Atmospheric Corrosion of Stainless Steels

Yabumoto, M.; Omata, Hiroyasu; Murata, Tetsuhito

doi:10.1016/b978-0-444-42252-1.50098-9

Cited by 4 publications

(3 citation statements)

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“…The chloride concentration thereby increases until pitting corrosion initiates, which is accompanied by a sharp drop in the open-circuit potential ͑OCP͒. 3,4 Tsutsumi et al exposed stainless steel 304 ͑SS304͒ samples to seashore and rural atmospheres. 5 No pits were found on samples in the rural area, while pitting initiated between 35 and 75% RH in the marine environment.…”

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confidence: 99%

Pitting Corrosion of Bare Stainless Steel 304 under Chloride Solution Droplets

Maier

Frankel

2010

J. Electrochem. Soc.

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Pitting corrosion behavior of stainless steel 304 ͑SS304͒ under droplets of chloride solution was investigated using a Kelvin probe ͑KP͒. Droplets of different volumes of MgCl 2 solution were placed on the steel surface and exposed to a constant low relative humidity ͑RH͒. As the concentration increased during the exposure of the drop to low RH, the open-circuit potential ͑OCP͒ and the shape change of the drop were monitored by the KP. Pit initiation was detected by a sudden decrease in the OCP. Pits initiated earlier under small droplets than under large drops. The chloride concentration at initiation was between 3.0 and 8.4 M for droplets with a starting concentration of 0.88 M Cl − . The initiation concentration increased when the initial concentration of the droplet was higher. The anodic current demand of pits growing at the OCP decreased with time as did the available cathodic current. When the current demand exceeded the available cathodic current, the active pit area decreased. A mechanism for pit formation and growth under droplets of MgCl 2 solution was proposed. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3467850͔ All rights reserved. Stainless steels and other corrosion resistant alloys exhibit strong passivity but are susceptible to localized corrosion in the presence of chloride or other aggressive ions.1,2 These alloys are often immune to attack in dilute solutions, but breakdown can occur during atmospheric or alternate immersion conditions by the following scenario. A droplet of salt solution on the surface loses water due to a temperature increase or a decrease in relative humidity ͑RH͒. The chloride concentration thereby increases until pitting corrosion initiates, which is accompanied by a sharp drop in the open-circuit potential ͑OCP͒. 3,4Tsutsumi et al. exposed stainless steel 304 ͑SS304͒ samples to seashore and rural atmospheres.5 No pits were found on samples in the rural area, while pitting initiated between 35 and 75% RH in the marine environment. A humidity of 35% corresponds to a saturated magnesium chloride solution, and 75% RH relates to 3 M MgCl 2 ͑6 M Cl − ͒. According to these results, the chloride concentration for pit initiation under a thin electrolyte layer is around 6 M. This finding agrees with the results of other papers by the same authors.6,7 Tsutsumi et al. determined the onset of pitting, which is associated with a critical chloride concentration, from the sudden drop in the OCP of the stainless steel electrode measured vs an Ag/AgCl reference electrode ͑RE͒.7 The Cl − concentration of the thin electrolyte layer was controlled by varying the RH. The initiation chloride concentration increased with increasing drying rate and with decreasing amount of salt on the surface. The same researchers also studied the influence of electrolyte drop size on the occurrence of the pitting and concluded that pitting is less likely under drops with a small diameter ͑Ͻ5 mm͒ due to a small cathode area. 6,8 The placement of the RE relative to the sample is complicated for a thin-...

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Pitting Corrosion of Bare Stainless Steel 304 under Chloride Solution Droplets

Maier

Frankel

2010

J. Electrochem. Soc.

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“…The other silica-coated samples exhibited only a single sharp decrease similar to the bare samples. A sharp decrease in OCP is associated with initiation of pitting at open circuit as was shown by Ito and coworkers 6 and later by Vera Cruz, et al 5 The potential fluctuations on silica-coated stainless steel likely indicate the occurrence of metastable pitting. The absence of small potential drops on the bare sample suggests that metastable pitting did not take place in the absence of the silica particle layer.…”

Section: Determination Of Pit Volumementioning

confidence: 81%

“…Pit initiation is accompanied by a sharp drop in the open-circuit potential (OCP). [5][6] It has been suggested that a surface contamination layer might also act as a crevice former. 3 Tada and Frankel investigated the influence of silica particles on the localized corrosion behavior of Type 304 (UNS S30400) (1) SS.…”

Section: Introductionmentioning

confidence: 99%

Pitting Corrosion of Silica-Coated Type 304 Stainless Steel Under Thin Electrolyte Layers

Maier¹,

Frankel²

2011

CORROSION

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The pitting corrosion behavior of Type 304 (UNS S30400) stainless steel (SS) under an electrolyte droplet with a layer of silica particles on the surface was investigated using a Kelvin probe. Droplets of 2.5 M magnesium chloride (MgCl 2 ) solution were placed on an electrophoretically silica-coated steel surface and exposed to a constant low relative humidity. As a result of water evaporation, the chloride concentration increased and pitting corrosion initiated, which was detected by a sudden drop in open-circuit potential. Metastable pits repassivated slower under the silica particle layer than on bare stainless steel. Pits on silica-coated Type 304 SS initiated within a narrow chloride concentration and time range unlike pits on bare Type 304 SS. Pit growth rate was not influenced by the silica layer, but the particles acted as diffusion barrier. A mechanism for pit growth under a layer of inert particles was proposed.

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