Crevice Mouth Research Articles

Crevice Corrosion of Nickel Alloy 625 in an Ocean Water Environment: New Insight into the Crevice Environment

Nickel alloy 625 is widely used in marine applications due to its excellent corrosion resistance when exposed to highly oxidizing and reducing environments. However, nickel alloy 625 has been found to be susceptible to localized corrosion when crevices with a large aspect ratio (depth/gap) are exposed to seawater. In this study, two different electrochemical techniques were used to evaluate the mechanisms of crevice corrosion in nickel alloy 625: potentiostatic polarization of remote crevice assemblies (RCAs) exposed to ASTM artificial ocean water and potentiodynamic polarization curves in simulated critical crevice solutions (CCSs). From the electrochemical response of the RCAs, i.e. current vs. time curves, it was found that crevice corrosion damage under potentiostatic conditions occurred in three stages: Stage (I) CCS development, stage (II) crevice corrosion under IR control, and stage (III) crevice corrosion under diffusion control. It was also found that the CCS formed near the crevice tip and moved toward the crevice mouth. Once the CCS reached a critical distance from the mouth, presumably IR*, the corrosion rate drastically increased and severe damage occurred. During the RCA experiments, light green deposits around the outside edge of the RCA were found. When the crevices were opened after the test, additional corrosion products were found. For short exposure times, dark green and brown corrosion products were found spread out over the etching damage while at longer exposure times, accumulation of dark brown corrosion products were found closer to the crevice mouth. Energy Dispersive Spectroscopy (EDS) analysis showed that the crevice corrosion products formed inside the crevice were rich in Mo, Nb, and O, suggesting the possible formation of Mo and Nb oxides. The crevice corrosion products outside of the crevice were rich in Ni, Cr, Fe, Mo and O. The behavior of 625 in the CCS was characterized using potentiodynamic polarization in concentrated metal salt solutions prepared by dissolving NiCl2∙6H2O, CrCl3∙6H2O, FeCl2∙4H2O, MoCl3, and NbCl5 salts in deionized water at concentrations ranging from 3 to 5 molal. It was found that Mo and Nb content increased the current density of the active peak. The properties of these simulated CCSs were determined using thermodynamic calculations via the OLI Stream Analyzer software. Specifically, OLI software was used to predict the precipitation products and solution pH at 25°C. The predictions were used to compare the polarization data generated with the traditional simulated CSS using HCl base solutions.

Effect of Sulfate Ions on Repassivation Behavior of Crevice Corrosion on Type 316L Stainless Steel

Crevice corrosion is known to be a serious problem of stainless steel structures in Cl- containing environments. The growth and repassivation behavior of crevice corrosion are significantly influenced by the solution composition of corrosion environments. To clarify the repassivation behavior of crevice corrosion, an in situ observation is a promising technique. This is because the quantitative relationship between current values and corrosion morphology could be analyzed. The current distribution inside the crevice can be estimated from the spreading of crevice corrosion depth. In this study, an in situ observation technique was applied to the study of the crevice corrosion of stainless steel. In addition, to clarify the effect of the solution composition outside the crevice on repassivation behavior, an electrochemical flow cell was newly designed. Type 316L stainless steel was used as specimens. The specimens were heat-treated at 1373 K for 3.6 ks and then water-quenched. An electrochemical flow cell was fabricated (Fig. 1). The crevice was made by pressing a glass sheet to the specimen surface, and the specimen was polarized at 0.25 V (vs. Ag/AgCl, 3.33 M KCl). Crevice corrosion tests were initially performed in a flowing 1 M NaCl solution (298 K). During the corrosion tests, the corrosion behavior of the specimen surface inside the crevice was observed using an optical microscope through the glass sheet, and then the time-lapse video was produced by capturing one frame per 10 seconds. In some cases, the flowing solution was changed from 1.0 M NaCl to 0.88 M Na2SO4, after the initiation of the crevice corrosion. The solution was changed when the current reached a value of 100 µA. Figure 2a shows the time variations of the current during the crevice corrosion tests. In the case of test A, the solution was not changed. In test B, the solution was changed from NaCl to Na2SO4 when the current reached the value of 100 µA. In both cases, the current first decreased to ca. 5 µA with the lapse of time and at about 400 s, it became to increase rapidly due to the initiation of crevice corrosion. In test A, the current increased up to ca. 5 mA. On the other hand, in test B where the solution was changed, the current decreased after reaching a maximum value of 3 mA at ca. 2.5 ks. The results of in situ observation of the specimen surface are shown in Fig. 2b. In test A, the corroded area propagated along the crevice mouth (Fig. 2b). At the beginning of crevice corrosion in test B, its propergation was similar to that of test A. When the current began to decrease at ca. 2.5 ks, the direction of corrosion propagation changed toward the inside of crevice (Fig. 2c). Finally, when the current decreased to ca. 1.2 µA, no lateral propagation of the corroded area was observed, suggesting that the repassivation inside the crevice was completed. Figure 1

Crevice corrosion of N80 carbon steel in CO2-saturated environment containing acetic acid

Crevice corrosion of N80 carbon steel in CO2-saturated environment containing acetic acid (HAc) was studied by electrochemical measurements and surface analysis. No obvious corrosion is observed on the half-electrode outside crevice while severe corrosion occurs on the half-electrode inside crevice, and deep corrosion groove appears at the crevice mouth. Crevice corrosion of carbon steel is triggered by the galvanic effect between the two half-electrodes inside and outside crevice. Crevice corrosion is promoted by increasing the HAc concentration because the galvanic effect between the two half-electrodes inside and outside crevice is strengthened with the increase of HAc concentration.

High-Resolution Studies of Crevice Corrosion of Nickel and Aluminum with Real Time Multiple Beam Interferometry and Microscopy

Crevice corrosion (CC) of engineering metals remains a serious concern for structural materials. Yet combining both, a real-time and high-resolution in-situ visualization of corrosion within confined geometries remains very challenging. In this contribution, we will discuss how multiple-beam interferometry (MBI) and simultaneous microscopy can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within well-defined confinement geometries. Here we will directly compare results of accelerated corrosion tests of confined Aluminum and Nickel surfaces in a modified surface forces apparatus1. With MBI, we can detect and track active sites of aluminum corrosion in NaCl solution within confined geometries in real time. We find that CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO3, while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. Interestingly, Nickel CC shows distinctly different and unexpected corrosion mechanism depending on the NaCl concentration. We find that low Chloride concentration lead to “preferential pitting corrosion” inside of confined zones, while high Chloride concentrations lead to “crevice corrosion in the crevice mouth”. We will discuss these surprising results and we will show real time high-resolution videos of CC in confined geometries that detail this behavior. Literature 1. Shrestha, B. R.; Hu, Q.; Baimpos, T.; Kristiansen, K.; Israelachvili, J. N.; Valtiner, M., Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus. Journal of the Electrochemical Society 162 2015, C327-C332

Oxidation Behavior of 304 Stainless Steel During Crevice Corrosion in High-Temperature Pure Water

Characteristics of oxide films formed on 304 (UNS S30400) stainless steel during crevice corrosion in 290°C pure water have been investigated. It was found that the oxide films were different at different sites along the crevice. Decreased dissolved oxygen within the crevice resulted in a potential gradient. Such a potential drop affected the development of oxide films. The lamellar oxide near the crevice mouth was mainly FeCr2O4. The regular oxide far from the crevice mouth was mainly Fe3O4. Possible mechanisms of crevice corrosion and growth of the oxide films at different sites in high-temperature water are also discussed.

High Resolution in Situ Studies of Localized and Crevice Corrosion with Multiple Beam Interferometry and Atomic Force Microscopy

Crevice corrosion (CC) and localized corrosion of metals remains a serious concern for structural materials. Yet both, a real-time and in-situ visualization of (1) initiation of localized corrosion, and (2) corrosion within confined geometries, remains very challenging. In this contribution, we will discuss how multiple-beam interferometry (MBI) can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within well-defined confinement geometries[1]. Also, we will discuss how electrochemical AFM can be utilized to study localized phenomena such as dealloying on patterned surfaces[2]. We will particularly aim to discuss and describe techniques and electrochemical cells, that we recently developed and will discuss how they may become useful in the field of corrosion and localized corrosion. With MBI, we can detect and track active sites of aluminum corrosion in NaCl solution within confined geometries[3]. We find that CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO3, while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. With our newly developed electrochemical AFM cell we can accurately track localized initiation sites of corrosion in model de-alloying experiments on patterned surfaces with nm resolution in x/y and atomic resolution in vertical directions[4]. The time resolution of our EC-AFM is currently limited to about 10 seconds per frame. In both parts of this contribution we will discuss experiments with model systems and we aim to specifically focus on technical hurdles and pros/cons of our techniques, including an outlook into what may be achieved in the future.

ICONE23-2021 INTERGRANULAR OXIDATION WITHIN CREVICE OF AUSTENITIC STAINLESS STEEL IN HIGH TEMPERATURE WATER

Intergranular oxidation (corrosion) occurred within crevice of austenitic low-carbon stainless steel (solution treated, almost no applied stress) after immersion in hightemperature water (288°C, 8.5MPa, dissolved oxygen conc. 32ppm, electrical conductivity: 1.2±0.2 μS・cm^<-1> (measured value at 25℃)) for 500h. The intergranular oxidation occurred at specific position within the crevice that is relatively distant from the crevice mouth with relatively low crevice gap. Both the grain boundary and grain matrix were oxidized. In the oxidized area, Fe and Ni were depleted and Cr was enriched compared to the matrix. Maximum penetration depth of the oxidation was approximately 50μm after 500h. In order to understand potential-pH condition within the crevice, surface oxide layer was microscopically and thermodynamically investigated. Thermodynamic properties of the surface oxides near the intergranular oxidized area indicated lowered pH of approximately 3.2 to 3.4. In-situ measurement of local solution electrical conductivity was carried out using small electrodes (dia. 800μm) imbedded into the crevice former plate. The solution pH was estimated using theoretically calculated pH vs. electrical conductivity relationship. In the area where the intergranular oxidation occurred, the solution electrical conductivity was nearly 100 times higher than that of bulk water and which indicated lowered pH of approximately 3.5. The above results suggested that, in the high temperature and relatively high purity water, acidification occurs within crevice of stainless steels and such aggressive corrosion condition result in the intergranular oxidation.

Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

Crevice corrosion (CC) of metals remains a serious concern for structural materials. Yet a real-time in situ visualization of corrosion, and its inhibition within a confined geometry, remains challenging. Here, we present how multiple-beam interferometry in a Surface Forces Apparatus can be utilized to directly visualize corrosion processes in real-time and with Ångstrom resolution within well-defined confinement geometries. We use atomically smooth muscovite mica surfaces to form round-shaped ∼1000 μm2 crevices on aluminum. After exposure to NaCl solutions we can detect and track active sites of aluminum corrosion within this confined geometry. CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20–300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO3, while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. Our technique may be adapted for monitoring CC, corrosion inside of crack-tips, and evaluation of inhibitor efficiencies in a variety of metals.

Effects of local radiolysis and geometric parameters on intergranular attack caused by crevice corrosion

Effects of γ-ray irradiation upon crevice corrosion (CC) of type 316L stainless steel (316L SS) as an initiation site of stress corrosion cracking in a boiling water reactor environment have been studied using a material corrosion test loop which could be irradiated with a 60Co γ-ray source during testing. The CC tests were conducted using crevice specimens with various sizes of crevice gaps. Many of the examined specimen surfaces exhibited a selective grain boundary dissolution; that is, intergranular attack (IGA) as a result of the CC when the crevice gap size was lower than a certain value. The IGA initiation time was shortened by the γ-ray irradiation. The IGA occurred mostly near the crevice mouth at a distance of less than 2 mm from the mouth edge. When γ-ray exposure had occurred, it was found that the number of IGA sites deeper in the crevice increased compared with the IGA site distribution under the no-irradiation condition. Since the electrochemical corrosion potential inside crevice specimens must be low under the conditions for which IGA could occur, it was assumed that γ-ray irradiation accelerated the corrosion rate of 316L SS by decreasing the Fe2+ surface activity inside the crevice or increasing the cathodic current of radiolytic oxidants on the crevice surface. It was concluded that γ-ray irradiation affects the IGA occurrence not only temporally but also spatially.

Single-boss crevice former for studying crevice corrosion of UNS S32003 in chloride-containing solution at high temperature

We studied crevice corrosion of UNS S32003 using a single-boss crevice former. This crevice assembly with a single boss at the center is a modification of the commonly used multiple-crevice assembly (MCA). This design effectively prevents unwanted crevice corrosion outside the crevice of interest. Our single-boss crevice assembly produces comparable repassivation potentials obtained using cyclic potentiodynamic polarization (CPP), Tsujikawa–Hisamatsu Electrochemical (THE), potentiodynamic–galvanostatic–potentiodynamic (PD–GS–PD), and potentiostatic (PS) techniques. Considering the degree of attack, we found that the THE technique is the most powerful for forming a deep, wide, and continuous crevice corrosion site, while the PS technique is the least powerful technique at potentials slightly above the repassivation potential. A galvanostatic hold in step 2 of the THE and PD–GS–PD techniques successfully grows a deep localized corrosion site, as indicated by a deep crevice corrosion attack found in samples tested with these techniques. The PS step (step 3) in the THE technique allows the grown localized corrosion site formed by a previous step (a galvanostatic hold) to propagate inward and along the crevice mouth, creating a wide and continuous crevice corrosion attack along the crevice mouth. Metastable pits play a role in crevice corrosion of UNS S32003 alloy in this study, as indicated by a large number of metastable pits in the crevice region. The ferrite phase is preferentially attacked by metastable pits.

Multilayered Surface Oxides within Crevices of Type 316L Stainless Steels in High-Temperature Pure Water

Surface oxide layers were formed within crevices of Type 316L (UNS S31603) stainless steels in pure water at 288°C and 8 MPa. Cross-sectional structures of the surface oxides were analyzed using transmission electron microscopy. In the condition of dissolved oxygen concentration of 2 ppm, the properties of the surface oxide layer changed with position and dual- or triplex-layered oxides were formed at a certain distance from the crevice mouth. The multilayered oxides were composed of Fe-based oxide in the core and a high-Cr content in the outer layer, which had not been observed on a boldly exposed surface. On the contrary, in deaerated conditions, the surface oxide layers were composed of a magnetite (Fe3O4)-based outer and a Cr-enriched inner oxide layer, regardless of the crevice position. Electrochemical condition within the crevice was identified by using a E–pH diagram. It was suggested that, at 400 μm distance from the crevice mouth, the potential lowered at the early stage of exposure, and then sh...

CREVICE CORROSION OF GRADE-2 Ti IN SIMULATED GROUNDWATER FOR GEOLOGICAL DISPOSAL OF HIGH-LEVEL RADIOACTIVE NUCLEAR WASTE

The influences of temperature and Cl~- concentration on the crevice corrosion of grade-2 Ti in the simulated geological disposal environment of high-level radioactive nuclear waste were investigated by potentiodynamic polarization curves,electrochemical impedance spectroscopy,galvanic current monitoring and potentiostatic polarization.The results showed that all the creviced specimens exhibited the passive characteristics in the initial immersion period at 25—95℃.With extending the immersion time,the crevice corrosion of Ti initiated as a result of the gradual aggressive environment (higher Cl~- concentration and more acidification) in the crevice.As increasing the temperature and Cl~- concentration,the galvanic current increased and the crevice corrosion resistance was decreased.In addition,the critical temperature of crevice corrosion decreased with increasing Cl~- concentration and the applied potential.The damage caused by anodic active dissolution in the crevice mainly located near the crevice mouth.

Predicting the chemistry, corrosion potential and corrosion rate in a crevice formed between substrate steel and a disbonded permeable coating with a mouth

A model developed in an earlier work was used in this work to investigate the effect of coating permeability on the evolution of solution chemistry, corrosion potential, and rate in a crevice formed between a steel surface and a coating disbonded from it. The crevice gap varies along distance from the mouth, and the coating is permeable to ions and/or oxygen (O2). The earlier work focused specifically on modeling the effect of variable gap (on crevice corrosion) with the coating impermeable to either ions or O2. In both works, the crevice chemistry was an aerated, diluted sodium chloride solution, which at the mouth was set to be different from that initially in the crevice. The results of this work show that a permeable coating behaves like a membrane, which, under a cathodic polarization at the crevice mouth, tends to raise the in-crevice sodium ion concentration and pH more rapidly relative to an impermeable coating. Later, as the sodium ion concentration and pH in the crevice become greater than at the mouth, the permeable coating tends to reverse the transport direction for ions. At a mouth potential of −0.900V vs. saturated Cu/CuSO4, the cathodic current is sufficient to suppress all O2 penetrating the crevice both from the mouth and through the coating. The practical implication is that in the presence of sufficient cathodic polarization, a permeable coating, when disbonded, can still be capable of protecting the substrate steel from corrosion attack.

The corrosion behavior of carbon steel in CO2‐saturated NaCl crevice solution containing acetic acid

AbstractThe corrosion behavior of X52 carbon steel electrodes in CO2‐saturated NaCl crevice solution containing HAc was investigated by electrochemical measurements. Chemical environment measurements by Cl− and pH microprobes show an enrichment of Cl− ions and an increase of pH values inside the crevice. Moreover, both increments could accelerate with the decreasing dimension of the crevice mouth due to the high diffusive resistance. When the electrode in the crevice solution is coupled with the electrode in bulk solution, the alkalization and the enrichment of Cl− ions in the crevice solution can result in a negative shift of potential of the electrode in crevice solution, while the potential of the electrode in bulk solution shifts positively during the corrosion process. Thus, a galvanic corrosion is established with the electrode in the crevice solution acting as anode while another in the bulk solution as cathode, i.e., the corrosion in the crevice solution was enhanced while the corrosion in the bulk solution was retarded. The anodic dissolution and the cathodic reduction processes dominate in the crevice solution and in the bulk solution, respectively.

Effect of the Passive Film on the Crevice Corrosion of Stainless Steels Experimental and Modeling Approaches

We investigate the crevice corrosion resistance of bright annealed (BA) or pickled (2B) AISI 430 type industrial stainless steel sheets. An artificial crevice is electrochemically coupled to a crevice free specimen through a low impedance ammeter measuring the crevice corrosion current at rest potential . After exposure the specimen show a corroded zone around the crevice bottom and a remaining passive zone at the crevice mouth. The active area and the corrosion current are much smaller for BA than for 2B but the average crevice current density does not depend on the surface condition. Modeling ionic concentrations and flows in the crevice allows determining the transition pH between active and passive zones, giving respectively 2.6 and 2.8 for BA and 2B. It fairly accounts for the better corrosion resistance of BA surface, as observed in practice. This coupled experimental and modeling approach provides a powerful tool for further crevice corrosion investigation.

Crevice corrosion behavior of X70 steel in HCO −3 solution under cathodic polarization

The crevice corrosion behavior of X70 steel was investigated with a wedge-shaped crevice assembly under −1000 mV (SCE) cathodic polarization in the solutions with various HCO−3 concentrations. The potential, current, pH and the oxygen content within the crevice were measured with or without outside coupled specimen. The results indicated that the polarization potential of X70 steel in the crevice dropped with the increase of time under the cathodic polarization. There was a remarkable influence of HCO−3 concentration on the potential of X70 steel in the crevice. When HCO−3 concentration was up to 0.125%, the surface of the metal was covered with the corrosion products that resulted in the polarization extent of X70 steel decreased. The pH value in the crevice rose and it dropped gradually from the crevice mouth to the bottom under the cathodic polarization. With the increasing of HCO−3 concentration, the hydrolyzation reaction of metal in the crevice bottom aggravated. Most of the dissolved oxygen in the crevice was consumed by the cathodic current. The maximum cathodic current on the metal surface was at the crevice mouth and it was much more than that at the crevice bottom.

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.

Crevice Corrosion of Titanium in High Temperature-Concentrated Chloride Environments

Crevice corrosion of titanium is activated in concentrated chloride media at 100 °C. This was possible only with the tightest gap (0.005 cm) between Ti-Ti surfaces. No crevice corrosion was observed with greater gap dimensions. The design of the crevice led to the occurrence of two concentric circular rings of corroded areas, with many pits on them. After potentiostating in the passive region for 5 h in 25% NaCl (pH = 4.7)—where hydrogen evolution is thermodynamically prohibited—hydrogen gas bubbles were observed to egress out of the crevice mouth during ongoing crevice corrosion. This indicates that hydrogen evolution occurs within the crevice. The results are compatible with the occurrence of gradually increasing ohmic potential shift and localized acidification in the crevice electrolyte as judged by the measured gradual increase of the crevice corrosion current. The high acidity of the bulk electrolyte does not seem to be sufficient or even a necessary condition for crevice corrosion to occur.

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

Close packed coupled multi-electrodes arrays (MEA) simulating a planar electrode were used to measure 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 derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCl at 50{degree sign}C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., 0 VSCE) and to spread inwards and outside the crevice with time. In the case of alloy 625, crevice corrosion initiates further inside the crevice (i.e., xcrit is large) and requires higher applied potential (e.g., 0.05 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases.

Coupled Multielectrode Investigation of Crevice Corrosion of AISI 316 Stainless Steel

Close packed coupled multielectrode arrays simulating a planar electrode were used to measure the current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel. Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCI at 50°C was found to initiate close to the crevice mouth and to spread inward and outward with time. The local crevice current density increased dramatically over a short period to reach a limiting value.