Research Papers: Design and Analysis

Effect of Precompression on Thickness of Pipe During Bending

[+] Author and Article Information
A. V. Kale

Department of Mechanical Engineering, Yashwantrao Chavan College of Engineering, Hingna Road, Nagpur-441110, Indiakanil_1960@yahoo.com

H. T. Thorat

Department of Mechanical Engineering, Visvesaraya National Institute of Technology, Nagpur-440011, Indiahtthorat@yahoo.com

J. Pressure Vessel Technol 131(3), 031201 (Feb 04, 2009) (8 pages) doi:10.1115/1.3067036 History: Received December 11, 2007; Revised June 19, 2008; Published February 04, 2009

Straight pipes with a circular cross section are processed into smooth bends by various pipe bending techniques. After bending, the initial circular cross section is deformed with thickness change. These changes from ideal are normally referred to as “ovality” and “thinning.” Their influence on the subsequent behavior of curved pipes is not yet fully understood. The aim of this paper is to present a factual method to reduce thinning of the wall thickness of pipe during bending. A new mechanism is developed for bending of pipes. This mechanism has a provision of precompression (radial squeeze) of the pipe along the directrix of maximum deformation during bending. This is achieved by clamping the pipe using two parallel plates from top and bottom. In fact, the pipe is wrapped using two rollers—one from inside and one from outside in the horizontal plane—and two plates parallel to the horizontal plane—one from the top and one from the bottom. Experimentation is carried out on this mechanism, and thicknesses are measured at the grid points along the length of the pipe. From the experimental values of thicknesses on the tension and compression sides, dimensionless variations in wall thickness of various groups of pipes are computed for different precompression values. In order to represent the thickness at any point, a mathematical equation is derived. Analytical values of thickness variations on tension and compression sides are computed using this equation. Experimental and analytical results are compared, and its methodical approach is presented in this paper. Results show that precompression reduces thickness variation of the pipe after bending.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Gaps between form die and pipe diameter

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Figure 2

Proposed concept

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Figure 3

Rotary compression bender

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Figure 4

Assembly of mechanism

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Figure 5

Grid pattern on the pipe

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Figure 6

Thickness versus thickness change

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Figure 7

Effect of precompression on thickness change

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Figure 8

Experimental thickness change versus bend angle

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Figure 9

Coordinate system used in the analysis

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Figure 10

Thickness variation along the line on the surface parallel to the axis

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Figure 11

Effect of constant K3 on thickness variation

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Figure 12

Analytical thickness variations

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Figure 13

Comparisons of experimental and analytical thickness change



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