Storage Tank Calculation

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Design Code API 650 Eleventh Editions June 2007

References

Appendix BAppendix EFormulae for Stress And StrainTank Data Sheet

Rules followed for designing All components are designed with API 650 June 2007

edition Shell are designed as per one foot method Wind force and moment are calculated as per API 650 Seismic force and moment are calculated as per API 650

CALCULATION

1. DESIGN DATA TO BE COLLECTED AS PER DATA SHEET

2. MATERIAL OF CONSTRUCTION

Materials are selected for the following

Shell/Bottom/Roof PlateRoof Structure/Curb Angle

NozzlesFlangesBolting For NozzlesBolting for Structures


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Wind Girder

Plate specification and Minimum Yield strength, Minimum Tensile Strengthand Product Design Stress are selected from Table 5.6.2 for the shell plates.

3. SHELL DESIGN CALCULATION

Allowable Stress for Shell in Design Condition

Sd = 2/3*Ys*Fy where Ys = Min. yield stressFy = Yield stress reduction factor Sd = 2/5*UTS UTS= Ultimate tensilesterength

Sd = Table 5.2

Three values of Sd are got and the least value is taken as Sd

Allowable Stress For Shell in Hydrostatic Test Condition

St = 3/4*Ys*Fy

St = 3/7*UTS

St = Table 5.2

Three values of St are got and the least value is taken as St


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4. Shell Thickness Calculation

One foot Method

The 1-foot method calculates the thicknesses required at design points 0.3 m(1 ft) above the bottom of each shell course. This method shall not be usedfor tanks larger than 60 m (200 ft) in diameter.

4.9 x D x (H - 0.3) x Gtd = ---------------------------------- + C.A.

Sd

4.9 x D x (H - 0.3)tt = ------------------------------

St

Where,

td = Design Shell Thickness in mmtt = Hydrostatic Test Shell Thickness in mmH = Design Liquid Height as per Cl. 5.6.3.2

Minimum required shell thickness is selected from the table 5.6.1.1

Thickness of each shell course is calculated using above formulae. Thethickness calculated must be greater than minimum thickness taken from thetable 5.6.3.2

Thickness of each shell course is tabulated.


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5. ANNULAR PLATE

Radial Width of annular plateAnnular bottom plates shall have a radial width that providesat least 600 mm

Therefore min required radial width = Projection outside the shell+Bottom plate

Thickness+ Lap of bottom plate(Refer 5.5.2)

Check for min. width of Annular PlateIn SI units:

Wheretb = thickness of the annular plate (see 5.5.3), in mm,

H = maximum design liquid level (see 5.6.3.2), in m,G = design specific gravity of the liquid to be stored.

Thickness of annular plate

Minimum thickness of the bottom plate is 6mm as per 5.4.1 (Excluding thecorrosion allowance)

Hydrostatic test stress in the lowest course Sth is calculated. As per Sthvalue thickness of the annular plate is checked with Table 5.1

6. Bottom PlateAs per API 650 5.4.1, the minimum required thickness shall be 6 mm + C.A.


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All rectangular and sketch plates shall have a minimum nominal width of 1800 mm (72 in.)

Tank bottoms requiring sloping shall have a minimum slope of 1:120upwards toward center of the tank.

7. Design of Roof Plate Thickness:As per API 650 5.10.2.2, the minimum nominal thickness shall be 5 mm +C.A.

Roof Slope / Angle 1 : 100

8. Sizing of Top Curb AngleAs per API 650 5.1.5.9.e, min. curb angle of size is L 76 X 76 X 6.4 THK.

9. Top Wind girder

The Top Wind Girder is provided at: 1100 mm From Top Curb Angle as per 5.9.4

As per API 650, 3.9.6 the required min. section modulus is,

H2 = Height of Tank ShellVz=Design wind velocity


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C = A(1)*Y(1) + A(2)*Y(2) + A(3)*Y(3)------------------------------------------------

A(1)+A(2)+A(3)I= BD^3 +AY^2

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Z =I/Ymax

Zprovided > Zreqd.

10. Intermediate Wind Girder

Transformed width of each shell stake is given by

Where,

Wtr = transposed width of each shell course, mm (in.),W = actual width of each shell course, mm (in.),t uniform = as ordered thickness, unless otherwise specified, of the topshell course, mm (in.),


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t actual = as ordered thickness, unless otherwise specified, of the shellcourse for which the transposed width is being calculated, mm (in.).

The values are tabulated as follows

The Cumm Wtr gives the Transformed Width Htr

As per API 650 5.9.7.1, the maximum height of the unstiffened shell H1 is

If Htr > H1 then intermediate wind girder must be provided

The section modulus of the intermediate wind girder shall be based on the properties of the attached members and may include a portion of the tank shell for a distance above and below the attachment to the shell, in mm (in.)

In SI units


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11. WEIGHT CALCULATION

Calculate Weight for each and every part of the tank

12. WIND ANALYSIS

Basic Wind Pressure on cylinder (Pcy) = P*Hc

Basic Wind Pressure on roof (Pr) =P*Hc

Hc = (v/160) ^2

(The value of P is given below)

(Refer 5.2.1 The design wind pressure shall be 0.86 kPa ( V /190)^2,([18lbf/ft2][ V /120]^2) on vertical projected areas of cylindrical surfaces and1.44 kPa (V/190)^2, ([30lbf/ft2][ V /120]^2) uplift on horizontal projectedareas of conical or doubly curved surfaces, where V is the 3-sec gustwindspeed.)

Wind load on cylinder section (Fcyl) =Dw *H*Pcy

Wind load on the roof section (Fr) =Ac*pr

Where Dw = effective tank diameter H = height of the tank Ac =Effective cone area

Resultant wind load F =Fcyl+Fc

Resultant Moment M = F*Z + Fr*(H+Hd/3)


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Hd=Dome height

Effective wind load on tank Fe =1.1*F

Effective wind moment on the base Me=1.1*M

13. Check For Over Turning Due To Wind

Overturning wind moment = Me

Wt of shell + wt of roof +wt of plate =W1

Force due to internal pressure =W2

Wt available to resist uplift (W) = W1-W2

Two third of the dead load resisting moment= 2/3 * (W*D/2)

14. CALCULATION FOR SESMIC MOMENT FOR OPERATING CONDITION

Find form factor (K) from Fig E-4

Find effective mass of the contents from Fig E-2 (W1/Wt and W2/Wt)

Find effective centroid of seismic force from Fig E-3 (X1/H and X2/H)

Over turning at the base of the tank

15. CHECK FOR OVERTURNING DUE TO SESMIC MOMENT


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Max weight of the tank content resisting overturning moment isWl = 99*tb*(Fby*G*H)

How ever overturning moment Wl should not exceed 196GHD

Wheretb= Thickness of the bottom plate

Fby= Yield Strength of the bottom plate

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Storage Tank Calculation