Corrosion Pits Research Articles

Bayesian inference of pit corrosion in prestressing strands using Markov Chain Monte Carlo method

Corrosion monitoring has been widely studied to maintain the structural capacity of bridges through direct visual and nondestructive inspections or indirect inverse analysis-based methods. This study proposes a Bayesian inference method for inferring pit corrosion in the prestressing strands of prestressed concrete (PSC) bridges, which is an indirect method for corrosion monitoring. First, the probabilistic relationship between the mechanical properties of the strands and the amount of pit corrosion was defined using Bayes’ rule. Subsequently, a Markov chain Monte Carlo method was introduced to infer the posterior probability, which is a conditional probability distribution of the amount of corrosion given a certain mechanical property. Based on the inference results, probabilistic bounds for the amount of corrosion were derived. The proposed method was applied to two examples: (a) probabilistic corrosion inference of strands based on the tensile test results, and (b) probabilistic corrosion inference of embedded strands in PSC girders based on the bending test results. The inference results demonstrated the applicability of the proposed method.

Breaking Mechanism and Performance of Coal Subjected to Water Jets Under High In Situ Stress

Abstract The effect of in situ stress on the coal-breaking characteristics of water jets remains unclear, prohibiting the deep coalbed methane (CBM) development. Water jet coal-breaking experiments under different mean three-dimensional (3D) stresses and horizontal stress differences were carried out with a self-developed in situ stress simulator. When the mean 3D stress increased, coal changed from shear and tensile failure to shear failure, and the volume of the erosion pit first decreased rapidly and then slowly. Upon increasing the mean 3D stress from 0 to 10 MPa, the volume of the erosion pit decreased by 79.7%, and the specific energy consumption increased nearly five times. With an increase in horizontal stress difference, coal transitioned from shear failure to shear and tensile failure, resulting in a shear crack farther from the erosion pit. At a horizontal stress difference of 15 MPa, the volume of the erosion pit and specific energy consumption had maximum and minimum values, respectively. Consequently, constructing a higher horizontal stress difference helps improve the coal-breaking efficiency of water jets. This study could lay the foundation for applying water jet technology in deep coal seams.

Superior Pitting Corrosion Resistance of Ultra-high Strength Low Alloy Steel Via Co-alloying Al and Cu

Superior Pitting Corrosion Resistance of Ultra-high Strength Low Alloy Steel Via Co-alloying Al and Cu

Oxidation behavior and corrosion properties of 2-GPa grade Co-reduced ultrahigh-strength stainless steel

This study investigated the oxidation behavior and corrosion resistance of 2-GPa grade ultrahigh-strength stainless steel. Results revealed that the addition of V to Co-reduced FerriumS53 (7Co1V) accelerated the precipitation of MC carbide during aging, while inhibiting the precipitation of Cr-rich M23C6 carbide. A significant amount of Cr was predicted in the microstructure of the alloys, and this microstructure increased the partitioning of Cr to the alloy surface and provided enhanced resistance against corrosion pitting. These findings suggest that the addition of V into Co-reduced stainless secondary hardening steels can enhance their oxidation and corrosion resistance without compromising their mechanical properties.

Fatigue life assessment of offshore wind support structures in the presence of corrosion pits

Offshore wind turbine support structures, which connect the wind turbine transition piece and/or tower to the seabed, are located below the sea level and are in direct contact with seawater during the entire lifespan; therefore, they are highly susceptible to corrosion damage and cracking. In particular, the pitting corrosion is very crucial in these support structures, as it leads to local stress concentrations and thus affects the fatigue life. Although corrosion protection mechanisms are commonly implemented in offshore wind turbines, they have a finite life and therefore corrosion damage cannot be completely avoided during the entire life cycle, and this can lead to pitting corrosion on the steel surface. This paper aims to investigate the impact of pitting corrosion on fatigue durability of steel structures by performing tests on lab-scale coupons, made of S355 structural steel which is widely employed in fabrication of offshore wind support structures. For this purpose, cross-weld uniaxial samples were initially exposed to seawater for different time durations and then tested under cyclic loading condition. Furthermore, the durability analysis of corroded samples was carried out using a modified NASGRO equation. The results show that the pitting corrosion significantly reduces the fatigue life, and its level of life reduction is strongly dependent on the seawater exposure time. Moreover, the results show that employment of a linear trend for lower stress ranges would result in significant underprediction of the fatigue life, hence over-conservatism in the design life, at longer seawater exposure times.

Effect of Ti on stress corrosion cracking behavior and mechanism of Monel K500 alloy in flowing seawater

Purpose The purpose of this paper is to investigate the effect Ti on stress corrosion cracking (SCC) and flow accelerated stress corrosion cracking (FA-SCC) behavior and mechanisms of Monel K500 alloy. Design/methodology/approach Monel K500 alloy with different Ti contents was designed. A metallurgical microscope (XJP-3C) and scanning electron microscopy (EV0 MA15 Zeiss) with an energy dispersive spectroscopy were used to analyze the microstructure of the Monel K500 alloy. In situ electrochemical tests were carried out in static and flowing seawater to study FA-SCC behavior. Findings The number of TiCN particles in the alloy increased as the increase of Ti content. The static corrosion and SCC of Monel K500 alloy are reduced as the content of Ti increases. Generally, the SCC of alloys was caused by the synergistic effect of the anodic dissolution at exposed metal matrix and the pit corrosion of metal matrix adjacent to TiCN particles, which was further accelerated by flowing. Originality/value The corrosion behavior and mechanism of Monel K500 alloy with different Ti contents in a complex flowing seawater environment are still unclear, which remain systematic study to insure the safe service of the alloy.

Study on the evolution process of corrosion behavior under the sulfate reducing bacteria biofilm in shale gas gathering pipelines

Pipeline corrosion induced by sulfate-reducing bacteria (SRB) is particularly severe during the hydraulic fracturing technology in shale gas exploitation. To investigate the evolution of corrosion beneath the SRB biofilms, 49-day corrosion experiments were performed with and without SRB. The weight loss experiment demonstrated that the corrosion in the Blank group was mitigated by the corrosion product film. In contrast, the SRB group exhibited an initial inhibitory phase followed by an exacerbation. Scanning electron microscopy (SEM) revealed stratification in the Blank group, whereas SRB initially formed colonies and extracellular polymeric substances (EPS), eventually the biofilm evolved into a mixed layer with the corrosion product. 3D microscopy showed a relatively flat surface in the Blank group. Conversely, corrosion pits beneath SRB biofilm were circular and could reach a depth of 29.77 μm, significantly greater than in the Blank group. Over time, SRB-induced pits deepened from the edges to the center and widened to approximately 740 μm, accompanied by an increase in quantity. Energy Dispersive Spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) analyses detected the presence of elements P, S, and FeS in the SRB group, serving as important indicators of SRB corrosion. Electrochemical experiments revealed significantly higher corrosion currents in the SRB group. The evolution of SRB corrosion consisted of three phases: initial, intermediate, and starvation phases. During the starvation phase, localized corrosion proved to be the most severe, with a corrosion rate of 1.28 mm/a. Therefore, the study of SRB-induced corrosion should be prioritized to study the localization phenomena.

Accelerated Microbial Corrosion by Magnetite and Electrically Conductive Pili through Direct Fe0 -to-Microbe Electron Transfer.

Electrobiocorrosion, the process in which microbes extract electrons from metallic iron (Fe0 ) through direct Fe0 -microbe electrical connections, is thought to contribute to the costly corrosion of iron-containing metals that impacts many industries. However, electrobiocorrosion mechanisms are poorly understood. We report here that electrically conductive pili (e-pili) and the conductive mineral magnetite play an important role in the electron transfer between Fe0 and Geobacter sulfurreducens, the first microbe in which electrobiocorrosion has been rigorously documented. Genetic modification to express poorly conductive pili substantially diminished corrosive pitting and rates of Fe0 -to-microbe electron flux. Magnetite reduced resistance to electron transfer, increasing corrosion currents and intensifying pitting. Studies with mutants suggested that the magnetite promoted electron transfer in a manner similar to the outer-surface c-type cytochrome OmcS. These findings, and the fact that magnetite is a common product of iron corrosion, suggest a potential positive feedback loop of magnetite produced during corrosion further accelerating electrobiocorrosion. The interactions of e-pili, cytochromes, and magnetite demonstrate mechanistic complexities of electrobiocorrosion, but also provide insights into detecting and possibly mitigating this economically damaging process.

Accelerated Microbial Corrosion by Magnetite and Electrically Conductive Pili through Direct Fe0‐to‐Microbe Electron Transfer

AbstractElectrobiocorrosion, the process in which microbes extract electrons from metallic iron (Fe0) through direct Fe0‐microbe electrical connections, is thought to contribute to the costly corrosion of iron‐containing metals that impacts many industries. However, electrobiocorrosion mechanisms are poorly understood. We report here that electrically conductive pili (e‐pili) and the conductive mineral magnetite play an important role in the electron transfer between Fe0 and Geobacter sulfurreducens, the first microbe in which electrobiocorrosion has been rigorously documented. Genetic modification to express poorly conductive pili substantially diminished corrosive pitting and rates of Fe0‐to‐microbe electron flux. Magnetite reduced resistance to electron transfer, increasing corrosion currents and intensifying pitting. Studies with mutants suggested that the magnetite promoted electron transfer in a manner similar to the outer‐surface c‐type cytochrome OmcS. These findings, and the fact that magnetite is a common product of iron corrosion, suggest a potential positive feedback loop of magnetite produced during corrosion further accelerating electrobiocorrosion. The interactions of e‐pili, cytochromes, and magnetite demonstrate mechanistic complexities of electrobiocorrosion, but also provide insights into detecting and possibly mitigating this economically damaging process.

X80 U-bend stress corrosion cracking (SCC) crack tip dissolution by fast corroding Desulfovibrio ferrophilus IS5 biofilm

Stress corrosion cracking (SCC) is a serious problem threatening structural integrity and safety. Metal corrosion pits can develop into more harmful cracks under mechanical stress. It is known in abiotic corrosion that fast corrosion does not necessarily cause more severe SCC. This is because fast corrosion can prevent or dissolve crack tips and convert them into less harmful pits if the uniform corrosion rate is fast enough. This work experimentally proved the hypothesis that the same phenomenon occurs in biotic corrosion. It was found that a highly corrosive SRB (sulfate reducing bacterium) strain, namely Desulfovibrio ferrophilus (strain IS5), caused fast uniform corrosion and dull pits, but no SCC cracks against X80 carbon steel U-bend coupons (stressed). In comparison, Desulfovibrio vulgaris, a far less corrosive SRB strain caused less corrosion, but generated sharp pits and SCC cracks in a 3-month lab test. This work also revealed that the X80 U-bend had a 44% higher sessile cell count and 34% higher weight loss after a 14-d D. ferrophilus incubation in deoxygenated enriched artificial seawater culture medium at 28 °C when compared with the (flat) square coupons (no stress). This weight loss trend was corroborated by transient electrochemical measurements.

Effect of pine oil on the adhesion and biofilm formation of Acidianus manzaensis on chalcopyrite

Pine oil, commonly used as a flotation frother, could affect the bioleaching process. The attachment and biofilm development of acidophiles on metal sulfides were essential for bioleaching. This study focused on the role of pine oil in the early adhesion and biofilm development by Acidianus manzaensis YN-25 on the chalcopyrite surface. It was revealed that pine oil had a negative effect on the adhesion amount of A. manzaensis on the chalcopyrite surface. After having reached adhesion equilibrium, the percentage of attached cells decreased as the concentration of pine oil increased. The addition of pine oil was found to decrease the negative charge of chalcopyrite and cells, resulting in a higher attraction of acid-base interaction energy and total interaction force. This ultimately led to a stronger adhesion force between chalcopyrite and A. manzaensis. While the addition of pine oil initially delayed the formation of cell microcolonies during the first stage of biofilm formation, which ultimately resulted in larger biofilm coverage compared with the control group. The microcolonies on the mineral surface were also larger and the corrosion pits were bigger with the addition of pine oil. Furthermore, the addition of pine oil weakened the passivation effect and promoted the biological dissolution of chalcopyrite. This study offers a better understanding of the effect of pine oil on the bioleaching of chalcopyrite.

Effect of corrosion on the fatigue crack propagation properties of butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution

AbstractThe corrosion fatigue crack propagation (FCP) of the butt weld with G20Mn5QT cast steel and Q355D steel in 3.5‐wt% NaCl solution was investigated experimentally. Considering the influences of stress ratio and loading frequency, the corrosion FCP rate curve was obtained. The results indicated that the corrosion FCP rate in the corrosion environment is three times that in air. Increasing the stress ratio or decreasing the loading frequency will increase the corrosion FCP rate. The fracture morphology of the specimens in the corrosion environment had more corrosion pits and intergranular characteristics due to anodic dissolution than that in air. Anodic dissolution and hydrogen embrittlement jointly promoted the corrosion FCP of butt weld in simulated seawater. The corrosion FCP rate model was established considering the effects of stress ratio and loading frequency.

Enhanced corrosion resistance of Mg and Mg alloys with fs-laser printed hydrophobic and periodically microrippled surface for armor application

Magnesium (Mg) and its alloys have properties such as high strength-to-weight ratio and good castability, which make them quite promising in industrial applications. Future widespread application of them needs to overcome the limitations such as the fast corrosion rate of Mg and Mg alloys. In this study, an anticorrosion armor with was printed using femtosecond (fs) laser direct writing method. This protective armor is covered with controllable micro-nano structures. Thus, it has a controllable water contact angle ranged from 68° to 158°. In addition, due to the fs laser energy deposition, a grain refined layer less than 15 μm consisting of nanocrystals forms on the surface. Under the synergistic effects of the superhydrophobic surface and nanocrystal layer, Mg and Mg alloys (AZ91D) exhibit significantly enhanced corrosion voltage and exponentially decreased corrosion current density. In particular, pitting on the surface is largely improved, and the corrosion pits on the surface after laser-treatment are approximately 200 times smaller in depth (<2.5 μm) than those of the pristine surface (531 μm). Therefore, the armor on Mg and Mg alloys with enhanced corrosion resistance can be successfully fabricated by the fs-laser direct printing method, extensively used in Mg and Mg alloys applications.

Study on the influence mechanism of material damage on the cavitation erosion properties of hydraulic concrete

Flood releasing safety is one of the three major safety problems of high dams due to the high-water head and large discharge, and the safety problems caused by cavitation erosion are increasingly prominent, which has become one of the challenging problems for the safety of high dam flood discharge. Particularly, flood discharge and energy dissipation structures are susceptible to varying degrees of damage under external loading and material performance degradation. However, the action mechanism of damage-cavitation erosion for concrete remains unknown and unclear. In this paper, the cavitation erosion properties of concrete with different damage variables and the influence mechanism of damage-cavitation erosion are systematically studied. Based on the ultrasonic cavitation erosion tests of undamaged and damaged concrete, it is found that the mass loss, harshness, volume of pits, and depth of damaged concrete increased rapidly at first and then slowly, the maximum loss rate is almost dependent on the degree of damage, and its relationship with the damage degree can be described by a piecewise linear function. More importantly, a damage variable threshold for the step surge of concrete cavitation erosion is suggested. The cementitious material in damaged concrete is more prone to cavitation erosion due to the potential microcracks caused by the damage. Compared with the results of tests and simulations, the incentive mechanism of the surge of concrete cavitation erosion due to the concrete damage - microcrack initiation - strength and fatigue life reduction - microjet impact - water wedge excitation in cracks - development, expansion, and penetration of erosion pits is revealed. The influence mechanism revelation of damage-cavitation erosion for concrete will enrich the theory and technology of cavitation erosion risk assessment for hydraulic concrete structures.

Time-Dependent Reliability Analysis of Fracture Failure of Corroded Cast Iron Water Pipes and Bayesian Updating for Lifetime Prediction

Affected by the underground soil environment, buried cast iron pipelines are subject to corrosion during their long-term service, resulting in damage accumulation to the pipe wall and the eventual fracture failure of pipes. This paper aims to propose a probabilistic method to quantitively assess the time-dependent reliability of fracture failure of corroded cast iron pipes. A Gamma-based corrosion process of the pipe wall is derived according to the reported corrosion models. The first-order reliability method and the Monte Carlo simulation are used to cross-validate and conduct the time-dependent reliability analysis based on the fracture failure criterion. Furthermore, uncertain physical parameters of the pipes are updated by the Bayesian Markov Chain Monte Carlo (MCMC) algorithm based on the regional historical data of failed pipes, and lifetime predictions of buried cast iron pipelines are then obtained. A worked example is provided to illustrate the application of the proposed method. It is found that the Gamma process can well simulate the corrosion process hence can be employed to calculate the probability of pipe fracture failure. Sensitivity analysis reveals that the pipe internal water pressure, the fracture toughness, and the geometry of corrosion pits are the most influential parameters to the probability of fracture failure. It is also found that the predicted lifetime of corroded cast iron pipes in the worked example decreases from 110 to 85 years after the Bayesian updating.

Regulation of localized corrosion of 316L stainless steel on osteogenic differentiation of bone morrow derived mesenchymal stem cells

Localized corrosion has become a concerning issue in orthopedic implants as it is associated with peri-implant adverse tissue reactions and implant failure. Here, the pitting corrosion of 316 L stainless steels (316 L SSs) was initiated by electrochemical polarization to simulate the in vivo localized corrosion of orthopedic implants. The effect of localized corrosion on osteogenic differentiation of bone marrow derived mesenchymal stem cells (BMSCs) was systematically studied. The results suggest that pitting corrosion of 316 L SS reduced the viability, adhesion, proliferation, and osteogenic differentiation abilities of BMSCs, especially for the cells around the corrosion pits. The relatively high concentrations of metallic ions such as Cr3+ and Ni2+ released by pitting corrosion could cause cytotoxicity to the BMSCs. The inhomogeneous electrochemical environment resulted from localized corrosion could promote reactive oxygen species (ROS) generation around the corrosion pits and cause oxidative stress of BMSCs. In addition, localized corrosion could also electrochemically interact with the cells and lead to cell membrane depolarization. The depolarized cell membranes and relatively high levels of ROS mediated the degradation of the osteogenic capacity of BMSCs. This work provides new insights into corrosion-mediated cell function degeneration as well as the material-cell interactions.

Corrosion Mechanism of Typical Shale Gas Gathering and Transportation Pipelines in Southwest China

The shale gas surface gathering and transportation pipeline in southwest China has experienced serious internal corrosion, which affects the production of shale gas wells and has great potential safety hazards. To find out the corrosion type and corrosion mechanism, the corrosion analysis and mechanism research of gathering and transportation pipelines are carried out, including corrosion morphology observation, corrosion product analysis, fluid mechanics calculation, etc. The results show that the corrosion products of the gathering and transportation pipeline are mainly FeCO3 with high S content, and the corrosion type is sulfate-reducing bacteria (SRB) and CO2 corrosion. At the same time, the corrosion pits are mainly distributed on the approach stream side, which is closely related to the scouring effect of the medium flow in the vertical branch pipe on the wall surface of the tee. The corrosion weight loss test shows that the corrosion rate of sterile solution is significantly lower than that of bacterium solution, indicating that the presence of SRB significantly expedites the corrosion of materials.

Effect of chloride and bicarbonate ions on corrosion behavior of carbon steel in anaerobic environment

This investigation was initiated to study the influence of chloride ions and bicarbonate ions on the corrosion behavior of Q345 carbon steel in anaerobic condition by electrochemical tests and surface characterizations. It was found that low concentration of Cl- tends to cause general corrosion of sample while high concentration of Cl- induces localized corrosion because of its migration to the corrosion defects, leading to the accelerated dissolution of matrix. The existence of individual HCO3- results in the passivation of sample. When Cl- co-exists in the solution, the increase concentration of HCO3- results in an overall decrease of corrosion pit depth and the disappearance of localized corrosion, revealing the inhibitory effect of HCO3- on corrosion due to the formation of dense FeCO3 film. This corrosion suppression behavior of HCO3- is opposite to its synergistic effect on pitting with Cl- in aerobic environment.

Improving corrosion resistance of Mg–Li alloys by Sn microalloying

It is well known that the corrosion resistance of ultra-light Mg–Li alloys is inferior to traditional Mg alloys due to the rapid oxidation of reactive Li on the surface. In this study, microalloying Sn has been found to improve the corrosion resistance of Mg–Li alloys due to the formation of Mg2Sn on the corrosion pits and reduction of electro-potential difference. Indeed, the addition of Sn not only reduced the corrosion rate to the minimum value of 4.27 mmpy but also promote the formation of dense corrosion oxide films. The volt potential difference between the matrix (α-Mg and β-Li) and Al-X (Gd, Y, Mn) phases has also been measured to reduce from 260 mV (α-Mg) and 343 mV (β-Li) to 220 mV (α-Mg) and 220 mV (β-Li). After homogenization, pitting was significantly reduced, as shown by the in-situ observation of the corrosion process using X-ray tomography. By quantifying the secondary phases, it has been found that the corrosion expansion was restricted by the Mg2Sn and Al-X phases. The corrosion products are primarily MgO, SnO, and Li2O oxides and the corrosion mechanism follows three stages: I. Breakthrough of MgO protective layer by corrosive fluid; II. Hydrogen evolution reaction (HER) between matrix phase and water immersion; III. Segregation of secondary phases and corrosion products. It has been found that all three processes are highly dependent on the Sn solutes and Mg2Sn precipitates, showing the bright future development of corrosion-resistant Mg–Li alloys by Sn microalloying.

Improving the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating by vacuum sealing with silicone resin

The properties of thermal sprayed WC based cermet coatings are limited by their structural defects, especially corrosion resistance. This article studied the influence of vacuum sealing with silicone resin on the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating in 3.5 wt.% NaCl solution. The surface morphologies of the unsealed and sealed coatings show the high compatibility between sealant and WC-Cr3C2-Ni coating. Benefiting from the block of sealant in defects, the sealed coating presents lower corrosion current density (5.843 × 10−8 A cm−2) after long-term corrosion than the unsealed coating (1.776 × 10−7 A cm−2). Owing to the vacuum treatment, sealant adequately penetrates and remains inside the WC-Cr3C2-Ni coating, and inhibits the growth of corrosion pits on the sealed coating surface. The vacuum sealing with silicone resin effectively hinders the diffusion of corrosion solution, and provides practicable strategy to improve the corrosion resistance of the coatings.