Localized Corrosion Processes Research Articles

Transient analysis of the electrochemical noise arising from the stainless steel local anodic events by the equivalent circuit approach

PurposeThis study aims to investigate the individual electrochemical transients arising from local anodic events on stainless steel, to uncover the potential mechanisms producing different types of transients and to derive appropriate parameters indicative of the corrosion severity of such transient events.Design/methodology/approachAn equivalent circuit model was used for the transient analysis, which was performed using a local current allocation rule based on the relative instant cathodic resistance of the coupled electrodes, as well as the kinetic parameters derived from the electrochemical polarization measurement.FindingsThe shape and size of the electrochemical current transients arising from SS 316 L were influenced by the film stability, local anodic dissolution kinetics and the symmetry of the cathodic kinetics between the coupled electrodes, where the ultralong transient might correspond to the propagation of film damage with a slow anodic dissolution rate. The dynamic cathodic resistance during the final stage of transient current growth can serve as a characteristic parameter that reflects the loss of passive film protection.Originality/valueEstimation of the local anodic current trace opens a new way for individual electrochemical transient analysis associated with the charges involved, local current densities and changes in film resistance throughout localized corrosion processes.

Effect of hydrostatic pressure on the anodic dissolution process of X80 steel

Based on the fact that hydrostatic pressure affects chemical potentials of reaction species and the structure evolution of electric double layer (EDL), the authors propose a generalized-BV equation to analyze the anodic dissolution process of X80 steel in deep-sea environment. Combined with the results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the following conclusions can be drawn: hydrostatic pressure can compress the electric double layer non-uniformly. The CHCD (CD: capacitance of diffused layer; CH: capacitance of compact layer) value increases first and then decreases with increasing hydrostatic pressure and reaches its maximum at 15 MPa, which is sure to influence the difference in electrical potential that drives chemical reaction at interface. Ultimately, the anodic dissolution current increases and then decreases with rising hydrostatic pressure at the same anodic polarized potential. Besides, low hydrostatic pressure may contribute to forming a dense corrosion product film and inducing a good inhibiting effect on further dissolution of X80 steel; However, when the hydrostatic pressure exceeds the critical value of 20Mpa, too high anodic dissolution rate along with promoted Cl− adsorption will deteriorate the protection performance of corrosion product film, and exacerbate local corrosion process.

Corrosion Investigation by Scanning Electrochemical Microscopy of AISI 446 and Ti-Coated AISI 446 Ferritic Stainless Steel as Potential Material for Bipolar Plate in PEMWE

AbstractThe components of proton exchange membrane water electrolysers frequently experience corrosion issues, especially at high anodic polarization, that restrict the use of more affordable alternatives to titanium. Here, we investigate localized corrosion processes of bare and Ti-coated AISI 446 ferritic stainless steel under anodic polarization by scanning electrochemical microscopy (SECM) in sodium sulphate and potassium chloride solutions. SECM approach curves and area scans measured at open-circuit potential (OCP) of the samples in the feedback mode using a redox mediator evidence a negative feedback effect caused by the surface passive film. For the anodic polarization of the sample, the substrate generation-tip collection mode enables to observe local generation of iron (II) ions, as well as formation of molecular oxygen. For the uncoated AISI 446 sample, localized corrosion is detected in sodium sulphate solution simultaneously with oxygen formation at anodic potentials of 1.0 V vs. Ag/AgCl, whereas significant pitting corrosion is observed even at 0.2 V vs. Ag/AgCl in potassium chloride solution. The Ti-coated AISI 446 sample reveals enhanced corrosion resistance in both test solutions, without any evidence of iron (II) ions generation at anodic potentials of 1.2 V vs. Ag/AgCl, where only oxygen formation is observed.

Identification of damage and corrosion effect in aging aircraft data transmission lines

Corrosion in aircraft structures and systems persists to pose significant problem in the aircraft industry. It affects both the aircraft structures and all the wiring systems including data transmission lines at the points of mechanical damage (missing or damaged insulation and jacket materials) and connections. Reliability of data transmission through aircraft data transmission lines (ATDL) is essential for maintaining performance capability and safety of flights. Unfortunately, there is no existing method for detecting corrosion and predicting its effect for wiring systems including ADTL. Detecting corrosion and predicting its effect on time would prevent unexpected system failures and catastrophes. This paper presents novel experimental method that has been employed, for the first time, to detect and study the effect of localized corrosion process on reflected and transmitted power signals passing through locally corroded ADTL with mechanically induced damage. ADTL with three types of induced damage were corroded in a Q-Fog cyclic accelerated corrosion chamber for over 14 weeks (2352 h) using ASTM G85-A5 Prohesion test that resembles the environment of aircraft operation. Cable specimens were taken out every week and investigated by measuring transmitted and reflected power signals passing through the corroded ADTL using Vector Network Analyzer (VNA), where signals from 0 to 6 GHz were swept into the ADTL. Reflected and transmitted power signals (S11 and S21 respectively) were acquired in time domain and processed in MATLAB. Analysis of results show that corrosion effect is not arbitrary and can be tracked over time and predicted. Reflected signal peak width changed over time of corrosion exposure and is proportional to corrosion propagation width inside the ADTL. It is also observed that corrosion induced extra distortion of signals passing through the corroded damage region. The results are very promising for detecting corrosion and predicting its effect in ADTL.

Effect of methane and acetylene pre-gases on the corrosion resistance of DLC coatings

Diamond-like carbon (DLC) coatings were applied to 304 stainless steel specimens using two different pre-gases: methane and acetylene.Compared to DLC prepared with acetylene pre-gas(DLC-C2H2). DLC prepared with methane pre-gas(DLC-CH4) has a denser coating body and a smoother surface.The DLC-C2H2 film shows crack defects on the surface, and the DLC-CH4 film has a lower sp2/sp3 ratio than DLC-C2H2. DLC-CH4 has better electrochemical characteristics and salt spray corrosion testing results than DLC-C2H2 films in NaCl solution. DLC-CH4 has a high charge transfer resistance of 9.54 × 103 Ω/cm2. Compared to DLC-C2H2, DLC-CH4 coatings form a more complete, continuous, smooth surface and a minor porosity in the coating body, inhibiting localized corrosion processes. The DLC-CH4 coatings have less sp2 phase, which results in lower electrical conductivity and limited electron transport at the coating surface. DLC-CH4 shows more excellent corrosion resistance.

High-precision in situ 3D ultrasonic imaging of localized corrosion-induced material morphological changes

We present an ultrasonic research technique that can carry out in situ, direct monitoring of the 3D morphologies of corrosion substrates. The technique has a customizable lateral resolution, an ultra-high axial resolution of 100 nm, and an experimentally proven measurement accuracy. In using the technique to monitor the localized corrosion processes of carbon steel under constant DCs, it was observed that during each of the experiments conducted in alkaline environments, iron dissolution accelerated for a certain period of time and then slowed down. Based on the various features of the ultrasonic signals acquired and the XRD spectra of the corrosion products obtained, it was deduced that an increase in iron dissolution rate as such was accompanied by the depositing of solid corrosion products onto the substrate used and driven by the formation of Fe3O4, which consumed electrons. After a while, the corrosion product layer collapsed and the formation of Fe3O4 was halted.

Electrode array probe designed for visualising and monitoring multiple localised corrosion processes and mechanisms simultaneously occurring on marine structures

An electrode array probe has been specially designed and demonstrated for in situ monitoring and visualising multiple localised corrosion processes and mechanisms, including crevice, weldment and pitting corrosion, occurring simultaneously on marine steel structures. It enabled the probing of time-dependent development of multiple localised corrosion processes, mechanisms and kinetics, thereby facilitating more in-depth understanding of the initiation, propagation and kinetics of localised corrosion of steel marine structures.

Internal localized corrosion of X100 pipeline steel under simulated flow conditions

In this paper, a wire beam electrode (WBE) was used to explore the local corrosion processes of X100 pipeline steel in simulated solution containing HCO3− in static and flow conditions. The results indicated that the WBE's current density mapper was remarkably consistent with the polarization curves. Therefore, WBE is an efficient online corrosion monitoring approach. The WBE discovered undetectable pitting and passivation qualities within the X100 pipeline steel under static conditions. However, the corrosion current density of X100 steel was substantially higher under flow conditions than under static ones. The addition of HCO3− ions significantly decreased the corrosion resistance of the X100 steel. In the 0.3 mol/L HCO3− simulated solution, dynamic corrosion was 92 times faster than static. The corrosion of X100 steel was enhanced by the combined effects of fluid movement and HCO3− ions. Additionally, X100 steel produced significant irregular edge pitting when the critical level of HCO3− was 0.2 mol/L under dynamic conditions, and an erosion theory was proposed to explain this phenomenon.

Use of Multielectrode Arrays and Statistical Analysis to Investigate the Pitting Probability of Copper: Part II. The Effect of Sulfate and Bicarbonate

Copper and copper alloys have found applications in various industries. One of the main reasons Cu and its alloys are utilized widely is that they have sufficient corrosion resistance in key environments, such as seawater and anoxic solutions; however, localized corrosion processes might occur in the presence of aggressive anions, oxygen, or an increase in solution pH. In critical applications of Cu, the susceptibility of Cu to localized corrosion, specifically pitting, must be carefully considered, as it could lead to material failure. In this study, the pitting probability of Cu in unary (sulfate) and binary (sulfate + bicarbonate) solutions was investigated using electrochemical techniques in conjunction with statistical analysis. We determined pitting probabilities based on two different defining criteria for pitting susceptibility, one based on the probability that the corrosion potential, Ecorr, could exceed the passivity breakdown potential, Eb, and the other, a more conservative approach, based on the likelihood that Ecorr would be greater than the repassivation potential, Erp. The pitting probability of Cu did not change significantly with sulfate concentration at pH 8 but was found to increase with increasing [] up to 0.005 M at pH 9 and then to decrease with a further increase in [].

Role of segregation behavior of Cu and Sb in the region of inclusions on initial corrosion

The distribution characteristics of corrosion-resistant elements in low-alloy steel affected the initial corrosion behavior of the matrix. In this article, the segregation behaviors of elements at grain boundaries and pearlite defects in low-alloy steel Q500 and the precipitation behavior of Cu in inclusions were studied. Cu, Ni and Sb had segregation behavior at the boundary of the inclusions, which was beneficial for reducing grain boundary segregation. Cu had the ability to capture Sb and Ni. Cu and Sb involvement in local corrosion process of inclusions were observised by multi-cycle 3.5% NaCl immersion test, during which Cu and Sb were oxidized to corresponding Cu2O and Sb2O3. Under the influences of the segregation of elements at the grain boundaries, the internal part of the crystal was preferentially corroded. Cr was enriched in the pearlite cementite, formed (Cr,Fe)7C3 and contributed to the corrosion process, forming Cr2O3 and CrO3.

Influence of Cr and Ni elements on the electrochemical and early corrosion behavior of FeMnAlC low-density steel

FeMnAlC low-density steel (LDS) is considered to be a promising material due to its good mechanical properties and light weight, its corrosion resistance, however, needs to be improved. In this paper, the effect of Cr and Ni on the electrochemical and early corrosion behavior of a Fe–25Mn–10Al–1.5C LDS in a 3.5% NaCl solution was studied through microstructure characterization, electrochemical tests and immersion tests. The results showed that Cr and Ni alloying reduced the austenite grain size and promoted the formation of the B2 phase. Adding 2% Cr or Ni to the Fe–25Mn–10Al–1.5C LDS clearly inhibited the electrochemical activity and initial micro galvanic effect between the second phases and the austenite. Moreover, the properties of the corrosion product film were optimized, and the local corrosion process beneath the product film was mitigated. Compared with 2% Cr addition, 2% Ni addition improved the corrosion resistance of the FeMnAlC LDS better from the aspects of electrochemistry, corrosion product film and corrosion mode.

Site-specific local polarisation curve measurements for probing localised corrosion and inhibition

Although polarisation curves have widely been used for corrosion behaviour, kinetics and mechanisms studies, their interpretation can be challenging specially for those measured from non-uniform electrode surfaces because such polarisation curves are a combination of many different local polarisation curves that could not be assessed individually. This short communication presents a new method for measuring local polarisation curves by means of an electrochemically integrated electrode array that enables site-specific local polarisation curve measurements. This approach is successfully illustrated by measuring and interpreting local polarisation curves from steel surfaces exposed to waterline corrosion environment, where highly localised corrosion processes occur.

Role of second phases in the corrosion resistance and cerium conversion coating treatment of as-extruded Mg–8Al–4Ca magnesium alloy

The presence of a second phase in the Mg–8Al–4Ca (at. %) alloy plays a significant role on both its corrosion behavior and the chemical conversion coating processes. Using scanning Kelvin probe force microscopy (SKPFM), a lower Volta-potential of the second phase present on the surface has been measured. The β-Al-Ca phase has a higher electrochemical activity than the α-Mg matrix and may act as the micro-galvanic anode in a local electrochemical corrosion process. Transmission electron microscopy (TEM) examinations reveal that the β-Al-Ca phase is more susceptible to corrosion than the α-Mg matrix in an aqueous solution, and its higher activity and higher corrosion rate accelerate the hydrogen evolution rate on the α-Mg matrix in the cerium (Ce) conversion coating process. It's also been discovered that by immersing the bare Mg–Al–Ca alloy in deionized (DI) water, the β-Al-Ca phase, exposed on the surface, can be dissolved and converted in situ into aluminum hydroxide (Al(OH)3), and the Ce conversion coating can be deposited via replacement reactions in the subsequent conversion coating process. A thicker Ce coating with smaller blisters has then been produced on the DI-treated Ce-coated Mg specimen; it indeed improves the corrosion resistance.

Investigating local corrosion processes of magnesium alloys with scanning probe electrochemical techniques: A review

The study of corrosion of magnesium and its alloys has emerged a hot topic in the applications of lightweight structural materials. The inherently high electrochemical activity of bare magnesium surfaces still lacks a convincing mechanism to describe the observed experimental characteristics, and it has prompted the development of various types of protective coatings with the aim of slowing metal dissolution. In recent years, new instruments and techniques have been developed to study with spatial resolution the local corrosion processes that occur in metallic materials in general, and for magnesium and its alloys in particular, both for bare surfaces and coated. Scanning microelectrochemical techniques, such as local electrochemical impedance spectroscopy (LEIS), scanning electrochemical microscopy (SECM), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) and scanning Kelvin probe (SKP) can provide information about the local electrochemical activity of metallic surfaces. In the present work, the applications of these techniques in corrosion studies of magnesium and its alloys are reviewed. Assessment of corrosion mechanisms, barrier properties of conventional coatings and active corrosion behavior of self-healing coatings are examined. Limitations and future developments in this area are discussed.

(Digital Presentation) The Effect of Tartaric-Sulfuric Acid (TSA) Anodizing on the Corrosion Resistance of the AA7475-T761

The microstructure of the high strength aluminum alloy, AA7475–T761, in the as-received condition was characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy, and statistical analyses of grain size and micrometer precipitates distribution and density were performed. An anodic aluminum oxide (AAO) film was potentiostatically grown on the alloy in tartaric sulfuric acid (TSA). The anodizing behavior of the alloy and the mechanisms of localized corrosion initiation and propagation in bare (not anodized) and anodized conditions were discussed. The alloy corrosion behavior was investigated in sodium chloride solutions using electrochemical techniques (cyclic potentiodynamic polarization) and the morphology and extent of corrosion propagation was investigated through optical microscopy, optical profilometry and scanning electron microscopy analyses. It was observed that the two alloy surface conditions (bare and anodized) play different roles in the propagation of the localized corrosion process. The bare alloy presented lower localized corrosion potentials and the propagation of the localized corrosion was shallower, but more heavily distributed, than in the anodized condition. However, the alloy in the anodized condition presented lower repassivation potentials due to the deeper pits formed. In addition, the variability of pitting potentials for the anodized condition was high, due to the heterogenous structure of the AAO film formed, and dependent on the time and drying storage conditions previous to electrochemical characterizations. The electrochemical results were correlated with the microstructural characteristics of the oxide surface film of the alloy in both conditions, bare (not anodized) and anodized.

In-situ AFM and quasi-in-situ studies for localized corrosion in Mg-9Al-1Fe-(Gd) alloys under 3.5 wt.% NaCl environment

Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance. The reliable monitor should be high distinguishability and real-time in liquid environment. Herein, Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour. In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys. SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys, and their volta potentials were measured by SKPFM. According to the real-time and real-space in-situ AFM monitor, the corrosion process consisted of dissolution of anodic α-Mg phase, accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase. Then, the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.

Contributions of Microelectrochemical Scanning Techniques for the Efficient Detection of Localized Corrosion Processes at the Cut Edges of Polymer-Coated Galvanized Steel

Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn2+ and OH− ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described.

Durability life prediction of RC piles subjected to localized corrosion in chloride environments

In this study, an analytical model for evaluating the durability life of reinforced concrete (RC) piles subjected to localized corrosion under chloride attack is proposed. The localized corrosion process is divided into three stages, and a predictive method is presented to predict the durability life of the pile by calculating the time of each stage. The time of each stage is determined based on the chloride diffusion model, the pitting corrosion model and the crack propagation model. The effects of the water-cement ratio, concrete cover thickness, pile concrete quality, relative humidity, chloride threshold level, pitting factor, corrosion current density and initial surface chloride ion concentration on the various stages of localized corrosion and the durability life of the pile are investigated. The analysis results show that the effects of the water-cement ratio and concrete cover thickness on the durability life of the pile are the most significant in the corrosion initiation stage. The durability life is increased by a reasonable choice of both concrete water-cement ratio and concrete cover thickness with constant concrete quality. The durability life of the pile increases with increasing concrete cover thickness, concrete quality, chloride threshold value and limit crack width, while it decreases with increasing water-cement ratio, relative humidity, corrosion current density and initial surface chloride concentration. The influence of the pitting factor is minimal and is mainly in the pit nucleation stage.

In Situ Atomic Force Microscopy Analysis of the Corrosion Processes at the Buried Interface of an Epoxy‐like Model Organic Film and AA2024‐T3 Aluminum Alloy

The application of characterization methods with high spatial resolution to the analysis of buried coating/metal interfaces requires the design and use of model systems. Herein, an epoxy‐like thin film is used as a model coating resembling the epoxy‐based coatings and adhesives widely used in technical applications. Spin coating is used for the deposition of a 30 nm‐thin bilayer (BL) composed of poly‐(ethylenimine) (PEI) and poly[(o‐cresyl glycidyl ether)‐co‐formaldehyde] (CNER). Fourier‐transform infrared spectroscopy (FTIR) results confirm that the exposure of coated AA2024‐T3 (AA) samples to the corrosive electrolyte solution does not cause the degradation of the polymer layer. In situ atomic force microscopy (AFM) studies are performed to monitor local corrosion processes at the buried interface of the epoxy‐like film and the AA2024‐T3 aluminum alloy surface in an aqueous electrolyte solution. Hydrogen evolution due to the reduction of water as the cathodic corrosion reaction leads to local blister formation. Based on the results of the complementary energy‐dispersive X‐ray spectroscopy (EDX) analysis performed at the same region of interest, most of the hydrogen evolved originates at the vicinity of Mg‐containing intermetallic particles.

Roles of Sb addition on the corrosion resistance of the low‐alloy steel in a real tropical marine atmosphere

AbstractThe corrosion behaviors of Sb‐free and Sb‐added low‐alloy structural steels were comparatively studied in a real tropical marine atmosphere. And the role of Sb addition on corrosion resistance was clarified by electrochemical measurement and rust analysis. The results showed that the addition of 0.05% Sb increased the polarization resistance, reduced the cathodic current density, and slowed down the oxygen reduction process. Meanwhile, Sb addition optimized the physical structure, promoted the transformation of phase, and improved the protection of the rust. More importantly, 0.05% Sb addition inhibited the local acidification at the bottom of the pits, thus slowing down the local corrosion process at the rust/matrix interface. Accordingly, the corrosion resistance of the Sb‐added low‐alloy steel was enhanced, causing a lower corrosion rate than that of Sb‐free steel in a tropical marine atmosphere.