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INTRODUCTION ABSTRACT The objective of this work is to understand how solution chemistry would impact on the corrosion of waste storage steel tanks at the Hanford Site. Future tank waste operations are expected to process wastes that are more dilute with respect to some current corrosion inhibiting waste constituents. Assessment of corrosion damage and of the influence of exposure time and electrolyte composition, using simulated (non-radioactive) waste, of the double-shell tank wall carbon steel alloys is being conducted in a statistically designed long-term immersion experiment. Corrosion rates at different times of immersion were determined using both weight-loss determinations and electrochemical impedance spectroscopy measurements. Localized corrosion susceptibility was assessed using short-term cyclic potentiodynamic polarization curves. The results presented in this paper correspond to electrochemical and weight-loss measurements of the immersed coupons during the first year of immersion from a two year immersion plan. A good correlation was obtained between electrochemical measurements, weight-loss determinations and visual observations. Very low general corrosion rates (<10 µm. yr-1) were estimated using EIS measurements, indicating that general corrosion rate of the steel in contact with liquid wastes would not be a cause of tank failure even for these out-of-chemistry limit wastes. This work is conducted under the auspices of the Joint Coordinating Committee for Radioactive and Mixed Waste Management (JCCRM), under the Science and Technology Implementing Arrangement for Cooperation on Radioactive and Mixed Waste Management and the Agreement for Scientific and Technical Cooperation between the National Atomic Energy Commission of Argentina (CNEA) and the U.S. Department of Energy (DOE). Florida State University through its Cooperative Agreement (DE-FC01-02EW52101) with the DOE (Task 6.0) coordinates this joint research project. The United States Department of Energy, Office of River Protection at the Hanford Site has identified a need to conduct a laboratory study to better understand the effects of radioactive waste chemistry on the corrosion of waste storage tanks at the Hanford Site. The DOE Science Need1 called for a multi-year effort to identify waste chemistries and temperatures within the double-shell tank (DST) operating limits for corrosion control and operating temperature range that may not provide the expected corrosion protection and to evaluate future operations for the conditions outside the existing corrosion database. The Hanford DST resource consists of 28 tanks, each of more than one-million-gallon capacity, organized into six tank farms. The DSTs presently contain over 21 million gallons of high-level waste with about 80 million curies of radioactivity. The DSTs have been in service for 20?35 years and were originally designed to provide a 20- to 50-year service life. To meet Hanford programmatic requirements, all the DSTs need to meet or exceed their design life before the mission is completed. No leaks have been detected in any DST to date. Figure 1 is an aerial photograph of a tank farm under construction, showing tanks in various stages of completion. The liquid transferred to the DSTs was typically concentrated by evaporation, so in many of the tanks, the waste separated into a supernatant liquid layer over a relatively deep layer of sediment formed by precipitation as the waste cooled. Figure 2 shows a typical simplified diagram of the DST structure, which is, in effect, two tanks in one, comprising an inner primary tank and a secondary outer tank with a reinforced concrete shell. The primary and secondary tanks are carbon
- Water & Waste Management > Solid Waste Management (1.00)
- Government > Regional Government > North America Government > United States Government (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
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Corrosion Behavior of Alloy 22 in Chloride Solutions Containing Organic Acids
Carranza, Ricardo M. (Comision Nacional de Energia Atomica) | Rodriguez, Martin A. (Comision Nacional de Energia Atomica) | Giordano, C. Mabel (Comision Nacional de Energia Atomica) | Rebak, Raul B. (Lawrence Livermore National Laboratory)
ABSTRACT Alloy 22 (N06022) is a nickel based alloy containing alloying elements such as chromium, molybdenum and tungsten. It is highly corrosion resistant both under reducing and under oxidizing conditions. Electrochemical studies such as cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behavior of Alloy 22 in 1M NaCl solutions at various pH values from acidic to neutral at 90ºC. Tests were also carried out in NaCl solutions containing oxalic acid or acetic acid. It is shown that the corrosion rate of Alloy 22 was higher in a solution containing oxalic acid than in a solution of the same pH acidified with HCl. Acetic acid was not corrosive to Alloy 22. The corrosivity of oxalic acid was attributed to its capacity to form stable complex species with metallic cations from Alloy 22. INTRODUCTION Alloy 22 (N06022) contains by weight approximately 22% chromium (Cr), 13% molybdenum (Mo), 3% tungsten (W) and approximately 3% iron (Fe). Alloy 22 was commercially designed to resist the most aggressive industrial applications, offering a low general corrosion rate both under oxidizing and reducing conditions. Under oxidizing and acidic conditions Cr exerts its beneficial effect in the alloy. Under reducing conditions the most beneficial alloying elements are Mo and W, which offer a low current for hydrogen discharge. Moreover, due to its balanced content in Cr, Mo and W, Alloy 22 is used extensively in hot chloride containing environments where austenitic stainless steels may fail by pitting corrosion and stress corrosion cracking (SCC). Alloy 22 is the material selected for the fabrication of the outer shell of the nuclear waste containers for the Yucca Mountain site. Several papers have been published recently describing the general and localized corrosion behavior of Alloy 22 regarding its application for the nuclear waste containers. It is also known that the addition of nitrate and other oxyanions to a chloride-containing environment, decreases the susceptibility of Alloy 22 to localized attack. It has been recently reported that fluoride ions may also act as an inhibitor to crevice corrosion of in Alloy 22. Little is known on the corrosion behavior of Alloy 22 in organic acids. It was shown that the corrosion rate of Alloy 22 increases as the concentration of oxalic acid increased from 0.01 M to 1 M. For a concentration of oxalic acid of 0.1 M, the corrosion rate increased as the temperature increased from 30°C to 90°C. Oxalic acid did not promote localized corrosion such as crevice corrosion in Alloy 22. Oxalic acid or ethanedioic (HOOCCOOH or H2O4C2) is an organic acid widely used in the pharmaceutical industry as an intermediate or as a component. Oxalic acid is also used as bleaching agent in the textile industry, as a precipitation agent in the production of rare earths, as a rust remover, in water treatment, etc. Oxalic acid is one of the most aggressive alkane acids. Oxalic acid is slightly oxidizing with dissociation constants pKa1 = 1.25 and pKa2 = 3.81 (Table 1). Table 1 also shows the complexing properties of oxalic acid when reacting with metal cations (Equation 1): M + nL /¿ MLn (1) Where M is a metal ion (e.g. Cr, Ni) L is the ligand (e.g. oxalic acid) and MLn is the metal complex. Acetic acid or ethanoic (CH3COOH or H4O2C2) is fabricated industrially by reaction of carbon monoxide and methanol. The primary use of acetic acid in the industry is to make acetate esters including cellulose acetate (used in films and clothing fabrics) and polyvynil acetate (latex paints and glue). Another important use of acetic acid is in the production of aspirin (acetylsalicyl
- North America > United States > Texas (0.29)
- North America > United States > Nevada > Nye County (0.25)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Power Industry > Utilities > Nuclear (0.54)
- Government > Regional Government > North America Government > United States Government (0.48)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.34)
ABSTRACT Alloy 22 (N06022) is highly resistant to localized corrosion. Alloy 22 may be susceptible to crevice corrosion in pure chloride (Cl-) solutions under aggressive environmental conditions. The effect of the fluoride (F-) over the crevice corrosion induced by chloride ions is still not well established. The objective of the present work was to explore the crevice corrosion resistance of this alloy to different mixtures of fluorides and chlorides. Cyclic potentiodynamic polarization (CPP) tests were conducted in deaerated aqueous solutions of pure halide ions and also in different mixtures of chloride and fluoride at 90°C and pH 6. The range of chloride concentration [Cl-] was 0.001 M = [Cl-] = 1 M and the range of molar fluoride to chloride ratio [F-]/[Cl-] was 0.1 = [F-]/[Cl-] = 10. Results showed that Alloy 22 was susceptible to crevice corrosion in all the pure chloride solutions but not in the pure fluoride solutions. Fluoride ions showed an inhibitor behavior only in mixtures with a molar ratio [F-]/[Cl-] > 2. For mixtures with a molar ratio [F-]/[Cl-] of 7 and 10 the inhibition of crevice corrosion was complete. INTRODUCTION Alloy 22 (N06022) is nickel (Ni) based and contains nominally 22% Chromium (Cr), 13% Molybdenum (Mo) and 3% tungsten (W). Alloy 22 is one of the most versatile alloys of the Ni-Cr-Mo family and was designed to withstand the most aggressive industrial applications, including reducing acids such as hydrochloric and oxidizing acids such as nitric. The base element (nickel) is very resistant to hot alkalies, and the alloying elements chromium and molybdenum enhance its protection against oxidizing and reducing conditions respectively. Alloy 22 has showed excellent resistance to pitting, crevice corrosion and environmentally assisted cracking in hot concentrated chloride solutions. Applications of Alloy 22 include a variety of chemical processing, pickling and metal finishing, pollution control, nuclear waste treatment and pulp and paper industry, but the widest applications is in flue-gas desulfurization (FGD) plants. Due to its excellent performance in a wide variety of environments Alloy 22 has been selected for the fabrication of the corrosion-resistant outer shell of the high-level nuclear waste container for the proposed Yucca Mountain repository. Alloy 22 can be considered not susceptible to pitting corrosion in practical applications in chloride containing environments. However, Alloy 22 might suffer crevice corrosion under certain aggressive conditions. The factors influencing crevice corrosion susceptibility of Alloy 22 can be classified into environmental (external) and metallurgical (internal). External factors include chloride concentration, temperature, applied potential, presence of inhibitors or deleterious species, pH, microbial activity, volume of electrolyte, crevice former geometry, crevicing material, etc. Internal factors include the metallurgical condition of the alloy (microstructure), presence of a weld seam, type of annealing, oxide film formed, surface finishing, etc. A more detailed discussion regarding this topic can be found elsewhere. Many of the factors listed above, such as chloride concentration, temperature and inhibitors (namely nitrate and sulfate) have been studied in some detail. The influences of other factors still need to be investigated. In particular the role of halides other than chloride is still not well established and will be briefly discussed in this paper.
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- Water & Waste Management > Solid Waste Management (1.00)
- Law > Environmental Law (0.88)
- Energy > Power Industry > Utilities > Nuclear (0.54)
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
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