AGENDA ITEM: 650-600 Aluminum Tank Appendix
DATE:February2, 2006
CONTACT: Randy Kissell, TGB Partnership
PH: 919-644-8250 FX: 919-644-8252, email:
PURPOSE: Provide rules for aluminum tanks
REVISION: 2
IMPACT: Including aluminum tanks in 650 will reduce the cost to owners and manufacturers to maintain a standard for aluminum tanks and provide additional options for tank material.
RATIONALE:
ASME hasn’t maintained their standard on aluminum tanks (B96.1), which API tank standards 620 and 650 reference for floating roofs and LNG inner tanks. API PV&T committee members would have to spend more time updating B96.1 than adding an aluminum tank appendix to 650, since an appendix can utilize the 650 steel provisions with only slight modifications.
Similar to Appendix S for stainless tanks, the Appendix for aluminum tanks includes only those provisions that differ from steel tank requirements.
This second ballot addresses affirmative comments received in the second ballot. There were no negatives.
Ballot to Add an Aluminum Tank Appendix to API 650
1) Change the title of API 650:
Welded Steel Tanks for Oil Storage
2) Change Foreword:
“This standard is based on the accumulated knowledge and experience of purchasers and manufacturers of welded steel oil storage tanks …”
3) “1.1.1 This standard covers material, design, fabrication, erection, and testing requirements for vertical, cylindrical, aboveground, closed- and open-top, welded steel storage tanks …”
4) Add: “1.1.26 Appendix AL provides requirements for aluminum tanks.”
5) Add to Table 1-1:
Appendix / Title / StatusAL / Aluminum Storage Tanks / Requirements
6) Change 8.1.1k: The maximum operating temperature, in degrees Celsius (Fahrenheit) (unless other units are specified by the purchaser), which shall not exceed 90oC (200oF) except in cases where Appendix M or Appendix AL appliesy.”
7) Change H.4.3.2: “Welded joints between aluminum members shall conform to Section 3.1 of ASME B96.1” and AL.5.1.
8) Change Appendix M.1.2 Note: “An exception may be made by the purchaser for Items d and e, if the following criteria are met: a. Allowable stress reductions for aluminum alloys are determined in accordance with ANSI/ASME B96.1, Welded Aluminum Alloy Storage TanksAppendix AL, and alloys are evaluated for the potential of exfoliation.”
9) Add Appendix AL as shown below:
Key:
red italics = commentary
APPENDIX AL – ALUMINUM STORAGE TANKS
1
API 650-600 2/2/06
AL.1 Scope
AL.1.1 Construction. This appendix provides material, design, fabrication, erection, and testing requirements for vertical, cylindrical, aboveground, closed- and open top, welded aluminum storage tanks constructed of the alloys specified in AL.4.
This wording follows Appendix S.
AL.1.2 Requirements. This appendix states only the requirements that differ from the rules in this standard. For requirements not stated, follow the rules of this standard.
This wording follows Appendix S.
AL.1.3 Temperature. This appendix applies for maximum design temperatures up to 200oC [400oF]. Alloys 5083, 5086, 5154, 5183, 5254, 5356, 5456, 5556, and 5654 shall not be used if the maximum design temperature exceeds 65oC [150oF].
For maximum design temperatures above 93 oC (200oF) designers shall consider thermal stresses and fatigue.
400oF is the maximum temperature addressed in B96.1. Alloys 5083, 5086, 5154, 5183, 5254, 5356, 5456, 5556, and 5654 have more than 3% nominal magnesium content and become susceptible to exfoliation corrosion if held at temperatures above 150oF.
AL.1.4 Units. Use consistent units in this Appendix’s equations. For example,in an equation,use inches for all lengths (stress in lb/in2 and tank diameter in inches) or use mm for all lengths (stress in N/mm2 and tank diameter in mm).
AL.1.5 Nomenclature. Variables used in this Appendix have the following meanings:
A = area of the roof-to-shell joint determined using Figure F-2
A1 = 0.3 m (1 ft)
CA = corrosion allowance, as specified by the purchaser (see 3.3.2)
D = nominal diameter of the tank (see 3.6.1.1)
E = modulus of elasticity (see Table AL-3)
Ej= joint efficiency, 1.0, 0.85, or 0.70 (see Table AL-2)
Fty = minimum tensile yield strength
G = design specific gravity of the stored liquid
H = design liquid level (see 3.6.3.2)
ph = greater of Appendix R load combinations (e)(1) and (e)(2)
Sd = allowable stress for the design condition (see Table AL-7)
St = allowable stress for hydrostatic test condition (see Table AL-7)
tb = nominal thickness of the annular bottom plate
th = nominal roof thickness
ts = nominal shell thickness
W = weight of the shell and any framing (but not roof plates) supported by the shell
γw = density of water
θ = roof slope to horizontal at the shell
ρh = density of the roof plate
AL.2 References
The following references are cited in this appendix. The latest edition shall be used.
ASTM
A 193 Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service
A 194 Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature Service, or Both
B 209 Aluminum and Aluminum-Alloy Sheet and Plate
B 209M Aluminum and Aluminum-Alloy Sheet and Plate [Metric]
B 210 Aluminum and Aluminum-Alloy Drawn Seamless Tubes
B 210M Aluminum and Aluminum-Alloy Drawn Seamless Tubes [Metric]
B 211 Aluminum and Aluminum-Alloy Bar, Rod, and Wire
B 211M Aluminum and Aluminum-Alloy Bar, Rod, and Wire [Metric]
B 221 Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
B 221M Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes [Metric]
B 241/B 241M Aluminum and Aluminum-Alloy Seamless Pipe and Seamless Extruded Tube
B 247 Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
B 247M Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings [Metric]
B 308/B 308M Aluminum-Alloy 6061-T6 Standard Structural Profiles
B 345/B 345M Aluminum and Aluminum-Alloy Seamless Pipe and Seamless Extruded Tube for Gas and Oil Transmission and Distribution Piping Systems
B 928 High Magnesium Aluminum Alloy Sheet and Plate for Marine Service
F 467 Nonferrous Nuts for General Use
F 467M Nonferrous Nuts for General Use [Metric]
F 468 Nonferrous Bolts, Hex Cap Screws, and Studs for General Use
F 468M Nonferrous Bolts, Hex Cap Screws, and Studs for General Use [Metric]
F 593 Stainless Steel Bolts, Hex Cap Screws, and Studs
F 594 Stainless Steel Nuts
AWS
A5.10/A5.10M Specification for Bare Aluminum and Aluminum-Alloy Welding Electrodes and Rods
D1.2 Structural Welding Code – Aluminum
AA1
Aluminum Design Manual (ADM)
1 The Aluminum Association Inc., 900 19th Street, N.W.Washington, D.C.20006.
Kissell, J. R. and Ferry, R. L., Aluminum Structures, Wiley, NY 2002 provides guidance on using the ADM.
AL.3 Definitions
For the purposes of this appendix, the following definitions apply:
Aluminum: Aluminum and aluminum alloys.
AL.4 Materials
AL.4.1 General. Alloys shall be selected from Table AL-1. Dimensional tolerances shall meet the material specifications given in AL.4. Impact testing and toughness verification are not required.
Aluminum does not have a brittle fracture transition temperature; it is more ductile at lower temperatures.
AL.4.2 Sheet and Plate. Sheet and plate shall meet ASTM B 209 or B 928. Tapered thickness plate may be used.
AL.4.3 Rod, Bar, and Structural Shapes. Rod, bar, and shapes shall meet ASTM B 211, B 221, or B 308.
AL.4.4Pipe and Tube. Pipe and tube shall meet ASTM B 210, B 241, or B 345.
AL.4.5 Forgings. Forgings shall meet ASTM B 247.
AL.4.6 Flanges. Flanges shall meet ASTM B 247 and be 6061-T6. Flange dimensions shall meet ASME B16.5 or B16.47.
AL.4.7 Bolting.
AL.4.7.1 Aluminum. Aluminum bolts shall meet ASTM F 468. Aluminum nuts shall meet ASTM F 467. Bolts and nuts of 2024 alloy shall have an anodic coating at least 0.005 mm [0.0002 in.] thick. Bolts shall not be welded.
B96.1 Table 8 called for bolts to meet F 468. Aluminum rivets are no longer used. Aluminum threads tend to gall, so aluminum threaded parts should not be used where they must be reinstalled.
AL.4.7.2 Stainless Steel. Stainless steel bolts shall meet ASTM F 593 alloy group 1 or 2, or ASTM A 193 B8. Stainless steel nuts shall meet ASTM F 594 alloy group 1 or 2 or ASTM A 194 Grade 8.
AL.4.7.3 Carbon Steel. Carbon steel bolts shall be galvanized.
B96.1 included aluminized steel bolts, but they are no longer available and so are not included here.
AL.4.8 Welding Electrodes. Welding electrodes shall meet AWS A5.10/A5.10M and shall be chosen in accordance with AWS D1.2.
AL.5 Design
AL.5.1 Joints
Joints shall be as prescribed in 3.1.5 unless otherwise specified below.
AL.5.1.1 Bottom Joints
(a) Bottom plates under the shell thicker than 8 mm [5/16 in.] shall be butt welded.
(b) Butt-Welded Bottom Joints. The butt welds may be made from both sides or from one side and shall have complete penetration and complete fusion. In the latter case, a backing strip 5 mm [3/16 in.] or thicker, of an aluminum alloy compatible with the bottom plate, shall be tacked to one of the plates, and the intersection joints of the strips shall be welded with full fusion.
AL.5.1.2 Roof and Top Angle Joints. The moment of inertia of the top angle and contributing portion of the shell shall equal or exceed that provided by the sizes listed below:
Diameter (m) / Size (mm)D 11 / 64 x 64 x 6.4
11 < D 18 / 64 x 64 x 7.9
18 < D / 76 x 76 x 9.5
Diameter (ft) / Size (in.)
D 35 / 2 ½ x 2 ½ x ¼
35 < D 60 / 2 ½ x 2 ½ x 5/16
60 < D / 3 x 3 x 3/8
The top angle requirements given in 650 3.1.5.9 and B96.1 3.3.4(a) differ:
Diameter (ft) / 650 / B96.1D 35 / 2 x 2 x 3/16 / 2.5 x 2.5 x ¼
35 < D 60 / 2 x 2 x ¼ / 2.5 x 2.5 x 5/16
60 < D / 3 x 3 x 3/8 / 3 x 3 x 3/8
The B96.1 angles for tanks under 60 ft have approximately the same bending stiffness (EI) as the API 650 sizes. For tanks over 60 ft diameter, the B96.1 bending stiffness is about 1/3 that of 650.
AL.5.2 Bottoms
AL.5.2.1 Annular Bottom Plate Width
Annular bottom plates shall have a radial width that meets the requirements of 3.5.2 except that the width must equal or exceed
This dimensionless equation gives the same results as B96.1 3.2.2(f).
AL.5.2.2 Annular Bottom Plate Thickness
The nominal thickness of annular bottom plates shall equal or exceed the requirements given in Table AL-5.
Table AL-5 is B96.1 Table 3.
AL.5.3 Shells
The minimum nominal thickness of the shell plates is the greater of the calculated design shell thickness tdincluding any corrosion allowanceand the hydrostatic test shell thicknesstt, not less than required by Table AL-6:
td =
tt=
St is based on100oFtemperature strengths. The basis for allowable stresses is given in Table AL-7 notes 5 and 6.
AL.5.4 Shell Openings
AL.5.4.1 Thermal Stress Relief
Thermal stress relief requirements of 3.7.4 do not apply.
AL.5.4.2 Shell Manholes
Shell manholes shall meet 3.7.5 except:
(1) Cover Plate and Flange Thickness: The cover plate and flange thickness shall comply with Figures AL-1 and AL-2. As an alternative to Figures AL-1 and AL-2, plate flanges may be designed in accordance with API 620 rules using the allowable stresses from Table AL-7.
(2) Neck Thickness: Where manhole neck thickness is controlled by thickness of the bolting flange (see note b of Table 3-4), the flangethickness determined in (1) above shall be used.
B96.1 requires ½” min for manhole necks, no matter the shell thickness. AL.5.4.2 follows API 650’s methodology for determining neck thickness which is based on both shell thickness and flange thickness requirements.
(3) Weld Sizes:Fillet Weld A shall comply withTable AL-8.
The weld sizes in Table 3-7 (weld A) for nozzles larger than 2” are smaller than those used in B96.1. The allowable shear stress on aluminum welds is less than steel’s. Therefore,AL.5.4.2 uses B96.1 weld sizes.
AL.5.4.3 Nozzles
Shell nozzles shall meet 3.7.6 except fillet weld A shall be per Table AL-7 requirements.
AL.5.4.4 Flush Type Cleanouts
Flush-type cleanout fittings shall comply with Figures AL-1, AL-2, and AL-3.
AL.5.5 Wind Girders
The length of the shell included in the area of wind girders shall be 0.424except for
unstiffened shell above top wind girders, the length shall be.
This is different than the 16t rule in 650 (which is based on 95t/√Fty) and accounts for the different modulus of elasticity of aluminum vs. steel. The derivation of the aluminum rule is given in Kissell and Ferry section 10.5.1.
AL.5.5.1 Wind Girders
The section modulus of wind girders shall equal or exceed
Z =
where
p = (1.48 kPa)(V/(190 km/hr))2
[p = (31 lb/ft2)(V/(120 mph))2]
V = 3 sec gust design wind speed (see 3.2.1(f))
Hw = for top wind girders on tanks with no intermediate wind girder, the tank height; for tanks with intermediate wind girders, the vertical distance between the intermediate wind girder and the top angle of the shell or the top wind girder of an open-top tank.
c = lesser of the distances from the neutral axis to the extreme fibers of the wind girder
This equation includes a safety factor of 2, comparable to 650 3.9.6.1. This equation does not use 650’s approach, which assumes a girder width-to-tank diameter ratio 0.015, because the ratio is larger for aluminum and varies considerably by diameter, so using one value for all cases would be too conservative. The equation given here is different from B96.1 because B96’s equation left the allowable stress as a variable but did not provide the allowable buckling stress of the wind girder.
The wind girder section modulus equation used in 650 and B96.1 is based on the classical buckling equation for a circular ring. Roark 6th edition Table 34 gives the buckling force/(unit length of circumference) for a ring with a moment of inertia I and diameter D as 3EI/(D/2)3. Setting this equal to pHwhere p is the wind pressure and H is the tank height and using a safety factor SF gives
pH =
solving for I,
I =
since I = Z/c and 650’s safety factor is 2,
Z =
AL.5.5.2 Intermediate Wind Girders
The height of the unstiffened shell shall not exceed
H1 =
where
H1 = vertical distance between the intermediate wind girder and the top angle of the shell or the top wind girder of an open-top tank
● t = as ordered thickness, unless otherwise specified, of the top shell course
This equation is the same as in B96.1except dimensionless. Since 650 and B96.1 assume elastic buckling of the shell, the only difference between them is the modulus of elasticity.
AL.5.6 Roofs
AL.5.6.1 Structural Members
The minimum nominal thickness of structural members shall be 4 mm [0.15 in.].
650’s minimum for steel is 0.17”, but aluminum is less corrosion-prone and standard aluminum shapes have webs with 0.15” thickness.
AL.5.6.2 Frangible Roofs
Roofs required to be frangible shall meet the requirements of 3.10.2.6 except that the cross sectional area A of the roof-to-shell joint shall not exceed 0.159W/(Ftytanθ) whereFty= the greatest tensile yield strength of the materials in the joint.
This equation is the same as 3.10.2.6, except with Fty as a variable. 3.10.2.6 assumes Fy = 32 ksi for all cases. The limit on A is intended to cause the roof-to-shell joint to yield when internal pressure equals the weight of the shell divided by the plan area of the tank. As for steel tanks, caution should be exercised in using frangible designs for small tanks since the frangibility of such tanks may not be reliably predicted.
AL.5.6.3 Allowable Stresses
Roofs shall be proportioned so that stresses from the load combinations specified in 3.10.2.1 do not exceed the allowable stresses given in the Aluminum Design Manual(ADM) Specification for Aluminum Structures – Allowable Stress Design for building type structures. Allowable stresses for ambient temperature service shall be calculated using the minimum mechanical properties given in the ADM. Allowable stresses for elevated temperature service shall be calculated using the minimum mechanical properties given in Table AL-3. Section 3.10.3.4 does not apply.
This approach simplifies what B96.1 has. In B96.1, not all of the elevated temperature properties are given, but rather, allowable stress expressions are given in numerous tables (Tables 10 thru 15). These tables are out of date (for example, Table 15 bearing stresses are based on the 1994 ADM; bearing stresses were revised in the 2000 ADM).
Section 3.10.3.4 provides the allowable stress for steel columns and does not apply to aluminum columns.
AL.5.6.4 Supported Cone Roofs
(a) The stresses determined from Figure AL-4 for dead load and dead and live loads for the thickness and span of roof plates shall not exceed the allowable stresses given in Table AL-4.
Figure AL-4 is the same as B96.1 Figure 12, which provided a quick way to determine roof plate stress given the load and plate span and thickness.
(b) The roof supporting structure shall be of 6061-T6 or 6063-T6 and proportioned so stresses do not exceed allowable stresses. Dead load stresses for temperatures over 120oC [250oF] shall not exceed 25% of allowable stresses.
It is unlikely dead load stresses will exceed 25% of allowable, since the dead load is usually less than 5 psf (3/16” plate is 2.7 psf) and dead + live load will be at least 22.1 psf under the load combinations in 650.
AL.5.6.5 Self-Supporting Cone Roofs
(a) The minimum nominal roof thickness isth
th =
This dimensionless equation matches 650 3.10.5.1 (a simplified elastic buckling expression for a cone) but includes the modulus as a variable. It includes the same combined knockdown for imperfections and safety factor as 650. This can be proved by the following example:
For D = 80 ft, θ = 20o, p = 60 psf, and E = 29,000,000 lb/in2, the above formula gives
th= = 0.673”
API 650 3.10.5.1gives
th == 0.675”
(b) The minimum area of the roof-to-shell joint isA
A=phD2/(8f tanθ)
where
f = least allowable tensile stress of the materials in the roof-to-shell joint
This dimensionless equation is the same as given in B96.1, just slightly rewritten for simplicity. It matches 650 3.10.5.2.
AL.5.6.6 Self-Supporting Dome and Umbrella Roofs
(a) The minimum nominal roof thickness isth
th =
where
rh = roof radius
This dimensionless equation matches 650 3.10.6.1 (elastic buckling of a sphere) but with the modulus as a variable. It includes the same combined knockdown for imperfections and safety factor as 650, as proved by the following example:
For D = 60 ft, rh = 1.0D, ph = 60 psf, and E = 29,000,000 lb/in2, the above formula gives
th = = 0.345 in.
API 650 3.10.6.1gives
th = = 0.346 in.
(b) The minimum area of the roof-to-shell joint Ais
A=phD2/(8f tanθ)
where
f = least allowable tensile stress of the materials in the roof-to-shell joint
This dimensionless equation is the same as given in B96.1, just slightly rewritten for simplicity. It matches 650 3.10.6.2 except it includes the roof slope as a variable whereas 650 conservatively uses the lowest roof slope for all cases.