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30120130405016

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 139 DESIGN AND ANALYSIS OF SADDLE SUPPORT: A CASE STUDY IN VESSEL DESIGN AND CONSULTING INDUSTRY Pallavi J.Pudke1 , Dr. S.B. Rane2 , Mr. Yashwant T. Naik3 1 Post Graduation Student- Department of Mechanical Engineering, Sardar Patel College of Engineering, Mumbai 2 Associate Professor, Department of Mechanical Engineering, Sardar Patel College of Engineering, Mumbai 400058 3 Design Engineer, Process Equipment Division, Engineering Department, Zamil Industry, Dammam 31421, Kingdom of Saudi Arabia ABSTRACT In order to investigate the impact of different geometrical parameters like number of gussets, and gusset thickness, on the design of saddle support, the horizontal pressure vessel is designed and analyzed by Finite Element Method. The saddle support of the horizontal pressure vessel is designed as per Handbook of the Pressure Vessel by Megyesy. The solid model of pressure vessel with realistic details of two saddle supports is analyzed by using FEA software package ANSYS APDL. The purpose of this paper is to optimize the geometrical parameters of the saddle and to find whether saddle support can sustain the horizontal pressure vessel under loading conditions. We found 28 % reduction in material requirement which results reduction in costs. Keywords: ANSYS, APDL Technology, Finite Element Method, Pressure Vessel, Saddle Supports 1. INTRODUCTION Saddle supports are commonly used to support Horizontal pressure vessels. A Pressure vessel is a closed cylindrical vessel, widely used in process industry, power, oil and gas industries, and also for the storage of fluid or gaseous products. Pressure vessels are subjected to pressure loading i.e. internal or external operating pressure different from ambient pressure. The pressure vessels are of horizontal or vertical type. For horizontal vessel the saddle supporting system plays an important role in the performance of the equipment. A proper saddle supporting system improves safety and facilitate to operate the pressure vessel at higher pressure conditions which finally leads to higher efficiency. The optimized designs parameters reduce the material cost. INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 5, September - October (2013), pp. 139-149 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 140 2. LITERATURE SURVEY Generally, horizontal cylindrical pressure vessels are supported by two symmetrically placed saddle supports, which cause stresses in the pressure vessel in addition to the stresses generated by the internal pressure in the vessel [1]. More than two supports would result in static indeterminacy and cause difficulty in predicting the load distribution in the event of foundation settlement [2] . One saddle is fixed to the foundation, while the other saddle is free to move axially. This incorporates an element of axial flexibility and prevents induced stresses due to overall temperature variation. The presence of supports has two distinct effects on the vessel. Firstly it interferes with the normal expansion of the vessel due to internal pressure or temperature change; secondly the concentrated support reaction induces highly localized stresses in the support region[2].A rigid support will give rise to greater stress concentration compared to a flexible one. The main cause of stress concentration is the abrupt transition of structural rigidity between the support and the vessel [3].The saddle structure itself is stressed, as all forces acting on the vessel are ultimately transferred to the support. The saddle support will have subsidiary stress and the internal stress of the pressure vessel, So the design of the saddle support is critical when designing the horizontal type pressure vessel [4]. Therefore the design of the saddle and determination of the stresses induced in it are important steps during the design of horizontal pressure vessel. The semi-empirical method [5-8], is based on the beam theory. It has assumption that the vessel cross-section remains circular under loadto simplify the problem. However, Zick’s analysis is better judged on the performance it has demonstrated, since it was first published, and therefore, it is also the basis of saddle design guidelines given in pressure vessel design handbook by E.Megyesy. A parametric study is presented to determine the peak circumferential stress at the saddle support of an un-stiffened horizontal cylindrical vessel [9-10] Wilson and Tooth were the "first to study flexible saddle supports using the "Finite Element Method [11].They used cylindrical shell theory to model the pressure vessel and a two-dimensional "finite element program to simulate the flexible saddle. The solution of the shell problem was obtained using a Double Fourier Series Expansion.However, moreaccurate analyses, based on cylindrical shell theory, are available [12-14].El-Abbasi performed a 3D finite element analysis of a flexible and loose fitting saddle supported pressure vessels using a newly developed finite element that accounts for the contact stresses between the vessel and the saddle supports. They concluded that a saddle radius 1-2 % larger than that of the vessel leads to a 50% reduction in the stresses and an overhang of 5-10% leads to25 – 40 % reduction. Widera also performed 3D FEA with welded support[15-16].Nash and Banks [17-18] used a standard penalty based approach to account for contact effects in sling-supported composite pressure vessels. Their solution was highly sensitive to the choice of the user-defined penalty parameter. A more accurate contact formulation was presented by Bisbos et al. [19] for horizontal pipes loosely resting on saddle supports. The unilateral contact conditions and Coulomb's friction law were used to formulate two linear complementary problems in the normal and tangential directions. Finite element analysis of Pressure vessel by David Heckman [23] also advocates the use of computer programs instead of hand calculations for analyzing the high stress areas and different end connections, Ong LS has also given a computer program for cylindrical shell analysis[24]. Ong and Lu[20] determined the optimal radius of the support with a preliminary clearance between the vessel and saddle. In the area of the vessel–saddle contact they assumed a constant distribution of the contact pressure along the vessel, but varying circumferentially. They performed a parametric analysis aimed at reducing the stress concentration at the saddle horn. Tooth analytically and experimentally determined the stresses in real supports of multilayered GRP vessel Banks presented the approximate solutionof the strain state. [21-22].Boutros discussed the results of parametric analysis of deformable saddle supports of circular cylindrical vessels of large diameter.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 141 He indicated the influence of proportions between vessel dimensions and support locations of the stresses occurring in the structure [25-26]. Therefore we have identified the following research gaps. 1. The stress analysis of saddle support by varying the gusset thickness is the area of research attention. 2. The stress analysis of saddle support by varying the number of gusset is theanother area of research attention. 3. The solid modeling is done in ANSYS Parametric Design Language for Analysis of saddle support. Therefore we have formulated the following problem statement taking into consideration the standard nomenclature. 3. NOMENCLATURE AS PER MEGYESY DESIGN CODE Q = Load on one saddle. R = Radius of shell ts = Wall thickness of shell th = Wall thickness of head. K = Constant values Ѳ = Constant angle of saddle degree R = Radius of the pressure vessel A = The distance from the tangent line to the saddle centre. H = The distance from the tangent line to the end of the head. L = The length from tangent to tangent line of pressure vessel. b = Width of saddle. P = Design pressure T = Design temperature Ww = Width of wear plate Wb = Web plate thickness F = Force Tw = Wear plate thickness 4. DEVELOPMENT OF PROBLEM STATEMENT 4.1 Material Properties Material used for shell and head, SA 516 Gr.70, maximum allowable stress value=133.6 N/mm². Material used for saddle support parts, SA 283 C, Maximum Allowable stress value = 105.2 N/mm². 4.2 Assumptions: The wall thickness of shell is assumed to be constant everywhere. 4.3 A sketch of the vessel is shown in Fig. 1.
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 142 Fig1. Pressure vessel and saddle structure 4.4. Geometric Parameters Table 1. Input data Inputs Geometry Parameters Values Geometric Shell Thickness 25 mm Shell Radius 2900 mm Shell Length 37350 mm Wear Plate Width 850 mm Base Plate Length 4000 mm Head Thickness 25 mm Wear Plate (Pad) Thickness 25 mm Contact Angle 160 ˚ Gusset Thickness 25 mm Material Saddle SA 283 C Heads SA 516 Gr.7 Shell SA 516 Gr.70 Loading Input Load On One Saddle 6012549 N Design Temp (Int.) 315° C Design Pressure (Int) 3.5 Kg/cm² Problem statement: To design and optimize the saddle support by using ANSYS APDL technology for above said horizontal pressure vessel resting on two saddle support where one is fixed and another is flexible for above said material and parameters for above said boundary conditions. 5. FINITE ELEMENT ANALYSIS FEA is now an extremely sophisticated tool for solving numerous engineering problems and is widely accepted in many branches of industry. It is a numerical technique for finding approximate solutions to boundary value problems. Finite Element Analysis is used to solve numerically the governing equations for stress within the wall material. The solutions provide a complete stress distribution in the saddle supports.
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 143 5.1 Finite Element Model It operates under the circumstances of ANSYS APDL Technology. We created the complete solid models of the pressure vessel and saddle support. The pressure vessel is filled with liquid and is subjected to the operating weight. Map meshing is done to the complete solid model. The scope of analysis is limited to study the stresses for saddle support region under defined loading conditions. Appropriate extents of support saddles located at sliding and fixed side are considered for application of displacement boundary condition. Fig.2. FEA model of Pressure Vessel on Saddle Support 5.2 Boundary Conditions The boundary conditions of the sliding support are free and constrained. The movements of saddle in Z-axis directions are not constrained:Uz≠0. The other movements of saddle are fixed: Uy = Ux = 0 While the boundary conditions of the fixed support are fixed. The movements around the three axes are constrained : Ux = Uy = Uz = 0 Fig. 3. FEA model with Boundary Conditions applied
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 144 5.3 Mesh Sensitivity Analysis A mesh sensitivity analysis is performed on the FEA model of pressure vessel on saddle support, to ensure the optimum mesh size for proper convergence and accurate numerical results. The value of maximum Von Mises stress occurring in the structure is used as a convergence criterion. The figure 4. shows that from the element number 2136061 the mesh become precise. It also shows that as the number of element reaches 2626264, themeshing in the model of pressure vessel on saddle support receives enough sensitivity. Fig. 4. Graph of Mesh Sensitive Analysis Fig.5. Meshed model of Saddle Support 6. RESULTS AND DISCUSSION 6.1 FEA Results In this section, the results gave a detailed distribution of local stresses in the saddle support area.It is seen that the maximum stress is located near the horn of the saddle. The effects of different design parameters on the stress values are investigated. The Reinforcement Pad [RF] width and thickness has been kept constant as they are suitable for large vessel.
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 145 Fig. 6. Stress pattern of saddle support Figure 6. illustrates the Stress pattern of saddle support which shows the location of maximum and minimum stress in saddle. Fig. 7. Impact of no. of gussets for saddle on primary stress The Figure 7 shows the effect of number of gussets on the value of primary stresses obtained from the analysis results. From the graph it is understood that for 18 mm gusset thickness with 6 gussets, the obtained Primary stress result value falls below the Primary stress limit. So design is safe.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 146 Fig.8. Variation of primary stress values and secondary stress values for gusset thickness The Figure 8. shows the variation of primary stress values and the secondary stress values with respect to gusset thickness obtained from the analysis results. Primary and Secondary ASME allowable values are plotted to check the design. From the graph it is seen that the obtained secondary stress values falls below the Secondary stress limit for the gusset thickness of 18 mm and for 10 gussets. 6.2 FEA and Megyesy Stress Results Table 2 Table 2: shows the stress results obtained by the FEA method and design calculations by MEGYESY.
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 147 Fig. 9. Graphical presentation of FEA and MEGESSY results The stress results obtained in the Megessy are the average stresses acting on the area of the Gusset plate in (N/mm²). From the results of design calculations and analysis it is observed that analysis results are closed to that design value which is acceptable. 7. CONCLUSION The empirical approach corresponds to design by rule and finite element analysis corresponds to design by analysis method are adopted and calculations were made according to Megyesy, (Pressure Vessel Handbook).The stress distribution of various geometric parameters of gussets and number of gussets of saddle is observed to select the optimal size of saddle. This shows that the design by analysis is the most desirable method to evaluate and predict the behaviour ofdifferent configurations of saddle supports. The comparison of these results helps to provide the most optimized design with an ability to meet the requirements. After analysing the stress behaviour of the pressure vessel with different geometrical parameters of saddle supports, it is concluded that the saddle support of given Horizontal pressure vessel is safe according to the both the results. The stress values obtain by empirical method and analysis stresses are below allowable limits which is acceptable. The recommended gusset thickness was 25mm in industry whereas the optimal value is 18mm. Therefore 28 % of thickness reduction of the gusset is achieved, which leads to saving material and cost associated with it.
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 148 8. REFERENCES Journal Papers [1] ShafiqueM.A.Khan, Stress distributions in a horizontal pressure vessel and the saddle supports, Int. J. Pres. Ves. & Piping, Vol 87 March(2010). pp 239-244. [2] Ong Lin Seng, Analysis of Twin-Saddle-Supported vessel subjected to Non-symmetric loadings, Int. J. Pres. Ves. & Piping ,Vol.35 March (1988).pp423-427. [3] L. S. Ongand G.Lu ,Stress reduction factor associated with saddle support with extended top plate ,Int. J. Pres. Ves. & Piping, Vol.62 March (1994).pp 205-208. [4] RenHaidong, PengErbao ,A Study on the stress distribution of the pressure vessel and saddle support, International Conference on Electronic & Mechanical Engineering and Information Technology, 2011. [5] ZICK L. P., Stresses in large horizontal cylindrical pressure vessels on two saddle supports , The Welding Journals Research Supplement ,September,( 1951). [6] L. P. Zick, Stresses in large horizontal cylindrical pressure vessels on two saddle supports, Welding Journal Research Supplement, 1971. [7] Zick LP.Stresses in large cylindrical vessels on two saddle supports, Pressure Vessel and Piping: Design and Analysis - A Decade of Progress, Vol. 2, 1985. New York: ASME, p. 959-70. [8] L. P. Zick and C. E. Carlson., Strain gage technique employed in studying propane tank stresses under service conditions, Steel. 86-88. April 12 (1948). [9] Lin Seng Ong, Parametric study of peak circumferential stress at the saddle support, Int. J. Pres.Ves. & Piping, Volume 48, Issue 2, 1991, Pages 183-207. [10] L.S. Ong ,J.S.T. Cheung ,H.W. Ng , A.S. Tooth, Parametric equations for maximum stresses in cylindrical vessels subjected to thermal expansion loading , Int. J. Pres.Ves. & Piping, Volume 75, Issue 3, March1998, Pages 255-262. [11] Wilson JD, Tooth AS., The support of unstiffened cylindrical vessels. Second International Conference on Pressure Vessel Technology, San Antonio, TX, 1973.p. 67-83. [12] Ong Lin Seng, Effectiveness of wear plate at the saddle support. Journal of Pressure Vessel Technology 1992;114:12-8 [13] Duthie G, White GC, Tooth AS., An analysis of cylindrical vessels under local loading - Application to saddle supported vessel problems. Journal of Strain Analysis Engine Design 1982;17:157-67. [14] G. Duthie and A. S. Tooth, The analysis of a horizontal cylindrical vessel supported by saddle welded to the vessel, The International Conference on Pressure Vessel Technology, Part I, Design and Analysis. Tokyo, Japan, (1977). [15] N. El-Abbasi, S.A. Meguid, and A. Czekanski, Three-dimensional finite element analysis of saddle supported pressure vessels, Int. J. of Mechanical Sciences, February Vol.43(2001). pp 1229-1242. [16] G. E. 0. Widera, Z. F. Sang and R. Natarajan. , On the design of a horizontal pressure vessel ",J. Pressure VesselTechnol., Trans. ASME 110, 393 (1988). [17] D.H. Nash, W.M. Banks, F. Bernaudon, Finite element modelling of sling-supported pressure vessels , Int. J. Pres.Ves. & Piping , Volume 30, Issue 1-4,June1998,Pages 95-110. [18] Nash DH, Banks WM. Numerical analysis of a sling support arrangement for GRP composite pressure vessels. Composite Structures 1997;38:679-87. [19] Bisbos CD, Thomopoulos K, Tzaferopoulos M.Computing the frictional contact loads of horizontal steel pipes, loosely resting on saddles. Internal Journal of Pressure Vessel Piping 1994;58:75-85
  11. 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 149 [20] Ong LS, Lu G. Optimal support radius of loose-fitting saddle support. International Journal of Pressure Vessel Piping 1993;54:465-79. [21] Tooth AS, Banks WM, Seah CP, Tolson BA, The twin-saddle support of horizontal multi- layered GRP vessels-theoretical analysis, experimental work and a design approach. Proc. Inst Mech Engng 1994;208:59-74. [22] Banks WM, Nash DH , Flaherty AE, Fok WC , Tooth AS, The derivation of a best fit equation for maximum strains in a GRP vessel supported on twin saddles. Proc Ninth Int Conf Pressure Vessel Technol, Sydney 2000 ;1:109-19. [23] Heckman David,Finite Element Analysis of Pressure Vessels, Monterey Bay Aquarium Research Institute, University of California, 1998, 1-7. [24] Ong, L.S., A computer program for cylindrical shell analysis, Int. J. Pres.Ves. & Piping, 30(1987),131-49 [25] Y.A. Boutros,Flexible saddle support for large diameter cylindrical vessels, Proc Ninth Int Conf Pressure Vessel Technol, Sydney, 1 (2000), pp. 91–98. [26] K. Magnucki, W. Szyc ,Stasiewicz P., Flexible saddle support of horizontal pressure vessel, Int. J. Pres.Ves. & Piping, 80(2003), 205-210. [27] Kalpesh D. Shirode, Dr. S. B. Rane and Mr. Yashwant Naik, “Comparison of Design and Analysis of Tube Sheet Thickness by using UHX Code of ASME and TEMA Standard”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 4, 2013, pp. 105 - 117, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. Books: [28] Eugene F. Megyesy, Pressure Vessel Handbook, Pressure Vessel Publishing Inc., 10 Edition, 1997.

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