Alloy 22 (UNS N60622) is a nickel-based alloy, which is extensively used in aggressive industrial applications, especially due to its resistance to localized corrosion and stress corrosion cracking in high chloride environments. The purpose of this work was to characterize the anodic behavior of Alloy 22 in concentrated calcium chloride (CaCl2) brines and to evaluate the inhibitive effect of nitrate, especially to localized corrosion. Standard electrochemical tests such as polarization resistance and cyclic polarization were used. Results show that the corrosion potential of Alloy 22 was approximately −360 mV in the silver-silver chloride (SSC) scale and independent of the tested temperature. Cyclic polarization tests showed that Alloy 22 was mainly susceptible to localized attack in 5 M CaCl2 at 75°C and higher temperatures. The addition of nitrate in a molar ratio of chloride to nitrate equal to 10 increased the onset of localized corrosion to approximately 105°C. The addition of nitrate to the solution also decreased the uniform corrosion rate and the passive current of the alloy.

The approach of isolating high-level nuclear waste in the designated site of Yucca Mountain (Nevada) is to separate it from the environment using a series of engineering and natural barriers. The container for the waste will consist of two concentric metal cylinders. The outer cylinder is going to be fabricated of Alloy 22 (N06022). If water is present at the site, several corrosion processes may occur. These include passive or general corrosion, localized corrosion and environmentally assisted cracking. The occurrence of one (or more) mode of corrosion over another will be determined by the redox potential of the aqueous electrolyte that may enter in contact with the container. This redox potential will also control the corrosion potential (E,,,) of the container. This paper summarizes the findings of an extensive laboratory testing aimed at measuring E,,, of Alloy 22 in presence of a variety of electrolyte solutions. Some of these solutions are multi-ionic electrolytes that may simulate concentrated ground waters. Other environments are chemical solutions of pure salts, which are highly unlikely for an underground repository but that may establish an extreme bounding condition. Current results show that the highest measured potential for Alloy 22 was approximately +0.3 to 0.4 V in the saturated silver chloride [SSC] scale. Most of the E, , values are in the order of 0 V [SSC] or below.

Nickel based Alloy 22 (N06022) is extensively used in aggressive industrial applications, especially due to its resistance to localized corrosion and stress corrosion cracking in high chloride environments. The purpose of this work was to characterize the anodic behavior of Alloy 22 in oxalic acid solution and to compare its behavior to sodium chloride (NaC1) solutions. Standard electrochemical tests such as polarization resistance and cyclic polarization were used. Results show that the corrosion rate of Alloy 22 in oxalic acid solutions increased rapidly as the temperature and the acid concentration increased. Extrapolation studies show that even at a concentration of M oxalic acid, the corrosion rate of Alloy 22 would be higher in oxalic acid than in 1 M NaCl solution. Alloy 22 was not susceptible to localized corrosion in oxalic acid solutions. Cyclic polarization tests in 1 M NaCl showed that Alloy 22 was susceptible to crevice corrosion at 90°C but was not susceptible at 60°C.

Powder and granulated sugars were exposed to the drop hammer impact test configured with 120-and 180-grit Si/C sandpapers. The sugars were selected as mock materials for HMX 3,5,3,5,. The drop heights ranged from 24.2 to 40.7 cm. Samples were examined by visible microscopy before and after testing and the appearance of yellow and brown discolorations in the spent samples were assigned as hot spots. These discolorations were divided into two types; those collocated with grit particles and those that were not. Hot spots are found in the spent samples in almost every test condition. Powder sugar appears to be more active in producing hot spots than the granulated sugar based on comparisons at identical conditions. Drop height, within this specific range, has little effect on the formation of hot spots, except for 40.7 cm high-end limit, which causes a dramatic increase in spot formation. The predominant hot spot type formed is collocated with grit particles, suggesting association of hot spot formation due to grit, something that has been discussed in previous treaties. Foreign objects were also observed, some imbedded and some not imbedded. Discoloration was not observed around these sites, suggesting these types of foreign materials are not responsible for hot spot formation, at least under these conditions. Grit associated with a visible tail was observed in some instances, suggesting that grit can be quite mobile through the sample when the pressure is applied by the drop weight (through the striker).

Alloy 22 (N06022) may be susceptible to crevice corrosion in chloride solutions. Nitrate acts as an inhibitor to crevice corrosion. Several papers have been published regarding the effect of nitrate on the corrosion resistance of Alloy 22 at temperatures 100°C and lower. However, very little is known about the behavior of this alloy in highly concentrated brines at temperatures above 100°C. In the current work, electrochemical tests have been carried out to explore the anodic behavior of Alloy 22 in high chloride high nitrate electrolytes at temperatures as high as 160°C at ambient atmospheres. Even though Alloy 22 may adopt corrosion potentials in the order of +0.5 V (in the saturated silver chloride scale), it does not suffer crevice corrosion if there is high nitrate in the solution. That is, the inhibitive effect of nitrate on crevice corrosion is active for temperatures higher than 100°C.