High Temperature Pure Water Research Articles

S1103-2-2 高温純水中におけるインパクトフレッティングの装置開発(第15回卒業研究コンテスト(2))

S1103-2-2 高温純水中におけるインパクトフレッティングの装置開発(第15回卒業研究コンテスト(2))

Effects of Flow Rate on Dissolution of Monocrystal Alumina and Monocrystal Yttria-Stabilized Zirconia in High-Temperature Pure Water

Effects of Flow Rate on Dissolution of Monocrystal Alumina and Monocrystal Yttria-Stabilized Zirconia in High-Temperature Pure Water

521 高温純水中におけるニッケル基690合金のSCC割れ感受性評価(金属/金属基複合材料)

521 高温純水中におけるニッケル基690合金のSCC割れ感受性評価(金属/金属基複合材料)

Effects of loading mode and water chemistry on stress corrosion crack growth behavior of 316L HAZ and weld metal materials in high temperature pure water

The stress corrosion cracking (SCC) growth rates of 316L weld heat-affected zone (HAZ) and weld metal materials in high temperature pure water at 288 °C were measured using contoured double cantilever beam (CDCB) specimens and an alternating current potential drop (ACPD) in situ crack-length monitoring system. The effects of loading mode and dissolved oxygen and hydrogen on crack growth rate (CGR) were experimentally quantified. Typical intergranular SCC was found in the HAZ specimen and interdendritic SCC was identified in the weld metal specimen. The HAZ specimen and the weld metal specimen showed quite a similar response to the applied loading modes and the water chemistry, even though their absolute CGR values were different. The crack growth rates under trapezoidal loading were moderately higher than those under constant loading by several tenths percent. Switching the water chemistry from the oxygen-bearing water to the hydrogen-bearing water drastically decreased the electrochemical potential and the crack growth rate, and vice versa. A time-lag period for crack growth was observed after switching the water chemistry back to the oxygen-bearing water, where the crack growth rate was low even the dissolved oxygen concentration and the electrochemical potential had become high. Strain hardening and the resultant uneven distribution of deformation contribute to the enhanced intergranular SCC growth behavior in the HAZ area. The crack growth kinetics is analyzed based on the deformation/oxidation interaction at the crack tip, considering the importance of the electric-charge transfer, mass transport kinetics and the crack tip strain rate.

Evaluation of Stress Corrosion Cracking of Type 304L Stainless Steel in Low Concentration Sodium Hydroxide Solution with High Temperature

Stress corrosion cracking (SCC) of austenitic stainless steel serviced in aggressive environment often occurs in power, petrochemical industry, and leads to premature equipment failure and great economic loss. This paper focuses on the problem of the SCC on the 304L stainless steel nozzle of a hydrogenation reactor, which is caused due to on-line alkali cleaning. Susceptibility for SCC was evaluated by Slow Strain Rate Test (SSRT) for as-rolled and sensitized 304L stainless steel in low concentration sodium hydroxide solution with high temperature. The effects of different strain rates, different concentration of sodium hydroxide and different solution temperatures on SCC were investigated. On the basis of this, the contrast tests were also performed in high temperature pure water. After SSRT, fractograph of the fractured specimens was analyzed by using scanning electron microscopy (SEM).

Effects of Hydrogen Peroxide on Corrosion of Stainless Steel (VI)

Anodic and cathodic polarization properties of stainless steel in high temperature pure water were measured to understand different responses of electrochemical corrosion potential (ECP) and frequency dependent complex impedance (FDCI) on H2O2 and O2. The findings are summarized as follows: 1. A Pt temporary reference electrode supported by an external Ag/AgCl reference electrode could be applied for stable measurement of polarization properties. 2. The cathodic current densities of the specimens exposed to H2O2 were determined by the H2O2 redox current, the anodic current densities were determined mainly by H2O2 oxidation current, and both were determined by [H2O2]. However, both anodic and cathodic current densities of the specimens exposed to O2 were not much influenced by [O2]. 3. ECP was saturated against [H2O2] and this resulted from the compensation of [H2O2] dependences of anodic and cathodic current densities. 4. Crack growth rate could be expressed as a function of modified ECP, which was designated as the potential on the anodic polarization curve of the specimens exposed to O2 with the same corrosion current density as the net corrosion current density of the specimens exposed to H2O2.

An Electrochemical Sensor Array for In-situ Measurements of Oxide Film Electric Resistance in High Temperature Water

Corrosive conditions in primary cooling systems of boiling water reactors are determined by oxidants, e.g., O2, H2O2 and other corrosive radiolytic species. A high temperature high pressure water loop, which controls H2O2 concentration with minimal O2 co-existence, was constructed in order to evaluate the effects of H2O2 on corrosive conditions, and then static and dynamic responses of stainless steel specimens exposed to H2O2 and O2 in high temperature pure water were evaluated by analyzing ECP (electrochemical corrosion potential) and FDCI (frequency dependent complex impedance). At the same time, in- situ measurements were carried out to determine changes in oxide film electric resistance. From the multilateral high temperature measurements, it was concluded that H2O2 concentrations could be determined by in- situ measurement based on a sensor complex for ECP and FDCI and that ECP and [H2O2] data could be used to evaluate occurrence and propagation of intergranular corrosion cracking of reactor internal components.

An ATEM study of oxidation behavior of SCC crack tips in 304L stainless steel in high temperature oxygenated water

Oxidation behavior at the tips of several stress corrosion cracking (SCC) crack, including intergranular SCC (IGSCC) and transgranular SCC (TGSCC) cracks, in heat-treated 304L stainless steel in high temperature oxygenated water was studied using a field emission gun-analytical transmission electron microscopy (FEG–ATEM). These SCC cracks were produced during SCC tests in two different heat-treated 304L stainless steels in high temperature pure water with two different levels of dissolved oxygen (DO). The study showed that oxygen played a key role in nucleation and propagation of SCC cracks. For the IGSCC crack, oxidation took place followed by nucleation and growth of microcracks in the oxide ahead of the crack tip on the grain boundary plane. The IGSCC crack then propagated by linkage with these microcracks. Oxides formed in the high temperature water with different DO had different configurations and microstructures. In the case of low DO, separate oxides of Cr 2O 3 and Fe 3O 4 types were formed, while the oxide formed in high DO consisted of mixed FeCr 2O 4 and Fe 3O 4. For the TGSCC crack, oxidation along deformation bands and nucleation and growth of microcracks within oxide were important mechanisms. It was found that Si was preferentially oxidized ahead of the crack tip, promoting SCC crack propagation. Ni enrichment at some SCC crack tips was also revealed.

The Influence of ZrO2 Treatment on the Electrochemical Behavior of Oxygen and Hydrogen on Type 304 Stainless Steels in High Temperature Water

For enhancing the effectiveness of hydrogen water chemistry (HWC) in boiling water reactors (BWRs) in the aspects of lower hydrogen consumption and of a more effective reduction in electrochemical corrosion potential (ECP), the technique of inhibitive protective coating on structural materials was brought into consideration. The application of inhibitive treatment is aimed at deterring the reduction reactions of oxidizing species occurring on metal surfaces and the oxidation reaction of metals. In the current study, electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of ZrO2 treated and untreated 304 stainless steel specimens in pure water with dissolved oxygen or hydrogen. The polarization results showed that the treated specimens exhibited lower corrosion potentials, corrosion current densities, exchange current densities, and cathodic current densities than the untreated one in high temperature pure water with dissolved oxygen. For the environment with dissolved hydrogen only, reductions in anodic current density and exchange current density were observed, indicating that the ZrO2 treatment also deterred the oxidation reaction of hydrogen. However, in comparison with the data obtained, the ZrO2 treatment seemed to be relatively more effective in inhibiting the oxygen reduction reaction than inhibiting the hydrogen oxidation reaction. One additional beneficial outcome was that the anodic current density of the metal was also decreased, leading to a much lower overall corrosion current density of the ZrO2 treated specimen.

The Influence of Dissolved Hydrogen on the Corrosion of Type 304 Stainless Steels Treated with Inhibitive Chemicals in High Temperature Pure Water

In order to assess the influence of dissolved hydrogen on the intergranular stress corrosion cracking (IGSCC) characteristics of Type 304 stainless steels treated with inhibitive chemicals, electrochemical corrosion potential (ECP) measurements and slow strain rate tensile (SSRT) tests were conducted in high temperature pure water. A number of thermally sensitized specimens were prepared and then pre-oxidized in a 288°C pure water environment with the presence of 300ppb dissolved oxygen for 360h. Most of the specimens were then separately treated with various inhibitive chemicals including powdered zirconium oxide (ZrO2), powdered titanium oxide (TiO2), and zirconyl nitrate [ZrO(NO3)2] via hydrothermal deposition at 150°C. Test environments with a dissolved oxygen concentration of 300ppb and various dissolved hydrogen concentrations at 288°C were created. Test results showed that the ECPs of the treated specimens were lower than that of the untreated one no matter what the dissolved hydrogen concentration was. In addition, IGSCC was observed on all specimens (treated or untreated) in all tested environments. However, the untreated specimen exhibited lower elongation, shorter failure time, and more secondary cracks on the lateral surfaces. It was therefore suggested that inhibitive chemicals such as ZrO2, TiO2, and ZrO(NO2)2 did provide a certain degree of enhancement in improving the mechanical behavior of the treated specimens and in prolonging IGSCC initiation times.

The Influence of Dissolved Hydrogen on the Corrosion of Type 304 Stainless Steels Treated with Inhibitive Chemicals in High Temperature Pure Water

The Influence of Dissolved Hydrogen on the Corrosion of Type 304 Stainless Steels Treated with Inhibitive Chemicals in High Temperature Pure Water

Effects of Environmental Factors on the Electronic Properties of Interfacial Oxide Film on 304L Stainless Steel in High Temperature Pure Water

The electronic properties of the interfacial oxide film formed on 304L stainless steel in high temperature water are investigated by contact electric resistance (CER) measurements. Tests are performed in pure water with a wide range of dissolved oxygen (DO) content at 200, 250, and 288°C. The electrochemical potential (ECP) moves in the noble direction and CER increases when increasing DO. Results show that DO content has a dominant effect on the electronic properties of oxide film. The change of oxide film properties can also be attributed to the variation of the electrochemical potential, which is directly affected by DO content. Critical potentials exist for the formation and reduction of oxide films in high temperature water. Multiple steps are found for the reduction of oxide films due to de-aeration in 200, 250, and 288°C water, implying the presence of multiple-layer interfacial oxide films. The film reduction process is relatively slower than the film formation process. Present results show that even in high purity water, a moderate change of DO content can result in different surface conditions. Dissolved hydrogen has a moderate effect on interfacial surface films in deaerated water. In-situ monitoring of the oxide film properties by CER technique provides information on the interfacial reactions that are related to the SCC behavior of materials in high temperature water environments.

Threshold for Stress Corrosion Cracking Initiation of Alloy X750 under Long-Term Uniaxial Constant Load Test in High-Temperature Water

Abstract Uniaxial constant load (UCL) tests of the nickel-based alloy X750 (UNS N07550) were performed in high-temperature pure water (288°C, 8 ppm dissolved oxygen [DO]) to investigate stress corrosion cracking (SCC) fracture time and the crack initiation process. The SCC fracture was initiated at a stress level below the 0.2% offset yield stress and many small cracks were observed in the middle of the nonfractured test specimens. The distribution of the crack length for each observation time is shown by Weibull probability distributions. Crack initiation and propagation process had different behavior depending on the applied stress level and the stress intensity factor at the crack tip. SCC initiation at the minimum applied stress is discussed with respect to the grain size, which depended on the size of an initial crack.

高温純水中応力腐食割れき裂進展速度の予測手法開発(第2報)(技術OS2-3 経年劣化,技術OS2 電力設備の健全性)

高温純水中応力腐食割れき裂進展速度の予測手法開発(第2報)(技術OS2-3 経年劣化,技術OS2 電力設備の健全性)

1015 残留応力場における高温純水中応力腐食割れき裂進展速度の予測手法開発(第 1 報)

1015 残留応力場における高温純水中応力腐食割れき裂進展速度の予測手法開発(第 1 報)

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (V)

The difference in electrochemical corrosion potential of stainless steel exposed to high temperature pure water containing hydrogen peroxide (H2O2) and oxygen (O2)is caused by differences in chemical form of oxide films. In order to identify differences in oxide film structures on stainless steel after exposure to H2O2 and O2 environments, characteristics of the oxide films have been examined by multilateral surface analyses, e.g., X-ray diffraction (XRD), Rutherford back scattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Preliminary characterization results of oxide films confirmed that the oxide film formed under the H2O2 environment consists mainly of hematite (α-Fe2O2), while that under the O2 environment consists of magnetite (Fe3O4). Furthermore oxidation at the very surface of the film is much more enhanced under the H2O2 environment than that under the O2 environment. It was speculated that metal hydroxide plays an important role in oxidation of stainless steel in the presence of H2O2. The difference in electric resistance of oxide film causes the difference in anodic polarization properties. It is recommended that several anodic polarization curves for specimens with differently oxidized films should be prepared to calculate ECP based on the Evans diagram.

Sensitization behavior of type 308 stainless steel weld metals after postweld heat treatment and low-temperature aging and its relation to microstructure

Type 308 weld metal overlaid on a low-alloy steel by a submerged arc welding (SAW) process using wide strip electrodes can become sensitized by not only postweld heat treatments (PWHTs) at around 600 °C but also low-temperature aging (LTA) at 500 °C for 24 hours after PWHT. A slow strain-rate test (SSRT) in oxygenated, high-temperature pure water revealed that type 308 SAW weld metals after PWHT were susceptible to intergranular stress corrosion cracking (IGSCC) when sensitized such that the intergranular corrosion (IGC) rate in the modified ASTM A262E test exceeds 1 µm/h. The effect of microstructure (ferrite phase distribution) on the sensitization behavior was evaluated using a microstructural parameter NLβ−γ. Though mostly useful, the average NLβ−γ was not always accurate in distinguishing IGC-susceptible, SAW overlay weld metals. However, local NLβ−γ, newly introduced to deal with a rather large fluctuation in ferrite distribution within SAW overlay weld metals, was partly able to explain the IGC susceptibility of a theoretically resistant heat with a high average NLβ−γ. The beneficial effect of surface remelting by plasma arc on the IGC resistance was described.

Intergranular stress corrosion cracking behavior of niobium-added Type 308 stainless steel weld overlay metal in a simulated BWR environment

Type 308 stainless steel weld metal as an internal cladding of reactor pressure vessels for boiling water reactors is subject to postweld heat treatment during fabrication and can suffer sensitization depending on carbon and ferrite contents. This sensitization can be avoided by using niobium-added Type 308 weld metal (specified as Type 308 NbL) which was developed for one-layer overlay welding application. In the present study, stress corrosion cracking (SCC) behavior of heat-treated Types 308 and 308NbL weld metals in oxygenated high temperature pure water was evaluated by slow strain rate test and U-bend tests with and without crevice. Every test showed that Type 308NbL weld metals were highly resistant to SCC compared to ordinary Type 308 weld metals. In single U-bend test, one-layer overlay weld metals of Type 308NbL produced by electroslag welding process using wide strip electrodes were crack free over 23,000 h. The U-bend test data of ordinary Type 308 weld metals were successfully analyzed by an SCC reaction model. Using this analysis, the SCC life margin for Type 308NbL over ordinary Type 308 weld metals, expressed as a ratio of respective times to SCC initiation, was estimated to be about 36.

X750合金の高温水中粒界応力腐食割れに及ぼす水素の影響

X750合金の高温水中粒界応力腐食割れに及ぼす水素の影響

Fatigue Life Evaluation Method of Carbon Steel in High Temperature Pure Water Environment.

It is well known that the fatigue life of carbon steel in oxygenated high-temperature pure water is much less than the fatigue life of carbon steel at room temperature in air when the applied strain rate is very low. The fatigue life of carbon steel was examined in order to develop an evaluation method. Cracks were found to initiate immediately after the fatigue test started in high-temperature pure water. The fatigue life was regarded to be the crack propagation life. The crack propagation rate was found to be constant against the fatigue life ratio, N/Nf. A time-domain evaluation method for fatigue crack growth rate was applied to evaluate the corrosion fatigue life. A time-based nominal crack growth rate was assumed as the reciprocal of time to failure by fatigue. The relationship between time-based nominal crack growth rates in high-temperature water and room temperature air was linear on a diagram of logarithms even when strain amplitudes and rates were changed. An environmental effect index, which was defined as the slope of this line, seemed to be influenced only by the environmental conditions. The newly developed evaluation method could successfully estimate the corrosion fatigue life of carbon steel in a high-temperature pure water environment.