Crevice Mouth Research Articles

Crevice Corrosion Behavior of 201 Stainless Steel in NaCl Solutions with Different pH Values by In Situ Monitoring.

Crevice corrosion (CC) behavior of 201 stainless steel (SS) in 1 M NaCl + x M HCl/y M NaOH solutions with various pH was investigated using SECM and optical microscopic observations. Results show that the CC was initiated by the decrease in pH value within the crevice. The pH value near the crevice mouth falls rapidly to 1.38 in the first 2 h in the strongly acidic solution, while the pH value was observed to rise firstly and then decrease in the neutral and alkaline solutions. It indicates there is no incubation phase in the CC evolution of 201-SS in a pH = 2.00 solution, while an incubation phase was observed in pH = 7.00 and 11.00 solutions. Additionally, there appeared to be a radial pH variation within the gap over time. The pH value is the lowest at the gap mouth, which is in line with the in situ optical observation result that the severely corroded region is at the mouth of the gap. The decrease in pH value inside results in the negative shift of open circuit potential (OCP) and the initiation of CC of 201-SS. The increased anodic dissolution rate in the acidic solution accelerates the breakdown of passive film inside, reducing the initiation time and stimulating the spread of CC.

Influence of protein migration on the fretting-corrosion behavior of 316 L stainless steel with artificial crevices

Fretting-crevice-corrosion at the modular interface of artificial joints can cause failure of the joint replacement. In this study, long-term fretting crevice corrosion tests of 316 L stainless steel were carried out at the center of an artificial crevice in a saline solution with and without proteins. The results showed that fretting initiated significant crevice corrosion without proteins and corrosion of large areas was observed in the non-contact area inside the crevice. In the presence of proteins, proteins can migrate into the crevice and block the crevice mouth. The enriched proteins had a lubricating effect and inhibited the occurrence of crevice corrosion.

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.

The stress corrosion cracking behavior of N80 carbon steel under a crevice in an acidic solution containing different concentrations of NaCl

Electrochemical and mechanical tests, surface analysis and hydrogen detection were used to investigate SCC of N80 carbon steel in acidic solution with varying NaCl concentrations. The SCC of steel with crevice was mixed-controlled by both anodic dissolution and hydrogen involvement. After crevice corrosion, a deep corrosion groove was formed, which dominated crack nucleation. The enhanced hydrogen uptake near crevice mouth was responsible to crack propagation. Cl– promoted crevice corrosion as indicated by increased depth of groove and hydrogen uptake content, which enhanced the SCC susceptibility. The role of Cl–, crevice and their synergistic effect in SCC was quantitatively estimated.

Role of protein in crevice corrosion of CoCrMo alloy: An investigation using wire beam electrodes

In this study, the effects of protein and crevice width on crevice corrosion of CoCrMo alloy were studied using wire beam electrodes. The results show that proteins inside and outside the crevice migrated to the crevice mouth, causing crevice mouth blockage and decreasing the Cl− concentration inside the crevice, which further affected the distribution and rate of corrosion. The accumulation of H+ inside the crevice promoted the occurrence of pitting corrosion, which led to crevice corrosion of CoCrMo alloy. The corrosion rate of the samples with 0.07 mm crevice width was 5 times greater than the samples without crevice.

Crevice Corrosion Behavior of Alloy 690 in High-Temperature Aerated Chloride Solution.

Crevice corrosion behavior of Alloy 690 in high-temperature aerated chloride solution was studied using a self-designed crevice device. The SEM, EDS, XRD, and XPS analyses results indicated that the oxide films outside the crevice consisted of Ni-Cr oxides containing a small amount of hydroxides, and the oxide films on crevice mouth consisted of a (Ni,Fe)(Fe,Cr)2O4 spinel oxides outer layer and a Cr(OH)3 inner layer, and the oxide films inside the crevice consisted of a α-CrOOH outer layer and a Cr(OH)3 inner layer. When crevice corrosion occurred, the hydrolysis of Cr3+ led to the formation of Cr(OH)3 inside the crevice, and caused the pH value of crevice solution to decrease, and Cl− migrated from outside the crevice into inside the crevice due to electrical neutrality principle and accumulation. When the water chemistry inside the crevice reached the critical value of active dissolution of metal, the active dissolution of metal inside the crevice occurred. In addition, (Ni,Fe)(Fe,Cr)2O4 spinel oxides on the crevice mouth were formed by the deposition of metal ions migrated from inside the crevice. The mechanism of crevice corrosion and the formation mechanism of oxide films at different regions were also discussed.

Long-term interactive corrosion between International Simple Glass and stainless steel

The interactive corrosion between stainless steel 316 (SS) and International Simple Glass (ISG) has been studied for 12 months. The samples were placed in intimate contact to create crevice corrosion conditions on SS in a 0.6 M NaCl solution with and without 142 ppm dissolved silica species enriched in 29Si. Corrosion on SS was observed with large pits located close to the crevice mouth at the end of 1 year in 0.6 M NaCl solution. The SS corrosion was also associated with the dissolution of nearby glass in a highly localized manner. When the leaching solution was saturated with silica species, the corrosion rate of SS was suppressed. However, the presence of SS enhances ISG dissolution in both conditions. The implications of the observed phenomena on the long-term storage of nuclear waste are discussed.

Effects of Potential on the Electrical Conductivity of a Solution within a Crevice of Stainless Steel in High-Temperature Water

This study investigates the effects of potential [electrochemical corrosion potential (ECP)] on the water chemistry within a crevice of stainless steel in 288°C water containing Cl− major anionic impurities. In situ measurements of the electrical conductivity of a solution within a 15-μm-gap crevice (σcrev) were conducted using small sensors installed at different crevice depths. The ECP at the external surface of the crevice specimen (Eext) was controlled by the dissolved oxygen concentration in the bulk water. An increase in Eext from approximately −0.49 VSHE (vs. a standard hydrogen electrode at 288°C) to −0.12 V resulted in an increase in σcrev from 12 μS/cm to 160.3 μS/cm at 21 mm from the crevice mouth. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. Cl− was considered to be the major anionic species transported into the crevice in this potential range. A further increase in Eext up to 0.3 V led to a decline in σcrev. An increase in the flux of oxidizing (O2 and and alkalizing species (OH−) into the crevice was considered the cause of this behavior.

Crevice corrosion of U75V high-speed rail steel with varying crevice gap size by in-situ monitoring

Crevice corrosion of high-speed rail steel U75V was studied with varying gap size by using self-designed device. Increasing gap size inhibited exterior cathodic reduction reaction of oxygen, inducing decrease of potential difference between interior and exterior. Gap size decrease after increase induced increase of potential difference after decrease, not completely reversible because rust kept expanding, acting as weaker depolarizer than oxygen. Anodic dissolution of interior was under ohmic-control, fastest near crevice mouth and slowest near but not at deepest site. Corrosion initiation was observed, closely related to pearlite nodules with larger interlamellar spacing and different lamellar directions, inducing deep attack.

A peridynamic model for crevice corrosion damage

A new peridynamic (PD) model for crevice corrosion damage is introduced and cross-validated with experimental results from the literature. Electrochemical mechanisms are reduced to a simple metal-ion concentration-dependent corrosion rate. Computations over domains with extreme aspect ratios like those seen in crevices are efficiently performed by modifying the PD formulation to accommodate arbitrary-shape horizons. The model is validated against experimental results on bolted washers. Simulations predict both the location and the depth of deep corrosion trenches that form at a distance from the crevice mouth. Far-field boundary conditions are used to autonomously reproduce the experimentally observed progression of crevice corrosion. The PD model results also show that the two factors considered here (diffusion-driven transport of dissolved metal ions, and dissolution being dependent on their concentration) are sufficient to predict the evolution of crevice corrosion.

The crevice corrosion behavior of N80 carbon steel in acidic NaCl solution: The effect of O2

AbstractThe effect of O2 on crevice corrosion of N80 carbon steel in acidic NaCl solution is investigated. Crevice corrosion of N80 carbon steel could be initiated with or without O2 in acidic NaCl solution. A deep corrosion groove could be formed near the crevice mouth after crevice corrosion. The crevice corrosion of N80 carbon steel is ascribed to the increased pH inside the crevice in acidic NaCl solution. The presence of O2 in the solution could enhance the cathodic reaction processes outside the crevice, but it is not significant for the cathodic reaction processes inside the crevice. The galvanic corrosion effect between inner and outer steels could be enhanced by O2 and then promote crevice corrosion.

Crevice corrosion of X80 carbon steel induced by sulfate reducing bacteria in simulated seawater

Crevice corrosion of X80 carbon steel in simulated seawater with the presence of SRB was studied by surface analysis and electrochemical measurements. The electrode inside crevice was seriously corroded. Large amount of corrosion products accumulated along the crevice mouth. Galvanic current densities measurements confirmed that there was a galvanic effect between the carbon steel at the crevice interior and exterior during the crevice corrosion. The difference in the sessile SRB cells quantities and SRB biofilms developments inside and outside crevice caused the galvanic effect between the carbon steel inside and outside the crevice, which further induced crevice corrosion. Increased crevice width reduced the galvanic effect, resulting in less crevice corrosion in wider crevice.

Effect of stress on the crevice corrosion of P110 steel in the CO2-saturated NaCl solution containing thiosulphate/H2S

ABSTRACT The effect of stress on the crevice corrosion of P110 carbon steel in the CO2-saturated 3.5 wt-% NaCl solution with a small amount of thiosulphate/H2S was investigated. The results showed that the composition of corrosion products on the steel surface did not change with elastic stress while the mackinawite film formed at the crevice mouth was more easily spalled off under higher stresses. Further, the elastic stress likely promoted localised corrosion but inhibited uniform corrosion both inside and outside crevice. Increasing the applied stress led to a deeper and sharper corrosion groove covering with corrosion products at the crevice mouth, suggesting the crevice corrosion was promoted by the applied stress. This is likely due to the peeling of mackinawite film and stress concentration at the crevice mouth.

Corrosion interactions between stainless steel and lead vanado-iodoapatite nuclear waste form part II

This paper studied the release of iodine from lead vanado-iodoapatite (I-APT, Pb9.85(VO4)6I1.7), a potential nuclear waste form for the radioactive waste element of I-129, which can be enhanced when crevice corrosion of stainless steel (SS) occurring nearby. Reference corrosion studies of I-APT were performed in different bulk solutions including DI water, 0.6 M and 6 M NaCl, and 0.1 M HNO3 without metal crevice corrosion interactions. The localized enrichment of Cl−, one of the major consequences of SS crevice corrosion, was found to be the decisive factor that led to the enhanced release of iodine. A surface alteration layer consisting of a mixture of nanocrystalline I-APT and Cl-rich apatite (Cl-APT) formed on I-APT surface. Meanwhile, large Cl-APT crystals formed at the crevice mouth on the I-APT surface. This study reveals a new near-field corrosion mechanism for ceramic waste forms when they are exposed to aggressive local corrosive conditions created by the electrochemical reactions of nearby metals. The insight gained in this study could be beneficial for a more accurate prediction of waste form degradation.

Crevice Corrosion Behaviors Between CFRP and Stainless Steel 316L for Automotive Applications

Carbon fiber reinforced plastics (CFRP) are promising lightweight materials for vehicle applications. 316L is one of the most widely used types of austenite stainless steels and applied in lots of automotive applications. The existence of crevices will result in galvanic corrosion and crevice corrosion when CFRPs and 316L are directly connected. A crevice former for the galvanic system was therefore designed and applied to evaluate the crevice corrosion behaviors and study the mechanism of galvanic crevice corrosion through several electrochemical techniques in this research. The results showed that the crevice corrosion of galvanic systems grew from crevice mouth to the inside crevice and could be divided into four steps, metastable pitting corrosion at the crevice mouth, initiating step of crevice corrosion, propagating step and ending step of crevice corrosion. Because of the influences of the galvanic system, electrode reaction rates were speeded up and the passivation region was shortened at the initiating stage of crevice corrosion. Corrosion rate was observed to be higher in the galvanic system than that in normal crevice systems.

Crevice corrosion behavior of Alloy 690 in high-temperature water

Characterizations of oxide films formed on Alloy 690 during crevice corrosion in 290 °C pure water were investigated. It was found that different hydrochemistry conditions and potential drop affected the development of oxide films within the crevice. The thick oxide film formed at crevice mouth mainly consisted of compact NiO and NiFe2O4 due to the precipitation of Ni2+ and Fe2+, while the thin oxide film formed within the crevice mainly consisted of an outer layer of Cr(OH)3 and (Fe, Ni)Cr2O4, and a continuous inner layer of Cr2O3, which was attributed to the hydrolysis of Cr3+ and decreased the pH value of the crevice solution. Possible mechanisms of crevice corrosion and growth of the oxide films at different sites along the crevice in high-temperature water are discussed.

(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

Effect of the Crevice Former on the Corrosion Behavior of 316L Stainless Steel in Chloride-Containing Synthetic Tap Water

To restrain the failure of the plate heat exchanger (PHE) in customer boiler working fluid, the effect of crevice former type on the corrosion behavior of the 316L stainless steel plate was investigated using electrochemical methods and surface analyses in chloride-containing synthetic tap water (60 °C). The localized corrosion under metal–metal crevice condition was initiated more easily than that under the metal-gasket crevice condition due to the restricted mass transport at the gasket crevice mouth. However, the anodic current under the metal–metal crevice condition was lower than that under metal-gasket crevice condition at a higher anodic potential, indicating that that the metal dissolution under EPDM crevice would be higher than that under metal crevice under the accelerated corrosion condition. Because narrow crevice gap that was formed under gasket accelerated the anodic dissolution at the crevice mouth, the perforation tendency under metal-gasket crevice condition is much higher than that under metal–metal crevice condition. As a result, the crevice geometry, especially the crevice gap, mainly affected the corrosion behavior of PHE material.

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

Once crevice corrosion is initiated on stainless steels in chloride environments, the hydrolysis of dissolved metal ions causes severe acidification inside the crevice, and Cl- ions migrate into the crevice from the bulk solution. This electromigration of Cl- ions promotes subsequent active dissolution inside the crevice. Therefore, neutralization of the pH inside the crevice is expected to be the predominant factor affecting the repassivation of crevice corrosion.To clarify the repassivation behavior of crevice corrosion, in situ observations were performed, and the quantitative relationship between current values and corrosion morphology was analyzed. In addition, to elucidate the effect of the solution composition on the repassivation behavior, an electrochemical flow cell was used. In this study, the effect of NO3 - ions on the repassivation behavior of Type 316L stainless steel was investigated. Type 316L stainless steel was used as specimens. The specimens were heat-treated at 1373 K for 3.6 ks and then water-quenched. A schematic illustration of the electrochemical flow cell is shown in Figure 1. An artificial crevice was formed between a glass plate and the specimen surface. The specimen was polarized at 0.25 V (vs. Ag/AgCl, 3.33 M KCl). Crevice corrosion tests were performed in a flowing 1 M NaCl solution at 298 K. In the case of the solution change experiment, the inlet solution was changed from 1 M NaCl to 1 M NaCl-1 M NaNO3. The solution was changed when the current exceeded 100 μA. The flow rate of the solution was 24 mL h-1 during the crevice corrosion tests. Since the volume of the cell was ca. 24 mL, it took about 1 h to change the solutions completely. During the crevice corrosion tests, the crevice corrosion behavior of the specimen surface inside the crevice was observed using an optical microscope, and the images were taken every 100 s. Figure 2a shows the time variations of the currents in the crevice corrosion test in 1 M NaCl, and Figure 2b shows the results of in situ observations of the specimen surface. From the beginning of the crevice corrosion test to ca. 250 s, the current decreased to ca. 4 μA with time. Around ca. 300 s, the current increased rapidly. This current increase was due to the initiation of crevice corrosion. At this time, two small dark spots were observed inside the crevice (Figure 2b1). These spots were the initiation sites of the crevice corrosion. As shown in Figures 2b1-b3, the crevice corrosion grew toward the crevice mouth. After that, the corroded areas proceeded along the crevice mouth (Figures 2b4-b7). Once the entire crevice mouth was corroded, the crevice corrosion propagated toward the inside of the crevice, and the current increased up to ca. 5 mA at ca. 10 ks. From the results shown in Figure 2, it was confirmed that the crevice corrosion was readily initiated in 1 M NaCl, and no spontaneous repassivation was generated in this solution. Figure 3a shows the time variations of the current in the solution change experiment from 1 M NaCl to 1 M NaCl-1 M NaNO3, and Figure 3b shows the results of in situ observations of the specimen surface. Around 300 s, the current increased rapidly due to the initiation of crevice corrosion. At 406 s, the current exceeded 100 μA, and the inlet solution was then changed to 1 M NaCl-1 M NaNO3. From 406 s to 3.75 ks the current increased to 2.9 mA. In this period, the corroded areas mainly grew along the crevice mouth as shown in Figures 3b2-b5. At 3.75 ks (Figure 3b6), the current started decreasing. Almost at the same time, the growth of the crevice corrosion along the crevice mouth was stopped. From this time, the crevice corrosion propagated toward the inside of the crevice. Afterwards, the current decreased to ca. 150 μA. After 26.1 ks, the current began decreasing again. As shown in Figure 3b8, no propagation of the corroded area was observed after 43.0 ks. This suggested that the surface of the corroded area was completely repassivated. This result indicated that NO3 - bring about the repassivation. Figure 1

Synergistic effect of stress and crevice on the corrosion of N80 carbon steel in the CO2-saturated NaCl solution containing acetic acid

The corrosion behaviour of N80 carbon steel under the coexistence of stress and crevice in the CO2-saturated NaCl solution containing acetic acid (HAc) was studied by electrochemical measurements, surface analysis, and stress analysis. It is demonstrated that the corrosion potential of steel shifts negatively and corrosion activity is enhanced with increasing stress. A deep corrosion groove is formed at crevice mouth, which causes stress concentration, increasing the susceptibility to stress corrosion cracking (SCC). The stress concentration also results in larger driving force for crevice corrosion. Therefore, there is a synergistic effect of stress and crevice on the corrosion of steel.