Effect of temperature on the crevice corrosion resistance of Ni-Cr-Mo alloys as engineered barriers in nuclear waste rep
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Effect of temperature on the crevice corrosion resistance of Ni-Cr-Mo alloys as engineered barriers in nuclear waste repositories Edgar C. Hornus1,2, C. Mabel Giordano1,2, Martín A. Rodríguez1,2,3 and Ricardo M. Carranza1,2 Departamento Materiales, Comisión Nacional de Energía Atómica, Argentina. 2 Instituto Sabato, UNSAM / CNEA, Argentina. 3 CONICET, Argentina. 1
ABSTRACT Ni-Cr-Mo alloys offer an outstanding corrosion resistance in a wide variety of highly corrosive environments. Alloys 625, C-22, C-22HS and HYBRID-BC1 are considered among candidates as engineered barriers of nuclear repositories. The objective of the present work was to assess the effect of temperature on the crevice corrosion resistance of these alloys. The crevice corrosion repassivation potential (ER,CREV) of the tested alloys was determined by the Potentiodynamic-Galvanostatic-Potentiodynamic (PD-GS-PD) method. Alloy HYBRID-BC1 was the most resistant to chloride-induced crevice corrosion, followed by alloys C-22HS, C-22 and 625. ER,CREV showed a linear decrease with temperature. There is a temperature above which ER,CREV does not decrease anymore, reaching a minimum value. This ER,CREV value is a strong parameter for assessing the localized corrosion susceptibility of a material in a long term timescale, since it is independent of temperature, chloride concentration and geometrical variables such as crevicing mechanism, crevice gap and type of crevice former. INTRODUCTION Ni-Cr-Mo alloys offer an outstanding corrosion resistance in a wide variety of highly corrosive environments [1]. They show excellent resistance to pitting corrosion, crevice corrosion and environmentally assisted cracking in hot concentrated chloride solutions [1]. These alloys are considered among candidates as engineered barriers of nuclear waste repositories [2]. Localized corrosion, in the forms of pitting and crevice corrosion, may occur when these alloys are exposed to chloride solutions at high temperatures [2-4]. Crevice corrosion is more likely since it is stabilized in occluded regions at lower potentials than pitting corrosion. In fact, some of these alloys are practically immune to pitting corrosion [2-4]. It is assumed that localized corrosion will only occur when the corrosion potential (ECORR) is equal or higher than a critical potential (ECRIT) [2]. The crevice corrosion repassivation potential (ER,CREV) has been proposed as the critical potential [3]. Factors affecting crevice corrosion susceptibility have been classified into metallurgical and environmental [3,4]. Chloride is the only known ion that is able to promote crevice corrosion of alloy C-22. Alloy susceptibility to crevice corrosion is increased by higher chloride concentrations and higher temperatures. Temperature is an important variable affecting the corrosion kinetics. Engineered barriers of a nuclear repository, such as waste containers, will be operating under a range of temperature determined by the heat transfer from the nuclear waste to the environment [2]. The effect of temperature on th
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