High Temperature Pure Water Research Articles

Thermal fatigue behavior of thin-walled cylindrical carbon steel specimens in simulated BWR environment

Thin-walled cylindrical carbon steel specimens were thermally fatigued in a pressurized autoclave. Since high and low temperature pure water were alternately supplied into the autoclave, the specimens were subjected to homogeneous thermal stress through the wall thickness. The thermal fatigue life was defined as the number of cycles to crack penetration to the inside of the cylindrical specimen. The thermal fatigue strength was compared with the mechanical fatigue strength performed in air and in high temperature water. Even if taking account of the Higuchi-Iida formula, which considers the effects of strain rate, dissolved oxygen concentration and water temperature on fatigue life, the thermal fatigue lives of carbon steel were found to be slightly shorter than the mechanical fatigue lives.

Development of thermal fatigue testing apparatus with BWR water environment and thermal fatigue strength of austenitic stainless steels

A thermal fatigue testing apparatus was developed in order to clarify the fatigue behavior in BWR environment. Pressurized high and low temperature pure water were alternately supplied into an autoclave with a small cylindrical specimen. Then a fatigue specimen was subjected to homogeneous thermal stress through the wall thickness. Fatigue crack initiation behavior was observed with the replication method and compared with the mechanical fatigue strength performed in air and high temperature water. The thermal fatigue strength of type 304 and 316 nuclear grade (316NG) stainless steels agreed closely with the mechanical fatigue strength, when transforming the nominal stress amplitude to the fictitious stress amplitude by using the mean value of strain amplitudes for room temperature and 288°C.

Ni-Ti系形状記憶合金の高温水中における応力腐食割れ

The effects of composition, heat treatment, test temperature and dissolved oxygen (DO) concentration on the stress corrosion cracking (SCC) behavior of Ni-Ti and Ni-Ti-Cu shape memory alloys in high temperature pure water were examined. The tests were conducted by using slow strain rate test machine.The 50∼50.9 at%Ni-Ti and 40∼41.5 at%Ni-Ti-10 at%Cu shape memory alloys were subjected to SCC in air saturated water of 561 K, except for the annealed 50 at%Ni-Ti alloy. The annealed 50 at%Ni-Ti was immune to SCC, but the SCC susceptibilities of the other Ni-Ti alloys were not affected by nickel concentration and heat treatment. In the case of Ni-Ti-Cu alloys both low nickel concentration and aging promoted SCC. SCC of Ni-Ti and Ni-Ti-Cu alloys initiated from the scratches and propagated transgranularly.At 473 K, SCC occurred and the susceptibilities were not largely different from those at 561 K. In the case of a stainless steel shape memory alloy, the martensite phase specimens were susceptible to SCC in deaerated low temperature water. On the contrary, the martensitic Ni-Ti alloys did not crack in the deaerated water at 287 K.The susceptibilities to SCC of Ni-Ti and Ni-Cu-Ti alloys in deaerated water of 561 K were the same as those in aerated water of the same temperature. Dissolved oxygen did not accelerate nor prevent SCC in high temperature water.

高温純水中のＺｒ‐２．５ｗｔ％Ｎｂ合金とＳＵＳ４０３Ｍｏｄのすき間腐食

Crevice corrosion characteristics of 13% chromium martensitic stainless steel bearing 3.5% nickel and zirconium alloy containing 2.5% niobium (Zr-2.5wt%Nb) were investigated in high temperature pure water. Corrosion of the stainless steel occurred in the crevice, while corrosion of the Zr-2.5wt%Nb was inhibited. Corrosion pits were formed on the stainless steel in the early period of the corrosion test. However, these pits were repassivated in the subsequent corrosion test and the pits did not propagate. The Zr-2.5wt%Nb allo absorbs the subsequent corrosion test and the pits did not propagate. The Zr-2.5wt%Nb allo absorbs the correlated with the corrosion of the stainless steel.

Effect of thermal aging on stress corrosion cracking of neutron-irradiated type 316 stainless steel in high temperature pure water

Susceptibility to the irradiation-assisted stress corrosion cracking (IASCC) of type 316 stainless steel irradiated in FBR was evaluated through slow strain rate tensile (SSRT) test in oxygenated high purity water. SSRT tests were carried out at 300°C under controlled potential condition. The material had been cold-worked 20% and irradiated to 40 displacement per atom (dpa) at 425°C. Some of the specimens were thermally aged after irradiation at 900°C for 0.1 min, 30 min and 12 h to investigate the effect of aging on IASCC behavior. An applied potential enhanced stress corrosion cracking, strength and elongation of the material obtained by SSRT testing showed prompt recovery by thermal aging. SEM observation of fracture surfaces revealed marked change of dominant cracking mode from intergranular (IG) type to transgranular (TG) type.

高温純水中におけるSUS304鋼の交流インピーダンス解析

高温純水中におけるSUS304鋼の交流インピーダンス解析

Analysis of stress corrosion cracking life based on reaction model

The stress corrosion cracking (SCC) lives of Type 304 stainless steel, Inconel alloy 600, and niobium stabilized, improved alloy 600 were obtained by an uniaxial constant load in high temperature pure water with 8 ppm dissolved oxygen, and were analyzed based on a reaction model and a certain correlation between SCC life parameters. The load dependency of SCC life was also discussed using the model and an expression in the form of a hyperbolic tangent function. The results showed that the analysis based on the model was useful for the quantitative evaluation of the SCC life of materials.

高温純水中におけるステンレス鋼の微量腐食溶出に及ぼす大気酸化処理皮膜構造の影響

高温純水中におけるステンレス鋼の微量腐食溶出に及ぼす大気酸化処理皮膜構造の影響

The role of molybdenum in intergranular stress corrosion cracking of SUS 316 stainless steel in high temperature pure water

Effects of solution treatment temperature and sensitization time on stress corrosion cracking (SCC) have been studies on SUS316 stainless steel in high temperature pure water at 562K containing dissolved oxygen of 8 ppm using a slow strain rate testing (SSRT) technique at 4.17x10-6s-1 and 8.35×10-7s-1. The Strauss test (ASTM A262E) and the oxalic acid etching test (ASTM A262A) were used to determine the degree of sensitization and Huey test (ASTM A262C) and anodic polarization test were used to determine the influence of step solution treatment on segregation of impurities at grain boundary.The specimens which were solution-treated at 1373K, had more precipitates of M23C6 and Laves phases than those at 1573K. For the width of attacked grain boundaries, this trend was coincident. In high temperature water, intergranular corrosion occurred owing to Cr depletion resulting from the precipitation of M23C6 and Laves phase at grain boundaries of sensitized specimens and then IGSCC occurred at these attacked grain boundaries at low strain and load. IGSCC changed to TGSCC according to the increase of strain.

Relationship between Pre-Oxidized Film Structures and Corrosion Resistance of Ferritic Stainless Steels in High Temperature Pure Water

The effect of pre-oxidation conditions on metal release of Ti-added SUSXM8 and410Ti ferritic stainless steels in deaerated pure water at 488 K was investigated. The pre-oxidation treatments in the atmosphere of low oxygen potential, such as high purity argon gas and high vacuum condition at 1 123 K for short time, were effective in decreasing the metal dissolution. The pre-oxide films were composed of outer Ti 2 O 3 and inner MnCr 2 O 4 , layers

Subcritical-crack growth behavior for carbon steel in high-temperature pure water.

Subcritical-crack growth rates for carbon steels in high-temperature pure water are obtained from fatigue and constant load tests. The test specimens, made of STS 42 and 49 carbon steel pipes are CT type and surface-cracked flat plate-type. The experimental environment is saturated pure water at 288°C and 7.8 MPa pressure. The subcritical-crack growth rates are influenced by several factors; the fatigue crack growth rate, da/dN in water is accelerated by low frequency and high stress ratio. The da/dN in water from a trapezoial load wave and for welded metal is less than from a triangular wave and for base metal. In addition, the da/dN in water at 150°C and in a steam environment is lower than in water at 288°C. The growth rate, da/dN, in the thickness and the width directions is almost equivalent to the results of the surface-cracked flat plate specimens. The curve of the crack growth rate, da/dt, is obtained from the constant load test. The threshold value of the stress intensity factor for stress corrosion cracking for STS base and welded metal of carbon steels is relatively large when compared with the sensitized Type 304 stainless steel and other carbon steels.

酸化皮膜処理したフェライト系ステンレス鋼の皮膜構造と高温純水中の耐食性

酸化皮膜処理したフェライト系ステンレス鋼の皮膜構造と高温純水中の耐食性

各種酸化皮膜処理したSUS 304Lステンレス鋼の皮膜構造と高温純水中の耐食性

各種酸化皮膜処理したSUS 304Lステンレス鋼の皮膜構造と高温純水中の耐食性

ＳＵＳ３１６鋼の高温高圧純水中の粒界応力腐食割れにおける Ｍｏ の役割

Effects of solution treatment temperature and sensitization time on stress corrosion cracking (SCC) have been studies on SUS316 stainless steel in high temperature pure water at 562K containing dissolved oxygen of 8 ppm using a slow strain rate testing (SSRT) technique at 4.17x10-6s-1 and 8.35×10-7s-1. The Strauss test (ASTM A262E) and the oxalic acid etching test (ASTM A262A) were used to determine the degree of sensitization and Huey test (ASTM A262C) and anodic polarization test were used to determine the influence of step solution treatment on segregation of impurities at grain boundary.The specimens which were solution-treated at 1373K, had more precipitates of M23C6 and Laves phases than those at 1573K. For the width of attacked grain boundaries, this trend was coincident. In high temperature water, intergranular corrosion occurred owing to Cr depletion resulting from the precipitation of M23C6 and Laves phase at grain boundaries of sensitized specimens and then IGSCC occurred at these attacked grain boundaries at low strain and load. IGSCC changed to TGSCC according to the increase of strain.

Relationships Between Corrosion Behavior of AISI 304 Stainless Steel in High-Temperature Pure Water and Its Oxide Film Structures

Abstract Effects of dissolved oxygen (DO) concentration on corrosion rates of AISI 304 stainless steel (SS) in high-temperature pure water were examined at temperatures between 200 and 320 C using impedance analysis techniques. A significant reduction in the corrosion rate >260 C and independence of the corrosion rate on the DO concentration at 320 C were observed as unique phenomena. To understand them, the oxide film structures were examined by scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS), and electrical capacity measurements. The oxide films could be divided into outer and inner layers. The outer layer consists of two sublayers, a porous precipitation sublayer and a cracked inner sublayer which is hypothesized to be formed by the breakdown of the inner layer. The outer layer was characterized by a decrease of Cr content towards the outer surface of the oxide film. The inner layer was defined as a residual oxide in which no decrease of Cr content occurred. The inner oxide f...

Study on SCC Susceptibility of Inconel X-750 in High-Temperature Pure Water: Effects of Aging Temperature and Time

Abstract The stress corrosion cracking (SCC) behavior of Inconel X-750 in high-temperature water has been examined in relation to aging conditions. SCC susceptibility for the two-step (solutioning + aging), heat-treated alloy (SA) varied with its aging condition, and the aging conditions that gave a high yield strength also gave a high SCC susceptibility. Wide chromium depletion produced by the formation of M23C6 along the grain boundary during aging was identified by energy dispersive x-ray analysis (EDXA) to be a cause of intergranular stress corrosion cracking (IGSCC) susceptibility for SA. The three-step (solutioning + stabilizing + aging), heat-treated alloy (SSA) was more susceptible to IGSCC than the SA alloy, in spite of the smaller corrosion rate in a modified ASTM Standard G-28 test. EDXA revealed titanium segregation and formation of titanium-rich phases along the grain boundary, and it is speculated that the poor resistance to IGSCC following a SSA treatment might be caused by formation of a l...

Ni含有13Crマルテンサイト系ステンレス鋼の選択腐食と高温水応力腐食割れ

Ni含有13Crマルテンサイト系ステンレス鋼の選択腐食と高温水応力腐食割れ

高温純水中におけるステンレス鋼の金属放出に及ぼす表面酸化処理条件の影響

高温純水中におけるステンレス鋼の金属放出に及ぼす表面酸化処理条件の影響

ステンレス鋼表面酸化処理材の流動高温純水中への金属放出挙動

ステンレス鋼表面酸化処理材の流動高温純水中への金属放出挙動

Experimental Study on Crack Growth Behavior for Austenitic Stainless Steel in High Temperature Pure Water

Crack growth behavior of Type 304 stainless steel in a simulated BWR water environment was investigated for the quantitative characterization of subcritical flaw growth in BWR piping systems. Crack propagation rates under corrosion fatigue and stress corrosion cracking were generated using compact specimens. The effects of several parameters on the rates were discussed. Furthermore, surface crack growth behavior was examined under different modes of cyclic loading, and results were discussed in comparison with compact specimen data. The corrosion fatigue crack propagation rates strongly depended on the frequency and the stress ratio. The rates became higher as the frequency lowered and the stress ratio increased. No effect from dissolved oxygen concentration and heat treatment of the steel was observed in tests, where transgranular cracking mainly took place. Stress corrosion cracking rate data indicated KISCC was above 15 MPa•m1/2. On the other hand, surface crack growth behavior included scattered crack propagation rates. However, the relationship between da/dN and ΔK was basically similar to that obtained in the compact specimens, except under given test conditions, where the acceleration for the crack growth rate at a crack tip on the panel surface was different from that at the deepest point.