A Study of Cathodic Polarization and pH Changes in Metal Crevices

Peterson, M. H.; Lennox, T. J.

doi:10.5006/0010-9312-29.10.406

Cited by 35 publications

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“…Thus, most recent studies have utilized the thermodynamic, rather than kinetic, approach, with emphasis on factors such as resultant crevice solution chemistry, pH, and electrode potential (8)(9)(10)(11). Little recent work has been done on the polarization kinetics of metals under crevices.…”

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confidence: 99%

Electrochemical Behavior of Iron Within Crevices in Nearly Neutral Chloride Solutions

McCafferty¹

1974

J. Electrochem. Soc.

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In crevices where the internal iron is not short-circuited to external metal, the corrosion rate is determined by the limiting cathodic current for oxygen reduction. This limiting current, and accordingly the corrosion rate, is independent of pH and C1-concentration but is suppressed to a constant value when the height of the crevice is less than the thickness of the oxygen diffusion layer. When iron in the crevice is short-circuited to external, open platinum, the initial crevice corrosion rate is independent of crevice height but increases with increasing C1-concentration and area of external electrode. At constant CI-concentration, the crevice corrosion rate of internal iron short-circuited to o~en external iron decreases with increasing chromate ion concentration. At a constant chromate ion concentration which does not give protection, the crevice corrosion rate is greater the greater the chloride ion concentration for short times, but at longer times the rates are essentially independent of bulk chloride concentration.Rosenfeld and Marshakov (1) have shown that crevice corrosion usually proceeds in two main stages: (i) initiation by differential aeration and (ii) propagation by crevice acidification. Initially, the sheltered metal in contact with a restricted oxygen supply becomes anodic relative to the open metal to which it is connected. At longer times, the presence of the crevice plays a different role, that of causing corrosion products to accumulate within the crevice so as to change the local solution composition and pH.Reports that not only crevices (1, 2) but also stresscorrosion cracks (3, 4) and pits (5, 6) acidify locally has led to the view that all three forms of localized corrosion share the unifying feature of being "occluded corrosion cells" (7) having restricted exchange with bulk electrolyte and thus common solution chemistries. Thus, most recent studies have utilized the thermodynamic, rather than kinetic, approach, with emphasis on factors such as resultant crevice solution chemistry, pH, and electrode potential (8-11). Little recent work has been done on the polarization kinetics of metals under crevices. One exception has been the correlation between the shape of cyclic anodic polarization curves for various engineering alloys in 3 89 % NaC1 with their longer range performances in natural seawater (12). Polarization curves have been reported in some well-defined but synthetic, generalized "occluded corrosion cells" sans crevices, in which the "internal" metal was activated by anodic polarization (13) or by deaeration (14). Other investigators have reported current-time (15) and potential-time (10, 16), but not current-potential relationships.The purpose of this study was to take up the systematic approach of Rosenfeld and Marshakov (1) in order to investigate in an organized manner kinetic aspects of a fairly simple crevice system. Iron was chosen, partly because of the attention given this metal in a wide variety of open systems. The effect of vari-* Electrochemical Society Active Mem...

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confidence: 99%

Electrochemical Behavior of Iron Within Crevices in Nearly Neutral Chloride Solutions

McCafferty¹

1974

J. Electrochem. Soc.

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“…have shown that there is only a 30–40 mV difference between the holiday and the bottom of the crevice after about 3 mouths at an applied potential of −850 mV (SCE) . Peterson and Lennox have concluded that the cathodic protection can be achieved for the crevices with a distance to crevice opening ratio of 12000:1 . The studies by Gan et al have shown that the local potentials of the steel X65 in the crevice are more negative than the potential of −850 mV vsCSE .…”

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confidence: 99%

Variations of Microenvironments with and without SRB for Steel Q 235 under a Simulated Disbonded Coating

Sun

Mao

et al. 2013

Ind. Eng. Chem. Res.

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Distributions of potential and current and variations of crevice environments are studied in a crevice under a simulated disbonded coating in soil extract solutions (SES) with and without sulfate-reducing bacteria (SRB). Results show that forming of the crevice blocks the penetration of cathodic currents in the crevice and weakens the cathodic polarization of the steel Q 235. The cathodic currents in the presence of SRB are nearly three times more than those without SRB at the same cathodic protective potential, which indicates that SRB increases the energy consumption of the cathodic protection systems. SRB leads to basification of the solution in the crevice. The forming of inner electric field enhances the anionic migration into the crevice. The forming of the reversed potential increases the cathodic current.

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“…7,8 Potentials inside a crevice were generally measured by placing microelectrodes with salt bridges at fixed distances along the crevice. [9][10][11][12][13][14][15] The pH and some aggressive ions (especially Cl 2 ) in a crevice are recognised as the most common physicochemical properties of a local electrolyte contributing to localised corrosion. As a challenging job for several decades, pH in a local environment, such as a crack and a pitting, has been detected through a freezing method, by inserting microelectrodes, 16 or by extraction of the localised environment solution.…”

Section: Introductionmentioning

confidence: 99%

“…As a challenging job for several decades, pH in a local environment, such as a crack and a pitting, has been detected through a freezing method, by inserting microelectrodes, 16 or by extraction of the localised environment solution. 2,17 The pH in a crevice under the disbonded coating has been measured commonly by in situ measurement using a glass electrode 9 or ex situ measurement extracting small amounts of localised environment solution by a syringe for analysis using pH reagent paper or glass electrodes. 2,14,17 The weakness of the ex situ measurement technique is distinct: not only errors occurring because of mixing of the solution, but also disturbing the equilibration of the local environment.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical measurements using combination microelectrode in crevice simulating disbonded of pipeline coatings under cathodic protection

Mao¹,

Wang²,

Han³

et al. 2007

Corrosion Engineering, Science and Technology

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A novel combination microelectrode was constructed based on an iridium pH microelectrode and an Ag/AgCl microelectrode, and was applied to simultaneously monitor the steel potential, pH and chloride ion concentration in a crevice simulating disbonding of pipeline coatings with cathodic protection (CP) applied or removed. The sensing characteristics and sensitivity of the microelectrode are described as well as the calibration procedures. A simulated crevice was formed between a pipeline steel surface and a polymethylmethacrylate plate. The results showed that in CP conditions, the evident potential gradient resulting from the IR potential drop was concentrated at the crevice opening. A protective local environment induced by CP under disbonded coatings was characterised by an increase in pH and removal of Cl 2 . After CP is removed, the protective effects can persist for a period of time, depending on the diffusion of soluble species.

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A Study of Cathodic Polarization and pH Changes in Metal Crevices

Cited by 35 publications

References 0 publications

Electrochemical Behavior of Iron Within Crevices in Nearly Neutral Chloride Solutions

Electrochemical Behavior of Iron Within Crevices in Nearly Neutral Chloride Solutions

Variations of Microenvironments with and without SRB for Steel Q 235 under a Simulated Disbonded Coating

Electrochemical measurements using combination microelectrode in crevice simulating disbonded of pipeline coatings under cathodic protection

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