floating roof

[dorios]

hi,
I have an external floating roof 60m dia tank experiencing problems with deformations possibly because of vapour bubbles underneath. Water accumulation on top exacerbates the deformation but as soon as the vents are open, the water comes back towards the central area which to me suggests that the internal vapour pressures are responsible for this deformation. This is a 5mm pontoon roof, oil tank to API 650 (designed to 0.7 specific gravity).
Q: what other factors can be responsible for slightly tilting the roof (pontoon corrosion?, flooded pontoon?)
some brainstorming would help
thanks

 

[Mutt]

Here'a an extract from

http://bulktransporter.com/mag/transportation_environmental_regulations_drive/

"Product true vapor pressure (TVP) is the single most critical design parameter when selecting the type of floating roof. Most current environmental regulations limit the product TVP to less than 11.1 psia. As the TVP increases above 11 to 12 psia, daily heating of the product under a center deck will produce enough vapors to balloon the deck. It is common for these vapors to condense during the cooler evening hours, allowing the roof to resume a normal flat shape."

Perhaps you have a one sided warm spot? Can check your TVP?

 

[IFRs]

Please clarify what "vents" you are opening.

Vapor can get under the floater from the inlet stream. The floater may be experiencing excessive perimeter seal friction or binding on a column, ladder or gauge pole. There may be a leak inthe floater. Could there be a floating suction under the roof that is exerting unusual force? Is there anything wrong with the rolling ladder?

 

[JoeTank]

You mention that the roof is tilted. By that, do you mean that it is lower one side of the tank than on the opposite wall? If that is the case, I'd suspect a leaking pontoon in addition to a gas accumulation under the roof..

If you are referring to the fact that the center of the roof is higher than the rest of the deck, then I'd attribute that to just a gas accumulation under the roof.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com