Crevice Corrosion Propagation Research Articles

Comparison of test methods for crevice corrosion propagation and repassivation potential of stainless steel AISI 316

The crevice corrosion propagation modes and repassivation potential of stainless steel AISI 316 in chloride solution were compared using cyclic potentiodynamic polarization (CPP), potentiodynamic-galvanostatic-potentiodynamic (PD-GS-PD) and Tsujikawa– Hisamatsu electrochemical (THE) methods. The PD-GS-PD method was found to be the most conservative electrochemical technique which delivered the lowest repassivation potential value in a relatively short time. The crevice corrosion propagation modes in these three electrochemical methods were also compared with crevice corrosion propagation mode in galvanically coupled small area stainless steel AISI 316 anode with large area titanium cathode. The crevice corrosion propagation mode achieved in galvanically coupled AISI 316 anode at open circuit potential simulated the crevice corrosion propagation mode in real systems. The crevice corrosion propagation modes achieved in PD-GS-PD and THE methods mimicked the crevice corrosion propagation in real systems.

Time-Lapse Observation of Crevice Corrosion in Grade 2205 Duplex Stainless Steel.

The objective of this study was to investigate and visualize the initiation and propagation of crevice corrosion in grade 2205 duplex stainless steel by means of time-lapse imaging. Transparent Poly-Methyl-Meth-Acrylate washer and disk were coupled with duplex stainless steel to create an artificial crevice, with electrochemical monitoring applied to obtain information about the nucleation and propagation characteristics. All nucleation sites and corroding areas inside crevices were recorded in situ using a digital microscope set-up. Localized corrosion initiated close to the edge of the washer, where the crevice gap was very tight, with active corrosion sites then propagating underneath the disk into areas with wider gaps, towards the crevice mouth. The growth was associated with a rise in anodic current interlaced with sudden current drops, with parallel hydrogen gas evolution also observed within the crevice. The current drops were associated with a sudden change in growth direction, and once corrosion reached the crevice mouth, the propagation continued circumferentially and in depth. This allowed different corrosion regions to develop, showing selective dissolution of austenite, a region with dissolution of both phases, followed by a region where only ferrite dissolved. The effect of applied electrochemical potential, combined with time-lapse imaging, provides a powerful tool for in situ corrosion studies.

Evaluation of Crevice Corrosion Propagation by Continuous Current Step Method for Various Stainless Steels in Artificial Seawater

Evaluation of Crevice Corrosion Propagation by Continuous Current Step Method for Various Stainless Steels in Artificial Seawater

A One Dimensional Crevice Experiment for Determining the Critical Factors Contributing to Crevice Corrosion Repassivation

From its inception more than 40+ years ago, the one-dimensional pencil electrode experiment (1-D pit) has allowed investigators to study factors on pitting corrosion such as ohmic drop, concentration of species as a function of pit depth and the stability of salt films.[1,2] In recent work, Srinivasan and Kelly have developed a 1-D transport model of repassivation for pencil electrodes made of SS 316L.[3] Unfortunately, for the phenomenon of crevice corrosion, the understanding of these critical factors (that no doubt control crevice propagation and repassivation) are far less understood. The primary reason for this has been the inability to simultaneously measure the location of the active crevice front (e.g. its depth) and the active area (which fixes the current density). These two parameters are easily measured in the 1-D pit experiment.Previously, we introduced a method for measuring both the depth of the active front in crevice corrosion and the active area.[4] The method, similar to that which Pickering introduced years ago,[5] records video of a propagating crevice in the optical microscope. The crevice (RCA) is formed by an alloy 625 washer covered by an acrylic washer that acts as a crevice former. The potential of the assembly is controlled potentiostatically using a traditional three electrode set up and the current is recorded as a function of time. A stereo microscope equipped with a digital camera is used to record images of the initiation and propagation of crevice corrosion. Image processing software is used to quantify the area of the active front. We calculate the actively corroding area, crevice current density and wall potential (Eapp-IR) all as a function of time.In this presentation, we will present the results from our crevice repassivation study on alloy 625. We use the THE method (ASTM G192) to analyze the transition to repassivation in the 625 RCA. Once initiated, the crevice was allowed to propagate for various times, equivalent to increasing charge passed. After a fixed time, the applied potential was decreased in a stepwise fashion. At a critical potential, forward movement of the active corrosion front towards the mouth (e.g. new damage area) stopped, though crevice propagation continued. Transport calculations reveal that this potential may be associated with salt film dissolution, consistent with the transition potential (ET / Esat) reported for one dimensional pitting experiments. The results are discussed in terms of traditional crevice corrosion models (such as Oldfield-Sutton[6] and IR*[5]) and more recent models for pit growth stability (Li Scully Frankel[7]). A mechanism for crevice growth and the transition to repassivation that is similar to that believed to controlled pit propagation and repassivation is proposed.AcknowledgmentsWork on this project was made possible by a grant from the US DoD TCC #1000000149, program directors Gregory A. Shoales, USAFA, and Daniel Dunmire, Corrosion Policy Oversight.References JW Tester, HS Isaacs, JES, 122, 1438, 1975.RC Newman, HS Isaacs, JES, 130, 1621, 1983.J Srinivasan, RG Kelly, JES, 163, C768, 2016.RS Lillard, S Mehrazi, DM Miller, JES, 16 7, 2020.5. K Cho, HW Pickering, JES, 138, L56, 1991.6. JW Oldfield, WH Sutton, Br. Corr. J., 13, 1978.7. T Li, JR Scully, GS Frankel, JES, 166, 2019.

Corrosion behaviour of 13Cr stainless steel under stress and crevice in 3.5 wt.% NaCl solution

The corrosion behaviour of 13Cr stainless steel under stress and crevice in 3.5 wt.% NaCl solution was studied by electrochemical measurements. It is demonstrated that the applied stress degrades the passive film, resulting in negative shift of pitting potential and enhanced susceptibility of pitting corrosion. The crevice corrosion of 13Cr stainless steel involves three stages: induction period, rapid development period and stable development period. In the coexistence of crevice and stress, the enhanced anodic reaction by applied stress accelerates the accumulation of H+ and Cl− ions inside crevice, which shortens the induction period and promotes the propagation of crevice corrosion.

(Invited) A One Dimensional Crevice Experiment for Determining the Critical Factors Contributing to Crevice Corrosion Stability and Repassivation

From its inception more than 40+ years ago, the one-dimensional pencil electrode experiment (1-D pit) has allowed investigators to investigate factors on pitting corrosion such as ohmic drop, concentration of species as a function of pit depth and the stability of salt films.[1,2] In fact, in recent work, Srinivasan and Kelly have developed a 1-D transport model of repassivation for pencil electrodes made of SS 316L.[3] Unfortunately, for the phenomena of crevice corrosion, the understanding of these critical factors (that no doubt control crevice propagation and repassivation) are far less understood. The primary reason for this has been the inability to simultaneously measure the location of the active crevice front (e.g. its depth) and the area of the front (which fixes the current density). These two parameters are easily measured in the 1-D pit experiment. In this presentation, we will introduce a method for measuring both the depth of the active front in crevice corrosion and the active area. The method is similar to that which Pickering introduced years ago,[4] we record video of a propagating crevice in the optical microscope. In this technique the crevice is formed by a set of washers, a piece of acrylic that acts as a crevice former and the metal specimen, nickel alloy 625. The potential of the assembly is controlled potentiostatically using a traditional three electrode set up and the current recorded as afunciton of time. A stereo microscope equipped with a digital camera is used to record images of the initiation and propagation of crevice corrosion. Image processing software is used to quantify the area of the active front. A typical result is presented in Figure 1 which shows the curent density of the active crevice front as a function of crevice depth. As seen in this figure, the crevice propagates from the deepest regions of the crevice towards the crevice mouth. this initial propagation direction is a result of an increase in the concentration of metal salts ahead of the active front and a corresponding decrease in pH. It can also be seen in this figure that at distances greater than 1 cm from the mouth, the crevice is able to propagate at current densities less than 1 mA/cm2. Once the active front reaches a distance of 1cm, an exponential increase in curent density is reorded. This increase is attributed to the IR* mechanism.[4] With the knowledge of the current density and distance from the crevice mouth we are able to use a simplification of the Nernst-Plank equation to calculate the concenrtation of species in solution. As might be anticipated from Figure 1, the concetration of metal salts increases with increasing current density. As such, concentration near the mouth is greater than at the tip, the saturation limit being reached at a distance of approximately 0.4cm from the mouth. Acknowledgments Work on this project was made possible by a grant from the US DoD TCC #1000000149, program directors Gregory A. Shoales, USAFA, and Daniel Dunmire, Corrosion Policy Oversight. References JW Tester, HS Isaacs, JES, 122, 1438, 1975.RC Newman, HS Isaacs, JES, 130, 1621, 1983.J Srinivasan, RG Kelly, JES, 163, C768, 2016.K Cho, HW Pickering, JES, 138, L56, 1991. Figure 1 Current density as a function of distance inside an alloy 625 crevice. Figure 1

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

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 NiCl2, CrCl3, FeCl2, MoCl3, and NbCl5 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 NiCl2 for MoCl3 and NbCl5, 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 Mo3+ 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.

The self-sustaining propagation of crevice corrosion on the hybrid BC1 Ni–Cr–Mo alloy in hot saline solutions

The initiation and propagation of crevice corrosion on the BC1 nickel-chromium-molybdenum alloy has been studied galvanostatically in concentrated chloride solution at 120°C, and the distribution of corrosion damage determined using surface analytical techniques. The distribution of damage was dependent on the applied current and showed an increased tendency to spread across the surface as the applied current was increased. Attempts to induce repassivation by galvanodynamically reducing the current to zero were unsuccessful. Galvanic coupling to a large BC1 counter electrode showed propagation could be maintained by oxygen reduction on the coupled electrode at a slow rate for >1200h.

自然海水中におけるSUS304の長期動的すきま腐食観察

自然海水中におけるSUS304の長期動的すきま腐食観察

すきま腐食進展過程に対するすきま内電位／電流密度分布の数値解析的考察

すきま腐食進展過程に対するすきま内電位／電流密度分布の数値解析的考察

Stifling of Crevice Corrosion and Repassivation: Cathode Area Versus Controlled Potential Decreases Assessed with a Coupled Multi-Electrode Array

The effects of limited remote cathode area on crevice corrosion propagation, repassivation, and anode site reorganization were investigated on AISI 316 stainless steel (UNS S31600) in 0.6 M NaCl at 50°C. Both multiple crevice assemblies and rescaled coupled multi-electrode arrays were utilized. Potentiostatically activated crevices were subjected to conditions that limited propagation by either: (i) stepping the potential downward below the repassivation potential, (ii) performing a downward scan of the potential from high potential, or (iii) decreasing the area of a galvanically coupled platinum cathode situated outside the crevice. In the first two cases, repassivation occurred when the potential reached the lower statistical limit of the repassivation potential measured on creviced specimens in a downward scan. During the galvanically coupled test, repassivation occurred when the galvanic cathodic current supplied became lower than the current required to maintain a couple potential equal to the repass...

The Effect of Change in Solution Chemistry of Bulk Solution on Crevice Corroson Propagation of Stainless Steel

Once crevice corrosion initiates, the hydrolysis of dissolved metal ions occurs to induce the acidification of solution inside the crevice and the migration of Cl- ions into the crevice from solution bulk. This Cl- ions migration promotes subsequent active dissolution and a further decrease of pH in the crevice. Therefore, the reduction of the concentration of Cl- ions is expected to be effective for suppressing crevice corrosion propagation. In this study, the influence of changes in solution chemistry on the propagation of crevice corrosion of stainless steel was investigated. After crevice corrosion was induced, in a chloride-containing solution the test solution was exchanged to chloride-free or chloride-containing solutions and corrosion propagation and repassivation behavior were monitored under the potentiostatic control. An austenitic stainless steel (0.017%C, 0.58%Si, 0.84%Mn, 0.028%P, 0.001%S, 12.15%Ni, 17.43%Cr, 2.08%Mo) was used to fabricate a crevice specimen schematically shown in Fig. 1. The steel was cut into 20 mm × 20 mm × ca. 5 mm, and the surface was polished down to 1 μm diamond paste. A through-hole with a diameter of 6 mm was formed at the center of the surface. Ultrasonic cleaning was carried out in ethanol, and then the specimen was passivated in 30 mass% HNO3 at 323 K for 1800 seconds. After that, the electrode surface area of the passivated specimen was polished down to 1μm diamond paste again. A lead wire was soldered to the electrode. An artificial crevice was formed between the electrode surface and a 20 mm × 20 mm × 2 mm polycarbonate sheet fixed by a bolt and a nut. The specimen was covered by insulating rubber except for the electrode surface. During the fabrication of the crevice, the electrode surface was kept being in contact with a NaCl solution (pH 5.0) dearated by N2 gas. The concentration of Cl- was adjusted to 20000 ppm. Potentiostatic polarization measurement at 0.3V (vs. Ag/AgCl) was conducted for 1000 seconds in a 20000 ppm Cl- containing NaCl (pH 5.0) at 298K to initiate crevice corrosion of the specimen. After that, the polarization was stopped and the test solution was exchanged to a chloride-free solution (test A) or a chloride containing-solution (test B), respectively. A Na2SO4 solution was selected as a chloride-free solution. The concentration of SO4 2- was adjusted to 20000 ppm. A chloride containing-solution was the same as the test solution used for the initiation of crevice corrosion. Subsequently, the potentiosstatic polarization at 0.3V was restarted and the change in current was monitored. After the test, the specimen surface was rinsed with deionized water and observed using an optical microscope. Figure 2a shows the time variation of current measured in the crevice corrosion tests. Figure 2b shows an enlarged view of the first 1000 seconds, that is, the current transient of the specimens in the NaCl solution. During this initial period, the currents gradually increased up to c.a. 1000 μA. It is therefore presumed that crevice corrosion occurred and propagated under the potentiostatic polarization at 0.3 V in the NaCl solution. After the solution was changed to the Na2SO4 solution, the current value increased to c.a. 700 μA until 4000 seconds passed and then decreased gradually to c.a. 30 μA. On the other hand, after the solution was exchanged to the NaCl solution, the current increased rapidly and remained at a high level until the end of the crevice corrosion test. These results suggest that the removal of Cl- ions from the bulk solution suppressed the propagation of crevice corrosion of stainless steel. Caption list: Figure 1 Schematic illustration of the specimen for crevice corrosion tests. Figure 2 (a) The time variation of current measured during the crevice corrosion tests at 0.3 V (b) An enlarged view of the first 1000 seconds of the crevice corrosion test. Figure 1

Crevice corrosion initiation and propagation on Alloy-22 under galvanically-coupled and galvanostatic conditions

The initiation and propagation of crevice corrosion on the Ni–Cr–Mo Alloy-22 has been studied in concentrated chloride solutions under galvanically-coupled and galvanostatic conditions. Under galvanically-coupled natural corrosion conditions crevice corrosion initiated but propagation was limited by repassivation. This was attributed to the slow kinetics of oxygen reduction on passive surfaces external to the crevice. Under galvanostatic conditions a potential more positive than 200 mV Ag/AgCl and an applied current greater than 5 μA were required to stabilize propagation. A minimum critical current density to establish active sites within the crevice was estimated to be around 250 μA cm −2.

Crevice corrosion of duplex stainless steels in natural and chlorinated seawater

Since contradictory data can be found in the literature, it is often difficult to assess the susceptibility of crevice corrosion of stainless steels in service conditions for a given marine application. The initiation and propagation of crevice corrosion in natural seawater were evaluated for five different duplex stainless steel grades together with some austenitic grades. A CREVCORR-type assembly was used to simulate crevice configurations involving the use of plastic crevice formers. The standard pressure applied on the crevice assembly was 3 N/mm2 . Pressure of about 20 N/mm2 was also applied on some selected specimens in order to assess the effect of crevice geometry on crevice corrosion. The effect of environmental parameters (i.e. temperature, flowing conditions, residual chlorine, and dissolved oxygen content) and of surface roughness on the crevice corrosion initiation and propagation were investigated, allowing the assessment of limits of applications for some tested stainless steel grades. The less alloyed duplex stainless steels were evaluated in stagnant seawater at 5 °C and 20 °C. The duplex stainless steel UNS S32205, with PREN = 37, was also evaluated under the same conditions of exposure. The high alloyed stainless steels with PREN above 40 were evaluated in the expected most severe conditions of exposure, namely in 0.5 ppm-chlorinated seawater at 20 °C, in seawater at 30 °C (not chlorinated and with 0.5 ppm of residual chlorine) and in seawater at 50 °C (not chlorinated and with 0.5 ppm of residual chlorine). As expected the less alloyed duplex stainless steels showed limited crevice corrosion resistance in the tested media while UNS S32205 showed better resistance in the less severe tested condition of exposure. In demanding media it was shown that the limits of application of highly alloyed stainless steels are highly dependent on the crevice geometry (i.e. specimen roughness and applied pressure at gasket location).

Influence of the alloying elements on crevice corrosion of stainless steels: a modeling approach

Crevice corrosion chemistry is modeled in galvanostatic mode using finite element method calculations. The results lead to the formulation of critical conditions for crevice propagation in terms of applied current and depassivation pHd . For a given stainless steel grade, the model predicts a linear relation IC (pHd ) between a “critical propagation current” IC and the depassivation pHd . Detailed computing is performed to compare the behavior of duplex 2304, ferritic AISI 430 and austenitic AISI 304 stainless steels. The model is shown to capture correctly the major asymptotic behaviors and to fairly predict the better corrosion resistance of the duplex grade, which is attributed to its slower dissolution kinetics in acidic environment. When comparing duplex stainless steels to ferritic or austenitic ones, it is now evident that the dissolution law and the depassivation pHd are the key factors that control the resistance to crevice corrosion propagation.

Effect of Polymer and Ceramic Crevice Formers on the Crevice Corrosion of Ni-Cr-Mo Alloy 22

Abstract One important factor affecting crevice corrosion of passive metals is the crevice geometry, e.g., the gap of the crevice. The crevice geometry can be affected by the properties of the materials used as the crevice formers, i.e., a polymeric crevice former can conform to the surface roughness of a metal specimen, which helps the creation of a tighter crevice gap. The objective of this work was to investigate the effects of crevice former materials on the evolution of crevice corrosion damage of Alloy 22 (UNS N06022). The factors that may limit the initiation and slow or stop the propagation of crevice corrosion are addressed. Crevice formers made from ceramic, polymers, and polytetrafluoroethylene (PTFE) tape-covered ceramic are compared in controlled crevice corrosion tests, which are performed under highly aggressive, accelerated conditions. Results show that crevice corrosion of Alloy 22 is affected by the crevice former materials and by the surface finishes of the crevice former and specimen. ...

Determination of Crevice Corrosion Susceptibility of Alloy 22 Using Different Electrochemical Techniques

AbstractAlloy 22 belongs to the Ni-Cr-Mo family and it is highly resistant to general and localized corrosion. It may suffer crevice corrosion in aggressive environmental conditions. This alloy has been considered as a corrosion-resistant barrier for high-level nuclear waste containers. It is assumed that localized corrosion may occurs when the corrosion potential (ECORR) is equal or higher than the crevice corrosion repassivation potential (ER,CREV). The latter is measured by means of different electrochemical techniques using artificially creviced specimens. These techniques include cyclic potentiodynamic polarization (CPP) curves, Tsujikawa-Hisamatsu electrochemical (THE) method or other non-standard methods, such as the PD-GS-PD technique.The aim of the present work was to determine reliable critical or protection potentials for crevice corrosion of Alloy 22 in pure chloride solutions at 90°C. Conservative methodologies (which include extended potentiostatic steps) were applied for determining protection potentials below which crevice corrosion cannot initiate and propagate. Results from PD-GS-PD technique were compared with those from these methodologies in order to assess their reliability. Results from the CPP and the THE methods were also considered for comparison. The repassivation potential resulting from the PD-GS-PD technique was conservative and reproducible, and it did not depend on the amount of previous crevice corrosion propagation.

Crevice Corrosion Damage Evolution in High Temperature Brines

The overall objective of this work is to provide deeper insight into chemical/electrochemical processes that control the initiation, propagation, stifling, and arrest of crevice corrosion. Crevice corrosion is an important degradation mode to be evaluated for corrosion performance of passive metals exposed to high temperature brines over long exposure periods. Both modeling and experimental work has been performed on the initiation and propagation of crevice corrosion. The requirements for the initiation and propagation of localized corrosion are analyzed and conditions for continued propagation are identified. Each of the components of the electrochemical corrosion cell can limit corrosion rates: electrolyte layer- resistance between the anode and cathode limits the current; cathode-current capacity cannot meet the anode demand; anode-current requirement for critical crevice chemistry stability is not met and anode/cathode-incompatibility of coupled processes for a given scenario.

Investigation of Crevice Corrosion of AISI 316 Stainless Steel Compared to Ni–Cr–Mo Alloys Using Coupled Multielectrode Arrays

Close-packed coupled multielectrode arrays simulating a planar electrode were used to monitor the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni–Cr–Mo alloy 625 (UNS N06625). Scaling laws vs and vs derived from polarization data in simulated crevice solutions guided the implementation of rescaled crevices with greater spatial resolution. and are the distances from the mouth to the location where the potential reaches two different critical values, and is the crevice gap. Scaling laws were also used along with anodic polarization data in simulated crevice solution to predict crevice corrosion behavior of alloy 22 (UNS N06022). Crevice corrosion of AISI 316 stainless steel in NaCl at readily initiated close to the crevice mouth (i.e., ) at modest applied potentials (e.g., ) and spread both inward and outside the crevice with time. Crevice corrosion initiated farther inside the crevice (i.e., is large) and required higher applied potentials (e.g., ) in the case of alloy 625. The local crevice current density increased dramatically over a short period of time to reach a limiting value in the case of AISI 316; while metastable dissolution behavior over a large area was observed for alloy 625. The ramification of the larger critical depth for Ni–Cr–Mo alloys toward crevice corrosion susceptibility in the case of crevice formers of finite length is discussed. Crevice corrosion shifts to the mouth of the crevice for the less corrosion-resistant materials in crevice solutions saturated in metal salts but remains confined at a distance for alloy 625 under the conditions tested.

Localized corrosion of alloy 22 in the potential Yucca Mountain repository environment

The U.S. Department of Energy (DOE) has indicated that it may use Alloy 22 as the waste package outer container material for the potential high-level waste repository at Yucca Mountain, Nevada. Additionally, a drip shield, made of titanium grade 7 and titanium grade 29, may extend the length of the emplacement drifts to enclose the top and sides of the emplaced waste package. Localized corrosion in the form of crevice corrosion could be one degradation process that may adversely affect the waste package performance. This paper will summarize the work conducted to evaluate the effects of environmental conditions relevant to the potential Yucca Mountain repository, metallurgical states (e.g., mill-annealed and welded plus solution annealed), and similar and dissimilar metal crevices on the crevice corrosion susceptibility of Alloy 22. This work also evaluates crevice corrosion propagation behavior resulting from contact with Alloy 22 or titanium grade 7.