Sample calculation of tank as per API 650Full description
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Design of a liquid storage tank per API 650 2013 Standard.
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Steel Welded Tank Dia.:15.75 m 18.00 m Height DESIGN CODE : API 650 Tank Diameter : 18 m =18x3.2808 =59 ft Specific Gravity : G=1.0 Vapour Pressure :22.5 in H2O Sd=22700 psi (Material of onstruction is st 37) St=24900 psi Tank has internal pressure : P= 22.5 in H2O=5.55 kPa= 555 kg/m²
Weight of roof =0.006*0.5*(18*3.14)*(10^2+1^2)^0.5*8000=12283 =0.006*0.5*(18*3.14)*(10^2+1^2)^0.5*8000=12283 kg
Design of shell Height of tank shell =16.1 m Liquid filling level =15.78 m
Wt - corr. kg 1176.7 1361.3 1840.0 2488.2 2797.5 3156.5 3515.6 3874.7 4233.7 Total in kg: 20210.5
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Steel Welded Tank Dia.:15.75 m 18.00 m Height Design of Roof 1) Acording to (3.10.2) the minimum thickness of roof plate is 5mm Take it 6mm 2) Roof structure design: To use 33 IPE200 this means each member will carry the following: Dead weight: 200 Kg Roof plate weight : 300 Kg Live weight :300 Kg Total :900 Kg Z= M/f =800x393.75/1650 =190.9 cm3 from steel table we will find : → IPE 200 is safe Zy=194.3 cm3 Maximum Design Pressure Permitted -Pf- API 650 APPENDIX F Pf =1.6xP- 4.8xth =1.6x22.5-4.8x0.1968= 35.05536 in of water Pf >P OK Let us calculate the weight of the shell without any corrosion : td Wt (in) (mm) Kg 0.629921 0.551181 0.472441 0.393701 0.314961 0.23622 0.23622 0.23622 0.23622
Roof plate weight=12283 kg = 27072.7 pd Roof structure weight=4482 kg = 9878 pd
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Steel Welded Tank Dia.:15.75 m 18.00 m Height
73.4 kg/m2
→
Wind load on tank wind velocity =48m/s=108mile h → wind force 0-16=860 kPa=87.6 kg/m2 wind force 16-17.2=720 kPa=73.4 kg/m2 according to API 650 3.11.1 →
17.2 16
87.6 kg/m2
→ 8
87.6 kg/m2
→ 0
Load between 0-16 : F1=87.6x16x18= 25229 kg
Load between 16-17.2 F3=73.4xArea=73.4x1.2x18x0.5=792.7 kg Overturning moment due to wind load: M=F1x8+F3x(16.4)= 214832 Kg.m Overturning stability (3.11) W= shell weight to resist uplift less corrosion+dead weight supported by shell minus uplift from internal pressure
W= 20210+ 27072.7 +9878-555x(18x18/4xπ)=42851 kg Stability Moment = 2/3x(WD/2)=257106 kg.m > So, It does not need Anchor Bolts. Seismic Design of the Storage Tank:
M
(APPENDIX E)
M =Zx I (C1xWsxXs + C1xWrxHt + C1xW1xX1+C2xW2xX2) Z : seismic zone factor=0.2 I=1.0 E3.1 C1=0.60 (API 650 - E3.3)
D/H=18/16=1.1→ K=0.58 (Figure E-4) T(natural period of the first sloshing mode, in second)
Mi xXi 14201.69 37279.44 53256.34 53256.34 56806.77 42937.93 48929.27 54920.6 60911.94 422500.3
Xs=6.1 m =20 ft Wr:Weight of roof structure and roof plates=27072.7+9878= 36950.7 pd H=52.5 ft
D/H=1.1→X1/H=0.4 (Figure E-3) →X2/H=0.71 (Figure E-3) → X1=21 ft X2=37.3 ft
WT:weight of tank content=(πD²/4)x15.68x1=3990 ton=8794123 pd W2/WT=0.27 (figure E-2)
→W2=2374413 pd W1/WT=0.78 (figure E-2)
→W1=6859416 pd M =Zx I (C1xWsxXs + C1xWrxHt + C1xW1xX1+C2xW2xX2) M=0.2x1x(0.6x90505x20+0.6x36950x52.5+0.6x6859416x21 + 0.25x2374413x37.3) M=22164005 pd .ft (overturning moment due to seismic loads)
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Steel Welded Tank Dia.:15.75 m 18.00 m Height Resistance to overturning (APPENDIX E.4) wL=7.9x tbx Fby xGxH tb=8 mm=0.315 in Fby=34000 psi (minimum yeild strength for st 37) G=1.0 H=52.5 ft
wL=7.9x0.315x 34000x1.0x52.5 =3324.7 pd/ft of circumference *1.25xGxHxD=1.25x1.0x52.5x59=3871.9 pd/ft WL shall be 3324.7 pd/ft