Intergranular Stress Corrosion Cracking Growth Behavior of Ni-Cr-Fe Alloys in Pressurized Water Reactor Primary Water Available to Purchase

The purpose of this research was to compare the stress corrosion cracking (SCC) resistance of materials used at the present time for steam generator (SG) tubing in pressurized water reactor (PWR) primary water. Our results in PWR primary water for 20% cold-worked (CW) Alloy 800 (UNS N08800) are compared with already published data for SCC growth from 20%CW Alloy thermally treated (TT)690 (UNS N06690), 20%CW Alloy mill-annealed (MA)600 (UNS N06600), and 20%CW austenitic stainless steels. The second purpose was to examine the dependence of SCC growth on nickel and chromium in PWR primary water; the objective was to obtain the basic knowledge to understand SCC behavior of SG tubing materials. The third objective was to understand whether accelerated testing at higher temperatures is appropriate for predicting SCC initiation and growth at lower temperatures. For these objectives, SCC growth was measured in PWR primary water at 290, 320, 330, 340, and 360°C under static load conditions. Tests were performed using 0.5T compact tension-type specimens using laboratory-melted 20%CW Alloy 800 (UNS N08800, CW800NG) and 20%CW X%Ni-16%CW-Fe alloys in the range of nickel concentration between 16% to 60%. Four important patterns were observed. First, excellent SCC growth resistance was observed for 20%CW 800NG at 320°C and 340°C; second, significant effect of nickel on IGSCC resistance was observed at 340°C and 360°C. The rate of IGSCC growth decreases with increasing nickel concentration in the range of nickel concentration between 10% to 25% nickel; then, the rate of IGSCC increases with increasing nickel concentration in the range of nickel content between 50% to 76%. This trend is quite similar to the results reported by Coriou and Staehle tested in dearated pure water at 350°C. No significant dependence of IGSCC in pure water at 320°C and 290°C was observed. The change in SCC growth dependence on nickel concentration suggested that the main rate-limiting processes on IGSCC growth seems to change between 320°C to 340°C. Third, significant beneficial effects of chromium in alloys were observed at 320°C. However, no beneficial effect of chromium addition in alloys was observed at 360°C. Finally, peak temperatures in growth rate of IGSCC were observed in almost all test materials except for 20%CW Alloy 600. The most important engineering meaning of the complicated temperature dependence with peak is that the mechanism of IGSCC growth at higher temperature is different from that at operating temperature. Furthermore, the order of SCC resistance at higher temperature is not the same at operating temperature. This means that we should pay careful attention to assess SCC from accelerated testing at higher temperatures.