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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  

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.

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