51316-7688-The Use of ASTM G192 to Evaluate the Susceptibility of Hanford Tank Steels to Pitting Corrosion

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Product Number: 51316-7688-SG

ISBN: 7688 2016 CP

Author: Kenneth Evans

Publication Date: 2016

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The Hanford site contains approximately 55 million gallons of radioactive and chemically hazardous wastes that are stored in 177 underground storage tanks of which 150 are single-shell tanks (SSTs) and the remaining are double-shell tanks (DSTs). Traditionally the cyclic potentiodynamic polarization (CPP) technique (ASTM G61) has been used in the DST integrity program to evaluate the susceptibility of different tank steels to localized corrosion in specific waste chemistries. However a number of waste chemistry conditions have been encountered where the CPP technique has produced an uncertain or undefined protection potential (Eprot) related to pitting corrosion. The ASTM G192 standard or Tsujikawa-Hisamatsu Electrochemical (THE) technique was originally developed to address similar problems in assessing the crevice corrosion susceptibility of corrosion resistant alloys. The ASTM G192 method basically consists of the sequential combination of three standard techniques (potentiodynamic galvanostatic and potentiostatic steps) to allow for a slower and more controlled method of applying anodic polarization to the specimen. This paper investigates the use of the ASTM G192 method to evaluate the pitting behavior of tank steels in various simulated waste chemistries. The protection potentials determined using the G192 method are compared to the CPP technique to highlight the cases where CPP tests could be overly conservative in estimating the protection potential related to pitting.Key words:Protection potential pitting corrosion tank steel Hanford radioactive waste