Steel In High Temperature Water Research Articles

Application of the FRI crack growth model for neutron-irradiated stainless steels in high-temperature water of a boiling water reactor environment

This study considered a methodology to reflect the effect on material properties by neutron irradiation onto the FRI model of the crack growth rate (CGR) of stress corrosion cracking developed at Tohoku University. Yield strength and strain hardening exponent were evaluated by a tensile test for irradiated stainless steels, and the relationship between mechanical property and strain to fracture of the oxide film was derived. Effect of the radiation-induced segregation on CGR was also discussed. The experimental tendencies for the CGR to increase with dose and almost saturate above 3dpa were well replicated by the model calculations.

Strain-rate dependent fatigue behavior of 316LN stainless steel in high-temperature water

Low cycle fatigue behavior of forged 316LN stainless steel was investigated in high-temperature water. It was found that the fatigue life of 316LN stainless steel decreased with decreasing strain rate from 0.4 to 0.004 %s−1 in 300 °C water. The stress amplitude increased with decreasing strain rate during fatigue tests, which was a typical characteristic of dynamic strain aging. The fatigue cracks mainly initiated at pits and slip bands. The interactive effect between dynamic strain aging and electrochemical factors on fatigue crack initiation is discussed.

Effect of Oxidation on the Fatigue Crack Propagation Behavior of Z3CN20.09M Duplex Stainless Steel in High Temperature Water

Abstract The fatigue crack propagation behaviors of Z3CN20.09M duplex stainless steel (DSS) were investigated by studying oxide films of specimens tested in 290°C water and air. The results indicate that a full oxide film that consisted of oxides and hydroxides was formed in 290°C water. By contrast, only a half-baked oxide film consisting of oxides was formed in 290°C air. Both environments are able to deteriorate the elastic modulus and hardness of the oxide films, especially the 290°C water. The fatigue lives of the specimens tested in 290°C air were about twice of those tested in 290°C water at all strain amplitudes. Moreover, the crack propagation rates of the specimen tested in 290°C water were confirmed to be faster than those tested in 290°C air, which was thought to be due to the deteriorative strength of the oxide films induced by the mutual promotion of oxidation and crack propagation at the crack tip. It is noteworthy that the crack propagation can be postponed by the ferrite phase in the DSS, especially when the specimens were tested in 290°C water.

Influence of Aluminum Addition on the Corrosion of 304 Stainless Steel in High Temperature Water

The influence of Al3+ addition on the corrosion of 304 stainless steel (SS) in high temperature water has been investigated by gravimetric analysis, potentiodynamic polarization and Mott-Schottky plots. After Al3+ addition, the amount of oxidized metal on 304 SS was reduced, the open circuit potential was shifted towards positive direction, the passive current density was declined, and the donor density of the oxide film formed on 304 SS surface was decreased. The corrosion kinetics of 304 SS in this work was curved to be parabolic with a 25% reduction of the parabolic rate constant by Al3+ addition. The activation energy of the corrosion process was increased due to the presence of Al which slowed down the 304 SS corrosion. The structure and composition of oxide film formed on 304 SS in high temperature water may be changed by Al3+ addition. The work may give a decent route for radiation field or consumption control in the essential circuit water of PWR.

高温水中での鋭敏化304鋼の応力腐食割れ発生挙動に及ぼす硫酸塩添加の影響

加速試験法検討の一環としてBWR一次冷却水系での応力腐食割れ発生挙動に及ぼす硫酸塩の影響を調べるために，288℃の硫酸ナトリウム水溶液中で鋭敏化304ステンレス鋼試験片のすきま付き曲げ試験（CBB試験）を行った．30～500 ppbのSO42−添加は，深さ1 μm以上の全き裂発生数，および深さ50 μm以上の進展性き裂発生数の両者を増加させた．SO42−濃度100 ppb以下では，他の多くの観測例と同様，応力腐食き裂発生の空間分布がPoisson分布に適合したが，300 ppb以上では不適合であった．き裂発生の累積確率の新たな推定方法としてPoisson分布近似法が提示され，その有効性が確認された．Poisson確率過程モデルに基づく解析により，き裂発生寿命分布下界値aestのSO42−濃度依存性として，aest＝683/[SO42−]が推定された．例えば，40 ppbのSO42−添加により，き裂発生の確率的性格を変えずにき裂発生寿命分布下界値を10分の1に短縮することができる．硫酸塩添加によるaestの短縮は，電気伝導率ではなく，SO42−そのものに依存する事象と考えられた．

The Effects of Trace PbO on the Oxide Behavior of 304L Stainless Steel in High Temperature Water

The Effects of Trace PbO on the Oxide Behavior of 304L Stainless Steel in High Temperature Water

Crack growth behavior of warm-rolled 316L austenitic stainless steel in high-temperature hydrogenated water

To investigate the effects of warm rolling on the crack growth of 316L austenitic stainless steel, the crack growth rate was measured and the oxide structure was characterized in high-temperature hydrogenated water. The warm-rolled specimens showed a higher crack growth rate compared to the as-received specimens because the slip bands and dislocations produced during warm rolling served as paths for corrosion and cracking. The crack growth rate increased with the dissolved hydrogen concentration. This may be attributed to the decrease in performance and stability of the protective oxide layer formed on the surface of stainless steel in high-temperature water.

Effects of chloride and oxygen on stress corrosion cracking of cold worked 316/316L austenitic stainless steel in high temperature water

Cold work of materials, dissolved oxygen and chloride in water are crucial factors that accelerate the stress corrosion cracking (SCC) crack growth rate of stainless steel in high temperature water. Cold worked austenitic stainless steel type 316 and 316L were studied in order to obtain their effects on SCC crack growth rates in 288 and 325°C water. Similar SCC behavior were identified for 316 and 316L. Cold working induced comparatively high crack growth rate up to 10−8mm/s even in hydrogenated water, and the collaboration of dissolved oxygen and chloride in water accelerated the SCC crack growth rates much more significantly.

Corrosion Mechanism of Low-Alloyed Steel in High-Temperature Water: Effect of Additives and Time of Exposure

The present paper investigates the effect of exposure time, chloride and sulfate additions on the corrosion mechanism of low-alloyed steel in a cladding flaw of a nuclear reactor pressure vessel using in-situ electrochemical impedance spectroscopy coupled to ex-situ characterization of the oxides by surface analytical techniques. A quantitative interpretation of impedance spectra using the Mixed-Conduction Model for oxide films formed in high-temperature water allows for a discrimination between the rates of inner layer formation and cation transmission through that layer. The values of the inner layer thickness and cation release estimated from impedance measurements are in good agreement with those stemming from ex-situ analysis. At short exposure times, higher film formation and cation release rates of LAS are measured in the presence of chloride and sulfate additives. However, the effect of exposure time itself appears to be stronger than that of the impurities, and the protective ability of the oxides at longer exposure times starts to dominate the overall corrosion process.

Effect of thermal aging on corrosion fatigue of Z3CN20.09M duplex stainless steel in high temperature water

The effects of 475°C embrittlement on the corrosion fatigue (CF) in 290°C water, mechanical and corrosion properties of Z3CN20.09M duplex stainless steel (DSS) were investigated. The results indicated that the hardness and modulus of the ferrite in this steel increased while the impact energy and corrosion resistance decreased with increasing aging time. It is interested that these results were reversed when the aging time is up to 2000h, suggesting that a self-healing behavior was occurred probably. The CF life of the specimens decreased with increasing aging time, which attributed to a combined effect of the deteriorated mechanical and corrosion properties subjected by the thermal aging.

Corrosion behavior of TiO2-treated type 304 stainless steels in high temperature water containing with hydrogen peroxide

ABSTRACTTitanium dioxide (TiO2) treatment coupled with ultraviolet irradiation was selected as a corrosion mitigation technique for Type 304 stainless steel (SS) in high-temperature pure water with the presence of hydrogen peroxide (H2O2). Type 304 SS specimens were pre-oxidized in oxygenated pure water at 288 °C and then coated with TiO2 nanoparticles by hydrothermal deposition. Electrochemical polarization analyses were conducted to investigate the corrosion behavior of both TiO2-treated and pre-oxidized specimens in 288 °C pure water with 300 ppb H2O2. Ultraviolet (UV) irradiation was then imposed upon the TiO2-treated specimens to examine if there was any distinct photoelectric effect on the corrosion behavior of the treated samples. It was found that the electrochemical corrosion potentials of the TiO2 treated specimens under UV irradiation were 10–20 mV lower than those without UV. In addition, the corrosion current densities of the treated specimens were also lower in the presence of UV radiation. Without UV radiation, however, no significant differences were observed between the TiO2 treated and untreated specimens. These results indicate that the TiO2 treatment in combination with UV radiation would reduce the corrosion rate of Type 304 SS in H2O2-rich, high-temperature pure water.

Effect of dissolved hydrogen on corrosion of 316NG stainless steel in high temperature water

Characterizations of oxide films formed on 316 stainless steel in high temperature, hydrogenated water were conducted. The results show the oxide film consists of an outer layer with oxide particles of Fe–Ni spinel and hematite, and an inner continuous layer of Fe–Cr–Ni spinel. Increasing dissolved hydrogen (DH) concentrations causes decrease of Cr- and increase of Fe-concentrations in the inner layer. A continuous decrease of Cr- and increase of Fe-concentrations was observed from the surface of the inner layer to the oxide/substrate interface. The DH effect is attributed to the enhanced diffusion of Fe ions in the oxide film by hydrogen.

Stress Corrsion Cracking of Austenitic Stainless Steels in High Temperature Water and Alternative Stainless Steel

In order to clarify the effect of SFE on SCC resistance of austenitic stainless steels and to develop the alternative material of Type 316LN stainless steel for BWR application, the effect of chemical composition and heat treatment on SFE value and SCCGR in oxygenated high temperature water were studied. The correlation factors between SFE values for 54 heats of materials and their chemical compositions for nickel, molybdenum, chromium, manganese, nitrogen, silicon and carbon were obtained. From these correlation factors, original formulae for SFE values calculation of austenitic stainless steels in the SHTWC, SHTFC and AGG conditions were established. The maximum crack length, average crack length and cracked area of the IGSCC for 33 heats were evaluated as IGSCC resistance in oxygenated high temperature water. The IGSCC resistance of strain hardened non-sensitized austenitic stainless steels in oxygenated high temperature water increases with increasing of nickel contents and SFE values. From this study, it is suggested that the SFE value is a key parameter for the IGSCC resistance of non-sensitized strain hardened austenitic stainless steels. As an alternative material of Type 316LN stainless steel, increased SFE value material, which is high nickel, high chromium, low silicon and low nitrogen material, is recommendable.

Evaluation of temperature effect on the corrosion process of 304 stainless steel in high temperature water with electrochemical noise

The effect of temperature on corrosion process of 304 stainless steel (SS) in high temperature water was investigated by electrochemical noise (EN), scanning electron microscope (SEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the corrosion process could be divided into two stages (passivity and active dissolution) with the increasing temperature. At 100°C, the oxide film was a single layer mainly consisting of Cr2O3. However, at 250°C, it became a double layer with an inner layer of Cr–Fe spinel compound and an out precipitated layer. The related growth mechanisms of the oxide film were also discussed.

Effect of chloride and sulfate additions on corrosion of low alloy steel in high-temperature water

The present paper investigates the effect of chloride and sulfate additions on corrosion of low-alloyed steel in a cladding flaw of a nuclear reactor pressure vessel using in-situ electrochemical impedance spectroscopy coupled to ex-situ characterization of the oxides by surface analytical techniques. Impedance data are interpreted by the mixed-conduction model for oxide films to yield estimates for the main kinetic and transport parameters of the corrosion process. It can be concluded that the effect of chloride/sulfate transients on low-alloyed steel oxides is moderate, concerns mostly the processes at the inner layer/coolant interface and is to a certain extent reversible.

Effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel in high temperature water

The effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel (SS) in 320°C water and air environments was investigated by corrosion fatigue cracking test system, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The experimental results indicated that the cracks were found to be initiated at first 20% of fatigue life of the specimens tested in 320°C water, while only a few cracks were found until fracture when tested in 320°C air. The crack propagation rates of the specimens tested in 320°C water were obviously faster than those tested in 320°C air especially at lower strain amplitude of ±0.5%. This can be attributed to the oxidation behavior of the 316LN SS specimens tested in 320°C water was more serious than those tested in 320°C air. The compositions were more complex of the oxide films formed in 320°C water than those tested in 320°C air, which lead to crack initiation easier in the former. Moreover, the 320°C water made the mechanical properties of the oxide films worse, resulting in a faster fatigue crack propagation rate at crack tip.

Effects of Forging and Heat Treatments on the Microstructure and Oxidation Behavior of 316LN Stainless Steel in High Temperature Water

Microstructure of 316LN stainless steel (ss), including the as-received material and samples processed by solution anneal treatment and stress relief treatment after forging, was characterized by Vickers hardness (HV) testing and electron back scattering diffraction (EBSD). The oxide film formed on samples after immersion in borated and lithiated water at 583.15 K was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results showed that the grain size of samples was largely reduced after forging. Higher fraction of coincidence site lattice (CSL) boundaries and lower residual strain were observed in samples with either solution anneal treatment or stress relief treatment. The proportion of CSL boundaries was largely enhanced by solution anneal treatment after forging, due to the recrystallization occurring during solution anneal treatment. The oxide film grown on 316LNss with solution anneal treatment after forging exhibited more strong protectiveness, as compared to the oxide film grown on samples with stress relief treatment after forging and the oxide film grown on as-received samples without forging. The mechanisms of oxidation were then discussed.

SCC behaviours of austenitic stainless steel Z3CN20-09M in high temperature water

Stress corrosion cracking (SCC) behaviours of Z3CN20-09M stainless steel in high temperature water containing Cl− were studied. The results indicated that SCC sensitivity was inconsistent with test temperature. The minimum and maximum of SCC sensitivity occurred at 320 and 290°C respectively, and SCC sensitivity at 250°C fell between them. SCC crack initiated preferentially at bottom of corrosion pit or along phase boundary between austenite and ferrite, and its propagation depended on relative orientation to the phase boundary. SCC crack parallel to the phase boundary propagated along the phase boundary, while that perpendicular to the phase boundary was hindered to propagate.

Effect of sigma phase on the low cycle fatigue property of Z3CN20.09M cast duplex stainless steel in high temperature water

The effect of sigma phase on the low cycle fatigue (LCF) property of Z3CN20.09M cast duplex stainless steel (DSS) was investigated by corrosion fatigue cracking test system and scanning electron microscopy (SEM). The results showed that the fatigue lives of the aged Z3CN20.09M DSS specimens decreased with the increase of aging time. The Cr‐depleted zones around the sigma phase are sensitive to pitting and preferential to forming fatigue cracks. Moreover, the precipitation of sigma phase was also found to degrade markedly the fatigue property of the DSS as it leads to fracture of ferrite during fatigue tests.

Electrochemical Noise Study on the Corrosion Behavior of 304NG Stainless Steel in High Temperature Water

This paper investigates the application of Electrochemical Noise (EN) to study the corrosion behavior of 304 nuclear-grade (NG) stainless steel (SS) in high purity water system at varying temperatures (105, 160, 190, 220, 250, 293°C) and pressures (0.6, 7, 9, 10.5, 16, 19MPa). An EN sensor has been developed and applied to the high temperature water system. The potential and coupling current noise were recorded simultaneously and a variety of analytical methods (such as wavelet transform, chaos theory, noise resistance (Rn), the spectral noise resistance (Rsn) and the direct current (DC) limit of the spectral noise resistance (R 0 sn )) have been used to obtain corrosion rate and corrosion form. EN analysis results demonstrated an increase in Rn with increasing temperature and pressure, except for a peak value at 293°C, 19MPa, which was possibly due to the change in the thickness of passive film; combined chaos analysis results with morphology analysis, we may infer that the corrosion form of 304NG SS under high purity water system at high temperature and high pressure is general corrosion.