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Research Papers: Design and Analysis

Structural Integrity Estimates of Steam Generator Tubes Containing Wear-Type Defects

[+] Author and Article Information
Yoon-Suk Chang, Jong-Min Kim, Nam-Su Huh

SAFE Research Center, School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Kyonggi-do 440-746, Korea

Young-Jin Kim1

SAFE Research Center, School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Kyonggi-do 440-746, Koreayjkim50@skku.edu

Seong-Sik Hwang, Hong-Pyo Kim

 Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353, Republic of Korea

1

Corresponding author.

J. Pressure Vessel Technol 130(3), 031204 (Jun 16, 2008) (8 pages) doi:10.1115/1.2937741 History: Received August 15, 2006; Revised January 28, 2007; Published June 16, 2008

It is requested that steam generator tubes with defects exceeding 40% of wall thickness in depth should be plugged to sustain all postulated loads with appropriate margin. This critical defect size has been determined based on a concept of plastic instability, however, which is known to be too conservative for some locations and types of defects. The application of this concept may even cause premature retirement of steam generator tubes. In reality, a reliable structural integrity estimation for steam generator tubes containing a defect has received increasing attention. Although several guidelines have been developed and used for assessing defect containing tubes, most of these guidelines are focused on stress corrosion cracking or wall-thinning phenomena. Because some of steam generator tubes fail due to fretting and so on, specific integrity estimation schemes for relevant defects are required. In this paper, more than a hundred three-dimensional finite element analyses of steam generator tubes under internal pressure condition are carried out to simulate the failure behavior of steam generator tubes with specific defect configurations: elliptical wear-type, tapered wedge-type, and flat wear-type defects. After investigating the effect of key parameters such as defect depth, defect length, and wrap or tapered angle on equivalent stress across the ligament thickness, burst pressure estimation equations are proposed in relation to material strengths. Predicted burst pressures agreeded well with the corresponding experimental data, so the proposed equations can be used to assess the structural integrity of steam generator tubes with wear-type defects.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Normalized stress-strain data of Alloy 600 and 690 materials

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Figure 2

Schematic illustration of wear-type defects in steam generator tubes. (a) Elliptical wear-type defect, (b) tapered wedge-type defect, and (c) flat wear-type defect.

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Figure 3

Typical 3D FE meshes employed in the present study. (a) Elliptical wear-type defect, (b) tapered wedge-type defect, and (c) flat wear-type defect.

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Figure 4

Comparison of the FE burst pressures with experimental data for elliptical wear-type defect. (a) l=15mm, (b) l=25mm, and (c) l=35mm.

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Figure 5

Burst pressure solution with experimental data for elliptical wear-type defect. (a) l=15mm, (b) l=25mm, and (c) l=35mm.

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Figure 6

Comparison of the FE burst pressures with experimental data for tapered wedge-type defect

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Figure 7

Comparison of the burst pressure prediction with experimental data for tapered wedge-type defect

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Figure 8

Burst pressure solution with FE results for flat wear-type defect. (a) l=15mm, (b) l=25mm, and (c) l=35mm.

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Figure 9

Lower bound and best-fit curves. (a) Elliptical wear-type defect, (b) tapered wedge-type defect, and (c) flat wear-type defect.

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