5.6.3.2API 650, 5.6.4, Calculation of Shell Thickness by the 1-Foot Method

Plant IDA Tank FarmEquipment Number: ABC-1234Equipment: Oil Storage Tank 02Equipment Type:API 650 Storage TankDate: 12th August 2014

DesignMaterial (Course 1):SA 283 CShell Course Height (in)Nominal thickness (in):Material (Course 2, 3 & 4):SA-515 60Course 1:960.957Corrosion Allowance (in):Course 2:960.710Nominal Diameter (ft):212Course 3:960.467Height (ft):32Course 4:930.375Specific Gravity:0.85

Calculation of Thickness by the 1-Foot Method, inchesReference: API 650, 11th edition, 5.6.3The 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 used for tanks larger than 61 m (200 ft) in diameter.The required minimum thickness of shell plates shall be the greater of the values computed by the following formulas:

and

wheretdbottom-course corroded shell thickness, (in.),tthydrostatic test shell thickness (in.),Dnominal tank diameter, in ft (see 5.6.1.1, Note 1),H design liquid level, (ft),height from the bottom of the course under consideration to the top of the shell including the topangle, if any; to the bottom of any overflow that limits the tank filling height; or to any other levelspecified by the Purchaser, restricted by an internal floating roof, or controlled to allow for seismic wave action,Gdesign specific gravity of the liquid to be stored, as specified by the Purchaser,CA corrosion allowance, (in.), as specified by the Purchaser (see 5.3.2),Sd allowable stress for the design condition, (lbf/in.2) (see 5.6.2.1), Tables 5-2a and 5-2bSt allowable stress for the hydrostatic test condition, (lbf/in.2) (see 5.6.2.2). Tables 5-2a and 5-2b

Course number: 1Course number: 2Course number: 3Course number: 4D =212ftD =212ftD =212ftD =212ftH =31.75ftH =23.75ftH =15.75ftH =7.75ftG =0.85G =0.85G =0.85G =0.85CA =0.000inCA =0.000inCA =0.000inCA =0.000inSd =20000psiSd =21300psiSd =21300psiSd =21300psiSt =22500psiSt =24000psiSt =24000psiSt =24000psitd = 0.720intd = 0.500intd = 0.324intd = 0.148intt =0.753intt =0.522intt =0.339intt =0.155in

5.6.4See Appendix K tab for API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point Method

Appendix KAPI 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage1

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Introduction

The following calculation of tank shell thickness by the Variable-Design-Point Method is based on API 650, edition 11, section 5.6.4, using the methods described in Appendix K, for tanks with diameter greater than 200 ft, to establish tmin values for corrosion monitoring purposes. The information required to perfom this calculation includes, the original specified nominal thickness of the bottom shell course, the specific gravity of the tank contents, the height, corrosion allowance and plate specification of each course (including the product design stress, Sd and the hydrostatic test stress, St).

Summary

CoursetminDescription10.962inBottom course20.782inSecond course30.531inThird course40.423inFourth course50.182inFifth course

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage2

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Design

Diameter (D)280ftSpecified nominal thickness of bottom shell course: Height (H)40ft1.000inSpecific Gravity (G)0.85CourseCourseHeight ft.Course Height (h) in.H ft.CA in.MaterialSdpsiStpsi

1896400.125A573-7028000300002896320.125A573-7028000300003896240.0625A573-7028000300004896160A362320024900589680A362320024900

Calculation for BOTTOM COURSE (COURSE 1) shell thickness, inchesReference: API 650, 11th edition, 5.6.4The required shell thickness for each course shall be the greater of the design shell thickness plus any corrosion allowance or the hydrostatic test shell thickness, but the total shell thickness shall not be less than the shellthickness required by 5.6.1.1, 5.6.1.3, and 5.6.1.4.To calculate the bottom-course thicknesses, preliminary values tpd and tpt for the design and hydrostatic test conditons shall first be calculated from the formulas in 5.6.3.2.

Design ConditionAPI 650 reference

0.987in5.6.3.2.

0.962in5.6.4.4.

t1d need not be greater than tpdt1d = minimum of above thicknesses = 0.962in

Hydrostatic Test Condition

0.946in5.6.3.2.

0.914in5.6.4.4.

t1t need not be greater than tptt1t = minimum of above thicknesses = 0.914intmin = minimum nominal thickness requiredthe greater of td or tt

tmin =0.962incontrolled by t1d

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage3

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Conditions for use of the Variable-Design-Point MethodReference: API 650, 11th edition, 5.6.4.1Design by the variable-design-point method gives shell thicknesses at design points that result in the calculated stresses being relatively close to the actual circumferential shell stresses. This method may only be used whenthe Purchaser has not specified specifiedthat the 1-foot method be used and when the following is true:

5.6.4.1

whereL (6 Dt)0.5 , (in),Dtank diameter, (ft),tbottom-course corroded shell thickness, (in.),Hmaximum design liquid level (see 5.6.3.2), (ft).

L =40.206inD =280ftt =0.962inH =40.0ftL/H = 1.01

Is L/H 2?YESThe Variable-Design-Point Method can be used

Calculation for SECOND COURSE (COURSE 2) shell thickness, inchesReference: API 650, 11th edition, 5.6.4.5To calculate the second-course thicknesses for both the design condition and the hydrostatic test condition, the value of the following ratio shall be calculated for the bottom course:

5.6.4.5

whereh1height of the bottom shell course, (in.),rnominal tank radius, (in.),t1calculated corroded thickness of the bottom shell course, (in.), used to calculate t2 (design). The calculated hydrostatic thickness of the bottom shell course shall be used to calculate t2 (hydrostatic test).

h1 =96inr = 1680int1 = 0.962in

h1/(rt1)0.5 =2.388ratio5.6.4.5

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage4

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for SECOND COURSE (COURSE 2) shell thickness, inches, contiuned

If the value of the ratio is less than or equal to 1.375: t2 = t1If the value of the ratio is greater than or equal to 2.625: t2 = t2aIf the value of the ratio is greater than 1.375 but less than 2.625,:

5.6.4.5

wheret2 = minimum design thickness of the second shell course, (in.),t2a = corroded thickness of the second shell course, (in.), as calculated for an upper shell course as described in 5.6.4.6 to 5.6.4.8. In calculating second shell course thickness (t2) for design case and hydrostatic test case, applicable values of t2a and t1 shall be used.

is ratio 1.375?NOt2 = N/Ain0.9622029502378601is ratio 2.625?NOt2 = N/Ain0.6338777562190413is ratio 1.375 & 2.625YESt2 = 0.657in0.6572425887164366

Design Condition

h1 = 96inr = 1680int1d = 1.000inCA = 0.125int1 = 0.875inh1/(rt1)0.5 =2.388ratiot2a = 0.634int2 = 0.657in5.6.4.5

t2d = t2 + CA = 0.782in

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage5

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for SECOND COURSE (COURSE 2) shell thickness, inches, contiuned

Hydrotest Test Condition

h1 = 96inr = 1680int1t = 1.000int1 = 1.000int2a = 0.699int2 = 0.767int2t = 0.767in

tmin = greater of t2d or t2t = 0.782in

tmin =0.782in

Calculation for SECOND COURSE (COURSE 2), as upper shell course, shell thickness, inchesReference: API 650, 11th edition, 5.6.4.6To calculate the upper-course thicknesses for both the design condition and the hydrostatic test condition, a preliminary value tu for the upper-course corroded thickness shall be calculated using the formulas in 5.6.3.2, and then the distance x of the variable design point from the bottom of the course shall be calculated using the lowest value obtained from the following:

wheretu = corroded thickness of the upper course at the girth joint, (in.),C = [K0.5 (K 1)]/(1 + K1.5),K = tL / tu,tL = corroded thickness of the lower course at the girth joint, (in.),this is the nominal specified thickness of the bottom shell course less the corrosion allowance.(this value will be the bottom course (course 1), tmin).H = design liquid level (see 5.6.3.2), (ft).(height from the bottom of the course under condideration to the top of the shell).r = tank radius, (in).

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage6

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for SECOND COURSE (COURSE 2), as upper shell course, shell thickness, inches

nominal thickness of bottom shell course = 1.000intL = 0.875inDesign conditiontL = 0.914inHydrotest conditionH = 32ftr = 1680in

Design Condition

Trials

with5.6.4.7

starting0.6851in

tu in.KCx1 in.x2 in.x3 in.x in.td-CA in.

10.6851.2770.12836.44949.23141.39036.4490.64020.6401.3670.16540.29863.42040.00640.0060.63430.6341.3810.17140.88565.57539.80139.8010.63440.6341.3800.17040.85165.45039.81339.8130.634

0.634in

0.759in

Hydrotest Condition

Trials

with5.6.4.7

starting0.752in

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage7

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for SECOND COURSE (COURSE 2), as upper shell course, shell thickness, inches

tu in.KCx1 in.x2 in.x3 in.x in.tt in.

10.7521.2150.10134.13738.90943.37134.1370.70820.7081.2920.13437.54851.61642.06137.5480.70130.7011.3050.14038.09853.65841.85538.0980.69940.6991.3070.14138.18853.98941.82238.1880.699

0.699in

Calculation for THIRD COURSE (COURSE 3), shell thickness, inches

wheretu = corroded thickness of the upper course at the girth joint, (in.),C = [K0.5 (K 1)]/(1 + K1.5),K = tL / tu,tL = td of lower shell course less CADesign conditiontL = calculated hydrostatic thickness of lower shell courseHydrostatic conditionH = design liquid level (see 5.6.3.2), (ft).(height from the bottom of the course under condideration to the top of the shell).r = tank radius, (in).

tL = 0.657inDesign conditiontL = 0.767inHydrotest conditionH = 24ftr = 1680in

Design Condition

Trials

with5.6.4.7

starting0.5083in

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage8

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for THIRD COURSE (COURSE 3), shell thickness, inches

tu in.KCx1 in.x2 in.x3 in.x in.td-CA in.

10.5081.2930.13530.25638.84635.65130.2560.47520.4751.3850.17233.08949.57234.45233.0890.46930.4691.4000.17833.55051.31034.26233.5500.46940.4691.4030.17933.62651.59534.23133.6260.468

0.468in

0.531in

Hydrotest Condition

Trials

with5.6.4.7

starting0.558in

tu in.KCx1 in.x2 in.x3 in.x in.tt in.

10.5581.3750.16834.18648.46137.35834.1860.51320.5131.4950.21437.63761.64135.82535.8250.51030.5101.5050.21837.90562.65935.70935.7090.51040.5101.5040.21737.88662.58635.71735.7170.510

0.510in

0.531in

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage9

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for FOURTH COURSE (COURSE 4), shell thickness, inches

wheretu = corroded thickness of the upper course at the girth joint, (in.),C = [K0.5 (K 1)]/(1 + K1.5),K = tL / tu,tL = td of lower shell course less CADesign conditiontL = calculated hydrostatic thickness of lower shell courseHydrostatic conditionH = design liquid level (see 5.6.3.2), (ft).(height from the bottom of the course under condideration to the top of the shell).r = tank radius, (in).

tL = 0.468inDesign conditiontL = 0.510inHydrotest conditionH = 16ftr = 1680in

Design Condition

Trials

with5.6.4.7

starting0.400in

tu in.KCx1 in.x2 in.x3 in.x in.td-CA in.

10.4001.1710.08220.82715.66531.62915.6650.39220.3921.1950.09321.33917.76931.30617.7690.38730.3871.2100.09921.64019.00131.11819.0010.38540.3851.2180.10321.81819.73231.00819.7320.383

0.383in

0.383in

API 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage10

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for fourth course (course 4), shell thickness, inches

Hydrotest Condition

Trials

with5.6.4.7

starting0.439in

tu in.KCx1 in.x2 in.x3 in.x in.tt in.

10.4391.16330.07821.35714.99933.11514.9990.43120.4311.18300.08721.76716.71332.83816.7130.42730.4271.19460.09221.97917.62432.67917.6240.42540.4251.20080.09522.13518.24532.59418.2450.423

0.423in

0.423in

Calculation for FIFTH COURSE (COURSE 5), shell thickness, inches

wheretu = corroded thickness of the upper course at the girth joint, (in.),C = [K0.5 (K 1)]/(1 + K1.5),K = tL / tu,tL = td of lower shell course less CADesign conditiontL = calculated hydrostatic thickness of lower shell courseHydrostatic conditionH = design liquid level (see 5.6.3.2), (ft).(height from the bottom of the course under condideration to the top of the shell).r = tank radius, (in).

tL = 0.383inDesign conditiontL = 0.423inHydrotest conditionH = 8ftr = 1680inAPI 650, 5.6.4, Calculation of Shell Thickness by the Variable-Design-Point MethodPage11

Plant IDA BIG TANK FARMEquipment Number: ABC-1234Equipment: Oil Storage Tank #280-01Equipment Type:API 650 Storage TankDate: 19th August 2014

Calculation for FIFTH COURSE (COURSE 5), shell thickness, inches

Design Condition

Trials

with5.6.4.7

starting0.187in

tu in.KCx1 in.x2 in.x3 in.x in.td-CA in.

10.1872.0510.38222.54636.69521.60721.6070.16520.1652.3160.44323.76242.48620.33420.3340.16830.1682.2770.43423.59641.69620.50720.5070.16840.1682.2820.43523.61941.80320.48420.4840.168

0.168in

0.168in

Hydrotest Condition

Trials

with5.6.4.7

starting0.205in

tu in.KCx1 in.x2 in.x3 in.x in.tt in.

10.2052.06850.38723.18837.11422.62222.6220.17920.1792.36790.45324.49743.51621.14321.1430.18230.1822.32120.44424.30842.59621.35521.3550.18240.1822.32780.44524.33542.72821.32521.3250.182

0.182in

0.182in

x1 = 0.61 (rtu)0.5 + 3.84 CHx2 = 12 CHx3 = 1.22 (rtu)0.5td - CA = td = tt = x1 = 0.61 (rtu)0.5 + 3.84 CHx2 = 12 CHx3 = 1.22 (rtu)0.5td - CA = td = tt = tmin = x1 = 0.61 (rtu)0.5 + 3.84 CHx2 = 12 CHx3 = 1.22 (rtu)0.5td - CA = td = tt = tmin = x1 = 0.61 (rtu)0.5 + 3.84 CHx2 = 12 CHx3 = 1.22 (rtu)0.5td - CA = td = tt = tmin =

Nominal plate tSteel plates size & weight - thickness range

Nominal Size Thickness (inches)Weight (lb/ft2)

3/160.18757.651/40.250010.205/160.312512.753/80.375015.307/160.437517.851/20.500020.409/160.562522.955/80.625025.5011/160.687528.053/40.750030.6013/160.812533.157/80.875035.7011.000040.801 1/81.12545.901 1/41.2551.001 3/81.37556.101 1/21.561.201 5/81.62566.301 3/41.7571.401 7/81.87576.502281.602 1/82.12586.702 1/42.2591.802 1/22.5102.002 3/42.75112.2033122.403 1/43.25132.603 1/23.5142.803 3/43.75153.0044163.204 1/44.25173.404 1/24.5183.6055204.005 1/25.5224.4066244.806 1/26.5265.2077285.607 1/27.5306.0088326.4099367.201010408.00