failure analysis of alloy 718 hold down springs presentation title … · 2016-07-29 · front end...

Property of AREVA NP - © AREVA NP All rights reserved, see liability notice

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016 Presentation title – Presenter/ref. - 26 May 2016 - p.1

FRONT END BUSINESS GROUP

Failure Analysis of Alloy 718 Hold Down Springs Mahendra Punatar Jacqueline Stevens AREVA, Inc., Lynchburg, VA, USA Keith J. Leonard, Maxim N. Gussev Oak Ridge National Laboratory, Oak Ridge, TN, USA Gabriel Ilevbare EPRI, Palo Alto, CA, USA J. Lawrence Nelson JLN Consulting, Mills River, NC, USA 2016 International LWR Material Reliability Conference and Exhibition August 1 – 4, 2016


Outline

Background Examination Results Discussion Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016


Background (1/2)

Alloy 718 material to AMS 5596 HDS under high stress state during operation PWR conditions – 2, 24-month cycles Approximately 0.5 dpa



Background (2/2)

Archive materials also investigated: Archive A – Representative of HDS which failed during operation, same

manufacturing lot as irradiated samples Archive B – Representative of HDS which completed operational life

without damage

Both archives manufactured from same alloy 718 ingot


Archive and irradiated samples examined at ORNL


Outline

Background

Examination Results Discussion Conclusion



Examination Results (1/4)




Sample surface after oxide removal Extensive slip lines around major cracks Slip line oxidation Secondary cracks (red arrows)





Delta phase

Twin Boundary




Archive A Archive B

Following 3.7% Bulk Strain


Outline

Background Examination Results

Discussion Conclusion



Discussion (1/2)



Discussion (2/2)

Precipitation Heat Treat Differences


0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1000

Tem

pera

ture

(°C

)

Time (minutes)

Archive A / Irradiated Samples

Archive B Samples


Outline

Background Examination Results Discussion

Conclusion



Conclusion (1/1)

Failed HDS (Archive A) 2, 24-month cycles – PWR

chemistry High Stress Approximately 0.5 dpa Negligible δ phase

precipitation on GBs


Non-Damaged HDS (Archive B) 3, 18-month cycles – PWR

chemistry High Stress Approximately 0.5 dpa Substantial δ phase precipitation

on GBs

δ precipitates on the grain boundaries of alloy 718 produce a PFZ which facilitates cross-slip leading to localized stress reduction

In the absence of a PFZ, the build up of slip bands at GBs under a high bulk stress state will initiate cracks

Cracks then readily propagate in alloy 718 in a PWR environment



Any reproduction, alteration, transmission to any third party or publication in whole or in part of this document and/or its content is prohibited unless AREVA Inc. has provided its prior and written consent.

This document and any information it contains shall not be used for any other purpose than the one for which they were provided. Legal action may be taken against any infringer and/or any person breaching the aforementioned obligations.


Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016 Presentation title – Presenter/ref. - 26 May 2016 - p.18

failure analysis of alloy 718 hold down springs presentation title … · 2016-07-29 · front end...

Documents