Electrochemical Noise Technique Research Articles

Corrosion Behavior of Carbon Steel in LiCl/H2O Mixtures

The corrosion behavior of 1018 carbon steel in LiCl/H2O mixtures has been evaluated by using potentiodynamic polarization curves, electrochemical noise and electrochemical impedance spectroscopy techniques. Two different concentrations of LiCl were employed, namely 35 and 40 wt. %, and the testing temperatures included 25, 35 and 70 °C. It was found that the steel showed a passive zone; the corrosion current density value increased with an increase in the solution temperature and concentration. The pitting potential value decreased with an increase in the testing temperature and the solution concentration. The corrosion process was under charge transfer control. This mechanism was unaltered either by the solution temperature or concentration. The charge transfer resistance value decreased with an increase in both the solution temperature and concentration. A localized, pitting type of corrosion dominated the corrosion morphology at 25 and 35 °C, whereas at 70 °C, the main type of attack was a mixed type of corrosion.

Identification of carbonation‐induced corrosion of steel in concrete by electrochemical testing

AbstractCarbonation‐induced corrosion of steel in concrete can allow for premature degradation of structures. Corrosion probes in health monitoring systems can assess concrete carbonation and steel corrosion rates. The electrochemical noise (EN) technique has advantages for corrosion sensing. Instrumented concrete columns were fitted with a carbonation chamber for accelerated testing. EN was assessed through statistical evaluation of noise time signatures, noise resistance, and spectral analysis. The mean noise potential for the electrodes showed electronegative potential and correspondingly high rms noise current, indicative of corrosion activation in carbonated concrete. The estimated corrosion rates obtained from the noise impedance were comparable to those resolved from the polarization resistance and noise resistance. The shot noise analysis indicated isolated spontaneous noise events associated with the activation of local steel anodes. The outcomes of the testing indicate that the placement of low‐cost sensors and passive EN measurements can be used to monitor the onset of carbonation‐induced corrosion of steel in concrete and provide estimates on corrosion rates.

Data Mining Applied to the Electrochemical Noise Technique in the Time/Frequency Domain for Stress Corrosion Cracking Recognition

In this paper, time/frequency domain data processing was proposed to analyse the EN signal recorded during stress corrosion cracking on precipitation-hardening martensitic stainless steel in a chloride environment. Continuous Wavelet Transform, albeit with some limitations, showed a suitable support in the discriminatory capacity among transient signals related to the different stress corrosion cracking mechanisms. In particular, the aim is to propose the analysis of electrochemical noise signals under stress corrosion cracking conditions in the time–frequency domain by using the Hilbert–Huang approach. The Hilbert–Huang Transform (performed by the Empirical Mode Decomposition approach) was finally proposed to carry out an identification of the corrosion mechanisms in comparison to conventional data processing methods. By using this approach, a detailed simultaneous decomposition of the original electrochemical noise data in the time and frequency domain was carried out. The method gave useful information about transitions among different corrosion mechanisms, allowing us to (i) identify a specific characteristic response for each corrosion damaging phenomenon induced by stress corrosion cracking, (ii) time each corrosion of the damaging phenomenon, and (iii) provide a topological description of the advancing SCC damaging stages. This characteristic evidences that the Hilbert–Huang Transform is a very powerful technique to potentially recognize and distinguish the different corrosion mechanisms occurring during stress corrosion cracking.

Understanding the galvanic corrosion of Cu-Ni alloy/2205 DSS couple using electrochemical noise and microelectrochemical studies

Microscopic aspects of electrochemical reactions in a B10 Cu-Ni alloy/2205 duplex stainless steel (DSS) galvanic couple immersed in NaCl solution were investigated by electrochemical noise (EN) technique, scanning kelvin probe force microscopy (SKPFM), scanning vibrating electrode technology (SVET) as well as by scanning electron microscopy (SEM) method. Wavelet analysis by EN technique and microscopic characterization showed that the galvanic corrosion process can be divided into five detail stages. SKPFM and SEM observations revealed that the B10 Cu-Ni alloy/2205 DSS is a small-scale B10/ferrite/austenitic galvanic corrosion system that reduces the resistance of 2205 DSS to pitting attack.

Investigation of the Effect Chloride Ions on Carbon Steel in Closed Environments at Different Temperatures

This paper investigated carbon steel corrosion in an enclosed environment, where one set of steel was immersed in 3.5 wt.% NaCl solution and another exposed to humid (condensation) conditions. The study employed electrochemical noise and electrochemical impedance spectroscopy techniques to monitor real time corrosion behaviour. The samples were evaluated with surface characterisation techniques including optical light microscope, scanning electron microscope with energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results showed that carbon steel immersed in the liquid phase at a constant temperature exhibited the highest weight loss. However, the carbon steel exposed to water condensation (gas phase) at 80 °C manifested extensive localised corrosion. EN results agreed with the microscopy findings.

Effect of loading conditions on corrosion fatigue process of FSW AA6061-T6 joint in 3.5% NaCl studied by electrochemical noise

Electrochemical noise (EN) signals generated during corrosion fatigue (CF) process of friction stir welded (FSW) AA6061-T6 joints in 3.5 wt% NaCl solution under different loading conditions were monitored. Wavelet analysis and cumulative probability calculations showed that the increase in peak stress, stress ratio and stress frequency all lead to a decrease in Rn and an increase in the incubation rate of local events. Under current experimental conditions, the influence of peak stress is the most significant, while the influence of frequency is the least. The combination of EN signal analysis and transmission electron microscopy (TEM) observations indicates that the coarsening of β′ phase and the extensive dissolution of β'' phase are the main reasons for preferential failure in the weakest heat affected zone. The main contribution of this study is preliminary investigating the CF behavior of FSW AA6061 joints under different low cycle fatigue conditions. Moreover, EN is an effective strategy for monitoring CF process and establishes a connection between an alternative EN technique and in-situ CF behavior research.

Short communication: Stockwell transform as an alternative method for the corrosion rate evaluation of 6061-T6 aluminum alloy

In this communication, the results of the corrosion rate analyses on 6061-T6 aluminum alloy submerged in sulfuric acid (H2SO4), sodium chloride (NaCl), and demineralized water (diH2O) are presented and evaluated. The analyses were performed using the electrochemical noise technique and applying the Stockwell transform and the spectral noise impedance method. The results showed that the corrosion rate evaluation calculated by the Stockwell transform is very similar to those results obtained with the fast Fourier transform, statistical method, and mass loss method.

Corrosion Fatigue Analysis in Power Steam Turbine Blade

The corrosion fatigue behavior of a martensitic stainless steel AISI 410 with 12% Cr, used in the fabrication of steam turbine blades at low pressure (L-P), was studied using the electrochemical noise technique (EN) under mechanical fatigue (immersion and aired) conditions. The tests were done in a simulated environment using four levels of mechanical stress (Δσ) in a 3 wt.% NaCl solution at 90 °C. The specimens underwent pitting corrosion when exposed to the corrosive environment; afterwards, such pits generated mechanical strength sites over the metallic surface, facilitating the initiation and propagation of cracks, which was already enhanced by the applied cyclic loads. From scanning electron microscope (SEM) images, it was possible to observe localized plastic deformation. In such instances, the fatigue damage was caused by the microplasticity (μ), i.e., the shear strength, resulting from the breakdown of the passive layer that was subjected to mechanical load, which led to a significant increment of the velocity of crack propagation, and therefore, a decrement of the useful life of the material. The obtained results show that the fatigue resistance limit in the corrosive medium was lower than that observed in aerated conditions due to the sum of the effects of mechanical fatigue and corrosion.

Electrochemical noise energy generated by nickel electroplating process

AbstractThe effects of current density (Jk) and bath temperature on the structure of deposition layer of nickel and electrochemical noise energy (ED) are studied, and the relationship between the structure of the deposit and ED is also discussed in detail using electrochemical noise technique in coupled with the scanning electron microscopy and the glancing angle X-ray diffraction techniques. The results show that ED theoretically mainly reflects the severity or rate of the local cathodic reaction rather than the integral cathodic reaction, and is markedly influenced by the electroplating current density (Jk)-depended nucleation/growth kinetics of the nickel deposit film. The proceeding of the nucleation (or the formation of new phase)/growth process of crystal nucleus on a foreign substrate possesses much more effect on ED value than the subsequent homogenous growth of the already formed film particles, and the factors which can accelerate the drastic change of the electrode surface state should result in large ED value.

Effect of Heat Treatment on the Electrochemical Behavior of AA2055 and AA2024 Alloys for Aeronautical Applications

Since their development, third-generation aluminum–lithium alloys have been used in aeronautical and other applications due to their good properties, replacing conventional Al-Cu and Al-Zn alloys and resulting in an increase in payload and fuel efficiency. The aim of this work was to investigate the influence of different heat treatments on the electrochemical corrosion behavior of the alloys AA2055 and AA2024 in the presence of three different electrolytes at room temperature, using an electrochemical noise (EN) technique in accordance with the ASTM-G199 standard. In the time domain, the polynomial method was employed to obtain the noise resistance (Rn), the localization index (IL), skewness, and kurtosis, and in the frequency domain, employing power spectral density analysis (PSD). The microstructure and mechanical properties of the alloys were characterized using scanning electron microscopy (SEM) and the Vickers microhardness test (HV). The results demonstrated better mechanical properties of the AA2055 alloy, which had a Vickers hardness of 77, 174, and 199 in the heat treatments T0, T6, and T8, respectively. An electrochemical noise resistance (Rn) of 2.72 × 105 Ω·cm2 was obtained in the AA2055 T8 alloy evaluated in a NaCl solution, while the lowest Rn resistance of 2.87 × 101 Ω·cm2 occurred in the AA2024 T8 alloy, which was evaluated in a HCl solution. The highest electrochemical noise resistance (Rn) was obtained in the AA2055 alloys, which had received the T6 and T8 heat treatments in the three solutions.

Corrosion mechanism of advanced high strength dual-phase steels by electrochemical noise analysis in chloride solutions

The corrosion behavior of ferrite-martensite and ferrite-bainite dual-phase steels in NaCl, CaCl2, and MgCl2 solutions was studied by cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN) techniques. The results showed a trend for mixed corrosion due to no passivation by a protective oxide layer. For the ferrite-martensite dual-phase steels, the ferrite phase was preferentially corroded compared with the martensite phase in test solutions. Bainite-microstructure in ferrite-bainite dual-phase steels was preferentially corroded compared with ferrite-phase in CaCl2 and MgCl2 solutions. The corrosion behavior in test solutions in dual-phase steels could be divided into three steps: dissolution in anodic-phase/microstructure, non-uniform corrosion, and localized corrosion. The results indicated that factors such as galvanic coupling between ferrite/martensite, ferrite/bainite, metallic-matrix/inclusion-phases, metallic-matrix/secondary phases, and self-corrosion of each phase and microstructure contributed to the non-uniform and localized corrosion in dual-phase steels.

Advancing the mechanistic understanding of corrosion in supercritical CO2 with H2O and O2 impurities

The effects of impurities H2O and O2 in transported s-CO2 on the corrosion modes and kinetics of pipeline steels were investigated using rotating cage methodology and in-situ electrochemical noise (EN) technique in an autoclave. In s-CO2 with H2O and O2, pressure acts as a key factor on the solubility of H2O in s-CO2 and corrosion extents, and there is a threshold pressure (∼10 MPa) above which corrosion rate remarkably increases with pressure. In-situ EN results in different CO2 environments further reveal that corrosion in s-CO2 with H2O and O2 is dominated by gas chemical reactions rather than electrochemical reactions.

Analysis of electrochemical current noise data arising from corrosion of Al alloy in a gel electrolyte by wavelet and recurrence methods

Gel electrolytes are preferred to liquid electrolytes due to the slower movement of ions, thereby lower damage. However, the use of gel electrolytes causes an increase in corrosion susceptibility due to the non-flat surfaces of cells. The use of corrosion inhibitors is one of the most practical methods for corrosion protection. The effect of penicillin as an inhibitor in a gel electrolyte containing 3.5% NaCl was investigated on the corrosion of 6061 Al alloy. Both electrochemical impedance spectroscopy (EIS) and electrochemical current noise (ECN) techniques were employed for data collection. The ECN data were analyzed by both the wavelet transform and the recurrence methods. According to EIS data, the inhibition efficiency (IE) increased from 77% to 94% for up to 15 days. The IE values obtained from ECN data increased from 81% to 90% over immersion time. The recurrence plots of the blank sample proved the increase of pit density with increasing the immersion time from 1 day to 15 days. However, the SDPS plots of the blank sample showed an increase of pit size with increasing the immersion time from 1 to 15 days. The recurrence plots proved the inhibition effect of penicillin on the corrosion of Al alloy that is apparent from the significant lowering of vertical black lines.

Localized corrosion of steel in alkaline solution with low-level chloride and elevated sulfate concentrations

Localized corrosion developed on post-tensioned steel strand in deficient grout, relating to elevated concentrations of sulfate ions. The deficient grout can also have low-level chloride ion concentrations below threshold values originating from the base materials. Open-circuit potential, linear polarization resistance (LPR), and electrochemical noise (EN) measurements were made on steel specimens exposed in saturated calcium hydroxide solution with 0.012 M Cl−, 0.04 M SO42−, or combined. Results showed that the combined presence of sulfates in low-level chloride alkaline solutions elevated the corrosion rate and the extent of corrosion pitting. The EN technique was shown to provide corrosion rate estimates consistent with LPR and was able to identify pitting characteristics. The outcomes of the research provides supporting evidence that analysis of deficient grout for chlorides alone may not capture the risk for corrosion and that corrosion associated with elevated sulfate concentrations can be exacerbated in presence of low-level chlorides.

Effect of heat treatments on metastable pitting of 316L stainless steel fabricated by selective laser melting

Effect of heat treatments on metastable pitting of 316L stainless steel fabricated by selective laser melting (SLM) was studied by scanning electron microscopy, potentiodynamic polarization, electrochemical noise (EN) and transient analysis techniques. The results show that the selective laser melted (SLMed) 316L stainless steel was composed of honeycomb cells with different orientations, and a small number of lack-of-fusion (LOF) pores were randomly distributed. After heat treatment, the honeycomb-like cellular structure transformed into austenite structure, and the non-metallic inclusions coarsened and grew. Non-metallic inclusions can be divided into two types according to the composition difference, one was manganese silicate enriched by Mn, Si and O and the other was MnS coexisted with the manganese silicate. The potentiodynamic polarization results show that the pitting potential of SLMed 316L stainless steel decreased after heat treatment. During the EN tests, three kinds of current transient were found, which corresponded to the metastable pitting initiated by the manganese silicate oxide inclusions, MnS coexisted with the manganese silicate and pore defects, respectively. Statistical analysis results of the transient signals show that the heat treatment reduced the nucleation rate of metastable pitting, and increased the transient amplitude, pit radius and pit stability product. The decreased pitting performance after heat treatment can be attributed to the low pit growth resistance.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Identification of steel corrosion associated with sulfate‐reducing bacteria by electrochemical noise technique

AbstractDeterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate‐reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.

Interpreting electrochemical noise signal arising from stress corrosion cracking of 304 stainless steel in simulated PWR primary water environment by coupling acoustic emission

Electrochemical noise (EN) signals arising from stress corrosion cracking (SCC) of 304 stainless steel (SS) in borated and lithiated high-temperature water were monitored. Acoustic emission (AE) signals were simultaneously measured to relate the EN signals with the SCC process. Through Weibull analysis of the EN signals, it was demonstrated that the EN technique can in-situ capture the SCC events in high-temperature water. With evolution of the SCC process, Hilbert time-frequency spectrum of the EN signals gradually migrated from high frequency to low frequency. The capacity of EN and AE techniques to monitor the SCC process in high-temperature water is compared.

Electrochemical noise studies on localized corrosion of Ni and Ni-20Cr in molten ZnCl2

The electrochemical noise (ECN) technique was employed to study corrosion of two model systems, i.e. pure Ni and a binary Ni-20 wt%Cr (Ni20Cr) alloy in molten ZnCl2 at 623 K. We measured ECN transients in current and open-circuit potential from two nominally identical Ni-Ni and Ni20Cr-Ni20Cr electrodes and one galvanic Ni-Ni20Cr electrode pair. The behavior of ECN is quite distinct among the three-electrode systems, and it is correlated with the various microscopic observations of micro- and nano-scale morphological features. Based on the ECN study coupled with the microstructural analysis, the origins of ECN in the molten salt environment as well as the mechanisms of localized corrosion in the three systems are discussed.

Plastic injection molding dies using hybrid additively manufactured 420/CX stainless steels: electrochemical considerations

This research focused on the corrosion resistance and microstructure of hybrid additively manufactured (HAM) samples of AISI 420/CX (420/CX SS) stainless steels. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analyses as well as the electrochemical noise (EN) technique were used to evaluate the electrochemical behavior of the as-built and heat-treated HAM parts in NaCl solution. The results showed a more protective passive layer formed on the CX SS side. The distribution of Cr-rich M23C6 carbides in matrix of 420 SS side resulted in a lower corrosion resistance compared to the CX SS side. The noise data analysis confirmed an increase in the galvanic currents of the HAM parts after heat treatment. The stochastic analysis revealed the interface in the heat-treated condition increases pit growth more than the as-built one due to the evolution of nano-sized intermetallic compounds of Al-N/ (Cr, Nb) (N, C) at the heat-treated interface area.