Mechanism Of Crevice Corrosion Research Articles

Electroactive Shewanella algae accelerates the crevice corrosion of X70 pipeline steel in marine environment

Crevice corrosion causes severe damage to metallic materials in marine environments. The inner mechanism of crevice corrosion in the presence of microbes deserves in-depth investigation. Herein, the electroactive Shewanella algae was found to accelerate the crevice corrosion of X70 pipeline steel through weight loss analysis, electrochemical tests, characterization of surface morphology, and analysis of corrosion products. The corrosion current increased to 2.3 μA cm−2, which was 2.3 folds of that in a sterile medium. Further electrochemical tests were carried out with exogenous addition of riboflavin. It confirmed that extracellular electron transfer accelerated the crevice corrosion in which S. algae participated.

Insight into the crevice corrosion mechanism of AA7075‐T651 high‐strength aluminum alloys in neutral nitrate solution: The effect of Cl−

AbstractThe crevice corrosion behavior and mechanism of AA7075‐T651 aluminum alloy was investigated by electrochemical measurements and surface analysis technologies in a neutral nitrate solution with different contents of NaCl. The Cl− was identified as crucial for the initiation and development of the crevice corrosion, with the phenomenon absent in the 0.05 M NaCl solution but initiated in the 0.5 and 1 M NaCl solutions. However, the crevice corrosion was more pronounced in the 0.5 M NaCl solution due to the establishment of a larger galvanic corrosion effect. The rapid dissolution of the anodic phase resulted in the increased Cl− inside the crevice, while the cathodic phase enhanced the localized dissolution through micro‐galvanic corrosion. This synergistic effect significantly facilitated the development of crevice corrosion.

A highly sensitive, long-time stable Ag/AgCl ultra-micro sensor for in situ monitoring chloride ions inside the crevice using SECM

Tracking the variation of Cl− timely within the crevice is of great significance for comprehending the dynamic mechanism of crevice corrosion. The reported chloride ion selective electrodes are difficult to realize the long-time Cl− detection inside the confined crevice, due to their millimeter size or a relative limited lifespan. For this purpose, an Ag/AgCl ultra-micro sensor (UMS) with a radius of 12.5 μm was fabricated and optimized using laser drawing and electrodeposition techniques. Results show the AgCl film's structure is significantly impacted by the deposited current density, and further affects the linear response, life span and stability of Ag/AgCl UMS. The UMS prepared at current density of 0.1 mA/cm2 for 2 h shows a rapid response (several seconds), excellent stability and reproducibility, strong acid/alkali tolerance, sufficient linearity (R2 > 0.99), and long lifespan (86 days). Moreover, combined with the potentiometric mode of scanning electrochemical microscope (SECM), the Ag/AgCl UMS was successfully applied to monitor the in-situ radial Cl− concentration in micro-regions inside a 100 μm gap of stainless steel. The findings demonstrated that there was obvious radial difference in Cl− concentration inside the crevice, where the fastest rise in Cl− concentration was at the opening. The proposed method which combines the UMS with SECM has attractive practical applications for microzone Cl− monitoring in real time inside crevice. It may further promote the study of other localized corrosion mechanism and the development of microzone ions detection method.

A closer look at the corrosion of steel liner embedded in concrete

Containment wall of nuclear power plants is an example of a concrete structure enveloping a steel liner plate. In this research, the situations observed in connection with liner failures were investigated, namely the presence of a piece of wood (foreign matter) and a delamination gap between steel liner and concrete, with the purpose to study and define the corrosion mechanism of the steel liner plate and identify which factors promote or impede the occurrence of corrosion.Specimens were concrete slabs containing a steel plate, an inlay to modify the conditions at the steel surface, and electrodes for electrochemical measurements. The inlays represented “normal” concrete, low-pH concrete, a piece of wood, and a delamination gap between concrete and steel, and the same systems supplemented with chlorides. The results from two-year tests with wetting-drying cycles revealed localized corrosion in steel underneath the piece of wood, close to the inlay perimeter. The attack could be explained mainly by the mechanism of crevice corrosion. In contrast, no corrosion attack of steel liner could be detected in specimens with the delamination gap. The results from the experiments and steel liner characterization are provided in this paper, together with the reasoning behind the proposed degradation mechanism.

Effect of crevice gap on crevice corrosion initiation and development of 2205 duplex stainless steel in NaCl solution

The crevice geometry has an important influence on the initiation and development of crevice corrosion. The crevice gap size determines the volume of the crevice solution and the cross-sectional area of the material exchange channel between the crevice solution and bulk solution, and it is the dominant factor of the initiation and development mechanism of crevice corrosion. In this paper, the effect of crevice gap size on the crevice corrosion behavior of 2205 duplex stainless steel (DSS) in NaCl solution was investigated by electrochemical method combined with modeling. The quantitative contribution of the volume effect of crevice solution and the diffusion effect of H+ on the crevice corrosion initiation period, as well as the corrosion characteristics and mechanism at initiation and development periods of crevice corrosion, were discussed. Results show that the initiation process of crevice corrosion of 2205 DSS in 3.5 wt% NaCl solution follows the critical crevice solution mechanism. The crevice gap size affects the acidification rate of the crevice solution and the initiation period time of crevice corrosion through the volume effect and the diffusion effect. The influence of diffusion effect on the initiation period time was more significant than volume effect. The corrosion development process is mainly determined by the potential and current density distribution within the crevice, and thus follows the IR drop mechanism (I refers to the current and R refers to the resistance). The crevice gap size is the dominant factor for the development mechanism of crevice corrosion.

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.

Proposed stability product criterion for open hemispherical metastable pits formed in the crevices of different aspect ratios (l/d) on 316L stainless steel in 3.5% NaCl solution

This work investigates the mechanism of crevice corrosion for a 316 L stainless steel in 3.5 % NaCl solution and assesses its characteristics. Potentiodynamic, potentiostatic, and galvanostatic techniques along with SEM were used to characterize the crevice corrosion at various gap sizes of 5, 10, 30, 60, 120 and 240 μm. Results revealed that the crevice corrosion initiates by pitting events stabilization. Using a novel approach and considering the crevice aspect ratio (l/d), it is discussed how the crevice geometry can affect pit stability product criterion. By increasing the crevice gap, the pit stability product decreased and the induction time increased.

Effect of the macro-segregation on corrosion behavior of CrMnFeCoNi coating prepared by arc cladding

The CrMnFeCoNi coatings were prepared by the tungsten arc cladding process on a substrate of X65 steel. A macroscopic scale solute segregation within the coated layer can be recognized, which is analyzed by coupling the fluid mechanics and calculation of phase diagram technique (CALPHAD). According to the no-slip boundary condition, a zero-velocity laminar fluid layer appears at the fusion pool boundary, which forms the macro-segregation zone. Energy dispersive spectroscopy (EDS) results demonstrated the macro-segregation zone possess higher Fe element portion (X65 steel enriched zone) compare to the other region in the coating layer. Electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) results indicated that the macro-segregated regions exhibited body-centered cubic structure that possess high-density dislocations, which proves that martensite transformation occurs within the X65 steel enriched macro-segregated regions. Potentiodynamic polarization curves indicated that CrMnFeCoNi coated samples experienced three stages including active, passive and transpassive dissolution. In active stage, preferential dissolution occurred on macro-segregated regions, which can be attributed to two factors: phase portion factor and alloying component factor. In the passive stage, the CrMnFeCoNi coating formed passive film while the macro-segregated zones exhibited active dissolution, resulting in forming deep crevices. Once macro-segregation zones formed deep crevices, the crevice corrosion mechanism would be dominant. As a result, some deeper and wider crevices were formed. In transpassive region, the passive film dissolved, which aggravates the corrosion of the sample.

Nanometer Resolved Real Time Visualization of Acidification and Material Breakdown in Confinement

AbstractLocalized surface reactions in confinement are inherently difficult to visualize in real‐time. Herein multiple‐beam‐interferometry (MBI) is extended as a real‐time monitoring tool for corrosion of nanometer confined bulk metallic surfaces. The capabilities of MBI are demonstrated, and the initial crevice corrosion mechanism on confined nickel and a Ni75Cr16Fe9 model material is compared. The initiation of crevice corrosion is visualized in real time during linear sweep polarization in a 1 × 10−3 m NaCl solution. Pre‐ and post‐experiment analysis is performed to complementarily characterize the degraded area with atomic force microscopy (AFM), optical microscopy, nano‐Laue diffraction (nano‐LD), scanning electron microscopy (SEM)/electron backscatter diffraction (EBSD), and X‐ray photoelectron spectroscopy (XPS). Overall, Ni75Cr16Fe9 displays a better corrosion resistance; however, MBI imaging reveals 200 nm deep severe localized corrosion of the alloy in the crevice opening. Chromium rich passive films formed on the alloy contribute to accelerated corrosion of the confined alloy by a strongly acidifying dissolution of the passive film in the crevice opening. Nano‐LD further reveals preferential crystallographic defect and corrosion migration planes during corrosion. MBI provides nanometer accurate characterization of topologies and degradation in confined spaces. The technique enables the understanding of the initial crevice corrosion mechanism and testing modeling approaches and machine‐learning algorithms.

Visualization of Potential Distribution inside Crevice of Type 430 and 304 Stainless Steels

Stainless steels are widely used in industries because of their high anti-corrosive performance due to their passivation ability. However, crevice corrosion sometimes occurs in chloride environments. It is known that crevice corrosion is initiated when electrode potential inside crevice changes from the passive to active state. Therefore, the potential is the important factor to understand the mechanism of crevice corrosion. In this research, visualization of the potential inside the crevice for type 430 and 304 stainless steels was performed in 0.01 M NaCl at pH 3.0. An indium-tin oxide (ITO) glass with a sensing layer was applied for visualizing the potential. In the sensing layer, a redox indicator was entrapped. Figure 1 shows the schematic illustration of apparatus for the calibration procedure for color change of the plate. The ITO glass with the sensing layer (sensing plate) was used as a working electrode. In an electrolyte, a mirror polished Pt plate was put below the sensing plate to reflect the image of the sensing plate, and the optical microscope images were taken through the sensing plate by a CCD camera system. Electrode potential of the sensing plate was changed from -0.52 to 1.08 V in 0.01 M NaCl (pH 3.0 adjusted with HCl). All potentials reported in this work refer to Ag/AgCl (3.33 M KCl). Figure 2 shows the optical micrographs of the sensing plate placed above the Pt. It is clear that the color was changed from light green to dark blue with increasing electrode potential. The sensing plate was applied to crevice corrosion tests in 0.01 M NaCl (pH 3.0 adjusted with HCl). In the crevice corrosion tests, the sensing plate was used as a crevice former. The distributions of electrode potentials inside the crevice of the stainless steels were monitored from the color of the sensing plate. Figure 1

The Critical Pitting Chloride Concentration of Various Stainless Steels Measured by an Electrochemical Method

Since chloride ion is one of the most dangerous accelerators for pitting, the chloride concentration allowed for stainless steels is always the concern of scientists and engineers. At present, a novel electrochemical method was designed to efficiently and precisely measure the critical pitting chloride concentration (CPCC) of various stainless steels in a buffered chloride solution. The current flowing from the working electrode was recorded at a constant potential in the buffered solution with an almost linearly increased chloride concentration. The given chloride concentration when the current density reached 10 μA cm−2 or 1000 μA cm−2 was defined as the CPCC of stainless steels. Abnormal corrosion morphologies were observed on the sample surface after the CPCC test and a pitting-induced crevice corrosion mechanism was introduced. The logarithm of the CPCC values showed an approximately linear relationship with both the temperature and the testing potential. The potentiodynamic polarization curves of AISI 304 samples in buffered solutions with various chloride concentrations at 50°C also certified the reliability of CPCC results. Furthermore, the pitting resistance of AISI 304, AISI 201 and AISI 316L stainless steels ranked by the CPCC results agreed well with the data trend derived from traditional electrochemical methods.

Crevice corrosion of copper for radioactive waste packaging material in simulated groundwater

The investigation described here was conducted to clarify the corrosion behaviour of high level radioactive waste containers made of copper. The influences of oxygen, chloride ion and sulphate ion on copper crevice corrosion were studied in solutions simulating groundwater characteristic of northwest China. The results showed that oxygen, chloride ion and sulphate ion promote crevice corrosion. Chloride ion was found to play a significant role in the crevice corrosion mechanism in copper, but sulphate ion had no effect on the mechanism.

Localized Corrosion of Carbon Steel in the Presence of Gamma Radiation

Canada’s long-term plan for used nuclear fuel includes permanent disposal in a deep geological repository (DGR) using a multiple-barrier system with a key barrier being the used fuel container (UFC). The UFC design consists of an inner vessel of carbon steel (CS), which provides the structural strength to withstand repository loads, and an outer layer of copper, which functions as an external corrosion barrier. The inner vessel of the current UFC design is composed of a pressure grade CS hemispherical head and pressure grade CS piping as a body, the two parts to be laser welded on-site. One of potential issues with this design is the effect of g-radiation on corrosion of the crevice near the weld region. The environment inside the sealed UFC would be humid air. Gamma-irradiation of humid air produces NOx and HNO3, and these species could accelerate the formation and condensation of water droplets in crevices (which might also have surface roughness features that act as preferential condensation sites). The chemical environment in such acidic condensed water, coupled with the presence of oxidizing water radiolysis products, could be very aggressive. Corrosion within the crevice between the head and the body of the container assembly or in the stressed regions near the welds could lead to a localized build-up of corrosion products (oxide deposits and H2gas). The effect of g-radiolysis on crevice corrosion of CS is being investigated using a combination of corrosion exposure tests and electrochemical measurements. These measurements are augmented by post-test analysis of oxide surface using SEM, XPS and Raman spectroscopy. In the corrosion tests reported here, a prepared CS crevice was wetted by adding a couple of water droplets to the mouth of the crevice. The test sample was then exposed to a desired environment in a sealed container for 20 h. Optical images of the corroded surfaces show that the corrosion of the wet bold surface progresses more extensively in air than in Ar, more at 80 oC than at 25 oC and more in the presence rather than in the absence of radiation. The composition of the oxide formed on the wet bold surface (as determined by Raman spectroscopy) shows the oxidation leads to formation of a mixed FeII/FeIII oxide/hydroxide in Ar, and to the formation of FeIII oxyhydroxide and FeIII oxide in addition to the FeII/FeIII oxide in air. Increasing temperature increases the ratio of oxide to hydroxide or oxyhydroxide but does not affect the metal oxidation states. More corrosion products are formed in the presence than absence of radiation. In contrast to the bold surface the interior surface of crevice remained smooth. The XPS analysis of the crevice surface indicates that the oxides formed there are thin (< ~ 9 nm) and that a larger fraction of the oxide is FeIII oxide/hydroxide rather than FeII/FeIII oxide. The thickness of the oxide formed at 80 oC is slightly higher than that formed at 25 oC. Radiation slightly decreases the oxide thickness at 25 oC while it increases the oxide thickness at 80 oC. The different corrosion behaviours of the crevice and bold surfaces raise the possibility of galvanic coupling between the two surfaces. This galvanic effect was investigated by monitoring the coupling current between two electrodes, one electrode representing the bold surface and the other representing the crevice surface, in the electrochemical coupling tests. To aid in interpretation of the galvanic coupling experiments, the corrosion potential and linear polarization measurements were made on each electrode separately. The post-test surfaces from these tests were examined by SEM and XPS. The observed effects of temperature and g-radiation on the corrosion potentials are consistent with the different oxide formation and growth observed in the coupon exposure study. The corrosion potential on the crevice electrode is always slightly higher than that of a bold electrode with the difference depending on temperature and radiation environment. A galvanic coupling current observed between the two electrodes shows that the crevice electrode is the net cathode. The measured coupling currents are consistent with the results from the dynamic polarization tests performed on each electrode. A CS crevice corrosion mechanism that can explain both the crevice corrosion tests and the electrochemical results is discussed.

Mill Scale Corrosion and Prevention in Carbon Steel Heat Exchanger

AbstractThe cause of material degradation of an ASTM A-124 grade carbon steel tube belonging to a heat exchanger has been investigated. Visual examination, followed by an in-depth microstructural characterization using optical microscopy, energy dispersive X-ray, and scanning electron microscopy, was carried out for understanding the primary cause of material degradation. Based on the results of an extensive examination as well as the background information provided on the heat exchanger, it was determined that the steel tubes were predominantly damaged by the mechanism of crevice corrosion facilitated by the presence of mill scale. It is concluded that the heat exchanger tubes were not properly investigated for defects after their fabrication. Based on the situation, the proper cleaning method was selected for preventing further corrosion in the system. A chemical cleaning process was designed using acid pickling along with an inhibitor and a surfactant.

Electrochemical and Salt Spray Corrosion Behavior of Copper Alloy Contact Wires in Chloride Solution

The effect of different alloying elements on corrosion behavior of copper alloys was investigated using electrochemical corrosion and salt spray corrosion test in NaCl solution. Cu-Ag has the most stable corrosion current in the potentiostatic scanning test, exhibiting a better corrosion resistant performance. It can be analyzed from corrosion surface morphologies that Cu-Ag presents exfoliation corrosion mechanism while Cu-Sn shows crevice corrosion mechanism. Cu-Mg has a complex corrosion process caused by multiple corrosion mechanism. In the salt spray corrosion test, the corrosion degree of Cu-Ag is lighter than those of Cu-Sn and Cu-Mg after 24h test. Therefore, the Cu-Ag alloy exhibits the best corrosion resistance in chloride solution.

An arbitrary Lagrangian–Eulerian model for modelling the time-dependent evolution of crevice corrosion

An arbitrary Lagrangian–Eulerian (ALE) model is proposed to model the time-dependent evolution of a crevice corrosion that can achieve the simulation of the transient potential distribution, the dynamic concentration profiles and the time-dependent geometry deformation for a corroding crevice. The time-dependent deformation of the crevice geometry, which is caused by metal dissolution and corrosion product precipitation, is implemented via the ALE method. The model reasonably predicted the dynamic pH distribution inside the crevice. It is also predicted that the deposition of corrosion product accelerates crevice corrosion. The current model would be helpful in elucidating the mechanism of crevice corrosion and other forms of related localised corrosion.

Crevice corrosion of biomedical alloys: A novel method of assessing the effects of bone cement and its chemistry

In this study, five commercially available poly(methyl methacrylate) PMMA bone cements were tested to investigate the effects of antibiotics on the severity of crevice corrosion. Bone cements with varying chemistry were also tested. A test method was developed in part reference to ASTM F746-04. Cylindrical specimens were fitted with a bone cement tapered collar, creating consistent crevice conditions. Crevice corrosion was then studied using potentiodynamic polarization techniques in 0.9% NaCl solution (pH7.4) at 37°C. Surface analyses using a light microscope and scanning electron microscopy were also conducted to investigate the surface morphology after accelerated electrochemical testing. Initial testing of commercially available bone cements indicated that different PMMA bone cements can affect the initiation and propagation mechanism of crevice corrosion. Further studies, utilising electrochemical and mass spectroscopy techniques, have identified that the addition of radiopaque agent and antibiotics affect the initiation mechanisms of 316L stainless steel, whilst significantly increasing the extent of propagation in CoCrMo alloys.

Microscopic investigation of mill scale and its proposed effect on the variability of chloride-induced depassivation of carbon steel rebar

Electrochemical experiments have shown that mill scale on carbon steel rebar affects corrosion initiation and variability associated with chloride-induced depassivation thresholds. In this study, scanning electron microscopy and focused ion beam microscopy were used to investigate the properties of mill scale and its effect on chloride thresholds of the underlying steel. The variability found in the literature for chloride thresholds is suggested to result, in part, from the variability in the physical and chemical properties of mill scale. A crevice corrosion mechanism is proposed to explain why as-received rebar is more susceptible to depassivation than rebar without mill scale.

Mapping the concentration changes during the dynamic processes of crevice corrosion by digital holographic reconstruction

The dynamic process of crevice corrosion during anodic dissolution of a crevice electrode in a 5.0 mmol dm-3 NaCl solution has been studied by digital holographic reconstruction. Digital holographic reconstruction has been proved to be an effective and in situ technique to detect the changes in the solution concentration because useful and direct information can be obtained from the three-dimensional images. It provides a valuable method for a better understanding of the mechanism of crevice corrosion by studying the dynamic processes of changes in the solution concentration at the interface of crevice corrosion.

Corrosion of electrodeposited copper by exposure to volatile organic compounds

In this paper we investigate the corrosive behaviour of various volatile organic compounds (VOCs) on electroplated copper. The VOCs we considered were of the following types: (i) aromatic and substituted-aromatic compounds (benzene, toluene and ethyl benzene); (ii) a chlorine-substituted hydrocarbon (dichloromethane) and (iii) an aliphatic alcohol (isopropyl alcohol). Contamination by VOCs is typical of ULSI (Ultra Large Scale Integration) manufacturing environments, and exposure of Cu to VOC-contaminated clean room air has been pinpointed as a serious cause of interconnects failure. SEM observation highlighted corrosion signature that are typical of the different classes of molecules. In particular, the corrosion of copper is almost absent following exposure to isopropyl alcohol, very slow in the case of aromatic molecules and severe in the case of dichloromethane. The obtained results can be interpreted in terms of a crevice corrosion mechanism under droplets, enhanced by pitting in the presence of chlorinated solvents.