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Research Papers: Materials and Fabrication

Effects of Initial Crack Location on Failure Assessment Curves in Dissimilar Metal Weld Joints in Nuclear Power Plants

[+] Author and Article Information
G. Z. Wang

e-mail address: gzwang@ecust.edu.cn

S. T. Tu

MOE Key Laboratory of Pressurized
System and Safety,
School of Mechanical and Power Engineering,
East China University of Science and Technology,
Shanghai 200237, China

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received November 7, 2011; final manuscript received March 24, 2012; published online October 18, 2012. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 134(6), 061405 (Oct 18, 2012) (7 pages) doi:10.1115/1.4006907 History: Received November 07, 2011; Revised March 24, 2012

Based on detailed three-dimensional finite element analyses, accurate, option 3, failure assessment curves (FACs) based on the R6 are constructed for a dissimilar metal weld joint (DMWJ) connecting the safe end to the pipe-nozzle of a reactor pressure vessel. The effects of initial crack location in the DMWJ structure on FACs are investigated. The results show that the plastic collapse of the DMWJ structure and the limit moment ML is mainly dominated by the plastic yield of the 316L material with lowest yield stress, and the crack locations in the DMWJ structure have less effect on the ML. When the load ratio Lr is less than 0.8, the crack locations have almost no effect on the FACs; while after the Lr is larger than 0.8, the crack locations have significant effect on the FACs. With the crack location moving from the safe end through the DMWJ toward the thickness transition in the pipe-nozzle, the FACs shift upward, which leads to a enlargement of the safe region in the failure assessment diagrams (FADs). This is mainly caused by the different properties of the materials in the DMWJ structure. To accurately assess the integrity of the DMWJ structure, the R6 option 3 FACs based on three-dimensional finite element analyses should be constructed and used for the cracks with different positions.

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Figures

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Fig. 1

Geometry and dimension for a typical pipe-nozzle of a reactor pressure vessel being connected to safe-end by the DMWJ (a) and the four materials (A, B, C, and D) and sizes composed of the DMWJ (b), A-ferritic steel A508, B-buttering Alloy 82, C-weld Alloy 182, D-austenitic stainless steel 316L

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Fig. 2

The true stress–strain curves of the four materials in the DMWJ at 340 °C

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Fig. 3

The meshes of the three-dimensional finite element model, (a) the whole structure, (b) dissimilar metal welded joint, and (c) the refined meshes around the crack tip

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Fig. 4

The crack locations in the structure of DMWJ

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Fig. 5

A typical failure assessment diagram

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Fig. 6

The limit moment ML calculated for the cracks with different locations

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Fig. 7

Distributions of the equivalent plastic strain PEEQ in the DMWJ pipe structure at the limit moment ML for the crack 1 in 316L (a), crack 4 in Alloy 182 (b), crack 6 in Alloy 82 (c), and crack 10 in A 508 (d)

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Fig. 8

The changes of the Je (a) and J (b) with increasing the external bending moment M for the cracks with different locations

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Fig. 9

Failure assessment curves of the 12 cracks at different locations in the DMWJ

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Fig. 10

Distributions of the equivalent plastic strain PEEQ in front of the crack tips for the typical crack 1(a), crack 4(b), crack 6(c), and crack 9 (d) at the same bending moment of 17,500 kN·m

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