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Research Papers: Design and Analysis

Welding Residual Stress in a Large Diameter Nuclear Reactor Pressure Vessel Nozzle

[+] Author and Article Information
Tao Zhang

e-mail: tzhang@emc-sq.com

Heqin Xu

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

Oscar Mazzantini

Nucleoelectrica Argentina S. A.,
Buenos Aires 2806, Argentina

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received March 21, 2012; final manuscript received October 20, 2012; published online March 18, 2013. Assoc. Editor: Somnath Chattopadhyay.

J. Pressure Vessel Technol 135(2), 021208 (Mar 18, 2013) (7 pages) Paper No: PVT-12-1032; doi: 10.1115/1.4007961 History: Received March 21, 2012; Revised October 20, 2012

The Atucha II nuclear power plant is a pressurized heavy water reactor (PHWR) being constructed in Argentina. The original plant was designed by Kraftwerk Union (KWU) in the 1970’s using the German methodology of break preclusion. The plant construction was halted for several decades, but a recent need for power was the driver for restarting the construction. Welding residual stresses in nuclear power plant piping can lead to cracking concerns later in the life of the plant, especially for stress-corrosion cracking. Hence, understanding the residual stress distribution from welding is important to evaluate the reliability of pipe and nozzle joints with welds. In this paper, a large-diameter reactor pressure vessel (RPV) hot-leg nozzle was analyzed. This is a nozzle from Atucha II nuclear power plant in Argentina. The main piping material is 20MnMoNi55 with Tenacito 65R weld metal, and inner diameter (ID) welded cladding at the girth weld locations is made of 309L. The special materials and weld geometry will lead interesting welding residual stress fields. In addition, postweld heat treatment (PWHT) of the girth welds and its boundary conditions could also play an important role in determining welding residual stress fields at the plant’s normal operating conditions. Sensitivity analyses were conducted and the technical observations and comments are provided.

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References

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Figures

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Fig. 1

Atucha II nozzle weld was modeled (a) overall model and (b) location of nozzle weld

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Fig. 2

Description of weld (a) metallographic section of the weld and (b) weld beads

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Fig. 3

True stress versus plastic strain curves for the 20MnMoNi55 base metal

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Fig. 4

True stress versus plastic strain curves for the Tenacito 65R annealed weld metal with the same microstructure as the final as-deposited weld with PWHT

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Fig. 5

Overall finite element model of the girth weld at a nozzle (a) and illustration of the various weld passes (b)

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Fig. 6

Axial stresses prior to PWHT for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained) constrainted) and (b) only the nozzle end is constrained

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Fig. 7

Hoop stresses prior to PWHT for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained)

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Fig. 8

Axial stresses after PWHT for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained)

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Fig. 9

Hoop stresses after PWHT for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained)

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Fig. 10

Selected PWHT region

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Fig. 11

Axial stresses after PWHT with selected region for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained)

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Fig. 12

Hoop stresses after PWHT with selected region for different boundary conditions (a) both ends of the pipe in the FE model are fixed (constrained) and (b) only the nozzle end of the FE model is fixed (constrained)

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Fig. 13

Applied PWHT region through sensitivity study

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Fig. 14

Applied temperature history and temperature history at the measured location (200 mm away from the weld centerline)

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Fig. 15

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

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Fig. 16

Hoop stress comparison (a) before PWHT (b) after PWHT

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Fig. 17

Path definition for line plots

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Fig. 18

Axial stress comparison through weld center

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Fig. 19

Hoop stress comparison through weld center

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Fig. 20

Axial stress comparison along ID

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Fig. 21

Hoop stress comparison along OD

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