Comparative Stress Analysis of Gasketed and Non- Gasketed Flange Joints under Preloading Condition-FEA Approach

Exploring the efficiency and environmental impact of supercritical coal-fired power plants

by Sanjay S. J.*, Dr. V. B. Math, E. Rakesh Sharma, Eraman Naik,

- Published in Journal of Advances in Science and Technology, E-ISSN: 2230-9659

Volume 12, Issue No. 25, Dec 2016, Pages 539 - 543 (5)

Published by: Ignited Minds Journals

ABSTRACT

Supercritical is a thermodynamic expression describing the state of a fluid above a certain pressure when there exists no clear distinction between the liquid and gaseous phases. The pressure at which such a transition to the supercritical state takes place is known as the critical pressure. For water this pressure is 22.064 Mpa. The corresponding saturation temperature is known as the critical temperature and for water it is 647.096 K. The term critical has been used for this thermodynamic state because it is a singularity in the fluid property states. Fluids below the supercritical pressure are termed as subcritical whereas those above the critical pressure are regarded as supercritical. Several modern plants operate at peak pressures of more than 24 Mpa and hence function as supercritical power plants. Supercritical coal fired power plants with efficiencies of around 45% have much lower emissions than subcritical plants for a given power output. Today’s state of the art in supercritical coal fired power plants permits efficiencies that exceed 45%, depending on cooling conditions. Options to increase efficiency above 50 % in ultra-supercritical power plants rely on elevated steam conditions as well as on improved process and component quality. Steam conditions up to 30 MPa/600°C/620°C are achieved using steels with 12 % chromium content. Pressures of up to 31.5 MPa/620°C/620°C have been proposed using Austenite, which is a proven, but expensive, material. Nickel-based alloys, e.g. Inconel, may permit 35 MPa/720°C/720°C, yielding efficiencies of nearly 50%.In order to improve coal-fired power plant efficiency leading to a proportional reduction in coal consumption and carbon dioxide emissions, it is widely accepted that the domestic power industry must move from sub critical to supercritical steam cycles. Medium to large capacity thermal power plants in India are now increasingly adopting the more efficient & bigger 660/800 MW supercritical units. Higher efficiency translates into reduced environmental impact. Less coal and water are used, smaller volumes of fly ash and scrubber waste is produced, and uncontrolled emissions of CO2 and mercury will be lowered.

KEYWORD

supercritical, gasketed flange joints, non-gasketed flange joints, preloading condition, FEA approach, coal-fired power plants, efficiency, steam cycles, environmental impact, coal consumption

INTRODUCTION

A pipe flange connection is an important part of a piping system. In Conventional gasket-flanged pipe joints are widely used in process industries for connecting pipes to pipes, and pipes to equipment‘s [1]. The pipe flanges can be available in different dimensions as per ASME specifications. Because of different loading conditions, especially high loads, bolted connections can separate. To minimize this effect, a pretension is applied to the bolt. This ensures that the connection will not separate, provided the applied load remains less than the pretension [1].

For the present study A Gasket and Non-Gasket flanged joint is used for Pre-loading conditions for the analysis of pre-stresses in the bolt and flange connections and results are compared, with change of flange geometry taper profile angle of 450 instead of flat faced flange geometry with variation of parameters like flange thickness, preloading conditions, Number of bolts.[1].

Analyzed the pre-stresses in bolts and flange during bolt-up conditions by change of flange geometry instead of flat face, considering as male and female

joint by varying profile taper angle, flange thickness, preload and number of bolts.[2]. Carried out experimental study on Gasketed flanged joint and verified the stress variation on flange and attached pipe during preloading and operating(Pressure)loading conditions.[3]. Analyzed the contact pressure distribution on sealing ring during bolt up and operating pressure conditions for 3‖ and 10‖ANSI RF flange tapered sealing ring with RF Gasket. Hydrostatic tests were carried out. [4]. Proposed the Modal analysis of Gasketed and Non-Gasketed Flange Joint with and without raised face under Bolt-Up conditions. Frequencies and Mode shapes of both joints were compared.[5].

Studied the behavior of flange and stress in bolts by varying the flange thickness, bolt preload and number of bolts by keeping flange dimensions constant, results obtained by ASME design approach were compared with analytically.

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Figure: 1. 2D Geometry of flange

A Common two dimensional geometry model for Gasket and Non-Gasket flange joint with nominal dimensions as per ASME boiler and pressure vessel code with change of profile taper angle is considered for stress analysis as shown in figure: 1.Analysis of three dimensional model flange joint require more space and time to solve the problem, hence 1/8th part of the model is used to study the whole behavior of flange joint as shown in figure: 2 and 3. A three dimensional model of flange joint is done using CAE software by using key points of two dimensional geometry.

Figure: 2. 1/8th part model of Flange joint (Gasketed) Figure: 3. 1/8th part model of Flange joint (Non-Gasketed) Figure: 4. Finite Element mesh for the flange joint (Gasketed) Figure: 5. Finite Element mesh for the flange joint (Non-Gasketed)

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Components of pipe flange joints are isotropic, elastic, and homogenous in nature different material properties of Gasket and Non-Gasket bolted flange are listed below in table: 1, 2 respectively as per ASTM standards and these properties are used for the finite element analysis. Table: 1. Material properties of Gasket flange joint Table: 2. Material properties of Non-Gasket flange joint

4. FINITE ELEMENT ANALYSIS AND MODEL

GEOMETRY:

A three dimensional finite element model has been developed for bolted joint connections with and without gaskets. For flange, bolts and Gaskets SOLID187 a higher order 3-D, 10-node element is used. Figure 4 show finite element mesh for the joint. The geometric three dimensional model can be done using any modeling software and meshing, definition of boundary conditions, preloading can be given using CAE package, in this study modeling, meshing, preloading, Boundary conditions is done using ANSYS11.0 APDL. For this model there is a contact between top of the flange and bottom of the bolt surface to predict the exact physical behavior, and Contact between male fitting and female weld neck is given for both joints and along with this there is a contact between flange and gasket for Gasketed joint as a 3D surface-to-surface CONTA174 and TARGE170 elements are used to simulate contact.

Fallowing boundary Conditions and loadings are used to perform Finite element analysis. The Pretension feature was used in ANSYS11.0.For this analysis, bolts were given a pre-load values in percentage like 30%, 35%, 40%, 45%, which are yield strength of the bolt material with variation of flange thickness, flange profile taper angles, and for number of bolts.

  • Symmetry conditions are applied on both sides of the bolt cross-sectional area, both sides of the flange ring, Gasket (Gasketed) and attached pipe.
  • A nominal preload i.e.35% of the yield strength of the bolt was chosen to perform stress analysis.

6. RESULTS AND DISCUSSION

Figure: 5 Y-Component of Stress Figure: 6 Y-Component of Stress

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Figure: 7 Y-Component of Stress

Figure: 5, 6, 7 Indicates the comparison of effect of Pre-stress by varying Preload and number of bolts for Gasket and Non-Gasket flange joint by keeping constant flange profile taper angle of 450and flange thickness of 45mm,Y direction of stress.

Figure: 8 Flange thickness of 45mm Figure: 9 Flange thicknesses of 55mm Figure: 10 Flange thicknesses of 65 mm

Figure: 8, 9 and 10: Stress distribution in Y-Component of stress for variation of flange thickness for 35% Preload and 450 taper angle. (Non-Gasketed with 8-Bolts)

Figure: 11 Effect of Pre-Stress by varying flange thickness and Number of bolts with 35% of Preload and 450 taper angle for Gasketed Joint. (Y-Component Stress)

7. CONCLUSIONS:

For present study a Gasketed and Non-Gasketed weld –neck flange is considered for comparative stress analysis with change of taper geometry and analysis is carried out, for different loading values for the bolt, as pretension. By, considering the Female weld neck and Male fitting there may a proper lock between the two parts of flanges and may protect from leakage due to gasket provided, for comparison the parameters like taper angle, flange thickness, Number of bolts and preload are varied.  Figure: 5, 6, 7 Indicates the comparison of effect of Pre-stress by varying Preload and number of bolts for Gasket and Non-Gasket

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geometry with gasket provision due to preloading the stresses in the bolt and flanges are higher as compared to Non-Gasketed flange.

  • Figure 8,9,10 stress distribution for flange thickness of 45mm, 55mm and 65mm which shows, as increase of flange thickness will increase the stresses in the flange and Bolt.
  • Figure: 11 stress distribution for flange thickness of 45mm, 55mm and 65mm which shows, as increase of flange thickness will decrease the stresses in the flange and Bolt.

8. REFERENCES:

S.J.Sanjay., E.Rakesh Sharma Eraman naik, “Stress Analysis of Non Gasket flange joint under Preloading conditions using FEA approach”, Proceedings of NCFME 2015, ISBN: 97-8-93-81195-82-6,National joint conference on innovations in engineering and technology(NJCIET2015),organized by Canara Engineering College, Mangalore on 29th April 2015. M.Abid, ―Stress Variation in the Flange of a Gasketed Flanged Pipe Joint during Bolt up and Operating Conditions‖, Scientia Iranica, Vol. 13 No. 3, pp 303-309, Sharif University of Technology, July -2006. Rajeev Madazhy., Sheril Mathews., Erik Howard, “Analysis of Contact Pressure Distribution on 3-Bolt Self-Energized Connector Seals‖, 2009 ASME Pressure Vessels and Piping Division Conference July 26-30, 2009. Muhammad Abid., Shahid Maqsood., Hafiz Abdul Wajid, ―Modal Analysis of Gasketed and Non-gasketed Bolted Flanged Pipe Joints”, Hindawi Publishing Corporation Advances in Mechanical Engineering, Volume 2012, Article ID 413583. Vishwanath V.H., S.J. Sanajy, V.B. Math, ―The study of the behavior of Bolted flange with Gaskets‖, International Journal of Engineering Research & Technology, ISSN: 2278-0181, Vol. 2 Issue 7, (2013).

Corresponding Author Sanjay S. J.*

Lecturer Department of Mechanical Engineering, Jnanabharathi Polytechnic College, Kudlgi, Bellary