United States Nuclear Regulatory Commission - Protecting People and the Environment

Pacific Northwest National Laboratory Investigation of Stress Corrosion Cracking in Nickel-Base Alloys: Behavior of Alloy 152 And 52 Welds (NUREG/CR-7103, Volume 4)

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Publication Information

Manuscript Completed: December 2017
Date Published:
April 2019

Prepared by:
S. M. Bruemmer
M. J. Olszta
R.J. Seffens
R.A. Bouffioux
N.R. Overman
M. B. Toloczko

Pacific Northwest National Laboratory
Richland, WA 99352

Margaret Audrain, NRC Project Manager

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

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Abstract

This report summarizes experimental results evaluating the primary water stress corrosion cracking (PWSCC) susceptibility of high-chromium, nickel-base weld metals and interface regions in more complex dissimilar metal welds. The primary research objectives were to establish quantitative measurements of SCC growth rates and determine relationships among cracking susceptibility, metallurgical characteristics and environmental conditions. Crack-growth rates have been determined under cyclic loading and at constant stress intensity (K) in simulated PWR primary water environments for 21 weld metal specimens including tests on nine alloy 152, one alloy 152M, three alloy 52, seven alloy 52M and one alloy 52MSS specimens. In addition, SCC response was investigated from alloy 182/82 into alloy 52M for 4 alloy 52M/182 overlay weld specimens and 2 alloy 52M/82 inlay weld specimens. Finally, crack-growth behavior was evaluated at various regions in dissimilar metal (DM) welds including 9 tests at DM interfaces covering those between two alloy 152 and low alloy steel, one alloy 52M and low alloy steel, two alloy 152M and carbon steel, two alloy 52M and carbon steel, and two alloy 152 and stainless steel interfaces. Most test specimens were machined from industry mockups to provide plant-representative materials, while a few were produced at laboratories using industry recommended procedures. In all cases, crack extension was monitored in situ by direct current potential drop (DCPD) with an estimated length resolution of about ±1 µm making it possible to measure extremely low growth rates approaching 5x10-10 mm/s. Most SCC tests were performed at 360°C with a dissolved hydrogen concentration of 25 cc/kg to establish an electrochemical potential (ECP) at the Ni/NiO stability line where many nickel-base alloys are most susceptible to SCC; however, environmental conditions were modified during a few experiments to evaluate the influence of temperature, water chemistry or ECP on propagation rates. Extensive characterizations have been performed on material microstructures and stress-corrosion cracks by optical and electron microscopy techniques and linked to crack-growth test results to help define material and environmental parameters controlling SCC susceptibility.

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