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Research Papers: Materials and Fabrication

Overload Fracture of Hydrided Region at Simulated Blunt Flaws in Zr-2.5Nb Pressure Tube Material

[+] Author and Article Information
Jun Cui

 Kinectrics Inc., 800 Kipling Avenue, Toronto, ON, M8Z 6C4, Canadajun.cui@kinectrics.com

Gordon K. Shek

 Kinectrics Inc., 800 Kipling Avenue, Toronto, ON, M8Z 6C4, Canadagordon.shek@kinectrics.com

Zhirui Wang

 University of Toronto, 184 College Street, Toronto, ON, M5S 3E4, Canadazhirui.wang@utoronto.ca

J. Pressure Vessel Technol 131(4), 041406 (Jul 01, 2009) (15 pages) doi:10.1115/1.3147743 History: Received October 29, 2007; Revised September 01, 2008; Published July 01, 2009

A crack initiation and growth mechanism known as delayed hydride cracking (DHC) is a concern for Zr-2.5Nb alloy pressure tubes of CANada Deuterium Uranium or CANDU (CANDU is a trademark of the Atomic Energy of Canada Limited, Ontario, Canada) nuclear reactors. DHC is a repetitive process that involves hydrogen diffusion, hydride precipitation, formation, and fracture of a hydrided region at a flaw tip. An overload occurs when the flaw-tip hydrided region is loaded to a stress, higher than that at which this region is formed. For the fitness-for-service assessment of the pressure tubes, it is required to demonstrate that the overload from the normal reactor operating and transient loading conditions will not fracture the hydrided region, and will not initiate DHC. In this work, several series of systematically designed, monotonically increasing load experiments are performed on specimens, prepared from an unirradiated pressure tube with hydrided region, formed at flaws with a root radius of 0.1 mm or 0.3 mm, under different hydride formation stresses and thermal histories. Crack initiation in the overload tests is detected by the acoustic emission technique. Test results indicate that the resistance to overload fracture is dependent on a variety of parameters including hydride formation stress, thermal history, hydrogen concentration, and flaw geometry.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a notched cantilever beam specimen

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Figure 2

Schematic of the test setup for hydride formation

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Figure 3

Schematic of the three-point bend loading jig used in monotonically increasing load tests

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Figure 4

Creep cycle for 45 ppm and 55 ppm samples (also single cooldown cycle for 45 ppm samples)

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Figure 5

Ratcheting cycle for 45 ppm and 55 ppm samples

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Figure 6

Overload test record of specimen No. 2003-343/Test series SN1-5

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Figure 7

Overload test record of a specimen in Test series SN1-6

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Figure 8

Overload test record of a specimen in Test series SN3-3

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Figure 9

Cracked notch-tip hydride in specimen No. 2003-343/Test series SN1-5 from overload test, as-polished condition

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Figure 10

Effect of hydride formation stress on overload fracture resistance Φov

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Figure 11

Effect of hydride formation stress on overload fracture stress σcr

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Figure 12

Notch-tip hydrides in a specimen in series SN1-3 after 52 ratcheting cycles HFI=0.52 by chemical etching

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Figure 13

Notch-tip hydrides in a specimen in series SN1-4 after 52 ratcheting cycles HFI=0.83 by chemical etching

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Figure 14

Notch-tip hydrides in a specimen in series SN1-5 after 50 ratcheting cycles HFI=1.03 by chemical etching

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Figure 15

Notch-tip hydride length as a function of hydride formation index

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Figure 16

Effect of number of ratcheting thermal cycles on overload fracture resistance Φov

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Figure 17

Notch-tip hydrides in a specimen in series SN1-2 after one cooldown cycle HFI=0.83 by anodizing

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Figure 18

Notch-tip hydrides in a specimen in series SN1–6 after 10 ratcheting cycles HFI=0.83 by anodizing

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Figure 19

Notch-tip hydrides in a specimen in series SN1-4 after 52 ratcheting cycles HFI=0.83 by anodizing

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Figure 20

Effect of bulk hydrogen concentration on overload fracture resistance Φov, HFI=0.83

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Figure 21

Notch-tip hydride length as a function of bulk hydrogen concentration HFI=0.83

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Figure 22

Effect of non-ratcheting and re-ratcheting conditions on overload fracture resistance Φov, HFI=0.83 for the mean KIH of tube A

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Figure 23

SEM micrograph of a specimen in series SN1-4 showing notch-tip hydrides formed after 52 ratcheting cycles HFI=0.83 after overload test

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Figure 24

SEM micrograph of a specimen in series SN3-2 showing notch-tip hydrides formed after 10 non-ratcheting cycles HFI=0.83 before overload test

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Figure 25

SEM micrograph of a specimen in series SN3-3 showing notch-tip hydrides formed after 20 non-ratcheting cycles HFI=0.83 before overload test

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Figure 26

SEM micrograph of a specimen in series SN3-4 showing notch-tip hydrides formed after 10 non-ratcheting plus 50 re-ratcheting cycles HFI=0.83 before overload test

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Figure 27

SEM micrograph of a specimen in series SN3-5 showing notch-tip hydrides formed after 20 non-ratcheting plus 50 re-ratcheting cycles HFI=0.83 before overload test

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Figure 28

Effect of notch root radius on overload fracture resistance Φov hydrides formed after 52 ratcheting cycles HFI=0.83

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