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Research Papers: Materials and Fabrication

Effect of Partial Welding on the Residual Stress and Structural Integrity of Piping Welds

[+] Author and Article Information
Kunio Onizawa

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

1Present address: Mizuho Information & Research Institute, Inc., 2-3 Nishiki-cho, Kanda, Chiyoda-ku, Tokyo 101-8443, Japan.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received September 20, 2012; final manuscript received June 11, 2013; published online October 10, 2013. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 135(6), 061403 (Oct 10, 2013) (8 pages) Paper No: PVT-12-1149; doi: 10.1115/1.4025087 History: Received September 20, 2012; Revised June 11, 2013

When weld defects are observed during an inspection after welding, repair welding is performed after removing the defects. However, partial repair welding can potentially complicate the weld residual stress distribution. In this study, we performed thermal-elastic-plastic analyses to evaluate the weld residual stress produced by repair welding after pipe butt-welding. The analysis results were validated through comparison with actual measurements. In addition, based on the analysis results for varying repair-welding conditions, we also performed structural integrity assessments related to stress corrosion cracking using the probabilistic fracture mechanics analysis code pascal-sp. It was clearly observed that the tensile stress in the repair-welded region increased and that compressive stresses occurred outside the repair-welded region. A deeper mechanical cutting depth caused larger increases in the tensile residual stress of the repair-welded region. It was also concluded that partial repair welding may favorably affect the break probability of piping welds.

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References

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Figures

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Fig. 1

Groove shape of the produced specimen and three-dimensional FEM model

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Fig. 2

Sequence of the repair-welding simulation

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Fig. 4

Evaluation flowchart of the PASCAL-SP code

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Fig. 5

Example of the division of the calculation area for considering the inhomogeneous distribution of the weld residual stress in the circumferential direction

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Fig. 6

Axial residual stress at the inner and outer surfaces for the as-welded condition

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Fig. 7

Comparison of the axial residual stress distribution between the FEM analysis and the experimental data for the RW01 specimen

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Fig. 8

Contour maps of the axial residual stress at the inner and outer surfaces and at the welding center cross section for the RW01 specimen

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Fig. 9

Comparison of the through-thickness distribution of the axial residual stress at the 180-deg position for three repair-welded and butt-welded conditions

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Fig. 10

Effect of the cutting depth on ΔRSmax at the inner surface caused by repair welding

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Fig. 11

Effect of the welding length on Linc at the inner surface caused by repair welding

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Fig. 12

Crack depth as a function of the operating time under several residual stresses resulting from butt- and repair-welding

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Fig. 13

Axial residual stress distribution at the welding center cross section for the RW02 specimen, and the area division necessary for considering the inhomogeneous distribution of the weld residual stress in the circumferential direction

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Fig. 14

Example of the through-thickness distribution of the average and standard deviations of the axial residual stress at the cross section nearest to the fusion zone for the RW02 specimen

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Fig. 15

Comparison of the conditional cumulative probability of a large leak or break in the piping for the as-welded and repair-welded conditions

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