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Research Papers: Materials and Fabrication

Assessment Procedure for Multiple Cracklike Flaws in Failure Assessment Diagram (FAD)

[+] Author and Article Information
Shinji Konosu

 Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japankonosu@mx.ibaraki.ac.jp

J. Pressure Vessel Technol 131(4), 041402 (May 15, 2009) (16 pages) doi:10.1115/1.3122026 History: Received May 01, 2008; Revised January 27, 2009; Published May 15, 2009

Assessment of multiple discrete cracklike flaws is one of the most common problems relating to pressure vessels and piping components. Under the current fitness for service (FFS) rules, such as ASME, BS, and so on, multiple cracklike flaws are usually recharacterized as an enveloping crack (defined as a single larger crack), following their assessment rules. The procedure, however, varies significantly in these FFS codes. In this paper, the interaction between nonaligned multiple unequal cracks is clarified by applying the body force method. Based on the interaction that indicates the magnification and shielding effects and the reference stress solutions, a newly developed assessment procedure for multiple discrete cracklike flaws in the failure assessment diagram is proposed.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Two nonaligned cracks of different sizes in a cylinder subjected to internal pressure or external bending moment and the equivalent aligned cracks

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Figure 2

Interaction factor at crack tip A of twin nonaligned cracks compared with the results obtained by Yokobori (8)

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Figure 3

(a) Interaction factor at the tips of two 2D nonaligned cracks of different sizes versus crack tip separation Y/(2c¯)=0.2. (b) Interaction factor at tips of two 2D nonaligned cracks of different sizes versus crack tip separation (Y/(2c¯)=0.5).

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Figure 4

Contour plot of the interaction factor γA=1.05 for Crack 1 of larger length

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Figure 5

Three-dimensional modification factor versus crack tip separation

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Figure 6

(a) Alignment rule for nonaligned cracks (Y/(2c¯)=0.2). (b) Alignment rule for nonaligned cracks (Y/(2c¯)=0.5).

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Figure 7

Effective crack depth aeff and cross-sectional area

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Figure 8

Predicted normalized limit pressure (the ratio of limit pressure of multiple longitudinally aligned cracks to that of the severest of the individual longitudinal cracks) versus crack tip distance

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Figure 9

Crack tip separation whereby interaction effect can be ignored under pure pressure action versus average length of two cracks

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Figure 10

Assumed stress distribution in the cross section of a cylinder containing multiple partly-through cracks

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Figure 11

Comparison between exact solution and approximate solution

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Figure 12

Predicted normalized limit bending moment (the ratio of limit moment of multiple circumferentially aligned cracks to that of the severest of the individual circumferential cracks) versus crack tip distance

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Figure 13

Crack tip separation angle whereby interaction effect can be ignored under pure bending moment action versus average angle of two cracks

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Figure 14

(a) Flowchart for nonaligned cracklike flaws assessment of Level 1 in FAD. (b) Flowchart for nonaligned cracklike flaws assessment of Level 2 in FAD.

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Figure 15

Comparison between the p-M method and API579/ASME-FFS rule for multiple cracks

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