Tanks Bund Wall or Dyke Wall Calculation:
What is bund wall?
Bund wall is a Bunding constructed alongside of storage tanks, where possibly polluting substances are stored and handled. Bund wall also referred as dike wall, but dyke is normally used to describe liquid containing tank facilities which prevent leaks and spillage from tanks and pipes. Often, the liquids or substances stored in these tanks or transferring from pipes are contaminated, polluted, or contains hydrocarbon. Hence bund wall or dyke wall is used to prevent, such stored liquid from causing damage due to its force or chemistry. If a large tank has a failure, the liquid alone can cause widespread destruction.
If built properly, bunding or bund wall shall large enough and strong enough to contain the contents of an entire tank, though regulations may require it to be up to a third larger. When multiple tanks share a common bund or dyke wall, the capacity is based on the largest tank. Most common designs for large tanks is a concrete or masonry wall around the tank with a concrete floor. Hence bund wall or dyke wall calculation is very important for any plants which stores chemicals / hydrocarbons or liquids in tanks.
Here we will see details about bund wall or dyke wall calculation.
As per general guidelines, if multiple tanks shares a common bund or dyke, capacity calculation shall be with largest tank.
Hence bund has a net volume capacity, equal to the volume of the largest tank in the bunded area
Step 1: We have to calculate net volume of the biggest tank.
If you look into fig. above Tank 1 is largest tank. Hence calculate volume of Tank 1.
Volume of Tank 1 = π x R 2 x H
Where,
“π” = 3.14159265, “R” is Radius of Tank and “H” is height of Tank.
Step 2: Calculate Volume of all intermediate fire walls and low level large bore piping. Or any other items located inside the bund.
Step 3: Calculate Tank pad volume with tank foundation.
Volume Occupied for foundation and tank pad = π x FR 2 x FH
Where,
“FR” is radius of foundation and “FH” is foundation and tank pad height.
Step 4: Finalise Bund wall dimensions.
Finally we need to finalise bund wall height, width, length and thickness will be decided by civil team based on volume of liquid inside the bund wall.
For e.g. if your calculated volume of largest tank including foundation is X m3, then tank bund wall volume shall be minimum X m3 excluding the volume of large tank below height of bund wall.
Bund wall volume – Large Tank volume below bund wall height > = Total Large Tank Volume
(BL x BW x BH) – (π x R 2 x BH) > = X m3
Where,
BL, BW & BH are Bund wall Length, width and Height respectively.
And “R” is large tank radius.
Example: Consider largest Tank Diameter as 3.5 M, Height as 5.5 M and Foundation/Tank Pad height as 0.3M.
Tank Volume is = 3.14159265 x 1.752 x (5.5+0.3) = 55.80 m3
If proposed Bund wall or dyke wall length (BL), width (BW) and height (BH) is 7m, 7m & 1.2m respectively then,
(BL x BW x BH) – (π x R 2 x BH) >=X m3
(7 x 7 x 1.2) – (3.14159265 x 1.752 x 1.2) >= 55.80
58.8 – 11.54 >= 55.80
47.26 >= 55.80
As calculated bund volume is less than tank volume, we need to change bund wall dimension.
We change length and width of dyke as 7.5 m and calculate again volume.
(7.5 x 7.5 x 1.2) – (3.14159265 x 1.752 x 1.2) >= 55.80
67.5 – 11.54 >= 55.80
55.96 >= 55.80
Hence proposed dyke dimensions are greater than tank volume.
In addition to this, we need to add free board volume of 0.3 m height.
Hence final bund wall dimension were 7.5 x 7.5 x (1.2+0.3).
Bund Length BL = 7.5 m
Bund Width BW = 7.5 m
Bund Height BH = 1.5 m
However bund or dyke wall length, width and height can be decided and finalised based on actual available configuration of space, for locating bund and thickness of bund wall, will be decided by civil team.
