DISCUS Engineered Products

Trust your inner roof

DISCUS Technical Bulletins

Sep 14

Written by:
David Rosenkrantz and Julie Anne Cormier

Posted in:
Internal Floating Tank Covers,
Uncategorized

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5 Potential causes of liquid on a cover, and what to do about it

F Topside at Seal and Funnel

The DISCUS cover does not have drains, and is built as a series of bulkheaded open compartments. We’ve had countless discussions on the various scenarios that can lead to liquid on the top of a cover, and what to do about it. In this post, we’ve highlighted some of the most common concerns.

1. Water on top of a floating cover, due to the fixed roof or geodesic dome leaking. Consider the scenario below if a dome panel is torn off during a storm:

  • Dome panels are about 50 ft²
  • Assuming two panels are torn off, there would be 100 ft² of opening
  • If the storm resulted in 2 feet of rain/ft², 200 cubic feet of water would get on the cover
  • 200 cubic feet of water weighs about 12,500 lbs
  • Each (DISCUS) panel holds about 1,500 lbs of water so this would result in filling about 8-9 panels

The DISCUS cover has 460% excess buoyancy, meaning relatively few panels are needed to keep the cover afloat (only 18% of panels). Even on smaller tanks, 8-9 panels full does not endanger the cover. Therefore the concern in the scenario above is limited to removing unwanted water by pumping or evaporation. Since DISCUS panels are bulkheaded compartments, the water is limited to a few panels, making removal easier.

Who wants water in their tank anyway? It contaminates the product, corrodes the tank bottom, etc.

2. Product on top of a cover is usually the result of a mistake, design error, operational issue or other preventable incident.

3. If from product fill, it is usually an upset condition, likely preventable with the installation of an adequate liquid only or liquid + gas inlet diffuser.

4. If from the use of a mixer (jet or propeller), engineering and/or operational controls can mitigate or eliminate such occurrences.

In each of these cases, the incident is likely preventable but if it does occur, it would be only by chance that drains would be in exactly the low point and completely effective. So in most cases, removal of product from the cover would be required with or without drains. The bulkheaded DISCUS cover minimizes evaporation by reducing the surface area of the liquid, therefore more can be cleaned up, as compared to a “flat” style cover, where much of the liquid can evaporate.

5. What if product burps up onto the roof and gets stuck on top of the cover?

If a significant amount of product were to burp on top, removal and cleaning on a bulkheaded cover would be easier than a “flat” style cover. Liquid runs to low points, however drains will often be high points because they are in raised, thicker, flatter skins, and rise as they work. In any case, product will need to be cleaned off, drains or no drains. The separate compartments characteristic of the DISCUS cover provides containment and limits the surface area that can evaporate.

Have more questions that weren’t answered in this post? Contact us.

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