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Research Papers: Design and Analysis

Assessment of Overlapped Internal and External Volumetric Flaws in p-M Diagram

[+] Author and Article Information
Shinji Konosu

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

Hikaru Miyata

 Mitsubishi Heavy Industries, Ltd., 2-2-1 Shinhama Arai, Takasago, Hyogo 676-8686, Japanhikaru.miyata@mhi.co.jp

J. Pressure Vessel Technol 133(3), 031208 (Apr 21, 2011) (13 pages) doi:10.1115/1.4002053 History: Received October 21, 2009; Revised June 15, 2010; Published April 21, 2011; Online April 21, 2011

Assessment of overlapped internal and external volumetric flaws is one of the most common problems related to pressure vessel and piping components. Under the current fitness for service rules, such as those provided in ASME, BS, and so on, the procedures for the assessment of these flaws have not yet been defined. In this paper, a reference stress, incorporating the decrease in the effective cross section as a function of flaw depth and flaw angle in a cylinder, has been proposed in order to assess the flaws using the simple p-M (pressure-moment) diagram method. Numerous finite element analyses for a cylinder with overlapped internal and external flaws were conducted to verify the proposed procedure. There is good agreement among them.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Configuration of overlapped internal and external volumetric flaws

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Figure 2

Overlapped internal and external longitudinal surface flaws

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Figure 3

Overlapped internal and external circumferential surface flaws

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Figure 4

True stress–true strain curve used in FEA

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Figure 5

Modification factor kp for a flaw under pure internal pressure condition where pL is equal to p_TES

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Figure 6

Mises stress around a flaw near TES load under internal pressure (τ=0.05)

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Figure 7

Modification factor km for a flaw under pure bending moment condition where ML is equal to M_TES

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Figure 8

Mises stress around a flaw near TES load under external bending moment

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Figure 9

Comparison of TES loads (Table 3) obtained by FEA under internal pressure versus p_mL predicted from plastic limit pressures (Eq. 12)

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Figure 10

Comparison of TES loads (Table 4) obtained by FEA under external bending moment versus M_mL predicted from plastic limit moment (Eq. 22)

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Figure 11

TES loads for overlapped internal and external volumetric flaws plotted on p-M diagram based on σf=σysmean

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Figure 12

TES loads for overlapped internal and external volumetric flaws plotted on p-M diagram based on σf=σysmean/1.5

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Figure 13

Allowable wall thickness for a single longitudinal flaw determined by p-M diagram based on σf=σysmin/1.5 compared with that per ASME N-597-2-3622.4 (safety factor=3) and that per API-579-1/ASME (safety factor=4)

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Figure 14

The ratio of proposed modified limit moment to conventional limit moment is plotted against flaw angle

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Figure 15

Allowable wall thickness for a single circumferential flaw determined by p-M diagram based on σf=σysmin/1.5

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