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Title: Long-Term Immersion Testing of Alloy 22 and Titanium Grade 7 Double U-bend Specimens

Abstract

Double U-bend specimens of Alloy 22 (N06022) and Titanium Grade 7 (R52400) were exposed to a naturally aerated concentrated Basic Saturated Water (BSW) electrolyte at 105 C for over six years. Different type of discoloration of the Ti Gr 7 and Alloy 22 specimens was observed. General Corrosion was minimal and not distinguishable under a scanning electron microscope. None of the tested specimens suffered environmentally assisted cracking (EAC) or localized corrosion under the tested conditions. The specimens retained their residual stress after the long environmental exposure.

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
913551
Report Number(s):
UCRL-PROC-228000
TRN: US200802%%870
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: 2007 ASME Pressure Vessels and Piping Division Conference, San Antonio, TX, United States, Jul 22 - Jul 26, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALLOYS; CORROSION; ELECTROLYTES; ELECTRON MICROSCOPES; ENVIRONMENTAL EXPOSURE; PRESSURE VESSELS; TESTING; TITANIUM; WATER

Citation Formats

Evans, K J, Stuart, M L, Hailey, P D, and Rebak, R B. Long-Term Immersion Testing of Alloy 22 and Titanium Grade 7 Double U-bend Specimens. United States: N. p., 2007. Web.
Evans, K J, Stuart, M L, Hailey, P D, & Rebak, R B. Long-Term Immersion Testing of Alloy 22 and Titanium Grade 7 Double U-bend Specimens. United States.
Evans, K J, Stuart, M L, Hailey, P D, and Rebak, R B. Thu . "Long-Term Immersion Testing of Alloy 22 and Titanium Grade 7 Double U-bend Specimens". United States. doi:. https://www.osti.gov/servlets/purl/913551.
@article{osti_913551,
title = {Long-Term Immersion Testing of Alloy 22 and Titanium Grade 7 Double U-bend Specimens},
author = {Evans, K J and Stuart, M L and Hailey, P D and Rebak, R B},
abstractNote = {Double U-bend specimens of Alloy 22 (N06022) and Titanium Grade 7 (R52400) were exposed to a naturally aerated concentrated Basic Saturated Water (BSW) electrolyte at 105 C for over six years. Different type of discoloration of the Ti Gr 7 and Alloy 22 specimens was observed. General Corrosion was minimal and not distinguishable under a scanning electron microscope. None of the tested specimens suffered environmentally assisted cracking (EAC) or localized corrosion under the tested conditions. The specimens retained their residual stress after the long environmental exposure.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Feb 08 00:00:00 EST 2007},
month = {Thu Feb 08 00:00:00 EST 2007}
}

Conference:
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  • This paper provides an update on research addressing the effects of material condition and applied stress on stress corrosion cracking (SCC) in waste package and drip shield materials for the Yucca Mountain Project. Time-to-failure experiments are being performed on smooth bar tensile specimens in a hot, concentrated, mixed-salt solution chosen to simulate concentrated Yucca Mountain water. The effects of applied stress, welding, surface finish, shot peening, cold work, crevicing, and aging treatment are being investigated for Alloy 22 (UNS N06022). Aging treatments were designed to produce topologically close-packed phases (TCP) and long-range ordering (LRO) and are under investigation as worse-casemore » scenarios for possible microstructures in Alloy 22 (UNS N06022). Titanium Grade 7 and 3 16NG stainless steel are included in the matrix, as they are identified for drip shield and waste package components, respectively. Sensitized 304SS specimens are included in the test matrix to provide benchmark data. This research complements high-resolution crack-growth-rate experiments currently being performed in a parallel research project.« less
  • Stress corrosion crack growth studies have been performed on annealed and cold worked Titanium Grade 7 and Alloy 22 in 110 C, aerated, concentrated, high pH salt environments characteristic of concentrated ground water. Following a very careful transition from fatigue precracking conditions to SCC conditions, the long term behavior under very stable conditions was monitored using reversing dc potential drop. Titanium Grade 7 exhibited continuous crack growth under both near-static and complete static loading conditions. Alloy 22 exhibited similar growth rates, but was less prone to maintain stable crack growth as conditions approached fully static loading.
  • The stress corrosion crack initiation and growth rate response was evaluated on as-received, as-welded, cold worked and aged Alloy 22 (UNS N06022) and titanium Grades 7 (UNS R52400), 28 (UNS R55323) and 29 (UNS R56404) at 105-165 C in various aerated, concentrated groundwater environments. Time-to-failure experiments on actively-loaded tensile specimens at 105 C evaluated the effects of applied stress, welding, surface finish, shot peening, cold work, crevicing, and aging treatments in Alloy 22 (UNS N06022), and found these materials to be highly resistant to SCC (none observed). Long-term U-bend data at 165 C corroborated these findings. Titanium Grade 7 andmore » stainless steels were also included in the 105 C test matrix. Long term crack growth rate data showed stable crack growth in titanium Grade 7. Recent creep tests in air confirm literature data that these alloys are quite susceptible to creep failure, even below the yield stress, and it is unclear whether cracking in SCC tests is only accelerated by the creep response, or whether creep is responsible for cracking. Alloy 22 exhibited stable growth rates under ''gentle'' cyclic loading, but was prone to crack arrest at fully static loading. No effect of Pb additions was observed.« less
  • Using an Atomic Force Microscope, we have examined the surface topographies associated with crevice coupons representing the six classes of coupons of Titanium Grade 16 removed from Long-Term Corrosion testing after two years of immersion. Only on coupons removed from Simulated Concentrated Well Water do we observe features which are likely to represent embryonic pit formation. The coupons removed from the Simulated Acidified Well Water were too rough to yield representative measurements.
  • Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. In conditions where tight crevices exist in hot chloride containing solutions and at anodic potentials, Alloy 22 may suffer crevice corrosion, a form of localized attack. The occurrence (or not) of crevice corrosion in a given environment (e.g. salt concentration and temperature), is governed by the values of the critical potential (E{sub crit}) for crevice corrosion and the corrosion potential (E{sub corr}) that the alloy may establish in the studied environment. If E{sub corr} is equal or higher than E{sub crit}, crevice corrosion may be expected.more » In addition, it is generally accepted that as Alloy 22 becomes passive in a certain environment, its E{sub corr} increases and its corrosion rate (CR) decreases. This paper discusses the evolution of E{sub corr} and corrosion rate (CR) of creviced Alloy 22 specimens in six different mixtures of sodium chloride (NaCl) and potassium nitrate (KNO{sub 3}) at 100 C. The effect of immersion time on the value of E{sub crit} was also determined. Two types of specimens were used, polished as-welded (ASW) and as-welded plus solution heat-treated (ASW+SHT). The latter contained the black annealing oxide film on the surface. Results show that, as the immersion time increases, E{sub corr} increased and the CR decreased. Even for highly concentrated brine solutions at 100 C the CR was < 30 nm/year after more than 250 days immersion. Some of the exposed specimens (mainly the SHT specimens) suffered crevice corrosion at the open circuit potential in the naturally aerated brines. Immersion times of over 250 days did not reduce the resistance of Alloy 22 to localized corrosion.« less