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51318-10816-Development of a testing method for crevice corrosion repassivation of Ni-Cr-Mo alloys by cooling

Picture for Development of a testing method for crevice corrosion repassivation of Ni-Cr-Mo alloys by cooling
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This paper discusses the development and optimization of a procedure for evaluating crevice corrosion repassivation by the cooling of corroding Ni-Cr-Mo alloys.

Product Number: 51318-10816-SG
Author: Edgar C. Hornus / Martín A. Rodríguez / Ricardo M. Carranza / Raul B. Rebak
Publication Date: 2018
Industry: Science of Corrosion
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This paper discusses the development and optimization of a procedure for evaluating crevice corrosion repassivation by the cooling of corroding Ni-Cr-Mo alloys. The procedure consists in 1) potentiodynamic polarization at 0.167 mV/s in the anodic direction until current density reaches 20 μA/cm2; 2) galvanostatic polarization of 4 hours at 20 μA/cm2; 3) potentiodynamic polarization at 0.0167 mV/s in the anodic direction until current density reaches 20 μA/cm2; 4) potentiostatic polarization at the final potential of the previous step for 4 hours; 5) cooling at a constant rate while the same potential of previous step is maintained. The procedure was successfully applied to alloys N06022, N06059, N07022, N06686 and N10362 in 0.1 and 1 mol/L chloride solutions, and alloy N06625 in 0.1 mol/L chloride solutions. Judicious application of this testing procedure is advised for more concentrated chloride solutions. The optimized procedure allowed a low and relatively constant current density over time in step 4. Consequently, current density drop in step 5 is almost purely due to the effect of cooling and repassivation temperature may be determined correctly. Slow cooling in step 5 led to repassivation at temperatures above expected values, but rapid cooling led to repassivation at temperatures below expected values.

Key words: N06625, N06022, N06059, N07022, N06686, N10362, localized corrosion, chloride, temperature

This paper discusses the development and optimization of a procedure for evaluating crevice corrosion repassivation by the cooling of corroding Ni-Cr-Mo alloys. The procedure consists in 1) potentiodynamic polarization at 0.167 mV/s in the anodic direction until current density reaches 20 μA/cm2; 2) galvanostatic polarization of 4 hours at 20 μA/cm2; 3) potentiodynamic polarization at 0.0167 mV/s in the anodic direction until current density reaches 20 μA/cm2; 4) potentiostatic polarization at the final potential of the previous step for 4 hours; 5) cooling at a constant rate while the same potential of previous step is maintained. The procedure was successfully applied to alloys N06022, N06059, N07022, N06686 and N10362 in 0.1 and 1 mol/L chloride solutions, and alloy N06625 in 0.1 mol/L chloride solutions. Judicious application of this testing procedure is advised for more concentrated chloride solutions. The optimized procedure allowed a low and relatively constant current density over time in step 4. Consequently, current density drop in step 5 is almost purely due to the effect of cooling and repassivation temperature may be determined correctly. Slow cooling in step 5 led to repassivation at temperatures above expected values, but rapid cooling led to repassivation at temperatures below expected values.

Key words: N06625, N06022, N06059, N07022, N06686, N10362, localized corrosion, chloride, temperature

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