Role of Metastable Pitting in Crevices on Crevice Stabilization in Alloys 625 and 22

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Description

The metastable pitting behavior inside crevices of alloys 625 and 22 was examined to obtain insight into differences in crevice corrosion susceptibility between alloys 625 and 22. Metastable corrosion event rates recorded as current-time transients were found to increase with increasing applied potential and temperature for both alloys. However, the increase was more significant for 625 as compared to alloy 22 and the cumulative number of events was greater. A strong correlation was obtained between the increase in event rates and decrease in crevice stabilization potential with temperature. Metastable peak heights, values for peak integrated charge, and current/pit depth (I/r) ... continued below

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44 pages

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Kehler, B.A. & Scully, J.R. January 11, 2005.

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Description

The metastable pitting behavior inside crevices of alloys 625 and 22 was examined to obtain insight into differences in crevice corrosion susceptibility between alloys 625 and 22. Metastable corrosion event rates recorded as current-time transients were found to increase with increasing applied potential and temperature for both alloys. However, the increase was more significant for 625 as compared to alloy 22 and the cumulative number of events was greater. A strong correlation was obtained between the increase in event rates and decrease in crevice stabilization potential with temperature. Metastable peak heights, values for peak integrated charge, and current/pit depth (I/r) ratios were not strongly affected by these driving forces. The alloying content in alloy 22, traced to increased molybdenum (Mo) and tungsten (W), was rationalized to decrease the metastable event rate and hence, the cumulative number of events after a given time. However, metastable peak heights, values for peak integrated charge, and I/r ratios, as well as metastable peak shapes associated with individual events, were not strongly affected by alloy type in the narrow range of Mo contents explored here. Observed differences in resistance to crevice corrosion stabilization are rationalized to depend on differences in the cumulative number of metastable events occurring sufficiently close in space and time to contribute to the development of a critical crevice chemistry at specific depths in a crevice. The properties of individual events did not have a significant effect. Stable crevice corrosion eventually occurred at the sites where a row of metastable pits formed at a critical distance from the crevice mouth. This row of pit sites focused acidification, which contributed to local depassivation.

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44 pages

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OSTI as DE00840137

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  • Other Information: PBD: 11 Jan 2005

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  • Report No.: NONE
  • Grant Number: NONE
  • DOI: 10.2172/840137 | External Link
  • Office of Scientific & Technical Information Report Number: 840137
  • Archival Resource Key: ark:/67531/metadc783110

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • January 11, 2005

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • Feb. 10, 2016, 6:31 p.m.

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Kehler, B.A. & Scully, J.R. Role of Metastable Pitting in Crevices on Crevice Stabilization in Alloys 625 and 22, report, January 11, 2005; Las Vegas, Nevada. (digital.library.unt.edu/ark:/67531/metadc783110/: accessed December 13, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.