Clues and issues in the SCC of high nickel alloys associated with dissolved lead

Roger W. Staehle

Research output: Chapter in Book/Report/Conference proceedingConference contribution

36 Scopus citations

Abstract

Effects of lead (Pb) on the SCC (PbSCC) of high nickel alloys are now well known to be a concern in modern steam generators (SG) including those using Alloy 690TT tubes. Pb has now been observed at the tips of SCC from numerous steam generator tubes of Alloy 600MA. The purpose of this discussion is to review special features associated with PbSCC and to assess what these mean to the occurrence of PbSCC in the future. Important characteristics of PbSCC seem to be the following: Occurrence in both Alloy 600MA/TT and 690TT, although the latter is less prominent than the former in neutral solutions; greatly accelerated PbSCC in alkaline steam and single phase water for Alloy 690TT; reduction in intensity at neutral pH for Alloy 690TT and significant PbSCC for Alloy 600; proneness to PbSCC in acidic solutions containing chloride and negligible effect of Pb in sulfate solutions; significant PbSCC for high nickel commercial alloys including Alloy 800; simultaneous formation of scales (PbGC) with PbSCC for higher chromium alloys; significant migration of Pb to crack tips in alkaline solutions with the largest accumulation midway in SCC; diminished Pb at crack tip in acidic solutions; generally intergranular SCC in MA heat treatments and transgranular SCC in TT, SN, and SR heat treatments; high Pb concentration of Pb and Pb compounds at heat transfer surfaces both in recirculating and once through SGs; significant accumulation on hot surfaces while the Pb concentration in feedwater is in the ppt range; and, finally, small extent of SCC in SGs even with Alloy 600 despite significant quantities of Pb observed in deposits. There is evidence that a significant amount of IGSCC in the past could be attributed to Pb in view of IGSCC nature of Alloy 600MA. To date, no SCC due to Pb has been observed in Alloy 690 in service. This may be due to a lesser concentration in deposits with line contact crevices on the secondary side of SGs or it may be due to the lower rate of PbSCC in relatively neutral solutions. Future PbSCC of Alloy 690TT should be considered in view of the propensity of this alloy to form scales on the surface and inside of PbSCC. Based on the trends to date together with the inherently possible PbSCC, additional research and modeling are proposed.

Original languageEnglish (US)
Title of host publicationProceedings of the Twelfth International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors
Pages1163-1210
Number of pages48
StatePublished - Dec 1 2005
Event12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors - Salt Lake City, UT, United States
Duration: Aug 14 2005Aug 18 2005

Publication series

NameProceedings of the Twelfth International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors

Other

Other12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors
CountryUnited States
CitySalt Lake City, UT
Period8/14/058/18/05

Keywords

  • High Nickel Alloys
  • Lead
  • Stress Corrosion Cracking

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