1. Welded steel tanks for storage oil

2. What is the function of storage
tank ?
It is a device used to store liquids
such as oil , water and petrol

3. Steel storage tanks built before 1950 generally
do not conform to current industry standards for
explosion and fire venting
Several organizations have developed standards and
specifications for storage tank design. Such as
API 650
“ Welded Steel Tanks for Oil Storage”
issued by the American Petroleum Institute (API).

4. Annular bottom plates
It must have a radial width minimum 600 mm
between the inside of the shell and any lap welded joint in
the remainder of the bottom
and the maximum radial width of the annular plate is
calculated from formula
R = 215*tb /(H*G)º·
tb = thickness of the annular plates
in mm ,
H = maximum design liquid level in m ,
G = specific gravity of the liquid to be stored

5. Annular bottom plate thickness
plate thickness of first
shell course (mm)
t<= 19
<=190
stress in the first
shell course (mm)

6. Shell design
By :
The 1-foot method
Variable - design - point
method
Elastic analysis

7. Calculation of thickness by the 1-foot method
• It calculate the thicknesses required at design
•
points 0.3 m above the bottom of each shell
course .
This method shall not be used for tanks larger
than 60 m in diameter .

8. The required minimum thickness of shell plates
shall be greater than this value
td =(4.9*D*(H-0.3)*G)/Sd +CA
tt = (4.9*D*(H-0.3))/St
td = design shell thickness in mm ,
tt = hydrostatic test thickness in mm ,
D = nominal tank diameter in m ,
H =design liquid level in m ,
G = specific gravity of the liquid to be storage ,
CA = corrosion allowance in mm ,
Sd = allowable stress for the design condition in MPa ,
St = allowable stress for the hydrostatic test condition in MPa ,

9. The minimum thickness of shell plates shall be
computed from the stress on the vertical joints
using the formula
t = (4.9*D*(H-0.3)*G/(145*E)+CA
t = minimum thickness in mm,
D = nominal tank diameter in m ,
H = design liquid level in m ,
G = specific gravity of the liquid to be storage ,
CA = corrosion allowance in mm ,
E = joint efficiency which is either 0.85 or 0.70 .

10. corrosion allowance :
1 mm for gases
3 mm for liquids
6 mm for Sulphate