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Research Papers: Design and Analysis

The Effect of the Welding on the Residual Contact Stress in the Expanded Zone of Expanded-Welded Tube-to-Tubesheet Joints

[+] Author and Article Information
H. F. Wang, Z. F. Sang, G. E. O. Widera

 College of Mechanical and Power Engineering, Nanjing University of Technology, Nanjing 210009, P.R.C.Department of Mechanical Engineering,  Marquette University, Milwaukee, WI 53233

J. Pressure Vessel Technol 133(6), 061209 (Oct 31, 2011) (6 pages) doi:10.1115/1.4005252 History: Received April 19, 2011; Accepted October 01, 2011; Published October 31, 2011; Online October 31, 2011

The fabrication of stainless steel tube-to-tubesheet joints of heat exchangers consists of welding after hydraulic expansion. Here, this process is simulated by use of the finite element method, which is carried out in a sequentially decoupled analysis: the welding temperature field is solved by a transient thermal analysis, and subsequently, a nonlinear elastic plastic stress analysis is carried out. The effect of the unexpanded zone length with reference to the expanded zone of the joints is investigated. The results indicate that welding after the expansion will produce a shrinkage deformation in the tube end. This further reduces the magnitude of the contact stress in the expanded zone and moves it toward the tubesheet secondary surface. The percentage reductions of the contact stress and the contact area are introduced to quantitatively describe the effect of the welding on the expansion zone of the joint. The results show that these reductions decrease linearly with change in the unexpanded zone length, and that the effect of the welding on the contact stress in the expanded zone cannot be neglected. Therefore, a reduction of the influence of the welding on the structural integrity of tube-to-tubesheet joints should be taken into account when utilizing the technique of welding after hydraulic expansion.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Structure of expanded-welded joint

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Figure 2

Diagram of analysis procedure

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Figure 3

Finite element mesh: (a) tube, tubesheet, and weld bead (b) weld bead alone

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Figure 4

Typical temperature distribution of tube-to-tubesheet joint with two weld passes

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Figure 5

Typical temperature distribution in wall of the tube and tubesheet in section A-A

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Figure 6

Contact stress of tube-to-tubesheet joint made by welding after expanding: (a) under expansion pressure (b) releasing expansion pressure (c) after first weld pass (d) after second weld pass (e) cooling down to ambient temperature

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Figure 7

Contact stress of joint along tube axis (θ = 180 deg)

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Figure 8

Residual radial displacement of tube end

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Figure 9

Radial deformation of tube outside wall along tube axis (θ = 180 deg)

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Figure 10

Effect of unexpanded zone length LX on contact stress in expanded zone of expanded-welded tube-to-tubesheet joint

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