Corrosion Pits Research Articles

Effect of static elastic stress on the corrosion behavior of 7A04 aluminum alloy exposed to real marine atmospheric environment

Aluminum alloy structural materials are widely subjected to the interactive effect of atmospheric corrosion under thin liquid film and elastic stress during the actual service. This study utilized the real marine atmospheric environment as the corrosion environment of thin liquid film for 7A04 aluminum alloy, and the specially designed outdoor device was used to apply varying levels of static elastic tensile stress at the same time, and then the corrosion damage behavior of 7A04 alloy under the interactive effect was studied. The research indicates that the 7A04 alloy suffers from pitting and exfoliation corrosion under the test conditions. The applied elastic tensile stress can accelerate the corrosion damage process of 7A04 alloy, and the degree of acceleration increases with increasing stress levels and exposure time. Moreover, the applied stress can also significantly accelerate the deterioration of the mechanical properties of 7A04 alloy, which has a more prominent effect on the elongation after fracture. Additionally, the corrosion mechanism of 7A04 alloy under the interactive effect was also discussed in this paper.

Pitting corrosion behavior and mechanism of 316L stainless steel induced by marine fungal extracellular polymeric substances

In this study, effect of extracellular polymeric substances (EPS) secreted by fungus Aspergillus terreus on the pitting corrosion of 316L stainless steels (SS) was deeply investigated by electrochemical measurements and surface analysis. Results demonstrated that adsorption of EPS can change surface wettability of 316L SS leading to a much more hydrophilic steel–water interface. EPS not only accelerates uniform corrosion but enhances pitting corrosion of 316L SS. EPS can promote the formation of metastable pitting corrosion and the subsequent growth of corrosion pits. The density of corrosion pits (>2 µm) reach (5.6 ± 0.5)× 103 pits/cm2 when EPS is 400 mg/L.

Influence of Oxygen Content in the Protective Gas on Pitting Corrosion Resistance of a 316L Stainless Steel Weld Joint.

Gas tungsten arc welding (GTAW) is commonly used for joining pipelines; however, it often leads to discoloration in the heat-affected zone (HAZ). In this study, 316L pipes were welded with different concentrations of oxygen present in the argon purge gas during welding. The objective of this study was to investigate the effect of oxygen concentration in the protective gas on the pitting corrosion resistance of welded pipes. The experimental results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas resulted in an increase in pitting corrosion resistance until a critical value, beyond which the resistance decreased. The results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas increased the pitting corrosion resistance until a critical value, beyond which the resistance decreased due to the formation of iron oxide. This study provides valuable insights for improving the corrosion resistance of welded pipes in the oil and gas industry.

Leakage failure analysis of a 60 m3 LNG storage tank

This work aimed to analyze a leak that occurred in a 60 m3 LNG storage tank made of 304 stainless steel. Optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), and mechanical property and hardness tests were conducted to characterize the failed storage tank. The results show that the crack originates near the circumferential weld of the lower head and propagates perpendicular to the weld. There are dense corrosion pits near the crack paths, and high contents of Cl and S in the crack and pits. Besides this, deformation-induced martensite transformation occurs during the cold spinning process of the head, and the microstructure undergoes embrittlement. In service, the lower head subjected to greater internal pressure, plus the structural stress caused by martensite transformation and the welding residual stress, combined with the action of corrosive medium, stress corrosion cracking (SCC) occurs near the circumferential weld of the lower head. To prevent SCC on storage tank, it is suggested to utilize 304 stainless steel with a low content of δ-ferrite, and apply solution treatment after spin molding of the head of tank.

Long-term salt spray corrosion behaviors of HVOF-sprayed WC-Cr3C2-Ni coatings before and after vacuum sealing with silicone resin

The application of thermal sprayed WC based cermet coatings is restricted by their structure defects including pores and cracks during thermal spraying. This article fabricated a corrosion-resistant WC-Cr3C2-Ni coating by high velocity oxy-fuel (HVOF) spraying and vacuum sealing with silicone resin. Experiment outcomes show that silicone resin fills into the defects of the WC-Cr3C2-Ni coating. Benefiting from the block of silicone resin in pores and cracks, the sealed coating shows less corrosion pits than the unsealed coating after long-term salt spray corrosion. The sealed coating shows surface without grooves, corrosion pits with smaller size and cracks with decreased amount in comparison with the as-sprayed coating. The vacuum sealing with silicone resin is a strategy with high potential for expanding the application range of thermal sprayed coatings.

Long-term corrosion of abandoned offshore steel infrastructure

ABSTRACT A common practice in the offshore oil and gas (O&G) industry is to leave abandoned decommissioned pipelines and other steel infrastructure on the seafloor. Decisions about long-term environmental and other impacts and about the possibility of recovery require estimates of the likely long-term rate of deterioration, including corrosion loss and pit depth. These are considered as functions of time and environmental conditions including seawater temperature, dissolved oxygen concentration, salinity, seawater velocity, water pollution, microbiological activity, water depth, calcareous deposition and the effect of burial, all interpreted using established physico-chemical behaviour relevant for long-term exposures. Data for exposures up to some 600 years in seawaters are reviewed. Remaining research gaps and future perspectives of marine corrosion control are briefly discussed. Specific attention is given, by way of an example, to the influence on long-term durability of protective coatings and remnant cathodic protection, both areas in which further research is required.

Numerical Investigation of Fatigue Crack Propagation Behaviour of 550E High-Performance Steel

The fatigue crack propagation behaviour of Q550E high-performance steel (HPS) is studied in this paper. Static tensile testing and fatigue crack propagation testing were carried out, and the results were compared with those of Q235. Finite element models were developed and verified against the experimental results. The impacts of the initial crack angle, crack depth ratio, stress ratio, thickness, and corrosion pitting on the fatigue crack propagation behaviour of the HPS were analysed. The results show that the fatigue life of Q550 was reduced by 18% due to the corrosion pitting, but it did not change the crack propagation path. When the stress intensity factor is higher than a certain value, the fatigue performance of Q235 is better than that of Q550E. The initial crack angle of 52.5° is the critical angle of the crack stress intensity factor. The steel tends to fracture as the crack depth ratio increases, and more attention should be paid to the effective crack length in engineering practice. An increasing stress ratio leads to a smaller stress intensity factor, and the thickness affects the stress intensity factor in the later stage. The crack stress intensity factor around the corrosion pits gradually decreases along the thickness direction, and the crack tips around the corrosion pits tend to reach the yield state initially, accelerating the fatigue fracture of the specimen and ultimately leading to a decrease in fatigue life.

Investigation of impact load and erosion behaviors on Ti-Ta alloy surface through the synergistic effect of ultrasonic cavitation and micro-abrasive particles

Ti–Ta alloy micro-nano surface processing is crucial for achieving biocompatibility. To investigate the cavitation and micro-abrasive particle damage characteristics, and the deformation mechanism of Ti–Ta alloy material surface, indentation theory, and the J-C constitutive model were adopted. Numerical load prediction models for ultrasonic cavitation and micro-abrasive particles' impact on Ti–Ta alloy surfaces were developed, and the erosion behaviors of ultrasonic cavitation and micro-abrasive particles’ impact on Ti–Ta alloy surfaces individually and in synergy were experimentally investigated. The inversion analysis shows that the range of ultrasonic cavitation impact load is 0.025–1.015 N, and there are material peeling and interconnection phenomena in the cavitation erosion pit. On the other hand, the impact load range of 10 μm spherical smooth SiO2 micro-abrasive particles is 0.107–0.814 N, and there is no material peeling or interconnection phenomenon in the micro-abrasive particle erosion pit. Additionally, the cavitation erosion rate is determined through changes in roughness and depression volume, resulting in a rate of 38.6%. In contrast, the cavitation-induced micro-abrasive particle erosion rate reached 166.4%. The results show that the impact load and erosion rate of ultrasonic cavitation-induced micro-abrasive particles are greater than those of cavitation impact load and erosion rate. Furthermore, ultrasonic cavitation-induced micro-abrasive particles impact is found to be more conducive to achieving micro-nano processing of Ti–Ta alloy surface.

Biomimetic superhydrophobic matrix constructed on a buffer aluminum layer: A compositing coating for Mg-Li alloy corrosion inhibition

The magnesium-lithium (Mg-Li) alloy, highly valued for its low density and high strength, has been hampered by its susceptibility to corrosion caused by the presence of active Mg and Li elements. In order to enhance the corrosion inhibition performance of Mg-Li alloy, a double-layer coating is fabricated on its surface in this report. Initially, a sealing aluminum layer is deposited onto the alloy using the magnetron sputtering (MS) technique. Subsequently, an alkyl-ketone dimer (AKD) layer is coated onto aluminum by spray method, resulting in a facile formation of superhydrophobic surface (SHS) at room temperature. In-depth characterization of the microstructure, chemical composition, topology and wettability is conducted using scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurement. The resulting aluminum/AKD composite coating exhibits superhydrophobic properties, displaying a static contact angle of 156.3° and a rolling angle of approximately 1°. The low frequency impedance (|Z|0.01 Hz) of the aluminum /AKD coating is ca. 7.85 × 103 Ω cm2, which is around 100 times of magnitude larger than that of bare Mg-Li alloy. Additionally, immersion of the SHS in a 3.5 wt% NaCl solution for 72 h reveals no visible corrosion pitting, confirming the enhanced corrosion resistance of this superhydrophobic coating.

A framework of cable wire failure mode deduction based on Bayesian network

Because of the cable structure comprises many parallel steel wires, the service performance of the cable structure is determined by the performance change of the parallel steel wires. The parallel steel wire will be subjected to cyclic load during the service period, which will reduce its fatigue life and even lead to the parallel steel wire broken. In addition, the corrosion pits may appear on the cable steel wire in corrosion environments, which will affect the fatigue life of parallel steel wires. In other words, the cable steel wire may be corroded and broken during its service life, which will decrease in the reliability of the cable system. In this paper, a component level to system-level fatigue reliability assessment model is proposed with considering parallel steel wire broken, corroded, and broken-corroded coupling based on the Bayesian network. Specially, the S-N curve considering the broken parallel steel wire is established based on the traditional S-N curve. In addition, the S-N curve for parallel steel wire corrosion is established with the influence of the corrosive environment in mind. Furthermore, the service state of each parallel steel wire, i.e., the failure probability of each parallel steel wire, can be calculated by using a Bayesian network. Finally, the five numerical simulation studies are used to validate the proposed model’s effectiveness and the effects of the number of broken parallel steel wires and the number of corrosion parallel steel wires on the fatigue reliability of cable systems is investigated.

Data-driven model to predict burst pressure in the presence of interacting corrosion pits

This paper presents a data-driven approach to predict the pipelines’ corrosion-induced Burst failure. In this approach, different aspects of pit growth progression and spatial distribution of pits are simulated. The proposed approach takes advantage of population characteristics to model these aspects of the degradation paths for each pipe section down to the size of single joints. The insights obtained from simulations are used to project the degradation of each pipe section. Understanding corrosion behavior and field data are used to model the corrosion-related parameters such as corrosion pit dimensions, probability and time of initiation, and location. The failure is modeled using the probabilistic simulation considering degradation rate, interactions among pits, and material properties as stochastic variables. The proposed approach and included models are tested using multiple real-life inline inspection datasets. Validation of predicted properties shows prediction errors ranging from 3%–10% depending on the three remaining strength calculation approaches. This work aimed to serve as an important tool for risk-based maintenance prioritization, inspection interval assessment, and the fitness of service assessment of pipelines.

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.