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Design and Analysis

Ratcheting Studies on Type 304LN Stainless Steel Elbows subjected to Combined Internal Pressure and In-Plane Bending Moment

[+] Author and Article Information
S. Vishnuvardhan1

CSIR - Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600 113, Indiasvvardhan@serc.res.in

G. Raghava, P. Gandhi, M. Saravanan, D. M. Pukazhendhi

CSIR - Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600 113, India

Sumit Goyal, Suneel K. Gupta, Vivek Bhasin, K. K. Vaze

Reactor Safety Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India

1

Corresponding author.

J. Pressure Vessel Technol 134(4), 041203 (Jul 17, 2012) (10 pages) doi:10.1115/1.4005886 History: Received April 01, 2011; Revised November 26, 2011; Online July 17, 2012; Published July 31, 2012

“Ratcheting” is a phenomenon which leads to reduction in fatigue life of a structural component by loss of ductility due to cycle by cycle accumulation of plastic strain. Ratcheting occurs in a structure subjected to a combination of steady/sustained and cyclic loads such that the material response is in inelastic region. Ratcheting studies were carried out on Type 304LN stainless steel elbows, subjected to steady internal pressure and cyclic bending. The elbows filled with water were pressurized between 27.6 MPa and 39.2 MPa. Cyclic bending load, under opening and closing moments, was applied on the elbows at ambient temperature. Number of cycles corresponding to occurrence of a through-wall crack was recorded. Crack was observed in the bent portion at one of the crown locations in all the four specimens. Maximum strain was observed at the intrados and crown locations of the elbows. The ratcheting strain increased with number of cycles at crown and intrados locations. However, the strain accumulation rate decreased with number of cycles. Strain was observed to be minimum at the extrados location and the same stabilized toward the end of the tests. The specimens have failed by occurrence of through-wall axial crack accompanied by simultaneous ballooning. The ballooning was found to be varying from 3.8% to 5.8% with respect to the original circumference in the bent portion. The reduction in thickness was found to be around 12%–15%.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 2

Details of axial and circumferential grid lines on elbows

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Figure 3

Variation of thickness in a typical elbow specimen QCE-RAT-6-L3

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Figure 4

Ratcheting test set-up arrangement

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Figure 5

Ratcheting test on an elbow

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Figure 6

Close-up view of strain gauge instrumentation

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Figure 7

Details of LVDT locations for ovality measurements during ratcheting test for the specimen QCE-RAT-6-L1

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Figure 8

Typical displacement time history during ratcheting test on QCE-RAT-6-L1

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Figure 9

Load versus load-line displacement hysteresis curves for QCE-RAT-6-L2

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Figure 10

Strain history for the specimen QCE-RAT-6-L1

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Figure 11

Strain history for the specimen QCE-RAT-6-L2

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Figure 12

Variation of ovality versus number of cycles during ratcheting test on the specimen QCE-RAT-6-L1

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Figure 13

Percentage increase in diameter versus number of cycles during ratcheting test on the specimen QCE-RAT-6-L1

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Figure 14

Appearance of through-wall crack indicated by a sharp water jet

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Figure 15

Percentage of ballooning versus number of cycles

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Figure 16

Close-up views of cracked portion

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Figure 1

Details of a typical elbow specimen QCE-RAT-6-L2

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