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Title: Long-Term Corrosion Behavior of Alloy 22 in 5M CaCl2 at 120 C

Abstract

In conditions where tight crevices exist in hot chloride containing solutions Alloy 22 may suffer crevice corrosion. 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}). This paper discusses the evolution of E{sub corr} and corrosion rate (CR) of creviced Alloy 22 specimens in 5 M calcium chloride (CaCl{sub 2}) at 120 C. Tested specimens included non-creviced rods and multiple creviced assemblies (MCA) both non-welded (wrought) and welded. Results show that Alloy 22 suffers crevice corrosion under the open circuit conditions in the aerated hot CaCl{sub 2} brine. However, after more than a year of immersion the propagation of crevice corrosion was not significant. The general corrosion rate decreased or remained unchanged as the immersion time increased. For rods and MCA specimens, the corrosion rate was lower than 100 nm/year after more than a year immersion time.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Yucca Mountain Project, Las Vegas, Nevada
Sponsoring Org.:
USDOE
OSTI Identifier:
893375
Report Number(s):
NA
MOL.20060626.0121, DC# 47520; TRN: US200625%%203
DOE Contract Number:
NA
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; HASTELLOYS; CALCIUM CHLORIDES; CREVICE CORROSION; CORROSIVE EFFECTS; CHEMICAL REACTION KINETICS

Citation Formats

J.C. Estill, G.A. Hust, K.J. Evans, M.L. Stuart, and R.B. Rebak. Long-Term Corrosion Behavior of Alloy 22 in 5M CaCl2 at 120 C. United States: N. p., 2006. Web. doi:10.2172/893375.
J.C. Estill, G.A. Hust, K.J. Evans, M.L. Stuart, & R.B. Rebak. Long-Term Corrosion Behavior of Alloy 22 in 5M CaCl2 at 120 C. United States. doi:10.2172/893375.
J.C. Estill, G.A. Hust, K.J. Evans, M.L. Stuart, and R.B. Rebak. Mon . "Long-Term Corrosion Behavior of Alloy 22 in 5M CaCl2 at 120 C". United States. doi:10.2172/893375. https://www.osti.gov/servlets/purl/893375.
@article{osti_893375,
title = {Long-Term Corrosion Behavior of Alloy 22 in 5M CaCl2 at 120 C},
author = {J.C. Estill and G.A. Hust and K.J. Evans and M.L. Stuart and R.B. Rebak},
abstractNote = {In conditions where tight crevices exist in hot chloride containing solutions Alloy 22 may suffer crevice corrosion. 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}). This paper discusses the evolution of E{sub corr} and corrosion rate (CR) of creviced Alloy 22 specimens in 5 M calcium chloride (CaCl{sub 2}) at 120 C. Tested specimens included non-creviced rods and multiple creviced assemblies (MCA) both non-welded (wrought) and welded. Results show that Alloy 22 suffers crevice corrosion under the open circuit conditions in the aerated hot CaCl{sub 2} brine. However, after more than a year of immersion the propagation of crevice corrosion was not significant. The general corrosion rate decreased or remained unchanged as the immersion time increased. For rods and MCA specimens, the corrosion rate was lower than 100 nm/year after more than a year immersion time.},
doi = {10.2172/893375},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 08 00:00:00 EDT 2006},
month = {Mon May 08 00:00:00 EDT 2006}
}

Technical Report:

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  • In conditions where tight crevices exist in hot chloride containing solutions Alloy 22 may suffer crevice corrosion. 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}). This paper discusses the evolution of E{sub corr} and corrosion rate (CR) of creviced Alloy 22 specimens in 5 M calcium chloride (CaCl{sub 2}) at 120 C. Tested specimens included non-creviced rods and multiple creviced assemblies (MCA) both non-welded (wrought) and welded. Results show that Alloy 22more » suffers crevice corrosion under the open circuit conditions in the aerated hot CaCl{sub 2} brine. However, after more than a year immersion the propagation of crevice corrosion was not significant. The general corrosion rate decreased or remained unchanged as the immersion time increased. For rods and MCA specimens, the corrosion rate was lower than 100 nm/year after more than a year immersion time.« less
  • Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. In very aggressive conditions (e.g. hot concentrated chloride containing brines) Alloy 22 could suffer localized attack, namely pitting and crevice corrosion. The occurrence of localized corrosion in a given environment 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}, localized corrosion may be expected. This paper discusses the evolution of E{sub corr} of Alloy 22 specimensmore » in 5 m CaCl{sub 2} + 5 m Ca(NO{sub 3}){sub 2} brines at 100 C and 120 C. Two types of specimens were used, polished as-welded (ASW) creviced and noncreviced specimens and as-welded plus solution heat-treated (ASW+SHT) creviced specimens. The latter contained the black annealing oxide film on the surface. Results show that, for all types of Alloy 22 specimens the E{sub corr} was higher at 120 C than at 100 C, probably because a more protective film formed at the higher temperature. Specimens with the black oxide film on the surface showed more oscillations in the potential. None of the tested specimens suffered crevice corrosion probably because of the relatively high concentration of nitrate in the electrolyte, R = [NO3]/[Cl] = 1.« less
  • Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. In very aggressive conditions (e.g. hot concentrated chloride containing brines) Alloy 22 could suffer localized attack, namely pitting and crevice corrosion. Chloride ion is known to be the most detrimental aggressive agent for Alloy 22 and is able to promote crevice corrosion when tight crevices exist in hot chloride containing solutions of different concentrations. Nitrate ion is an effective inhibitor of chloride induced crevice corrosion when present in a high enough [NO{sub 3}{sup -}]/[Cl{sup -}] ratio. The occurrence of localized corrosion in a given environment ismore » 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}, localized corrosion may be expected. This paper discusses the evolution of E{sub corr} and corrosion rate (CR) of Alloy 22 specimens in 18 m CaCl{sub 2} + 9 m Ca(NO{sub 3}){sub 2} and 18 m CaCl{sub 2} + 0.9 m Ca(NO{sub 3}){sub 2} brines at 155 C. Two types of specimens were used, polished as-welded (ASW) creviced and non-creviced specimens and as-welded plus solution heat-treated (ASW+SHT) creviced specimens. The latter contained the black annealing oxide film on the surface. Results show that, in a few immersion days E{sub corr} reached a stable value higher than the open circuit potential of a platinum electrode in 18 m CaCl{sub 2} + 9 m Ca(NO{sub 3}){sub 2} for all specimens tested. Specimens tested in this solution did not suffer any type of localized attack. On the other hand, E{sub corr} showed oscillations of up to 600 mV in 18 m CaCl{sub 2} + 0.9 m Ca(NO{sub 3}){sub 2} during the entire immersion period. These oscillations were due to pitting corrosion development. Crevice corrosion was not observed in any testing case. Corrosion rates for specimens in the latter solution ([NO{sub 3}{sup -}]/[Cl{sup -}] = 0.05) were one order of magnitude higher than for specimens in the second one ([NO{sub 3}{sup -}]/[Cl{sup -}] = 0.5). Nitrate showed to be able to inhibit localized attack even in hot concentrated chloride brines when present in a ratio of [NO{sub 3}{sup -}]/[Cl{sup -}] = 0.5. Localized corrosion occurred only in condition where E{sub corr} > E{sub crit}.« less
  • The approach of isolating high-level nuclear waste in the designated site of Yucca Mountain (Nevada) is to separate it from the environment using a series of engineering and natural barriers. The container for the waste will consist of two concentric metal cylinders. The outer cylinder is going to be fabricated of Alloy 22 (N06022). If water is present at the site, several corrosion processes may occur. These include passive or general corrosion, localized corrosion and environmentally assisted cracking. The occurrence of one (or more) mode of corrosion over another will be determined by the redox potential of the aqueous electrolytemore » that may enter in contact with the container. This redox potential will also control the corrosion potential (E{sub corr}) of the container. This paper summarizes the findings of an extensive laboratory testing aimed at measuring E{sub corr} of Alloy 22 in presence of a variety of electrolyte solutions. Some of these solutions are multi-ionic electrolytes that may simulate concentrated ground waters. Other environments are chemical solutions of pure salts, which are highly unlikely for an underground repository but that may establish an extreme bounding condition. Current results show that the highest measured potential for Alloy 22 was approximately +0.3 to 0.4 V in the saturated silver chloride [SSC] scale. Most of the E{sub corr} values are in the order of 0 V [SSC] or below.« less
  • We have used an atomic force microscope (AFM) to characterize the surface topographies of weight-loss coupons of Alloy C-22 which had been exposed to two different environments in the Long-Term Corrosion Test Facility at LLNL for one year. We have observed a silicate deposit on these coupons, with the most extensive coverage occurring on the coupon immersed in an acidified bath. We have not detected localized corrosion on these coupons.