Corrosion Morphology Research Articles

Experimental study on pipeline corrosion behavior coupled with microorganisms and dynamic alternating current interference

Underground pipelines buried deeper than 1.5 m or in specific soil conditions are susceptible to microbial corrosion and dynamic alternating current (AC) interference. Yet, research on the coupled effects of these factors remains limited, leaving their mechanisms unclear. The study employed microbial activity tests, electrochemical experiments, and microscopic morphology characterization to elucidate the coupled effect of sulfate-reducing bacteria (SRB) and dynamic AC interference on buried metallic pipelines. Results show that sinusoidal AC significantly reduces SRB growth activity. Initially, the active microbial film produced by microbial metabolism inhibited corrosion but later exacerbating it as the microbial film detachment. Microscopic examination reveals as the interference time increases, the corrosion morphology changed from pitting corrosion to honeycomb/ulcer shapes, under SRB and different AC interference conditions. Moreover, sulfide corrosion products and iron phosphide formation accelerate corrosion, while rectification and alternating electric field effects further aggravate the process. These findings provide insights into the complex mechanisms of microbial and AC corrosion in buried pipelines, aiding in anti-corrosion strategies and layout optimization.

Machine Learning-Assisted Prediction of Corrosion Behavior of 7XXX Aluminum Alloys

High-strength and lightweight 7XXX Al alloys are widely applied in aerospace industries. Stress corrosion cracking (SCC) in these alloys has been extensively discussed, and electrochemical corrosion should be brought to the forefront when these materials are used in marine atmospheric environments. This work obtained the corrosion potentials (Ecorr) and corrosion rates of 40 as-cast 7XXX Al alloys by potentiodynamic polarization tests and immersion tests, respectively; then, chemical compositions and physical features were used to build a machine learning model to predict these parameters. RFR was used for the prediction model of Ecorr with the features Cu, Ti, Al, and Zn, and GPR for that of the corrosion rate with the features of specific heat, latent heat of fusion, and proportion of p electrons. The physical meaning and reasonability were discussed based on the analysis of corrosion morphology and precipitated composition. This work provides a reference for the design of corrosion-resistant 7XXX Al alloys and shows a method of conducting corrosion mechanism evaluation by using machine learning.

Enhanced the SRB corrosion resistance of 316L stainless steel via adjusting the addition of Cu and Ce elements

316L stainless steel (SS) is the key raw material for the preparation of high-performance oil and gas pipelines, but even 316L with excellent properties will be attacked by sulfate-reducing bacteria (SRB) corrosion. Excellent antibacterial effects have been obtained in other SS systems by doping antibacterial elements. However, the current research on the preparation of antibacterial 316L SS is not comprehensive, and the quantitative analysis of the antibacterial mechanism and doping elements is still unclear. In this paper, the SS with Cu and Ce added were prepared by vacuum induction melting. Then the homogenization treatment combined with hot rolling was used to improve the structure segregation and mechanical properties. Further, the weight loss tests and electrochemical tests were conducted to evaluate the corrosion resistance of SS, the corrosion products and morphology were analysed, and the deformation structure was characterized to clarify the corrosion mechanism of the modified SS and quantify the doping elements. The results indicate that the microstructure after homogenization is mainly austenite, and with the increase of Ce content, the Ce-rich phase segregates. The inhibitory effect of Cu on SRB can be explained by the destructive effect of Cu ions on cell membranes. On this basis, adding a low content of Ce element can increase the permeability of the SRB cell wall and further enhance the attack effect of Cu ions on the cell membrane. The corrosion behavior of alloys shows the deformation structure dependence, with crystal defects and segregation increasing the corrosion rate. The optimal addition amount of Ce is 0.18 wt%, and the strength and elongation of SS are 511.18 MPa and 108.2%, respectively.

Microstructure, Mechanical Properties, and Lead–Bismuth Eutectic Corrosion Behaviors of FeCrAlY-Al2O3 Nanoceramic Composite Coatings

Seven FeCrAlY-Al2O3 nanoceramic composite coatings are deposited on F/M steel via plasma spraying and laser remelting. A systematic investigation is conducted to examine the dependence of microstructure, mechanical properties, and lead–bismuth eutectic (LBE) corrosion resistance on the nano-Al2O3 addition and different Cr and Al contents. With the increase in Al content in FeCrAlY, gradual refinement of the coating grains occurs. The addition of nano-Al2O3 promotes the elemental segregation and precipitation of the second phase. The nano-Al2O3 notably enhances the mechanical properties of the coatings that are primarily attributed to second-phase and fine-grain strengthening. After LBE corrosion tests, intergranular corrosion morphology could be observed, where the contents of Cr and Al significantly influence the corrosion behavior of the coatings at varying temperatures.

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.

Influence of cooling rate on the corrosion behavior of Al–Zn–In–Mg–Ag sacrificial anode

The cooling curves of the Al–Zn–In–Mg–Ag alloys in copper mold, iron mold, and 400 °C-preheated iron mold cast were simulated and three solidification rates were calculated to be 7.05 °C/s, 0.76 °C/s, and 0.28 °C/s. The effects of cooling rate on the microstructure, electrochemical characteristics, and corrosion morphologies of Al–Zn–In–Mg–Ag alloys are investigated. The results demonstrate that the alloy with a low cooling rate has the lowest self-corrosion rate (0.09 mm/year), the highest actual capacity (2503.16 Ah/Kg2), as well as the highest anode current efficiency (87.46%). The anode current efficiency of the Al alloys is affected by the self-corrosion and the detachment of the second phases and grains. As the cooling rate decreases, the grain size becomes larger, the amount of the MgZn2 second phase decreases, and the content of In, Zn, and Ag activation elements increases in the matrix. The corrosion of the Al–Zn–In–Mg–Ag alloy initiates from the micro-galvanic corrosion between the MgZn2 second phase and the Al matrix. It then extends along the grain boundaries and towards the intragranular, accompanied by the shedding of the MgZn2 particles and the grains.

Investigation of Cr and rare earth (RE) on the corrosion resistance of HRB400 rebar in simulated concrete pore solutions containing chloride and sulfate ions

The effect of Cr and rare earth (RE) on the corrosion resistance of HRB400 in simulate concrete pore solution containing Cl− and SO42− was investigated. The results of electrochemical tests and corrosion morphology observations revealed that HRB400 corrosion rates increased with sulfate concentration, but Cr/RE addition notably reduced rates and passive current density, particularly in high sulfate conditions, suggesting a sulfate-Cr/RE interaction. The mechanism involves structural changes in the surface passivation film. Furthermore, the combination of Cr and RE effectively mitigated localized corrosion risk compared to Cr alone, highlighting their synergistic corrosion resistance enhancement.

Effects of NaH2PO2 concentration and deposition potential on microstructural characteristics and corrosion properties of electrodeposited amorphous Fe–P coatings

ABSTRACT This study reports the influence of NaH2PO2 concentration and deposition potential on the microstructural characteristics and corrosion properties of fully amorphous electrodeposited Fe–P coatings. The morphology and P content of the coatings were observed and the effect of the processing parameters on the surface roughness, deposition rate, and current efficiency were investigated. The morphology and P content of the coating varied significantly with the NaH2PO2 concentration, but the deposition potential did not significantly influence these properties. As the P content and morphology determine electrochemical corrosion properties, the deposited Fe–P film with the best anti-corrosion properties was determined by analysing the corrosion properties of the coatings in 3.5 wt.% NaCl solution through potentiodynamic polarisation and electrochemical impedance spectroscopy; the corrosion morphology and corrosion products were also characterised. This study can provide new insights into the corrosion behaviour of amorphous Fe–P coatings and provide guidelines for industrial production.

Corrosion behavior and cellular automata simulation of carbon steel in salt-spray environment

Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to discuss the corrosion loss and morphology of the pit and rust layer of carbon steel. It was found that the corrosion process is largely influenced by the cyclic shedding of surface corrosion products, in addition to being controlled by the mechanism of oxide film shedding and pit evolution. A corrosion mechanism (the mechanism of rust layer shedding) is proposed. As a result, in this paper, the corrosion process of the test steel is simulated by the cellular automata. It was set up that the mechanism of oxide film shedding, the mechanism of pit evolution, and the mechanism of rust layer shedding in Cellular Automata Simulation. The optimal time ratio and simulation parameters were found, and a predictable cellular automata corrosion simulation model was built, providing a solution for carbon steel’s service life prediction.

Insight into the pitting corrosion behavior of laser‐welded R60702 zirconium alloy in chloride electrolyte

AbstractThis work aims to analyze the passivation and pitting corrosion behaviors of laser beam welded R60702 zirconium alloy in neutral and acidic chloride‐containing electrolytes. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements are carried out to investigate the electrochemical performance of the welding joint. Scanning electron microscope, X‐ray diffraction, and three‐dimensional profile digital microscope are utilized to reveal the microstructures and corrosion morphologies. The electrochemical results show that the heat‐affected zone (HAZ) and weld zone have nearly equal corrosion performance, and both of them are more corrosion‐resistant than the base metal. The corrosion morphologies suggest that the HAZ has the lowest sensitivity to pitting corrosion. Moreover, it is unraveled that, in chloride‐containing electrolytes, the quantity and distribution of Zr(Fe,Cr)2 particle phases are the main factors that determine the different corrosion performances of the welding joint.

Role of hygroscopic chloride salts on corrosion performance and hydrogen absorption of steel under cyclic wet-dry conditions

The corrosion morphology of steel under aqueous NaCl, MgCl2, and ZnCl2 droplets and the corresponding hydrogen permeation behaviour were investigated using surface characterization techniques and electrochemical methods. Under cyclic wet-dry conditions, Mg2+ and Zn2+-containing surface layers were formed on steel and the latter presented a high corrosion resistance. The most active hydrogen entry occurred under ZnCl2 during drying, while it happened under MgCl2 at low humidity. The effects of chloride salts on the formation of rust layers and hydrogen entry into steel during wet-dry cycles were discussed based on the hardness of metal cations and the deliquescence properties of salts.

The corrosion and tribological behaviors of DLC film in CO2 saturated NaCl solution with high Cl− concentration

The failure of pipelines during oil and gas exploitation is a pressing issue in the oil and gas industry. The high permeability of chloride ions (Cl−) alters the corrosion morphology of the N80 substrate and diminishes its ability to impede the penetration of corrosive substances. This study aims to deposit DLC films on the inner surface of N80 pipeline using plasma enhanced chemical vapor deposition (PECVD), and investigate the corrosion and friction behavior of DLC films in CO2 saturated NaCl solutions with varying Cl− concentrations. The results indicate that the change in Cl− concentration possess minimal impact on the DLC film. The corrosion current density of DLC films in CO2 saturated NaCl solution with three different Cl− concentrations is one order of magnitude lower than that of the N80 substrate. Moreover, a transfer film can still form in high-concentration CO2-saturated NaCl solutions, reducing wear. DLC film demonstrates exceptional stability, corrosion resistance, and wear resistance, making it an ideal material for safeguarding pipelines during oil and gas exploitation.

Experimental behaviour of hybrid carbon steel – stainless steel bolted connections subjected to electrochemical corrosion

To minimise cost in practical applications whilst still obtaining a satisfactory performance, stainless steel is often employed in aggressive marine environments to ensure the durability of the structure, whilst parts of the structure less susceptible to corrosion employ conventional carbon steel. When the two materials are in direct contact in the connection region, galvanic corrosion can occur over time thus leading to an increased level of corrosion of the less noble carbon steel parts and an associated degradation in the structural performance. A comprehensive experimental study on the shear behaviour of hybrid carbon steel – stainless steel bolted connections subjected to electrochemical corrosion is presented in this paper. A total of 30 bolted connection specimens were designed and assembled from hot-rolled carbon steel and stainless steel plates. Two bolt grades, the high strength bolts 10.9 and the precipitation hardening stainless steel bolts 10.9 were used to connect the plates. Employing the electrochemical corrosion method, the specimens were subjected to various levels of corrosion by adjusting the duration over which the specimens were sunk in the corrosive medium, which resulted in both different corrosion morphology as well as different levels of mass loss of the carbon steel plates due to corrosion. The corroded connection specimens were thereafter tested to failure under shear exhibiting 4 different failure modes. The load versus deformation curves were recorded and are reported herein, whilst the observed failure modes were also documented. It was revealed that increased level of corrosions led to decreased levels of bolt pretention forces and ultimate resistances of the connections, albeit the severity of the degradation strongly depended on the adopted joint configuration and resulting failure mode.

Enhancing corrosion resistance and mechanical properties of laser-direct energy deposited 316 stainless steel via W addition

Additions of 1–5 wt% W element enhanced corrosion resistance and mechanical properties of LDED-316 SS. Microstructure characterized the grain refinement and precipitation of ferrite and W-Mo carbides. Mechanical tests showed enhanced tensile strength and hardness of 316–5 W by 37.4% and 30.8%, respectively. Electrochemical tests indicated an increasing pitting potential and polarization resistance of 316–3 W in 3.5 wt% NaCl solution by 0.535 VSCE and 1679 kΩ·cm2, respectively. Corrosion morphology showed the preferential dissolution of ferrite and W-Mo carbides rather than austenite cell. The change in corrosion processes and presence of WO3 in the passivation film significantly contributed corrosion resistance.

Long-term corrosion of copper alloys in the soil: new aspects of corrosion morphology in archaeological vessels from south-western Iran

A group of copper-based objects excavated at Deh Dumen cemetery, in south-western Iran, was studied and analysed to examine the long-term corrosion morphology and mechanism in the soil burial environment. For this purpose, twenty-two samples from twenty-one copper-based vessels were studied and analysed using X-ray diffraction, scanning electron microscopy—energy dispersive X-ray spectroscopy, micro-Raman spectroscopy and metallography techniques. The results of the analyses showed that the majority of vessels are made of tin bronze, along with two arsenical copper samples. The extent of corrosion observed ranges from very thin corrosion crusts to thick crusts and entirely corroded structures. These three identified corrosion morphologies display a multi-layered corrosion stratigraphy as well as the preserved limit of the original surface. The corrosion crusts include internal tin-rich and external copper-rich layers, and the main corrosion mechanism for the formation of multi-layered corrosion crusts is decuprification or selective dissolution of copper during the long-term burial time in a moderately Cl-contaminated soil. The three identified corrosion morphologies are similar to the previously published morphologies, but some clear deviations are apparent and are discussed here.

Galvanic Corrosion of E690 Offshore Platform Steel in a Simulated Marine Thermocline

Marked changes in temperature, pH, dissolved oxygen (DO) content, and nutrient content typically occur in marine thermoclines, which are key factors that affect the corrosion of metals. Offshore platforms require marine metals to be exposed to deep-sea environments and thus increase their penetration into the marine thermocline. This study investigates the galvanic corrosion of E690 steel in a marine thermocline using a simulated marine thermocline (SMT). Specifically, the corrosion of E690 steel was analyzed using the wire beam electrode (WBE) technique, linear polarization (LP), corrosion morphology, and weight loss measurement. Results indicated that the SMT had a stable multilayer structure, and the variations in temperature, DO, pH, and nutrient concentration in the SMT were similar to those in the natural marine thermocline. There were two forms of E690 steel corrosion in the SMT: galvanic corrosion and seawater corrosion. The corrosion rate of seawater corrosion was influenced by the DO concentration. Galvanic corrosion occurred after the intrusion of E690 steel into the marine thermocline. The driver of galvanic corrosion was the difference values for Ecorrs of E690 steel at various depths of the marine thermocline. The Ecorr of E690 steel was influenced by the temperature, pH, and DO of the seawater, in the following order: DO >> T > pH. The continuous reduction in Ecorr with depth contributed to large-scale galvanic corrosion, and the oscillation variation in Ecorr with depth was the reason for small-scale galvanic corrosion. The primary anodic regions of galvanic corrosion were located in the area with the fastest temperature variation in the thermocline, and the position of the anodic regions rose with time. The anodic regions gradually expanded with time. The proportion of galvanic corrosion in the average corrosion rate could increase up to approximately 80% in the stable anodic region. There were many hemispherical corrosion pits on the surface of the single electrodes that were at the depths of 75 cm, 105 cm, and 135 cm. These single electrodes comprised a long-term, sustainable anodic region of galvanic corrosion.

Inhibition Effect of Triphenylmethane Dyes for the Corrosion of Carbon Steel in CO2-Saturated NaCl Corrosion Medium.

Carbon dioxide corrosion presents a significant challenge in the oil and gas field. This study simulates the corrosive environment characteristics of oil and gas fields to investigate the corrosion inhibition properties of three triphenylmethane dyes. The inhibitive performance and mechanisms of these dyes were analyzed through weight loss and electrochemical testing, revealing that crystal violet (CV) exhibited a superior inhibition effectiveness over malachite green (MG) and Fuchsine basic (FB). At a concentration of 150 ppm in a CO2-saturated 5% NaCl solution at 25 °C, CV achieved an impressive maximum inhibition efficiency of 94.89%. With the increase in temperature, the corrosion rate slightly decreased, and the corrosion rate was 92.94% at 60 °C. The investigated CV acted as a mixed-type corrosion inhibitor and its protection obeyed the Langmuir adsorption isotherm. The corrosion morphology was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and confocal laser scanning microscopy (CLMS). Quantum chemical calculations and molecular dynamics simulations were employed to validate the corrosion inhibition mechanisms, providing guidance for the further application of these dyes in corrosion control.

A Comparative Study of the Corrosion Behavior of P110 Casing Steel in Simulated Concrete Liquid Containing Chloride and Annulus Fluid from an Oil Well

The corrosion behavior of P110 casing steel in simulated concrete liquid and simulated annulus fluid was investigated to reveal the corrosion pattern and protective properties of corrosion products in the two environments. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), Mott–Schottky tests, and electrochemical noise (EN) tests were used to study the corrosion behavior of P110 casing steel in simulated concrete liquid and simulated annulus fluid saturated with CO2. Scanning electron microscopy (SEM) combined with Energy-Dispersive Spectrometer (EDS) mapping was used to characterize the corrosion morphology and elemental distribution of P110 casing steel. The results show that the corrosion resistance of P110 casing steel deteriorates with the increasing immersion days in the simulated annulus fluid, the impedance decreases gradually, and the corrosion-product film shows a loose and porous structure. In the simulated concrete liquid, under the condition of containing a low concentration of Cl−, the protection of the corrosion products gradually increases with the extension of immersion days. With the increasing concentration of Cl− and the extension of immersion days, the electrochemical noise resistance and charge transfer resistance of P110 steel decrease gradually, and the protective property of the corrosion-product film decreases, which is capable of forming steady pitting corrosion.

Excellent corrosion inhibition and lubrication performance of MMT based ionic liquids as ester oil additives

In this work, electrochemical experiments and friction tests were conducted to investigate anti-corrosion properties and lubrication performance of the 2-mercapto-5-methyl thiadiazole (MMT) based ILs as additives of ester oil. The outcomes of electrochemical experiments were further supported by quantum chemical simulation which clarified the reason for corrosion inhibition from a microscopic perspective. Electrochemical impedance spectroscopy obtained from different temperatures (from 293 K to 323 K) showed that the inhibitors could reach a higher corrosion inhibition efficiency at 293 K. The experimental data exhibited that the adsorption behavior obeys Langmuir adsorption isotherm and the inhibitors adsorbed on the surface in a laying way seen from the results of theoretical simulation. Besides, SEM and XPS were employed to analyze the corrosion morphologies of immersion tests corroborating the presence of adsorption film on the steel surface. The tribological performance of MMT based ILs as base oil additives were examined by four-ball tester. The friction coefficient dropped by 47% and wear scar diameter decreased by 28% contrast to the base oil sample. The outstanding corrosion inhibition properties and friction-reducing and anti-wear performance could make it prospect for some industrial applications in energy saving.

Simulation of Pitting Corrosion Under Stress Based on Cellular Automata and Finite Element Method

Abstract A new cellular automaton (CA) program was written in python language to simulate the random pitting evolution process, which can not only obtain a variety of different corrosion products but also obtain a variety of common corrosion morphologies on the surface of metal pipes, bridge steel members, etc. In addition, commercial finite element (FE) software abaqus was redeveloped using python scripting language, and the FE mesh with the same size as the cellular mesh was established based on the consistent mesh algorithm, which ensured the efficiency and accuracy of the cyclic iterative algorithm. The stress and strain fields were calculated in real-time by applying the force load, the dissolution probability parameter P was updated in python according to the force-chemical coupling model, and a new corrosion morphology was obtained in python. At the same time, the birth and death element method was applied in abaqus to kill the corrosion elements in this iterative step simultaneously, and the new stress-strain field was recalculated in abaqus. The established consistent grid modeling strategy and cyclic iterative algorithm can significantly improve the solving efficiency of pitting evolution under the coupled action of corrosive medium and load. The results show that the stress concentration caused by pit expansion and the corrosion acceleration effect dominated by plastic deformation will promote each other, leading to the continuous growth of pitted pits. The established modeling strategy and cyclic iterative algorithm can significantly improve the solving efficiency of pitting evolution under the coupled action of corrosive medium and load.