Design of Obround Flange for Pressure Vessel Application

Design Of Obround Flange For Pressure Vessel Application-Free PDF

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Vol 1 Issue 2 2015 IJARIIE ISSN O 2395 4396, NOMENCLATURE. a Nominal diameter of bolts mm n Total number of bolts. A Outside diameter of flange mm N Gasket width mm . A Area of cross section mm2 P Design pressure MPa . b Effective gasket seating width mm P Wetted perimeter mm . B Inside diameter of flange mm R Radial distance from bolt circle to point of intersection of. bo Basic gasket seating width mm hub and back of flange mm . C Bolt circle diameter mm Sa Allowable bolt stress at gasket seating temperature. c Clearance between OD of shell and ID of flange mm atmospheric temperature MPa . d Bolt hole diameter mm Sb Allowable bolt stress at operating temperature MPa . D Hydraulic diameter mm Sfa Allowable stress for flange material at gasket seating. D m Equivalent mean gasket diameter assumed for design temperature atmospheric temperature MPa . purpose mm Sfb Allowable stress for flange material at operating. DL Maximum inside diameter of obround shell mm temperature MPa . Dm1 maximum mean gasket diameter for non circular flange mm SH Calculated longitudinal stress in hub MPa . Dm2 minimum mean gasket diameter for non circular flange mm SR Calculated radial stress in flange MPa . DS Minimum inside diameter of obround shell mm ST Calculated tangential stress in flange MPa . E Radial distance from bolt circle to outside diameter of STS Minimum tensile strength MPa . flange mm SY Minimum yield strength MPa , G Diameter at location of gasket load reaction mm T Design temperature C . hD Radial distance from bolt circle to circle on which H D acts mm t Flange thickness mm . HD Hydrostatic end force on area inside flange N tg Thickness of gasket mm . hG Radial distance from gasket load reaction to bolt circle mm tn Nominal thickness of the shell pipe or nozzle to which the. HG Gasket load Wm1 H for operating condition N flange is attached mm . hT Radial distance from bolt circle to circle on which H T acts mm W Design bolt load for the gasket seating condition N . HT Difference between total hydrostatic end force and the w Width of the straight portion of obround flange mm . hydrostatic end force on area inside flange H HD N y Gasket joint contact surface unit seating stress MPa . J Flange rigidity z Factor for conversion of obround shape to circular shape. m Gasket factor, Appendix 2 rules for bolted flange connections with ring type gaskets Australian Standard AS1210 also follows this. approach These methods is adapted from of the Taylor Forge method developed by Waters Wesstrom Rossheim. and Williams of the Taylor Forge company in Chicago in the 1930 s and subsequently formed the basis of the ASME. code for flanged joint design 5 The assumptions made by this method are now generally regarded as simplistic This. method gave rise to the m and y gasket factors in ASME section VIII as well as other codes The calculation is. based on the axial forces balance between the bolt load the resulting axial force due to the end thrust effect of the. internal pressure and the reaction on the gasket , Adolf E Blach 1 in one of his work describes the two design methods for bolted flanged connection of non circular. cross section of obround and rectangular type One method is applicable to unreinforced almost square rectangular. shapes using an equivalent circular flange and standard flange design methods The other is based on a. decomposition of frame and flange bending stresses and may also be used for rib reinforced pressure vessel flanges . Calculations experimental values and finite element results were obtained for flange with ring gaskets gasket fully. inside the flange bolt line and full face gaskets Comparing numerical values with experimental data he proved that. the method of equivalent circular flanges is suitable for obround and rectangular pressure vessel flanges within certain. limits The results are on the safe side and become increasingly conservative as the length to width ratio increases . Muhsen Al Sannaa and Abdulmalik Alghamdi 3 studied the results obtained using Finite Element Analysis FEA . of large diameter welded neck steel flanges under different loading conditions They give the stress analysis of flanged. joint made up of the flange and the gasket for large diameter steel flanges They showed that clamping pressure is a. determinate factor for the sealing condition and that clamping pressure needs to be carefully selected to get proper. sealing of the flange gasket assembly Increasing the clamping pressure will result in better contact pressure but at the. cost of higher flange stress Gasket has to be made of soft material with low modulus of elasticity to ensure better. sealing of the assembly Axial end load may results in gasket leakage if the clamping pressure is not sufficient . M Murali Krishna M S Shunmugam and N Siva Prasad 4 worked on the finite element analysis of bolted flange. joint considering non linearity of the gasket material under various loading and operating conditions Gaskets. behaviour is complex due to nonlinear material properties combined with permanent deformation They found that. 1162 www ijariie com 212, Vol 1 Issue 2 2015 IJARIIE ISSN O 2395 4396.
variation of contact stresses due to the rotation of the flange and the material properties of the gasket play important. roles in achieving a leak proof joint Flange rotation causes variable compression across the gasket from the inner. radius to the outer radius Due to the variation in compression the contact stresses also vary along the radius . This paper aims to find the appropriate analytical method to be used for the obround flange which can comply with. ASME code The obround flange is designed using equivalent circular flange method The finite element analysis. FEA is used to predict levels of stress and deflection of a particular flanged joint and stresses are linearized These. FEA results are compared with ASME allowable limit and are on safe side The analytical design method is. approximate method which results on positive error side . 3 FLANGE DESIGN, The obround flange designed here is for the particular application in generator shell of vapour absorption chiller unit . The chiller unit is mainly used in industries and hotels for food storage or air conditioning purpose Mostly the fitment. of this unit is in parking area or basement where the height is restricted So to reduce the machine height one of the. option is to reduce the height of the generator shell and its flange with the use of non circular shape . 3 1 Forces Acting on Flange, The forces acting on flange joint subjected to internal pressure with ring type gasket i e gasket is wholly within the. circle enclosed by a bolt hole and no point of contact beyond this circle 7 8 are as shown in figure 1 The various. forces acting on flange can be represented on cross sectional view in the required directional sense 7 11 as shown. in figure 2, Fig 1 forces acting in a bolted flange joint assembly Fig 2 Forces represented on flange Slip on flange. without hub , The initial bolt load generated upon tightening is transferred to the gasket via the flanges This initial seating stress. compresses the gasket and tightens it within itself The hydrostatic force generated by the system pressure tends to. unload and reduce the stress on the gasket The stress remaining on the gasket is considered to be the operating or. residual stress It should be seen that on a raised face assembly as shown in figure 1 there will be some deflection. of the flanges themselves flange rotation This is a function of the load applied the flange material and the geometry. of the flanges Thus the operational stress towards the outside edge of the gasket tends to be greater than on the inside. The calculations use four loads bolt loads gasket load face pressure load and hydrostatic end force represented in. figure 2 and two conditions seating and operating 11 Load HD is created by the pressure on the pipe attached to the. flange During operation Pressure is applied to the exposed edge of the gasket and gasket tries to expand but is held. in place by the flange faces The flange faces push back and gives rise to uniformly varying pressure along gasket. width whose average value is represented by load HT Load HG is the force required to seat the gasket into the flange. gasket face which is based on gasket physical properties . 3 2 Methods for Non Standard Flange Design, As per the literature survey the different methods which can be used for non standard flange design either obround.
or rectangular are ,1162 www ijariie com 213, Vol 1 Issue 2 2015 IJARIIE ISSN O 2395 4396. 1 As per Swedish standard for piping, 2 Equivalent circular flange method. 3 Frame bending method, 4 Hydraulic diameter method. These methods either convert the non circular shape into circular shape and then we can design that circular flange or. considers the change in shape into various formulae in design process for designing flange to be safe . 1 As per Swedish standard for piping 15 , In the Swedish piping code for flange joint the design procedure of rectangular oval and obround flange is. given by converting these shapes into equivalent circular shapes This method uses the factor k4 multiplied with. the maximum mean gasket diameter Dm1 to get equivalent mean gasket diameter D m. D m k 4 Dm1 a , 2 Equivalent circular flange method 1 10 11 .
The method for design of non circular pressure vessel flange is developed by Adolf E Blach 1 It covers the. design of obround and rectangular shaped flanges which comply with the ASME BPVC codes It has given two. methods of designing flange as per the shell construction The first method is for flange mounted on. unreinforced pressure vessels This method uses the part of the procedure used in the ASME code section VIII. div 1 article UG 34 for the design of non circular flat covers In the code a factor z is defined which relates a. flat cover of obround rectangular shape to a circular one The factor z is given by. z 3 4 DL, b , But factor z should not be larger than 2 5 and length to width ratio should be less than 2 is the requirement . The square root of this factor is used as a multiplier of the small side of the obround rectangular flange to. obtain an equivalent circular shape , B DS z c , Any obround or rectangular flange which satisfies the above criteria can then simply be designed or analysed. as an equivalent circular flange and all flange design code rules as per appendix 2 of the ASME BPVC section. VIII division 1 are applicable without modification . 3 Frame bending method 1 , The other method given by Adolf Blach is frame bending approach for non circular pressure vessel flanges . This method is applicable to the flanges with obround or rectangular shapes mounted on reinforced vessels . The method uses a combination of frame analysis for the ability of the flange to retain its shape and bending. of an infinitely long flanged section in a perpendicular plane with respect to the frame . In this case the flange must also act as a stiffener for the vessel side plates in addition to providing a tight seal. between components Thus such flanges have to resist frame bending stresses stresses which occur when a. frame is subjected to internal pressure These stresses cause deflections in a plane perpendicular to the vessel. axis In addition flanges also have to resist flange bending stresses in planes parallel to the axis of the vessel . stresses which occur when a flange is bolted up about the gasket or when internal pressure effects tend to open. up the bolted connection , 4 Hydraulic diameter method . This method uses the conversion of non standard shape into circular shape using the logic of hydraulic diameter . Hydraulic diameter is the commonly used term when handling flow in non circular tubes and channels Using. this term one can calculate many things in the same way as for a round tube This is given by. B d , This gives the equivalent inside diameter of flange which can be used in design calculations as per ASME.
BPVC section VIII appendix 2 ,3 3 Input Parameters for Design. The generator on which this obround flange is going to be mounted contains hot water on tube side and weak solution. of Li Br on shell side The working parameters needed for design of flange are as given in table I . 1162 www ijariie com 214, Vol 1 Issue 2 2015 IJARIIE ISSN O 2395 4396. Table 1 Input Parameters for Flange Design, Parameter Label Value Unit. Design Pressure P 1 054 MPa, Design temperature T 200 C. Corrosion allowance 1 5 mm, Vessel or nozzle wall thickness tn 16 mm.
Minimum inside diameter of shell DS 500 mm, Maximum inside diameter of shell DL 856 mm. Clearance between OD of shell and ID of flange c 1 mm. Flange thickness assumed t 70 mm, The existing circular flange outer diameter is 873 76mm which is needed to be replaced for height reduction The. bolting is selected as in 7 and its dimensions are taken from 17 which is given in table below Similarly for the. given operating parameters gasket is selected and which has following parameters required in design as specified in. table III , Table 2 Bolting Specifications 17 Table 3 Gasket Specifications 11 . Selected Bolt Parameters Selected Gasket Parameters. Parameter Label Value Unit Selected Gasket Spitman AF 154. Selected Bolting M30 Parameter Label Value Unit, Bolt diameter a 30 mm Gasket. Design of Obround Flange for Pressure Vessel Application by Analytical Method and FEA to Comply with ASME code Y P Shah1 M N Pradhan2 1 Research Scholar ME student Department of Mechanical Engineering Maharashtra Institute of Technology Pune Maharashtra India

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