Sizing of Storage Tanks and Dikes

Advertisement

Deciding optimal size of tanks and associated dikes are done through trial and error. Various factors that govern this decision includes :

  1. Availability of real estate,
  2. Possible use of standard sized tanks for smaller capacities, and
  3. The nature of potential foundation design problems caused by early tank-size selections.

The designer should refer to “API 12F : Specification for Shop Welded Tanks for Storage of Production Liquids”  for standardized shop-fabricated tank sizes.

Larger field-fabricated storage tanks must be sized to suit each site.

Example Calculation

As an example of how to develop tank height and dike size, a 150,000-barrel (42 gallons per barrel), 150- foot-diameter tank is used.

Step 1  : Convert the tank volume into cubic feet, as follows:

(150,000 x42)/7.48 = 842,245 Ft3 of liquid

Tank height is calculated according to the following equation:

H=4V/ΠD2

Where:h = height D = diameter V = volume (in cubic feet)

Therefore:

h = (4 x 842,245)/(3.1417)(1502) = 47.66 ft or 48 ft high

The volume of the tank berm is calculated as follows, using the data shown in figure below:

V = (Πh/3)(r2 + rR +R2)

where:
r = top of berm radius (78 ft)
R = bottom of berm radius (79.5 ft)
b = berm height (1 foot)

Therefore:
V = (3.1417 X 1)(6084 + 6201 + 6320) = 1.047 x 18.605 = 19,479 ft3 of soil in the berm

Calculation of the volume required in the diked area is as follows:

842,245 ft3 of stored liquid + 19,479 ft3 of berm soil = 861,724 dike area required

The chart is used to find the dimensions of a square dike.

For example, for a dike height of 6 ft, the designer first finds the 6-foot dike data line that corresponds to 861,724 ft3 and then reads directly left to the vertical axis to find the dike dimensions. In this example, a 390-square-foot dike would contain the liquid.

K is the volume of liquid held within dike that is constructed to a 1.5:1 slope. The exhibit may also be used to calculate the dimensions of a rectangular dike. First, the designer locates the point on the vertical axis for the known length of one side of the rectangle—for example, 425 ft.

Next, the designer reads to the right until the desired capacity (861,724 ft3) is found and then reads down vertically until the 6-foot dike data line is reached.

Finally, the designer reads left to the vertical axis of the chart to find the missing dimension of the rectangle, 350 ft in this example.

Dikes containing multiple tanks are sized to hold the capacity of the largest tank.

For the dimensions of dikes containing more than one tank, it is necessary not only to subtract the volume of each tank from the dike’s capacity but to subtract the volume of the soil in each berm.

%d bloggers like this: