Pacific Northwest National Laboratory Investigation of Stress Corrosion Cracking in Nickel-Base Alloys: Stress Corrosion Cracking of Cold Worked Alloy 690 (NUREG/CR-7103, Volume 3, PNNL-24647)

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Publication Information

Manuscript Completed: September 2015
Date Published: July 2016

Prepared by:
M.B. Toloczko, N.R. Overman, M.J. Olszta, and S.M. Bruemmer

Pacific Northwest National Laboratory
902 Battelle Boulevard
Richland, Washington 99352

Greg Oberson
NRC Contracting Officer's Representative

NRC Job Code Number N6925

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

The report summarizes the results of a testing program to evaluate the effects of cold work, including rolling, forging, and tensile straining, on the primary water stress corrosion cracking (PWSCC) susceptibility of alloy 690. Alloy 690 is a high-chromium, nickel-base material used in reactor pressure vessel head penetration nozzles, steam generator divider plates, and other components. Prior testing indicated that an increase in the amount of cold work increases the crack growth rate in alloy 690, but the relationships between the degree of cold work, the material microstructure, and the cracking behavior were not systematically investigated. For this study, PWSCC growth rates were measured for a total of 37 different alloy 690 specimens in simulated primary water reactor environments. The alloy 690 test materials included six different heats of extruded control-rod-drive mechanism (CRDM) tubing and five plate/bar heats with variations in the degree of cold work, from no cold work to cold work greater than 30%. In addition, different thermo-mechanical treatments were applied to some heats of material before cold working, thereby altering properties such as the grain boundary carbide morphology, to assess how this would affect the PWSCC response. Materials were examined by optical microscopy, electron microscopy, electron backscatter diffraction, and other characterization techniques to devise a mechanistic explanation for the test results and to identify the key parameters that control the PWSCC susceptibility.