5/14/2013 gu” rr fo STORAGE TANKS 101 vr a of An Introduction Po ‘ale to Ne + Lt Tank Design Basics . vr oe Tanks 101 Topics « Basic Introduction to Tank Design = History of API Tank Standards = Comments About Tank Inspection = Effects of Internal Pressure5/14/2013 = Topics Liquid pressures = Loads on tank shells » Allowable stresses = Joint efficiencies a Shell design methods = Shell-to-bottom joint a Shell openings « Internal Pressure 4 =. Water Pressure A cubic foot of (4 water weighs 62.4# The pressure at any depth, H(ft) below the water surface is... P = 62.4 x H psf P = 0.433 x H psigy jot all tanks contain water oh Not all tanks . = 62.4 (G) (H)... Specific Gravity and __ Liquid Pressure Loads in pst = Specific Gravity of product... aes =10 Sulfuric Acid = 1.85 Caustic Soda = 1.55 Fertilizer, Black Liquor = 1.35 Ethanol = 0.79 Heavier Oils = 0.95 (crude, #6, Bunker C, etc) Mid-distillates = 0.85 (kero, diesel, #2 FO, etc) Lighter Oils = 0.72 (gasoline, naptha) 5/14/2013Hydrostatic Forces on Shell Product Weight = 62.46 pef } |, Pressure, P_| P. |_Diameter, D__| D Pressure ae =624GH Shell Hoop Tension Force = Px D = 2T Hoop Tension, T = PD/2 = PR 5/14/2013ry Hoops Forces = Wood stave barrels = Balloons ® Tight belts «= For any cylinder... » Hoop Tension, T = Pressure x Radius = Applies to Tanks, Pressure Vessels, Pipes Shell Hoop Tension Hoop Tension... T = PR = PD/2 T = (62.4GH)D/2 = 31.2 HDG... #/foot = 31.2 HDG/12... #/inch T = 2.6HDG... #/in€This is our equation Using... , D = Tank Diameter, in feet H = Product Depth, in feet “ G = Product Specific Gravity, no units 7 5/14/2013” X 5/14/2013 T= Gxh aI Shell Design . 7 ___Hoop Tension Required Thickness = Jllowable Stress ts ak ais _ 2.6HDG eee [Se ye : . f API Shell Design Equation y 4 | (One-Foot Method) , a 2) an .6(H-1)D i. 1280-2 G i 0 ols te « (H-1) is substituted for H » Calculations made at bottom of a course = Thicker course below “reinforces” the thinner course above wwtdling © Ie _brtlonn of ea ao ty a dime oe alast i nore a an th ae wy? we is vied ‘ na :_ 2.6(H-1)DG t H SE Based on HOOP forces D *Design EACH course *VERTICAL seams govern Calculate Course Thickness, t —— 2.6(H-1)DG SE t= 5/14/2013_Calculate Shell Stress, S tE , A g 2.6(H-1)D6 oy Calculate Safe Fill Height, H H ~~ SEL 2.6DG 5/14/2013of API Shell Design (OFM)... Used since 1928!!! 2,6(H-1)DG SE a t = Required shell thickness, inches ~ a H = Product depth, feet ~ a D = Tank diameter, feet ~ = Product specific gravity ~ llowable shell stress, psi ~ « E= Joint efficiency - t= One-Foot Method... 4 From 1928 thru 1980 2.6(H-1)DG SE t = Required shell thickness, inches = Product depth, feet = Tank diameter, feet = Product specific gravity (G = 1.0 min) = Allowable shell stress = 21,000 psi E = Joint efficiency = 0.85 t= 5/14/2013Improved Design Method 1964 API-650, Appendix D = Check TWO conditions... = Design Condition... 2.6(H-1)DG tye ot Sq CA = Test Condition... 4 -2:6(H-1)D oes S, Improved Materials 4 1967 API-650, Appendix G » Added new materials for construction = Materials of higher strength a Materials of improved toughness = Higher allowable stresses 5/14/20134 API Timeline for Design Rules API-12A (Riveted) 1928-1951, API-12C (Welded) API-650 Appx A, _a—rrerers 1936 - 1961, i ‘Since 1980 App’x 6 API-650 App’xD_| Since 1980 1920 1930 1940 1950 1960 1970 1980 1990 4 Allowable Shell Stresses = API Standard 12A... 1928 (Riveted) = S = 21,000 psi = API Standard 12C... 1936 (Welded) # S = 21,000 psi = AWWA D100... 1940 (Water Tanks) » S = 15,000 psi 5/14/20134 API-12C Allowable Stresses = 1936 API-12C... S = 21,000 psi = 1958 API-12C... S = 21,000 psi = 1961 API-650... S = 21,000 psi API-650 Allowable Stresses GP 1961 thru 1980... = 1961, 1% Edition... S = 21,000 psi a 1964, Appendix D « Sy = 21,000 psi for design = S, = 23,000 psi for hydrotest a 1967, Appendix G « Sy = 26,300 to 32,000 psi for design « S, = 28,000 to 34,300 psi for hydrotest 5/14/2013mo API-650 Allowable Stresses 1980 to date... = 1980... 7% Edition « Appx D & G rules moved to Basic Std. « 2007... 11% Edition... current = Sy = 20,000 to 32,000 psi # S, = 22,500 to 34,300 psi » Appendix A... the “old” API standard « S = 21,000 psi for all materials 4 Why Higher Stresses? = Improved Materials = Higher strength = Improved notch toughness « Material Restrictions » Material toughness considered = Based on Design Metal Temperature (DMT) 5/14/2013 iL4 Why Higher Stresses? = Improved Design Details «= Stringent weld spacing rules = Nozzle construction improved, w/ PWHT « Full penetration horizontal welds « Bottom annular plate requirements = Improved NDE « Additional radiography « Expanded use of NDE y Horizontal Shell Seams Shell Plates > 3/8” Partial (2/3) Penetration Full Penetration API 1936 thru 1980 APT 1964 to Present 5/14/2013 124 Shell Nozzles Full Penetration Shell-to-Neck N Basic API Si Nozzle Centerline | 3” (nominal) Basic API 1936-1980 3”to 10” (minimum) ic API 5/14/2013oy Weld Joint Efficiency, E a API-12C... 1936 to 1958 E = 0.85 for all butt welded tanks E = 0.35 to 0.70 for lap welded tanks = API-650... 1961 to 1980 E = 0.85 for Basic tank E = 1.00 for Appendices D and G » API-650... 1980 to date E = 1.00 for Basic tank E = 0.85 for Appx A w/ spot RT E = 0.70 for Appx A w/ no RT + Shell Openings Basics... = Hoop tension in shell plate # Shell is weakened at openings = Hoop forces must pass around opening = Openings normally require reinforcement = Expect to see reinforcing plates!!! 5/14/2013 145/14/2013 Loads Transfer Near Openings T=2,6HDG < + > T=2.6HDG 4 |_ Tank Shell Openings = “Appurtenances” per API « Shell nozzles and shell manholes = Flush-type cleanout doors « Flush-type shell nozzles = Reinforcement required for > 2 NPS = For AWWA D100... > 4 NPS 15pa 24” Shell Manhole o 34 alo tel SL 120ft diameter x 48ft high AST a Shell Hoop Tension, T T = 2.6HDG = 2.6 (48-3) (120) 1.0 = 14,040 #/in » Force passing thru “Hole”, F F = Hole Diameter x Hoop Tension = 26 in x 14,040 #/in = 365,040 # (183 tons) a For an NPS 8 nozzle... F = 9.25 in x 14,040 #/in = 129,870 # Load at Shell Openings Hoop Tension, T = 2.6HDG #/in... on a 1” hoop Hoop Tension <-> Hoop Tension T T | @ = 5/14/2013Reinforcement of Openings = Consists of four components... a Reinforcing plate « Nozzle neck » Excess shell plate » Weld metal = Shell loads transfers to reinforcement = Loads pass through attachment welds API Reinforcement... Rules-of-Thumb « Repad thickness = Shell plate thickness = Repad OD = Twice shell hole diameter = Pipe schedule = Extra-strong = Weld sizing... « Full penetration of shell-to-nozzle neck « Full fillet weld around repad « Full fillet weld around nozzle neck = Atest hole in repad is required (open) 9 5/14/2013 7Tank Bottom Basics... a Bottoms designed for leak tightness # Lap welded construction typical = Weld seams vacuum-box tested for leaks « Shell-to-Bottom joint... « Highly stresses area « Additional requirements for design, welding and NDE Tank Bottom... Typical of Smaller Tanks Perimeter Sketch Plates ‘Tank Shell Reetangular Bottom Plates Woks Three-Plate Lap 5/14/2013 185/14/2013 Tank Bottom Weld Seams 1/4 1/4” Bottom Plates A (Typical) Tank Bottom ‘Annular Plates ‘Tank Bottom w/Annular RingShell-to-Bottom 5 Joint Movements Product __-—" Pressures init Radial growth is restrained at base of tank Comer joint rotates Uplifting of bottom plate Shell-to-Bottom Joint... 4 Bending Stresses > Yield Stress Very high tensile stresses at toe of fillet weld due to bending moments in the bottom sketch plate/annular plate Tank Shell Tank Bottom Plate 5/14/2013 20Shell-to-Bottom Joint » Most highly strained part of a tank = Bending stresses > yield for large tanks » Basic weld sizing per API rules » Materials requirements (toughness) = Construction requirements (welding) = Testing (NDE and hydrotest) = “Critical Zone”... API-653 Annular Plates a Required for... = Tanks designed of higher strength material = D > 100ft if operation is above 200°F a Welding typically... = Low hydrogen electrodes « Two-pass welding required « Additional RT and NDE « Often thicker than remainder of bottom 5/14/2013 a1Tank Shell Inspection Basics hell must be evaluated = Thickness reading by UT a Physical dimensions, plate layout ... D, H « Year of construction... S and E = Stuff in the tank... G a Shell openings must be examined = Critical zone must be examined Inspection of Shell Openings = Visual examination of each = Properly designed and installed? = Repad size and thickness = Weld sizing = Open test hole » Proper weld spacing? « to the bottom a to shell weld seams « to adjacent openings 5/14/2013 22“4 Foundation Inspection = Foundation must provide proper shell and bottom support » Examine for signs of deterioration and settlement = Examination includes checks for... « General condition & drainage « Shell settlement profile » Bottom settlement pattern Tank Bottom Inspection a Bottom must be leak tight = Vacuum box the bottom seams « MFL / UT the bottom plates is typical = Shell-to-bottom joint... Critical Zone « Close visual examination of weld = MT or PT of weld, as required 5/14/2013 23An “API-653 Inspection” = Not well defined in API-653 = API checklists are not complete enough = Owner is required to define scope, extent and methods of inspection + API-653 Tank Inspection = Tank evaluation methods are identified, so we have pretty good idea what we should be looking for during inspection = Requesting an “Inspection in accordance with API-653” is not a proper tank inspection specification 5/14/2013 244 Effect of Internal Pressure = A pressure that exceeds the roof weight will cause uplift of the roof plate = Uplift resisted by top angle of tank only Root Pate mn Top “ Angle Roof Plate Downward “Pressure” | P = 8x Plate Thickness (#4 = For 3/16” Plate... P = 8(3/16) = 1.5”H,0 = For 1/4” Plate... P = (1/4) = 2.0"H,0 bs) 5/14/2013 254 Effect of Roof Uplift = Roof acts as a membrane « Large inward forces develop = Top Angle = Compression Ring ” 1:12 Slope Roof Plate Uplift 12* Thrust Top ae Angle Tank Shell = Top Angle Compression # Proper design is required to prevent compression or buckling failure of top angle = API-650, Appendix F... to 2.5 psi max. || # API-620... not exceeding 15 psi 5/14/2013 26Bact 2) Tank Uplift. Bottom Stresses Uplift [sae Less Than Shell Reis Weight = Tank aan {I | | L_ Tank Uplift = Large tanks may uplift at low pressures = API-650 does not permit uplift at the base of an unanchored tank during normal operation s Anchorage is required if uplift exceeds dead load of tank (plus a partial contribution from product weight) 5/14/2013 27