Propagation Of Localized Corrosion Research Articles

Effect of Microstructure on Corrosion Behavior of Cold Sprayed Aluminum Alloy 5083

This paper investigates the effect of the microstructure on the corrosion behavior of cold sprayed (CS) AA5083 compared to its wrought counterpart. It has been shown that the microstructure of CS aluminum alloys, such as AA2024, AA6061, and AA7075, affects their corrosion behavior; however, investigations of the corrosion behavior of CS AA5083 with a direct comparison to wrought AA5083 have been limited. The microstructure and corrosion behavior of CS AA5083 were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), electrochemical and immersion tests, and ASTM G67. The CS process resulted in microstructural changes, such as the size and spatial distribution of intermetallic particles, grain size, and misorientation. The refined grain size and intermetallic particles along prior particle boundaries stimulated the initiation and propagation of localized corrosion. Electrochemical tests presented enhanced anodic kinetics with high pitting susceptibility, giving rise to extensive localized corrosion in CS AA5083. The ASTM G67 test demonstrated significantly higher mass loss for CS AA5083 compared to its wrought counterpart due to preferential attack within prior particle boundary regions in the CS microstructure. Possible mechanisms of intergranular corrosion (IGC) propagation at prior particle boundary regions have been discussed.

PREDICTION OF ELECTROCHEMICAL PROCESSES OF LOCAL DISSOLUTION OF STAINLESS STEELS. PART 1. SPECTRAL –FREQUENCY ANALYSIS OF POTENTIAL FLUCTUATIONS

The propagation of localized corrosion of stainless steels was investigated by spectral frequency analysis (HPA) of potential fluctuations in the modes of stationary and cyclic galvanostatic polarization. Corrosion-resistant austenitic and austenitic-ferritic chromium-nickel steels were studied: 12X18N10T, 10X17N13M2T, 08X22N6T, resistant to pitting corrosion, in an aqueous solution of 0.1 M NaCl with a cyanide-containing complexing agent, a corrosion stimulator - 0.01 g/l (K3[Fe(CN)6]). The studies were carried out in the range of low densities (0.5–10 µA /cm2) due to the small values of the limiting diffusion current density in oxygen. To find the time of the origin of macropittings, it is proposed to use the NAV of chronopotentiograms with their subsequent statistical processing (Fourier transform). It has been established that fluctuations in the boundary polarization regime are characteristic of the process of the origin, development and passivation of macropittings. In the mode of stationary galvanostatic polarization, frequency characteristics were studied in the range of 1.0 ± 0.5 µA/cm2. When analyzing spectral density graphs, it was found that the dominant frequency characterizes the time of formation of the macropitting, and the sections of the chronopotentiogram should be divided into sections with a duration of no more than 50-100 s. In non-stationary conditions of galvanostatic polarization in the range of 1.0-10 µA/cm2 in a cyclic mode, it was found that the processes of nucleation and passivation of macropittings can be traced with a changing value of the polarizing current. Based on the frequency range of chronopotentiograms, it was found that the average macropitting lifetime is 250-300 s (frequency range 0.033 - 0.004 Hz). The dominant frequencies are determined to identify the characteristic dependencies of the envelopes along the upper (fhg) and lower (fhg) boundaries of the potential change, based on them, an algorithm is proposed for selecting the values of the parameters of the prediction mode of the formation of macropitting processes.

Localized corrosion propagation of steel in cracked mortar and long-term corrosion of steel reinforcement in cracked concrete in seawater environment

A custom-designed wire beam electrode (WBE) covered by cracked mortar was applied to study the localized corrosion propagation of steel reinforcement in seawater. Additionally, steel-reinforced concrete specimens with cracks were monitored by EIS methods to study the long-term corrosion of steel in a real marine environment for 1920 days. The results revealed that corrosion initiates from the crack and then propagates to other electrodes through the steel-mortar interface. The number of anodic areas first increases and then decreases. The corrosion current density of steel reinforcement in cracked concrete increases exponentially with prolonged exposure time in a real marine environment.

Localized Corrosion Behavior and the Relationship to the Second Phases in Biodegradable ZX21 Mg Alloy in Hanks' Balanced Salt Solution

Mg alloys are considered promising biodegradable implant materials owing to their high activity, which makes Mg alloys degradable in the human body and can avoid second removal surgeries. Also, compared with other biodegradable implant materials, Mg alloy has a similar density and Young’s modulus to human bones, which minimizes the stress shielding effect. ZX series Mg alloys, which contain Zn and Ca, are designed to increase the alloy strength but maintain biocompatibility. However, even with all the advantages, the high degradation rate limits the clinical applications of ZX series Mg alloys. With fast degradation, not only the mechanical properties are affected, but also a large amount of hydrogen gas and hydroxide ions would accumulate around the implant in the patient. Therefore, it is essential to investigate the corrosion mechanism of the ZX series Mg alloys to mitigate the degradation rates.Localized corrosion is one of the noticeable features in the corrosion process of ZX series Mg alloys, which is the main reason for the low corrosion resistance and high degradation rate of the alloy. However, the origin and detailed mechanism of the initiation and propagation of localized corrosion on ZX series Mg alloys are still unclear. The second phases, which contain Zn and Ca, play complex roles in the corrosion process owing to the inhomogeneous elemental distribution and different electrochemical potentials with respect to the Mg alloy matrix. Thus, this study aims to investigate the microstructure of the localized corrosion sites and the galvanic effects around the second phases in a ZX series Mg alloy.In this study, an Mg-2 wt%Zn-1 wt%Ca (ZX21) alloy was prepared, and the localized corrosion behavior was investigated in a Hanks’ balanced salt solution (HBSS) at 37°C. By scanning electron microscope (SEM)/focused ion beam (FIB) cross-sectional observations, two kinds of second phases were identified in the ZX21 Mg alloy, one is enriched with Zn and the other is not. After immersion in HBSS, galvanic corrosion sites were found in the Mg alloy matrix next to the second phase enriched with Zn, while the Mg alloy matrix next to the second phase with lower Zn concentration was intact. Furthermore, the second phases in the ZX21 Mg alloy were found to hinder the propagation of localized corrosion. The complex roles of the second phases in the ZX21 Mg alloy on the localized corrosion behavior will be discussed based on electrochemical measurements and microstructure characterizations. Figure 1

Inhibition of Localized Corrosion Propagation on Carbon Steel: A Potentiostatic Study

The occurrence of localized corrosion in carbon steel pipelines, even when the uniform corrosion rate remains low, is a major concern in the hydrocarbon production and transmission industry. The propagation of these pits, caused by the galvanic coupling between the inhibited surface and the active pit, can lead to serious consequences such as financial loss, environmental damage, production interruption, and even loss of life. To better understand this phenomenon, this work focuses on using the potentiostatic technique to evaluate the tendency of localized corrosion propagation. The experiments were conducted using a primarily imidazolinium-based corrosion inhibitor in produced water conditions (5 wt% NaCl, pH 4.5, CO2-saturated) at 55°C and 80°C. The baseline results were obtained through linear polarization resistance and potentiodynamic polarization tests. The potentiostatic experiments were then conducted to artificially simulate different levels of galvanic coupling that could exist in case of active localized corrosion. The results showed that, at certain anodic potentials, increased inhibitor dosage was necessary to significantly decrease the current. However, at high current levels, further injections were insufficient, indicating that substrate dissolution may affect the adsorption of the inhibitor. This work provides insights into the role of inhibitors and important factors in stopping the propagation of localized corrosion of carbon steel. Further research, such as designing a proper zero-resistance ammeter setup, will be necessary to fully understand this complex phenomenon. The results show that the potentiostatic methodology can be a rapid and easy alternative to obtain electrochemical information and improve understanding of localized corrosion propagation.

Performance of a Volatile Corrosion Inhibitor for Mitigating Corrosion Under Insulation

This study evaluated the efficacy of a commercial volatile corrosion inhibitor (VCI) in mitigating the corrosion of carbon steel insulated with mineral wool insulation, especially as a retrofitted solution to corrosion under insulation (CUI) management. When VCI was added in dry insulation before the test solution was introduced, the severity of CUI was reduced after 14 d of exposure. However, when the exposure time was extended to 90 d, no significant mitigation effect was observed. Furthermore, VCI was ineffective when added to precorroded insulated systems, indicating that it could not be used as a retrofitted solution to alleviate CUI problems. A separate set of tests with bare steel samples exposed to 10 mL VCI in closed jars showed that VCI was adsorbed on the corrosion products but could not effectively impede the propagation of localized corrosion. The possible influences of insulation jacketing, insulation properties, VCI dosages, and dosing methods were also discussed, suggesting the need for further investigations.

Initiation and Propagation of Localized Corrosion on Cold-Sprayed Aluminum Alloy 2024 and 7075

This paper investigates the initiation and propagation of localized corrosion on cold-sprayed (CS) aluminum alloy 2024 and 7075 deposits. CS deposits on AA2024-T351 and AA7075-T651 substrates were produced with commercially available AA2024 and AA7075 powders using helium as carrier gas. Electrochemical and immersion tests in 0.6 M NaCl and ASTM G110 test were used to evaluate the corrosion properties of CS AA2024 and AA7075 deposits. For analysis, optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction were utilized before and after the experiment. The results indicated that the initiation and propagation of localized corrosion highly depend on microstructural characteristics, such as the distribution and chemical composition of intermetallic networks with the matrix and propagated along these networks and prior particle boundaries, where an ultrafine grain structure is present. Accelerated localized corrosion tests generated deep penetration as well as a large area of defects owing to the coalescence of fissures.

Corrosion propagation monitoring using electrochemical noise measurements on carbon steel in hydrogenocarbonated solution containing chloride ions

The propagation of localized corrosion on API 5L X65 carbon steel in hydrogenocarbonated solution containing chloride ions was monitored during long immersion times by electrochemical noise (EN) measurements in ZRA mode. Monitoring corrosion propagation from the EN amplitude is possible but interpreting the potential and current transients after long immersion times is made difficult by the different corrosion processes (metastable or stable pits, crevices, corrosion products detachment…) occurring simultaneously. The noise impedance at 0.1 Hz, directly derived from the EN measurements, is shown to decrease and stabilize in the same time scale as the coupled potential of the electrodes.

Investigation of the evolution of an iron carbonate layer and its effect on localized corrosion of X65 carbon steel in CO2 corrosion environments

The general and localized corrosion of X65 carbon steel in CO2-saturated environments conducive to iron carbonate (FeCO3) formation has been studied using electrochemical measurements, together with post-test surface analysis. This research offers new insights into the evolution of FeCO3 layer and its link to the subsequent initiation and propagation of localized corrosion. We identify crevice-like regions forming at boundaries/edges of the FeCO3 crystals, which constitute the crystalline layer, where small cavities filled with electrolyte are restricted between developing crystals. It is apparent that such crevice-like features act as precursors to the localized/pitting corrosion on carbon steel over longer durations. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Effect of Microstructural Bands on the Localized Corrosion of Laser Surface-Melted 316L Stainless Steel

The localized corrosion of laser surface melted (LSM) 316L stainless steel is investigated by a combination of potentiodynamic anodic polarization in 0.1 M HCl and microscopic investigation of the initiation and propagation of localized corrosion. The pitting potential of LSM 316L is significantly lower than the pitting potential of wrought 316L. The LSM microstructure is highly banded as a consequence of the high laser power density and high linear energy density. The bands are composed of zones of changing modes of solidification, cycling between very narrow regions of primary austenite solidification and very wide regions of primary ferrite solidification. Pits initiate in the outer edge of each band where the mode of solidification is primary austenite plane front solidification and primary austenite cellular solidification. The primary austenite regions have low chromium concentration (and possibly low molybdenum concentration), which explains their susceptibility to pitting corrosion. The ferrite is enriched in chromium, which explains the absence of pitting in the primary ferrite regions. The presence of the low chromium regions of primary austenite solidification explains the lower pitting resistance of LSM 316L relative to wrought 316L. The influence of banding on localized corrosion is applicable to other rapidly solidified processes such as additive manufacturing.

Initiation and propagation of localized corrosion induced by (Zr, Ti, Al)-Ox inclusions in low-alloy steels in marine environment

The effects of inclusions on localized corrosion of Zr–Ti deoxidized low-alloy steels in marine environment were investigated by various analytical techniques including scanning electron microscopy with X-ray microanalysis (SEM/EDS), confocal Raman microscopy (CRM), and in situ scanning vibrating electrode technique (SVET). It was found that complex (Zr, Ti, Al)-Ox inclusions were responsible for the initiation of localized corrosion. Localized corrosion preferentially occurred at Fe matrix adjacent to these inclusions and formed micro-gaps. In the early stage of corrosion, catalytic-occluded cells and the diffusion of chloride ions played a major role in the propagation of corrosion, further accelerating the dissolution of Fe matrix and (Zr, Ti, Al)-Ox inclusions. Combining SVET and CRM results, it revealed that the maximum anodic current density in local area gradually decreased with prolonged exposure time, indicating that corrosion products covered the steel surface and lowered the propagation rate of corrosion. In the later stage of corrosion, the barrier effect of corrosion products played an important role in inhibiting localized corrosion.

Corrosion behavior of anodized Al-Cu-Li alloy: The role of intermetallic particle-introduced film defects

The role of intermetallic particle (IMP)-introduced anodic film defects in the initiation and propagation of localized corrosion in an anodized Al-Cu-Li alloy prior to sealing is investigated. Anodizing of IMPs results in cavity defects of micrometer-scale in the anodic film. Corrosion is preferentially initiated in the regions with anodized IMPs at the film/alloy interface. Localized corrosion then propagates in the alloy substrate beneath the anodic film, which ultimately results in cracking of the bulk anodic film. It is suggested that the barrier and porous layers of the anodic film play different roles in different stages of a localized corrosion event.

Galvanic corrosion of Ti6Al4V -AA2024 joints in aircraft environment: Modelling and experimental validation

This study focuses on the development of a physico-chemical model based on mechanistic and kinetics understanding of the corrosion process in galvanic couple Ti6Al4V-AA2024. Proposed model provides deeper insights at macro level for initiation and propagation of localized corrosion of AA2024 in galvanically coupled multi-material assemblies. The model is able to reveal the localized corrosion, related to heterogeneity of AA2024 microstructure, including local pH changes, the deposition of the reaction products, and emphasizes the important role of AA2024 self-corrosion in galvanic assemblies. The validation of the developed model was performed using relevant data collected by advanced in situ localized techniques.

Effects of heat treatment on the mechanical properties and corrosion behaviour of the Mg-2Zn-0.2Mn-xNd alloys

The selected-dissolution behaviour of metals after the film rupture determines the propagation of localized corrosion. Meanwhile, excessive Cl− aggregations and too fast resorption behaviour may prematurely lead to the loss of mechanical properties. In this study, the degradation behaviour and mechanical properties of the heat-treated Mg-2Zn-0.2Mn-xNd (MZM-xNd) in the simulated body fluid were analyzed using XRD, XPS, FT-IR, TEM, 3D/CLSM and AFM/SKPFM. Besides, the film formation and rupture mechanism were illuminated through the spectroscopic analysis, and its role on the propagation of localized corrosion was also discussed. The results demonstrate that the localized corrosion propagates inside the matrix (underneath the surface film layers) and exhibits a filiform-like corrosion morphology. Immersion and polarization tests together with morphology observations indicate that the MZM-0.6Nd has the moderate degradation rate by giving rise to the densification of the film layer, with the corrosion rate of 0.83 mm/y. However, the corrosion rate progressively increased (1.83 mm/y, 3.08 mm/y), as the Nd content increased (1.22%, 1.88%), due to the more large-size phases present in the matrix. It will exacerbate the corrosion resistance by facilitating the localized dissolution of the degradation layers, enhancing the adsorption for Cl− and promoting the mass transport, thereby retarding the self-healing capability and the occurrence of the localized corrosion. The significant improvement in mechanical strength of MZM-0.6Nd, with the ultimate tensile strength and elongation of 224 MPa and 19.2%, making it appear the ductile fracture feature with small dimples. It was attributed to the role of interactions with the fine-grained microstructure, the pinning dislocations, and the strengthening phases dispersedly distributed in the matrix.

Galvanic Corrosion between AA5052 Aluminum-Magnesium Alloy and SS400 Carbon Steel in Aqueous NaCl Solutions

Aluminum alloys (AAs) such as 5000 and 6000 series have relatively good corrosion resistance and plastic workability. The use of these alloys for automobile body parts have been increased significantly because of reducing the weight of the body and improvement of fuel consumption. Although aluminum alloys themselves have relatively good corrosion resistance in atmospheric environments, galvanic corrosion between aluminum alloys and other materials should be taken into consideration in automotive application. This is because the body parts made of Al alloys should be jointed with other materials such as steel parts by welding or other methods and because the jointed parts can be exposed to atmospheric corrosion environments. In this study, galvanic corrosion between AA5052 aluminum-magnesium alloy and SS400 carbon steel is investigated in aqueous NaCl solutions. A galvanic couple used in this study was made of AA5052 Al-Mg alloy (Mg: 2.65, Si: 0. 08, Fe: 0.27, Cu: 0.01, Cr: 0.17, Zn: 0.01, Al: bal. (mass%)) and carbon steel (JIS SS400). The plate of both materials was 10-mm width and 15-mm length and 3-mm thickness. After lead wire was connected on the surface of the plates, they were embedded in an epoxy resin. At this time, both materials were separated with a 500-um gap. The surface of the galvanic couple was polished with SiC papers up to JIS 2000 grit and rinsed in EtOH. Galvanic corrosion experiments were performed for 2 hours in aqueous NaCl solutions at various concentrations ranging from 5 mM to 500 mM. Galvanic current and corrosion potential of the couple were measured during the immersion in the solutions. Corrosion potentials measured during the immersion in various concentrations of NaCl were almost constant for 2 h. The corrosion potentials changed in the less noble direction with increasing NaCl concentrations. Galvanic currents between AA5052 and SS400 showed positive values during the immersion in the solutions, indicating that aluminum-alloy side was basically an anode. However, the galvanic currents were almost the same independent of NaCl concentrations. From the results of polarization behaviors for AA5052 and SS400, a significant anodic current increase due to the propagation of localized corrosion on aluminum alloy and a diffusion-limiting current for the reduction of dissolved oxygen on steel were observed at the corrosion potentials of the galvanic corrosion tests. These results indicated that galvanic corrosion between AA5052 and SS400 in the early stage of immersion progressed under a diffusion-limiting condition for the reduction of dissolved oxygen on steel.

The Influence of Chloride Ion Concentration on Passivity Breakdown in Magnesium

An empirically derived dependence of an apparent breakdown potential (Eb) of magnesium (Mg) on chloride ion concentration is reported. In situations where spontaneous breakdown in the absence of external polarization is observed, leading to the subsequent propagation of localized corrosion, Eb can be determined by following time-dependent changes in free corrosion potential (Ecorr). Breakdown of temporary passivity is marked by a clear inflection in the time-dependent value of Ecorr, characterized by a sharp decrease in potential from a maximum value where Ecorr = Eb. Characterization of localized corrosion behavior by in situ scanning vibrating electrode studies, prior to and following the point of breakdown, is used to explain the observed Ecorr vs. time characteristics. Examples of typical behavior upon immersion in aqueous solutions containing different chloride ion concentrations ([Cl−]) are given for commercially pure Mg and an AZ31 alloy. For high purity Mg, which remains passive at pH 11 at all ch...

Effect of Temperature on the Localized Corrosion of AA2024-T3 and the Electrochemistry of Intermetallic Compounds During Exposure to a Dilute NaCl Solution

In this study, the electrochemical properties of synthesized intermetallic compounds (IMCs) similar to those commonly found in AA2024-T3 were studied in neutral 0.1 M NaCl at 10, 30, 50, and 70°C using the electrochemical microcell method. Results on the synthesized IMCs were combined with and supported by analysis of free corrosion experiments performed on AA2024-T3. Results reveal that, in general, corrosion rates of the IMCs increase with temperature and pitting potentials of most IMCs show a slight decrease with temperature. Increased dealloying kinetics of S-phase with increasing temperature was evident in both open-circuit potential transients and post-exposure corrosion morphology characteristics, leading to increased Cu surface areas and a higher likelihood of the propagation of localized corrosion into the matrix. The corrosion potential of synthesized Al-Cu-Mn-Fe type particles was found to be cathodic to the matrix at low temperatures, but anodic to the matrix at high temperatures. This high-te...

Effect of Coastal Soil Environment on Localized Corrosion for Oil and Gas Pipelines

The direct cause for the explosion accident occurred by Dong Huang pipeline is that the corrosion of pipeline was enhanced by coastal soil, which in turn resulted in thinning and then cracking of the pipe. Because localized corrosion cracking in coastal soils is a serious threat to the integrity and security for the pipeline, the effect of the coastal soil environment on localized corro- sion for oil and gas pipelines was analyzed systematically. Typical corrosion environmental charac- teristics were acquired and then analyzed firstly for the specified coastal soil, which in general is rather different from the terrestrial soil and seabed soil distinctly. The coastal soil is characterized as a mixture of gas/liquid/solid multi-phases with high salt- and water-content and good air aera- tion, while it experiences dry-wet cycles periodically. The effect of the coastal soil environment on the initiation and propagation of localized corrosion for oil and gas pipelines is discussed. Finally, the trends and difficulties of the study in oil and gas pipeline localized corrosion are analyzed, and in the end, a scheme of micro-e electrochemical study is peculiarly prospected.

Influence of thermomechanical treatments on localized corrosion susceptibility and propagation mechanism of AA2099 Al–Li alloy

In order to manifest the influence of specific microstructural component on the development of severe localized corrosion in an AA2099 aluminum–lithium alloy, the corrosion behavior of the alloy subjected to solution heat treatment, cold working and artificial ageing was investigated. Immersion testing and potentiodynamic polarization were employed to introduce localized corrosion; scanning electron microscopy and transmission electron microscopy were used to characterize the alloy microstructure and corrosion morphology. It was found that the susceptibility of the alloy to severe localized corrosion was sensitive to thermomechanical treatments. Additionally, the state of alloying elements influenced the mechanism of localized corrosion propagation. Specifically, the alloy in T8 conditions showed higher susceptibility to severe localized corrosion than that in other conditions. During potentiodynamic polarization, the alloy in solution heat-treated and T3 conditions displayed crystallographic corrosion morphology while the alloy in T6 and T8 conditions exhibited selective attack of grain interiors and grain boundaries in local regions.

The propagation of localized corrosion in Al‐Cu‐Li alloy

The mechanism of localized corrosion in 2A97 aluminium alloy has been investigated. Electron backscatter diffraction analysis was performed at the localized corrosion site to determine the grain‐stored energy. The relationship between the grain‐stored energy, namely the population density of crystallographic defects, and the corrosion susceptibility of the alloy has been established. It was revealed that the grain boundaries that surrounded grains of relatively high stored energy were preferentially attacked. Intergranular corrosion could occur at grain boundaries where second phase precipitate was absent. Non‐uniform attack of the adjacent grain interior was also observed along the attacked grain boundary, with preferential dissolution of the grains with high stored energy. Copyright © 2015 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.