The effect of water vapor on the corrosion of carbon steel at 65{degree}C

AISI 1020 carbon steel was exposed to air at various relative humidities at 65{degrees}C. A ``critical relative humidity`` (CRH) of 75--85% was determined. The CRH is the transitional relative humidity where oxidation/corrosion changes from dry oxidation to aqueous film electrochemical corrosion. Short term testing suggests that aqueous film electrochemical corrosion results in the formation of an inner oxide of Fe{sub 3}O{sub 4}, and an outer oxide of a powdery Fe{sub 2}O{sub 3} and/or Fe{sub 2}O{sub 3}{center_dot}xH{sub 2}O

Crevice Repassivation Potential of Alloy 22 in High-Nitrate Dust Deliquescence Type Environments

The nitrate ion (NO{sub 3}{sup -}) is an inhibitor for crevice corrosion of Alloy 22 (N06022) in chloride (Cl{sup -}) aqueous solutions. Naturally formed electrolytes may contain both chloride and nitrate ions. The higher the ratio R = [NO{sub 3}{sup -}]/[Cl{sup -}] in the solution the stronger the inhibition of crevice corrosion. Atmospheric desert dust contains both chloride and nitrate salts, generally based on sodium (Na{sup +}) and potassium (K{sup +}). Some of these salts may deliquescence at relatively low humidity at temperatures on the order of 150 C and higher. The resulting deliquescent brines are highly concentrated and especially rich in nitrate. Electrochemical tests have been performed to explore the anodic behavior of Alloy 22 in high chloride high nitrate electrolytes at temperatures as high as 150 C at ambient atmospheres. Naturally formed brines at temperatures higher than 120 C do not induce crevice corrosion in Alloy 22 because they contain high levels of nitrate. The inhibitive effect of nitrate on crevice corrosion is still active for temperatures higher than 100 C

Integrated Corrosion Facility for long-term testing of candidate materials for high-level radioactive waste containment

A long-term-testing facility, the Integrated Corrosion Facility (I.C.F.), is being developed to investigate the corrosion behavior of candidate construction materials for high-level-radioactive waste packages for the potential repository at Yucca Mountain, Nevada. Corrosion phenomena will be characterized in environments considered possible under various scenarios of water contact with the waste packages. The testing of the materials will be conducted both in the liquid and high humidity vapor phases at 60 and 90{degrees}C. Three classes of materials with different degrees of corrosion resistance will be investigated in order to encompass the various design configurations of waste packages. The facility is expected to be in operation for a minimum of five years, and operation could be extended to longer times if warranted. A sufficient number of specimens will be emplaced in the test environments so that some can be removed and characterized periodically. The corrosion phenomena to be characterized are general, localized, galvanic, and stress corrosion cracking. The long-term data obtained from this study will be used in corrosion mechanism modeling, performance assessment, and waste package design. Three classes of materials are under consideration. The corrosion resistant materials are high-nickel alloys and titanium alloys; the corrosion allowance materials are low-alloy and carbon steels; and the intermediate corrosion resistant materials are copper-nickel alloys

Localized Corrosion Susceptibility Of Alloy 22 In Na-K-Cl_NO3 Brines At 110 To 150?C

Electrochemical cyclic potentiodynamic polarization experiments were conducted to assess crevice corrosion of Alloy 22 in de-aerated aqueous solutions of chloride and nitrate salts of potassium and sodium in the temperature range 110-150 C. The tests were run in neutral and slightly acidic aqueous solutions. The Alloy 22 specimens were multiple creviced weld prisms. No evidence of crevice corrosion was observed in the range 125-150 C. In the 120 to 160 C temperature range, the anionic concentration of stable aqueous solutions is dominated by nitrate relative to chloride. At nominally 120 C, the minimum nitrate to chloride ratio is about 4.5, and it increases to about 22 at nominally 155 C. The absence of localized corrosion susceptibility in these solutions is attributed to the known inhibiting effect of the nitrate anion. Aqueous solution chemistry studies indicate that nitrate to chloride ratios of less than 0.5 are possible for temperatures up to nominally 116 C. At 110 C, aqueous solutions can have dissolved chloride well in excess of nitrate. Localized corrosion was observed at nitrate to chloride ratios up to 1.0, the highest ratio tested. The extent of localized corrosion was confined to the crevice region of the samples, and was limited for nitrate to chloride ratios greater than or equal to 0.3

Effect of Nitrate on the Repassivation Potential of Alloy 22 in Chloride Containing Environments.

The study of Alloy 22 was undertaken in several selected nitrate/chloride (NO{sub 3}{sup -}/Cl{sup -}) electrolytes with chloride concentrations [Cl{sup -}] of 1.0, 3.5 and 6.0 molal with [NO{sub 3} {sup -}]/[Cl{sup -}] ratios of 0.05, 0.15 and 0.5 at temperatures up to 100 C. Results showed that the repassivation potentials increased with increase in [NO{sub 3} {sup -}]/[Cl{sup -}] ratio and decreased with increase in temperature. The absolute [Cl{sup -}] was found to have less of an effect on the repassivation potential compared with temperature and the NO{sub 3} {sup -}/Cl{sup -}. Regression analyses were carried out and expressions were derived to describe the relationship between the repassivation potential, temperature, [Cl{sup -}] and [NO{sub 3} {sup -}] for the conditions tested

Selection of candidate container materials for the conceptual waste package design for a potential high level nuclear waste repository at Yucca Mountain

Preliminary selection criteria have been developed, peer-reviewed, and applied to a field of 41 candidate materials to choose three alloys for further consideration during the advanced conceptual design phase of waste package development for a potential high level nuclear waste repository at Yucca Mountain, Nevada. These three alloys are titanium grade 12, Alloy C-4, and Alloy 825. These selections are specific to the particular conceptual design outlined in the Site Characterization Plan. Other design concepts that may be considered in the advanced conceptual design phase may favor other materials choices

A Framework for the Analysis of Localized Corrosion at the Proposed Yucca Mountain Repository

The proposed Repository presents a familiar materials performance application that is regularly encountered in energy, transportation and other industries. The widely accepted approach to dealing with materials performance is to identify the performance requirements, to determine the operating conditions to which materials will be exposed and to select materials of construction that perform well in those conditions. A special feature of the proposed Yucca Mountain Repository is the extremely long time frame of interest, i.e. 10,000's of years and longer. Thus, the time evolution of the environment in contact with waste package surfaces and the time evolution of corrosion damage that may result are of primary interest in the determination of expected performance. An approach is presented to the analysis of localized corrosion during a time period when it is possible for waters from drips and seepage to contact the waste package surfaces, and the analysis is demonstrated for the water chemistry of mixed salt solutions and a set of time-temperature-relative humidity profiles for a hot, mid and cool temperature waste package. Based on the analysis, there are large time periods when localized corrosion can not be supported, and no corrosion damage will occur. Further analysis can then focus on time periods when it is possible for localized corrosion to occur and the determination of the evolution of any corrosion damage

Survey of degradation modes of four nickel-chromium-molybdenum alloys

This report examines the degradation modes of four Ni-Cr-Mo alloys under conditions relevant to the Yucca Mountain Site Characterization Project (YMP). The materials considered are Alloys C-276, C-4, C-22, and 625 because they have desirable characteristics for the conceptual design (CD) of the high-level radioactive-waste containers presented in the YMP Site Characterization Plan (SCP). The types of degradation covered in this report are general corrosion; localized corrosion, including pitting and crevice corrosion; stress corrosion cracking in chloride environments; hydrogen embrittlement (HE); and undesirable phase transformations due to a lack of phase stability. Topics not specifically addressed are welding concerns and microbiological corrosion. The four Ni-Cr-Mo alloys have excellent corrosion resistance in chloride environments such as seawater as well as in more aggressive environments. They have significantly better corrosion resistance than the six materials considered for the CD waste container in the YMP SCP. (Those six materials are Types 304L and 3161L stainless steels, Alloy 825, unalloyed copper, Cu(70)-Ni(30), and 7% aluminum bronze.) In seawater, the Ni-Cr-Mo alloys have negligible general corrosion rates and show little evidence of localized corrosion. The four base materials of these alloys are expected to have nearly indistinguishable corrosion resistance in the YMP environments. The strength requirements of the SCP-CD waste container are met by these materials in the annealed condition; in this condition, they are highly resistant to HE. Historically, HE has been noted when these materials have been strengthened (cold-worked) and used in sour gas (H{sub 2}S and CO{sub 2}) well service -- conditions that are not expected for the YMP. Metallurgical phase stability may be a concern under conditions favoring (1) the formation of intermetallics and carbides, and (2) microstructural ordering