Anodic Behavior of Alloy 22 in Bicarbonate Media: Effect of Alloying

AbstractThe alloy 22 (UNS N06022) is one of the candidates for the manufacture of containers of radioactive waste high level. These containers provide services in natural environments characterized by multi-ionic solutions, it is estimated they could suffer three types of deterioration: general corrosion, localized corrosion (specifically crevice) and stress corrosion cracking (SCC). It has been confirmed to produce cracking, requires the presence of bicarbonate and chloride ions. It has also determined that susceptibility to SCC could be related to the occurrence of an anodic peak in the polarization curves in these media to at potentials previous transpassive zone.The aim of this work is to study the anodic behavior of alloy 22 and its alloying effect in different media containing bicarbonate and chloride ions in different concentrations and temperatures.Polarization curves were made of alloy 22 (Ni-22% Cr-13% Mo), Ni-Mo (Ni-28, 5% Mo) and Ni-Cr (Ni-20% Cr) under the following conditions: 1mol/L NaCl at 90°C, and 1.148mol/L NaHCO3, 1.148mol/L NaHCO3 + 1 mol/L NaCl, 1.148mol/L NaHCO3 + 0.1mol/L NaCl at 90°C, 75°C, 60°C and 25°C.It was found that the alloy 22 has a current peak in the anodic at potential previous to transpassive zone, only when the medium has bicarbonate ions. Curves performed in 1mol/L NaCl did not show any anodic peak, in any of the alloys tested. The curves made to alloys Ni-Mo and Ni-Cr in the media with bicarbonate ions, allowed to determine that Cr, is responsible for the appearance of the anodic peak in the Alloy 22. The curves of alloy B-3 showed no current peak in the conditions studied. The potential, at which the peak appears in the Alloy 22 and Ni-Cr alloy, increases with decreasing temperature. It also presents a variation of the peak with the composition of the solution. When the chloride ion is added to bicarbonate solution, the peak is shifted potential and higher current densities, depending on the concentration of added chloride ions

The Influence of Composition upon Surface Degradation and Stress Corrosion Cracking of the Ni-Cr-Mo Alloys in Wet Hydrofluoric Acid

At concentrations below 60%, wet hydrofluoric acid (HF) is extremely corrosive to steels, stainless steels and reactive metals, such as titanium, zirconium, and tantalum. In fact, only a few metallic materials will withstand wet HF at temperatures above ambient. Among these are the nickel-copper (Ni-Cu) and nickel-chromium-molybdenum (Ni-Cr-Mo) alloys. Previous work has shown that, even with these materials, there are complicating factors. For example, under certain conditions, internal attack and stress corrosion cracking (SCC) are possible with the Ni-Cr-Mo alloys, and the Ni-Cu materials can suffer intergranular attack when exposed to wet HF vapors. The purpose of this work was to study further the response of the Ni-Cr-Mo alloys to HF, in particular their external corrosion rates, susceptibility to internal attack and susceptibility to HF-induced SCC, as a function of alloy composition. As a side experiment, one of the alloys was tested in two microstructural conditions, i.e. solution annealed (the usual condition for materials of this type) and long-range ordered (this being a means of strengthening the alloy in question). The study of external corrosion rates over wide ranges of concentration and temperature revealed a strong beneficial influence of molybdenum content. However, tungsten, which is used as a partial replacement for molybdenum in some Ni-Cr-Mo alloys, appears to render the alloys more prone to internal attack. With regard to HF-induced SCC of the Ni-Cr-Mo alloys, this study suggests that only certain alloys (i.e., those containing tungsten) exhibit classical SCC. It was also discovered that high external corrosion rates inhibit HF-induced SCC, presumably due to rapid progression of the external attack front. With regard to the effects of long-range ordering, these were only evident at the highest test temperatures, where the ordered structure exhibited much higher external corrosion rates than the annealed structure

Methods to Calculate Corrosion Rates for Alloy 22 from Polarization Resistance Experiments

The general corrosion rate may be measured using immersion tests or electrochemical tests. Electrochemical tests are fast and can be used for a rapid screening of environmental effects such as temperature and electrolyte composition. Electrochemical tests are described in ASTM standards G 59 and G 102. The basis of these tests is to calculate the resistance to polarization (R{sub p}) in a voltage vs. current plot and to convert these values to corrosion rates using Faraday's law. Commercial software can calculate the corrosion rate based on inputs from the operator. This paper discusses three ways of calculating the corrosion rate (Methods 1, 2, and 3) based on a fixed set of acquired data of voltage vs. current. It is concluded that the way the corrosion rate is calculated does not greatly impact the absolute value of the corrosion rate. Variations in the acquired data (current, potential) from one experiment to another seem more important than the manner in which data is fitted with the R{sub p} slope

Influence of Thermal Aging on the Mechanical and Corrosion Properties of C-22 Alloy Welds

The phase stability of C-22 alloy (UNS No. N06022) gas tungsten arc welds was studied by aging samples at 427, 482, 538, 593, 649, 704, and 760 C for times up to 40,000 hours. The tensile properties and the Charpy impact toughness of these samples were measured in the as-welded condition as well as after aging. The corrosion resistance was measured using standard immersion tests in acidic ferric sulfate (ASTM G 28 A) and 2.5% hydrochloric acid solutions at the boiling point. The microstructures of weld samples were examined using scanning electron microscopy (SEM). One weld sample (aged 40,000 hours at 427 C) was examined using transmission electron microscopy (TEM). The structure of the unaged welds was dendritic with tetrahedrally close-packed (TCP) phase particles in the interdendritic regions. Long-range order was seen in the weld aged at 427 C for 40,000 hours and was assumed to also occur in other welds aged below approximately 600 C. At temperatures above about 600 C, TCP phase nucleation and growth of existing particles occurred. This precipitation occurred near the original particles presumably in regions of the highest molybdenum (Mo) segregation. Lower temperatures had little or no effect on the morphology of TCP phases. The C-22 weld samples were approximately 25% stronger but 30-40% less ductile than the base metal. Strengthening of the weld during aging occurred significantly only at 593 C for the aging times investigated. Because strengthening was not seen at higher temperatures, it was assumed to be due to ordering which has been seen in C-22 base metal at this temperature. A small amount of strengthening was seen at 427 C after 40,000 hours where ordering was just beginning. The Charpy impact toughness was reduced dramatically with aging. The time at which this reduction occurred decreased as aging temperature increased suggesting that the reduced ductility is due to the presence and growth of the brittle TCP phases. The corrosion rate of weld samples tested in the standard ASTM G 28 A solution and in a 2.5% HCl solution was higher than was seen with C-22 base metal. After aging, however, the corrosion rate of weld and base metal samples became comparable

Cyclic and Linear Polarization of Yttrium-Containing Iron-Based Amorphous Alloys

Iron-based amorphous alloys are produced by rapid solidification from the melt. These alloys may possess unique mechanical and corrosion resistant properties. The chemical composition of the alloy may influence the cooling rate that is necessary for the alloys to be completely vitreous. At the same time, the corrosion resistance of the amorphous alloys may also depend on their chemical composition. This paper examines the anodic behavior of iron-based amorphous alloys containing three different concentrations (1, 3 and 5 atomic %) of yttrium (Y) in several electrolyte solutions. Results from polarization resistance potentiodynamic polarization show that when the alloy contains 5% atomic Y, the corrosion resistance decreases

Terneza, grasa intramuscular y de cobertura en carne de novillos faenados en Corrientes (Argentina)

La terneza de la carne es el atributo más apreciado por los consumidores, encontrándose condicionada por muchos factores. El objetivo de este trabajo fue generar información sobre terneza objetiva post maduración de la carne bovina y determinar valores de grasa intramuscular y de cobertura en animales de diferentes biotipos y edades faenados en Corrientes. El trabajo se realizó en un frigorífico tipo A y en la Facultad de Ciencias Veterinarias de la UNNE. Se evaluó el músculo longisimus dorsi de novillos tipo Brangus y Braford, de 4, 6 y 8 dientes. Se registró el peso individual de res caliente, así como la conformación y terminación. Las muestras divididas en dos fueron maduradas durante 7 y 14 días envasadas al vacío. La terneza se evaluó por la cizalla de Warner-Bratzler, la grasa total por el método de Soxhlet y la grasa de cobertura con un escalímetro. Se utilizó el análisis de la covarianza a tres vías incluyendo el peso de la res como covariable. El periodo de maduración afectó la terneza. Se registraron diferencias estadísticas entre tratamientos a los 14 días, no así a los 7 días. Durante este periodo, la diferencia de peso lograda se atribuyó al número de dientes y la covariable. El espesor de grasa dorsal se vio afectado por el número de dientes al igual que en la grasa intramuscular, donde además afectó la covariable. La maduración al vacío mejoró la terneza de la carne, siendo este efecto manifiesto en individuos más jóvenes, incrementándose la grasa de cobertura con la edad, no así la grasa intramuscular. La carne producto de animales faenados en la Provincia de Corrientes debe ser considerada de buena calidad, ya que según características de terneza y porcentajes de grasa intramuscular y de cobertura encontradas, responde a las más altas exigencias del mercado.The tenderness of meat is the most valued attribute for the market, being influenced by many factors. The aims of this study were to generate information on post objective tenderness values of beef maturation and to estimate both intramuscular and cover fat values in animals of different ages and biotypes slaughtered in Corrientes, Argentina. Assay was performed in a type A slaughterhouse and at the Faculty of Veterinary Science UNNE. Longisimus dorsi muscle of 4, 6 and 8 teeth Brangus and Braford steers was evaluated. Individual weight, conformation and termination on the hot carcass were registered. The samples were divided in two groups vacuum packed, maturated for 7 and 14 days. Tenderness was assessed by Warner-Bratzler shear, total fat by the Soxhlet method, and fat coverage with a scaler. We used analysis of covariance for three tracks including the carcass weight as covariable. The period of maturation affected tenderness. There were statistical differences between treatments at 14 days, but not at 7. During this period, the difference of weight achieved was attributable to number of teeth and the covariable. The back fat thickness was affected by the number of teeth as in intramuscular fat which also affected the covariable. Vacuum maturation accentuated the tenderness of beef, being more evident in younger individuals, with cover fat increasing according age; on the contrary, this effect was not observed for intramuscular fat. Meat products from animals slaughtered in Corrientes must be consid-ered of very good quality, according to the characteristics of tenderness and intramuscular as well as cover fat percentages that meet high market demands.EEA MercedesFil: Ynsaurralde Rivolta, Amanda Eugenia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mercedes; ArgentinaFil: Rebak, Gladis I. Universidad Nacional del Nordeste. Facultad de Ciencias Veterinarias; ArgentinaFil: Sanchez, S. Universidad Nacional del Nordeste. Facultad de Ciencias Veterinarias; ArgentinaFil: Capellari, Adriana. Universidad Nacional del Nordeste. Facultad de Ciencias Veterinarias; Argentin

Comparative Dissolution Modes of Iron-Based Amorphous Alloys and Other Corrosion Resistant Polycrystalline Materials

Metallic amorphous alloys or metallic glasses have been studied extensively for the last three decades due to their unique characteristics, including superior mechanical properties and corrosion resistance. Iron-based amorphous alloys have in general better corrosion resistance than their polycrystalline cousins such as the austenitic 18-8 stainless steel series (e.g. 316L SS). Fe-based amorphous alloys have even higher localized corrosion resistance than the nickel-based Alloy 22 under many laboratory tested conditions. Electrochemical laboratory tests have shown that when polycrystalline alloys such as Alloy 22 are anodically polarized in hot concentrated chloride brines, they dissolve unevenly following patterns associated with their crystalline character. However, amorphous alloys, when polarized to even higher potentials than the polycrystalline alloys, they dissolve in a desirable uniform manner. This is because the amorphous Fe-based alloys do not offer defects in the metal that can be preferentially attacked. Comparative studies will also be presented on the dissolution modes of Ni-gadolinium and borated stainless steels

Effect of High Temperature Aging on the Corrosion Resistance of Iron Based Amorphous Alloys

Iron-based amorphous alloys can be more resistant to corrosion than polycrystalline materials of similar compositions. However, when the amorphous alloys are exposed to high temperatures they may recrystallize (or devitrify) thus losing their resistance to corrosion. Four different types of amorphous alloys melt spun ribbon specimens were exposed to several temperatures for short periods of time. The resulting corrosion resistance was evaluated in seawater at 90 C and compared with the as-prepared ribbons. Results show that the amorphous alloys can be exposed to 600 C for 1-hr. without losing the corrosion resistance; however, when the ribbons were exposed at 800 C for 1-hr. their localized corrosion resistance decreased significantly

Influence of Black Annealing Oxide Scale on the Anodic Behavior of Alloy 22

The resistance of Alloy 22 (N06022) to localized corrosion, mainly crevice corrosion, has been extensively investigated in the last few years. The effect of influencing variables such as temperature, applied potential, chloride concentration and nitrate inhibitor concentration have been addressed previously. At this time, it was important to address the effect an oxide film or scale that forms during the high temperature annealing process or solution heat treatment (SHT) and its subsequent water quenching. Electrochemical tests such as cyclic potentiodynamic polarization (CPP) have been carried out to determine the repassivation potential for localized corrosion and to assess the mode of attack on the specimens. Tests have been carried out in parallel using mill annealed (MA) specimens free from oxide on the surface. The comparative testing was carried out in six different electrolyte solutions at temperatures ranging from 60 to 100 C. Results show that the repassivation potential of the specimens containing the black anneal oxide film on the surface was practically the same as the repassivation potential for oxide-free specimens