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RESEARCH PAPERS

Modified Equation To Predict Leak/Rupture Criteria For Axially Through-Wall Notched X80 and X100 Linepipes Having a Higher Charpy Energy

[+] Author and Article Information
Shinobu Kawaguchi

 Pipeline Technology Center, Tokyo Gas Co., Ltd. 1-7-7, Suehiro-cho, Tsurumi-ku, Yokohama, Japanshino-k@tokyo-gas.co.jp

Naoto Hagiwara

 Pipeline Technology Center, Tokyo Gas Co., Ltd. 1-7-7, Suehiro-cho, Tsurumi-ku, Yokohama, Japannhagi@tokyo-gas.co.jp

Mitsuru Ohata

Dept. of Manufacturing Science, Osaka Univ. 2-1, Yamada-oka, Suita, Osaka, Japanohata@mapse.eng.osaka-u.ac.jp

Masao Toyoda

Dept. of Manufacturing Science, Osaka Univ. 2-1, Yamada-oka, Suita, Osaka, Japantoyoda@mapse.eng.osaka-u.ac.jp

J. Pressure Vessel Technol 128(4), 572-580 (Dec 26, 2005) (9 pages) doi:10.1115/1.2349570 History: Received April 27, 2005; Revised December 26, 2005

A method of predicting the leak/rupture criteria for API 5L X80 and X100 line pipes was evaluated based on the results of hydrostatic full-scale tests for X60, X65, X80, and X100 line pipes with an axially through-wall (TW) notch. The TW notch test results defined the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The defined leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner, Maxey This comparison revealed that the CVN-based equation was not applicable to the pipes having both a CVN energy greater than 120 or 130 J and flow stress greater than the level of X65. In order to predict the leak/rupture criteria for these line pipes, the static absorbed energy for ductile cracking, (Cvs)i, was introduced as representing the fracture toughness of a pipe material. The (Cvs)i value was determined from the microscopic observation of the cut and polished Charpy V-notch specimens after static three-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, (Cv)eq, which was defined as follows: (Cv)eq=4.5(Cvs)i. The leak/rupture criteria for the X80 and X100 line pipes with higher CVN energies were reasonably predicted by the modified equation using the (Cvs)i value.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

An illustration of an axial TW notch

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Figure 2

Internal patch for the TW notch

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Figure 3

Typical fractured pipe after the TW notch test (pipe E)

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Figure 4

A comparison of the leak/rupture criteria between the through-wall notch test results and the prediction using the original CVN-based equation

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Figure 5

A comparison between the experimental and the predicted hoop stresses representing the leak/rupture criteria

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Figure 6

Correlation of full-size CVN absorbed energy with Gc value calculated from Kc in Eq. 4

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Figure 7

Flow stress dependence on the TW notch test results for X65 pipes (pipes B and C)

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Figure 8

Limitation of the original CVN-based equation determined from the TW notch tests

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Figure 9

Instrumented Charpy test results: load versus load-point displacement curves for the tested pipes

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Figure 10

Determination of the critical load-point displacement for ductile cracking during three-point bending tests for Charpy V-notch specimens

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Figure 11

A comparison of load versus load-point displacement curves and critical load-point displacement for ductile cracking when static load is applied

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Figure 12

Static absorbed energy determined from the static three-point bending test results

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Figure 13

Verification of the static absorbed energy for ductile cracking to evaluate the leak/rupture criteria

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Figure 14

Prediction of the leak/rupture criteria obtained from the modified equation [Eq. 8] using the static absorbed energy for ductile cracking, (Cvs)i

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