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Research Papers: Materials and Fabrication

Analytical Study of the Relaxation of Welding Residual Stress by Excessive Loading for Austenitic Stainless Steel Piping Welds

[+] Author and Article Information
Jinya Katsuyama, Kunio Onizawa

Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan

J. Pressure Vessel Technol 133(3), 031402 (Apr 01, 2011) (9 pages) doi:10.1115/1.4002260 History: Received January 25, 2010; Revised July 09, 2010; Published April 01, 2011; Online April 01, 2011

Welding residual stress is one of the most important factors of stress corrosion cracking (SCC) for austenitic stainless steels of the pressure boundary piping in nuclear power plants. For the assessment of the integrity of piping particularly for a long-term operation, it is necessary to understand the effect of excessive loading, such as an earthquake, on the residual stress. Three-dimensional finite element analyses were performed using three-dimensional model for a 250A pipe butt weld of low-carbon stainless steel of type 316L. The welding simulation method considering the moving heat source with the double ellipsoid model was confirmed by comparing with some experimental measurements. After conducting the welding simulation and residual stress analysis, several loading patterns of bending moment and axial displacements have been applied to the model by varying amount of moment and displacement in order to study the effect of excessive loading. The analyses indicated that higher loading of bending and axial stresses caused higher relaxation on welding residual stress near piping welds. The difference in the effect of loading direction was observed for both cases. It is concluded that excessive loading to piping butt-welds has an influence on the suppression of SCC growth due to the decrease in tensile residual stress at the inner surface.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Finite element models for welding residual stress simulation

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Figure 2

Material properties used for finite element analysis (12)

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Figure 3

Heat source model (13)

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Figure 4

Schematic image of loading condition against piping welded joint

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Figure 5

Relationship between bending angle and strain at the inner surface for 250A pipes

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Figure 6

Shape and modeling of crack and analysis method of crack growth

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Figure 7

Crack growth rate as a function of stress intensity factor provided by JSME code on FFS (15)

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Figure 8

Comparison of residual stress distribution between 3D analyses

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Figure 9

Change of axial stress distribution in parallel section to bending angle at several levels (case 1, at 180 deg)

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Figure 10

Change of axial stress distribution in perpendicular section to bending angle at several levels (case 1, at 90 deg)

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Figure 11

Comparison of circumferential distribution of axial stress at the inner surface after bending for case 1 (x=15 mm)

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Figure 12

Comparison of effect of prescribed bending on the relaxation of axial residual stress at the inner surface for cases 1–3

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Figure 13

Change of axial stress distribution for tension at several levels (case 1)

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Figure 14

Change of axial stress distribution for compression at several levels (case 2)

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Figure 15

Change of axial stress distribution for excessive loading at several levels (cases 1 2, x=15 mm, 180 deg)

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Figure 16

Change of axial stress distribution for excessive loading at several levels (cases 3 and 4, x=15 mm, 180 deg)

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Figure 17

Comparison of effect of excessive loading on the relaxation of axial residual stress at the inner surface for cases 1–4

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Figure 18

SCC growth behavior in the through-thickness direction under as-welded residual stress

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Figure 19

SCC growth behavior in the through-thickness direction under residual stress by welding and several levels of loading in Case 1. Initiation location of SCC is 180 deg from start-finish point.

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Figure 20

SCC growth behavior along the inner surface under residual stress by welding and several levels of loading in case 1. Initiation location of SCC is 180 deg from start-finish point.

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