51313-02355-Corrosion Testing of Carbon Steel in Oxalic Acid That Contains Dissolved Iron

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Product Number: 51313-02355-SG

ISBN: 02355 2013 CP

Author: Bruce Wiersma

Publication Date: 2013

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Radioactive liquid waste has been stored in underground carbon steel tanks for nearly 60 years at the Savannah River Site. The site is currently in the process of removing the waste from these tanks in order to place it into a vitrified stable state for longer term storage. The last stage in the removal sequence is a chemical cleaning step that breaks up an dissolves the metal oxide solids that cannot be easily pumped out of the tank. Oxalic acid (OA) will be used to chemically clean the tank after waste retrieval is completed. The waste tanks at SRS were constructed from carbon steel materials and thus are vulnerable to corrosion in acidic media. In addition to structural impacts the influence of corrosion on the hydrogen generated during the process must be assessed. Electrochemical and coupon immersion tests were performed to investigate the corrosion mechanism at anticipated process conditions. The testing showed that the corrosion rates were dependent upon the reduction of the iron species that had dissolved in solution. Initial corrosion rates were elevated due to the reduction of the ferric oxalate complex. At later times as the ferric oxalate species was depleted the corrosion rate decreased. On the other hand the hydrogen evolution reaction became more dominant.