Up to What height is required to drill slot holes on stilling well ?

[sxz]

I have a question on the large crude oil tank with internal floating roof, can we drill the holes up to HHLL? Is any evaporation loss a big concern? Or keep the holes under LLLL?

Thanks for any inputs.

XZS

 

[IFRs]

The holes are generally required to ensure that the liquid in the pole is similar to the liquid outside the pole, to get an accurate temperature, liquid height or sample from inside the pole. If you are only storing one product in the tank then you only need holes or slots above the water bottom. If you are blending products or are storing products that will settle out and stratify in the tank then you need holes or slots for the full liquid height. Any holes above the IFR will add to evaporation losses because there will be a path to the liquid surface from above the IFR seal plate. These losses can be minimized with sleeves which come in two basic variations and/or floats.

 

[sxz]

IFR,
Thank you very much.
XZS

 

[Clamont]

IFRs.... Is there anywhere we can get some literature on your statement? We are about to install a Floating Roof into a tank and the client has requested slots to the top just as it is convention. The product is only going to be gasoline so would be good to advise them accordingly however would like some backup material.

Thanks

 

[IFRs]

Here is one of many:

Emission Factor Documentation for AP-42
Section 7.1
Organic Liquid Storage Tanks
Final Report

page 8 paragraphs 7 and 8 describe the difference between slotted and un-slotted.

7. Unslotted guidepoles and wells. A guidepole is an antirotational device that is fixed to the
top and bottom of the tank, passing through a well in the floating roof. The guidepole is used to
prevent adverse movement of the roof and thus damage to deck fittings and the rim seal system. In
some cases, an unslotted guidepole is used for gauging purposes, but there is a potential for differences
in the pressure, level, and composition of the liquid inside and outside of the guidepole. A typical
guidepole and well are shown in Figure 7.1-11.

8. Slotted (perforated) guidepoles and wells. The function of the slotted guidepole is similar
to the unslotted guidepole but also has additional features. Perforated guidepoles can be either slotted
or drilled hole guidepoles. A typical slotted guidepole and well are shown in Figure 7.1-11. As
shown in this figure, the guide pole is slotted to allow stored liquid to enter. The same can be
accomplished with drilled holes. The liquid entering the guidepole is well mixed, having the same
composition as the remainder of the stored liquid, and is at the same liquid level as the liquid in the
tank. Representative samples can therefore be collected from the slotted or drilled hole guidepole.
However, evaporative loss from the guidepole can be reduced by modifying the guidepole or well or
by placing a float inside the guidepole. Guidepoles are also referred to as gauge poles, gauge pipes, or
stilling wells.