Table of Contents1.0 DESIGN OF A QUENCH TOWER..................................................................................4 1.1 Problem Statement........................................................................................................4 1.2 General Overview on Quench Towers..........................................................................4 1.2.1 Spray towers...........................................................................................................4 1.2.2 Venture scrubber.....................................................................................................5 1.2.3 Packed tower...........................................................................................................6 1.3 MATERIAL BALANCE...............................................................................................6 Chemical engineering design..............................................................................................8 1.4.1 The density of the gas mixture is calculated as......................................................8 1.4.2 The volumetric flowrate of the gas (QG) can be calculated by...............................9 1.4.3 The ratio of the liquid mass flow rate to the gas mass flow rate is given by..........9 1.4.5 Calculation of pressure drop at flooding..............................................................10 1.4.6 Superficial gas velocity calculation......................................................................10 1.4.7 The diameter of the column can be calculated from.............................................11 1.4.8 The wall factor can be important for columns with an inadequate ratio of effective particle diameter to inside column diameter, and is given by:.......................12 1.4.9 The effective particle diameter, dp, is given by.....................................................12 1.4.10 The Reynolds number of the gas can be calculated as.......................................13 1.4.11 Calculation of dry-gas-pressure drop..................................................................13 1 1.4.12 The liquid mass velocity can be calculated as....................................................14 1.4.13 The Froude number of the liquid can be calculated as:......................................14 1.4.14 Calculation of specific liquid holdup.................................................................15 1.4.15 Calculation of pressure drop when the bed is irrigated......................................16 1.4.16 Height Equivalent of Theoretical Plate (HETP).................................................16 1.4.17 Number of Transfer Units (NTU).......................................................................17 1.4.18 Height of Overall Gas Transfer Unit (HOG)......................................................18 1.4.19 COLUMN HEIGHT...........................................................................................18 1.5 MECHANICAL ENGINEERING CALCULATIONS...............................................20 1.5.1 Design Pressure....................................................................................................20 1.5.2 Design Temperature..............................................................................................20 1.5.3 Minimum Vessel Thickness..................................................................................20 1.5.4 Dead Weight of Vessel..........................................................................................21 1.5.5 Weight of Empty Vessel........................................................................................21 1.5.6 Wind Loading.......................................................................................................21 1.5.7 Analysis of Stress..................................................................................................22 1.5.8 Dead-Weight Stress...............................................................................................22 1.5.9 Total Longitudinal Stress......................................................................................23 1.5.10 Maximum Stress Intensity..................................................................................23 1.5.11 Vessel Support.....................................................................................................23 REFERENCES..................................................................................................................28 2 Tables Table 1.1 Inlet stream of quench tower……………………………………………………...6 Table 1.2 Outlet 1 of quench tower………………………………………………………….7 Table 1.3 Outlet 2 of quench tower………………………………………………………….8 Table 1.4 Summary of chemical engineering design of quench tower…………………….19 Table 1.5 Summary of mechanical engineering calculations………………………………27 3 The temperature of the gases discharged from the quencher is at the adiabatic saturation temperature of the gases if the operation is adiabatic and the gas leaves the quencher with little or no water vapours.0 DESIGN OF A QUENCH TOWER 1. The inlet gas stream usually enters the bottom of the tower and moves up.1 Problem Statement To Design a quench tower to cool hot gases flowing at a rate of 5730 kg/h using water flowing at 18400 kg/h.2.1 Spray towers Spray towers or spray chambers consists of empty cylindrical vessels made of steel or plastic and nozzles that spray liquid into the vessels. 1 . There are 3 types of quenchers Spray towers Venturi scrubbers Packed towers 1. while the liquid is sprayed downward from one or more levels.1. the energy necessary to heat up the liquid is obtained at the expense of hot combustion gases. thereby enhancing the heat transfer. resulting in the reduction of gas temperature. exposes the gas to the liquid. When the liquid evaporates or gets heated up.2 General Overview on Quench Towers Quenching of reactor products is sometimes needed for sudden cooling. 1. Cooling by liquid quenching is essentially accomplished by introducing the hot gases into a liquid contacting device. for removing impurities and to avoid side reactions. This flow of inlet gas and liquid in the opposite direction (counter current flow). This is an inexpensive and control device primarily used for gas conditioning. both gas velocity and turbulence increases.Many nozzles are placed across the tower at different heights to spray all of the gas as it moves up through the tower. a throat section is built into the duct that forces the gas stream to accelerate as the duct narrows and then expands. Construction is complex. 1.2 Venture scrubber A venturi scrubber accelerates the gas stream to atomize the scrubbing liquid and to improve gas-liquid contact. or upwards against the gas flow in the throat. In a venturi scrubber. This feature eliminates many of the scale buildup and plugging problems associated with other scrubbers. the scrubbing liquid is sprayed into the gas stream before the gas encounters the venturi throat. Advantages of spray tower The design is completely open. The liquid droplet must be large enough not to be carried out of the scrubber by the scrubbed outlet gas. 2 . It is simple to construct. Disadvantage of venturi scrubbers Contact area available for water and gas is less.2. or in the throat. Depending on the scrubber design. As the gas enters the venturi throat. Its installation and operating cost are generally considered to be less than that of other cooling methods. Large amount of water is required for cooling. The reason for using many nozzles is to maximize the heat transfer. Very little space is required and only that amount of water that is needed to maintain the desired temperature of the gases at the discharge is used. The packing is held in place by wire mesh retainers and supported by a place near the bottom of the scrubber.9 1% C5+ 109 2% N2 83.1.1 Inlet stream of quench tower COMPONEN MASSS MASS T FLOW.3 MATERIAL BALANCE Table 1.3 Packed tower Packed bed quenchers consist of a chamber containing layers of variously shaped packing materials.kg/hr FRACTION H2 + CH4 542 9% Ethylene 1630 28% Propylene 168 3% Butadiene 39. interlock saddles. Cooling liquid is evenly introduced above the packing and flows down through the bed. such as Raschid rings.1 1% CO2 194 3% Mixed 3 . Their function is to cool the superheated gas in order to eliminate any further reaction that may occur and to also decrease the temperature of the gas. pall ring. berl saddles.6 1% butenes 44.2. that provide large surface area for liquid gas contact. 1. Quench towers can either be cooled by a water or oil medium which gives the name quench-water tower or quench-oil tower. 42E+02 14% Ethylene 1.95E+03 100% Mixed Table 1.3 Outlet 2 of quench tower COMPONE MASSS MASS 4 .11E+00 0% TOTAL 3.11 0% TOTAL 5730 100% Table 1.06E+03 27% propane 7.2 Outlet 1 of quench tower COMPONEN MASSS MASS T FLOW.68E+02 4% Butadiene 3.63E+03 41% Propylene 1.09E+02 3% N2 8.kg/hr FRACTION H2 + CH4 5.49E+01 1% C5+ 1.94E+02 5% ethane 1.9 1% butane 9.31E+01 2% CO2 1.H2O 1780 31% ethane 1060 18% propane 70.96E+01 1% butenes 4.09E+01 2% butane 9. 0. 0.6 m2/m3.NT FLOW PERCENTA kg/hr GE WATER 18400 100% Chemical engineering design Parameters to be calculated are: The superficial gas velocity The diameter of the column The dry-gas-pressure drop The liquid holdup in the column The actual pressure drop when the bed is irrigated The overall gas-phase transfer units The height of the gas-phase transfer unit The height of the liquid-phase transfer unit The overall height of a gas-phase transfer unit The packed height Residence time Data: The packing used is 50mm metal pall ring random packing Cp = is a packing constant.1 The density of the gas mixture is calculated as ρg = P×M R ×T ρg = 2.4.784 Mass flowrate of gas. Ch = is a characteristic of the particular type and size of packing. G = 5370 kg/h = 1. ɛ = packing void fraction.951.73 kg/m3 5 .5 kg/s 1.26 0.763. a = specific surface area of packing.3 × 68. 27m2/m3. 1997) ρg = 3. FP = packing factor. 112. 0.08206× 613 (Perry et al. 41 Where.2 The volumetric flowrate of the gas (QG) can be calculated by G ρg QG = Where.5 0.11 kg/s Flooding data for quench columns with countercurrent flow of gas and liquid can be correlated in terms of the flow parameter(X) given by X= ρG L ¿ G ( ρL 3. L = liquid flowrate = 5.5 = 3.1.4.402 m3/s 1.73 = 0.028lnX+ 0.73 ¿ X = 3.41 ( 1000 0.5 3.208 Flooding curve in quench tower can be accurately described by the polynomial regression lnYflood = [3.11 1.5 = 0.4.5 kg/s QG = 1. ρG = gas density = 3.50221+1.11093(lnX)2] 6 (Leva.73 kg/m3 G = gas mass flowrate = 1.1954) .3 The ratio of the liquid mass flow rate to the gas mass flow rate is given by L G = 5. 5 ρL −ρG ¿ Csflood ¿ ¿ (Leva.1954) Where.001Pa-s (Sinnot.0010.115 0.4. 0.73 ¿ ¿ ¿ 0.2 −[ 3.028 lnx+ 0.73 1000−3.115 Csflood = ( µL ¿ ¿ F p¿ Y flood ¿ )0.1 ) = 0. 1987) µL = liquid viscosity.11093( lnx) ] Yflood = e Yflood = 0. 2005) Csflood = ( 0. VGF = the superficial gas velocity at flooding.092 ¿ = 1. m/s VGF = 3.5 (Leva.092 m/s 1.5 m/s The superficial gas velocity at flooding is 1.5 m/s 7 . 27m2/m3 (Wiley and Jaime.5 27 × 0.50221+1. FP = packing factor. 1954) Where.4 Calculation of the superficial gas velocity at flooding The superficial gas velocity can be calculated as VGF ρG ¿0. 4. m/s f = a fraction of flooding and is usually 0.236 Pa/m of packing 1.5 4 ×0.1.05 m/s 1.4.6 Superficial gas velocity calculation For a given fluid flow rates and properties.1987) VG = 1. VG = superficial gas velocity. 1991) Where ∆Pflood has units of Pa per meter of packed height ∆Pflood = 93.7 (Kister and Gill.05 × π (Kister.402 D = ( 0. 1987) Where.9(FP)0. superficial gas velocity can be calculated from the expression given by: VG = VGF × f (Wiley and Jaime.9(27)0. 1992) )0.7 = 943.83 m 8 . VFG = 1.4.5 × 0.05 m/s Hence the superficial gas velocity.7 The diameter of the column can be calculated from 4 × QG D = ( f ×V gf × π )0.7× 1.5 = 0.7 for quench towers (Wiley and Jaime.5 Calculation of pressure drop at flooding The pressure drop at flooding is strongly dependent on the packing factor for both random and structured packing and it is given by the empirical expression: ∆Pflood = 93.83 m D = 0. and a given packing material.7 = 1. m a = specific surface area of packing. dp.951 ) 0.6 m2/m3 (Wiley and Jaime.4.83 9 . 112.0026110 0.83 m The area of the column can be calculated as: 2 A= π ×D 4 A= π ×(0. dp = the effective particle diameter.951 112.Hence the diameter of the column is 0.1987) Kw = wall factor 1.0026110 2 1 ( 3 1−0.9 The effective particle diameter. ɛ = packing void fraction = 0. 1956) Where.83)2 4 = 0.4.951 (Wiley and Jaime. 1956) Where. is given by dp = 6( 1−ɛ a ) (Leibson et al.1987) dp = 6( 1−0.8 The wall factor can be important for columns with an inadequate ratio of effective particle diameter to inside column diameter. and is given by: 1 =¿ KW 1+ 2 1 ( 3 1−ɛ dp ) D (Leibson et al.6 1 =¿ KW 1+ ) = 0.541 m2 1. 8 64 Ψ =0. is given by the empirical expression: 1.9590 (1−0.686 10 .s ReG = 1.763.4.08 ) = 0.73 ×0.24)0.0026110 ×3.686 The dry-packing resistance coefficient = 0. 1956) Where.24 The dry-packing resistance coefficient (a modified friction factor).24 + (6671.00003) The Reynolds number of the gas ReG = 6671. 3×10-5Pa.763 ( 6671.1987) 1. Ψ = the dry-packing resistance coefficient (a modified friction factor) Cp = is a (packing constants) characteristic of the particular type and size of packing = 0.043 KW = 0.8 64 Ψ = Cp ( R eG + ( ReG )0. µG = kinematic viscosity of the gas mixture.08 ) (Leibson et al.959 1.05 × 0.10 The Reynolds number of the gas can be calculated as ReG = v G ×d p × ρG × K W (1−ɛ)(µG ) Where. (Wiley and Jaime.1 KW = 1.951)(0. 05) (0. Pa ∆ Po Z 2 = 0.s 1.83) 4 = 9.11 2 π ×(0. ∆ Po Z = 177.39 Pa/m 1.6 ×3.73 ×(1.4. m △PO = the dry-gas-pressure drop.12 The liquid mass velocity can be calculated as Gx = L 2 π ×(D) 4 (Seader and Henley.s Gx = 5.444 kg/m2.1.686× 112.9900 Hence the dry-gas-pressure drop.951)3 ×2 ×0. Z= packing height.12 The Reynolds number of the liquid can be calculated as: 11 . 1989) Where. kg/m2.4.4. 1998) Where.11 Calculation of dry-gas-pressure drop The dry-gas-pressure drop can be calculated from the dimensionally consistent correlating equation given by: V ∆ Po Z (¿¿ G)2 Ѱ × a× ρ × G = ( ɛ)3 ×2 × K w ¿ (Stichlmair et al. Gx = liquid mass velocity. 85 Ch ׿ a (Seader and Henley) Where.6 2 100 × 9.1987) 2 FrL = G x × 112.4.1998) = 9.1028 For ReL ≥ 5. the ratio of specific areas is given by : R eL ¿ ¿ ah =0. FrL = Froude number of the liquid g = acceleration due to gravity.1998 ) Where.444 112.ReL = ReL = Gx a× µ L Gx a× µ L (Seader and Henley. 9. (Wiley and Jaime.1987) 12 .81m/s2 (Wiley and Jaime. Ch = is a (packing constant) characteristic of the particular type and size of packing = 0.87 Hence the Reynolds number of the liquid ReL = 83.784.001 = 83.81 FrL = 0.13 The Froude number of the liquid can be calculated as: FrL = G x2 × a g (Seader and Henley.6 ×0.87 1. 606 ¿ 3 = 0.724 Hence the liquid holdup in the column is = 0.724 h L = 0.724 13 .028) 83.4. = specific liquid holdup. m2/m3 R eL ¿ ¿ ah =0. m3 holdup/m3 packed bed VL = superficial liquid velocity. volume of liquid holdup/volume of packed bed) in the preloading hL =( region can be calculated from the dimensionless expression: 12 F rL ReL ¿¿ 1 3 ( ah a ¿¿ 2 3 (Billetand Schultes. m/s hL =( 12(1.e.85 Ch ׿ a Therefore. the ratio of specific areas is ah =¿ 1. hL.1995) Where.87 ¿¿ 1 3 2 ( 1.14 Calculation of specific liquid holdup The specific liquid holdup (i. or effective. specific area of packing.606 a 1.ah = hydraulic. 16 Height Equivalent of Theoretical Plate (HETP) HETP is calculated as.5 The actual pressure drop when the bed is irrigated is therefore ∆P Z = 645.5 = 5.87 200 ¿¿ 1. Pa ∆P 0.4.15 Calculation of pressure drop when the bed is irrigated When the packed bed is irrigated. HETP = A −0. A = Size of packing σ = 50 mm = surface tension of liquid = 69.5 = 5.951 =¿ ( ∆ PO 0.951−0.24 Pa/m 1.21 [ ] [ ] σ 20 μ 0. △P = Actual pressure drop when the bed is irrigated.4.724 ) exp ( ∆P ∆ PO 83.5 Where. The Correct pressure drop for liquid holdup is calculated with the equation ∆P ɛ =¿ ( ɛ−hL ) exp( ∆ PO R eL 200 (Billet and Schultes) ¿ ¿1.2 Where.19 0. the liquid holdup causes the pressure drop to increase.1.8 mN/m 14 . 19 ( ) ( 0.83 m μ = Overall viscosity of feed stream = 0.2 0. β = L/HG = 0.00 y1 = Solute contents in gas at bottom mole fraction Substituting the above values into equation (5).8 HETP = 50 ×10 20 −0.000381 L = Molar liquid flow rate = 1022.0006 Pa s −3 69.0116 m 1.17 Number of Transfer Units (NTU) Number of transfer units is given by. NTU = [ x −y 1 ln ( 1−β ) 2 1 + β 1−β x 1− y 1 ] Where.00 x1 = Solute contents in liquid exit stream mole fraction = 0.0006 0.4.D = 0.74 kmol/h H = Henry’s Law Constant = 3410Pa/mol fraction x2 = Solute contents in liquid inlet stream mole fraction = 0.21 ) HETP ¿ 0.22 kmol/h G = Molar gas flow rate = 78. 15 = 0.00 . 51 m Therefore.19 COLUMN HEIGHT Packing height is calculated as.18 Height of Overall Gas Transfer Unit (HOG) Height of overall gas transfer unit is given as. Htotal = Hog x NTU Htotal = 2. Htotal = 10.01 m 1. total height of tower = 10.3 NTU = 5 1.457 allowance for disengagement of vapors at top and at bottom for liquid.01 x 5 Htotal = 10.4.05 m Giving 0.4.51 m 16 . Hog = 1 −1 β HETP 1 ln β ( ( )) (6) Hog = 2.NTU = 4. 352 kPa 17 . m 0.4 The liquid holdup in the column 0.5.5 MECHANICAL ENGINEERING CALCULATIONS The material of construction is carbon steel.Table 1. Pa/m 645 Number of transfer units 5 The overall height of a gas-phase transfer unit.05 The diameter of the column. 1. m 2.51 1. 2005a) : Pi = 110 100 × 233.4 Summary of chemical engineering design of quench tower Parameter value The superficial gas velocity. m 10.83 The dry-gas-pressure drop.724 The actual pressure drop when the bed is irrigated. m/s 1.047 kPa = 256.01 The packed column height.1 Design Pressure Design pressure (Pi) is taken as 110% of operating pressure (Sinnott. Pa/m 117. 3 Minimum Vessel Thickness Pi D i . 2005e) 18 .256 830 (2 100) 0. 2005d). The weight of the empty vessel (Wv) The weight of the material (Wm) 1.256 e= 2 mm Allowing a corrosion allowance of 2 mm (Sinnott. Di is the internal diameter = 0.352 kPa = 0.4 Dead Weight of Vessel The major sources of dead weight for the unit are.Pi e= (Sinnott.2 Design Temperature Highest Operating temperature = 340oC 1.256 N/mm2 0. 1.1.8D m t Wv (Sinnott.5. the minimum thickness required to withstand internal pressure is 4 mm. 2005c) Pi is the internal design pressure of the shell = 256.5 Weight of Empty Vessel C v π ρ m g D m H v 0.5. 2005b) Where.5.83 m = 830 mm e is the minimum thickness required f is the design stress of stainless steel at 340oC = 100 N/mm2 (Sinnott.5. 2f i . 83 + 2(0.96 Nm 19 .838)] × 0. 10.004) m = 0.838 ) =1072. 2005f).81 m/s2 t = wall thickness of vessel = 4 mm = 0. Hv = height of the cylindrical section. but offset from the vessel centre line (Sinnott.08 π × 8000 × 9. W (loading per unit length)=Pw Deff =1280 ( 0.004 = 9988.6 Wind Loading Bending stresses result from the bending moments to which the vessel is subjected.81 × 0. Dynamic wind pressure ( Pw ) is 1280 N/m2 (Sinnott. 2005g).512 = 59241. which can be taken as 1.51 m g = gravitational acceleration = 9.521 + (0. Bending moments will be caused by the wind loads on tall self-supported vessels.98 N Thus.004 m ρm = density of vessel material (carbon steel) = 8000 kg/m3 Dm = width of vessel = 0. Mx = (1072. dead weight and wind loads on piping and equipment which is attached to the vessel.64/2) x 10.98 N 1.5. CV = factor to account for the weight of nozzles.838 [10. dead weight of vessel = 9988.Where. man ways.838 m Wv = 1.64 N /m Bending moment at bottom tangent line. internal supports etc.08 for vessels with few fittings.8 × 0. 8 Dead-Weight Stress Dead-weight stress of the vessel is given as σw WT π D i t t (Sinnott.7.1 Circumferential Stress Circumferential stress due to pressure is given by Pi d i 2t σ h 2 13.7.1 Longitudinal Stress Longitudinal stress due to pressure is given by Pi d i 4t σl (Sinnott.7 Analysis of Stress 1.5.5.5.28 N/mm 2 4x4 1.28 σh 2 i σh = 26.256 x 830 13. σl 0. 2005i) Where WT is the total weight which is supported by the vessel wall 20 .5.56 N/mm2 1. 2005h) Hence.1. (Sinnott.953=14. Since this stress is higher than the maximum stress intensity at any point in the material.56−14.5. 2005j) 1. the design temperature and pressure. and the internal and external fittings and attachments.28+ 0. the vessel location and arrangement. and weight of the vessel.σw 9988.11.9 Total Longitudinal Stress σ Total axial or longitudinal stress ( z ) σ c ( compressive )=σ l + σ w =13.1 Skirt Support Thickness Data 21 .5.5.98 0. Its thickness is designed to withstand the deadweight loads and bending moments imposed on it by the separator. shape. 1.11 Vessel Support The support system designed for a separator and all tall vessels depends on the size.10 Maximum Stress Intensity σ s ( tensile ) =σ h−σ z=26. 2005k) 1.233 N /mm2 (Sinnott. A skirt support is used for vertical columns.233 ¿ 11.5.33 N /mm2 The maximum allowable stress for the material of construction is 100 N/mm 2.953 N / mm2 π 830 4 4 1. the design is not prone to failure under stress. 045 N Wind loading = 1072.64 N /m Bending moment at base of skirt = 59241. (σ max ) and Young’s modulus. (E) at ambient conditions are 165 N/mm2 and 11350 N/mm2 respectively. The maximum dead-weight load on the skirt will occur when the vessel is full of water. σ ws = W π ( D s +t s ) t s Where. Approximate Maximum Dead-Weight = (Di2 x Hv x (π/4) x ρw x g) ρw = density of water g = acceleration due to gravity Approximate Maximum Dead-Weight = 0.832 x 10.05 N Dead-weight of vessel = 9988+ 55785.05 N = 65773. σ bs = bending stress in the skirt 22 .Specified skirt angle = 90 °C (straight cylinder skirt) Maximum allowable stress.96 Nm Assuming a skirt thickness of 20 mm σ bs= 4 Ms π ( Ds +t s ) t s .81 = 55785.51 x (π/4) x 1000 x 9. 16 N/mm2 Criteria for design The skirt thickness should be such that under the worst combination of wind and deadweight loading the following design criteria are not exceeded: 23 .044 = 6. σ s ( tensile ) =σ bs −σ ws σ s ( compressive )=σ bs +σ ws σ bs= 4 ×59241.05 ×1 03 π ( 830+ 20 ) × 20 σ ws (operational)= 3 = 5.19=5.35 N/mm2 =1.044 N/mm2 9988 ×1 03 π ( 830+ 20 ) × 20 = 0.394 N/mm2 ^ Maximum σ s ( tensile ) =5.96 Nm ×1 0 π ( 830+20 ) 830× 20 σ ws (test )= 55785.35 + 1.Ms = maximum bending stress at the base of skirt W = total weight of vessel Ds = inside diameter of the skirt ts = skirt thichness Resultant stresses in skirt are.19 N/mm2 ^ Maximum σ s (compressive)=¿ 5.35−0. 394< 0. 5. if applicable = 0.85 × 165 × sin(90) = 114.16 < 140. 2005 m) Ds ( ) Where.σs (tensile) < fsJsinϴs (Sinnott.75 5. 02 6.25 Testing for maximum compressive strength 6. Testing for maximum tensile strength fsJsinϴs.17 Since both criteria are satisfied.85 ϴs = base angle of a conical skirt.125× 11350 × 20 ( 830 ) sin ( 90)=246. 2005l) σ s ( compressive ) <0.394 < 34.16 < 0. 20 0C J = weld joint factor. normally 800 to 900 E is the Young’s modulus of steel = 210 kN/mm2 at ambient temperature. normally taken at ambient temperature. fs = maximum allowable design stress for the skirt material. 24 . a thickness of 20 mm can be used for the skirt.125 E ts sin θ s ( Sinnott . mm Longitudinal stress. mm Wind Loading.5 Summary of mechanical engineering calculations .56 0.64 11.953 9988 14.233 20 1072. oC Vessel thickness. N/mm2 Circumferential stress. N/mm2 Skirt support thickness.Parameter Material Design pressure. N/mm2 Dead weight. N/mm2 Value Stainless steel 304 256 340 4 13. N Total longitudinal stresses.33 25 Table 1.28 26. N/m Maximum stress intensity. N/mm2 Dead weight stress. kPa Design temperature. R... R. 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