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

Industrial Experience on the Caustic Cracking of Stainless Steels and Nickel Alloys -A Review INDUSTRIAL EXPERIENCE ON THE CAUSTIC CRACKING OF STAINLESS STEELS AND NICKEL ALLOYS -A REVIEW

ABSTRACT Caustic environments are present in several industries, from nuclear power generation to the fabrication of alkalis and alumina. The most common material of construction is carbon steel but its application is limited to a maximum temperature of approximately 80°C. The use of Nickel (Ni) alloys is recommended at higher temperatures. Commercially pure Ni is the most resistant material for caustic applications both from the general corrosion and the stress corrosion cracking (SCC) perspectives. Nickel rich alloys also offer a good performance. The most important alloying elements are Ni and chromium (Cr). Molybdenum (Mo) is not a beneficial alloying element and it dissolves preferentially from the alloy in presence of caustic environments. Austenitic stainless steels such as type 304 and 316 seem less resistant to caustic conditions than even plain carbon steel. Experimental evidence shows that the most likely mechanism for SCC is anodic dissolution

Corrosion Resistance of Aluminum-Copper Alloys with Different Grain Structures

Electrochemical studies and microstructure analysis of directionally solidified hypoeutectic and eutectic aluminum-copper alloys were performed. Optical and scanning electron microscopy studies of corroded specimens with columnar and equiaxed microstructures in 0.1 M, 0.5 M, and 1 M NaCl solutions were conducted. Low-rate potential scanning and alternating current (AC) electrode impedance measurements were conducted to study the corrosion resistance of four aluminum-copper alloys. The concentration of Cu in the alloys proved to be a key factor in the corrosion resistance of the Al-Cu alloys, which controlled the fraction of α and θ phases and the morphological distribution of these phases. The addition of Cu provides cathodic sites that increase adjacent anodic activity and higher corrosion susceptibility of the Al-Cu alloys, as compared with pure Al. Arise in the Cu amount that is linked to an increased concentration of the Al2Cu intermetallic or theta phase results in a higher susceptibility to corrosion for the studied alloys. A microstructural morphology related to a decreased area of contact between the α-phase and the Al2Cu intermetallic phase enhances the corrosion resistance of the Al-Cu alloys. For the Al-1wt.%Cu alloy increasing the content of Cl− produces a beneficial result related to a more resistive passive film. For the rest of the studied alloys with nobler corrosion potentials, the increase in Cl− results in a decrease in their corrosion resistance.Fil: Roman, Alejandra Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Mendez, Claudia Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Gervasi, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Rebak, Raúl B.. No especifíca;Fil: Ares, Alicia Esther. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentin

Corrosion Enhanced Enrichment of Sulfur and Implications for Alloy 22 CORROSION ENHANCED ENRICHMENT OF SULFUR AND IMPLICATIONS FOR ALLOY 22

ABSTRACT The uniform corrosion rate of Alloy 22 will define the lifetime of a component such as a waste container if all other degradation modes are not operative. This represents the best-case scenario because the experimentally determined uniform corrosion rates from multi-year tests is 0.01 µm/yr or 0.1 mm in 10,000 years. This lifetime depends on the stability of the passive film over the lifetime of the container; however, this stability is unknown. One potential breakdown mechanism is corrosion-enhanced enrichment of sulfur to the surface leading to sulfur induced breakdown of the passive film. There are numerous studies that confirm that sulfur causes passive film breakdown in nickel based alloys and evidence exists for corrosion enhanced enrichment of sulfur in nickel and nickel alloys. However, neither sulfur enrichment nor sulfur induced breakdown of the passive film on Alloy 22 has been demonstrated. The results of preliminary studies suggest sulfur enrichment does occur at the alloy surface and that sulfur shifts the corrosion potential to more active potentials. No clear affect of sulfur was noted on the corrosion rate but the sulfur concentrations were about only 2−3 % of a monolayer, well below the concentrations that are possible

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

The 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: 1 mol/L NaCl at 90 °C, and 1.148 mol/L NaHCO3, 1.148 mol/L NaHCO3 + 1 mol/L NaCl, 1.148 mol/L NaHCO3 + 0.1 mol/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 1 mol/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.Fil: Zadorozne, Natalia Silvina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; Argentina. Universidad Nacional de San Martin. Instituto Sabato; ArgentinaFil: Giordano, Mabel Cristina. Universidad Nacional de San Martin. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Constituyentes); ArgentinaFil: Rebak, Raúl B.. GE Global Research; Estados UnidosFil: Ares, Alicia Esther. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; ArgentinaFil: Carranza, Ricardo M.. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; Argentina. Universidad Nacional de San Martin. Instituto Sabato; Argentin

Anodic Stress Corrosion Cracking Suspectibility of Nickel and Nickel-Chromium Alloys Containing Molybdenum and Iron in Bicarbonate Plus Chloride Solutions at 90°C

It is reported in the literature that Alloy C-22 (N06022) was foundsusceptible to stress corrosion cracking (SCC) in presence of bicarbonate ions, at temperatures higher than 60°Cand anodic applied potentials in the order of +400 mVSCE, when using slow strain rate tests (SSRT). This potential range of cracking susceptibility was associated to the instability of a film that may form on the surface. In order to elucidate the role of the alloying elements on the SCC susceptibility of nickel (Ni) based alloys, the following four Alloy C-22 (N06022), Alloy 600 (N06600), Alloy 800H (N08800) and Alloy Ni-201 (N02201)were tested under the same conditions. Results showed that even though C-22, 600 and 800 may have similar electrochemical anodic behavior, only C-22 may present a clear case of SCC at anodic potentials.Fil: Zadorozne, Natalia Silvina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; ArgentinaFil: Giordano, Mabel Cristina. Universidad Nacional de San Martín; ArgentinaFil: Rebak, Raúl B.. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; ArgentinaFil: Ares, Alicia Esther. Universidad Nacional de San Martín; ArgentinaFil: Carranza, Ricardo M.. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; Argentin

Effect of Environmental Variables on Crevice Corrosion Susceptibility of Ni–Cr–Mo Alloys for Nuclear Repositories

AbstractThe crevice corrosion repassivation potential was determined by the Potentiodynamic–Galvanostatic-Potentiodynamic (PD–GS–PD) method. Alloys 625, C–22, C–22HS and HYBRID–BC1 were used. Specimens contained 24 artificially creviced spots formed by a ceramic washer (crevice former) wrapped with a PTFE tape. Crevice corrosion tests were performed in 0.1 mol/L and 1 mol/L NaCl solutions at temperatures between 20 and 90°C, and CaCl2 5 mol/L solution at temperatures between 20 and 117°C. The crevice corrosion resistance of the alloys increased in the following order: 625 < C–22 < C–22HS < HYBRID–BC1. The repassivation potential (ECO) showed the following relationship with temperature (T) and chloride concentration ([Cl−]) ECO = (a + b T) log [Cl−] + c T + d; where a, b, c and d are constants. At temperatures above 90°C, ECO for alloy 625 stabilized at a minimum value of –0.26 VSCE