External Floating Roof Tanks

If it is coming from the center only, check to see if your ladder isn't too heavy on the center and weighing it down too low. Should be easy to check with a lazer level moved around the outside and different parts measured in the center, or where the puking is occurring.

On a span that long, you could have buckling or warpage from the temperature, uneven weight distribution etc. I think the first step is to find out if it is lower than it should be anywhere.

Drew

Drew,

Thanks, unfortunately the ladder re-location is not an option. was trying to think of other ideas..maybe introduce some kind of sealing?

Like Abel said, make the legs longer. But first investigate to determine if that is your problem; the laser level trick should work, they have cool ones that emit a flat plane of light and all you have to do is walk around with a measuring stick and spirit level.

If the center does indeed depress a bit making the risers on the legs should solve the problem. Trying to seal it up is just a bandaid on the real problem and bandaids often fail.

If your problem is something different, you will need a different solution. After thinking for awhile I thought your problem could be from vapors or air accumulating under the center and forcing some product up the leg stacks. This could be solved by installing a vent for the floating pan's open center area (if your's is open underneath in the center). If you install a pressure/vacuum vent your evaporation will be minimal.

Drew

• The problem may be due to the excess weight of ladder affecting on the middle of floating roof as mentioned at post #1 of our friend Drew K. And this weight should be used and added to the weight of all components of floating roof, and this was necessary at the 1`st step of design

• Another reason is the widely range of tank diameter 88.5 m (and in turn higher range of internal pontoon diameter, D2), where there must be an enough width of pontoon width W, during the 1^st step of buoyancy calculation of floating roof..

• This problem may be avoided if you stored a liquid with higher specific gravity than 0.77.

• Using a sealing will not solve the problem, but I recommend enlargement of the height of legs' sleeves especially for those located at the middle of the floating roof, taking into consideration the gas free before welding

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Excellent, Thanks Abdel and Drew, Looks like due to the fact that the roof are designed for submerged 75% (designer to confirm), maybe increasing the length of the sleeve would help. We are waiting for the tank designer to comeback with their opinions. Will post all about the outcome.

Sounds good, I look forward to hearing what you use for a solution.

If your roof is 75% submerged you want to make sure your water drain is adequate and does not get plugged. I had to walk out on a roof that had about 16 inches of water on it across most of it's surface. It was designed with an outer ring of pontoons and an open center that accumulated water during a heavy storm when the drain was plugged with paint chips (from a previous repainting) dirt and bird excrement. We don't know how close it came to sinking but I was kinda scared walking out on it.

Drew

If it was the length of the roof sleeves, you should be seeing it in more areas than that shown in the pictures. Is it just in this one area or is it throughout the tank? If it is in this one area I have a few questions.

What size is your fill nozzle?

Does the fill nozzle have a diffuser on it?

Is the fill nozzle outlet in this location?

Does it only happen when filling the tank?

It could be that the fill nozzle is creating an agitation in the tank and this is forcing the product up the sleeves. This often happens with large fill nozzles not equiped with a diffuser.

Filling nozzles has an extention of 4 to 5 mts into the tank internal which acts as a diffuser, morover the flow rate is very low (750 m³/Hr.) the nozzle size being 28" Ø the issue of turbulance etc does not arise. Outlet location is 90° to the inlet.

Looks like this is happening during both filling / emptying. Practically we cannot watch 100% by placing crews on top of the tank.

only at the centre portion of the deck the problem exists, the remaining part of the roof is OK with no issues, (saw that same issue during the first fill and did not repeat).

Guys, Came back from a short vacation, Visited the tank recently, what I saw was really good to share with all.

I would say that the puking was not the case, Due to extreme temperature and the product Sp. Gravity being 0.745 the product was actually evapourating. Local temperature around here touches 45ºC +, the vapours created at the shell contact points are making their way (path of least resistance) i.e to the central portion and exhaling thru those legs sleeves. Due to the presense of vapour socks and contineous flow of vapours were condensing and flowing as droplets from inside of these neoprene rubber socks.

What was decided was that we would wait for the coming months and observe the behaviour when the temp. falls below 30ºC. If this continuies the tank may require external insulation.

Please advice me if any one of you have some thoughts on this.

Sounds good, much better than some of the thoughts we had.

You could try to seal up the leg sleeves better, if the evaporation is happening right at the legs. I thought the point to the floating roof was to reduce evaporation by reduction of the surface area exposed to evaporation. If the roof is not in contact with the product across it's surface you will get excess evaporation and it will come out anywhere it can escape.

45 C sucks. I endured that in Turkey, it gets into the mid 30's sometimes 40 here in Texas. I liked it best in England where it stayed in the 20's most of the time.

Drew