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Journal Articles

In-situ measurement of electrical conductivity of solution within crevice of stainless steel in high temperature and high purity water

Soma, Yasutaka; Komatsu, Atsushi; Ueno, Fumiyoshi

Zairyo To Kankyo, 67(9), p.381 - 385, 2018/09

In-situ measurement of electrical conductivity of solution within crevice of SUS316L stainless steel in 288$$^{circ}$$C water has been conducted with newly developed electrochemical sensor system. The sensor measures local electrical conductivity of crevice solution beneath the electrode ($$kappa$$$$_{crev}$$) with electrochemical impedance method. The sensors were installed at different positions within tapered crevice of SUS316L stainless steel. The crevice specimen with the sensors were immerged into 288$$^{circ}$$C, 8 MPa, pure oxygen saturated high purity water for 100 h. $$kappa$$$$_{crev}$$ at a position with crevice gap of $$approx$$59.3$$mu$$m was 8-11$$mu$$S/cm, least deviate from conductivity of 288$$^{circ}$$C pure water (4.4$$mu$$S/cm) and no localized corrosion occurred. On the contrary, $$kappa$$$$_{crev}$$ at a position with crevice gap of $$approx$$4.4$$mu$$m increased with time and showed maximum value of $$approx$$1600$$mu$$S/cm at 70 h. Localized corrosion occurred in the vicinity of this position. Thermodynamic equilibrium calculation showed $$kappa$$$$_{crev}$$ of 1600$$mu$$S/cm being equivalent to pH of 3 to 3.7. It can be concluded that acidification occurred in tight crevice even under high purity bulk water and resulted in localized corrosion.

Journal Articles

Localized corrosion in crevice of SUS316 stainless steel in oxygenated high temperature and high purity water

Soma, Yasutaka; Ueno, Fumiyoshi

Zairyo To Kankyo, 67(5), p.222 - 228, 2018/05

Localized corrosion in crevice of SUS316 stainless steel after immersion in 288$$^{circ}$$C high purity water with dissolved oxygen concentration of 32 ppm for 100 h was analyzed. Two different types of localized corrosion initiated on grain boundary and inclusions. The former initiated on grain boundary and oxide grown into grain matrix. The oxidized area showed duplex structure composed of microcrystalline FeCr$$_{2}$$O$$_{4}$$ and island-shaped residual metals. The latter initiated on inclusions containing Ca and S and microcrystalline FeCr$$_{2}$$O$$_{4}$$ grown into metal matrix. These localized corrosion occurred selectively in oxygen depleted area indicated formation of macroscopic corrosion cell with the corroded area as anode and surrounding oxygenated area as cathode.

Journal Articles

In situ electrochemical study on crevice environment of stainless steel in high temperature water

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Vol.2, p.509 - 521, 2018/00

In-situ electrochemical measurement within crevice of stainless steel in 288$$^{circ}$$C water has been conducted to analyze crevice water chemistry. Small sensors ($$phi$$ $$sim$$ 250$$mu$$m) measured local solution electrical conductivity, $$kappa$$$$_{rm crev}$$, polarization resistance, and electrochemical corrosion potential. Real-time response of the $$kappa$$$$_{rm crev}$$ as functions of bulk water conductivity, dissolved oxygen (DO) concentration has been quantitatively analyzed. The effect of geometrical factors on the crevice environment was also studied. The $$kappa$$$$_{rm crev}$$ differ more than an order of magnitude depending on the oxygen potential inside the crevice. The $$kappa$$$$_{rm crev}$$ increased by small amount of bulk DO (e.g. 30 ppb). Maximum $$kappa$$$$_{rm crev}$$ was observed with DO of 32000 ppb and became more than 100 times higher than that of bulk water. Crevice geometry affected significantly on the water chemistry inside.

Journal Articles

Leakage flows in high-temperature gas-cooled reactor graphite fuel elements

; Takizuka, Takakazu

Journal of Nuclear Science and Technology, 22(5), p.387 - 397, 1985/00

 Times Cited Count:6 Percentile:34.44(Nuclear Science & Technology)

no abstracts in English

JAEA Reports

Leakage Flow of Gases through Gaps between Contacting Surfaces

; Takizuka, Takakazu;

JAERI-M 84-128, 19 Pages, 1984/07

JAERI-M-84-128.pdf:0.7MB

no abstracts in English

Oral presentation

In-situ measurement of solution electrical conductivity within crevice of SUS316L stainless steel in high temperature pure water

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi

no journal, , 

To understand the effect of crevice solution chemistry on stress corrosion cracking of stainless steel in high temperature pure water, local solution electrical conductivity was measured using artificial crevice with small sensors. If the crevice gap was narrow enough, local solution electrical conductivity increased more than 100 times than that of bulk pure water and intergranular corrosion occurred.

Oral presentation

In-situ measurement of solution electrical conductivity within crevice of stainless steels in high temperature water

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi

no journal, , 

Stress corrosion cracking (SCC) on stainless steels have been recognized as one of the most important corrosion-related failure in light water reactors. Many researches have been pointed out that the SCC advances under altered solution chemistry condition at the crack tip region compared to the bulk pure water. However, little works have been done to clarify degree of the alteration as function of bulk water condition, geometrical factor, and time. In this work, we carried out in-situ measurement of solution electrical conductivity within crevice of stainless steels. To create crevice specimen, a couple of stainless steel plate was fixed with bolts and nuts. Small sensors were imbedded into the crevice plate at three different positions with different crevice gaps. The crevice specimen with sensors was exposed to 288$$^{circ}$$C water with pressure of 8 MPa, dissolved oxygen concentration of 32 ppm. The solution electrical conductivity at the crevice gap of 6e-5 m was almost same to that of bulk pure water. At the crevice position with 1e-5 m gap, the maximum conductivity value was nearly 1000 times higher than that of bulk water and that is equivalent to decrease in pH of 3 from the neutral value. This indicates, if the crevice gap was narrow enough, local acidification occurred at the tip of the crevice.

Oral presentation

Numerical simulation and experimental evaluation of dissolved oxygen diffusion behavior into crevice of stainless steel in high temperature pure water

Soma, Yasutaka; Ueno, Fumiyoshi; Yamamoto, Masahiro

no journal, , 

Diffusion behavior of dissolved oxygen into crevice of stainless steel in high temperature is very important to understand crevice environment. In this research, we developed 3D model of crevice and using it, we carried out numerical simulation of dissolved oxygen diffusion into the crevice. The result of numerical simulation showed good agreement with experimentally obtained result.

Oral presentation

Measurement of crevice environment using sensor and the effect of geometrical factors

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi; Aoki, So; Inagaki, Hiromitsu*

no journal, , 

Crevice environment was measured by electrochemical sensors in high temperature pure water. Crevice environment and surface oxide layer on the crevice surface was analyzed in terms of crevice's geometrical factors (crevice gap, g and depth, d). The results were plotted on the g-d plane. It was shown that electrical conductivity of crevice solution was very high in oxygen depleted zone and the zone shrinked with increasing crevice gap, g.

Oral presentation

Crevice corrosion in high temperature water

Soma, Yasutaka

no journal, , 

Crevice corrosion have been studied.

Oral presentation

Effect of crevice geometry on corrosion environment within crevice of stainless steel in high temperature water

Soma, Yasutaka; Ueno, Fumiyoshi; Inagaki, Hiromitsu*

no journal, , 

Effect of crevice geometry on corrosion environment within crevice of stainless steel in high temperature water was studied.

Oral presentation

Mechanisms to understand high electrical conductivity of solution within crevice of stainless steel in high temperature water

Soma, Yasutaka; Komatsu, Atsushi; Ueno, Fumiyoshi; Inagaki, Hiromitsu*

no journal, , 

Corrosion condition within crevice of stainless steel is important to understand dissolution mechanisms of crack tip of stress corrosion cracking (SCC) in high-temperature water. We have reported that electrical conductivity of solution within crevice of stainless steel ($$kappa$$crev) exposed to high temperature and high purity water containing sufficient dissolved oxygen (DO) become more than 2 orders of magnitude higher than that for bulk pure water. In this study effect of conductivity and DO concentration of bulk water on $$kappa$$crev of Type-316L stainless steel have been studied in 288$$^{circ}$$C water. Following conclusion have been obtained: (1) $$kappa$$crev increased with increasing DO concentration from 3 ppb to approximately 300 ppb. Above 300 ppb, $$kappa$$crev did not simply increased with DO concentraion. (2) maximum $$kappa$$crev was not affected by bulk water conductivity suggested that $$kappa$$crev would be determined by chemical equilibrium reaction. (3) $$kappa$$crev-time curves were not affected by crevice depth. It was assumed that anion required to increase $$kappa$$crev generated within the crevice.

Oral presentation

Effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution in high temperature water

Soma, Yasutaka; Komatsu, Atsushi; Kato, Chiaki

no journal, , 

In this study, the effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution (K) has been studied. Crevice specimens were made of as-polished Type-316L stainless steel (standard-SS), standard-SS exposed to 60% nitric acid to dissolve sulfur containing inclusions (acid-picked SS), and 316EHP steel in which sulfur and phosphorous concentration was decreased compared to standard-SS (EHP-SS). These crevice specimens were immersed into 561 K, 8 MPa water the K values were measured as a function of time with stepwise increase in dissolved oxygen levels. In addition, effect of 50 ppb Cl$$^{-}$$ added to bulk water was investigated using standard-SS crevice. The all of the standard-SS, acid-picked SS, and 316EHP showed similar K vs time curves. It can be concluded that impurities dissolved from the steel itself do not significantly contribute to the increase of K. The effect of 50 ppb Cl$$^{-}$$ on K vs time curve was obvious because maximum K value became more that 2 times larger than the solution without Cl$$^{-}$$ addition. This indicate that small concentration of impurities can be migrated into the crevice.

Oral presentation

Mechanism of localized corrosion in crevice of stainless steel in high temperature and high purity water

Soma, Yasutaka

no journal, , 

Commemorative speech for "The Award of JSCE for young researcher" of Japan Society of Corrosion Engineering on May 21st 2020, entitled "Characterization of the mechanism of localized corrosion in the crevices of stainless steel in high-temperature, high-purity water" will be made. In this study, we conducted followings: (i) Corrosion test of Type 316L stainless steel to analyze susceptibility to localized corrosion within a crevice in 561K high purity water, and (ii) Develop a sensor system to measure the solution conductivity in a crevice and study relationship between crevice water chemistry and the localized corrosion. These studies were done for the purpose of clarifying the mechanism of stress corrosion cracking (SCC). It was shown that Type-316L stainless steel is susceptible to intergranular corrosion inside the crevice. The developed sensors detected very high solution conductivity in the vicinity of the intergranular corroded area indicate highly corrosive environments were formed in crevice with small gaps. This system can be applied to clarify the mechanism of corrosion related failure, such as SCC, and is expected to contribute to the safety improvement of nuclear reactors.

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