Effect of Alloying Elements on Crevice Corrosion Inhibition of Nickel-Chromium-Molybdenum-Tungsten Alloys Under Aggressive Conditions: An Electrochemical Study

Mishra, Ajit; Shoesmith, D.W.

doi:10.5006/1170

Cited by 53 publications

(52 citation statements)

References 26 publications

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“…The results presented herein suggest that W in solid solution plays a decisive role in increasing localized corrosion resistance when added to SDSS at about 2.2 wt%. Moreover, the higher CCRT measured by CPP on creviced samples also suggested that W additions led to a faster repassivation kinetics than that of low-W or W-free SDSS, results that are in line with the effect of W additions to Ni-based alloys [83][84][85]. Adding W to the PRE formula as detailed by ISO 21457 5 translates to a PREN,W of 43.87(Table 3), similar to that of super austenitic stainless steel grades containing 6 wt% Mo (e.g., UNS S31254).75 The results of this investigation clearly indicated that UNS S39274 has a localized corrosion resistance equivalent to that of stainless steels containing higher amounts of Cr and Mo.…”

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confidence: 59%

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Effect of Tungsten on the Pitting and Crevice Corrosion Resistance of Type 25Cr Super Duplex Stainless Steels

et al. 2016

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The oil and gas industry regularly uses Type 25Cr super duplex stainless steels (SDSS) for components exposed to seawater and hydrocarbon environments in topside facilities, downhole, and subsea equipment. Much debate still exists concerning the effect of tungsten on pitting and crevice corrosion resistance, particularly in standardization committees.Whereas some researchers claim that tungsten has a strong synergistic effect with molybdenum when added above a certain threshold value, others argue that tungsten additions at the expense of molybdenum could lower corrosion resistance. The objective of this investigation was to examine the effect of tungsten on localized corrosion of two super duplex stainless steels: a low-W (modified UNS S32750) and a high-W (UNS S39274) grade. Both crevice-free and creviced samples were studied. Tests were conducted in 3.5 wt% NaCl or natural seawater with temperatures ranging from 20°C to 95°C. Various independent methodologies including cyclic potentiodynamic polarization, electrochemical critical pitting temperature testing per ASTM G150, and long-term open-circuit potential exposure in natural seawater were used. Results showed that, in the solution annealed condition, tungsten additions to super duplex stainless steels had a marked positive effect on pitting and crevice corrosion resistance, increasing critical crevice temperatures by as much as 30°C. These findings suggested that tungsten-containing SDSS had a corrosion resistance on par with super austenitic stainless steel grades containing 6 wt% molybdenum. A new parametric definition of the pitting resistant equivalent is proposed to reflect the alloy's localized corrosion resistance and to support standardization efforts in the materials oil and gas community.

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supporting

confidence: 59%

“…It is important to emphasize that the parametric PRE definition proposed herein exclusively applies to SDSS. In Ni-based alloys, where the beneficial effects of W have been broadly recognized,[83][84][85] there shall be no limitation on the W content allowed in the PREN,W…”

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confidence: 99%

Effect of Tungsten on the Pitting and Crevice Corrosion Resistance of Type 25Cr Super Duplex Stainless Steels

et al. 2016

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“…The chemical composition for these alloys is shown in Table VIII As shown in Figure 16, the calculated pH values of 625, C-276, C-22, and G3 decrease as the molality of the solution increases. Using the pH of the 4.0 m solution as a reference and the general trend that crevice corrosion resistance increases in the order G3 < 625 < C22 < C276, 7,24 there does not appear to be a correlation between crevice corrosion susceptibility and critical crevice solution pH. On the contrary, from the trend in pH in Figure 16, one might predict that G3 would be the most resistant to crevice corrosion.…”

Section: Discussionmentioning

confidence: 98%

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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“…6 Other studied nickel-based CRAs include the recently developed alloys C-22HS (UNS N07022), HYBRID-BC1 (UNS N10362), 59 (UNS N06059), C-2000 (UNS N06200), etc. [16][17][18][19] Selection of a nickel-based alloy as the material for the corrosion-resistant layer of waste containers for saturated and unsaturated repositories has distinct advantages relative to other metals/alloys: 20,21 • The expected containment is very long, synonymous with low corrosion rates.…”

mentioning

confidence: 99%

“…2, as a function of the weight percentages of Cr, Mo and W. [16][17][18] The crevice corrosion resistance of Ni-Cr-Mo and Ni-Cr-Fe alloys generally increases with PRE, though there are some examples of changes in the alloy ranking depending on environmental conditions. 32 Even though there is some criticism on the use of PRE, it is widely used as a rough indication of the localised corrosion resistance of nickel-based alloys and stainless steels.…”

mentioning

confidence: 99%

Crevice corrosion of nickel-based alloys considered as engineering barriers of geological repositories

Carranza

Rodríguez

2017

npj Mater Degrad

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Nickel-based alloys are considered among other candidate materials as engineering barriers of geological repositories due to their excellent corrosion resistance. These alloys possess unique advantages: they may be used in saturated and unsaturated repositories, hosted by practically any rock type, while also compatible with any (or no) backfill, and have minimal impact in other barriers. Alloy-22 (UNS N06022) has been the most studied of this class of alloys for its potential application in the proposed repositories (namely Yucca Mountain, USA). Crevice corrosion is however an important and often unintended degradation process that may limit the waste container lifetime if a nickel-based alloy is selected. Alloy susceptibility to crevice corrosion is influenced by environmental and metallurgical variables. This review gives an account of the current knowledge regarding crevice corrosion of nickel-based alloys as candidate materials for the corrosion-resistant layer of high-level nuclear waste containers. Although there is a significant amount of research supporting the use of nickel-based alloys for this application, the effect of the different variables on crevice corrosion resistance is described. Special focus is given to the current criterion for crevice corrosion occurrence in repository environments, recent works and criticisms. The presently established criterion appears robust for ruling out crevice corrosion in saturated repositories; however, the development of a less conservative criterion for crevice corrosion occurrence is necessary to use these alloys in unsaturated repositories.

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Effect of Alloying Elements on Crevice Corrosion Inhibition of Nickel-Chromium-Molybdenum-Tungsten Alloys Under Aggressive Conditions: An Electrochemical Study

Cited by 53 publications

References 26 publications

Effect of Tungsten on the Pitting and Crevice Corrosion Resistance of Type 25Cr Super Duplex Stainless Steels

Effect of Tungsten on the Pitting and Crevice Corrosion Resistance of Type 25Cr Super Duplex Stainless Steels

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

Crevice corrosion of nickel-based alloys considered as engineering barriers of geological repositories

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