MONITORING OF CORROSION UNDER CATHODIC PROTECTION CONDITIONS UTILIZING COUPLED MULTIELECTRODE SENSORS
Real-time corrosion monitoring for carbon steel materials in simulated seawater under cathodic protection conditions was conducted, utilizing coupled multielectrode sensors. It was demonstrated that the coupled multielectrode sensor is an effective real-time tool for monitoring the effectiveness of cathodic protection and for measurement of the threshold value of the protection potential for specific equipment.
MEASUREMENT OF CORROSION IN SATURATED SOLUTIONS UNDER SALT DEPOSITS USING COUPLED MULTIELECTRODE ARRAY SENSORS
The corrosion rates of type 1010 carbon steel, and types 304 and 316 stainless steels in saturated solutions under salt deposits were measured using coupled multielectrode sensors. The measurements were carried out in the presence of the following salts: KCl, NaCl, NaNO3, MgCl2, NiCl2, FeCl3, FeCl2, CuCl2, and an NaCl+NaNO3 mixture. The results indicate that the corrosiveness of the salts increased in the following order: KCl ~ NaCl ~ NaNO3 ~ NaCl+NaNO3 ~ MgCl2 < NiCl2 < FeCl3 < FeCl2 < CuCl2 for carbon steel, and KCl ~ NaCl ~ MgCl2 ~ NiCl2 ~ NaCl+NaNO3 < FeCl3 ~ FeCl2 ~ CuCl2 for type 304 stainless steel. Some inhibition of corrosion of type 316 stainless steel by NaNO3 was observed in a mixture of NaCl+NaNO3, but not in pure NaNO3 solution.
Deliquescence Behavior of Multicomponent Salts: Effects on the Drip Shield and Waste Package Chemical Environment of the Proposed Nuclear Waste Repository at Yucca Mountain, Nevada
Thermodynamic calculations were conducted to determine the deliquescence behavior of salt mixtures and to simulate the evaporation of Yucca Mountain groundwaters. The results are consistent with published experimental data that show the deliquescence points of salt mixtures are lower than that of individual salts. For mixtures of NaCl and KCl salts, the deliquescence point of pure NaNO3 salt is an appropriate lower bound. However, mixtures containing magnesium and calcium salts have much lower deliquescence points than pure NaNO3. If magnesium and calcium salts are deposited on waste package and drip shield surfaces, it could lead to earlier initiation of aqueous corrosion than assumed by the DOE in its performance assessment abstractions. Such salt mixtures can be formed by evaporation of waters with compositions similar to some Yucca Mountain porewaters and would be characterized by low deliquescence relative humidity, high chloride concentration, and low concentrations of anions such as free (uncomplexed) nitrate and sulfate that could mitigate against the chloride-enhanced corrosion of the waste package. Evaporation of Yucca Mountain groundwaters also could lead to fluoride concentrations that are above the threshold for accelerated corrosion of the titanium drip shield.