Crevice Corrosion Propagation on Alloy 625 and Alloy C276 in Natural Seawater

McCafferty, E.; Bogar, F. D.; Thomas, E D; Creegan, C. A.; Lucas, Keith; Kaznoff, A.I.

doi:10.5006/1.3290259

Cited by 17 publications

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“…Due to the hydrolysis of the metal elements, 32,33 the local environment in the corroding crevice region had a pH value much lower and even less than zero. 6,36 The stable species for dissolved metals in the critical crevice chemistry and the bulk solution outside of the crevice can be related to E-pH diagrams for product stability. The E-pH diagrams were calculated with FactSage and OLI software.…”

Section: Discussionmentioning

confidence: 99%

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

Payer

2009

J. Electrochem. Soc.

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The crevice corrosion performance of Alloy 22 was tested under potentiostatic polarization more positive than the repassivation potential in 4 M NaCl solution at 100°C. Under this aggressive condition, crevice corrosion initiated under the crevice contacts and four stages of corrosion behavior were observed: initiation, propagation, stifling ͑corrosion slowed͒, and arrest ͑corrosion stopped͒. During the exposure, dark green deposits were found on the uncorroded metal surface around the crevice contacts, light green precipitations were found in the test solution, and the solution color changed from clear to light green. After exposure, loose black corrosion products were found under the crevice contacts. Surface analyses at the sites of varying corrosion penetrations showed similar composition depth profiles, and the results indicated that a 3-5 nm thick, chromium-rich oxide film was formed on the alloy surface. The composition depth profiles indicated that the crevice corrosion occurred by a uniform, nonselective dissolution. Surface analysis results showed that the corrosion products in the crevice were rich in O, enriched with Mo and W, and depleted of Ni and Cr relative to the bulk alloy. A solution analysis showed that Ni was the main element dissolved into the solution during the exposure. Alloy 22 ͑UNS N06022͒, a nickel-chromium-molybdenum ͑Ni-Cr-Mo͒ alloy, has a high uniform corrosion resistance in oxidizing environments and a superior corrosion resistance in reducing corrosion media. It also exhibits an excellent resistance to localized corrosion, such as pitting and crevice corrosion in low pH, high chloride oxidizing environments. The corrosion resistance of Alloy 22 is due to a passive film on the alloy surface. For Alloy 22, the uniform corrosion rate is very low in a wide range of solutions.1,2 The corrosion rate of Alloy 22 in brine solution decreases with increasing immersion time, and the corrosion rate is less than 30 nm/year after more than 250 days of immersion in highly concentrated brine solutions at 100°C.1 Localized corrosion is an important degradation mode to be evaluated for the corrosion performance of Alloy 22 over long exposure periods, and it has been examined by a number of researchers.3-13 Many factors affecting the localized corrosion behavior of Alloy 22 have been studied, such as the effects of Cl − and oxyanions, 3,4,[14][15][16] the effects of potential and temperature, 5,17 and the propagation and stifling of the crevice corrosion. 5,9,18,19 During the crevice corrosion process, corrosion products are formed. Corrosion products can exist as gas phase, such as hydrogen, soluble species, and insoluble corrosion precipitations. The composition and structure of the corrosion products give evidence to the discernment of the corrosion propagation and arrest processes. The insoluble corrosion products formed in the crevice can increase the ohmic resistance, and they can also affect transport in solution. The increase in ohmic resistance changes the potential distribution in the cre...

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Section: Discussionmentioning

confidence: 99%

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

Payer

2009

J. Electrochem. Soc.

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“…The pH in the crevice can be much lower and even lower than zero. [18,31] Based upon E-pH (Pourbaix) diagrams, W, Mo, and Cr can form stable oxides in highly acidic environments, while Fe and Ni form soluble corrosion products in highly acidic environments. The former elements are primarily retained within the corroded crevice, while the latter elements diffuse/migrate out of the crevice and into the bulk test solution.…”

Section: Corrosion Productsmentioning

confidence: 99%

Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

Payer

2008

Metall Mater Trans A

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The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl solution at 100°C with cyclic potentiodynamic polarization and constant-potential tests. The corrosion damage morphologies, corrosion products, and the compositions of corroded surfaces of these two alloys were studied with optical three-dimensional reconstruction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant-potential tests. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained a high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys corroded congruently in the crevice corrosion damage areas.

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“…ASTM D1148-981 artificial ocean water was prepared from a commercially available sea salt, containing elements found in natural seawater in quantities greater that 0.0004% (Lake Products). 13 After mixing the salt in deionized water (18.2 M · cm at 25…”

Section: Methodsmentioning

confidence: 99%

“…Analysis of the dissolved metal cations in solution indicated that the relative dissolution rates of the alloy elements were Fe≥Ni>Mo>Cr. Hakkarainen 11 was the earliest to study the anodic polarization response of stainless steels in a variety of saturated metal 13 From those results, a polarization curve for alloy 625 was generated in a metal salt solution containing the metal cations Ni, Cr, Fe, and Mo. It was found that i crit values from the anodic polarization response of alloy 625 in these metal-containing solutions was on order of 100 μA/cm 2 .…”

mentioning

confidence: 99%

“…It was found that i crit values from the anodic polarization response of alloy 625 in these metal-containing solutions was on order of 100 μA/cm 2 . Although additional minor elements, such as Nb, are present within real crevices, they were not included in the artificial crevices solutions produced by McCafferty, et al 13 The purpose of the present study was to systematically evaluate a series of simulated critical crevice solutions for nickel alloy 625 based on metal salt solutions. As such, the effect of the metal cations on the polarization response of nickel alloy 625 was studied.…”

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confidence: 99%

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Metal Salt Solutions as a Simulant for the Chemistry in Crevices of Nickel Alloy 625

Salgado

Lillard

2017

J. Electrochem. Soc.

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The development of a critical crevice solution plays an important role in crevice corrosion propagation in nickel alloy 625. In this investigation, the polarization response of alloy 625 in a set of simulated crevice chemistries using metal chloride salts has been studied. Specifically, solutions were made from NiCl 2 , CrCl 3 , FeCl 2 , MoCl 3, and NbCl 5 in the same stoichiometric ratio as they appear in the alloy and ranging in concentration from 3.0 to 5.0 molal (m). It was found that Mo and Nb contributed to lower open circuit potentials (OCP) and increased critical peak current densities (i.e. activation). Solutions that substituted NiCl 2 for MoCl 3 and NbCl 5 , such that the chloride content was equivalent to that of the NiCrFeMoNb solution, presented high OCP values and passive behavior. To better understand the polarization data, solution speciation and pH were calculated using a commercially available software package. It was found that for concentrations ranging from 3.0 to 5.0 m, the pH values were on the order of −1.0. In addition, the active to passive transition appeared to correlate with an increase of Mo 3+ concentration in solution. For comparison, the polarization response of alloy 625 in HCl-based solutions was investigated. Over the range of HCl concentrations studied, the critical peak current densities were typically lower than the metal salt solutions at equivalent calculated pH. In addition, an equation for preparing HCl solutions at the needed pH to obtain an equivalent critical peak current density as observed in the NiCrFeMoNb solutions is presented. Oldfield and Sutton's model 1,2 has been widely used for explaining crevice corrosion initiation and propagation based on the solution chemistry change within crevices. According to Oldfield's and Sutton's model, the initiation stage of crevice corrosion is divided into three processes occurring inside the crevice: 1) depletion of oxygen, 2) metal hydrolysis resulting in lower pH and chloride-migration, and ultimately 3) formation of a critical crevice solution (CCS). Once crevice corrosion initiates, the propagation stage immediately follows (stage 4). The passive current density (i pass ) and the crevice geometry (depth-to-gap ratio) are the key parameters that aid the development of a CCS. The model predicts that for a constant i pass , larger crevice gaps required deeper crevices to initiate crevice corrosion. Thus, occluded regions with large depth-to-gap ratios have increased susceptibility to crevice corrosion damage. The Oldfield-Sutton-model does not, however, consider the effect of the IR-drop within the crevice (i.e. the electrode-potential variation between the cavity and the outer surface), nor does it predict the location and rate of the crevice damage that occurs within the crevice.A model based solely on IR-drop as the cause for initiating and propagating crevice corrosion was proposed by Pickering.3,4 Early versions of the Pickering model did not separate the initiation and propagation stages. Instead, the critical requi...

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Crevice Corrosion Propagation on Alloy 625 and Alloy C276 in Natural Seawater

Cited by 17 publications

References 0 publications

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

Characterization of the Corrosion Products of Crevice Corroded Alloy 22

Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

Metal Salt Solutions as a Simulant for the Chemistry in Crevices of Nickel Alloy 625

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