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STUDY AND EXPERIMENTAL ANALYSIS OF LINEAR AND NON LINEAR BEHAVIOUR OF
PIPE BEND WITH OVALITY
Balaji A#1
, Faheem Ashkar H#...
thickness divided by the nominal thickness of the pipe bend. The
percentage change in thinning and thickening is calculate...
Sm = Allowable Stress Value.
= Bend Factor (Rt/r2
)
Long Radius SCH40 Bend =613.54N-m
=1067.64N (108.8kg)
Short Radius SCH...
Figure 4.4 Isometric View of CREO Elements Model
Figure 4.5 Isometric View of the Setup
The bend section which is to be te...
Figure 5.1.5 Out of Plane bending model
Figure 5.1.6 Out of Plane bending (clockwise)
Figure 5.1.7 Stress Distribution of ...
Graph 6.1 Displacement Variations for Analysis Results
Graph 6.2 Displacement Variations for Experimental Results
Graph 6....
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Iaetsd study and experimental analysis of linear and non linear behaviour of

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Iaetsd study and experimental analysis of linear and non linear behaviour of

  1. 1. STUDY AND EXPERIMENTAL ANALYSIS OF LINEAR AND NON LINEAR BEHAVIOUR OF PIPE BEND WITH OVALITY Balaji A#1 , Faheem Ashkar H#2 , Jahir Hussain H#3 , Elamparithi R#4 #1 Assistant Professor #2, #3,#4 UG Scholars Department of Mechatronics Engineering, Kongu Engineering College Perundurai, Erode, Tamil Nadu, India-638052 1 bala2009mct@gmail.com 2 faheem.ashkar@gmail.com 3 iamjahirhussain@gmail.com 4 elamparithiramasamy@gmail.com Abstract— the present study performed a series of experiments using real-scale experimentation process to evaluate the effects of load variation with respect to ovality for various schedule numbers such as SCH 40 long radius, SCH 40 short radius and SCH 80 short radius bends with and without internal pressure. The experiments has been conducted at ambient temperature within elastic limit of the bend for under in-plane opening & in-plane closing bending moments and also out of plane clockwise & out of plane anticlockwise bending moments. The experiments included to calculate the displacement as well as percentage change in ovality in the intrados, crown and extrados regions of the bend. The displacement in the intrados and extrados region increased almost linearly with respect to load for both in- plane and out of plane bending moments. This allowable limit loads and ovality are suggested for different diameters of pipe bends and for different pipe material. This helps in avoiding rejection of pipes due to insufficient wall thickness. The mathematical results and software results are compared with experimental results to get the optimised output. Keywords: Pipe bends, Internal Pressure, In-plane and Out of plane bending moments. I INTRODUCTION Large pipelines and pipe networks are part of almost every industrial setup today. These are most commonly found in petroleum rigs, refineries, factories producing chemicals and pharmaceuticals, and in power plants. In these and other industrial applications, pipes are very often used to carry substances that, by virtue of their pressure, temperature, physical and chemical characteristics, can have serious negative effects on health, property and the environment, if released into the atmosphere. Examples of such substances include steam, oil and chlorine gas. Failure in a piping system could cause problems, like an unscheduled, and hence costly, plant shutdown for maintenance or even a catastrophe, like exposing the core of a nuclear reactor. Therefore, the integrity of pipes in industrial contexts is of paramount importance. This integrity relies heavily on the correctness of pipe design, which can only be achieved through a thorough understanding of the behavior of piping components and systems under different types of loads. II Equations used for calculating basic parameters The ovality of a bend section is shown in figure 1.1. The minimum required wall thickness at the pipe bend during the bending process does not produce a difference between the maximum and minimum diameters greater than 8 % for internal pressure service and 3 % for external pressure service (Engineering Design and Analysis Ltd.,). The center line radius of pipe bends should typically be a minimum of 3 times the nominal pipe diameter. The codes have certain requirements for the acceptability of finished bends. It depends upon the following parameters i. Thinning and Thickening. ii. Ovality. iii. Buckling. Figure 1.1Bend Ovality A Thinning and Thickening In every bending operation the outer portion of the bend stretched and the inner portion compressed. This leads to thinning at the extrados and a thickening at the intrados of the pipe bend. The thinning is defined as the ratio of the difference between the nominal thickness and the minimum thickness to the nominal thickness of the pipe bend. The thickening is defined as the difference between the maximum thickness and the nominal INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 64 ISBN: 378-26-138420-01
  2. 2. thickness divided by the nominal thickness of the pipe bend. The percentage change in thinning and thickening is calculated by using the formula as shown in the equation 2.1 and 2.2 (Veerappan A and Shanmugam S, 2012). Because of uncertainties introduced by the pipe-manufacturing method, it is not possible to exactly predetermine the degree of thinning. ------- (2.1) ------- (2.2) Where, Tnom =Nominal Thickness of the Bend (mm). Tmax =Maximum Thickness of the Bend (mm). Tmin =Minimum Thickness of the Bend (mm). B Ovality During the bending operation the cross section of the bend assumes to be an oval shape whose major axis is perpendicular to the plane of bend. The degree of ovality is determined by the difference between the major and minor axes divided by the nominal diameter of the pipe. When the bend is subjected to internal pressure, it tries to reround the cross section by creating secondary stress in hoop direction. The percentage change in ovality is calculated using the equation 2.3 (Veerappan A and Shanmugam S, 2012). -------- (2.3) Where, Dmax =Maximum Outside Diameter of the Bend (mm). Dmin =Minimum Outside Diameter of the Bend (mm). Dnom =Nominal Outside Diameter of the Bend (mm). III STANDARD PARAMETERS The specification such as bend dimensions and chemical compositions of the bend section were taken from ASME B36.10 catalogue for 1inch diameter bend. The bends are classified into the following categories. 1) SCH40 (Wall Thickness-3.4mm) 2) SCH80 (Wall Thickness-4.5mm) 3) SCH160 (Wall Thickness-6.4mm) The outer diameter of the bend is kept constant and the bore size will be varied according to the schedule number of bend. In schedule number itself the bends are classified into two categories. 1) Long Radius Bend. 2) Short Radius Bend. In our investigation three types of specimens has been used according their availability. 1) SCH40 – Long Radius Bend. 2) SCH40 – Short Radius Bend. 3) SCH80 – Short Radius Bend In each section a straight pipe of six inch length has been attached at the both side of the bend section. The standard parameters and chemical composition of the pipe is given in the table 3.1 and 3.2 which is taken from ASME B36.10 and ASTM A106 Grade B catalogue. Table 3.1 Standard Parameters Description Parameters Pipe Standard ASTM 106 Grade B Schedule Number (SCH) 40 and 80 Pipe Size 25 mm Outside Diameter (D) 33.4 mm Inside Diameter 26.6 mm and 24.4mm Wall Thickness (t) 3.4 mm and 4.5mm Tensile Strength(min) 413MPa Yield Strength(min) 241MPa Table 3.2 Chemical Compositions Composition Percentage Carbon(max) 0.30 Manganese 0.29 to 1.06 Phosphorous(max) 0.025 Sulfur(max) 0.025 Silicon(min) 0.10 IV EXPERIMENTATION SETUP ` The diagrammatical model of the experimentation setup is shown in figure 4.1 for testing the elbow under in-plane bending mode. One end of the pipe end is clamped at the ground and other end is kept free for applying the in-plane moment load. A long rod is attached at the end of the free end for applying the in-plane load easily. The length of the straight pipe EB and GH is equal to six times the diameter of the bend section. In-plane bending mode can be created when the load applied in vertical direction on the beam BA. When the load applied in vertically upward direction, the bend section is subjected to in-plane opening mode and vertically downward direction, the bend section is subjected to in-plane closing mode. And out-of-plane bending mode is created by applying the load in horizontal direction on the beam. Spring balance and load cell is used to measure the magnitude of the applying load which is placed at the free end of the rod. Dial gauges are used to measure the deflection in the bend section by fixing it in the intrados, crown and extrados regions. The maximum elastic bending moment that can be applied in the test specimen is calculated by using the formula given below which is taken from ASME BPVC, Section III is shown in the equation 4.1. Figure 4.1 Diagrammatical Model of Set-up [Karmanos et al.] Maximum bending moment (Mi (max)) = ------ (4.1) Where, z = Section Modulus. INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 65 ISBN: 378-26-138420-01
  3. 3. Sm = Allowable Stress Value. = Bend Factor (Rt/r2 ) Long Radius SCH40 Bend =613.54N-m =1067.64N (108.8kg) Short Radius SCH40 Bend =468.25.1N-m =814.91N (83.09kg) Short Radius SCH80 Bend =675.40N-m =1175.43N (119.81kg) The Pro/E model and photographic view of the setup is shown in the figure 4.1 and 4.2 which is shown in different views. By rotating the hand wheel the desired load is applied to the corresponding bend section. FRONT VIEW SIDE VIEW TOP VIEW Figure 4.2 CREO Elements Model SIDE VIEW FRONT VIEW TOP VIEW Figure 4.3 Photographic View of the Setup INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 66 ISBN: 378-26-138420-01
  4. 4. Figure 4.4 Isometric View of CREO Elements Model Figure 4.5 Isometric View of the Setup The bend section which is to be tested is fixed in the base frame. One end of the long rod is attached to the bend section and other side of the rod is clamped in the plate which moves up and down for applying the in-plane bending modes. The movement of the plate can be attained by rotating the hand wheel. Spring balance is placed in the bottom of the vertical frame when the bend is subjected to in-plane opening mode and it is placed in the top of the vertical frame when the bend is subjected to in- plane closing mode. Two supports which are resting on the base frame for applying out of plane bending in clockwise and anticlockwise modes. Dial gauges are used to measure the deflection in the bend section by fixing it in the intrados, crown and extrados regions. During experimentation the load is applied in the incremented manner up to maximum bending moment that can be applied to bend section. For each mode three sets of reading has been taken and then it is averaged. In this experimental setup the readings are taken without any internal pressure like water, oil, steam etc. V RESULTS AND DISCUSSION V.I ANALYSIS RESULTS Using Finite Element Analysis (FEA) method, ansys 12.1 were performed with solid element type. The following values of material properties were used in present calculations E = 193 GPa, Poisson’s ratio of γ = 0.3 and the limiting stress of σ= 193 MPa. The FEA models were subjected to internal pressure, in-plane bending and out of plane bending mode. Internal pressures were applied as a distributed load to the inner surface of the FEA model. Figure 5.1.1 Cross Section of the Pipe bend with attached to straight pipe Figure 5.1.2 Pipe bend with attached to straight pipe Figure 5.1.3 In plane bending mode (closing) Figure 5.1.4 Stress Distribution of the pipe bend in In-plane bending mode (closing) INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 67 ISBN: 378-26-138420-01
  5. 5. Figure 5.1.5 Out of Plane bending model Figure 5.1.6 Out of Plane bending (clockwise) Figure 5.1.7 Stress Distribution of the pipe bend in Out of plane bending mode (clockwise) The same procedure was performed for in plane opening mode and out of plane anticlockwise mode and the graph was plotted for displacement and deflections. These values are compared with experimental setup values. V.II EXPERIMENTAL RESULTS A In plane Closing Bending Mode: The maximum displacements results in intrados, crown and extrados regions as well as the percentage change in ovality of the bend during Inplane Closing Bending Mode is shown in table. The readings are taken as five sets and the average values are shown in the following table. Table 5.2.1 Displacement and percentage change in ovality B Out of Plane Clockwise Mode: The maximum displacements results in intrados, crown and extrados regions as well as the percentage change in ovality of the bend during Out of Plane Clockwise mode is shown in table. The readings are taken as five sets and the average values are shown in the following table. Table 5.2.2 Displacement and percentage change in ovality The same procedure was performed for inplane opening mode and out of plane anticlockwise mode and the graph was plotted for displacement and deflections. VI GRAPHS AND DISCUSSIONS The displacement variation for analysis results were compared with experimental results, it shows the approximately same variation and percentage change in ovality for various schedule number of pipe bends are plotted as below. S. No Schedule Number Maximum Displacement (mm) Percentage change in Ovality Intrados Region Crown Region Extrados Region Zero Load (kg) Maximum Load (kg) 1 40-Long Radius 1.69 0.92 1.48 4.310 3.070 2 40-Short Radius 0.74 0.151 0.62 1.417 0.299 3 80-Short Radius 0.75 0.258 0.99 3.333 1.856 S. No Schedule Number Maximum Displacement (mm) Percentage change in Ovality Intrados Region Crown Region Extrados Region Zero Load (kg) Maximum Load (kg) 1 40-Long Radius 0.79 0.56 0.74 4.32 2.09 2 40-Short Radius 0.54 0.05 0.35 0.35 0.299 3 80-Short Radius 0.65 0.154 0.59 0.59 1.57 INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 68 ISBN: 378-26-138420-01
  6. 6. Graph 6.1 Displacement Variations for Analysis Results Graph 6.2 Displacement Variations for Experimental Results Graph 6.3 Percentage Change in Ovality for SCH 40 radius pipe bends in experimental values. VII CONCLUSIONS The experimental results and analytical results show inplane bending moment has more deflections compared to out of plane bending moment. Percentage variation in ovality during inplane closing mode and out of plane clockwise mode from zero to maximum loading is increased from schedule 40 long radius to schedule 40 short radius that is from 28.77 to 72.89 but decreased from schedule 40 short radius to schedule 80 short radius that is from 72.89 to 44.31 . For inplane opening mode and out of plane anticlockwise mode the percentage variation in ovality behaves the same manner as that of out of plane clockwise mode. The experimental results describe that maximum displacement occurs in the intrados region and hence the intrados region exhibit more flexible property than the extrados region. When the schedule number is increased rigidity of the bend material is increased as well as the percentage variation in ovality is also increased. The present work can be extended to include the effect of internal pressure on the pipe bend with in-plane and out of plane bending moment, temperature effects involved, material microstructure analysis to control geometrical irregularities due to ovality. The influence of initial ovality in pipe bends is considered to be one of the major factors in reducing the percentage ovality which demands analysis of the behavior to avoid geometrical irregularities. The temperature effects involved in the pipe bends while introducing internal pressure needs to be analyzed to find the exact reason for geometrical irregularities in pipe bends due to ovality. The material microstructure analysis can help to predict the behavior of various materials at elevated temperature and pressure to predict the grain size changes when loading is done on a pipe bend. VIII REFERNCES 1. Veerappan AR, Shanmugam.S and T.Christo Michael., ‘Effect of ovality and variable wall thickness on collapse loads in pipe bends subjected to in-plane bending closing moment’, Engineering Fracture mechanics, Vol.7, pp.138- 148,2012. 2. Veerappan A and Soundrapandian S., ‘The Accepting of Pipe Bends With Ovality and Thinning Using Finite Element Method’, Journal of Pressure Vessel Technology, Vol .132(3), pp.031204, 2010. 3. Chattopadhyay J., ‘The effect of internal pressure on in- plane collapse moment of elbows’, Nuclear Engineering and Design, Vol .212, pp.133- 144, 2002. 4. Weib E., 'Linear and nonlinear finite-element analyses of pipe bends', International Journal of Pressure Vessels and Piping, Vol .67(2), pp.211-217.1996. INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 INTERNATIONAL ASSOCIATION OF ENGINEERING & TECHNOLOGY FOR SKILL DEVELOPMENT www.iaetsd.in 69 ISBN: 378-26-138420-01

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