Corrosion Pits Research Articles

Investigation on the Corrosion Resistance of 3003 Aluminum Alloy in Acidic Salt Spray under Different Processing States

3003 aluminum alloy exhibits commendable corrosion resistance, ease of processing, and good formability, rendering it extensively utilized across many industrial sectors. In this study, the corrosion behavior of 3003 aluminum alloy in a homogenized state and after hot extrusion deformation in an acidic salt spray environment for different times was studied. The microstructure of the 3003 aluminum alloy in the homogenized state and after hot extrusion was characterized using scanning electron microscopy (SEM), optical microscope (OM), laser scanning confocal microscope (LSCM) etc., while electrochemical methods were employed to study the difference in corrosion resistance between these two states. The results show that corrosion pits on the surface of the homogenized 3003 aluminum alloy increase with time, and corrosion extends along the second phase arrangement, while the hot extruded 3003 aluminum alloy mainly exhibits corrosion pit extension. The grain size of the homogenized 3003 aluminum alloy is larger than that of the hot extruded state, and the second phase is distributed in a reticular pattern. Hot extrusion deformation ensures not only a uniform distribution of the second phase in the 3003 aluminum alloy but also a reduced grain size, an increased grain boundary density, a heightened electrochemical activity in acidic environments, and an augmented pitting density. Compared with the homogenized 3003 aluminum alloy, the pitting density, maximum pitting depth, and weight loss of the hot extruded state are increased.

Analytical modeling of particle size effect on impact wear deformation characteristics of ductile materials

AbstractThis study aims to analytically predict the material impact wear rate and improve the prediction accuracy and applicability of existing impact wear prediction models. The ABAQUS software was used to numerically model and analyze the erosion pit morphology and stress distribution characteristics. Micromorphological testing was used to investigate the impact wear damage mechanism, and an improved impact wear prediction model was developed by introducing the particle size. The results show that the maximum von Mises stress in the impact area of the target material can reflect the severity of the damage to the target material. The peak stress varies with the impact angle. The target material significantly absorbs the energy of small particles at higher impact angles and large particles at vertical impacts. The depth of the hardened layer resulting from particle impact increases from 3 to 10 μm with increasing impact angle. When the impact angle is unchanged, the depth of the hardened layer increases by 3% to 5% with an increase in particle size. The hardened layer limits further plastic deformation of the metal material. Comparing the analysis results with the experimental results reveals that the proposed formula that uses the size factor can predict the volume loss of plastic metallic materials with different particle sizes, impact angles, and impact velocities more accurately.

Study on corrosion characteristics of reinforcing bars in concrete under industrial SO2 environment

Sulfur dioxide (SO2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO2 corrosion utilizing an SO2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (Ecorr) and corrosion current density (icorr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe2O3), rozenite (FeSO4·4 H2O). The formation of FeSO4·4 H2O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO2.

Corrosion at the Steel–Medium Interface

Corrosion on the interface between a metal alloy, such as steel, and a wet, permeable non-metallic medium is of considerable practical interest. Examples include the interface between steel and water, the atmosphere or concrete, as for steel reinforcement bars; between metal and soil, as for buried cast iron or steel pipes; deposits of some type, as in under-deposit corrosion; and the interface with insulation, protective coatings, or macro- or micro-biological agents. In all cases, corrosion initiation depends on the characteristics of the interfacial zone, both of the metal and the medium, and the spatial variability. For (near-)homogeneous semi-infinite media with good interfacial contact, the pitting, crevices and general corrosion of the metal will be largely controlled by the metal (micro-)characteristics, including its inclusions, imperfections and surface roughness. In other cases, these may be overshadowed by the macro-characteristics of the medium and the degree of interfacial contact, possibly with severe resulting corrosion. Where the build-up of corrosion products can occur at the interface, they will dominate longer-term corrosion and govern the long-term corrosion rate. For media of finite thickness, diffusion issues and material deterioration may also be involved. The practical implications are outlined. It is argued that with the presence of a suitable medium, it is possible to achieve negligible long-term corrosion but only if certain practical actions are taken.

Corrosion behavior and magnetocaloric property of pure phase La1-xCexFe11.5Si1.5 (x=0.1,0.2,0.3) compounds

To further study the corrosion mechanism of pure phase La(Fe,Si)13, Ce were added into the LaFe11.5Si1.5 compounds to facilitate phase formation and improve corrosion resistance and magnetic properties. The corrosion test conducted on the pure phase La1-xCexFe11.5Si1.5 (x = 0.1, 0.2, 0.3) revealed a significant number of minute corrosion pits with irregular shapes such as round, square and triangular after only 1 h of corrosion in tap water. However, in the case of La0.7Ce0.3Fe11.5Si1.5 compound, the number of corrosion pits was significantly lower. Potentiodynamic polarization curves showed that Ecorr goes up from −0.76 V to −0.59 V, and the Icorr goes down from 4.92 × 10−6 A/cm2 to 2.46 × 10−6A/cm2 as a result of Ce addition from 0.1 to 0.3. With the increase of Ce content, the corrosion resistance of La1-xCexFe11.5Si1.5 compounds was improved. Adding Ce element in the LaFe11.5Si1.5 compounds can also enhance the magnetocaloric effect. Significant extra spike-shaped peaks were observed on the M-H curves of La0.8Ce0.2Fe11.5Si1.5 and La0.7Ce0.3Fe11.5Si1.5, indicating a strong first-order magnetic phase transition. Furthermore，-△SM values improved from 21.2 J/kg K to 51.6 J/kg K by increasing Ce from 0.1 to 0.3.

Experimental Investigation of the Evolution Process of Suspended Pipelines through River Bottoms under Unsteady Flow Conditions

One of the major geological hazards that can cause harm to long-distance oil and gas pipelines are water-induced disasters. These disasters are quite common and widespread. Pipelines that cross river channels are at a higher risk of facing damage due to flood-induced erosion. To shed light on the evolution pattern of riverbeds adjacent to pipelines under the influence of unsteady flow conditions, a flume model test was conducted, and the underlying mechanisms of local scour were elucidated. The experimental results demonstrate that pipelines are more susceptible to suspension during flood conditions. The suspension process of pipelines under flood conditions could be broadly divided into five stages. In comparison to constant flow conditions, the evolution process of local scour and the suspension of pipelines under unsteady flow lacked the erosion pit expansion stage, and the scour duration was shorter. Each stage exhibited distinct erosion characteristics, and both the peak flow rate and the number of flood peaks significantly impacted the maximum range and depth of the erosion pit. During pipeline-laying projects, selecting a covering layer with a larger particle size can enhance the erosion resistance of the riverbed around the pipeline. The study of the local erosion process of underwater crossing pipelines under unstable flow conditions can provide a reference for pipeline engineering design and riverbed pipeline protection strategies.

Study of erosion wear to concrete by different gravel particle sizes: Laboratory test and numerical simulation

Concrete bridge piers face relentless erosion from Wind Gravel Flow (WGF) in Lanzhou–Xinjiang High–Speed Railway, resulting in pronounced wear on their surfaces, which could potentially induce additional structural defects. This study aims at the erosion wear performance and its corresponding damage mechanisms in concrete under WGF, using the airborne sandblasting method as a tool for this analysis. The study suggests that the Concrete Erosion Rate (CER) intensifies parallel to increases in both erosion angle and wind speed. Low angle erosion predominantly causes surface damage through cutting, while high angle erosion results in erosion pits and cracks. Notably, CER initially rises but eventually stabilizes with varying erosion times. A widened gravel particle size interval leads to a consistent reduction in the CER, but it concurrently heightens the likelihood of erosion caused by individual gravel particles on the concrete surfaces. An expanded gravel particle size interval results in a considerable increase in both the size and depth of erosion pits on the concrete surface. On the other hand, a narrowed particle size interval contributes to a significant upsurge in the number of erosion pits, causing the CER to diminish as the particle size interval increases. A novel model adapted for concrete exposed to the windy conditions of the Gobi has been developed. The model’s accuracy has been substantiated via numerical simulations, which illustrates that an uptick in erosion wind speed considerably boosts the airflow velocity around the concrete sample. In contrast, the pressure distribution on the surface steadily decreases from the center to the periphery. As erosion wind speed increases, airflow velocity and surface pressure around the concrete specimen rise significantly. Furthermore, the surface pressure of concrete increases with a broader gravel particle size interval. In conclusion, this study provides a strong scientific and theoretical underpinning for the protection of concrete bridge piers in the wind–prone Gobi regions.

Study on the ablation behavior of C/SiC composite materials under the action of local structural thermal sources

This study uses ablation testing on C/SiC composite materials under local structured thermal sources with a wide range of heat flux densities, simulating the harsh local conditions caused by discontinuous structural interference on spacecrafts. The thermal response, ablation laws, and ablative perforation time of C/SiC composite materials are obtained under different heat flux densities. The experimental findings demonstrate that there are notable differences in the morphology of the ablation pits under various heat flux conditions. As the heat flux density increases, the temperature of the local structure heat source action center on the target surface increases, the depth and outer diameter of the erosion pits increase, and the wall surface of the erosion pits gradually tends to be smooth. Under the influence of local structural heat sources, the creation of material ablation pits and the process of material perforation are predicted using the improved Umeshmotion+ALE+birth and death element method. For various conditions, the temperature field results and ablation morphology are well predicted by the numerical simulation results. Numerical calculations can be used to analyze the thermal stress and oxidation sublimation contribution rates of targets under the action of structural heat sources.

Quantifying the influence of microstructure on the corrosion of Mg-Li alloys by using X-ray CT

The microstructure of multi-component Mg-Li alloys played a decisive role in their corrosion properties due to the potential differences between the matrix and the secondary phases. In this study, the effects of secondary phases (AlLi, AlX(Gd, Y, Mn), and Mg2Sn) on the corrosion behavior of Mg-Li alloys have been quantified by using in situ X-ray CT. The microstructure-property correlation was established between the type, morphology, distribution, and dimensions of the secondary phases and the microscopic corrosion behavior. The corrosion parameters, such as average equivalent diameter, distance, number density, and volume fraction of the secondary phases and corrosion pits, were quantified as a function of corrosion time. The dominating secondary phase was identified by combining SKPFM analysis and electrochemical testing, giving quantitative information on corrosion control by designing secondary phases.

Temperature and Reaction Time’s Effects on N80 Steel Corrosion Behavior in Supercritical CO2 and Formation Water Environments

In the present study, an immersion experiment was carried out to examine how N80 steel corrodes when exposed to formation water containing dissolved CO2 and supercritical CO2 (Sc-CO2) along with water vapor. We employed electrochemical and surface analysis methods to examine the influence of various factors, including the temperature and duration of immersion, on the extent of corrosion. The results show that the corrosion patterns of N80 steel in a supercritical CO2 environment and CO2-saturated formation water differed significantly. The presence of similar corrosion features was suggested by the constant structure of the corrosion products identified in the formation water. However, the morphology of the corrosion product was complex in the supercritical CO2 environment, exhibiting features of pitting and localized corrosion. Furthermore, a non-linear trend in the corrosion rate was observed between 40 °C and 120 °C. Specifically, the rate of corrosion declined from 40 °C to 80 °C, but it then resumed its growth from 80 °C to 120 °C. These findings suggest that very high temperatures could lead to the destruction of corrosion products and subsequently enhance the corrosion process.

Analysis of the Sand Erosion Effect and Wear Mechanism of Wind Turbine Blade Coating

The wind–sand climate prevalent in the central and western regions of Inner Mongolia results in significant damage to wind turbine blade coatings due to sand erosion. This not only leads to a decline in power generation but also poses safety risks. This study replicated the wind–sand environment of Alashan and numerically simulated the erosion and wear process of the blade coatings of a 1.5 MW horizontal axis wind turbine under rotational conditions using the DPM model. Additionally, erosion tests were conducted on the operating wind rotor in a wind tunnel. The simulation results demonstrate that sand particle trajectories in the rotating domain are influenced by vortex, incoming wind speed, and sand particle size. For small-sized sand particles, variations in wind speed do not substantially alter the number of particles in contact with the wind turbine blades. However, alterations in the momentum of these particles lead to changes in the impact force on the coating surface. Conversely, the change of wind speed will not only alter the number of large-size sand particles in contact with the wind rotor but also modify the impact force on the coating surface. Furthermore, after impacting the blade, small sand particles continue to move along an approximate helical trajectory with the airflow, while large-size sand particles swiftly rebound. Through statistical analysis of erosion pits on the blade surface after the erosion experiments, it was observed that, in comparison among the leading edge, windward side, trailing edge, and leeward side, the leading edge presents the greatest number of erosion pits, whereas the leeward side has the fewest. Along the spanwise direction, the 0.7R-blade tip segment exhibits the highest count, while the blade root-0.3R section displays the fewest number of pits. The wear morphology of the blade coating was observed from the blade root to tip. The leading edge coating exhibits a range from shallow pits to coating flaking and deeper gouge pits. On the windward side, the coating displays wear patterns varying from tiny cutting pits to cutting marks, and then to gouge pits and coating flaking. Erosion morphology of the trailing edge evolves from only minor scratches to spalling pits, further deepening and enlarging. These research findings provide a basis for the study of zoning-adapted coating materials for wind turbine blades in wind–sand environments.

Experimental and numerical study on axial compression behavior of slender CFST columns with localized pitting corrosion damage

In order to investigate the axial compression behavior of slender circular concrete-filled steel tubes (CFSTs) with localized pitting corrosion damage, an experimental and numerical study was performed in this paper. In the experimental study, mechanically drilled cylindrical pits were employed to simulate localized pitting corrosion damage. Seven specimens were tested, with six specimens containing corrosion pits located at mid-height and one intact specimen. The experimental results showed that the localized pitting corrosion damage degraded the axial compression behavior of the specimens. Numerical models were developed and validated by the experimental results and used to consider the random characteristics of corrosion pits. A parametric analysis was then performed based on the validated numerical models. It was revealed that the ultimate strength of CFST was influenced by the location and dimensions of the pitting corrosion. Considering the random nature of localized pitting corrosion damage located at the midheight, practical calculation models for predicting the ultimate strength of CFSTs were put forward based on the methods provided in existing codes. On account of the obtained data pool, the predictions were verified against the results from the tests and parametric analysis. In addition, considering the random locations of the pitting region on the surface of the member, a method based on the controlling section was proposed to determine whether the corrosion should be considered and to calculate the ultimate strength.

Corrosion behavior and microstructure analysis of butt welds of Q690 high strength steel in simulated marine environment

Steel components that have served in the marine environment for extended periods often face challenges in preventing surface damage caused by corrosion protection measures. These challenges can ultimately diminish the expected service life of structures. To investigate the corrosion behavior and time-varying effects in butt welds of Q690 high strength steel in the ocean splash zone, a macroscopic morphology analysis was conducted using various corrosion times involving indoor saltwater immersion and hot-humid cycling accelerated corrosion. Quantitative analysis of corrosion pits' size and distribution range was performed in both the weld zone (WZ) and heat-affected zone (HAZ) to establish a relationship between roughness parameters and corrosion time. Experimental results were compared with corrosion parameters of regular steel. The findings reveal a gradual reduction in metallic luster with increasing corrosion time on specimen surfaces. Moreover, a greater accumulation of corrosion products is observed in the butt weld region, leading to progressive corrosion damage. High strength steel (HSS) exhibits superior corrosion resistance compared to ordinary steel. However, the corrosion damage of HSS weld joints gradually approaches that of ordinary steel in the later stage of corrosion. Microscopic scanning indicates that the accumulated corrosion layer effectively impedes the penetration of corrosive media into the matrix's interior, while the surface microstructure transitions from pitting to corrosion pits. These research findings significantly contribute to assessing the performance and analyzing the reliability of high strength steel in marine environments.

Numerical simulation of corroded circular hollow section steel columns: A corrosion evolution approach

This study introduces a numerical simulation method for corroded circular hollow section steel columns, utilising a newly developed corrosion evolution model. This model was formulated by characterising the corrosion morphology and calibrating parameters throughout the entire corrosion process. An interpolation method was implemented to estimate the number of corrosion pits, based on experimentally measured corrosion ratios. Consequently, this allowed for the numerical prediction of the time-varying corrosion morphologies. Finite element (FE) models, incorporating this corrosion evolution model, were constructed. These corroded column models underwent validation through comparison with experimental findings. To further establish the effectiveness of the proposed FE models in predicting the structural behaviour of corroded members, FE models were also developed using the traditional uniform thickness reduction approach for comparative analysis. The results revealed that the proposed FE models for corroded structures offer a more accurate prediction of mechanical performance, particularly in instances of severe corrosion damage.

In vitro degradation and dry sliding wear characteristics of AZ31/TiO2 nanocomposites for biomedical application

This study concentrated on the degradation and wear characteristics of nanocomposites reinforced with (0, 0.5, 1.5 and 2.5 wt%) titanium dioxide (TiO2) nanoparticles on the AZ31 Mg alloy fabricated by the stir casting method. Optical microscopy and FESEM images showed that the TiO2 nanoparticles were distributed uniformly and the intermetallic phase Mg17Al12 observed along the grain boundaries. The surfaces of the nanocomposite samples was gradually covered with a magnesium hydroxide (Mg(OH)2) protective layer after 48 h of immersion in simulated body fluid (SBF). The immersed composite samples contained several white hydroxyapatite and magnesium phosphate particles. The addition of up to 1.5 wt% TiO2 nanoparticles reduced the degradation rate of the nanocomposites in SBF, while further addition increased it. FESEM images of the immersed samples revealed the presence of corrosion pits and cracks on the AZ31 alloy and its nanocomposites. Under dry conditions with varying loads, the wear characteristics of fabricated nanocomposites were studied using computerised pin-on-disc equipment. The addition of TiO2 nanoparticles up to 1.5 wt% improved the wear resistance of the nanocomposites. However, the further addition increased the coefficient of friction (COF) and wear loss due to agglomeration and porosity in the nanocomposites. The FESEM morphology of the worn surface and wear debris revealed that abrasion was the primary wear mechanism at low loads, and abrasion with severe plastic deformation and delamination were dominant at higher loads.

Microstructural characteristics of different heat-affected zones in welded joints of UNS S32304 duplex stainless steel using the GMAW process: analysis of the pitting corrosion resistance

Abstract The influence of specific microstructural characteristics on the properties of single-pass welding joints was assessed by optical processed images, transmission electron microscopy, microhardness measurements and corrosion tests conducted in various regions of the heat-affected zone (HAZ) in a lean duplex stainless steel. The welded joints were obtained with heat inputs of 1.5 and 2.5 kJ/mm using a gas metal arc welding (GMAW) process with a shielding gas enriched in Ar. Three selected regions in the HAZ showed different ferrite grain sizes and austenite fractions. The place in the welded joint where the HAZ was narrowest, and therefore experiences the highest cooling rate, is most prone to the formation of cubic CrN metastable nitrides. Conversely, the place where the HAZ was wider promotes the precipitation of stable Cr2N nitrides with more coalesced intragranular austenite (IGA) particles, where presumably random interfaces predominate. The HAZ region where the cooling rate was the highest presented more pitting corrosion resistance.

Inhibiting general and pitting corrosion of Ni in dilute sulfuric acid solutions with some tetrazole derivatives

5-(Benzylthio)− 1H-tetrazole (BST), ethyl-1H-tetrazole-5-acetate (ETA), and 5-(ethylthio)− 1H-tetrazole (EST) were utilized to inhibit the pitting and general corrosion of nickel in dilute sulfuric acid solutions. The galvanostatic anodic polarization under a constant current and mass loss measurement complemented by a scanning electron microscope is utilized. The tetrazole inhibitors retard the pitting corrosion by shifting the pitting potential, Ep into the more noble direction while lowering the amount of electricity, Qinh, needed to attain Ep. The protection efficiency, η, increased with increasing the amount of tetrazole in the solution to follow the order EST < ETA < BST. The protection influence of such inhibitors is accompanied by the blocking of the investigated metal surface by their molecules through an adsorption process that follows Langmuir's model. The computed -∆G⸰ads values are 37.17, 36.82, and 36.57 kJ/mol for BST, ETA, and ETA, successively, at 298 K. Such values are harmonious with a mixed chemo-, physisorption mechanism. A coordinate link is supposed to originate between the tetrazole compound and the investigated nickel surface.

Effect of B. subtilis in simulated acid red soil on the corrosion behavior of X80 pipeline steel

The eastern section of China's West-east gas transmission project is laid in acidic red soil. NRB are widespread in soils and play an important role in metal corrosion. In this article, the corrosion failure behavior and mechanism of X80 pipeline steel under the action of NRB in simulated acidic soil were studied. It was found that the biofilm of B. subtilis had significant inhibitory on the overall corrosion of X80 steel. Electrochemical results prove that the corrosion rate of the sterile group after 14 days of immersion was about 4.5 times that of the bacterial group. However, the biofilm promotes the formation of local corrosion pits. Confocal laser scanning microscopy images indicate that that the corrosion pit depth of the bacterial group (46.1 μm) was three times that of the bacterial-free group (15.7 μm) after 14 days. The pH of the acidic environment was slightly improved by B. subtilis. XPS results proved that B. subtilis complicates the corrosion products of X80 steel through its nitrate reduction ability and metabolism.

Bond behavior between CFRP and steel structures with random corrosion defects

Steel structures in long-term service are difficult to avoid corrosion and can be reinforced by carbon fiber reinforced polymer (CFRP) bonding method. To investigate the corrosion effect on the bond behavior between CFRP and steel, a modified cohesive zone model was proposed and verified by experiment. Then, a series of random corrosion morphologies controlled by the size and the shape of corrosion pit were generated. Finally, by importing the random corrosion morphologies and the corresponding cohesive parameters distributions into the model, a parametric analysis was executed. Results showed that the ultimate load of CFRP-corroded steel bonding system was sensitive to the size of corrosion pit, while the stiffness had identical sensitivities to the pit size and pit shape. The ultimate load would reach the peak value when the average pit width Wp,avg was 1.0 mm and the average pit depth-to-width ratio (Dp/Wp)avg was between 0.12 and 0.14, whereas the stiffness would reach a high level when the Wp,avg was between 1.0 mm and 1.2 mm and the (Dp/Wp)avg was between 0.12 and 0.14. Moreover, the effective bond length would reach a high level when the Wp,avg was between 1.0 mm and 1.2 mm and the (Dp/Wp)avg was about 0.10.

Morphological characteristics and geometric prediction model of pits in complex corrosion environment

AbstractFor aircraft serving in coastal environments, the aluminum alloy skin is exposed to high temperature, humidity, and salt environment for a long time. Pitting and exfoliation will affect its normal service life. In this article, static salt spray experiments and electrochemical tests were carried out on 2198‐T8 Al–Li alloy in nine different corrosive environments. The effects of salt concentration, temperature, and humidity on the corrosion behavior were analyzed and compared. The relationship between corrosion environment parameters and pits was established. The results show that, under the same corrosion environment, the length, width, and depth of the pits all follow the log‐normal distribution; compared with the salt concentration and humidity, the increase in temperature has the most obvious promotion on the corrosion rate. Based on the frequency statistics of pit size and electrochemical test results, the pit morphology was simplified to a semiellipsoid geometric model, and the pit size in different corrosive environments was predicted. The predicted size data all fall within the 1.5‐fold dispersion region.