Calculations of the Cathodic Current Delivery Capacity and Stability of Crevice Corrosion under Atmospheric Environments

Chen, Z. Y.; Cui, Fushuang; Kelly, Robert G.

doi:10.1149/1.2926557

Cited by 90 publications

(73 citation statements)

References 34 publications

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“…In addition, it implicitly assumes that WL, , and O 2 solubility ͑needed for calculations of limit current density͒ are independent, but in reality, two other physiochemical parameters control these. As discussed in a previous work, 10 the relative humidity ͑RH͒ and the amount of salt͑s͒ present on the surface determine the electrolyte thickness and conductivity. The RH determines the equilibrium concentration of salt in solution through the deliquescent behavior of the salt͑s͒ of interest.…”

Section: 11mentioning

confidence: 72%

Computational Modeling of Bounding Conditions for Pit Size on Stainless Steel in Atmospheric Environments

Chen¹,

Kelly²

2010

J. Electrochem. Soc.

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118

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This paper presents analytic expressions for calculating bounding conditions for pitting under atmospheric conditions. These expressions allow the prediction of the maximum pit size that can develop under known atmospheric conditions by considering the factors that can control the inherent galvanic coupling between a circular pit under a thin electrolyte layer surrounded by a concentric cathodic area. Expressions are developed for the maximum cathodic current and the minimum anodic current required for pit stability. An analytic expression for the maximum cathodic current that the surrounding area can supply to the pit is developed and validated by comparison to calculations using the finite element method. The effects of the controlling environmental parameters ͑deposition density and relative humidity͒ on the cathode bounding parameters are explored, as is the effect of the size of the pit. The analytical expression for the maximum cathodic current is then coupled to the Galvele pit stability product to estimate the maximum pit size that could develop for a given set of environmental conditions. Those results are then compared to data available in the literature from outdoor exposures of stainless steels for up to 26 years. Corrosion resistant alloys such as stainless steels rely on their passive films for the maintenance of their characteristically low dissolution rates. Under most conditions, this film provides outstanding protection against uniform corrosion. Corrosion resistant alloys do suffer from localized corrosion when discrete locations lose this protection. It is generally accepted that such local loss of protection occurs spontaneously in the presence of aggressive ions, although in most cases, the alloy surface is able to repassivate the failed oxide film, thereby limiting the damage. These metastable events have been the subject of many investigations 1-4 to understand the underlying processes that lead to the more damaging, stable pits. Models have been constructed that relate the frequency of metastable pitting to the likelihood of stable pitting. [1][2][3]5 Such models are of use for predicting the likelihood of corrosion damage occurring in service if the material and exposure conditions are known, although they generally do not predict the extent of damage, although there are exceptions.5 In many applications of corrosion resistant alloys, only stable pitting creates sufficient damage to be of concern. Others have fit exposure data to develop empirical power laws for pit propagationwhere d pit is the maximum pit depth measured, t is the exposure time, and A and n are constants that depend on the material and environment. While useful for the environments and materials used in the exposure testing, such approaches are difficult to extend to other material/environment systems as the underlying factors controlling pit size are usually not clearly delineated.In applications where the intended service life is very long, it may be considered unwise to extrapolate empirical power laws to times orde...

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Section: 11mentioning

confidence: 72%

Computational Modeling of Bounding Conditions for Pit Size on Stainless Steel in Atmospheric Environments

Chen¹,

Kelly²

2010

J. Electrochem. Soc.

Self Cite

118

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“…This change in morphology is in line with the idea that the maximum pit size under thin electrolyte films is controlled by ohmic drop between the cathodic and anodic sites and the cathodic current available to sustain a pit. 68 If areal coverage of catholyte (secondary spreading) relates to cathodic current, minimizing this area would minimize the pit size and cause shallower pits. The spatial frequency of pitting would be higher as the individual salt crystals would not interact.…”

Section: Discussionmentioning

confidence: 99%

Effect of Relative Humidity on Corrosion of Steel under Sea Salt Aerosol Proxies

Schindelholz

Risteen

Kelly

2014

J. Electrochem. Soc.

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This paper is the first of two that examine the relationship between relative humidity, the hygroscopic behavior of sea salt aerosol proxies, and the atmospheric corrosion of mild steel contaminated with them. Here, the association between the deliquescence phase transitions (solid-aqueous) of a single salt, NaCl, and the corrosion response of steel contaminated with this salt is examined. Specific focus is given to mechanisms that allow corrosion below the deliquescence relative humidity of NaCl (76% RH). Mild steel loaded with aqueous NaCl drops or crystals (9 μg · cm −2 ) was subjected to isohumidity exposures for up to 300 days. The resulting damage was quantified by optical profilometry. The corrosion chemistry that developed was identified using EDS and Raman spectroscopy. The wetting and drying of simulated corrosion chemistries were characterized by impedance measurements across an interdigitated electrode sensor. Taken together, these results show that corrosion can initiate by adsorbed water on NaCl crystals at as low as 33% RH. At 53% RH and above, attack proceeded at rates comparable to that observed above the deliquescence RH due to the development of hygroscopic corrosion chemistry. The governing role of the hygroscopic properties of this chemistry on attack rate and morphology is discussed.

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“…In this manner, salt load can control available anode-cathode area through electrolyte coverage and corrosion cell efficiency (volume and geometry); higher salt loads generally increase coverage and volume and tend towards thin, continuous films. Factors affecting efficiency include electrolyte resistance, which can reduce the effective cathode area, 20,21 along with the electrolyte path length for oxygen to reach the surface when oxygen reduction is the rate limiting step. 22,23 While the individual relationships of these factors with electrolyte geometry are generally understood under ideal conditions at the initial stage of corrosion, less is known regarding their combined influence or competition experienced as corrosion advances.…”

Section: Introductionmentioning

confidence: 99%

The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

et al. 2017

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Aluminum and aluminum alloys are widely used in many outdoor applications due to their inherent corrosion resistance attributed to the formation of a protective oxide layer. While corrosion rates are generally considered low for aluminum in many atmospheric environments, understanding of the corrosion performance over time is necessary to predict the cost, safety, and esthetics of these materials. The vast majority of the knowledgebase of atmospheric aluminum corrosion is built on environment-response relationships; often based on statistical correlation of corrosion rate data with atmospheric environmental conditions. However, there is still a limited mechanistic understanding of corrosion processes associated with this linkage. This lack in knowledge prevents interpretation and limits the extrapolation of these statistical datasets for prediction purposes. Here, the mechanistic dependence of aluminum corrosion rate on salt loading is explored through complimentary experimental and theoretical analysis relating corrosion rate to electrolyte chemistry, volume and corrosion products. From these results a reaction pathway is proposed for the atmospheric corrosion of aluminum that accounts for the governing effects of CO 2 and salt loading on corrosion rate. This reaction pathway provides a new perspective that highlights the importance of the formation and growth of dawsonite (NaAlCO 3 (OH) 2 ), and the subsequent gettering of sodium from the electrolyte leading to the stifling of corrosion kinetics. This study highlights the importance of accounting for the dynamic physical and chemical state of the electrolyte during corrosion in process models and measurement techniques to better understand and predict atmospheric corrosion behavior.

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Calculations of the Cathodic Current Delivery Capacity and Stability of Crevice Corrosion under Atmospheric Environments

Cited by 90 publications

References 34 publications

Computational Modeling of Bounding Conditions for Pit Size on Stainless Steel in Atmospheric Environments

Computational Modeling of Bounding Conditions for Pit Size on Stainless Steel in Atmospheric Environments

Effect of Relative Humidity on Corrosion of Steel under Sea Salt Aerosol Proxies

The controlling role of sodium and carbonate on the atmospheric corrosion rate of aluminum

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