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Research Papers: Design and Analysis

Weld Residual Stress in Various Large Diameter Nuclear Nozzles

[+] Author and Article Information
Tao Zhang

e-mail: tzhang@emc-sq.com

Gery Wilkowski

Engineering Mechanics
Corporation of Columbus,
3518 Riverside Drive - Suite 202,
Columbus, OH 43221

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 18, 2011; final manuscript received April 28, 2012; published online November 21, 2012. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 134(6), 061214 (Nov 21, 2012) (9 pages) doi:10.1115/1.4007036 History: Received August 18, 2011; Revised April 28, 2012

Weld residual stresses in nuclear power plants can lead to cracking concerns caused by stress corrosion. Many factors can lead to the development of the weld residual stresses, and the distributions of the stress through the wall thickness can vary markedly depending on the weld processing parameters, nozzle and pipe geometries, among other factors. Hence, understanding the residual stress distribution is important in order to evaluate the reliability of pipe and nozzle welded joints. This paper represents an examination of the weld residual stress distributions which occur in different nozzles. The geometries considered here are large diameter thick wall pipe and nozzles. The detailed weld residual stress predictions for these nozzles are summarized. These results are categorized and organized in this paper and general trends for the causes of the distributions are established. The solutions are obtained using several different constitutive models including kinematic hardening, isotropic hardening, and mixed hardening model. Necessary fabrication procedures such as weld repair, overlay, and postweld heat treatment are also considered. The residual stress field can therefore be used to perform a crack growth and instability analysis. Some general discussions and comments are given in the paper.

Copyright © 2012 by ASME
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References

Figures

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Fig. 1

RPV nozzle with weld overlay repair dimensions (unit: inch)

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Fig. 2

Finite element mesh (a) overall mesh; (b) magnified view

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Fig. 3

Axial stress contour plots (a) isotropic; (b) mix; (c) nonlinear kinematic hardening rules

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Fig. 4

Hoop stress contour plots (a) isotropic; (b) mix; (c) nonlinear kinematic hardening rules

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Fig. 5

Axial stress at room temperature comparison for different hardening rules

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Fig. 6

Hoop stress at room temperature comparison for different hardening rules

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Fig. 7

Axial stress development after repair, SS weld, and weld overlay

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Fig. 8

Hoop stress development after repair, SS weld, and weld overlay

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Fig. 9

Axial stress comparison for different hardening rules and measurements before weld overlay

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Fig. 10

Hoop stress comparison for different hardening rules and measurements before weld overlay

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Fig. 11

Axial stress comparison for different hardening rules and measurements after weld overlay

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Fig. 12

Hoop stress comparison for different hardening rules and measurements after weld overlay

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Fig. 13

Key dimensions of steam generator (unit: millimeter)

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Fig. 14

Developed steam generator finite element mesh

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Fig. 15

Weld axial residual stresses in steam generator–hot leg nozzle DMW at room temperature with no service stresses applied (using nonlinear-kinematic hardening)

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Fig. 16

Weld hoop residual stresses in steam generator–hot leg nozzle DMW (using nonlinear-kinematic hardening) at room temperature with no service stresses applied

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Fig. 17

Operation weld residual stresses for steam generator–hot leg nozzle at 325 °C. (Comparison of nonlinear-kinematic hardening and isotropic hardening)

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Fig. 18

Axial stress plots along weld center for SG nozzle (nonlinear kinematic hardening case)

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Fig. 19

Hoop stress plots along weld center for SG nozzle (nonlinear kinematic hardening case)

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Fig. 20

Axial stress plots along weld center for SG nozzle (isotropic hardening case)

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Fig. 21

Hoop stress plots along weld center for SG nozzle (isotropic hardening case)

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Fig. 22

Metallographic section of the weld (a) and weld beads (b)

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Fig. 23

Overall finite element of the model (a) and weld passes (b)

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Fig. 24

Postweld heat treatment history

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Fig. 25

Axial stress comparison (a) before PWHT and (b) after PWHT

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Fig. 26

Hoop stresses comparison (a) before PWHT and (b) after PWHT

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Fig. 27

Path definition for line plots

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Fig. 28

Axial (a) and Hoop (b) stress comparison through weld center

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