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Research Papers: Materials and Fabrication

Estimation of Stress Corrosion Cracking Growth Behavior Under Weld Residual Stress in the Bottom of a Reactor Pressure Vessel by Finite Element Analysis

[+] Author and Article Information
Fuminori Iwamatsu

Hitachi Research Laboratory, Hitachi, Ltd.,
832-2, Horiguchi,
Hitachinaka, Ibaraki 312-0034, Japan
e-mail: fuminori.iwamatsu.vt@hitachi.com

Katsumasa Miyazaki

Hitachi Research Laboratory, Hitachi, Ltd.,
Ohmika 7-1-1,
Hitachi, Ibaraki 319-1292, Japan

Masahito Mochizuki

Division of Materials and Manufacturing Science,
Graduate School of Engineering,
Osaka University,
Yamadaoka 2-1,
Suita, Osaka 565-0871, Japan

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 25, 2013; final manuscript received November 21, 2014; published online February 20, 2015. Assoc. Editor: Wolf Reinhardt.

J. Pressure Vessel Technol 137(4), 041402 (Aug 01, 2015) (8 pages) Paper No: PVT-13-1073; doi: 10.1115/1.4029256 History: Received April 25, 2013; Revised November 21, 2014; Online February 20, 2015

A method for evaluating crack growth by repeatedly modeling and analyzing the transitional crack shapes is developed for a general computing environment in which a commercial finite element preprocessor and analysis code are used. The proposed method calculates stress intensity factors (SIFs) by finite element analysis (FEA) by directly distributing estimated weld residual stress obtained from noncracked components on the crack surface on the basis of the superposition principle. In present case, to specify a nonuniform residual stress distribution, a subroutine for a commercial FEA code (ABAQUS) was developed. Arbitrary crack shapes during the crack propagation were expressed by applying the submodeling technique which allowed arbitrary crack shapes to be meshed. The sequence of steps in the proposed method was designed to make it possible to consider complicated stress distributions, such as weld residual stress, and to express arbitrary crack shapes. The applicability of the proposed FEA based method was verified by comparing the result of a stress corrosion cracking (SCC) growth analysis results of a flat plate obtained with the proposed method and with the ASME code procedure. As an application example, the SCC growth behavior of a crack at the bottom of a nuclear reactor pressure vessel (RPV) involving a dissimilar metal weld and a unique geometry was evaluated by the proposed method. The evaluation results were compared with results obtained using a conventional method, i.e., the influence function method (IFM). Since both sets of results were in reasonable agreement, it was concluded that IFM can be applied to this case. Previously, it was difficult to assess the applicability of conventional methods, such as the code procedure and IFM, to a complicated problem because of the existence of complicated residual stress fields, dissimilar metals, and the complicated crack shapes involved. The proposed method using FEA allows the applicability of conventional methods to complicated crack growth evaluations to be assessed.

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References

Figures

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Fig. 1

Procedure of crack growth evaluation by FEA

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Fig. 2

Finite element model: (a) global model and (b) submodel

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Fig. 3

Crack growth evaluation: (a) conventional method and (b) developed method using FEA

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Fig. 4

Definition of crack shape

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Fig. 5

Schematic of analytical model: (a) surface crack in a flat plate model and (b) initial crack for SCC growth evaluation

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Fig. 6

Comparison of SCC growth evaluation results: (a) transition of crack sizes and (b) transition of SIF at point 1

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Fig. 7

Schematic of RPV structure: (a) bottom part of RPV and (b) cross section of H11 weld line

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Fig. 8

Hoop stress contour of H11 weld line

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Fig. 9

Assumed geometry for crack growth evaluation

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Fig. 10

Crack growth rates [9,12]

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Fig. 11

Stress distribution applied to IFM

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Fig. 12

Evaluated crack growth behavior: (a) proposed evaluation using FEA and (b) IFM

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Fig. 13

Comparison of time transition of crack size: (a) comparison of crack depth and (b) comparison of crack length

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