TY - JOUR

T1 - Effect of specimen size on hydrogen embrittlement cracking of 2.25Cr-1Mo heavy section steel for pressure vessels

AU - Wada, Yoru

AU - Tanaka, Yasuhiko

AU - Iwadate, Tadao

AU - Ohmi, Toshihito

AU - Yokobori, Toshimitsu

N1 - Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.

PY - 2007/9

Y1 - 2007/9

N2 - By means of charging large thick specimens with hydrogen, we investigated the effects of specimen size on hydrogen-embrittlement cracking. Crack extension in a hydrogen-charged 3.5T-CT specimen extended over a longer duration than was the case for a 1.0T-CT specimen. However, the values of the lower-bound threshold stress intensity factor (K IH) for 1.0T-CT and 3.5TCT specimens were similar to one another when these were determined with a short-term rising load (dK/dt= 0.005 MPa·m 1/2;· s -1). We conducted numerical analysis on the hydrogen diffusion and accumulation around a crack tip, taking into consideration the hydrogen distribution in the specimen. This analysis demonstrated that the maximum hydrogen concentration for cracking can be reached under the conditions present during a short-term rising load test (dK/dt= 0.005 MPa· m 1/2/s). Thus, the results of the numerical analysis confirm that a minimum value of K IH equivalent to that of a heavy section steel can be obtained with a small fracture mechanics specimen. We also attempted to explain long-term crack extension characteristics, taking into consideration hydrogen dissipation from a specimen. The analysis predicts that when the mean hydrogen concentration falls below a certain level (e.g., about 1.6 ppm under certain assumptions), the value of K IH increases significantly. This increase in K IH occurs because when the necessary stress intensity factor for cracking increases as a result of a decrease in the mean hydrogen concentration, the gradient of the maximum hydrostatic stress distribution becomes moderate, especially when the applied stress intensity factor is more than about 48 MPa·m 1/2. Finally, we propose a method for the prediction of the long-term crack extension behavior of a large thick specimen; the method takes into consideration the hydrogen dissipation curve and the effect on K IH of a decrease in the mean hydrogen concentration.

AB - By means of charging large thick specimens with hydrogen, we investigated the effects of specimen size on hydrogen-embrittlement cracking. Crack extension in a hydrogen-charged 3.5T-CT specimen extended over a longer duration than was the case for a 1.0T-CT specimen. However, the values of the lower-bound threshold stress intensity factor (K IH) for 1.0T-CT and 3.5TCT specimens were similar to one another when these were determined with a short-term rising load (dK/dt= 0.005 MPa·m 1/2;· s -1). We conducted numerical analysis on the hydrogen diffusion and accumulation around a crack tip, taking into consideration the hydrogen distribution in the specimen. This analysis demonstrated that the maximum hydrogen concentration for cracking can be reached under the conditions present during a short-term rising load test (dK/dt= 0.005 MPa· m 1/2/s). Thus, the results of the numerical analysis confirm that a minimum value of K IH equivalent to that of a heavy section steel can be obtained with a small fracture mechanics specimen. We also attempted to explain long-term crack extension characteristics, taking into consideration hydrogen dissipation from a specimen. The analysis predicts that when the mean hydrogen concentration falls below a certain level (e.g., about 1.6 ppm under certain assumptions), the value of K IH increases significantly. This increase in K IH occurs because when the necessary stress intensity factor for cracking increases as a result of a decrease in the mean hydrogen concentration, the gradient of the maximum hydrostatic stress distribution becomes moderate, especially when the applied stress intensity factor is more than about 48 MPa·m 1/2. Finally, we propose a method for the prediction of the long-term crack extension behavior of a large thick specimen; the method takes into consideration the hydrogen dissipation curve and the effect on K IH of a decrease in the mean hydrogen concentration.

KW - 1.0t-Compact Tension

KW - 2.25% Chrome-1%Molybdenum

KW - 3.5t-Compact Tension

KW - Autoclave

KW - Crack

KW - Dissipation

KW - Hydrogen charge

KW - Hydrogen diffusion

KW - Hydrogen embrittlement

KW - K

KW - Large specimen

KW - Stress intensity factor

KW - Thick specimen

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U2 - 10.2320/jinstmet.71.772

DO - 10.2320/jinstmet.71.772

M3 - Article

AN - SCOPUS:35348900129

VL - 71

SP - 772

EP - 780

JO - Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

JF - Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

SN - 0021-4876

IS - 9

ER -