Shore Tank with Cone-down Floor
Shore Tank with Cone-up Floor
3.2.7 Floating Roof Tanks There are two types of floating roof tanks, internal and external. In both cases, the roof floats on top of the liquid, forming a seal to help minimize vapor losses and atmospheric pollution. A tank with an internal floating roof also has a fixed roof, while a tank with an external floating roof does not. The internal floating roof is typically made of very light material whereas an external floating roof is usually a steel structure and may weigh as much as 150 tons.
Gauge point for water cuts only
Reference gauge point
Reference gauge point
No water indicated at ref. gauge height
Cone-up tank floor
Water cut
Water cut
External Floating Roof Tank with Slotted Standpipe
Cone-down floor
Sump
There are numerous different manufacturers of water finding paste. It is recommended that two different pastes be used until it has been established which paste works best for a given product. Water cut gauging in heavy fuel and crude oils can be problematical due to the heavy oil adhering to the paste and obscuring the reading. The application of a coating of light lubricating oil to the water paste, prior to immersing it in the product, can help shedding of the product from the paste after it has been withdrawn from the tank. Alternatively, lightly pour or spray a solvent over the water paste, taking care not to distort the clarity of the water cut.
If the water cut reading falls within the area of the clasp, the water cut should be retaken, using a longer bob. Some shore tanks are fitted with "cone down" floors, see diagram above. In these situations, it is necessary to gauge for water from the center of the tank. Also, there is usually a special section of the tank capacity table showing volumes taken at this point.
Slotted standpipe
Vapor control barrier
Roof legs
Pontoon
Product level
Product level
Roof deck
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