pontoon is it ok to take the full pontoon geometry into consideration for cross sectional area, Section Modulus etc..provided the pontoons are fully stiffened? i.e. Each Pontoon compartment stiffened by using a number of beams attached radially to the top and bottom pontoon plates. Also using a heavy pontoon inner rim plate thickness where the deck plates are connected to the pontoon.

I appreciate any thoughts or feedback on the above.


RE: External Floating Roof Design

I think the intent is to design for the 10" of rainfall with drains inoperative. Whether that rainfall is actually all on the deck or not would be determined by the geometry.

The standard doesn't address detailed design, so you're on your own for the second question.

RE: External Floating Roof Design

(OP)
Is there anyone on this forum that has any experience in the design of these type of floating roofs?

thanks

RE: External Floating Roof Design

I know that there are those on this forum, including myself, who have experience in the design of external floating roofs. However, design details of such items are often company specific and closely guarded. The standard is written in such a way as to allow a great variety in the design of these items to maximize economy for the company producing the roof, and thus the tank owner.

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