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Research Papers: Materials and Fabrication

Assessment of Residual Stress Due to Overlay-Welded Cladding and Structural Integrity of a Reactor Pressure Vessel

[+] 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.

2Present address: Research Organization for Information Science & Technology, 2-4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received July 23, 2012; final manuscript received May 19, 2013; published online September 16, 2013. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 135(5), 051402 (Sep 16, 2013) (9 pages) Paper No: PVT-12-1103; doi: 10.1115/1.4024617 History: Received July 23, 2012; Revised May 19, 2013

In this study, the residual stresses generated within the overlay-welded cladding and base material of reactor pressure vessel (RPV) steel were measured for as-welded and postwelded heat-treated conditions using the sectioning and deep-hole-drilling (DHD) techniques. In addition, thermo–elastic–plastic creep analyses considering the phase transformation in the heat-affected zone using the finite element method (FEM) were performed to evaluate the weld residual stress produced by overlay-welding and postweld heat treatment (PWHT). By comparing the analytical results with the experimentally determined values, we found a good agreement for the residual stress distribution within the cladding and the base material. The tensile residual stress in the cladding is largely due to the difference in the thermal expansion of the cladding and the base material. It was also shown that considering phase transformation during welding was important for improving the accuracy of the weld residual stress analysis. Using the calculated residual stress distribution, we performed fracture mechanics analyses for a vessel model with a postulated flaw during pressurized thermal shock (PTS) events. The effect of the weld residual stress on the structural integrity of RPVs was evaluated through some case studies. The results indicated that consideration of the weld residual stress produced by overlay-welding and PWHT is important for assessing the structural integrity of RPVs.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Overlay-welded test plate specimen

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Fig. 2

Location for measurement by the sectioning and DHD techniques and schematic image of the sectioning technique

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Fig. 3

FEM analysis model for a cladded plate

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Fig. 4

FEM analysis model for RPV (vessel model)

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Fig. 5

Material properties

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Fig. 6

Through-thickness distribution of Vickers hardness near the cladding

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Fig. 7

Wide width double-ellipsoid model

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Fig. 8

Temperature history measured at 15 mm from the cladded surface, as determined experimentally and using FEM, and the molten pool shape from the FEM. (The gray region corresponds to the molten pool.)

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Fig. 9

Longitudinal and transverse residual stresses after cladding at the center of the cladded ESW specimen

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Fig. 10

Through-thickness distribution of the weld residual stress for the cladded ESW specimen

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Fig. 11

Relationship between the residual stress and phase transformation during welding

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Fig. 12

Longitudinal and transverse residual stresses after PWHT at the center of the cladded ESW specimen

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Fig. 13

Through-thickness distributions of the residual stress after PWHT for the cladded SAW and ESW specimens

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Fig. 16

SIFs at the deepest point of the postulated flaw as a function of the temperature during the SBLOCA

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Fig. 15

Through-thickness distributions for cases 1, 2, and 3 at 1950 s after the start of the SBLOCA

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Fig. 14

Through-thickness distributions in case 3 during the weld-overlay cladding process, PWHT, a hydrostatic test, and normal operation

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