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Long-Term Aging Behavior Of Cold-Worked Alloy 690 In Simulated PWR Primary Water

Alloy 690 has been utilized since the late 1980s as a replacement for Alloy 600 in pressurized water reactors (PWR) pressure boundary components due to laboratory data indicating higher resistance to stress corrosion cracking (SCC). Although to date no SCC incidents have been reported on Alloy 690 components in service, the growing interest of extending the operation life of PWRs beyond 60 or even 80 years has raised concerns for the potential occurrence of long-range ordering (LRO) in Alloy 690 and its compatible weld metals.

Product Number: ED22-18358-SG
Author: Ziqing Zhai, Matthew J. Olszta, Mychailo B. Toloczko
Publication Date: 2022
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A study on long-term aging (LTA) effects with a focus on evaluating the potential presence of long-range ordering (LRO) was carried out on seven cold-worked tensile stress corrosion crack initiation (SCCI) specimens made from four commercial, thermally treated Alloy 690 heats. These specimens were removed at test interruptions from an on-going long-term stress corrosion crack initiation test at PNNL, and hardness tests were performed. Prior to performing LTA assessment, most of these specimens were SCCI tested at their yield stress for 18,400 hours in 360°C simulated pressurized water reactor primary water, except for one specimen that was only tested for 7,110 hours. A small hardness increase between ~5–12% was observed in four out of the seven examined specimens. The magnitude of the hardness increase tended to scale with cold work level, while no systematic correlation was found between hardness and the Fe content. Preliminary X-ray diffraction analysis indicated that the hardness increase might be related to LRO, but direct microscopic evidence has yet to be obtained.


A study on long-term aging (LTA) effects with a focus on evaluating the potential presence of long-range ordering (LRO) was carried out on seven cold-worked tensile stress corrosion crack initiation (SCCI) specimens made from four commercial, thermally treated Alloy 690 heats. These specimens were removed at test interruptions from an on-going long-term stress corrosion crack initiation test at PNNL, and hardness tests were performed. Prior to performing LTA assessment, most of these specimens were SCCI tested at their yield stress for 18,400 hours in 360°C simulated pressurized water reactor primary water, except for one specimen that was only tested for 7,110 hours. A small hardness increase between ~5–12% was observed in four out of the seven examined specimens. The magnitude of the hardness increase tended to scale with cold work level, while no systematic correlation was found between hardness and the Fe content. Preliminary X-ray diffraction analysis indicated that the hardness increase might be related to LRO, but direct microscopic evidence has yet to be obtained.