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Laboratory Studies Related To External Corrosion Of Hanford’S Double-Shell Tanks In Contact With Concrete Liner

Picture for Laboratory Studies Related To External Corrosion Of Hanford’S Double-Shell Tanks In Contact With Concrete Liner
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Product Number: 51321-16576-SG
Author: K.J. Evans/ S. Chawla/ K.M. Sherer/ B.C. Rollins/ J.A. Beavers/ N. Sridhar/ T.J. Venetz/ N.M. Young/ C.L. Girardot
Publication Date: 2021
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Radioactive and chemically hazardous wastes are stored at the Hanford site in underground double-shell tanks (DSTs) constructed of carbon steel. The corrosion management of these tanks has mainly focused on the complex waste chemistries that are contained in the primary tank. More recently, attention has been given to the corrosion that has been found on the exterior of the secondary liners of the DSTs. The cause of the external corrosion could be related to the intrusion and accumulation of water in the tertiary leak detection systems, which exist under the concrete foundation of the DSTs. However, site investigations have discovered significant reductions in wall-thickness (up to 70%) for DSTs that do not have a history of water intrusion. Furthermore, site measurements have indicated that wall-thinning may not be as severe at locations where the tank exterior is in contact with the slotted concrete foundation. Laboratory tests involving periodic wetting and condensing moisture on steel specimens were conducted to better understand this external corrosion threat. A simulated groundwater solution of near-neutral pH served as the wetting or moisture source in the tests. The laboratory tests consisted of weight-loss evaluations along with more involved studies using a multi-electrode array (MEA). The effect of concrete on the corrosion of steel was also examined by incorporating areas of metal-to-concrete contact on the weight-loss specimens and MEA. The results of this testing revealed that corrosion rates, calculated from weight-loss, can underestimate wall-thinning due to the severe localized attack that was found. Also, the inhibition of corrosion due to concrete-contact may relate more to the obstruction of condensation on the steel rather than an influence on the local pH.

Keywords: Hanford, carbon steel, vapor phase corrosion, pitting, multi-electrode array, concrete

Radioactive and chemically hazardous wastes are stored at the Hanford site in underground double-shell tanks (DSTs) constructed of carbon steel. The corrosion management of these tanks has mainly focused on the complex waste chemistries that are contained in the primary tank. More recently, attention has been given to the corrosion that has been found on the exterior of the secondary liners of the DSTs. The cause of the external corrosion could be related to the intrusion and accumulation of water in the tertiary leak detection systems, which exist under the concrete foundation of the DSTs. However, site investigations have discovered significant reductions in wall-thickness (up to 70%) for DSTs that do not have a history of water intrusion. Furthermore, site measurements have indicated that wall-thinning may not be as severe at locations where the tank exterior is in contact with the slotted concrete foundation. Laboratory tests involving periodic wetting and condensing moisture on steel specimens were conducted to better understand this external corrosion threat. A simulated groundwater solution of near-neutral pH served as the wetting or moisture source in the tests. The laboratory tests consisted of weight-loss evaluations along with more involved studies using a multi-electrode array (MEA). The effect of concrete on the corrosion of steel was also examined by incorporating areas of metal-to-concrete contact on the weight-loss specimens and MEA. The results of this testing revealed that corrosion rates, calculated from weight-loss, can underestimate wall-thinning due to the severe localized attack that was found. Also, the inhibition of corrosion due to concrete-contact may relate more to the obstruction of condensation on the steel rather than an influence on the local pH.

Keywords: Hanford, carbon steel, vapor phase corrosion, pitting, multi-electrode array, concrete

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