Tomoki Miyamoto

Corrosion Behavior of Stainless Steels in Simulated PWR Primary Water : Effect of Chromium Content in Alloys and Dissolved Hydrogen

The structure and composition of surface oxide films on austenitic stainless steels in hydrogenated high-temperature water were examined by changing the chromium content in alloys and the concentration of dissolved hydrogen in high-temperature water. Auger electron spectroscopy, X-ray diffraction and analytical transmission electron microscopy revealed that the oxide films had a double-layer structure: ironbased spinels as the outer layer and chromium-rich spinel oxide as the inner layer. Increasing the chromium content suppressed the corrosion rate and produced fine oxide particles with a higher chromium concentration in the inner layer. Increasing the concentration of dissolved hydrogen enhanced the corrosion rate without a notable change in oxide structure. These influences are considered to originate from changes in cation diffusion through the inner layer, such as a decrease in the lattice diffusion of iron in the inner layer due to a higher concentration of chromium in the oxide as a diffusion barrier for a high chromium content in the alloys and due to a lower oxygen partial pressure for a higher concentration of dissolved hydrogen.

Dependence of Stress Corrosion Cracking of Alloy 690 on Temperature, Cold Work, and Carbide Precipitation—Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for cold-worked, thermally treated Alloy 690 (UNS N06690, CW TT 690) and cold-worked, solution-treated Alloy 690 (CW ST 690) in hydrogenated pressurized water reactor (PWR) primary water under static load condition. Three important patterns were observed. First, intergranular stress corrosion cracking (IGSCC) was observed in CW TT 690 in PWR primary water in the range between 320°C and 360°C; this rate of SCC growth was slower than in CW mill-annealed Alloy 600 (UNS N06600, CW MA 600). No significant IGSCC was observed in CW ST 690 after 5,109 h in hydrogenated PWR primary water at 360°C. This is opposite of the behavior reported in the literature for high-temperature caustic solutions. Second, to assess the role of creep, rates of creep crack growth were measured in air, argon, and hydrogen gas environments using 20% CW TT 690 and 20% CW MA 600 in the range between 360°C and 460°C; intergranular creep cracking (IG creep cracking) wa...

Dependence of Stress Corrosion Cracking for Cold-Worked Stainless Steel on Temperature and Potential, and Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for nonsensitized and sensitized, cold-worked Type 316 (UNS S31600, CW316) and Type 304 (UNS S30400, CW304) in hydrogenated ...

Formation of Cavities Prior to Crack Initiation and Growth on Cold-Worked Carbon Steel in High-Temperature Water

Abstract The rate of growth of stress corrosion cracking (SCC) was measured for cold-worked carbon steel (ASTM A106 [UNS K03006]) in hydrogenated pure water under static load condition. Four import...

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

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 us...

Role of Cavity Formation in Crack Initiation of Cold-Worked Carbon Steel in High-Temperature Water

Crack initiation behavior was studied to understand the underlying processes during the incubation period for prediction of crack initiation after long-term exposure in high-temperature water. Tests were performed using blunt-notched compact tension-type specimens of cold-worked carbon steel (ASTM A106 [UNS K03006]) exposed under static load condition in hydrogenated pure water and in air in the range of temperatures between 320°C and 450°C. Five important patterns were observed. First, intergranular cracking was observed in both water and air, even in static load conditions when steel specimens had been cold-worked. Second, 1/T-type temperature dependencies of initiation times were observed for cold-worked (CW) carbon steel (CW carbon steel), and the crack initiation time in an operating plant (Point Lepreau Nuclear Generating Station, Point Lepreau, New Brunswick, Canada) seemed to lie in the extrapolated line of the experimental results. Third, cavities were identified at the grain boundaries at the bo...

Rapid nickel diffusion in cold-worked carbon steel at 320–450 °C

The diffusion coefficient of nickel in cold-worked carbon steel was determined with the diffusion couple method in the temperature range between 320 and 450 °C. Diffusion couple was prepared by electro-less nickel plating on the surface of a 20% cold-worked carbon steel. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time to 12,000 h. The diffusion coefficient (DNi) of nickel in cold-worked carbon steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 0% of nickel. The temperature dependence of DNi is expressed by DNi = (4.5 + 5.7/−2.5) × 10−11 exp (−146 ± 4 kJ mol−1/RT) m2s−1. The value of DNi at 320 °C is four orders of magnitude higher than the lattice diffusion coefficient of nickel in iron. The activation energy 146 kJ mol−1 is 54% of the activation energy 270.4 kJ mol−1 for lattice diffusion of nickel in the ferromagnetic state iron.

Role of Cavity Formation on Crack Growth of Cold‐Worked Carbon Steel, TT 690 and MA 600 in High Temperature Water

The role of cavity formation on crack growth of intergranular stress corrosion cracking (IGSCC) in high temperature water and creep cracking was examined in quantitatively for cold worked carbon steel (ASTM A106 (UNS K03006, CW carbon steel), Alloy 690 (UNSN06690, CW TT 690), and Alloy 600 (UNSN06600, CW MA 600). Three important patterns were observed: First, cavities were observed at grain boundaries just ahead crack tips and crack wall after tests in gas and high temperature water for all test materials. Second, population of cavities decreased with distance from crack tips and crack wall. This result seems to suggest that cavities will form at high stress region such as crack tips before crack advance as crack embryos. Third, good correlation was observed between the rate of cavity formation and crack growth of IGSCC and intergranular creep cracking not only carbon steel, but also TT690 and MA600. Finally, the formation of crack embryos from the collapse of vacancies induced by cold work and absorbed hydrogen play an important role on the process of crack growth both of SCC and creep for CW carbon steel, CW TT690, and CW MA600 in high temperature water.

Rapid nickel diffusion in cold-worked type 316 austenitic steel at 360–500 °C

Abstract The diffusion coefficient of nickel in cold-worked Type 316 austenitic steel was determined by the diffusion couple method in the temperature range between 360 and 500 °C. A diffusion couple was prepared by electroless nickel plating on the surface of a 20 % cold-worked Type 316 austenitic steel specimen. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time until 14 055 h. The diffusion coefficient of nickel (DNi) in cold-worked Type 316 austenitic steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 11 at.% of nickel. The value of DNi at 360 °C was about 5 000 times higher than the lattice diffusion coefficient of nickel in Type 316 austenitic steel. The determined activation energy 117 kJ mol−1 was 46.6 % of the activation energy 251 kJ mol−1 for the lattice diffusion of nickel in Type 316 austenitic steel.

Stress Corrosion Cracking Growth of Alloy 800NG in Pressurized Water Reactor Primary Water

The primary purpose of this research is to examine the stress corrosion cracking (SCC) resistance of Alloy 800NG in pressurized water reactor (PWR) primary water and pressurized heavy water reactor (PHWR) primary water. Rates of SCC growth of 20% cold-worked (CW) Alloy 800NG measured over the temperature range between 270°C and 360°C were compared with previously reported results for 20% CW Alloy TT690 and 20% CW Alloy 600 in order to consider which material is the most SCC resistant among materials presently being used for steam generator (SG) tubing worldwide. The secondary purpose is to examine the effect of chromium addition on SCC growth in PWR primary water of a series of alloys based on the Alloy 800 composition. SCC growth measurements were performed in PWR primary water over the chromium concentration range from 16% to 27% to obtain fundamental knowledge useful for considering a future alternative SCC-resistant material for SG tubing in extended life PWRs and PHWRs. The third objective is to exam...