Chemical and Electrical Stability of Reference Electrodes in Sand Bed Dosed with Volatile Corrosion Inhibitors

摘要

Various types of reference electrodes including Copper-Copper Sulfate (Cu/CuSO_4) are widely used to monitor the structure to electrolyte potential of above-ground storage tank (AST) bottoms. Reference electrodes intended for long-term monitoring are installed under the tank bottom and typically difficult to be practically retrieved or replaced. Dependability of the reference electrodes is therefore of paramount importance since electrical and chemical instabilities would lead to erroneous potential measurements and contamination respectively. This work was conducted to diligently evaluate chemical and electrical stability of commercially available reference electrodes in contact with sand treated with VCIs. Several types of commercially available reference electrodes were tested, including Cu/CuSO_4, bentonite-clay clad Cu/CuSO_4, and bentonite-clay clad Zn/ZnSO_4 reference electrodes. The testing was conducted using two-electrode corrosion cells with each cell containing a reference electrode as the working electrode in conjunction with a saturated silver-silver chloride reference electrode serving as the counter electrode. The potential of the working electrode with respect to the saturated silver-silver chloride reference electrode was monitored over several months. This paper provides details of the experimental work conducted to understand the chemical and electrical stability of the reference electrodes in contact with VCI dosed sand.